what medium do radio waves travel through

? When a radio wave hits a material some of the power is reflected at the surface and some of the power is transmitted into and possibly through the material. If the material is metal, almost all of the radio power is reflected within the first few atoms of the material.

How are Radio Waves Blocked?

"How are Radio Waves Blocked? Print Email Save Image Credit: www.sciencebuddies.org What is common between the radio, TV, radio controlled cars, and cell phones? They all use invisible waves to transmit information.

These waves, called radio waves, are a type of electromagnetic radiation. Radio waves are not harmful; in fact they are an extremely useful method of global communication. Being a simple form of electromagnetic radiation, they move in waves from place to place with limited change.

However, the blocking of radio waves happens in the form of either deliberate or unintentional events. For instance, a military may opt to block radio waves of an enemy. Other situations result in the natural interruption of a broadcast due to a myriad of reasons.

The challenging part with this form of communication is the fact that different naturally-occurring phenomena like mountains, along with certain materials such as copper and aluminum, can create a situation in which the radio waves might blocked. Content What is the speed and voltage of radio waves? What are the essential components for global communication? What makes Radio waves best for the Global communication? What are Dielectrics? What is Attenuation Coefficient?

How Reflection and transmittance comes into play? How will Diffraction determine the blocking of Radio waves? Will plant materials block radio waves? What is the speed and voltage of radio waves? Radio waves are electromagnetic waves and travel at the speed of light which is 186, 280 miles per second (983,558,400 feet per second).

The voltage in a radio wave alternates back and forth between plus and minus many times per second and we call this the frequency of the radio wave in cycles per second. A radio frequency of 100 megahertz (100 MHz) means 100 million (100,000,000) cycles per second. This is usually marked 100 on the middle of FM (frequency modulation) radio dials.

What are the essential components for global communication? Two essential components for global communication are a transmitter and a receiver. Transmitting Antenna (transmitter) - A radio signal from a device travels to the transmitting antenna.

The signal creates a corresponding electromagnetic field called a ‘ radio wave’. This radio wave moves outward in all directions from the transmitting antenna.

Receiving Antenna (receiver) - A receiving antenna picks up the radio wave. If the receiving antenna is far away from the transmitter, the signal is very weak. What makes Radio waves best for the Global communication? The ability of a wave to travel through a material is called transmittance, and materials can be alienated into good transmitters and poor transmitters.

One best transmitting material for radio waves is the air in our lower atmosphere, which is why radio waves can be transmitted through the air over very long distances. One poor transmitter is the ionosphere of the earth, the uppermost layer of the earth's atmosphere which contains high energy, ionized radiation from the sun. Radio waves that are reflected by our ionosphere stay within the inner atmosphere of the earth. This phenomenon is what makes radio waves so great for global communications, because radio wave signals stay close to the surface of the earth.

Similar to the earth's ionosphere, being a poor transmitter is not always awful. Poor transmitters materials are occasionally positive since they can block radio waves from moving through them and become insulators. What are Dielectrics? There are two general types of matter (substances) in the universe that affect electromagnetic waves, conductors and insulators which are called “dielectrics”.

Majority of them except some conductors are metals, such as copper, aluminum, silver and gold. Nevertheless, salt water is also a rather poor conductor. Pure water is a good dielectric substance. Most, but not all, dielectrics are non metals. Examples of dielectrics are paper, plastic, Teflon, glass, ceramic and dry wood.

As the radio wave travels through the dielectric material, some of the power is absorbed generating heat and some of the power travels through and comes out of the other side. What is Attenuation Coefficient? The attenuation coefficient is the level by which a material will block or interfere with radio waves.

This coefficient depends heavily on the thickness and composition of the material. Cardboard, paper, many plastics, water, and glass are all substances with very low attenuation coefficients. In addition, wood, brick, and cement have a limited effect on making radio waves blocked. However, metallic compounds, steel-reinforced concrete and the Earth reflect signals, preventing radio signals from passing through. How Reflection and transmittance comes into play

Since the actual oscillations take place at right angles to the direction of wave propagation, radio waves are transverse waves. Since radio waves are not mechanical, they do not need a medium to travel in; they can travel even in a vacuum. Like all types of electromagnetic waves, radio waves travel at a speed of about 300 000 km per second in a vacuum. When radio waves enter into other material, they slow down a little. When you tune a radio to listen to a particular frequency, the radio takes in the signals at that frequency.

Difference Between Radio Waves and Sound Waves

Difference Between Radio Waves and Sound Waves October 14, 2015 by Nipun 4 min read Main Difference – Radio Waves vs. Sound Waves Sounds are made of waves and radios produce sound. However, when we talk about radio waves, we are not talking about the sound waves produced by the rad

io. Rather, we are talking about the waves that transmit radio signals. The main difference between radio waves and sound waves is that radio waves are a type of electromagnetic wave that can travel when there is no medium, whereas sound waves are a type of mechanical wave that cannot travel if there is no medium. What are Radio Waves Radio waves are electromagnetic waves. These are waves composed of electric and magnetic fields, which are oscillating at right angles to each other. The energy of an electromagnetic wave propagates at a direction at right angles to the oscillations in both the electric and magnetic fields.

In the diagram below, the black arrows show the oscillations in electric and magnetic fields. The direction of propagation of the wave is indicated by the grey arrow. Oscillations in an electromagnetic wave.

Radiating Energy When the transfer of energy happens by radiation, there is no conductive medium (such as in space). That lack of medium means there is no matter there for the heat to pass through. Radiation is the energy carried by electromagnetic waves (light). Those waves could be radio waves, infrared, visible light, UV, or Gamma rays. Heat radiation is usually found in the infrared sections of the EM spectrum.

Energy Likes to Move

"Energy Likes to Move If there is a temperature difference in a system, heat will naturally move from high to low temperatures. The place you find the higher temperature is the heat source. The area where the temperature is lower is the heat sink.

When examining systems, scientists measure a number called the temperature gradient. The gradient is the change in temperature divided by the distance. The units are degrees per centimeter. If the temperature drops over a specific distance, the gradient is a negative value. If the temperature goes up, the gradient has a positive value. The greater the gradient, the more energy will be exchanged.

Ever Hear of Convection Ovens? Convection is the way heat is transferred from one area to another when there is a ""bulk movement of matter."" It is the movement of huge amounts of material, taking the heat from one area and placing it in another. Warm air rises and cold air replaces it. The heat has moved. It is the transfer of heat by motion of objects.

Convection occurs when an area of hot water rises to the top of a pot and gives off energy. Another example is warm air in the atmosphere rising and giving off energy. They are all examples of convection. The thing to remember is that objects change position.

If the temperature of an object doubles (in Kelvin), the thermal radiation increases 16 times. Therefore, if it goes up four times, it increases to 32 times the original level. Scientists have also discovered that objects that are good at giving off thermal radiation are also good at absorbing the same energy.

Usually the amount of radiation given off by an object depends on the temperature. The rate at which you absorb the energy depends on the energy of the objects and molecules surrounding you. Conducting Energy and Heat Conduction is a situation where the heat source and heat sink are connected by matter. As we discussed before, the heat flows from the source down the temperature gradient to the sink. It is different from convection because there is no movement of large amounts of matter, and the transfers are through collisions.

The source and the sink are connected. If you touch an ice cream cone, the ice cream heats up because you are a warmer body. If you lie on a hot sidewalk, the energy moves directly to your body by conduction. When scientists studied good thermal radiators, they discovered that good thermal conductors are also good at conducting electricity. So when you think of a good thermal conductor, think about copper, silver, gold, and platinum. Or search the sites for a specific topic. "

The Ionosphere is part of Earth’s upper atmosphere, between 80 and about 600 km where Extreme Ultra Violet (EUV) and x-ray solar radiation ionizes the atoms and molecules thus creating a layer of electrons. the ionosphere is important because it reflects and modifies radio waves used for communication and navigation.

Ionosphere

Rnone Snone Gnone Current Space Weather Conditions on NOAA Scales Ionosphere Ionosphere

Other phenomena such as energetic charged particles and cosmic rays also have an ionizing effect and can contribute to the ionosphere. The atmospheric atoms and molecules are impacted by the high energy the EUV and X-ray photons from the sun. The amount of energy (photon flux) at EUV and x-ray wavelengths varies by nearly a factor of ten over the 11 year solar cycle.

The density of the ionosphere changes accordingly. Due to spectral variability of the solar radiation and the density of various constituents in the atmosphere, there are layers are created within the ionosphere, called the D, E, and F-layers. Other solar phenomena, such as flares, and changes in the solar wind and geomagnetic storms also effect the charging of the ionosphere.

Since the largest amount of ionization is caused by solar irradiance, the night-side of the earth, and the pole pointed away from the sun (depending on the season) have much less ionization than the day-side of the earth, and the pole pointing towards the sun.

Impacts Radio Communication Radio Navigation (GPS) Satellite Communication Tags:phenomenon Earth Sun Relationship:near_earth Impacts: Space Weather and GPS Systems Electric Power Transmission

Electromagnetic radiation is energy that is propagated through free space or through a material medium in the form of electromagnetic waves, such as radio waves, visible light, and gamma rays. The term also refers to the emission and transmission of such radiant energy.

"Electric Charge: Readings: Electricity Field Theory Electromagnetismelectricity = phenomenon involving electric chargescommon examples are static electricity and lightening The existence of electricity, the phenomenon associated with stationary or moving electric charges, has been known since the Greeks discovered that amber, rubbed with fur, attracted light objects such as feathers. Ben Franklin proved the electrical nature of lightning (the famous key experiment) and also established the conventional use of negative and positive types of charges.

Coulomb quantifies amount of charge and discovers force law between chargeselectrical force is similar to gravity in that it is inverse proportional to the square of the distance between chargescharges are assigned positive or negative valueslike charges repel, opposites attract It was also known that certain materials blocked electric charge, called insulators, such as glass or cork.

Other materials transfered electric charge with ease, called conductors, such as metal. By the 18th century, physicist Charles Coulomb defined the quantity of electricity later known as a coulomb, and determined the force law between electric charges, known as Coulomb's law. Coulomb's law is similar to the law of gravity in that the electrical force is inversely proportional to the distance of the charges squared, and proportional to the product of the charges.

By the end of the 18th century, we had determined that electric charge could be stored in a conducting body if it is insulated from its surroundings.

The first of these devices was the Leyden jar. consisted of a glass vial, partly filled with sheets of metal foil, the top of which was closed by a cork pierced with a wire or nail.

To charge the jar, the exposed end of the wire is brought in contact with a friction device.modern atomic theory explains the origin of electric charge to the existence of small negative particles (electrons) and small positive particles (protons)an atom can gain electrons in its outer shells to gain negative charge orlose electrons increasing the strength of the proton charge (positive)while each atomic charge is small, the number of atoms in a typical macroscopic piece of matter is very largethus, electric power becomes the primary source of energy for civilization Modern atomic theory explains this as the ability of atoms to either lose or gain an outer electron and thus exhibit a net positive charge or gain a net negative charge (since the electron is negative).

Today we know that the basic quantity of electric charge is the electron, and one coulomb is about 6.24x10 18 electrons. The battery was invented in the 19th century, and electric current and static electricity were shown to be manifestations of the same phenomenon, i.e.

current is the motion of electric charge. Once a laboratory curiosity, electricity becomes the focus of industrial concerns when it is shown that electrical power can be transmitted efficiently from place to place and with the invention of the incandescent lamp. Electric Fields:the mathematical problem of describing motion of electric charges leads to the development of the field conceptthe use of fields (as in electric field, gravitational field, force field) is mathematical tool to describe physical eventsthe field itself is not observable, only its effects (motion)The discovery of Coulomb's law, and the behavior or motion of charged particles near other charged particles led to the development of the electric field concept.

A field can be considered a type of energy in space, or energy with position. A field is usually visualized as a set of lines surrounding the body, however these lines do not exist, they are strictly a mathematical construct to describe motion.

Fields are used in electricity, magnetism, gravity and almost all aspects of modern physics.the shape, and resulting strength, of an electric field is dependent on the number and position of the electric chargeseach point in space can be assigned a vector to determine the direction and magnitude of motion An electric field is the region around an electric charge in which an electric force is exerted on another charge.

Instead of considering the electric force as a direct interaction of two electric charges at a distance from each other, one charge is considered the source of an electric field that extends outward into the surrounding space, and the force exerted on a second charge in this space is considered as a direct interaction between the electric field and the second charge.

Magnetism:related to electricity, is the phenomenon of magnetismmagnetism results from the motion of electric charges, although historically we know of the behavior of magnetic fields from bar magnetsmagnetic fields deflect moving charges or other magnetsmagnets have north and south poles, similar to positive and negative charge, but poles can never be separated Magnetism is the phenomenon associated with the motion of electric charges, although the study of magnets was very confused before the 19th century because of the existence of ferromagnets, substances such as iron bar magnets which maintain a magnetic field where no obvious electric current is present (see below).

Basic magnetism is the existence of magnetic fields which deflect moving charges or other magnets. Similar to electric force in strength and direction, magnetic objects are said to have `poles' (north and south, instead of positive and negative charge).

However, magnetic objects are always found in pairs, there do not exist isolated poles in Nature.the simplest magnetic field results from an electric current circulating in a loopbar, or permanent, magnets result from small atomic dipole loops which sum to produce a macroscopic magnetic field The most common source of a magnetic field is an electric current loop. The motion of electric charges in a pattern produces a magnetic field and its associated magnetic force. Similarly, spinning objects, like the Earth, produce magnetic fields, sufficient to deflect compass needles.

Today we know that permanent magnets are due to dipole charges inside the magnet at the atomic level. A dipole charge occurs from the spin of the electron around the nucleus of the atom. Materials (such as metals) which have incomplete electron shells will have a net magnetic moment. If the material has a highly ordered crystalline pattern (such as iron or nickel), then the local magnetic fields of the atoms become coupled and the material displays a large scale bar magnet behavior.

Electromagnetism:in a key development for modern physics, electricity and magnetism were `unified' into electromagnetismthe connection develops from the fact that an electric current (the flow of electrons in a metal) produces a magnetic field Faraday shows that a changing electric field produces a magnetic field and, vice-versus, a changing magnetic field produces an electric current Maxwell completes the theory with a full mathematical description of the relationship between electric and magnetic fields = electromagnetism Although conceived of as distinct phenomena until the 19th century, electricity and magnetism are now known to be components of the unified theory of electromagnetism.

A connection between electricity and magnetism had long been suspected, and in 1820 the Danish physicist Hans Christian Orsted showed that an electric current flowing in a wire produces its own magnetic field. Andre-Marie Ampere of France immediately repeated Orsted's experiments and within weeks was able to express the magnetic forces between current-carrying conductors in a simple and elegant mathematical form. He also demonstrated that a current flowing in a loop of wire produces a magnetic dipole indistinguishable at a distance from that produced by a small permanent magnet; this led Ampere to suggest that magnetism is caused by currents circulating on a molecular scale, an idea remarkably near the modern understanding.

Faraday, in the early 1800's, showed that a changing electric field produces a magnetic field, and that vice-versus, a changing magnetic field produces an electric current.

An electromagnet is an iron core which enhances the magnetic field generated by a current flowing through a coil, was invented by William Sturgeon in England during the mid-1820s.

It later became a vital component of both motors and generators. The unification of electric and magnetic phenomena in a complete mathematical theory was the achievement of the Scottish physicist Maxwell (1850's). In a set of four elegant equations, Maxwell formalized the relationship between electric and magnetic fields.

In addition, he showed that a linear magnetic and electric field can be self-reinforcing and must move at a particular velocity, the speed of light. Thus, he concluded that light is energy carried in the form of opposite but supporting electric and magnetic fields in the shape of waves, i.e.

self-propagating electromagnetic waves. Maxwell's new theory provides a new description of light, as electromagnetic waveselectromagnetism represents a sharp change in the way Nature is described, i.e.

the use of invisible fields and understanding that can only be communicated with mathematics In doing this, Maxwell moved physics to a new realm of understanding. By using field theory as the core to electromagnetism, we have moved beyond a Newtonian worldview where objects change by direct contact and into a theory that uses invisible fields.

This introduces a type of understanding which can only be described with a type of mathematics that cannot be directly translated into language. In other words, scientists where restricted in talking about electromagnetic phenomenon strictly through the use of a new type of language, one of pure math. Electromagnetic Radiation (a.k.a. Light):light is electromagnetic radiation propagating through spacethe wavelength of the light determines its energy and characteristics

Electromagnetic radiation is energy that is propagated through free space or through a material medium in the form of electromagnetic waves, such as radio waves, visible light, and gamma rays. The term also refers to the emission and transmission of such radiant energy.

The wavelength of the light determines its characteristics. For example, short wavelengths are high energy gamma-rays and x-rays, long wavelengths are radio waves. The whole range of wavelengths is called the electromagnetic spectrum. In 1887 Heinrich Hertz, a German physicist, provided experimental confirmation of Maxell's ideas by producing the first man-made electromagnetic waves and investigating their properties.

Subsequent studies resulted in a broader understanding of the nature and origin of radiant energy.light always travels at the same speed in a vacuum, 299,792 meters per second It has been established that time-varying electric fields can induce magnetic fields and that time-varying magnetic fields can in like manner induce electric fields. Because such electric and magnetic fields generate each other, they occur jointly, and together they propagate as electromagnetic waves.

An electromagnetic wave is a transverse wave in that the electric field and the magnetic field at any point and time in the wave are perpendicular to each other as well as to the direction of propagation.

In free space (i.e., a space that is absolutely devoid of matter and that experiences no intrusion from other fields or forces), electromagnetic waves always propagate with the same speed--that of light (299,792,458 m per second, or 186,282 miles per second)--independent of the speed of the observer or of the source of the waves. Electromagnetic radiation has properties in common with other forms of waves such as reflection, refraction, diffraction, and interference. Moreover, it may be characterized by the frequency with which it varies over time or by its wavelength. Electromagnetic radiation, however, has particle-like properties in addition to those associated with wave motion.

It is quantized in that for a given frequency , its energy occurs as an integer times h , in which h is a fundamental constant of nature known as Planck's constant. A quantum of electromagnetic energy is called a photon. Visible light and other forms of electromagnetic radiation may be thought of as a stream of photons, with photon energy directly proportional to frequency. Electromagnetic radiation spans an enormous range of frequencies or wavelengths, as is shown by the electromagnetic spectrum. Customarily, it is designated by fields, waves, and particles in increasing magnitude of frequencies--radio waves, microwaves, infrared rays, visible light, ultraviolet light, X rays, and gamma rays.

The corresponding wavelengths are inversely proportional, and both the frequency and wavelength scales are logarithmic.various wavelengths are absorbed by the Earth's atmosphere (for example, to protect us from damaging high energy light)different types of astronomy questions require different wavelengths = different technology Electromagnetic radiation of different frequencies interacts with matter differently.

A vacuum is the only perfectly transparent medium, and all material media absorb strongly some regions of the electromagnetic spectrum.

For example, molecular oxygen (O2), ozone (O3), and molecular nitrogen (N2) in the Earth's atmosphere are almost perfectly transparent to infrared rays of all frequencies, but they strongly absorb ultraviolet light, X rays, and gamma rays. The frequency (or energy equal to hv) of X rays is substantially higher than that of visible light, and so X rays are able to penetrate many materials that do not transmit light.

Moreover, absorption of X rays by a molecular system can cause chemical reactions to occur. When X rays are absorbed in a gas, for instance, they eject photoelectrons from the gas, which in turn ionize its molecules.

If these processes occur in living tissue, the photoelectrons emitted from the organic molecules destroy the cells of the tissue. Gamma rays, though generally of somewhat higher frequency than X rays, have basically the same nature. When the energy of gamma rays is absorbed in matter, its effect is virtually indistinguishable from the effect produced by X rays.

There are many sources of electromagnetic radiation, both natural and man-made. Radio waves, for example, are produced by cosmic objects such as pulsars and quasars and by electronic circuits. Sources of ultraviolet radiation include mercury vapor lamps and high-intensity lights, as well as the Sun.

The latter also generates X rays, as do certain types of particle accelerators and electronic devices. Wave Properties: Due to its wave-like nature, light has three properties when encountering a medium:reflectionrefractiondiffraction Reflection is the abrupt change in the direction of propagation of a wave that strikes the boundary between different mediums.

At least part of the oncoming wave disturbance remains in the same medium. Regular reflection, which follows a simple law, occurs at plane boundaries. The angle between the direction of motion of the oncoming wave and a perpendicular to the reflecting surface (angle of incidence) is equal to the angle between the direction of motion of the reflected wave and a perpendicular (angle of reflection). Reflection at rough, or irregular, boundaries is diffuse. The reflectivity of a surface material is the fraction of energy of the oncoming wave that is reflected by it.

Refraction is the change in direction of a wave passing from one medium to another caused by its change in speed. For example, waves in deep water travel faster than in shallow; if an ocean wave approaches a beach obliquely, the part of the wave farther from the beach will move faster than that closer in, and so the wave will swing around until it moves in a direction perpendicular to the shoreline.

The speed of sound waves is greater in warm air than in cold; at night, air is cooled at the surface of a lake, and any sound that travels upward is refracted down by the higher layers of air that still remain warm. Thus, sounds, such as voices and music, can be heard much farther across water at night than in the daytime.

The electromagnetic waves constituting light are refracted when crossing the boundary from one transparent medium to another because of their change in speed. A straight stick appears bent when partly immersed in water and viewed at an angle to the surface other than 90.

A ray of light of one wavelength, or color (different wavelengths appear as different colors to the human eye), in passing from air to glass is refracted, or bent, by an amount that depends on its speed in air and glass, the two speeds depending on the wavelength. A ray of sunlight is composed of many wavelengths that in combination appear to be colorless; upon entering a glass prism, the different refractions of the various wavelengths spread them apart as in a rainbow.

Diffraction is the spreading of waves around obstacles. Diffraction takes place with sound; with electromagnetic radiation, such as light, X-rays, and gamma rays; and with very small moving particles such as atoms, neutrons, and electrons, which show wavelike properties. One consequence of diffraction is that sharp shadows are not produced. The phenomenon is the result of interference (i.e., when waves are superimposed, they may reinforce or cancel each other out) and is most pronounced when the wavelength of the radiation is comparable to the linear dimensions of the obstacle.

When sound of various wavelengths or frequencies is emitted from a loudspeaker, the loudspeaker itself acts as an obstacle and casts a shadow to its rear so that only the longer bass notes are diffracted there.

When a beam of light falls on the edge of an object, it will not continue in a straight line but will be slightly bent by the contact, causing a blur at the edge of the shadow of the object; the amount of bending will be proportional to the wavelength.

When a stream of fast particles impinges on the atoms of a crystal, their paths are bent into a regular pattern, which can be recorded by directing the diffracted beam onto a photographic film.

The angle of refraction is greater for a denser medium and is also a function of wavelength (i.e. blue light is more refracted compared to red and this is the origin to rainbows from drops of water)Diffraction is the constructive and destructive interference of two beams of light that results in a wave-like patternclick here to see interference movie Doppler effect: The Doppler effect occurs when on object that is emitting light is in motion with respect to the observer The speed of light does not change, only the wavelength If the object is moving towards the observer the light is ``compressed'' or blueshifted If the object is moving away from the observer the light is ``expanded'' or redshifted Kirchhoff's Laws: There are three types of spectra emitted by objects: Continuous spectrum - a solid or liquid body radiates an uninterrupted, smooth spectrum ( Planck curve )Emission spectrum - a radiating gas produces a spectrum of discrete spectral lines Absorption spectrum - a continuous spectrum that passes through a cool gas has specific spectral lines removed (inverse of an emission spectrum)Planck's curve: One of the primary results from the field of spectroscopy was the discovery of how the energy outputed by an object (its spectrum) changes with temperature Stefan-Boltzmann law: the amount of energy emitted from a body increases with higher temperature Wien's law: the peak of emission moves to bluer light as temperature increasesthe energy outputed by an object (a star, a piece of metal, a human body) takes on a particular shape called Planck's curve, shown in the following plot of energy versus wavelengthnotice that all objects emit all kinds of electromagnetic radiation.

Except, cool objects (like humans) emit very little at short wavelengths (x-rays) and long wavelengths (radio). Most of our energy comes out in the infrared (our peak emission is at 10 microns)The quantum theory of absorption and emission of radiation announced in 1900 by Planck ushered in the era of modern physics.

He proposed that all material systems can absorb or give off electromagnetic radiation only in ""chunks"" of energy, quanta E, and that these are proportional to the frequency of that radiation E = h. (The constant of proportionality h is, as noted above, called Planck's constant.

)Planck was led to this radically new insight by trying to explain the puzzling observation of the amount of electromagnetic radiation emitted by a hot body and, in particular, the dependence of the intensity of this incandescent radiation on temperature and on frequency.

The quantitative aspects of the incandescent radiation constitute the radiation laws. The Austrian physicist Josef Stefan found in 1879 that the total radiation energy per unit time emitted by a heated surface per unit area increases as the fourth power of its absolute temperature T (Kelvin scale). This means that the Sun's surface, which is at T = 6,000 K, radiates per unit area (6,000/300)4 = 204 = 160,000 times more electromagnetic energy than does the same area of the Earth's surface, which is taken to be T = 300 K. In 1889 another Austrian physicist, Ludwig Boltzmann, used the second law of thermodynamics to derive this temperature dependence for an ideal substance that emits and absorbs all frequencies.

Such an object that absorbs light of all colors looks black, and so was called a blackbody. The wavelength or frequency distribution of blackbody radiation was studied in the 1890s by Wilhelm Wien of Germany.

It was his idea to use as a good approximation for the ideal blackbody an oven with a small hole. Any radiation that enters the small hole is scattered and reflected from the inner walls of the oven so often that nearly all incoming radiation is absorbed and the chance of some of it finding its way out of the hole again can be made exceedingly small.

The radiation coming out of this hole is then very close to the equilibrium blackbody electromagnetic radiation corresponding to the oven temperature. Wien found that the radiative energy d W per wavelength interval d has a maximum at a certain wavelength m and that the maximum shifts to shorter wavelengths as the temperature T is increased, as illustrated in the figure below.

Wien's law of the shift of the radiative power maximum to higher frequencies as the temperature is raised expresses in a quantitative form commonplace observations.

Warm objects emit infrared radiation, which is felt by the skin; near T = 950 K a dull red glow can be observed; and the color brightens to orange and yellow as the temperature is raised. The tungsten filament of a light bulb is T = 2,500 K hot and emits bright light, yet the peak of its spectrum is still in the infrared according to Wien's law. The peak shifts to the visible yellow when the temperature is T = 6,000 K, like that of the Sun's surface. "

Mechanical waves use the substrate to move along (the medium). Electromagnetic 'waves' are a combination of a particle and a wave (they have the same properties of both) == photons. Electromagnetic waves encompass light, microwaves, radio waves, and gamma waves (to name a few). Since EM particles act as waves, but also have a mass they actually exist in the Space-Time continuum and can travel without a medium.

How do electromagnetic waves travel through a vacuum (Space)?

"Science & Mathematics Physics How do electromagnetic waves travel through a vacuum (Space)? I understand Mechanical waves that use a 'medium'.7 following 13 answers Answers Relevance Rating Newest Oldest Best Answer: em waves are able to travel thru space because they have a quantum particle associated with them. It is the particle travelling thru space, although the particle is of course massless and weightless.

All quantum particles, including matter, are just packets of energy, and it's the properties of an individual particle that determines how it will behave (ie, will it behave like matter or energy). So light is able to exist on its own for the same reason matter can. Compressional waves cannot; they are simply a travelling perturbation of matter.

Santa Claus · 1 decade ago3 2 Comment Asker's rating Electromagnetic Waves In Space Source (s):https://shorte.im/ba Evelagnionjr · 1 year ago0 0 Comment Electromagnetic radiation is a transverse waveform.

Basically the wave is produced because magnetic fields take a finite time to collapse. When the periodic time of an alternating current becomes shorter than the collapse time for its associated magnetic field, the magnetic field becomes free standing and is subsequently repelled from the electricity conductor by the developing magnetic field, which will be of the same polarity. Like poles repel. Since variable electro-magnetic fields have an associated transverse ""E-field"", that also becomes detached and repelled.

The unexplained part of this simplistic concept is the fact that, anywhere along the advancing electromagnetic wavefront, spherical emissions will be experienced (Huygen's Theorem, which has been demonstrated to be fact, through the development of Fresnel Lenses). It might be reasonably explained in gases, but not in a vacuum! Hence the ""invention"" of the Aether........... Bob P · 1 decade ago2 0 Comment

brytersward · 1 decade ago0 1 Comment..or try this ..any charged body has an electric field surrounding it, capable of propag8ing thro' a vac.. If said particle is acceler8ed or oscill8ed Electric waves are produced in the field. These in turn produce (according 2 maxwell and faraday) induced magnetic waves which in turn produce induced electric waves (both mutually orthogonal) In such a way an accelerated system of charges is able to produce travelling electromagnetic waves which can travel thro the vacuum without any material medium.

Their speed depends only on the inverse sqrt of the permittivity/permeability consts for electric/magnetic fields respectively.

This should have been the answer btw when Faraday famously asked if Maxwell's eponymous equations could be explained in non-mathematical terms... Or..if u prefer.. Grad vectprod [E]=-d B/dt and Gradvectprod [B]= (perm E*perm B)*d E/dtazteccameron1 · 1 decade ago0 0 Comment For a really long time, physicists looked for a medium which was everywhere that light could travel through, they called it the ether.

But today we know more and less at the same. We know there is no ether, but we don't know exactly how it does work.

We really don't know if light is a particle or a wave, it behaves like both at the same time. String theory suggests that small (like way way way smaller than an electron, or even a quark) particles carry energy, and mass, and all other properties of matter.

If this is true (it has yet to be made compatable with quantum mechanics), it means light is a particle (exactly like a baseball), with wave behaviors. Light being transmitted and absorbed would then be exactly like throwing a baseball aroud with friends. One of you would emit a photon (throw the ball) and whoever was in the way would absorb it (catch it).

Note that these photons have no mass at all. Scooter_Mac Gyver · 1 decade ago1 1 Comment I agree with Santa Claus here, that it has to be explained in terms of particles. An electric field is a region around a charge where a force is experienced by a test charge. Similarly a magnetic field is a region around moving charge where force is experienced by another moving charge. There fields propagate through a vacuum and they do so by means of exchange particles, called photons.

Photons do have mass: they don't have rest mass.paul · 1 decade ago2 0 Comment I believe electromagnetic waves travel through wimps. Wimps out number matter as we know millions to one .. whimps are nothing more than"" dead "" partcles. Wimps fill the the vacumn of spce all around us .....but without any charge they react very differently with particles as we know them .

Particles being the matter that we see around us and make up our visible universe. Ludwig · 3 years ago0 0 Comment WAves by definition is the result of a disturbance of a Medium causing the motion of forces. A vaccuun is the absence of air. Space there fore is considered a vacuun. However it is a Medium not devoid of any Substance.

Light is a micromass flux moving at frequencies which are relative to the power Given to the radiation. All substances of Structured Mass, in the Universe ,move in oscilliatory manner ,Hence follow the rules of a wave. The motion of the Sun causes a disturbance of Space structure ,therefore a Gravity wave of a low frequency results. What is called radio waves are really high frequency gravity waves. Its very vely simple Source (s): The structure of the substance of Space and its Creation.goring · 1 decade ago2 4 Comment Unlike sound, the em spectrum exists as waves and as oscillating quantum particles.xenobyte72 · 1 decade ago0 0 Comment1 2 next Perhaps you would like to learn more about one of these? Interested in Life Alert? Can cloud services help you? Need a Small Business Loan? Best Home Security System? "

The velocity (v), wavelength () and frequency (f) are related by (1)All electromagnetic radiation, radio waves through x-rays, moves in vacuum at a universal speed. This is the speed of light, c=30,000,000,000 centimeters per second (usually written in powers of ten, c=3x10 10 cm/sec).

"The Photoelectric Effect The focus in this course is on the interaction of electromagnetic waves ( photons) with electrons to understand the creation and absorption of light. Electromagnetic waves have wavelengths that range from 1 nanometer (10 -9 meter) for x-rays to 1 kilometer (10 3 meters) for radiowaves.

Wavelengths of visible light are in the range of 400 to 700 nanometers (nm). In this appendix we consider the formulation of photon wavelength and energy as well as the absorption of a photon by an electron. Moving waves can be described by their frequency, or number of waves per second, as well as by their wavelengths.

If a train of waves is moving past a stationery observer at a frequency of f complete cycles, or waves per second, and if each of these has a wavelength () of centimeters (cm) per cycle, then the wave must be moving at a speed of v cm per second (s).

The constant value of the speed of light in vacuum goes against our intuition: we would expect that high energy (short wavelength) radiation would move faster than low energy (long wavelength) radiation. We can consider light as a stream of minute packets of energy, photons, which create a pulsating electromagnetic disturbance. A single photon differs from another photon only by its energy. In empty space (vacuum) all photons travel with the same speed or velocity.

Photons are slowed down when they pass through different media such as water, glass or even air. This slowing down accounts for the refraction or bending of light by optical lenses. The energy of the photon is not changed, but the wavelength is. Different energy optical photons are slowed by different amounts in glass or water; this leads to the dispersion of light and the appearance of rainbows.

Because the speed of light in vacuum is constant, if we know either the frequency of the wavelength of electromagnetic radiation we can calculate the other quantity from equation 1. The frequency of the electromagnetic vibration we call light is given in units of ""hertz"" (abbreviated Hz and named after Henrich Hertz, 1857-1894, a famous German investigator of electromagnetism).

One hertz is one vibration per second; the range of the pure spectrum perceived by the eye extends from about 4.3x10 14 Hz in the red to about 7.5x10 14 in the violet. This aspect of the discussion suggests that light and other electromagnetic radiation are waves. It was very disturbing, therefore, when phenomena were discovered (around 1900) that clearly indicated that light was made up of particles called photons.

One such phenomenon involved the photoelectric effect. It was known that if one shines a beam of light on a clean surface of a metal, electrons will be ejected from the metal.

The light has to exceed a certain energy, to remove electrons from the metal surface. If the light has more than the minimum energy required, then the extra energy will be given to the ejected electrons as kinetic energy of motion.

Light of a single wavelength behaved as if it consisted of separate particles, photons, all with the same energy, with each ejected electron being the result of a collision between one photon and one electron in the metal. Greater intensity of light meant only that more photons were hitting the metal per second and more electrons were being ejected, not that there was more energy per photon. The energy of the outgoing electrons depended on the frequency of light used. The energy (E) of the incoming photons is directly proportional to the light frequency which can be written as, (2)in which h is a constant.

Max Planck first proposed this relationship between energy and frequency in 1900 as part of his study of the way in which heated solids emit radiation.

The constant h is called Planck's constant in his honor and has a value, h=4.136x10 -15 e V-sec. For photons, the property most readily measured is their energy. The different colors of light for example, are thought of as representing photons of different energy.

The link between the particle theory and the wave theory lies in Planck's fundamental postulate of quantum theory given by equation (2). There is an inverse relation between the energy E, of the photon and the wavelength, (3)The energy E in equation 3 can be expressed in many units.

In the analysis of art and in the description of light, the most convenient unit of energy to use is the electron volt, abbreviated e V. In terms of wavelength,, in nanometers (nm), and energy (E), in electronvolts (ev), equation 3 can be expressed for light travelling in a vacuum as: (4)as show in Fig.

1. The constants and numerical relations found in equations 3 and 4 are found from Planck's equation (Eqn. 2) by writing the relationship for frequency (f) in Eqn. 1 as (5)so that Planck's equation becomes (6)The value of Planck's constant, h, is 4.136x10 -15 e V-sec and the velocity of light, c, is 3x10 8 m/sec or 3x10 17 nm/sec so that hc=12.4x10 2 or 1240 e V-nm.

Visible light is composed of photons in the energy range of around 2 to 3 e V. Orange light with a wave length of 620 nanometers is composed of photons with energy of 2 e V. It is the energy range of 2 to 3 e V which triggers the photo receptors in the eye.

Lower energies (longer wavelengths) are not detected by the human eye but can be detected by special semiconductor infared sensors.

Higher energies (shorter wavelengths) such as x-rays damage human tissue and are detected by x-ray sensitive photographic film or again by special semiconductor devices. Figure 1. A curve that shows the relationship, E (ev)=1240/ (nm) given in Eqn. 4 for the energy in e V versus photon wavelength in nanometers for the visible region of the electromagnetic spectrum. Return to the Readings Page Page authored by the ACEPT W 3Group Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504 Copyright © 1995-2000 Arizona Board of Regents. All rights reserved. "

Best Answer: A sound wave is a type of pressure wave which can also be called a compression wave. Pressure waves depend on the presence of a medium such as air for it to travel through. Without the medium they cannot travel. Therefore neither A, C or D could travel through space as space is a vacuum lacking a medium. However, radio waves can travel through space. Radio waves form a section of the electromagnetic spectrum.

Which type of wave can be transmitted through the vacuum of space ?

Science & Mathematics Physics Which type of wave can be transmitted through the vacuum of space ? Which type of wave can be transmitted through the vacuum of space A) sound waves B) radio waves C) pressure waves D) compression waves Follow 3 answers Answers Relevance Rating Newest Oldest

Visible light is another part of the electromagnetic spectrum. Therefore one could say that radio waves and visible light are simply different forms of light, the difference being in their wavelength and therefore their frequency. Visible light's wavelength is on the order of 10^-7 metres (that's 0.0000001 metres!) yet radio waves can be on the order of whole metres.

I'm going off point though, electromagnetic waves have a special property allowing them to travel through vacuums, as in they do not require a medium to travel through.

This is how the light from the sun reaches us. Source (s): Leaving Certificate Physics Conor · 5 years ago0 0 Comment Asker's rating A) sound is just waves of air, and there is no air in a vaacum C) There is no pressure in a vacuum.

D) there is nothing to compress in a vacuum. So it must be B. The Devil · 5 years ago0 0 Comment Radio waves Tasha · 12 months ago0 0 Comment Maybe you would like to learn more about one of these? Get an MBA while working Psoriatic arthritis symptoms? Best Home Security System? Try online nursing courses?

(This includes visible light, radio waves, gamma rays, x-rays, ultraviolet rays, infra-red waves, and microwaves.) They both are able to travel through a medium of gas, liquid, or solid. Also, electromagnetic waves have the weird quantum property of sometimes acting like waves, and sometimes acting like particles.

What are the similarities and differences between mechanical waves and electromagnetic waves?

Answers.com ® Wiki Answers ® Categories Science Physics Mechanics Waves Vibrations and Oscillations What are the similarities and differences between mechanical waves and electromagnetic waves? Flag What are the similarities and differences between mechanical waves and electromagnetic waves? Answer by Helmutcore3 Confidence votes 198

Mechanical waves need matter to transfer energy, while electromagnetic waves do not, they can travel through space, or a vaccum. Electromagnetic waves include the electromagnetic spectrum...

t Best Answer: How, five circular answers so far (radio waves don't need a medium because electromagnetic waves don't need a medium). There actually is a medium, of sorts. It's called the vacuum. It differs from media made of matter though in being ""Lorentz Invariant"

How do radio waves travel through space if they don't have a medium to travel through?

"Science & Mathematics Physics How do radio waves travel through space if they don't have a medium to travel through? Follow 13 answers Answers Relevance Rating Newest Oldes

". That means, amongst other things, it has no preferred reference frame in which it can be said to be stationary. Most people thing of ""vacuum"" as being equivalent to ""nothing"", but nothing can be farther from the truth. It's actually a rather busy place full of virtual fields and has many tangible properties such as curvature and a metric.

Nothing, on the other hand, has no properties. Modern physics treats radio waves (indeed all forms of particles and waves) as a sort of excitation of the vacuum state.

Dr. R · 1 decade ago2 1 Comment Asker's rating Radio waves are a part of the electromagnetic spectrum. They do not require a ""medium"" to travel through. A radio wave is composed of an electrical wave, and a magnetic wave.

The 2 waves travel together, creating each other as the wave travels through what ever medium it is in, be that air, wire, or what we call ""space"".kerry k · 1 decade ago0 2 Comment Consider two oppositely charged plates parallel to each other placed in a vacuum bulb.

If we now change the charges in one of the plates, the charge in the other plate is simultaneously changed even though there is nothing in between them. If we drop an objects inside a long vertical evacuated vertical glass tube, the objects is pulled down by gravity even though there is nothing in between them.

On one side of an evacuated glass bulb if we place an iron piece and keep a magnet on the other side, the iron piece sticks to the bulb even though there is nothing in between them.

The radio waves and all other electro magnetic radiations like heat rays [infra red rays] light and X-rays work in the principle that a variation of charge and magnetic properties in a conductor is affected in a conductor placed far away from the initial conductor.

Thus they require no material medium for their transformations. Energy can travel through vacuum. The answer to your question lies in the answer to the question why should one expect a medium for radio waves to travel. Pearlsawme · 1 decade ago0 0 Comment Radio and light waves do not need a 'medium' to propagate through.

They are electro-magnetic waves. This is why light from the sun and radio waves from the space station and the shuttle are received on Earth through the almost perfect vacuum of Space. Norrie · 1 decade ago0 2 Comment Radio waves are simply light emitted on frequencies outside the visible spectrum.

I think you're confusing radio waves with sound waves. Sound waves indeed cannot travel through the vacuum of space. (In space, no one can hear you scream!) But light travels easily through space, and in fact travels easier because there's no atmosphere to impede it.

Source (s): I'm really smart.jobahed · 1 decade ago0 1 Comment Radio waves are basically the same as light, that is, electromagnetic radiation. They easily travel through vacuums because electric fields do not need matter in which to travel through. William D · 1 decade ago1 1 Comment For the best answers, search on this site https://shorturl.im/av2xn Electromagnetic radiation can propagate through free space.

It doesn't need a medium. It travels at a speed c = 1 foot / nanosecond Josephine · 2 years ago0 0 Comment Radio waves are one type of electromagnetic radiation, they do not require a medium to travel through.

King Freshy LOVES Milan · 1 decade ago0 1 Comment When the Michelson Morley experiment was done the concept of a ""medium"" that had no viscosity and therefore no observable effect on wave propagation.

Since then we have ""discovered"" superfluid’s which do have that property among others and some scientists are speculation that the ""aether"" does exist and that dark matter and dark energy may actually be superfluid’s (or even that the whole universe is s superfluid universe Malcolm · 3 years ago0 0 Comment Radio waves are photons which are actually particles albeit massless ones. As you know particles don't need a medium to travel through Adam B · 1 decade ago1 0 Comment1 2 next Maybe you would like to learn more about one of these? Try online nursing courses? Consolidate Your Student Loans Look For Franchises For Sale Graphic Design Degrees "

A: Quick Answer Radio waves travel at a velocity that is equal to the speed of light traveling in a vacuum, which is 186,282 miles per second. Top speed is only possible in empty space; passing through transparent liquids and solids like crystals cause waves to bend, which slows down their speed. Continue Reading

How Fast Do Radio Waves Travel?

Science Physics Optics & Waves Q: How Fast Do Radio Waves Travel?

Keep Learning What Is the Speed of Radio Waves? What Are Some of the Properties Common to All Electromagnetic Waves? What Do All Electromagnetic Waves Have in Common? Full Answer The unit that measures radio waves, hertz, was named after Heinrich Hertz, who first proved the existence and speed of radio waves.

Hertz also proved that radio waves are actually a form of light. Albert Einstein and other scientists have established that nothing with mass can travel as fast as light speed, but light and sound waves sometimes travel slower. Learn more about Optics & Waves Sources: missionscience.nasa.gov space.com Related Questions Q: What Is the Speed of Light in Miles Per Second?

A: The speed of light is 186,282 miles per second. An object travelling at the speed of light would make approximately 7.5 rounds around the Earth in one seco... Full Answer >Filed Under: Optics & Waves Q: How Fast Is the Speed of Light in Mph? A: The speed of light in mph (miles per hour) is 6.702 x 108 mph or more precisely 670,616,629 mph.

In metric units, the speed of light in a vacuum is 2.998 x... Full Answer >Filed Under: Optics & Waves Q: How Fast Is the Speed of Light?

A: When light travels in a vacuum, its speed is 186,282 miles per second. The fastest aircraft, which is the Boeing-43 scramjet, has a speed of 7,546 miles pe... Full Answer >Filed Under: Optics & Waves Q: How Fast Does Light Travel in Air?

A: Light travels through a vacuum at 186,282 miles per second; through the Earth's atmosphere, it moves at 186,227 miles per second. The speed of light, in ge... Full Answer >Filed Under: Optics & Waves You May Also Like Q: What Is the Difference Between Infrasonic and Ultrasonic Waves? Q: How Can You Make Cash Fast? Q: What Is Infrared Used For? Q: How Does a Stroboscope Work? Q: What Is the Amplitude of a Wave? Q: How Fast Is USPS Next-Day Delivery Mail?

e. They transmit radio waves through space to antennas here on the ground. )Sound travels at approximately 1,100 feet per second (766 miles per hour). Radio waves travel at the speed of light, which is approximately 186,000 miles per second. This means that in the time radio waves travel the length of a football field, light can travel further than all the way around the world.

Grade Level:6-12Curriculum Standards: PS-M-C1 PS-H-G1Overview: One of the primary goals of this unit is to ensure that students know the fundamental differences between radio and sound waves. Through participation in this lesson, students will examine the characteristics of both types of waves. Purpose: To identify and explore various characteristics of radio and sound waves. Objectives: Students will: Examine their own prior knowledge and understanding of radio and sound waves. Discuss the characteristics of each type of wave. View and experiment demonstrated by the teacher to show the differences in the two waves.

Internet Sites:http://www.askjeeves.com Students can use this site to research and report on special topics related to sound including: ultrasound, infrasound, echolocation, sonar, and breaking the sound barrier.

They can also research the different types of waves included in the electromagnetic spectrum, which include: cosmic rays, gamma rays, x rays, ultraviolet rays, light rays, infrared rays, microwaves, and radio waves. Procedures: Have students answer the following questions individually: How are sound waves produced? How are radio waves produced? How do sound waves travel? How do radio waves travel? How fast do sound waves travel?

How fast do radio waves travel? Have students work in pairs to compare answers and make any needed changes to their answers. Have students work in groups to compare answers and make any needed changes to their answers. Record each group’s answers on the board.

Lead a class discussion, which will lead students to the correct answers and provide demonstrations to help develop student understanding. Sound waves are produced by objects, which vibrate rather rapidly. This can be demonstrated by feeling your throat while speaking, seeing a speaker vibrate as the sound comes out, or striking a tuning fork.

Radio waves are produced by moving charged particles. An example of this is an electric current in a wire. This can be demonstrated with a wire, a 6-volt battery and a small radio. Turn the radio on AM so that static can be heard, attach one end of the wire to the battery.

Touch the other end of the wire to the other battery terminal and have students record their observations.

(When the other end of the wire is touched to the other battery terminal, you will hear the radio waves, which reach the radio get turned into sound waves, which your ears can hear. )Sound waves travel through a medium. If there is no medium then there will be no sound. Show the included video of a bell in a vacuum. When all air is removed there is no medium for the sound waves to travel through so no sound is heard.

Here is a video demonstrating this concept: MPEG Video (10MB - 1 hour on 56k modem, 1-2 minutes on high speed connection) Radio waves travel like light waves. They can be absorbed, reflected or transmitted. Using the same demo from above, wrap the radio in heavy-duty aluminum foil. Now touch the wire to the battery and have students record their observations. (When the wire is touched to the battery the radio waves cannot reach the radio because some of the energy is absorbed and some is reflected by the aluminum foil so very little is able to get through. These waves do not require a medium to travel through. A perfect example of this is satellites orbiting in outer spac

You can demonstrate this on the football field with a balloon and 2 walkie-talkies from Radio Shack. Have two students walk across the football field with the balloon and one walkie-talkie. Turn on the both walkie-talkies.

The students with the balloon should then press and hold the talk button before popping the balloon. On the other end simply listen. Have students record their observations. (You should observe that the sound of the balloon was first heard over the radio and shortly afterwards through the air.

)Evaluation: Have students answer the following questions: Which type of wave is produced by a vibrating object? (sound)Which type of wave can travel through outer space? (radio)Which type of wave travels at the fastest speed?

(radio)Describe one situation when it would be better to communicate with a sound wave instead of a radio wave. Describe one situation when it would be better to communicate with a radio wave. Draw a picture of the last experiment.

In your drawing include both people, their ears, their walkie-talkies, and the balloon. Show the paths of the sound waves using one color and of the radio waves using a different color. From your drawing, explain why you first heard the balloon pop on the walkie-talkie.

Radio frequency is produced by oscillating current a specified number of times and then radiating it off a conductor, referred to as an antenna, into empty space (this refers to space occupied by air rather than solid objects and does not refer to outer space) as electromagnetic radio waves.

Radio Frequency (RF)

"Radio Frequency (RF)Definition - What does Radio Frequency (RF)mean? Radio frequency (RF) refers to the rate of oscillation of electromagnetic radio waves in the range of 3 k Hz to 300 GHz, as well as the alternating currents carrying the radio signals.

This is the frequency band that is used for communications transmission and broadcasting. Although RF really stands for the rate of oscillation of the waves, it is synonymous to the term ""radio,"" or simply wireless communication. Techopedia explains Radio Frequency (RF)Radio frequency is being used in a lot of fields, but in the context of information and communications technology it refers to the frequency band at which wireless telecommunications signals are being transmitted and broadcast.

The frequency band is being divided into different parts, which are then assigned to different technology industries. This is known as the radio spectrum. For example, the VHF (very high frequency) band, which ranges from 30-300 MHz, is being used for FM radio, TV broadcasts, and amateur radio and its counterparts. For a lot of electronic communication devices, the ultra-high frequency (UHF) band is being used. This is the space used by mobile phones, wireless LAN, Bluetooth, and TV and land radio.

RF signals are sent and received using conductors through the phenomenon known as the skin effect, where RF current latches itself and flows through the surface of conductors rather than penetrating and passing through them like it does with other non-conducting solids. This effect is the core and basis of radio technology. "

. Earth's atmosphere, however, acts an opaque barrier to much of the electromagnetic spectrum. The atmosphere absorbs most of the wavelengths shorter than ultraviolet, most of the wavelengths between infrared and microwaves, and most of the longest radio waves. For radio astronomers this leaves only short wave radio to penetrate the atmosphere and bring information about the universe to our Earth-bound instruments. The main frequency ranges allowed to pass through the atmosphere are referred to

"The Effects of Earth's Upper Atmosphere on Radio Signals Needed Materials 1.) AM radio 2.) Aluminum screen (can be purchased at home supply store such as Home Depot) Introduction The electromagnetic spectrum consists of waves of many wavelengths ranging from very long wavelength radio waves to very short wavelength gamma rays.

Visible light, consisting of short wavelength waves, is placed near the middle of this spectrum. Visible light can pass through window glass, but a solid wall will absorb a portion of the light and reflect the remaining portions. Scientists would say that glass is transparent to visible light, but a wall is opaque. Since the atmosphere is transparent to visible light (while absorbing some of the light), astronomers who use telescopes can see things from far away using visible light to form images

as the radio window. The radio window consists of frequencies which range from about 5 MHz (5 million hertz) to 30 GHz (30 billion hertz). The low-frequency end of the window is limited by signals being reflected by the ionosphere back into space, while the upper limit is caused by absorption of the radio waves by water vapor and carbon dioxide in the atmosphere.

As atmospheric conditons change the radio window can expand or shrink. On clear days with perfect conditions signals as high as 300GHz have been detected. It is the effects of the ionosphere on the lower end of the radio spectrum that we will investigate in this exercise.

The ionosphere The ionized part of the Earth's atmosphere is known as the ionosphere. Ultraviolet light from the sun collides with atoms in this region knocking electrons loose. This creates ions, or atoms with missing electrons. This is what gives the Ionosphere its name and it is the free electrons that cause the reflection and absorption of radio waves.

How does this affect our observations of Jupiter? When the sun is overhead during the day, most of the ionosphere is ionized due to the large amount of ultraviolet light coming from the sun.

As radio waves enter Earth's atmosphere from space some of the waves are absorbed by the electrons in the ionosphere while others pass through and are detectable to ground based observers.

The frequency of each of these waves is what determines whether or not it is absorbed or able to pass through the atmosphere. Low frequency radio waves do not travel very far through the atmosphere and are absorbed rather quickly.

Higher frequency waves are able to pass through the atmosphere entirely and reach the ground. This process also works in reverse for radio waves produced on the earth. The high frequency waves pass through the ionosphere and escape into space while the low frequency waves reflect off the ionosphere and essentially ""skip"" around the earth. The diagram below will help illustrate this: What's all this talk about high frequency and low frequency radio waves?

What types of things fall in each range? Astronomical radio sources emit over a wide range of frequencies. Their emission can be measured ranging from low frequencies to high frequencies. Jupiter for example emits radio waves from about 10 k Hz up to about 300 GHz. This emission is broken into several groupings. The lowest being the kilometric emission which ranges from 10k Hz up to 1000k Hz.

Other frequency groups include hectometric (1000KHz to 3MHz), decametric (3MHz to 40MHz), and decimetric (100MHz to 300GHz). It is the decametric emissions that we are concerned about with Radio Jove. The Radio Jove receiver is tuned to a frequency of 20.1MHz.

Radio waves produced on Earth are mostly manmade and are often at one specific frequency. In fact, this is one way astronomers can tell a signal created on Earth apart from an astronomical signal.

If they are able to tune their receivers to a slightly higher or lower frequency and the signal disappears it is most likely an Earth based signal. Radio waves fall into three main categories with a variety of uses: H. F. (High Frequency 3 to 30MHz)Long Range communications.

Shipping, Aircraft, World Broadcast Communications, Radio Amateurs. Use involves reflecting the signal off the ionosphere back down to waiting recieving stations. Prone to atmospheric changes causing fading and noise. Range from 500 to thousands of Kilometres.

V. H. F. (Very High Frequency 30 - 300 MHz)Medium range communications. Fleet vehicles, mobile, coastal shipping and air to tower communications. Range 70-100km (aircraft several hundred km). U. H. F (Ultra High Frequency 300-3000 MHz)This is the domain of such things as Police handheld radios, cell-phones, T. V., and spacecraft to ground communications.

In the high U. H. F. range the signal can ""bounce"" off buildings and reflect until it is detected by a receiver. Activities We can use the aluminum screens to mimic the effects of the ionosphere. To do this follow the following steps: 1.)

Take the AM radio outside and tune in an AM station. 2.) Using the aluminum screen construct a small cage which you can place over the AM receiver. After placing the cage over the receiver observe how the station is weaker or disappears. 3.) Remove the cage and the station returns. The screen acts as a solid object to the incoming radio waves. We can imagine the radio as an Earth based receiving station.

The screen, like the ionosphere, reflects the low energy AM radio waves and they are not detectable. Below is an animation comparing the ionospheric conditions during a typical day with that of a day containing an ionospheric storm.

An ionospheric storm is caused by a coronal mass ejection from the sun that strikes the Earth's atmosphere. These mass ejections contain large amounts of particles that smash into the ionosphere and knock electrons loose from atoms. As discussed above the loose electrons reflect radio waves from astronomical sources back into space.

The addition of loose electrons as a result of a mass ejection makes observations and communications difficult. The dark blue and purple areas are the areas where the number of loose electrons is low. In these areas there are few electrons to reflect radio waves and thus lower frequency waves are able to reach the ground.

As can be seen from the animations the night time and early morning hours are best for observations due to the fact that the sun is not in the sky and its ultraviolet light is not reaching the atmosphere at this time.

The density of electrons (how many electrons there are per every cubic centimeter) is represented by the varying colors. Bands of high density that appear at high latitudes during the storm but disappear rapidly as it subsides are due to the high velocity particles smashing into the atoms in the atmosphere and knocking electrons free.

These same high velocity particles produce the auroral lights. We can use these maps and the varying colors to find the lowest frequency that is detectable from the ground.

The lowest frequency detectable, known as the critical frequency, is related to the density of electrons by the equation: f = 9x10^-3 x sqrt (N) MHz. In this equation f is the critical frequency and N is the electron density, sqrt means to take the square root of the electron density.

In the maps above the electron density ranges from 33300 electrons/cm^3 (dark blue) to 249750 electrons/cm^3 (green) to 552780 electrons/cm^3 (red).

Exercise Use these values to calculate the critical frequency for the dark blue, green and red areas on the maps.dark blue = 1.8 MHz, green = 5 MHz and red = 7.2 MHz Questions and Problems The speed of all electromagnetic waves (the speed of light, or c) is 300,000,000 meters per second (3 x 10^8 m/s). The distance traveled (d) by an electromagnetic wave in time (t) is given by the equation: d = c x t. The frequency and wavelength of an electromagnetic wave are related by the equation: c = x f where f is the frequency of the wave, c is the speed of light, and is the wavelength in meters.

Example 1.) How long would it take a radio wave to travel to Earth from the moon? The moon is 400,000 kilometers from Earth. (Note: 400,000 kilometers = 4x10^8 meters. )d = c x t 4x10^8 = 3x10^8 t t = 1.33 seconds Example 2.) What is the wavelength of a radio wave with a frequency of 500k Hz?c = x f 3x10^8 = (500x10^3) = 600m1.)

If radio astronomers are studying 20MHz radio signals from the sun which is 1.5x10^11 meters away from the Earth, how long did take for the radio signals to reach Earth?t = 500 seconds2.) 3MHz is the lowest frequency which will pass through the ionosphere. Calculate the wavelength of these waves.= 100 meters3.)

A general rule is that a spacing on the order of 1/10 of a wavelength will seem solid to a radio wave.

What size would the spacings in our mesh screen have to be in order to block the 20MHz solar radio waves discussed in problem 1?= 15 meters, spacing = 1.5 meters4.) As shown above, the ionosphere can act as a solid object to radio waves. Using this idea do you think it is possible to build a radio dish that is not solid?

If so, what are the benefits and advantages of a mesh dish?lightweight, saves building costs, not much gathers inside (rain, snow, leaves, etc. ), in cases of large antennas a mesh can allow sunlight to reach the ground below and help prevent erosion of soil by allowing growth of grass and plant life.5.)

If spacings of 1/10 of a wavelength seem solid to electromagnetic waves would imperfections in a solid radio dish (holes or knicks) of this size matter? Radio studies deal with waves ranging from about 100m to 1mm. If we built a solid dish for each of these extremes (100m and 1mm) how small could the imperfections in our antenna be?10 meters and .1mm (or .0001m)Credits The H. F/V. H. F./U. H. F. image located in the section describing high and low frequency radio waves as well as the Earth image under the ionosphere section are courtesy of Elbate Engineering LTD. http://www.voyager.co.nz/~elbate/propo.htm http://www.voyager.co.nz/~elbate/propo2.htm "

swer The ionosphere is the layer of the atmosphere that reflects radio waves. This effect is caused by the ionization, or electrical charging, of the gas particles present in the upper atmosphere by X-rays and ultraviolet rays emitted by the sun. Continue Reading

Which Layer of the Atmosphere Reflects Radio Waves?

Science Earth Science Atmosphere Q: Which Layer of the Atmosphere Reflects Radio Waves? A: Quick An

Keep Learning How Is the Ionosphere Useful to Man? How Is the Atmosphere Heated? What Is the Importance of the Exosphere? Full Answer The ionization of gas particles in the ionosphere aids in the transmission of radio waves by reflecting waves back to Earth, rather than allowing them to escape the atmosphere.

Solar flares, the spontaneous eruption of high-energy radiation from the surface of the sun, can cause a sharp increase in the number of ionized particles in the upper atmosphere and can interfere with radio wave transmissions.

Learn more about Atmosphere Sources: ds9.ssl.berkeley.edu teachertech.rice.edu hesperia.gsfc.nasa.gov Related Questions Q: What Are the Layers of Earth's Atmosphere From Highest to Lowest? A: The outermost layer of the Earth's atmosphere is the exosphere, followed by the thermosphere, mesosphere, stratosphere and troposphere. The exosphere begin... Full Answer >Filed Under: Atmosphere Q: What Are Some Facts About the Stratosphere?

A: Moving up from the surface, the stratosphere is the second layer of the Earth's atmosphere, beginning between 5 and 10 miles (26,000 to 53,000) feet up. Th... Full Answer >Filed Under: Atmosphere Q: What Is the Basis for Dividing the Atmosphere Into Four Layers? A: The atmosphere is divided into four layers because each layer has a distinctive temperature gradient.

The four layers of the atmosphere are the troposphere... Full Answer >Filed Under: Atmosphere Q: What Are Characteristics of the Troposphere?

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In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from the ionosphere, an electrically charged layer of the upper atmosphere.

Skywave

"From Wikipedia, the free encyclopedianavigation search For the satellite terminal company in Ottawa, see Sky Wave Mobile Communications. Radio waves (black) reflecting off the ionosphere (red) during skywave propagation

Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the shortwave frequency bands. As a result of skywave propagation, a signal from a distant AM broadcasting station, a shortwave station, or—during sporadic E propagation conditions (principally during the summer months in both hemispheres) a distant VHF FM or TV station can sometimes be received as clearly as local stations.

Most long-distance shortwave ( high frequency) radio communication—between 3 and 30 MHz—is a result of skywave propagation. Since the early 1920s amateur radio operators (or ""hams""), limited to lower transmitter power than broadcast stations, have taken advantage of skywave for long distance (or "" DX "") communication.

Skywave propagation is distinct from:groundwave propagation, where radio waves travel near Earth's surface without being reflected or refracted by the atmosphere—the dominant propagation mode at lower frequencies,line-of-sight propagation, in which radio waves travel in a straight line, the dominant mode at higher frequencies.

Contents [ hide ]1 Explanation2 Other considerations3 History3.1 Discovery of skywave propagation3.2 Marconi4 See also5 References6 Further reading7 External links Explanation [ edit]The ionosphere is a region of the upper atmosphere, from about 80 km to 1000 km in altitude, where neutral air is ionized by solar photons and cosmic rays. When high frequency signals enter the ionosphere obliquely, they are back-scattered from the ionized layer as scatter waves.

[1] If the midlayer ionization is strong enough compared to the signal frequency, a scatter wave can exit the bottom of the layer earthwards as if reflected from a mirror. Earth's surface (ground or water) then diffusely reflects the incoming wave back towards the ionosphere.

Consequently, like a rock ""skipping"" across water, the signal may effectively ""bounce"" or ""skip"" between the earth and ionosphere two or more times (multihop propagation). Since at shallow incidence losses remain quite small, signals of only a few watts can sometimes be received many thousands of miles away as a result.

This is what enables shortwave broadcasts to travel all over the world. If the ionization is not great enough, the scatter wave is initially deflected downwards, and subsequently upwards (above the layer peak) such that it exits the top of the layer slightly displaced. Sky wave propagation occurs in the waveguide formed by the ground and ionosphere, each serving as reflectors.

With a single ""hop,"" path distances up to 3500 km may be reached. Transatlantic connections are mostly obtained with two or three hops. [2]The layer of ionospheric plasma with equal ionization (the reflective surface) is not fixed, but undulates like the surface of the ocean. Varying reflection efficiency from this changing surface can cause the reflected signal strength to change, causing "" fading "" in shortwave broadcasts.

Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves. Other considerations [ edit]VHF signals with frequencies above about 30 MHz usually penetrate the ionosphere and are not returned to the Earth's surface. E-skip is a notable exception, where VHF signals including FM broadcast and VHF TV signals are frequently reflected to the Earth during late Spring and early Summer.

E-skip rarely affects UHF frequencies, except for very rare occurrences below 500 MHz. Frequencies below approximately 10 MHz (wavelengths longer than 30 meters), including broadcasts in the mediumwave and shortwave bands (and to some extent longwave ), propagate most efficiently by skywave at night.

Frequencies above 10 MHz (wavelengths shorter than 30 meters) typically propagate most efficiently during the day. Frequencies lower than 3 k Hz have a wavelength longer than the distance between the Earth and the ionosphere. The maximum usable frequency for skywave propagation is strongly influenced by sunspot number. Skywave propagation is usually degraded—sometimes seriously—during geomagnetic storms.

Skywave propagation on the sunlit side of the Earth can be entirely disrupted during sudden ionospheric disturbances. Because the lower-altitude layers (the E-layer in particular) of the ionosphere largely disappear at night, the refractive layer of the ionosphere is much higher above the surface of the Earth at night.

This leads to an increase in the ""skip"" or ""hop"" distance of the skywave at night. History [ edit]Discovery of skywave propagation [ edit]Amateur radio operators are credited with the discovery of skywave propagation on the shortwave bands.

Early long-distance services used surface wave propagation at very low frequencies, [3] which are attenuated along the path. Longer distances and higher frequencies using this method meant more signal attenuation. This, and the difficulties of generating and detecting higher frequencies, made discovery of shortwave propagation difficult for commercial services.

Radio amateurs conducted the first successful transatlantic tests [4] in December 1921, operating in the 200 meter mediumwave band (1500 k Hz)—the shortest wavelength then available to amateurs. In 1922 hundreds of North American amateurs were heard in Europe at 200 meters and at least 30 North American amateurs heard amateur signals from Europe.

The first two-way communications between North American and Hawaiian amateurs began in 1922 at 200 meters.

Although operation on wavelengths shorter than 200 meters was technically illegal (but tolerated as the authorities mistakenly believed at first that such frequencies were useless for commercial or military use), amateurs began to experiment with those wavelengths using newly available vacuum tubes shortly after World War I.

Extreme interference at the upper edge of the 150-200 meter band—the official wavelengths allocated to amateurs by the Second National Radio Conference [5] in 1923—forced amateurs to shift to shorter and shorter wavelengths; however, amateurs were limited by regulation to wavelengths longer than 150 meters (2 MHz).

A few fortunate amateurs who obtained special permission for experimental communications below 150 meters completed hundreds of long distance two way contacts on 100 meters (3 MHz) in 1923 including the first transatlantic two way contacts [6] in November 1923, on 110 meters (2.72 MHz)By 1924 many additional specially licensed amateurs were routinely making transoceanic contacts at distances of 6000 miles (~9600 km) and more.

On 21 September several amateurs in California completed two way contacts with an amateur in New Zealand. On 19 October amateurs in New Zealand and England completed a 90-minute two-way contact nearly halfway around the world.

On October 10, the Third National Radio Conference made three shortwave bands available to U. S. amateurs [7] at 80 meters (3.75 MHz), 40 meters (7 MHz) and 20 meters (14 MHz). These were allocated worldwide, while the 10-meter band (28 MHz) was created by the Washington International Radiotelegraph Conference [8] on 25 November 1927.

The 15-meter band (21 MHz) was opened to amateurs in the United States on 1 May 1952. Marconi [ edit]In June and July 1923, Guglielmo Marconi 's transmissions were completed during nights on 97 meters from Poldhu Wireless Station, Cornwall, to his yacht Ellette in the Cape Verde Islands. In September 1924, Marconi transmitted during daytime and nighttime on 32 meters from Poldhu to his yacht in Beirut.

Marconi, in July 1924, entered into contracts with the British General Post Office (GPO) to install high speed shortwave telegraphy circuits from London to Australia, India, South Africa and Canada as the main element of the Imperial Wireless Chain. The UK-to-Canada shortwave ""Beam Wireless Service"" went into commercial operation on 25 October 1926.

Beam Wireless Services from the UK to Australia, South Africa and India went into service in 1927. Far more spectrum is available for long distance communication in the shortwave bands than in the long wave bands; and shortwave transmitters, receivers and antennas were orders of magnitude less expensive than the multi-hundred kilowatt transmitters and monstrous antennas needed for long wave.

Shortwave communications began to grow rapidly in the 1920s, [9] similar to the internet in the late 20th century. By 1928, more than half of long distance communications had moved from transoceanic cables and long wave wireless services to shortwave ""skip"" transmission and the overall volume of transoceanic shortwave communications had vastly increased.

Shortwave also ended the need for multimillion-dollar investments in new transoceanic telegraph cables and massive long wave wireless stations, although some existing transoceanic telegraph cables and commercial long wave communications stations remained in use until the 1960s.

The cable companies began to lose large sums of money in 1927, and a serious financial crisis threatened the viability of cable companies that were vital to strategic British interests. The British government convened the Imperial Wireless and Cable Conference [10] in 1928 ""to examine the situation that had arisen as a result of the competition of Beam Wireless with the Cable Services"".

It recommended and received Government approval for all overseas cable and wireless resources of the Empire to be merged into one system controlled by a newly formed company in 1929, Imperial and International Communications Ltd.

The name of the company was changed to Cable and Wireless Ltd. in 1934. See also [ edit]Radio propagation MW DXTV-FM DXNear Vertical Incidence Skywave F-layer Over-the-horizon radar Groundwave Schumann resonances Kennelly–Heaviside layer Skip zone Radio frequency Clear-channel station Tropospheric ducting Geomagnetic storm History of radio Amateur radio history List of electronics topics References [ edit]^ Sony Corporation. (1998). Wave Handbook. p.14. OCLC 734041509.^ K. Rawer: Wave Propagation in the Ionosphere. Kluwer Acad.

Publ., Dordrecht 1993. ISBN 0-7923-0775-5.^ Stormfax. Marconi Wireless on Cape Cod^ ""1921 - Club Station 1BCG and the Transatlantic Tests"". Radio Club of America. Retrieved 2009-09-05.^ ""Radio Service Bulletin No. 72"". Bureau of Navigation, Department of Commerce. 1923-04-02. pp. 9–13. Retrieved 2018-03-05.^ [1] Archived November 30, 2009, at the Wayback Machine.^ ""Recommendations for Regulation of Radio: October 6-10, 1924"". Earlyradiohistory.us. Retrieved 2012-08-31.^ ""Report"". twiar.org.^ ""Full text of ""Beyond the ionosphere : fifty years of satellite communication "" "".

Archive.org. Retrieved 2012-08-31.^ Cable and Wireless Pl c History Archived 2015-03-20 at the Wayback Machine. Further reading [ edit]Davies, Kenneth (1990). Ionospheric Radio. IEE Electromagnetic Waves Series #31.

London, UK: Peter Peregrinus Ltd/The Institution of Electrical Engineers. ISBN 0-86341-186-X. External links [ edit]Navy - Propagation of Waves Radio wave propagation basics HFRadio Propagation forums Rare gamma-ray flare disturbed ionosphere Articles on sporadic E and 50 MHz Radio Propagation Radio propagation overview Details of many forms of radio propagation [ hide]v t e Telecommunications History Beacon Broadcasting Cable protection system Cable TV Communications satellite Computer network Drums Electrical telegraph Fax Heliographs Hydraulic telegraph Internet Mass media Mobile phone Optical telecommunication Optical telegraphy Pager Photophone Prepay mobile phone Radio Radiotelephone Satellite communications Semaphore Smartphone Smoke signals Telecommunications history Telautograph Telegraphy Teleprinter (teletype) Telephone The Telephone Cases Television Timeline of communication technology Undersea telegraph line Videoconferencing Videophone Videotelephony Whistled language Pioneers Edwin Howard Armstrong John Logie Baird Paul Baran Alexander Graham Bell Tim Berners-Lee Jagadish Chandra Bose Vint Cerf Claude Chappe Donald Davies Lee de Forest Philo Farnsworth Reginald Fessenden Elisha Gray Erna Schneider Hoover Charles K. Kao Hedy Lamarr Innocenzo Manzetti Guglielmo Marconi Antonio Meucci Radia Perlman Alexander Stepanovich Popov Johann Philipp Reis Nikola Tesla Camille Tissot Alfred Vail Charles Wheatstone Vladimir K. Zworykin Transmission media Coaxial cable Fiber-optic communication Optical fiber Free-space optical communication Molecular communication Radio waves Transmission line Network topology and switching Links Nodes Terminal node Network switching ( circuit packet) Telephone exchange Multiplexing Space-division Frequency-division Time-division Polarization-division Orbital angular-momentum Code-division Networks ARPANET BITNET Cellular network Computer CYCLADES Ethernet Fido Net Internet ISDN LAN Mobile NGN NPL network Public Switched Telephone Radio Telecommunications equipment Television Telex WANWireless World Wide Web Category Portal Categories: Broadcast engineering Ionosphere Radio frequency propagation "

What do the radio, TV, radio controlled cars, and cell phones all have in common? They all use invisible waves to transmit information. Find out which materials block radio waves, and which materials allow radio waves to pass through by doing this experiment.

Wave Blockers

"Difficulty Time Required Very Short (≤ 1 day)Prerequisites None Material Availability Readily available Cost Low ($20 - $50)Safety No issues Abstract

Objective Test different materials to see if they block radio waves. Share your story with Science Buddies!Yes, I Did This Project!

Please log in (or create a free account) to let us know how things went. Credits This project was adapted from a student project submitted to the Marin County Science Fair in California. Sara Agee, Ph. D., Science Buddies Cite This Page MLA Style Science Buddies Staff. ""Wave Blockers"" Science Buddies .

Science Buddies, 28 July 2017. Web. 9 Apr. 2018 <https://www.sciencebuddies.org/science-fair-projects/project-ideas/Matl Sci_p036/materials-science/wave-blockers>APA Style Science Buddies Staff. (2017, July 28). Wave Blockers. Retrieved April 9, 2018 from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Matl Sci_p036/materials-science/wave-blockers Last edit date: 2017-07-28 "

. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated.

Radar

"From Wikipedia, the free encyclopedianavigation search For other uses, see Radar (disambiguation). Long-range radar antenna, used to track space objects and ballistic missiles. Radar of the type used for detection of aircraft. It rotates steadily, sweeping the airspace with a narrow beam. Radar is an object-detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain.

A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna (often the same antenna is used for transmitting and receiving) and a receiver and processor to determine properties of the object (s). Radio waves (pulsed or continuous) from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed.

Radar was developed secretly for military use by several nations in the period before and during World War II. A key development was the cavity magnetron in the UK, which allowed the creation of relatively small systems with sub-meter resolution.

The term RADAR was coined in 1940 by the United States Navy as an acronym for RA dio D etection A nd R anging [1] [2] or RA dio D irection A nd R anging.

[3] [4] The term radar has since entered English and other languages as a common noun, losing all capitalization. The modern uses of radar are highly diverse, including air and terrestrial traffic control, radar astronomy, air-defence systems, antimissile systems, marine radars to locate landmarks and other ships, aircraft anticollision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring, altimetry and flight control systems, guided missile target locating systems, ground-penetrating radar for geological observations, and range-controlled radar for public health surveillance.

[5] High tech radar systems are associated with digital signal processing, machine learning and are capable of extracting useful information from very high noise levels.

Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "" lidar "", which uses predominantly infrared light from lasers rather than radio waves.

Contents [ hide ]1 History1.1 First experiments1.2 Just before World War II1.3 During World War II2 Applications3 Principles3.1 Radar signal3.2 Illumination3.3 Reflection3.4 Radar equation3.5 Doppler effect3.6 Polarization3.7 Limiting factors3.7.1 Beam path and range3.7.2 Noise3.7.3 Interference3.7.4 Clutter3.7.5 Jamming4 Radar signal processing4.1 Distance measurement4.1.1 Transit time4.1.2 Frequency modulation4.2 Speed measurement4.3 Pulse-Doppler signal processing4.4 Reduction of interference effects4.5 Plot and track extraction5 Engineering5.1 Antenna design5.1.1 Parabolic reflector5.1.2 Types of scan5.1.3 Slotted waveguide5.1.4 Phased array5.2 Frequency bands5.3 Radar modulators5.4 Radar coolant6 Regulations7 See also8 Notes and references9 Bibliography9.1 References9.2 General9.3 Technical reading10 External links History [ edit]Main article: History of radar First experiments [ edit]As early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects.

In 1895, Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes. The next year, he added a spark-gap transmitter. In 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel.

In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation. [6]The German inventor Christian Hülsmeyer was the first to use radio waves to detect ""the presence of distant metallic objects"".

In 1904, he demonstrated the feasibility of detecting a ship in dense fog, but not its distance from the transmitter. [7] He obtained a patent [8] for his detection device in April 1904 and later a patent [9] for a related amendment for estimating the distance to the ship.

He also got a British patent on September 23, 1904 [10] for a full radar system, that he called a telemobiloscope.

It operated on a 50 cm wavelength and the pulsed radar signal was created via a spark-gap. His system already used the classic antenna setup of horn antenna with parabolic reflector and was presented to German military officials in practical tests in Cologne and Rotterdam harbour but was rejected. [11]In 1915, Robert Watson-Watt used radio technology to provide advance warning to airmen [12] and during the 1920s went on to lead the U. K. research establishment to make many advances using radio techniques, including the probing of the ionosphere and the detection of lightning at long distances.

Through his lightning experiments, Watson-Watt became an expert on the use of radio direction finding before turning his inquiry to shortwave transmission. Requiring a suitable receiver for such studies, he told the ""new boy"" Arnold Frederic Wilkins to conduct an extensive review of available shortwave units. Wilkins would select a General Post Office model after noting its manual's description of a ""fading"" effect (the common term for interference at the time) when aircraft flew overhead.

Across the Atlantic in 1922, after placing a transmitter and receiver on opposite sides of the Potomac River, U. S. Navy researchers A. Hoyt Taylor and Leo C. Young discovered that ships passing through the beam path caused the received signal to fade in and out.

Taylor submitted a report, suggesting that this phenomenon might be used to detect the presence of ships in low visibility, but the Navy did not immediately continue the work.

Eight years later, Lawrence A. Hyland at the Naval Research Laboratory (NRL) observed similar fading effects from passing aircraft; this revelation led to a patent application [13] as well as a proposal for further intensive research on radio-echo signals from moving targets to take place at NRL, where Taylor and Young were based at the time.

[14]Just before World War II [ edit]Experimental radar antenna, US Naval Research Laboratory, Anacostia, D. C., late 1930s Before the Second World War, researchers in the United Kingdom, France, Germany, Italy, Japan, the Netherlands, the Soviet Union, and the United States, independently and in great secrecy, developed technologies that led to the modern version of radar.

Australia, Canada, New Zealand, and South Africa followed prewar Great Britain's radar development, and Hungary generated its radar technology during the war.

[15]In France in 1934, following systematic studies on the Split Anode Magnetron, the research branch of the Compagnie Générale de Télégraphie Sans Fil (CSF) headed by Maurice Ponte with Henri Gutton, Sylvain Berline and M. Hugon, began developing an obstacle-locating radio apparatus, aspects of which were installed on the ocean liner Normandie in 1935.

[16] [17]During the same period, Soviet military engineer P. K. Oshchepkov, in collaboration with Leningrad Electrophysical Institute, produced an experimental apparatus, RAPID, capable of detecting an aircraft within 3 km of a receiver. [18] The Soviets produced their first mass production radars RUS-1 and RUS-2 Redut in 1939 but further development was slowed following the arrest of Oshchepkov and his subsequent gulag sentence. In total, only 607 Redut stations were produced during the war. The first Russian airborne radar, Gneiss-2, entered into service in June 1943 on Pe-2 fighters.

More than 230 Gneiss-2 stations were produced by the end of 1944. [19] The French and Soviet systems, however, featured continuous-wave operation that did not provide the full performance ultimately synonymous with modern radar systems.

Full radar evolved as a pulsed system, and the first such elementary apparatus was demonstrated in December 1934 by the American Robert M. Page, working at the Naval Research Laboratory.

[20] The following year, the United States Army successfully tested a primitive surface-to-surface radar to aim coastal battery searchlights at night. [21] This design was followed by a pulsed system demonstrated in May 1935 by Rudolf Kühnhold and the firm GEMA in Germany and then another in June 1935 by an Air Ministry team led by Robert A. Watson-Watt in Great Britain.

The first workable unit built by Robert Watson-Watt and his team A Chain Home tower in Great Baddow, Essex, United Kingdom Memorial plaque commemorating Robert Watson-Watt and Arnold Wilkins In 1935, Watson-Watt was asked to judge recent reports of a German radio-based death ray and turned the request over to Wilkins.

Wilkins returned a set of calculations demonstrating the system was basically impossible. When Watson-Watt then asked what such a system might do, Wilkins recalled the earlier report about aircraft causing radio interference. This revelation led to the Daventry Experiment of 26 February 1935, using a powerful BBC shortwave transmitter as the source and their GPO receiver setup in a field while a bomber flew around the site.

When the plane was clearly detected, Hugh Dowding, the Air Member for Supply and Research was very impressed with their system's potential and funds were immediately provided for further operational development.

[22] Watson-Watt's team patented the device in GB593017. [23] [24] [25]Development of radar greatly expanded on 1 September 1936 when Watson-Watt became Superintendent of a new establishment under the British Air Ministry, Bawdsey Research Station located in Bawdsey Manor, near Felixstowe, Suffolk.

Work there resulted in the design and installation of aircraft detection and tracking stations called "" Chain Home "" along the East and South coasts of England in time for the outbreak of World War II in 1939.

This system provided the vital advance information that helped the Royal Air Force win the Battle of Britain; without it, significant numbers of fighter aircraft would always need to be in the air to respond quickly enough if enemy aircraft detection relied solely on the observations of ground-based individuals. Also vital was the "" Dowding system "" of reporting and coordination to make best use of the radar information during tests of early deployment of radar in 1936 and 1937.

Given all required funding and development support, the team produced working radar systems in 1935 and began deployment.

By 1936, the first five Chain Home (CH) systems were operational and by 1940 stretched across the entire UK including Northern Ireland. Even by standards of the era, CH was crude; instead of broadcasting and receiving from an aimed antenna, CH broadcast a signal floodlighting the entire area in front of it, and then used one of Watson-Watt's own radio direction finders to determine the direction of the returned echoes.

This fact meant CH transmitters had to be much more powerful and have better antennas than competing systems but allowed its rapid introduction using existing technologies.

During World War II [ edit]Main article: Radar in World War IIA key development was the cavity magnetron in the UK, which allowed the creation of relatively small systems with sub-meter resolution.

Britain shared the technology with the U. S. during the 1940 Tizard Mission. [26] [27]In April 1940, Popular Science showed an example of a radar unit using the Watson-Watt patent in an article on air defence.

[28] Also, in late 1941 Popular Mechanics had an article in which a U. S. scientist speculated about the British early warning system on the English east coast and came close to what it was and how it worked. [29] Watson-Watt was sent to the U. S. in 1941 to advise on air defense after Japan’s attack on Pearl Harbor. [30] Alfred Lee Loomis organized the Radiation Laboratory at Cambridge, Massachusetts which developed the technology in the years 1941–45.

Later, in 1943, Page greatly improved radar with the monopulse technique that was used for many years in most radar applications. [31]The war precipitated research to find better resolution, more portability, and more features for radar, including complementary navigation systems like Oboe used by the RAF's Pathfinder. Applications [ edit]Commercial marine radar antenna. The rotating antenna radiates a vertical fan-shaped beam.

The information provided by radar includes the bearing and range (and therefore position) of the object from the radar scanner. It is thus used in many different fields where the need for such positioning is crucial. The first use of radar was for military purposes: to locate air, ground and sea targets.

This evolved in the civilian field into applications for aircraft, ships, and roads. In aviation, aircraft can be equipped with radar devices that warn of aircraft or other obstacles in or approaching their path, display weather information, and give accurate altitude readings. The first commercial device fitted to aircraft was a 1938 Bell Lab unit on some United Air Lines aircraft.

[29] Aircraft can land in fog at airports equipped with radar-assisted ground-controlled approach systems in which the plane's position is observed on radar screens by operators who radio landing instructions to the pilot, maintaining the aircraft on a defined approach path to the runway.

Military fighter aircraft are usually fitted with air-to-air targeting radars, to detect and target enemy aircraft. In addition, larger specialized military aircraft carry powerful airborne radars to observe air traffic over a wide region and direct fighter aircraft towards targets.

Marine radars are used to measure the bearing and distance of ships to prevent collision with other ships, to navigate, and to fix their position at sea when within range of shore or other fixed references such as islands, buoys, and lightships.

In port or in harbour, vessel traffic service radar systems are used to monitor and regulate ship movements in busy waters. Meteorologists use radar to monitor precipitation and wind. It has become the primary tool for short-term weather forecasting and watching for severe weather such as thunderstorms, tornadoes, winter storms, precipitation types, etc. Geologists use specialized ground-penetrating radars to map the composition of Earth's crust. Police forces use radar guns to monitor vehicle speeds on the roads.

Smaller radar systems are used to detect human movement. Examples are breathing pattern detection for sleep monitoring [32] and hand and finger gesture detection for computer interaction.

[33] Automatic door opening, light activation and intruder sensing are also common. Principles [ edit]Radar signal [ edit]Further information: Radar signal characteristics A radar system has a transmitter that emits radio waves called radar signals in predetermined directions.

When these come into contact with an object they are usually reflected or scattered in many directions. But some of them absorb and penetrate into the target to some degree. Radar signals are reflected especially well by materials of considerable electrical conductivity —especially by most metals, by seawater and by wet ground.

Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either toward or away from the transmitter, there is a slight equivalent change in the frequency of the radio waves, caused by the Doppler effect. Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, they can be strengthened by electronic amplifiers. More sophisticated methods of signal processing are also used in order to recover useful radar signals

. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated.

Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapour, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars, except when their detection is intended.

Illumination [ edit]Radar relies on its own transmissions rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This process of directing artificial radio waves towards objects is called illumination, although radio waves are invisible to the human eye or optical cameras.

Reflection [ edit]Main article: Reflection (physics)Brightness can indicate reflectivity as in this 1960 weather radar image (of Hurricane Abby ). The radar's frequency, pulse form, polarization, signal processing, and antenna determine what it can observe.

If electromagnetic waves travelling through one material meet another material, having a different dielectric constant or diamagnetic constant from the first, the waves will reflect or scatter from the boundary between the materials. This means that a solid object in air or in a vacuum, or a significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves from its surface.

This is particularly true for electrically conductive materials such as metal and carbon fibre, making radar well-suited to the detection of aircraft and ships. Radar absorbing material, containing resistive and sometimes magnetic substances, is used on military vehicles to reduce radar reflection. This is the radio equivalent of painting something a dark colour so that it cannot be seen by the eye at night.

Radar waves scatter in a variety of ways depending on the size (wavelength) of the radio wave and the shape of the target. If the wavelength is much shorter than the target's size, the wave will bounce off in a way similar to the way light is reflected by a mirror. If the wavelength is much longer than the size of the target, the target may not be visible because of poor reflection.

Low-frequency radar technology is dependent on resonances for detection, but not identification, of targets. This is described by Rayleigh scattering, an effect that creates Earth's blue sky and red sunsets. When the two length scales are comparable, there may be resonances. Early radars used very long wavelengths that were larger than the targets and thus received a vague signal, whereas many modern systems use shorter wavelengths (a few centimetres or less) that can image objects as small as a loaf of bread. Short radio waves reflect from curves and corners in a way similar to glint from a rounded piece of glass. The most reflective targets for short wavelengths have 90° angles between the reflective surfaces.

A corner reflector consists of three flat surfaces meeting like the inside corner of a box. The structure will reflect waves entering its opening directly back to the source. They are commonly used as radar reflectors to make otherwise difficult-to-detect objects easier to detect. Corner reflectors on boats, for example, make them more detectable to avoid collision or during a rescue. For similar reasons, objects intended to avoid detection will not have inside corners or surfaces and edges perpendicular to likely detection directions, which leads to ""odd"" looking stealth aircraft.

These precautions do not completely eliminate reflection because of diffraction, especially at longer wavelengths. Half wavelength long wires or strips of conducting material, such as chaff, are very reflective but do not direct the scattered energy back toward the source.

The extent to which an object reflects or scatters radio waves is called its radar cross section. Radar equation [ edit]The power P r returning to the receiving antenna is given by the equation:where P t = transmitter power G t = gain of the transmitting antenna A r = effective aperture (area) of the receiving antenna; this can also be expressed as, where= transmitted wavelength G r = gain of receiving antenna [34]σ = radar cross section, or scattering coefficient, of the target F = pattern propagation factor R t = distance from the transmitter to the target R r = distance from the target to the receiver.

In the common case where the transmitter and the receiver are at the same location, R t = R r and the term R t ² R r ² can be replaced by R 4, where R is the range.

This yields: This shows that the received power declines as the fourth power of the range, which means that the received power from distant targets is relatively very small. Additional filtering and pulse integration modifies the radar equation slightly for pulse-Doppler radar performance, which can be used to increase detection range and reduce transmit power.

The equation above with F = 1 is a simplification for transmission in a vacuum without interference. The propagation factor accounts for the effects of multipath and shadowing and depends on the details of the environment.

In a real-world situation, pathloss effects should also be considered. Doppler effect [ edit]Main articles: Doppler radar and Pulse-Doppler radar Frequency shift is caused by motion that changes the number of wavelengths between the reflector and the radar.

This can degrade or enhance radar performance depending upon how it affects the detection process. As an example, Moving Target Indication can interact with Doppler to produce signal cancellation at certain radial velocities, which degrades performance.

Sea-based radar systems, semi-active radar homing, active radar homing, weather radar, military aircraft, and radar astronomy rely on the Doppler effect to enhance performance. This produces information about target velocity during the detection process. This also allows small objects to be detected in an environment containing much larger nearby slow moving objects. Doppler shift depends upon whether the radar configuration is active or passive. Active radar transmits a signal that is reflected back to the receiver.

Passive radar depends upon the object sending a signal to the receiver. The Doppler frequency shift for active radar is as follows, where is Doppler frequency, is transmit frequency, is radial velocity, and is the speed of light: [35]. Passive radar is applicable to electronic countermeasures and radio astronomy as follows:. Only the radial component of the velocity is relevant.

When the reflector is moving at right angle to the radar beam, it has no relative velocity. Vehicles and weather moving parallel to the radar beam produce the maximum Doppler frequency shift.

When the transmit frequency () is pulsed, using a pulse repeat frequency of, the resulting frequency spectrum will contain harmonic frequencies above and below with a distance of.

As a result, the Doppler measurement is only non-ambiguous if the Doppler frequency shift is less than half of, called the Nyquist frequency, since the returned frequency otherwise cannot be distinguished from shifting of a harmonic frequency above or below, thus requiring: Or when substituting with: As an example, a Doppler weather radar with a pulse rate of 2 k Hz and transmit frequency of 1 GHz can reliably measure weather speed up to at most 150 m/s (340 mph), thus cannot reliably determine radial velocity of aircraft moving 1,000 m/s (2,200 mph).

Polarization [ edit]Further information: Polarization (waves)In all electromagnetic radiation, the electric field is perpendicular to the direction of propagation, and the electric field direction is the polarization of the wave. For a transmitted radar signal, the polarization can be controlled to yield different effects. Radars use horizontal, vertical, linear, and circular polarization to detect different types of reflections.

For example, circular polarization is used to minimize the interference caused by rain. Linear polarization returns usually indicate metal surfaces. Random polarization returns usually indicate a fractal surface, such as rocks or soil, and are used by navigation radars.

Limiting factors [ edit]Beam path and range [ edit]See also: Beam forming and Over-the-horizon radar Echo heights above ground The radar beam would follow a linear path in vacuum, but it really follows a somewhat curved path in the atmosphere because of the variation of the refractive index of air, that is called the radar horizon. Even when the beam is emitted parallel to the ground, it will rise above it as the Earth curvature sinks below the horizon.

Furthermore, the signal is attenuated by the medium it crosses, and the beam disperses. The maximum range of a conventional radar can be limited by a number of factors: Line of sight, which depends on height above ground.

This means without a direct line of sight the path of the beam is blocked. The maximum non-ambiguous range, which is determined by the pulse repetition frequency.

The maximum non-ambiguous range is the distance the pulse could travel and return before the next pulse is emitted. Radar sensitivity and power of the return signal as computed in the radar equation. This includes factors such as environmental conditions and the size (or radar cross section) of the target.

Noise [ edit]Main articles: Noise (electronics) and Noise (radio)Signal noise is an internal source of random variations in the signal, which is generated by all electronic components. Reflected signals decline rapidly as distance increases, so noise introduces a radar range limitation.

The noise floor and signal to noise ratio are two different measures of performance that affect range performance. Reflectors that are too far away produce too little signal to exceed the noise floor and cannot be detected.

Detection requires a signal that exceeds the noise floor by at least the signal to noise ratio. Noise typically appears as random variations superimposed on the desired echo signal received in the radar receiver. The lower the power of the desired signal, the more difficult it is to discern it from the noise. Noise figure is a measure of the noise produced by a receiver compared to an ideal receiver, and this needs to be minimized. Shot noise is produced by electrons in transit across a discontinuity, which occurs in all detectors.

Shot noise is the dominant source in most receivers. There will also be flicker noise caused by electron transit through amplification devices, which is reduced using heterodyne amplification. Another reason for heterodyne processing is that for fixed fractional bandwidth, the instantaneous bandwidth increases linearly in frequency.

This allows improved range resolution. The one notable exception to heterodyne (downconversion) radar systems is ultra-wideband radar. Here a single cycle, or transient wave, is used similar to UWB communications, see List of UWB channels. Noise is also generated by external sources, most importantly the natural thermal radiation of the background surrounding the target of interest. In modern radar systems, the internal noise is typically about equal to or lower than the external noise.

An exception is if the radar is aimed upwards at clear sky, where the scene is so ""cold"" that it generates very little thermal noise. The thermal noise is given by k BT B, where T is temperature, B is bandwidth (post matched filter) and k B is Boltzmann's constant.

There is an appealing intuitive interpretation of this relationship in a radar. Matched filtering allows the entire energy received from a target to be compressed into a single bin (be it a range, Doppler, elevation, or azimuth bin). On the surface it would appear that then within a fixed interval of time one could obtain perfect, error free, detection.

To do this one simply compresses all energy into an infinitesimal time slice. What limits this approach in the real world is that, while time is arbitrarily divisible, current is not. The quantum of electrical energy is an electron, and so the best one can do is match filter all energy into a single electron.

Since the electron is moving at a certain temperature ( Plank spectrum) this noise source cannot be further eroded. We see then that radar, like all macro-scale entities, is profoundly impacted by quantum theory. Noise is random and target signals are not. Signal processing can take advantage of this phenomenon to reduce the noise floor using two strategies. The kind of signal integration used with moving target indication can improve noise up to for each stage.

The signal can also be split among multiple filters for pulse-Doppler signal processing, which reduces the noise floor by the number of filters. These improvements depend upon coherence. Interference [ edit]Main article: Interference (wave propagation)Radar systems must overcome unwanted signals in order to focus on the targets of interest.

These unwanted signals may originate from internal and external sources, both passive and active. The ability of the radar system to overcome these unwanted signals defines its signal-to-noise ratio (SNR). SNR is defined as the ratio of the signal power to the noise power within the desired signal; it compares the level of a desired target signal to the level of background noise (atmospheric noise and noise generated within the receiver).

The higher a system's SNR the better it is at discriminating actual targets from noise signals. Clutter [ edit]Main article: Clutter (radar)Clutter refers to radio frequency (RF) echoes returned from targets which are uninteresting to the radar operators.

Such targets include natural objects such as ground, sea, and when not being tasked for meteorological purposes, precipitation (such as rain, snow or hail), sand storms, animals (especially birds), atmospheric turbulence, and other atmospheric effects, such as ionosphere reflections, meteor trails, and Hail spike.

Clutter may also be returned from man-made objects such as buildings and, intentionally, by radar countermeasures such as chaff. Some clutter may also be caused by a long radar waveguide between the radar transceiver and the antenna.

In a typical plan position indicator (PPI) radar with a rotating antenna, this will usually be seen as a ""sun"" or ""sunburst"" in the centre of the display as the receiver responds to echoes from dust particles and misguided RF in the waveguide. Adjusting the timing between when the transmitter sends a pulse and when the receiver stage is enabled will generally reduce the sunburst without affecting the accuracy of the range, since most sunburst is caused by a diffused transmit pulse reflected before it leaves the antenna.

Clutter is considered a passive interference source, since it only appears in response to radar signals sent by the radar. Clutter is detected and neutralized in several ways. Clutter tends to appear static between radar scans; on subsequent scan echoes, desirable targets will appear to move, and all stationary echoes can be eliminated.

Sea clutter can be reduced by using horizontal polarization, while rain is reduced with circular polarization (meteorological radars wish for the opposite effect, and therefore use linear polarization to detect precipitation).

Other methods attempt to increase the signal-to-clutter ratio. Clutter moves with the wind or is stationary. Two common strategies to improve measure or performance in a clutter environment are: Moving target indication, which integrates successive pulses and Doppler processing, which uses filters to separate clutter from desirable signals.

The most effective clutter reduction technique is pulse-Doppler radar. Doppler separates clutter from aircraft and spacecraft using a frequency spectrum, so individual signals can be separated from multiple reflectors located in the same volume using velocity differences. This requires a coherent transmitter. Another technique uses a moving target indicator that subtracts the receive signal from two successive pulses using phase to reduce signals from slow moving objects.

This can be adapted for systems that lack a coherent transmitter, such as time-domain pulse-amplitude radar. Constant false alarm rate, a form of automatic gain control (AGC), is a method that relies on clutter returns far outnumbering echoes from targets of interest. The receiver's gain is automatically adjusted to maintain a constant level of overall visible clutter.

While this does not help detect targets masked by stronger surrounding clutter, it does help to distinguish strong target sources. In the past, radar AGC was electronically controlled and affected the gain of the entire radar receiver. As radars evolved, AGC became computer-software controlled and affected the gain with greater granularity in specific detection cells.

Radar multipath echoes from a target cause ghosts to appear. Clutter may also originate from multipath echoes from valid targets caused by ground reflection, atmospheric ducting or ionospheric reflection / refraction (e.g., anomalous propagation ). This clutter type is especially bothersome since it appears to move and behave like other normal (point) targets of interest.

In a typical scenario, an aircraft echo is reflected from the ground below, appearing to the receiver as an identical target below the correct one.

The radar may try to unify the targets, reporting the target at an incorrect height, or eliminating it on the basis of jitter or a physical impossibility. Terrain bounce jamming exploits this response by amplifying the radar signal and directing it downward. [36] These problems can be overcome by incorporating a ground map of the radar's surroundings and eliminating all echoes which appear to originate below ground or above a certain height.

Monopulse can be improved by altering the elevation algorithm used at low elevation. In newer air traffic control radar equipment, algorithms are used to identify the false targets by comparing the current pulse returns to those adjacent, as well as calculating return improbabilities. Jamming [ edit]Main article: Radar jamming and deception Radar jamming refers to radio frequency signals originating from sources outside the radar, transmitting in the radar's frequency and thereby masking targets of interest.

Jamming may be intentional, as with an electronic warfare tactic, or unintentional, as with friendly forces operating equipment that transmits using the same frequency range. Jamming is considered an active interference source, since it is initiated by elements outside the radar and in general unrelated to the radar signals.

Jamming is problematic to radar since the jamming signal only needs to travel one way (from the jammer to the radar receiver) whereas the radar echoes travel two ways (radar-target-radar) and are therefore significantly reduced in power by the time they return to the radar receiver.

Jammers therefore can be much less powerful than their jammed radars and still effectively mask targets along the line of sight from the jammer to the radar ( mainlobe jamming ). Jammers have an added effect of affecting radars along other lines of sight through the radar receiver's sidelobes ( sidelobe jamming ).

Mainlobe jamming can generally only be reduced by narrowing the mainlobe solid angle and cannot fully be eliminated when directly facing a jammer which uses the same frequency and polarization as the radar. Sidelobe jamming can be overcome by reducing receiving sidelobes in the radar antenna design and by using an omnidirectional antenna to detect and disregard non-mainlobe signals.

Other anti-jamming techniques are frequency hopping and polarization. Radar signal processing [ edit]Distance measurement [ edit]Transit time [ edit]Further information: Time of flight Pulse radar: The round-trip time for the radar pulse to get to the target and return is measured.

The distance is proportional to this time. Continuous wave (CW) radar One way to obtain a distance measurement is based on the time-of-flight: transmit a short pulse of radio signal (electromagnetic radiation) and measure the time it takes for the reflection to return.

The distance is one-half the product of the round trip time (because the signal has to travel to the target and then back to the receiver) and the speed of the signal. Since radio waves travel at the speed of light, accurate distance measurement requires high-speed electronics.

In most cases, the receiver does not detect the return while the signal is being transmitted. Through the use of a duplexer, the radar switches between transmitting and receiving at a predetermined rate. A similar effect imposes a maximum range as well. In order to maximize range, longer times between pulses should be used, referred to as a pulse repetition time, or its reciprocal, pulse repetition frequency.

These two effects tend to be at odds with each other, and it is not easy to combine both good short range and good long range in a single radar. This is because the short pulses needed for a good minimum range broadcast have less total energy, making the returns much smaller and the target harder to detect.

This could be offset by using more pulses, but this would shorten the maximum range. So each radar uses a particular type of signal. Long-range radars tend to use long pulses with long delays between them, and short range radars use smaller pulses with less time between them. As electronics have improved many radars now can change their pulse repetition frequency, thereby changing their range.

The newest radars fire two pulses during one cell, one for short range (about 10 km (6.2 mi)) and a separate signal for longer ranges (about 100 km (62 mi)).

The distance resolution and the characteristics of the received signal as compared to noise depends on the shape of the pulse. The pulse is often modulated to achieve better performance using a technique known as pulse compression. Distance may also be measured as a function of time. The radar mile is the time it takes for a radar pulse to travel one nautical mile, reflect off a target, and return to the radar antenna.

Since a nautical mile is defined as 1,852 m, then dividing this distance by the speed of light (299,792,458 m/s), and then multiplying the result by 2 yields a result of 12.36 μs in duration. Frequency modulation [ edit]Main article: Frequency modulation Another form of distance measuring radar is based on frequency modulation. Frequency comparison between two signals is considerably more accurate, even with older electronics, than timing the signal.

By measuring the frequency of the returned signal and comparing that with the original, the difference can be easily measured. This technique can be used in continuous wave radar and is often found in aircraft radar altimeters. In these systems a ""carrier"" radar signal is frequency modulated in a predictable way, typically varying up and down with a sine wave or sawtooth pattern at audio frequencies.

The signal is then sent out from one antenna and received on another, typically located on the bottom of the aircraft, and the signal can be continuously compared using a simple beat frequency modulator that produces an audio frequency tone from the returned signal and a portion of the transmitted signal.

Since the signal frequency is changing, by the time the signal returns to the aircraft the transmit frequency has changed. The frequency shift is used to measure distance. The modulation index riding on the receive signal is proportional to the time delay between the radar and the reflector. The frequency shift becomes greater with greater time delay. The frequency shift is directly proportional to the distance travelled.

That distance can be displayed on an instrument, and it may also be available via the transponder. This signal processing is similar to that used in speed detecting Doppler radar. Example systems using this approach are AZUSA, MISTRAM, and UDOP. A further advantage is that the radar can operate effectively at relatively low frequencies. This was important in the early development of this type when high frequency signal generation was difficult or expensive. Terrestrial radar uses low-power FM signals that cover a larger frequency range. The multiple reflections are analyzed mathematically for pattern changes with multiple passes creating a computerized synthetic image.

Doppler effects are used which allows slow moving objects to be detected as well as largely eliminating ""noise"" from the surfaces of bodies of water. Speed measurement [ edit]Speed is the change in distance to an object with respect to time. Thus the existing system for measuring distance, combined with a memory capacity to see where the target last was, is enough to measure speed. At one time the memory consisted of a user making grease pencil marks on the radar screen and then calculating the speed using a slide rule.

Modern radar systems perform the equivalent operation faster and more accurately using computers. If the transmitter's output is coherent (phase synchronized), there is another effect that can be used to make almost instant speed measurements (no memory is required), known as the Doppler effect. Most modern radar systems use this principle into Doppler radar and pulse-Doppler radar systems ( weather radar, military radar).

The Doppler effect is only able to determine the relative speed of the target along the line of sight from the radar to the target.

Any component of target velocity perpendicular to the line of sight cannot be determined by using the Doppler effect alone, but it can be determined by tracking the target's azimuth over time. It is possible to make a Doppler radar without any pulsing, known as a continuous-wave radar (CW radar), by sending out a very pure signal of a known frequency.

CW radar is ideal for determining the radial component of a target's velocity. CW radar is typically used by traffic enforcement to measure vehicle speed quickly and accurately where range is not important.

When using a pulsed radar, the variation between the phase of successive returns gives the distance the target has moved between pulses, and thus its speed can be calculated. Other mathematical developments in radar signal processing include time-frequency analysis (Weyl Heisenberg or wavelet ), as well as the chirplet transform which makes use of the change of frequency of returns from moving targets (""chirp"").

Pulse-Doppler signal processing [ edit]Main article: Pulse-Doppler signal processing Pulse-Doppler signal processing.

The Range Sample axis represents individual samples taken in between each transmit pulse. The Range Interval axis represents each successive transmit pulse interval during which samples are taken. The Fast Fourier Transform process converts time-domain samples into frequency domain spectra. This is sometimes called the bed of nails.

Pulse-Doppler signal processing includes frequency filtering in the detection process. The space between each transmit pulse is divided into range cells or range gates. Each cell is filtered independently much like the process used by a spectrum analyzer to produce the display showing different frequencies. Each different distance produces a different spectrum. These spectra are used to perform the detection process.

This is required to achieve acceptable performance in hostile environments involving weather, terrain, and electronic countermeasures. The primary purpose is to measure both the amplitude and frequency of the aggregate reflected signal from multiple distances. This is used with weather radar to measure radial wind velocity and precipitation rate in each different volume of air. This is linked with computing systems to produce a real-time electronic weather map. Aircraft safety depends upon continuous access to accurate weather radar information that is used to prevent injuries and accidents. Weather radar uses a low PRF. Coherency requirements are not as strict as those for military systems because individual signals ordinarily do not need to be separated.

Less sophisticated filtering is required, and range ambiguity processing is not normally needed with weather radar in comparison with military radar intended to track air vehicles. The alternate purpose is "" look-down/shoot-down "" capability required to improve military air combat survivability. Pulse-Doppler is also used for ground based surveillance radar required to defend personnel and vehicles.

[37] [38] Pulse-Doppler signal processing increases the maximum detection distance using less radiation in close proximity to aircraft pilots, shipboard personnel, infantry, and artillery. Reflections from terrain, water, and weather produce signals much larger than aircraft and missiles, which allows fast moving vehicles to hide using nap-of-the-earth flying techniques and stealth technology to avoid detection until an attack vehicle is too close to destroy.

Pulse-Doppler signal processing incorporates more sophisticated electronic filtering that safely eliminates this kind of weakness. This requires the use of medium pulse-repetition frequency with phase coherent hardware that has a large dynamic range.

Military applications require medium PRF which prevents range from being determined directly, and range ambiguity resolution processing is required to identify the true range of all reflected signals. Radial movement is usually linked with Doppler frequency to produce a lock signal that cannot be produced by radar jamming signals. Pulse-Doppler signal processing also produces audible signals that can be used for threat identification. [37]Reduction of interference effects [ edit]Signal processing is employed in radar systems to reduce the radar interference effects. Signal processing techniques include moving target indication, Pulse-Doppler signal processing, moving target detection processors, correlation with secondary surveillance radar targets, space-time adaptive processing, and track-before-detect.

Constant false alarm rate and digital terrain model processing are also used in clutter environments. Plot and track extraction [ edit]Main article: Track algorithm A Track algorithm is a radar performance enhancement strategy.

Tracking algorithms provide the ability to predict future position of multiple moving objects based on the history of the individual positions being reported by sensor systems. Historical information is accumulated and used to predict future position for use with air traffic control, threat estimation, combat system doctrine, gun aiming, and missile guidance. Position data is accumulated radar sensors over the span of a few minutes. There are four common track algorithms.

[39]Nearest neighbour algorithm Probabilistic Data Association Multiple Hypothesis Tracking Interactive Multiple Model (IMM)Radar video returns from aircraft can be subjected to a plot extraction process whereby spurious and interfering signals are discarded. A sequence of target returns can be monitored through a device known as a plot extractor. The non-relevant real time returns can be removed from the displayed information and a single plot displayed. In some radar systems, or alternatively in the command and control system to which the radar is connected, a radar tracker is used to associate the sequence of plots belonging to individual targets and estimate the targets' headings and speeds. Engineering [ edit]Main article: Radar engineering details Radar components A radar's components are: A transmitter that generates the radio signal with an oscillator such as a klystron or a magnetron and controls its duration by a modulator.

A waveguide that links the transmitter and the antenna. A duplexer that serves as a switch between the antenna and the transmitter or the receiver for the signal when the antenna is used in both situations. A receiver. Knowing the shape of the desired received signal (a pulse), an optimal receiver can be designed using a matched filter.

A display processor to produce signals for human readable output devices. An electronic section that controls all those devices and the antenna to perform the radar scan ordered by software. A link to end user devices and displays. Antenna design [ edit]Main article: Antenna (radio)Radio signals broadcast from a single antenna will spread out in all directions, and likewise a single antenna will receive signals equally from all directions.

This leaves the radar with the problem of deciding where the target object is located. Early systems tended to use omnidirectional broadcast antennas, with directional receiver antennas which were pointed in various directions. For instance, the first system to be deployed, Chain Home, used two straight antennas at right angles for reception, each on a different display.

The maximum return would be detected with an antenna at right angles to the target, and a minimum with the antenna pointed directly at it (end on). The operator could determine the direction to a target by rotating the antenna so one display showed a maximum while the other showed a minimum.

One serious limitation with this type of solution is that the broadcast is sent out in all directions, so the amount of energy in the direction being examined is a small part of that transmitted. To get a reasonable amount of power on the ""target"", the transmitting aerial should also be directional.

Parabolic reflector [ edit]Main article: Parabolic antenna More modern systems use a steerable parabolic ""dish"" to create a tight broadcast beam, typically using the same dish as the receiver. Such systems often combine two radar frequencies in the same antenna in order to allow automatic steering, or radar lock.

Parabolic reflectors can be either symmetric parabolas or spoiled parabolas: Symmetric parabolic antennas produce a narrow ""pencil"" beam in both the X and Y dimensions and consequently have a higher gain.

The NEXRAD Pulse-Doppler weather radar uses a symmetric antenna to perform detailed volumetric scans of the atmosphere. Spoiled parabolic antennas produce a narrow beam in one dimension and a relatively wide beam in the other. This feature is useful if target detection over a wide range of angles is more important than target location in three dimensions. Most 2D surveillance radars use a spoiled parabolic antenna with a narrow azimuthal beamwidth and wide vertical beamwidth.

This beam configuration allows the radar operator to detect an aircraft at a specific azimuth but at an indeterminate height. Conversely, so-called ""nodder"" height finding radars use a dish with a narrow vertical beamwidth and wide azimuthal beamwidth to detect an aircraft at a specific height but with low azimuthal precision.

Surveillance radar antenna Types of scan [ edit]Primary Scan: A scanning technique where the main antenna aerial is moved to produce a scanning beam, examples include circular scan, sector scan, etc. Secondary Scan: A scanning technique where the antenna feed is moved to produce a scanning beam, examples include conical scan, unidirectional sector scan, lobe switching, etc.

Palmer Scan: A scanning technique that produces a scanning beam by moving the main antenna and its feed.

A Palmer Scan is a combination of a Primary Scan and a Secondary Scan. Conical scanning: The radar beam is rotated in a small circle around the ""boresight"" axis, which is pointed at the target. Slotted waveguide [ edit]Slotted waveguide antenna Main article: Slotted waveguide Applied similarly to the parabolic reflector, the slotted waveguide is moved mechanically to scan and is particularly suitable for non-tracking surface scan systems, where the vertical pattern may remain constant.

Owing to its lower cost and less wind exposure, shipboard, airport surface, and harbour surveillance radars now use this approach in preference to a parabolic antenna. Phased array [ edit]Phased array: Not all radar antennas must rotate to scan the sky. Main article: Phased array Another method of steering is used in a phased array radar.

Phased array antennas are composed of evenly spaced similar antenna elements, such as aerials or rows of slotted waveguide. Each antenna element or group of antenna elements incorporates a discrete phase shift that produces a phase gradient across the array. For example, array elements producing a 5 degree phase shift for each wavelength across the array face will produce a beam pointed 5 degrees away from the centreline perpendicular to the array face. Signals travelling along that beam will be reinforced. Signals offset from that beam will be cancelled.

The amount of reinforcement is antenna gain. The amount of cancellation is side-lobe suppression. [40]Phased array radars have been in use since the earliest years of radar in World War II ( Mammut radar ), but electronic device limitations led to poor performance. Phased array radars were originally used for missile defence (see for example Safeguard Program ).

They are the heart of the ship-borne Aegis Combat System and the Patriot Missile System. The massive redundancy associated with having a large number of array elements increases reliability at the expense of gradual performance degradation that occurs as individual phase elements fail.

To a lesser extent, Phased array radars have been used in Weather Surveillance. As of 2017, NOAA plans to implement a national network of Multi-Function Phased array radars throughout the United States within 10 years, for meteorological studies and flight monitoring.

[41]Phased array antenna can be built to conform to specific shapes, like missiles, infantry support vehicles, ships, and aircraft. As the price of electronics has fallen, phased array radars have become more common. Almost all modern military radar systems are based on phased arrays, where the small additional cost is offset by the improved reliability of a system with no moving parts.

Traditional moving-antenna designs are still widely used in roles where cost is a significant factor such as air traffic surveillance and similar systems. Phased array radars are valued for use in aircraft since they can track multiple targets. The first aircraft to use a phased array radar was the B-1B Lancer.

The first fighter aircraft to use phased array radar was the Mikoyan Mi G-31. The Mi G-31M's SBI-16 Zaslon Passive electronically scanned array radar was considered to be the world's most powerful fighter radar, [42] until the AN/APG-77 Active electronically scanned array was introduced on the Lockheed Martin F-22 Raptor.

Phased-array interferometry or aperture synthesis techniques, using an array of separate dishes that are phased into a single effective aperture, are not typical for radar applications, although they are widely used in radio astronomy. Because of the thinned array curse, such multiple aperture arrays, when used in transmitters, result in narrow beams at the expense of reducing the total power transmitted to the target.

In principle, such techniques could increase spatial resolution, but the lower power means that this is generally not effective. Aperture synthesis by post-processing motion data from a single moving source, on the other hand, is widely used in space and airborne radar systems.

Frequency bands [ edit]Main article: Radio spectrum § IEEEThe traditional band names originated as code-names during World War II and are still in military and aviation use throughout the world. They have been adopted in the United States by the Institute of Electrical and Electronics Engineers and internationally by the International Telecommunication Union.

Most countries have additional regulations to control which parts of each band are available for civilian or military use. Other users of the radio spectrum, such as the broadcasting and electronic countermeasures industries, have replaced the traditional military designations with their own systems.

Radar frequency bands Band name Frequency range Wavelength range Notes HF 3–30 MHz 10–100 m Coastal radar systems, over-the-horizon radar (OTH) radars; 'high frequency'VHF30–300 MHz 1–10 m Very long range, ground penetrating; 'very high frequency'P < 300 MHz > 1 m 'P' for 'previous', applied retrospectively to early radar systems; essentially HF + VHFUHF300–1000 MHz 0.3–1 m Very long range (e.g.

ballistic missile early warning ), ground penetrating, foliage penetrating; 'ultra high frequency'L 1–2 GHz 15–30 cm Long range air traffic control and surveillance; 'L' for 'long'S2–4 GHz 7.5–15 cm Moderate range surveillance, Terminal air traffic control, long-range weather, marine radar; 'S' for 'short'C4–8 GHz 3.75–7.5 cm Satellite transponders; a compromise (hence 'C') between X and S bands; weather; long range tracking X8–12 GHz 2.5–3.75 cm Missile guidance, marine radar, weather, medium-resolution mapping and ground surveillance; in the United States the narrow range 10.525 GHz ±25 MHz is used for airport radar; short range tracking.

Named X band because the frequency was a secret during WW2. K u12–18 GHz 1.67–2.5 cm High-resolution, also used for satellite transponders, frequency under K band (hence 'u')K18–24 GHz 1.11–1.67 cm From German kurz, meaning 'short'; limited use due to absorption by water vapour, so K u and K a were used instead for surveillance.

K-band is used for detecting clouds by meteorologists, and by police for detecting speeding motorists. K-band radar guns operate at 24.150 ± 0.100 GHz. K a24–40 GHz 0.75–1.11 cm Mapping, short range, airport surveillance; frequency just above K band (hence 'a') Photo radar, used to trigger cameras which take pictures of license plates of cars running red lights, operates at 34.300 ± 0.100 GHz.mm 40–300 GHz 1.0–7.5 mm Millimetre band, subdivided as below.

The frequency ranges depend on waveguide size. Multiple letters are assigned to these bands by different groups. These are from Baytron, a now defunct company that made test equipment. V 40–75 GHz 4.0–7.5 mm Very strongly absorbed by atmospheric oxygen, which resonates at 60 GHz.

W75–110 GHz 2.7–4.0 mm Used as a visual sensor for experimental autonomous vehicles, high-resolution meteorological observation, and imaging. Radar modulators [ edit]Modulators act to provide the waveform of the RF-pulse. There are two different radar modulator designs: High voltage switch for non-coherent keyed power-oscillators [43] These modulators consist of a high voltage pulse generator formed from a high voltage supply, a pulse forming network, and a high voltage switch such as a thyratron.

They generate short pulses of power to feed, e.g., the magnetron, a special type of vacuum tube that converts DC (usually pulsed) into microwaves. This technology is known as pulsed power. In this way, the transmitted pulse of RF radiation is kept to a defined and usually very short duration.

Hybrid mixers, [44] fed by a waveform generator and an exciter for a complex but coherent waveform. This waveform can be generated by low power/low-voltage input signals. In this case the radar transmitter must be a power-amplifier, e.g., a klystron tube or a solid state transmitter. In this way, the transmitted pulse is intrapulse-modulated and the radar receiver must use pulse compression techniques. Radar coolant [ edit]Main article: Coolant Coherent microwave amplifiers operating above 1,000 watts microwave output, like travelling wave tubes and klystrons, require liquid coolant.

The electron beam must contain 5 to 10 times more power than the microwave output, which can produce enough heat to generate plasma. This plasma flows from the collector toward the cathode. The same magnetic focusing that guides the electron beam forces the plasma into the path of the electron beam but flowing in the opposite direction.

This introduces FM modulation which degrades Doppler performance. To prevent this, liquid coolant with minimum pressure and flow rate is required, and deionized water is normally used in most high power surface radar systems that utilize Doppler processing.

[45]Coolanol ( silicate ester) was used in several military radars in the 1970s. However, it is hygroscopic, leading to hydrolysis and formation of highly flammable alcohol. The loss of a U. S. Navy aircraft in 1978 was attributed to a silicate ester fire. [46] Coolanol is also expensive and toxic.

The U. S. Navy has instituted a program named Pollution Prevention (P2) to eliminate or reduce the volume and toxicity of waste, air emissions, and effluent discharges. Because of this, Coolanol is used less often today. Regulations [ edit]Radar (also: RADAR) is defined by article 1.100 of the International Telecommunication Union´s (ITU) ITU Radio Regulations (RR) as: [47]A radiodetermination system based on the comparison of reference signals with radio signals reflected, or retransmitted, from the position to be determined.

Each radiodetermination system shall be classified by the radiocommunication service in which it operates permanently or temporarily. Typical radar utilizations are primary radar and secondary radar, these might operate in the radiolocation service or the radiolocation-satellite service.

See also [ edit]Electronics portal Nautical portal Main article: Radar configurations and types Main category: Radar Radar imaging Radar navigation Wave radar Acronyms and abbreviations in avionics Definitions Amplitude-comparison monopulse Constant false alarm rate Sensitivity time control Application Proximity fuze Hardware Cavity magnetron Crossed-field amplifier Gallium arsenide Klystron Omniview technology Radar engineering details Radar tower Radio Travelling-wave tube Similar detection and ranging methods Lidar LORANSonar Historical radars List of radars Chain Home and Chain Home Low Hohentwiel radar H2S radar SCR-270 radar Notes and references [ edit]^ Translation Bureau (2013).

""Radar definition"". Public Works and Government Services Canada. Retrieved November 8, 2013.^ Mc Graw-Hill dictionary of scientific and technical terms / Daniel N. Lapedes, editor in chief.

Lapedes, Daniel N. New York ; Montreal : Mc Graw-Hill, 1976. [xv], 1634, A26 p.^ ""ABBREVIATIONS and ACRONYMS"". Navy dot MIL. United States Navy. Retrieved 9 January 2017.^ ""Small and Short-Range Radar Systems"". CRC Net Base. Retrieved 9 January 2017.^ L. L., M. P., M. S., M. R., etc (2011). ""Automatic fall detection based on Doppler radar motion signature"".

IEEE Pervasive Health.^ Kostenko, A. A., A. I. Nosich, and I. A. Tishchenko, ""Radar Prehistory, Soviet Side,"" Proc. of IEEE APS International Symposium 2001, vol.4. p. 44, 2003^ ""Christian Huelsmeyer, the inventor"". radarworld.org.^ Patent DE165546; Verfahren, um metallische Gegenstände mittels elektrischer Wellen einem Beobachter zu melden.^ Verfahren zur Bestimmung der Entfernung von metallischen Gegenständen (Schiffen o. dgl.

), deren Gegenwart durch das Verfahren nach Patent 16556 festgestellt wird.^ GB 13170 Telemobiloscope^ ""gdr_zeichnungpatent.jpg"". Retrieved February 24, 2015.^ ""Making waves: Robert Watson-Watt, the pioneer of radar"". BBC. 16 February 2017.^ Hyland, L. A, A. H. Taylor, and L. C. Young; ""System for detecting objects by radio,"" U. S. Patent No. 1981884, granted 27 Nov. 1934^ Howeth, Linwood S.; ""Radar,"" Ch. XXXVIII in History of Communications -Electronics in the United States Navy, 1963; Radar^ Watson, Raymond C., Jr. (2009-11-25).

Radar Origins Worldwide: History of Its Evolution in 13 Nations Through World War II. Trafford Publishing. ISBN 978-1-4269-2111-7.^ Hearst Magazines (December 1935). Popular Mechanics. Hearst Magazines. p. 844.^ Frederick Seitz, Norman G. Einspruch, Electronic Genie: The Tangled History of Silicon - 1998 - page 104^ John Erickson. Radio-Location and the Air Defence Problem: The Design and Development of Soviet Radar. Science Studies, vol.

2, no. 3 (Jul., 1972), pp. 241–263^ ""The history of radar, from aircraft radio detectors to airborne radar"". kret.com. 17 February 2015. Archived from the original on 20 June 2015. Retrieved 28 April 2015.^ Page, Robert Morris, The Origin of Radar, Doubleday Anchor, New York, 1962, p. 66^ Bonnier Corporation (October 1935).

Popular Science. Bonnier Corporation. p. 29.^ Alan Dower Blumlein (2002). ""The story of RADAR Development"". Archived from the original on 10 July 2011. Retrieved 2011-05-06.^ (in French) Copy of Patents an Obstacle-Locating Radio Apparatus Archived 16 January 2009 at the Wayback Machine.

on www.radar-france.fr^ British man first to patent radar official site of the Patent Office Archived 19 July 2006 at the Wayback Machine.^ GB 593017 Improvements in or relating to wireless systems^ Angela Hind (February 5, 2007).

""Briefcase 'that changed the world ' "". BBC News. Retrieved 2007-08-16. It not only changed the course of the war by allowing us to develop airborne radar systems, it remains the key piece of technology that lies at the heart of your microwave oven today. The cavity magnetron's invention changed the world.^ Harford, Tim (9 October 2017). ""How the search for a 'death ray' led to radar"".

BBC World Service. Retrieved 9 October 2017. But by 1940, it was the British who had made a spectacular breakthrough: the resonant cavity magnetron, a radar transmitter far more powerful than its predecessors....

The magnetron stunned the Americans. Their research was years off the pace.^ Bonnier Corporation (December 1941). Popular Science. Bonnier Corporation. p. 56.^ a b Hearst Magazines (September 1941). Popular Mechanics. Hearst Magazines. p. 26.^ ""Scotland's little-known WWII hero who helped beat the Luftwaffe with invention of radar set to be immortalised in film"". Daily Record. 16 February 2017.^ Goebel, Greg (2007-01-01). ""The Wizard War: WW2 & The Origins Of Radar"".

Retrieved 2007-03-24.^ ""The Technology Behind S+"". Sleep.mysplus.com. Retrieved 29 October 2017.^ ""Project Soli"". Atap.google.com. Retrieved 29 October 2017.^ Stimson, George (1998). Introduction to Airborne Radar. Sci Tech Publishing Inc. p. 98. ISBN 1-891121-01-4.^ M. Castelaz. ""Exploration: The Doppler Effect"". Pisgah Astronomical Research Institute.^ Strasser, Nancy C. ""Investigation of Terrain Bounce Electronic Countermeasure"". DTIC.^ a b ""Ground Surveillance Radars and Military Intelligence"" (PDF). Syracuse Research Corporation; Massachusetts Institute of Technology.

Archived from the original (PDF) on 22 September 2010.^ ""AN/PPS-5 Ground Surveillance Radar"". You Tube; jaglavaksoldier's Channel.^ ""Fundamentals of Radar Tracking"". Applied Technology Institute. Archived from the original on 24 August 2011.^ ""Side-Lobe Suppression"". MIT.^ National Severe Storms Laboratory. ""Multi-function Phased Array Radar (MPAR) Project"". NOAA. Retrieved February 8, 2017.^ John Pike. ""Mi G-31 FOXHOUND"". globalsecurity.org.^ ""Radar Modulator"".

radartutorial.eu.^ ""Fully Coherent Radar"". radartutorial.eu.^ J. L. de Segovia. ""Physics of Outgassing"" (PDF). Madrid, Spain: Instituto de Física Aplicada, CETEF “L. Torres Quevedo”, CSIC. Retrieved 2012-08-12.^ Stropki, Michael A. (1992). ""Polyalphaolefins: A New Improved Cost Effective Aircraft Radar Coolant"" (PDF). Melbourne, Australia: Aeronautical Research Laboratory, Defense Science and Technology Organisation, Department of Defense.

Retrieved 2010-03-18.^ ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.100, definition: radar / RADARBibliography [ edit]This "" further reading "" section may contain inappropriate and/or excessive suggestions.

Please ensure that only a reasonable number of balanced, topical, reliable, and notable further reading suggestions are given. Consider utilising appropriate texts as inline sources or creating a separate bibliography article. (November 2014)References [ edit]Barrett, Dick, "" All you ever wanted to know about British air defence radar "".

The Radar Pages. (History and details of various British radar systems)Buderi, "" Telephone History: Radar History "". Privateline.com. (Anecdotal account of the carriage of the world's first high power cavity magnetron from Britain to the US during WW2.

)Ekco Radar WW2 Shadow Factory The secret development of British radar. ES310 "" Introduction to Naval Weapons Engineering."". (Radar fundamentals section)Hollmann, Martin, "" Radar Family Tree "". Radar World. Penley, Bill, and Jonathan Penley, "" Early Radar History —an Introduction "". 2002. Pub 1310 Radar Navigation and Maneuvering Board Manual, National Imagery and Mapping Agency, Bethesda, MD 2001 (US govt publication '...intended to be used primarily as a manual of instruction in navigation schools and by naval and merchant marine personnel.

')Wesley Stout, 1946 "" Radar - The Great Detective "" Early development and production by Chrysler Corp. during WWII. Swords, Seán S., ""Technical History of the Beginnings of Radar"", IEE History of Technology Series, Vol. 6, London: Peter Peregrinus, 1986General [ edit]Reg Batt (1991). The radar army: winning the war of the airwaves.

ISBN 978-0-7090-4508-3. E. G. Bowen (1998-01-01). Radar Days. Taylor & Francis. ISBN 978-0-7503-0586-0. Michael Bragg (2002-05-01). RDF1: The Location of Aircraft by Radio Methods 1935–1945. Twayne Publishers. ISBN 978-0-9531544-0-1. Louis Brown (1999). A radar history of World War II: technical and military imperatives.

Taylor & Francis. ISBN 978-0-7503-0659-1. Robert Buderi (1996). The invention that changed the world: how a small group of radar pioneers won the Second World War and launched a technological revolution. ISBN 978-0-684-81021-8. Burch, David F., Radar For Mariners, Mc Graw Hill, 2005, ISBN 978-0-07-139867-1. Ian Goult (2011). Secret Location: A witness to the Birth of Radar and its Postwar Influence. History Press.

ISBN 978-0-7524-5776-5. Peter S. Hall (March 1991). Radar. Potomac Books Inc. ISBN 978-0-08-037711-7. Derek Howse; Naval Radar Trust (February 1993). Radar at sea: the royal Navy in World War 2. Naval Institute Press. ISBN 978-1-55750-704-4. R. V. Jones (August 1998). Most Secret War. Wordsworth Editions Ltd. ISBN 978-1-85326-699-7. Kaiser, Gerald, Chapter 10 in ""A Friendly Guide to Wavelets"", Birkhauser, Boston, 1994. Kouemou, Guy (Ed.

): Radar Technology. In Tech, 2010, ISBN 978-953-307-029-2, ( Radar Technology - Free Open Access Book | In Tech Open ). Colin Latham; Anne Stobbs (January 1997). Radar: A Wartime Miracle. Sutton Pub Ltd. ISBN 978-0-7509-1643-1. François Le Chevalier (2002). Principles of radar and sonar signal processing. Artech House Publishers. ISBN 978-1-58053-338-6. David Pritchard (August 1989). The radar war: Germany's pioneering achievement 1904-45.

Harpercollins. ISBN 978-1-85260-246-8. Merrill Ivan Skolnik (1980-12-01). Introduction to radar systems. ISBN 978-0-07-066572-9. Merrill Ivan Skolnik (1990). Radar handbook. Mc Graw-Hill Professional. ISBN 978-0-07-057913-2. George W. Stimson (1998). Introduction to airborne radar. Sci Tech Publishing.

ISBN 978-1-891121-01-2. Younghusband, Eileen., Not an Ordinary Life. How Changing Times Brought Historical Events into my Life, Cardiff Centre for Lifelong Learning, Cardiff, 2009., ISBN 9780956115690 (Pages 36–67 contain the experiences of a WAAF radar plotter in WWII.

)Younghusband, Eileen., One Woman's War. Cardiff. Candy Jar Books. 2011. ISBN 978-0-9566826-2-8David Zimmerman (February 2001). Britain's shield: radar and the defeat of the Luftwaffe. Sutton Pub Ltd. ISBN 978-0-7509-1799-5. Technical reading [ edit]Skolnik, M I. RADAR HANDBOOK. Mc Graw-Hill, 1970. Nadav Levanon, and Eli Mozeson. Radar signals. Wiley. com, 2004. Hao He, Jian Li, and Petre Stoica. Waveform design for active sensing systems: a computational approach. Cambridge University Press, 2012. Solomon W. Golomb, and Guang Gong. Signal design for good correlation: for wireless communication, cryptography, and radar. Cambridge University Press, 2005. M. Soltanalian. Signal Design for Active Sensing and Communications. Uppsala Dissertations from the Faculty of Science and Technology (printed by Elanders Sverige AB), 2014. Fulvio Gini, Antonio De Maio, and Lee Patton, eds. Waveform design and diversity for advanced radar systems. Institution of engineering and technology, 2012. E. Fishler, A. Haimovich, R. Blum, D. Chizhik, L. Cimini, R. Valenzuela, ""MIMO radar: an idea whose time has come,"" IEEE Radar Conference, 2004. Mark R. Bell, ""Information theory and radar waveform design."" IEEE Transactions on Information Theory, 39.5 (1993): 1578–1597. Robert Calderbank, S. Howard, and Bill Moran. ""Waveform diversity in radar signal processing."" IEEE Signal Processing Magazine, 26.1 (2009): 32–41. External links [ edit]Look up radar in Wiktionary, the free dictionary. Wikimedia Commons has media related to Radar. MIT Video Course: Introduction to Radar Systems A set of 10 video lectures developed at Lincoln Laboratory to develop an understanding of radar systems and technologies. Authority control GND: 4176765-2Categories: Radar Avionics Aircraft instruments Microwave technology Measuring instruments Navigational equipment Air traffic control Science and technology during World War II Targeting (warfare)Radio stations and systems ITU Words coined in the 1940s "

. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated.

Radar

"For other uses, see Radar (disambiguation). Long-range radar antenna, used to track space objects and ballistic missiles. Radar of the type used for detection of aircraft. It rotates steadily sweeping the airspace with a narrow beam. Radar is an object detection system which uses radio waves to determine the range, altitude, direction, or speed of objects.

It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio waves or microwaves which bounce off any object in their path.

The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter. Radar was secretly developed by several nations before and during World War II. The term RADAR itself, not the actual development, was coined in 1940 by the United States Navy as an acronym for RA dio D etection A nd R anging.

[1] [2] The term radar has since entered English and other languages as the common noun radar, losing all capitalization.

The modern uses of radar are highly diverse, including air traffic control, radar astronomy, air-defense systems, antimissile systems; marine radars to locate landmarks and other ships; aircraft anticollision systems; ocean surveillance systems, outer space surveillance and rendezvous systems; meteorological precipitation monitoring; altimetry and flight control systems; guided missile target locating systems; and ground-penetrating radar for geological observations.

High tech radar systems are associated with digital signal processing and are capable of extracting useful information from very high noise levels.

Other systems similar to radar make use of other parts of the electromagnetic spectrum. One example is "" lidar "", which uses visible light from lasers rather than radio waves. Contents [ show]History Edit Main article: History of radar As early as 1886, German physicist Heinrich Hertz showed that radio waves could be reflected from solid objects.

In 1895, Alexander Popov, a physics instructor at the Imperial Russian Navy school in Kronstadt, developed an apparatus using a coherer tube for detecting distant lightning strikes. The next year, he added a spark-gap transmitter. In 1897, while testing this equipment for communicating between two ships in the Baltic Sea, he took note of an interference beat caused by the passage of a third vessel.

In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation. [3]The German inventor Christian Hülsmeyer was the first to use radio waves to detect ""the presence of distant metallic objects"".

In 1904 he demonstrated the feasibility of detecting a ship in dense fog, but not its distance from the transmitter. [4] He obtained a patent [5] for his detection device in April 1904 and later a patent [6] for a related amendment for estimating the distance to the ship.

He also got a British patent on September 23, 1904 [7] for a full system, that he called a telemobiloscope.

A Chain Home tower in Great Baddow, United Kingdom In 1922 A. Hoyt Taylor and Leo C. Young, researchers working with the U. S. Navy, had a transmitter and a receiver on opposite sides of the Potomac River and discovered that a ship passing through the beam path caused the received signal to fade in and out.

Taylor submitted a report, suggesting that this might be used to detect the presence of ships in low visibility, but the Navy did not immediately continue the work. Eight years later, Lawrence A. Hyland at the Naval Research Laboratory observed similar fading effects from a passing aircraft; this led to a patent application [8] as well as a proposal for serious work at the NRL (Taylor and Young were then at this laboratory) on radio-echo signals from moving targets.

[9]Before the Second World War, researchers in France, Germany, Italy, Japan, the Netherlands, the Soviet Union, the United Kingdom, and the United States, independently and in great secrecy, developed technologies that led to the modern version of radar. Australia, Canada, New Zealand, and South Africa followed prewar Great Britain, and Hungary had similar developments during the war.

[10]In France in 1934, following systematic studies on the magnetron, the research branch of the Compagnie Générale de Télégraphie Sans Fil (CSF), headed by Maurice Ponte, with Henri Gutton, Sylvain Berline, and M. Hugon began developing an obstacle-locating radio apparatus, a part of which was installed on the Normandie liner in 1935.

[11] [12]During the same time, the Soviet military engineer P. K. Oshchepkov, in collaboration with Leningrad Electrophysical Institute, produced an experimental apparatus, RAPID, capable of detecting an aircraft within 3 km of a receiver. [13] The French and Soviet systems, however, had continuous-wave operation and could not give the full performance that was ultimately at the center of modern radar.

Full radar evolved as a pulsed system, and the first such elementary apparatus was demonstrated in December 1934 by the American Robert M. Page, working at the Naval Research Laboratory. [14] The following year, the United States Army successfully tested a primitive surface-to-surface radar to aim coastal battery search lights at night.

[15] This was followed by a pulsed system demonstrated in May 1935 by Rudolf Kühnhold and the firm GEMA in Germany and then one in June 1935 by an Air Ministry team led by Robert A. Watson Watt in Great Britain.

Development of radar greatly expanded on 1 September 1936 when Watson-Watt became Superintendent of a new establishment under the British Air Ministry, Bawdsey Research Station located in Bawdsey Manor, near Felixstowe, Suffolk. Work there resulted in the design and installation of aircraft detection and tracking stations called Chain Home along the East and South coasts of England in time for the outbreak of World War II in 1939.

This system provided the vital advance information that helped the Royal Air Force win the Battle of Britain . The British were the first to fully exploit radar as a defence against aircraft attack. This was spurred on by fears that the Germans were developing death rays. [16] The Air Ministry asked British scientists in 1934 to investigate the possibility of propagating electromagnetic energy and the likely effect.

Following a study, they concluded that a death ray was impractical but that detection of aircraft appeared feasible. [16] Robert Watson Watt's team demonstrated to his superiors the capabilities of a working prototype and then patented the device.

[17] [18] [19] It served as the basis for the Chain Home network of radars to defend Great Britain, which detected approaching German aircraft in the Battle of Britain in 1940.

In April 1940, Popular Science showed an example of a radar unit using the Watson-Watt patent in an article on air defence, but not knowing that the U. S. Army and U. S. Navy were working on radars with the same principle, stated under the illustration, ""This is not U. S. Army equipment.""

[20] Also, in late 1941 Popular Mechanics had an article in which a U. S. scientist speculated about the British early warning system on the English east coast and came close to what it was and how it worked. [21] Alfred Lee Loomis organized the Radiation Laboratory at Cambridge, Massachusetts which developed the technology in the years 1941-45. Later, in 1943, Page greatly improved radar with the monopulse technique that was used for many years in most radar applications.

[22]The war precipitated research to find better resolution, more portability, and more features for radar, including complementary navigation systems like Oboe used by the RAF's Pathfinder . Applications Edit Commercial marine radar antenna. The rotating antenna radiates a vertical fan-shaped beam.

The information provided by radar includes the bearing and range (and therefore position) of the object from the radar scanner. It is thus used in many different fields where the need for such positioning is crucial. The first use of radar was for military purposes: to locate air, ground and sea targets.

This evolved in the civilian field into applications for aircraft, ships, and roads. In aviation, aircraft are equipped with radar devices that warn of aircraft or other obstacles in or approaching their path, display weather information, and give accurate altitude readings. The first commercial device fitted to aircraft was a 1938 Bell Lab unit on some United Air Lines aircraft.

[21] Such aircraft can land in fog at airports equipped with radar-assisted ground-controlled approach systems in which the plane's flight is observed on radar screens while operators radio landing directions to the pilot.

Marine radars are used to measure the bearing and distance of ships to prevent collision with other ships, to navigate, and to fix their position at sea when within range of shore or other fixed references such as islands, buoys, and lightships. In port or in harbour, vessel traffic service radar systems are used to monitor and regulate ship movements in busy waters.

Meteorologists use radar to monitor precipitation and wind. It has become the primary tool for short-term weather forecasting and watching for severe weather such as thunderstorms, tornadoes, winter storms, precipitation types, etc. Geologists use specialised ground-penetrating radars to map the composition of Earth's crust. Police forces use radar guns to monitor vehicle speeds on the roads.

Principles Edit A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity —especially by most metals, by seawater and by wet lands.

Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either toward or away from the transmitter, there is a slight equivalent change in the frequency of the radio waves, caused by the Doppler effect . Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, they can be strengthened by electronic amplifiers. More sophisticated methods of signal processing are also used in order to recover useful radar signals

. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated.

Such weather phenomena as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases (especially oxygen) are avoided in designing radars, except when their detection is intended.

Radar relies on its own transmissions rather than light from the Sun or the Moon, or from electromagnetic waves emitted by the objects themselves, such as infrared wavelengths (heat). This process of directing artificial radio waves towards objects is called illumination, although radio waves are invisible to the human eye or optical cameras. Reflection Edit Brightness can indicate reflectivity as in this 1960 weather radar image (of Hurricane Abby ).

The radar's frequency, pulse form, polarization, signal processing, and antenna determine what it can observe. If electromagnetic waves traveling through one material meet another, having a very different dielectric constant or diamagnetic constant from the first, the waves will reflect or scatter from the boundary between the materials.

This means that a solid object in air or in a vacuum, or a significant change in atomic density between the object and what is surrounding it, will usually scatter radar (radio) waves from its surface. This is particularly true for electrically conductive materials such as metal and carbon fiber, making radar well-suited to the detection of aircraft and ships. Radar absorbing material, containing resistive and sometimes magnetic substances, is used on military vehicles to reduce radar reflection.

This is the radio equivalent of painting something a dark color so that it cannot be seen by the eye at night. Radar waves scatter in a variety of ways depending on the size (wavelength) of the radio wave and the shape of the target. If the wavelength is much shorter than the target's size, the wave will bounce off in a way similar to the way light is reflected by a mirror.

If the wavelength is much longer than the size of the target, the target may not be visible because of poor reflection. Low-frequency radar technology is dependent on resonances for detection, but not identification, of targets.

This is described by Rayleigh scattering, an effect that creates Earth's blue sky and red sunsets. When the two length scales are comparable, there may be resonances. Early radars used very long wavelengths that were larger than the targets and thus received a vague signal, whereas some modern systems use shorter wavelengths (a few centimeters or less) that can image objects as small as a loaf of bread.

Short radio waves reflect from curves and corners in a way similar to glint from a rounded piece of glass. The most reflective targets for short wavelengths have 90° angles between the reflective surfaces. A corner reflector consists of three flat surfaces meeting like the inside corner of a box. The structure will reflect waves entering its opening directly back to the source.

They are commonly used as radar reflectors to make otherwise difficult-to-detect objects easier to detect. Corner reflectors on boats, for example, make them more detectable to avoid collision or during a rescue.

For similar reasons, objects intended to avoid detection will not have inside corners or surfaces and edges perpendicular to likely detection directions, which leads to ""odd"" looking stealth aircraft.

These precautions do not completely eliminate reflection because of diffraction, especially at longer wavelengths. Half wavelength long wires or strips of conducting material, such as chaff, are very reflective but do not direct the scattered energy back toward the source.

The extent to which an object reflects or scatters radio waves is called its radar cross section .

Radar equation Edit The power P r returning to the receiving antenna is given by the equation:where P t = transmitter power G t = gain of the transmitting antenna A r = effective aperture (area) of the receiving antennaσ = radar cross section, or scattering coefficient, of the target F = pattern propagation factor R t = distance from the transmitter to the target R r = distance from the target to the receiver.

In the common case where the transmitter and the receiver are at the same location, R t = R r and the term R t ² R r ² can be replaced by R 4, where R is the range. This yields: This shows that the received power declines as the fourth power of the range, which means that the received power from distant targets is relatively very small. Additional filtering and pulse integration modifies the radar equation slightly for pulse-Doppler radar performance, which can be used to increase detection range and reduce transmit power.

The equation above with F = 1 is a simplification for transmission in a vacuum without interference. The propagation factor accounts for the effects of multipath and shadowing and depends on the details of the environment.

In a real-world situation, pathloss effects should also be considered. Doppler effect Edit Main articles: Doppler radar and Pulse-Doppler radar Frequency shift is caused by motion that changes the number of wavelengths between the reflector and the radar.

That can degrade or enhance radar performance depending upon how that affects the detection process. As an example, Moving Target Indication can interact with Doppler to produce signal cancellation at certain radial velocities, which degrades performance. Sea-based radar systems, semi-active radar homing, weather radar, military aircraft, and radar astronomy rely on the Doppler effect to enhance performance.

This produces information about target velocity during the detection process. This also allows small objects to be detected in an environment containing much larger nearby slow moving objects. Doppler shift depends upon whether the radar configuration is active or passive. Active radar transmits a signal that is reflected back to the receiver.

Passive radar depends upon the object sending a signal to the receiver. The Doppler frequency shift for active radar is as follows, where is Doppler frequency, is transmit frequency, is radial velocity, and is the speed of light: [23]Passive radar is applicable to electronic countermeasures and radio astronomy as follows: Only the radial component of the speed is relevant.

When the reflector is moving at right angle to the radar beam, it has no relative velocity. Vehicles and weather moving parallel to the radar beam produce the maximum Doppler frequency shift. Doppler measurement is reliable only if the sampling rate exceeds the Nyquist frequency for the frequency shift produced by radial motion.

As an example, Doppler weather radar with a pulse rate of 2 k Hz and transmit frequency of 1 GHz can reliably measure weather up to 150 M/s (330 mile/hour), but cannot reliably determine radial velocity of aircraft moving 1,000 M/s (3,300 mile/hour). Polarization Edit In all electromagnetic radiation, the electric field is perpendicular to the direction of propagation, and this direction of the electric field is the polarization of the wave.

In the transmitted radar signal the polarization can be controlled for different effects. Radars use horizontal, vertical, linear and circular polarization to detect different types of reflections. For example, circular polarization is used to minimize the interference caused by rain. Linear polarization returns usually indicate metal surfaces.

Random polarization returns usually indicate a fractal surface, such as rocks or soil, and are used by navigation radars.

Limiting factors Edit Beam path and range Edit Echo heights above ground The radar beam would follow a linear path in vacuum, but it really follows a somewhat curved path in the atmosphere because of the variation of the refractive index of air, that is called the radar horizon. Even when the beam is emitted parallel to the ground, it will rise above it as the Earth curvature sinks below the horizon.

Furthermore, the signal is attenuated by the medium it crosses, and the beam disperses. The maximum range of a conventional radar can be limited by a number of factors: Line of sight, which depends on height above ground.

This means with out a direct line of sight the path of the beam is blocked. The maximum non-ambiguous range, which is determined by the pulse repetition frequency. The maximum non-ambiguous range is the distance the pulse could travel and return before the next pulse is emitted. Radar sensitivity and power of the return signal as computed in the radar equation. This includes factors such as environmental conditions and the size (or radar cross section) of the target.

Noise Edit Signal noise is an internal source of random variations in the signal, which is generated by all electronic components. Reflected signals decline rapidly as distance increases, so noise introduces a radar range limitation.

The noise floor and signal to noise ratio are two different measure of performance that impact range performance. Reflectors that are too far away produce too little signal to exceed the noise floor and cannot be detected. Detection requires a signal that exceeds the noise floor by at least the signal to noise ratio . Noise typically appears as random variations superimposed on the desired echo signal received in the radar receiver.

The lower the power of the desired signal, the more difficult it is to discern it from the noise. Noise figure is a measure of the noise produced by a receiver compared to an ideal receiver, and this needs to be minimized. Shot noise is produced by electrons in transit across a discontinuity, which occurs in all detectors.

Shot noise is the dominant source in most receivers. There will also be flicker noise caused by electron transit through amplification devices, which is reduced using heterodyne amplification. Another reason for heterodyne processing is that for fixed fractional bandwidth, the instantaneous bandwidth increases linearly in frequency.

This allows improved range resolution. The one notable exception to heterodyne (downconversion) radar systems is ultra-wideband radar. Here a single cycle, or transient wave, is used similar to UWB communications, see List of UWB channels .

Noise is also generated by external sources, most importantly the natural thermal radiation of the background surrounding the target of interest. In modern radar systems, the internal noise is typically about equal to or lower than the external noise.

An exception is if the radar is aimed upwards at clear sky, where the scene is so ""cold"" that it generates very little thermal noise. The thermal noise is given by k B T B, where T is temperature, B is bandwidth (post matched filter) and k B is Boltzmann's constant. There is an appealing intuitive interpretation of this relationship in a radar. Matched filtering allows the entire energy received from a target to be compressed into a single bin (be it a range, Doppler,elevation, or azimuth bin).

On the surface it would appear that then within a fixed interval of time one could obtain perfect, error free, detection.

To do this one simply compresses all energy into an infinitesimal time slice. What limits this approach in the real world is that, while time is arbitrarily divisible, current is not. The quantum of electrical energy is an electron, and so the best one can do is match filter all energy into a single electron.

Since the electron is moving at a certain temperature (Plank spectrum) this noise source cannot be further eroded. We see then that radar, like all macro-scale entities, is profoundly impacted by quantum theory. Noise is random and target signals are not. Signal processing can take advantage of this phenomenon to reduce the noise floor using two strategies. The kind of signal integration used with Moving Target Indication can improve noise up to for each stage.

The signal can also be split among multiple filters for pulse-Doppler signal processing, which reduces the noise floor by the number of filters. These improvements depend upon coherence . Interference Edit Radar systems must overcome unwanted signals in order to focus only on the actual targets of interest.

These unwanted signals may originate from internal and external sources, both passive and active. The ability of the radar system to overcome these unwanted signals defines its signal-to-noise ratio (SNR). SNR is defined as the ratio of a signal power to the noise power within the desired signal; it compares the level of a desired target signal to the level of background noise (atmospheric noise and noise generated within the receiver).

The higher a system's SNR, the better it is in isolating actual targets from the surrounding noise signals. Clutter Edit Clutter refers to radio frequency (RF) echoes returned from targets which are uninteresting to the radar operators.

Such targets include natural objects such as ground, sea, precipitation (such as rain, snow or hail), sand storms, animals (especially birds), atmospheric turbulence, and other atmospheric effects, such as ionosphere reflections, meteor trails, and three body scatter spike. Clutter may also be returned from man-made objects such as buildings and, intentionally, by radar countermeasures such as chaff . Some clutter may also be caused by a long radar waveguide between the radar transceiver and the antenna.

In a typical plan position indicator (PPI) radar with a rotating antenna, this will usually be seen as a ""sun"" or ""sunburst"" in the centre of the display as the receiver responds to echoes from dust particles and misguided RF in the waveguide. Adjusting the timing between when the transmitter sends a pulse and when the receiver stage is enabled will generally reduce the sunburst without affecting the accuracy of the range, since most sunburst is caused by a diffused transmit pulse reflected before it leaves the antenna.

Clutter is considered a passive interference source, since it only appears in response to radar signals sent by the radar.

Clutter is detected and neutralized in several ways. Clutter tends to appear static between radar scans; on subsequent scan echoes, desirable targets will appear to move, and all stationary echoes can be eliminated. Sea clutter can be reduced by using horizontal polarization, while rain is reduced with circular polarization (note that meteorological radars wish for the opposite effect, and therefore use linear polarization to detect precipitation). Other methods attempt to increase the signal-to-clutter ratio. Clutter moves with the wind or is stationary.

Two common strategies to improve measure or performance in a clutter environment are: Moving Target Indication, which integrates successive pulses and Doppler processing, which uses filters to separate clutter from desirable signals.

The most effective clutter reduction technique is pulse-Doppler radar. Doppler separates clutter from aircraft and spacecraft using a frequency spectrum, so individual signals can be separated from multiple reflectors located in the same volume using velocity differences. This requires a coherent transmitter. Another technique uses a moving target indicator that subtracts the receive signal from two successive pulses using phase to reduce signals from slow moving objects.

This can be adapted for systems that lack a coherent transmitter, such as time-domain pulse-amplitude radar . Constant False Alarm Rate, a form of Automatic Gain Control (AGC), is a method that relies on clutter returns far outnumbering echoes from targets of interest. The receiver's gain is automatically adjusted to maintain a constant level of overall visible clutter.

While this does not help detect targets masked by stronger surrounding clutter, it does help to distinguish strong target sources. In the past, radar AGC was electronically controlled and affected the gain of the entire radar receiver. As radars evolved, AGC became computer-software controlled and affected the gain with greater granularity in specific detection cells.

Radar multipath echoes from a target cause ghosts to appear. Clutter may also originate from multipath echoes from valid targets caused by ground reflection, atmospheric ducting or ionospheric reflection / refraction (e.g., Anomalous propagation ). This clutter type is especially bothersome since it appears to move and behave like other normal (point) targets of interest.

In a typical scenario, an aircraft echo is reflected from the ground below, appearing to the receiver as an identical target below the correct one. The radar may try to unify the targets, reporting the target at an incorrect height, or eliminating it on the basis of jitter or a physical impossibility.

Terrain bounce jamming exploits this response by amplifying the radar signal and directing it downward. [24] These problems can be overcome by incorporating a ground map of the radar's surroundings and eliminating all echoes which appear to originate below ground or above a certain height. Monopulse can be improved by altering the elevation algorithm used at low elevation. In newer air traffic control radar equipment, algorithms are used to identify the false targets by comparing the current pulse returns to those adjacent, as well as calculating return improbabilities.

Jamming Edit Radar jamming refers to radio frequency signals originating from sources outside the radar, transmitting in the radar's frequency and thereby masking targets of interest.

Jamming may be intentional, as with an electronic warfare tactic, or unintentional, as with friendly forces operating equipment that transmits using the same frequency range. Jamming is considered an active interference source, since it is initiated by elements outside the radar and in general unrelated to the radar signals. Jamming is problematic to radar since the jamming signal only needs to travel one way (from the jammer to the radar receiver) whereas the radar echoes travel two ways (radar-target-radar) and are therefore significantly reduced in power by the time they return to the radar receiver.

Jammers therefore can be much less powerful than their jammed radars and still effectively mask targets along the line of sight from the jammer to the radar ( mainlobe jamming ). Jammers have an added effect of affecting radars along other lines of sight through the radar receiver's sidelobes ( sidelobe jamming ).

Mainlobe jamming can generally only be reduced by narrowing the mainlobe solid angle and cannot fully be eliminated when directly facing a jammer which uses the same frequency and polarization as the radar. Sidelobe jamming can be overcome by reducing receiving sidelobes in the radar antenna design and by using an omnidirectional antenna to detect and disregard non-mainlobe signals.

Other anti-jamming techniques are frequency hopping and polarization . Radar signal processing Edit Distance measurement Edit Transit time Edit Pulse radar: The round-trip time for the radar pulse to get to the target and return is measured.

The distance is proportional to this time. Continuous wave (CW) radar One way to obtain a distance measurement is based on the time-of-flight: transmit a short pulse of radio signal (electromagnetic radiation) and measure the time it takes for the reflection to return.

The distance is one-half the product of the round trip time (because the signal has to travel to the target and then back to the receiver) and the speed of the signal. Since radio waves travel at the speed of light, accurate distance measurement requires high-performance electronics. In most cases, the receiver does not detect the return while the signal is being transmitted. Through the use of a duplexer, the radar switches between transmitting and receiving at a predetermined rate.

A similar effect imposes a maximum range as well. In order to maximize range, longer times between pulses should be used, referred to as a pulse repetition time, or its reciprocal, pulse repetition frequency.

These two effects tend to be at odds with each other, and it is not easy to combine both good short range and good long range in a single radar. This is because the short pulses needed for a good minimum range broadcast have less total energy, making the returns much smaller and the target harder to detect.

This could be offset by using more pulses, but this would shorten the maximum range. So each radar uses a particular type of signal. Long-range radars tend to use long pulses with long delays between them, and short range radars use smaller pulses with less time between them.

As electronics have improved many radars now can change their pulse repetition frequency, thereby changing their range. The newest radars fire two pulses during one cell, one for short range (10 km / 6 miles) and a separate signal for longer ranges (100 km /60 miles).

The distance resolution and the characteristics of the received signal as compared to noise depends on the shape of the pulse. The pulse is often modulated to achieve better performance using a technique known as pulse compression .

Distance may also be measured as a function of time. The radar mile is the amount of time it takes for a radar pulse to travel one nautical mile, reflect off a target, and return to the radar antenna.

Since a nautical mile is defined as 1,852 meters, then dividing this distance by the speed of light (299,792,458 meters per second), and then multiplying the result by 2 yields a result of 12.36 microseconds in duration. Frequency modulation Edit Another form of distance measuring radar is based on frequency modulation. Frequency comparison between two signals is considerably more accurate, even with older electronics, than timing the signal.

By measuring the frequency of the returned signal and comparing that with the original, the difference can be easily measured. This technique can be used in continuous wave radar and is often found in aircraft radar altimeters. In these systems a ""carrier"" radar signal is frequency modulated in a predictable way, typically varying up and down with a sine wave or sawtooth pattern at audio frequencies.

The signal is then sent out from one antenna and received on another, typically located on the bottom of the aircraft, and the signal can be continuously compared using a simple beat frequency modulator that produces an audio frequency tone from the returned signal and a portion of the transmitted signal. Since the signal frequency is changing, by the time the signal returns to the aircraft the transmit frequency has changed.

The amount of frequency shift is used to measure distance. The modulation index riding on the receive signal is proportional to the time delay between the radar and the reflector. The amount of that frequency shift becomes greater with greater time delay. The measure of the amount of frequency shift is directly proportional to the distance traveled.

That distance can be displayed on an instrument, and it may also be available via the transponder. This signal processing is similar to that used in speed detecting Doppler radar. Example systems using this approach are AZUSA, MISTRAM, and UDOP . A further advantage is that the radar can operate effectively at relatively low frequencies. This was important in the early development of this type when high frequency signal generation was difficult or expensive.

Terrestrial radar uses low-power FM signals that cover a larger frequency range. The multiple reflections are analyzed mathematically for pattern changes with multiple passes creating a computerized synthetic image.

Doppler effects are used which allows slow moving objects to be detected as well as largely eliminating ""noise"" from the surfaces of bodies of water. Speed measurement Edit Speed is the change in distance to an object with respect to time. Thus the existing system for measuring distance, combined with a memory capacity to see where the target last was, is enough to measure speed. At one time the memory consisted of a user making grease pencil marks on the radar screen and then calculating the speed using a slide rule.

Modern radar systems perform the equivalent operation faster and more accurately using computers. If the transmitter's output is coherent (phase synchronized), there is another effect that can be used to make almost instant speed measurements (no memory is required), known as the Doppler effect.

Most modern radar systems use this principle into doppler radar and pulse-doppler radar systems ( weather radar, military radar, etc...). The Doppler effect is only able to determine the relative speed of the target along the line of sight from the radar to the target.

Any component of target velocity perpendicular to the line of sight cannot be determined by using the Doppler effect alone, but it can be determined by tracking the target's azimuth over time. It is possible to make a doppler radar without any pulsing, known as a continuous-wave radar (CW radar), by sending out a very pure signal of a known frequency. CW radar is ideal for determining the radial component of a target's velocity. CW radar is typically used by traffic enforcement to measure vehicle speed quickly and accurately where range is not important.

When using a pulsed radar, the variation between the phase of successive returns gives the distance the target has moved between pulses, and thus its speed can be calculated.

Other mathematical developments in radar signal processing include time-frequency analysis ( Weyl Heisenberg or wavelet ), as well as the chirplet transform which makes use of the change of frequency of returns from moving targets (""chirp""). Pulse-Doppler signal processing Edit File: Pulse doppler signal processing.png Pulse-Doppler signal processing includes frequency filtering in the detection process.

The space between each transmit pulse is divided into range cells or range gates. Each cell is filtered independently much like the process used by a spectrum analyzer to produce the display showing different frequencies. Each different distance produces a different spectrum. These spectra are used to perform the detection process.

This is required to achieve acceptable performance in hostile environments involving weather, terrain, and electronic countermeasures. The primary purpose is to measure both the amplitude and frequency of the aggregate reflected signal from multiple distances.

This is used with weather radar to measure radial wind velocity and precipitation rate in each different volume of air. This is linked with computing systems to produce a real-time electronic weather map. Aircraft safety depends upon continuous access to accurate weather radar information that is used to prevent injuries and accidents.

Weather radar uses a low PRF. Coherency requirements are not as strict as those for military systems because individual signals ordinarily do not need to be separated. Less sophisticated filtering is required, and range ambiguity processing is not normally needed with weather radar in comparison with military radar intended to track air vehicles.

The alternate purpose is "" look-down/shoot-down "" capability required to improve military air combat survivability. Pulse-Doppler is also used for ground based surveillance radar required to defend personnel and vehicles.

[25] [26] Pulse-Doppler signal processing increases the maximum detection distance using less radiation in close proximity to aircraft pilots, shipboard personnel, infantry, and artillery. Reflections from terrain, water, and weather produce signals much larger than aircraft and missiles, which allows fast moving vehicles to hide using nap-of-the-earth flying techniques and stealth technology to avoid detection until an attack vehicle is too close to destroy.

Pulse-Doppler signal processing incorporates more sophisticated electronic filtering that safely eliminates this kind of weakness. This requires the use of medium pulse-repetition frequency with phase coherent hardware that has a large dynamic range. Military applications require medium PRF which prevents range from being determined directly, and range ambiguity resolution processing is required to identify the true range of all reflected signals.

Radial movement is usually linked with Doppler frequency to produce a lock signal that cannot be produced by radar jamming signals. Pulse-Doppler signal processing also produces audible signals that can be used for threat identification.

[25]Reduction of interference effects Edit Signal processing is employed in radar systems to reduce the radar interference effects. Signal processing techniques include moving target indication, Pulse-Doppler signal processing, moving target detection processors, correlation with secondary surveillance radar targets, space-time adaptive processing, and track-before-detect.

Constant false alarm rate and digital terrain model processing are also used in clutter environments. Plot and track extraction Edit Main article: Track_algorithm A Track algorithm is a radar performance enhancement strategy.

Tracking algorithms provide the ability to predict future position of multiple moving objects based on the history of the individual positions being reported by sensor systems. Historical information is accumulated and used to predict future position for use with air traffic control, threat estimation, combat system doctrine, gun aiming, and missile guidance. Position data is accumulated radar sensors over the span of a few minutes. There are four common track algorithms.

[27]Nearest Neighbor Probabilistic Data Association Multiple Hypothesis Tracking Interactive Multiple Model (IMM)Radar video returns from aircraft can be subjected to a plot extraction process whereby spurious and interfering signals are discarded. A sequence of target returns can be monitored through a device known as a plot extractor. The non-relevant real time returns can be removed from the displayed information and a single plot displayed.

In some radar systems, or alternatively in the command and control system to which the radar is connected, a radar tracker is used to associate the sequence of plots belonging to individual targets and estimate the targets' headings and speeds. Engineering Edit Radar components A radar's components are: A transmitter that generates the radio signal with an oscillator such as a klystron or a magnetron and controls its duration by a modulator .

A waveguide that links the transmitter and the antenna. A duplexer that serves as a switch between the antenna and the transmitter or the receiver for the signal when the antenna is used in both situations. A receiver. Knowing the shape of the desired received signal (a pulse), an optimal receiver can be designed using a matched filter .

A display processor to produce signals for human readable output devices . An electronic section that controls all those devices and the antenna to perform the radar scan ordered by software. A link to end user devices and displays. Antenna design Edit Radio signals broadcast from a single antenna will spread out in all directions, and likewise a single antenna will receive signals equally from all directions.

This leaves the radar with the problem of deciding where the target object is located. Early systems tended to use omnidirectional broadcast antennas, with directional receiver antennas which were pointed in various directions. For instance, the first system to be deployed, Chain Home, used two straight antennas at right angles for reception, each on a different display.

The maximum return would be detected with an antenna at right angles to the target, and a minimum with the antenna pointed directly at it (end on). The operator could determine the direction to a target by rotating the antenna so one display showed a maximum while the other showed a minimum.

One serious limitation with this type of solution is that the broadcast is sent out in all directions, so the amount of energy in the direction being examined is a small part of that transmitted. To get a reasonable amount of power on the ""target"", the transmitting aerial should also be directional.

Parabolic reflector Edit More modern systems use a steerable parabolic ""dish"" to create a tight broadcast beam, typically using the same dish as the receiver. Such systems often combine two radar frequencies in the same antenna in order to allow automatic steering, or radar lock .

Parabolic reflectors can be either symmetric parabolas or spoiled parabolas: Symmetric parabolic antennas produce a narrow ""pencil"" beam in both the X and Y dimensions and consequently have a higher gain. The NEXRAD Pulse-Doppler weather radar uses a symmetric antenna to perform detailed volumetric scans of the atmosphere.

Spoiled parabolic antennas produce a narrow beam in one dimension and a relatively wide beam in the other. This feature is useful if target detection over a wide range of angles is more important than target location in three dimensions. Most 2D surveillance radars use a spoiled parabolic antenna with a narrow azimuthal beamwidth and wide vertical beamwidth.

This beam configuration allows the radar operator to detect an aircraft at a specific azimuth but at an indeterminate height. Conversely, so-called ""nodder"" height finding radars use a dish with a narrow vertical beamwidth and wide azimuthal beamwidth to detect an aircraft at a specific height but with low azimuthal precision.

Surveillance radar antenna Types of scan Edit Primary Scan: A scanning technique where the main antenna aerial is moved to produce a scanning beam, examples include circular scan, sector scan, etc. Secondary Scan: A scanning technique where the antenna feed is moved to produce a scanning beam, examples include conical scan, unidirectional sector scan, lobe switching, etc. Palmer Scan: A scanning technique that produces a scanning beam by moving the main antenna and its feed.

A Palmer Scan is a combination of a Primary Scan and a Secondary Scan. Slotted waveguide Edit Slotted waveguide antenna Main article: Slotted waveguide Applied similarly to the parabolic reflector, the slotted waveguide is moved mechanically to scan and is particularly suitable for non-tracking surface scan systems, where the vertical pattern may remain constant. Owing to its lower cost and less wind exposure, shipboard, airport surface, and harbour surveillance radars now use this approach in preference to a parabolic antenna.

Phased array Edit Phased array: Not all radar antennas must rotate to scan the sky. Main article: Phased array antenna Another method of steering is used in a phased array radar. Phase array antennas are composed of evenly spaced similar antenna elements, such as aerials or rows of slotted waveguide.

Each antenna element or group of antenna elements incorporates a discreet phase shift that produces a phase gradient across the array. For example, array elements producing a 5 degree phase shift for each wavelength across the array face will produce a beam pointed 5 degree away from the centerline perpendicular to the array face. Signals traveling along that beam will be reinforced. Signals offset from that beam will be canceled. The amount of reinforcement is antenna gain. The amount of cancellation is side-lobe suppression.

[28]Phased array radars have been in use since the earliest years of radar in World War II, but electronic device limitations led to poor performance. Phased array radars were originally used for missile defense. They are the heart of the ship-borne Aegis combat system and the Patriot Missile System. The massive redundancy associated with having a large number of array elements increases reliability at the expense of gradual performance degradation that occurs as individual phase elements fail.

Phased array antenna can be built to conform to specific shapes, like missiles, infantry support vehicles, ships, and aircraft. As the price of electronics has fallen, phased array radars have become more common. Almost all modern military radar systems are based on phased arrays, where the small additional cost is offset by the improved reliability of a system with no moving parts.

Traditional moving-antenna designs are still widely used in roles where cost is a significant factor such as air traffic surveillance, weather radars and similar systems.

Phased array radars are valued for use in aircraft since they can track multiple targets. The first aircraft to use a phased array radar was the B-1B Lancer. The first aircraft fighter to use phased array radar was the Mikoyan Mi G-31. The Mi G-31M's SBI-16 Zaslon phased array radar is considered to be the world's most powerful fighter radar. [29]Phased-array interferometry or aperture synthesis techniques, using an array of separate dishes that are phased into a single effective aperture, are not typical for radar applications, although they are widely used in radio astronomy.

Because of the thinned array curse, such multiple aperture arrays, when used in transmitters, result in narrow beams at the expense of reducing the total power transmitted to the target. In principle, such techniques could increase spatial resolution, but the lower power means that this is generally not effective.

Aperture synthesis by post-processing motion data from a single moving source, on the other hand, is widely used in space and airborne radar systems .

Frequency bands Edit Main article: Radio spectrum#IEEE USThe traditional band names originated as code-names during World War II and are still in military and aviation use throughout the world. They have been adopted in the United States by the Institute of Electrical and Electronics Engineers and internationally by the International Telecommunication Union. Most countries have additional regulations to control which parts of each band are available for civilian or military use.

Other users of the radio spectrum, such as the broadcasting and electronic countermeasures industries, have replaced the traditional military designations with their own systems.

Radar frequency bands Band name Frequency range Wavelength range Notes HF 3–30 MHz10–100 m coastal radar systems, over-the-horizon radar (OTH) radars; 'high frequency'P < 300 MHz 1 m+ 'P' for 'previous', applied retrospectively to early radar systems VHF 30–300 MHz 1–10 m Very long range, ground penetrating; 'very high frequency'UHF 300–1000 MHz 0.3–1 m Very long range (e.g.

ballistic missile early warning ), ground penetrating, foliage penetrating; 'ultra high frequency'L 1–2 GHz 15–30 cm Long range air traffic control and surveillance; 'L' for 'long'S2–4 GHz 7.5–15 cm Moderate range surveillance, Terminal air traffic control, long-range weather, marine radar; 'S' for 'short'C4–8 GHz 3.75–7.5 cm Satellite transponders; a compromise (hence 'C') between X and S bands; weather; long range tracking X8–12 GHz 2.5–3.75 cm Missile guidance, marine radar, weather, medium-resolution mapping and ground surveillance; in the USA the narrow range 10.525 GHz ±25 MHz is used for airport radar; short range tracking.

Named X band because the frequency was a secret during WW2. K u12–18 GHz 1.67–2.5 cm high-resolution, also used for satellite transponders, frequency under K band (hence 'u')K18–24 GHz 1.11–1.67 cm from German kurz, meaning 'short'; limited use due to absorption by water vapour, so K u and K a were used instead for surveillance.

K-band is used for detecting clouds by meteorologists, and by police for detecting speeding motorists. K-band radar guns operate at 24.150 ± 0.100 GHz. K a24–40 GHz 0.75–1.11 cm mapping, short range, airport surveillance; frequency just above K band (hence 'a') Photo radar, used to trigger cameras which take pictures of license plates of cars running red lights, operates at 34.300 ± 0.100 GHz.mm 40–300 GHz 7.5 mm – 1 mm millimetre band, subdivided as below.

The frequency ranges depend on waveguide size. Multiple letters are assigned to these bands by different groups.

These are from Baytron, a now defunct company that made test equipment. V40–75 GHz 4.0–7.5 mm Very strongly absorbed by atmospheric oxygen, which resonates at 60 GHz. W75–110 GHz 2.7–4.0 mm used as a visual sensor for experimental autonomous vehicles, high-resolution meteorological observation, and imaging.

UWB1.6–10.5 GHz 18.75 cm – 2.8 cm used for through-the-wall radar and imaging systems. Radar modulators Edit Modulators act to provide the waveform of the RF-pulse. There are two different radar modulator designs:high voltage switch for non-coherent keyed power-oscillators [30] These modulators consist of a high voltage pulse generator formed from a high voltage supply, a pulse forming network, and a high voltage switch such as a thyratron.

They generate short pulses of power to feed, e.g., the magnetron, a special type of vacuum tube that converts DC (usually pulsed) into microwaves. This technology is known as pulsed power. In this way, the transmitted pulse of RF radiation is kept to a defined and usually very short duration.hybrid mixers, [31] fed by a waveform generator and an exciter for a complex but coherent waveform.

This waveform can be generated by low power/low-voltage input signals. In this case the radar transmitter must be a power-amplifier, e.g., a klystron tube or a solid state transmitter. In this way, the transmitted pulse is intrapulse-modulated and the radar receiver must use pulse compression techniques.

Radar coolant Edit Coolanol (silicate ester) was used in several military radars in the 1970s. However, it is hygroscopic, leading to formation of highly flammable alcohol. The loss of a U. S. Navy aircraft in 1978 was attributed to a silicate ester fire. [32] Coolanol is also expensive and toxic. The U. S. Navy has instituted a program named Pollution Prevention (P2) to reduce or eliminate the volume and toxicity of waste, air emissions, and effluent discharges.

Because of this, Coolanol is used less often today. Coherent microwave amplifiers operating above 1,000 watts microwave output, like traveling wave tubes and klystrons, require liquid coolant. The electron beam must contain 5 to 10 times more power than the microwave output, which can produce enough heat to corrupt the vacuum with plasma.

This flows from the collector toward the cathode. Magnetic focusing for the electron beam forces ionized gas atoms into the same location as the electron beam. Plasma ions flow in the opposite direction of the electron beam. This introduces FM modulation, and that degrades Doppler performance.

Liquid coolant with minimum pressure and flow rate is required to control collector gassing, and deionized water is normally used with most high power surface radar systems that utilize Doppler processing. [33]See also Edit Main article: Radar configurations and types Acronyms and abbreviations in avionics Definitions Amplitude-comparison monopulse Constant false alarm rate Sensitivity time control Hardware Radar engineering details Klystron Cavity magnetron Radio Traveling-wave tube Crossed-field amplifier Gallium arsenide Similar detection and ranging methods LIDARLORANSonar Historical radars List of radars Chain Home and Chain Home Low Hohentwiel radar H2S radar SCR-270 radar Notes Edit↑ Translation Bureau (2013).

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A. Tishchenko, ""Radar Prehistory, Soviet Side,"" Proc. of IEEE APS International Symposium 2001, vol.4. p. 44, 2003↑ Christian Hülsmeyer by Radar World↑ Patent DE165546; Verfahren, um metallische Gegenstände mittels elektrischer Wellen einem Beobachter zu melden.↑ Verfahren zur Bestimmung der Entfernung von metallischen Gegenständen (Schiffen o. dgl.

), deren Gegenwart durch das Verfahren nach Patent 16556 festgestellt wird.↑ GB 13170 Telemobiloscope↑ Hyland, L. A,, A. H. Taylor, and L. C. Young; ""System for detecting objects by radio,"" U. S. Patent No. 1981884, granted 27 Nov. 1934↑ Howeth, Linwood S.; ""Radar,"" Ch. XXXVIII in History of Communications -Electronics in the United States Navy, 1963; Radar↑ Watson, Raymond C., Jr. (2009-11-25).

Radar Origins Worldwide: History of Its Evolution in 13 Nations Through World War II. Trafford Publishing. ISBN 978-1-4269-2111-7. http://books.google.com/?id=g-r QQg AACAAJ.↑ Hearst Magazines (1935-12). Popular Mechanics. Hearst Magazines. p. 844. http://books.google.com/?id=x98DAAAAMBAJ&pg=PA844.↑ Frederick Seitz, Norman G. Einspruch, Electronic Genie: The Tangled History of Silicon - 1998 - page 104↑ John Erickson.

Radio-Location and the Air Defence Problem: The Design and Development of Soviet Radar. Science Studies, vol. 2, no. 3 (Jul., 1972), pp. 241-263↑ Page, Robert Morris, The Origin of Radar, Doubleday Anchor, New York, 1962, p. 66↑ Bonnier Corporation (1935-10). Popular Science. Bonnier Corporation. p. 29. http://books.google.com/?id=byg DAAAAMBAJ&pg=PA29.↑ 16.0 16.1Alan Dower Blumlein (2002).

""The story of RADAR Development"". http://www.doramusic.com/Radar.htm. Retrieved 2011-05-06.↑ (French) Copy of Patents an Obstacle-Locating Radio Apparatus on www.radar-france.fr↑ British man first to patent radar official site of the Patent Office [ dead link]↑ GB 593017 Improvements in or relating to wireless systems↑ Bonnier Corporation (1941-12).

Popular Science. Bonnier Corporation. p. 56. http://books.google.com/?id=h Cc DAAAAMBAJ&pg=PA56.↑ 21.0 21.1Hearst Magazines (1941-09). Popular Mechanics. Hearst Magazines. p. 26. http://books.google.com/?id=69k DAAAAMBAJ&pg=PA26.↑ Goebel, Greg (2007-01-01). ""The Wizard War: WW2 & The Origins Of Radar"". http://www.vectorsite.net/ttwiz_01.html. Retrieved 2007-03-24.↑ M. Castelaz. ""Exploration: The Doppler Effect"". Pisgah Astronomical Research Institute.↑ Strasser, Nancy C.. ""Investigation of Terrain Bounce Electronic Countermeasure"". DTIC. http://oai.dtic.mil/oai/oai?verb=get Record&metadata Prefix=html&identifier=ADA101208.↑ 25.0 25.1 ""Ground Surveillance Radars and Military Intelligence"".

Syracuse Research Corporation; Massachusetts Institute of Technology. http://www.mit.edu/~lrv/cornell/publications/Ground%20Surveillance%20Radars%20and%20Military%20Intelligence.pdf.↑ ""AN/PPS-5 Ground Surveillance Radar"". You Tube; jaglavaksoldier's Channel. http://www.youtube.com/watch?v=B0q1Pgz6Cm8.↑ ""Fundamentals of Radar Tracking"". Applied Technology Institute. http://www.aticourses.com/fundamentals_radar_tracking.htm.↑ ""Side-Lobe Supression"". MIT. http://mit.edu/6.933/www/Fall2000/mode-s/sidelobe.html.↑ Mi G-31 FOXHOUND↑ Radartutorial↑ Radartutorial↑ Stropki, Michael A.

(1992). ""Polyalphaolefins: A New Improved Cost Effective Aircraft Radar Coolant"". Melbourne, Australia: Aeronautical Research Laboratory, Defense Science and Technology Organisation, Department of Defense. http://www.dtic.mil/cgi-bin/Get TRDoc? AD=ADA250517&Location=U2&doc=Get TRDoc.pdf. Retrieved 2010-03-18.↑ J. L. de Segovia. ""Physics of Outgassing"". Madrid, Spain: Instituto de Física Aplicada, CETEF “L. Torres Quevedo”, CSIC.

http://www.cientificosaficionados.com/libros/CERN/vacio9-CERN.pdf. Retrieved 2012-08-12. References Edit Barrett, Dick, "" All you ever wanted to know about British air defence radar "". The Radar Pages. (History and details of various British radar systems)Buderi, "" Telephone History: Radar History "". Privateline.com. (Anecdotal account of the carriage of the world's first high power cavity magnetron from Britain to the US during WW2.

)Ekco Radar WW2 Shadow Factory The secret development of British radar. ES310 "" Introduction to Naval Weapons Engineering. "". (Radar fundamentals section)Hollmann, Martin, "" Radar Family Tree "". Radar World . Penley, Bill, and Jonathan Penley, "" Early Radar History —an Introduction "".

2002. Pub 1310 Radar Navigation and Maneuvering Board Manual, National Imagery and Mapping Agency, Bethesda, MD 2001 (US govt publication '...intended to be used primarily as a manual of instruction in navigation schools and by naval and merchant marine personnel.

')Swords, Seán S., ""Technical History of the Beginnings of Radar"", IEE History of Technology Series, Vol. 6, London: Peter Peregrinus, 1986Further reading Edit Reg Batt (1991). The radar army: winning the war of the airwaves. ISBN 978-0-7090-4508-3. E. G. Bowen (1998-01-01). Radar Days. Taylor & Francis. ISBN 978-0-7503-0586-0.

Michael Bragg (2002-05-01). RDF1: The Location of Aircraft by Radio Methods 1935-1945. Twayne Publishers. ISBN 978-0-9531544-0-1. Louis Brown (1999). A radar history of World War II: technical and military imperatives. Taylor & Francis. ISBN 978-0-7503-0659-1. Robert Buderi (1996). The invention that changed the world: how a small group of radar pioneers won the Second World War and launched a technological revolution.

ISBN 978-0-684-81021-8. Burch, David F., Radar For Mariners, Mc Graw Hill, 2005, ISBN 978-0-07-139867-1 . Ian Goult (2011). Secret Location: A witness to the Birth of Radar and its Postwar Influence. History Press.

ISBN 978-0-7524-5776-5. Peter S. Hall (1991-03). Radar. Potomac Books Inc. ISBN 978-0-08-037711-7. Derek Howse; Naval Radar Trust (1993-02). Radar at sea: the royal Navy in World War 2. Naval Institute Press. ISBN 978-1-55750-704-4. R. V. Jones (1998-08). Most Secret War. Wordsworth Editions Ltd. ISBN 978-1-85326-699-7. Kaiser, Gerald, Chapter 10 in ""A Friendly Guide to Wavelets"", Birkhauser, Boston, 1994. Kouemou, Guy (Ed.

): Radar Technology. In Tech, 2010, ISBN 978-953-307-029-2, ( Radar Technology - Free Open Access Book | In Tech Open ). Colin Latham; Anne Stobbs (1997-01). Radar: A Wartime Miracle. Sutton Pub Ltd. ISBN 978-0-7509-1643-1. François Le Chevalier (2002). Principles of radar and sonar signal processing. Artech House Publishers.

ISBN 978-1-58053-338-6. David Pritchard (1989-08). The radar war: Germany's pioneering achievement 1904-45. Harpercollins. ISBN 978-1-85260-246-8. Merrill Ivan Skolnik (1980-12-01). Introduction to radar systems. ISBN 978-0-07-066572-9. Merrill Ivan Skolnik (1990). Radar handbook. Mc Graw-Hill Professional. ISBN 978-0-07-057913-2. George W. Stimson (1998). Introduction to airborne radar. Sci Tech Publishing.

ISBN 978-1-891121-01-2. Younghusband, Eileen., Not an Ordinary Life. How Changing Times Brought Historical Events into my Life, Cardiff Centre for Lifelong Learning, Cardiff, 2009., ISBN 9780956115690 (Pages 36–67 contain the experiences of a WAAF radar plotter in WWII. )Younghusband, Eileen., One Woman's War. Cardiff. Candy Jar Books. 2011. ISBN 978-0-9566826-2-8David Zimmerman (2001-02). Britain's shield: radar and the defeat of the Luftwaffe. Sutton Pub Ltd. ISBN 978-0-7509-1799-5. External links Edit Wikimedia Commons has media related to Radar. MIT Video Course: Introduction to Radar Systems A set of 10 video lectures developed at Lincoln Laboratory to develop an understanding of radar systems and technologies.

Popular Science, August 1943, What Are the Facts About RADAR one of the first detailed factual articles on radar history, principles and operation published in the US""The Great Detective"", 1946.

Story of the development of radar by the Chrysler Corporation Christian Hülsmeyer and the early days of radar Radar: The Canadian History of Radar - Canadian War Museum Radar technology principles History of radar Radar invisibility with metamaterials Radar Research Center-Italy Early radar development in the UKPrinciples of radar target acquisition and weapon guidance systems Cloaking and radar invisibility RAF Air Defence Radar Museum Radar - A case study highlighting the vital contribution physics research has made to major technological development The short film Radar and Its Applications (1962) is available for free download at the Internet Archive [ more]Fraunhofer Institute for High Frequency Physics and Radar Techniques FHRSpace Observation Radar TIRA (Tracking and Imaging Radar) of Fraunhofer FHRThis page uses Creative Commons Licensed content from Wikipedia ( view authors) . Categories: Articles with French-language external links All articles with dead external links Articles with dead external links from November 2013 Articles incorporating text from Wikipedia Avionics Aircraft instruments Radar Microwave technology Measuring instruments Navigational equipment Air traffic control Science and technology during World War IITargeting (warfare)Add category "

These extreme temperatures are caused by the absorption of the sun's shortwave ultraviolet radiation. This radiation penetrates the upper atmosphere, stripping atoms of their electrons and giving them a positive charge. Electrically charged atoms build up to form a series of layers within the thermosphere. These charged layers are often referred to as the ionosphere, which deflects some radio signals. Before the modern use of satellites, this deflection by the ionosphere was essential for long distance radio communication.

The Atmosphere (click on layers for details) The atmosphere describes all the air surrounding the earth, from the ground all the way up to the edge of deep space. The atmosphere is composed of several layers, each defined because of the various phenomena which occur within the layer. These transitions are gradual, and most heights and measurements mentioned below refer to the average area of transition from one layer to another.

The Troposphere Oxygen and nitrogen make up the majority of the gases in the earth's atmosphere, even at much higher altitudes. But it is the lowest level of earth's atmosphere where the right mixture works to support life. Here, living things are also free from the radiation showers which flow down through most of the earth's atmosphere.

Compared to the rest of the atmosphere, the troposphere is a tiny layer,extending at most ten miles (16km) up from the earth's surface.

Within this small layer almost all of our weather is created—the short term changes in temperature, wind, pressure, and moisture that we experience as part of our daily lives. The lower altitudes are the warmest part of the troposphere, in part because the earth's surface absorbs solar radiation and transfers this heat to the air.

Generally, as altitude increases, temperature decreases steadily. But the earth's topography—mountain ranges and plateaus—can cause some lower regions in the troposphere to experience temperature inversions, where temperature actually increases with altitude.

Towards the top of the troposphere temperatures fall to an average low of -70deg. F (-57deg. C) and wind speeds increase significantly, making the top of the troposphere an extremely cold and windy place. (back to illustration)The Stratosphere The gradual change from the troposphere to the stratosphere begins at approximately 7 miles (11km) high. The temperature in the lower stratosphere is extremely stable and cold at -70deg. F (-57deg. C).

Here, strong winds occur as part of defined circulation patterns. High cirrus clouds sometimes form in the lower stratosphere, but for the most part there are no significant weather patterns in the stratosphere.

From the middle of the stratosphere and up, the temperature pattern undergoes a sudden change, sharply increasing with height. Much of this temperature change is due to increasing levels of ozone concentration which absorbs ultraviolet radiation.

The temperature can reach a balmy 65deg. F (18deg. C) in the upper stratosphere near an altitude of 25 miles (40km) high. (back to illustration)The Mesosphere25 miles (40km) above the earth's surface marks the transition to the mesosphere. In this layer, temperature once again begins to fall as altitude increases, to temperatures as low as -225deg. F (-143deg. C) near its top, 50 miles (81km) above the earth. Such extreme cold allows the formation of so-called noctilucent clouds, thought to be made of ice crystals clinging to dust particles.

(back to illustration)The Thermosphere The transition from the mesosphere to the final thermosphere layer begins at a height of approximately 50 miles (81km). The thermosphere receives its name from the return to increasing temperature which can reach a staggering 3,600deg. F (1982deg. C).

Today, radio frequencies which pass through the ionosphere unaffected are chosen for satellite communication.

Beautiful auroras, also known as the Northern and Southern lights, occur in the thermosphere when solar flares from the sun create magnetic storms near the poles. These magnetic storms strip atoms of their electrons. Brilliant green and red light is emitted when the electrons rejoin the atom, returning the atoms to their original state.

Even higher—above the auroras and the ionosphere—the gases of this final atmospheric layer begin to dissipate, until finally, several hundred miles above the earth, they fade off into the depths of space.

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When a radio wave reaches the ionosphere, the electric field in the wave forces the electrons in the ionosphere into oscillation at the same frequency as the radio wave. Some of the radio-frequency energy is given up to this resonant oscillation.

Ionosphere

"Ionosphere From Wikipedia, the free encyclopedianavigation search The ionosphere ( / aɪ ˈ ɒ n ə ˌ s f ɪər / [1] [2]) is the ionized part of Earth's upper atmosphere, from about 60 km (37 mi) to 1,000 km (620 mi) altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere.

It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.

[3]Relationship of the atmosphere and ionosphere Contents [ hide ]1 History2 Geophysics3 The ionospheric layers3.1 D layer3.2 E layer3.3 E s3.4 F layer4 Ionospheric model5 Persistent anomalies to the idealized model5.1 Winter anomaly5.2 Equatorial anomaly5.3 Equatorial electrojet6 Ephemeral ionospheric perturbations6.1 X-rays: sudden ionospheric disturbances (SID)6.2 Protons: polar cap absorption (PCA)6.3 Geomagnetic storms6.4 Lightning7 Applications7.1 Radio communication7.1.1 Mechanism of refraction7.2 Other applications8 Measurements8.1 Overview8.2 Ionograms8.3 Incoherent scatter radars8.4 GNSS radio occultation9 Indices of the ionosphere9.1 Solar intensity9.2 Geomagnetic disturbances10 GPS/GNSS ionospheric correction11 Ionospheres of other planets and natural satellites12 See also13 Notes14 References15 External links History [ edit]As early as 1839, the German mathematician and physicist Carl Friedrich Gauss postulated that an electrically conducting region of the atmosphere could account for observed variations of Earth's magnetic field.

Sixty years later, Guglielmo Marconi received the first trans-Atlantic radio signal on December 12, 1901, in St. John's, Newfoundland (now in Canada) using a 152.4 m (500 ft) kite-supported antenna for reception.

The transmitting station in Poldhu, Cornwall, used a spark-gap transmitter to produce a signal with a frequency of approximately 500 k Hz and a power of 100 times more than any radio signal previously produced. The message received was three dits, the Morse code for the letter S. To reach Newfoundland the signal would have to bounce off the ionosphere twice.

Dr. Jack Belrose has contested this, however, based on theoretical and experimental work. [4] However, Marconi did achieve transatlantic wireless communications in Glace Bay, Nova Scotia, one year later. [ citation needed]In 1902, Oliver Heaviside proposed the existence of the Kennelly–Heaviside layer of the ionosphere which bears his name.

Heaviside's proposal included means by which radio signals are transmitted around the Earth's curvature. Heaviside's proposal, coupled with Planck's law of black body radiation, may have hampered the growth of radio astronomy for the detection of electromagnetic waves from celestial bodies until 1932 (and the development of high-frequency radio transceivers).

Also in 1902, Arthur Edwin Kennelly discovered some of the ionosphere's radio-electrical properties. In 1912, the U. S. Congress imposed the Radio Act of 1912 on amateur radio operators, limiting their operations to frequencies above 1.5 MHz (wavelength 200 meters or smaller).

The government thought those frequencies were useless. This led to the discovery of HF radio propagation via the ionosphere in 1923. In 1926, Scottish physicist Robert Watson-Watt introduced the term ionosphere in a letter published only in 1969 in Nature: We have in quite recent years seen the universal adoption of the term 'stratosphere'..and..the companion term 'troposphere'...

The term 'ionosphere', for the region in which the main characteristic is large scale ionisation with considerable mean free paths, appears appropriate as an addition to this series. In the early 1930s, test transmissions of Radio Luxembourg inadvertently provided evidence of the first radio modification of the ionosphere; HAARP ran a series of experiments in 2017 using the eponymous Luxembourg Effect.

[5]Edward V. Appleton was awarded a Nobel Prize in 1947 for his confirmation in 1927 of the existence of the ionosphere. Lloyd Berkner first measured the height and density of the ionosphere. This permitted the first complete theory of short-wave radio propagation.

Maurice V. Wilkes and J. A. Ratcliffe researched the topic of radio propagation of very long radio waves in the ionosphere. Vitaly Ginzburg has developed a theory of electromagnetic wave propagation in plasmas such as the ionosphere.

In 1962, the Canadian satellite Alouette 1 was launched to study the ionosphere. Following its success were Alouette 2 in 1965 and the two ISIS satellites in 1969 and 1971, further AEROS-A and -B in 1972 and 1975, all for measuring the ionosphere. On July 26, 1963 the first operational geosynchronous satellite Syncom 2 was launched. [6] The board radio beacons on this satellite (and its successors) enabled – for the first time – the measurement of total electron content (TEC) variation along a radio beam from geostationary orbit to an earth receiver. (The rotation of the plane of polarization directly measures TEC along the path.) Australian geophysicist Elizabeth Essex-Cohen from 1969 onwards was using this technique to monitor the atmosphere above Australia and Antarctica. [7]Geophysics [ edit]

The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth, stretching from a height of about 50 km (31 mi) to more than 1,000 km (620 mi).

It exists primarily due to ultraviolet radiation from the Sun. The lowest part of the Earth's atmosphere, the troposphere extends from the surface to about 10 km (6.2 mi). Above that is the stratosphere, followed by the mesosphere. In the stratosphere incoming solar radiation creates the ozone layer.

At heights of above 80 km (50 mi), in the thermosphere, the atmosphere is so thin that free electrons can exist for short periods of time before they are captured by a nearby positive ion. The number of these free electrons is sufficient to affect radio propagation. This portion of the atmosphere is partially ionized and contains a plasma which is referred to as the ionosphere.

Ultraviolet (UV), X-ray and shorter wavelengths of solar radiation are ionizing, since photons at these frequencies contain sufficient energy to dislodge an electron from a neutral gas atom or molecule upon absorption.

In this process the light electron obtains a high velocity so that the temperature of the created electronic gas is much higher (of the order of thousand K) than the one of ions and neutrals. The reverse process to ionization is recombination, in which a free electron is ""captured"" by a positive ion. Recombination occurs spontaneously, and causes the emission of a photon carrying away the energy produced upon recombination. As gas density increases at lower altitudes, the recombination process prevails, since the gas molecules and ions are closer together.

The balance between these two processes determines the quantity of ionization present. Ionization depends primarily on the Sun and its activity. The amount of ionization in the ionosphere varies greatly with the amount of radiation received from the Sun. Thus there is a diurnal (time of day) effect and a seasonal effect. The local winter hemisphere is tipped away from the Sun, thus there is less received solar radiation. The activity of the Sun is associated with the sunspot cycle, with more radiation occurring with more sunspots. Radiation received also varies with geographical location (polar, auroral zones, mid-latitudes, and equatorial regions).

There are also mechanisms that disturb the ionosphere and decrease the ionization. There are disturbances such as solar flares and the associated release of charged particles into the solar wind which reaches the Earth and interacts with its geomagnetic field.

The ionospheric layers [ edit]Ionospheric layers.... At night the F layer is the only layer of significant ionization present, while the ionization in the E and D layers is extremely low.

During the day, the D and E layers become much more heavily ionized, as does the F layer, which develops an additional, weaker region of ionisation known as the F 1 layer. The F 2 layer persists by day and night and is the main region responsible for the refraction and reflection of radio waves. D layer [ edit]The D layer is the innermost layer, 60 km (37 mi) to 90 km (56 mi) above the surface of the Earth.

Ionization here is due to Lyman series -alpha hydrogen radiation at a wavelength of 121.6 nanometre (nm) ionizing nitric oxide (NO). In addition, high solar activity can generate hard X-rays (wavelength < 1 nm) that ionize N 2 and O 2.

Recombination rates are high in the D layer, so there are many more neutral air molecules than ions.

Medium frequency (MF) and lower high frequency (HF) radio waves are significantly attenuated within the D layer, as the passing radio waves cause electrons to move, which then collide with the neutral molecules, giving up their energy. Lower frequencies experience greater absorption because they move the electrons farther, leading to greater chance of collisions.

This is the main reason for absorption of HF radio waves, particularly at 10 MHz and below, with progressively less absorption at higher frequencies. This effect peaks around noon and is reduced at night due to a decrease in the D layer's thickness; only a small part remains due to cosmic rays.

A common example of the D layer in action is the disappearance of distant AM broadcast band stations in the daytime. During solar proton events, ionization can reach unusually high levels in the D-region over high and polar latitudes. Such very rare events are known as Polar Cap Absorption (or PCA) events, because the increased ionization significantly enhances the absorption of radio signals passing through the region.

[8] In fact, absorption levels can increase by many tens of d B during intense events, which is enough to absorb most (if not all) transpolar HF radio signal transmissions. Such events typically last less than 24 to 48 hours. E layer [ edit]The E layer is the middle layer, 90 km (56 mi) to 150 km (93 mi) above the surface of the Earth.

Ionization is due to soft X-ray (1–10 nm) and far ultraviolet (UV) solar radiation ionization of molecular oxygen (O 2 ). Normally, at oblique incidence, this layer can only reflect radio waves having frequencies lower than about 10 MHz and may contribute a bit to absorption on frequencies above. However, during intense sporadic E events, the E s layer can reflect frequencies up to 50 MHz and higher.

The vertical structure of the E layer is primarily determined by the competing effects of ionization and recombination. At night the E layer weakens because the primary source of ionization is no longer present. After sunset an increase in the height of the E layer maximum increases the range to which radio waves can travel by reflection from the layer.

This region is also known as the Kennelly–Heaviside layer or simply the Heaviside layer. Its existence was predicted in 1902 independently and almost simultaneously by the American electrical engineer Arthur Edwin Kennelly (1861–1939) and the British physicist Oliver Heaviside (1850–1925). However, it was not until 1924 that its existence was detected by Edward V. Appleton and Miles Barnett.

E s [ edit]The E s layer ( sporadic E-layer) is characterized by small, thin clouds of intense ionization, which can support reflection of radio waves, rarely up to 225 MHz.

Sporadic-E events may last for just a few minutes to several hours. Sporadic E propagation makes VHF-operating radio amateurs very excited, as propagation paths that are generally unreachable can open up. There are multiple causes of sporadic-E that are still being pursued by researchers. This propagation occurs most frequently during the summer months when high signal levels may be reached. The skip distances are generally around 1,640 km (1,020 mi). Distances for one hop propagation can be anywhere from 900 km (560 mi) to 2,500 km (1,600 mi).

Double-hop reception over 3,500 km (2,200 mi) is possible. F layer [ edit]Main article: F region The F layer or region, also known as the Appleton–Barnett layer, extends from about 150 km (93 mi) to more than 500 km (310 mi) above the surface of Earth. It is the layer with the highest electron density, which implies signals penetrating this layer will escape into space.

Electron production is dominated by extreme ultraviolet (UV, 10–100 nm) radiation ionizing atomic oxygen. The F layer consists of one layer (F 2) at night, but during the day, a secondary peak (labelled F 1) often forms in the electron density profile. Because the F 2 layer remains by day and night, it is responsible for most skywave propagation of radio waves and long distances high frequency (HF, or shortwave) radio communications. Above the F layer, the number of oxygen ions decreases and lighter ions such as hydrogen and helium become dominant.

This region above the F layer peak and below the plasmasphere is called the topside ionosphere. From 1972 to 1975 NASA launched the AEROS and AEROS B satellites to study the F region. [9]Ionospheric model [ edit]An ionospheric model is a mathematical description of the ionosphere as a function of location, altitude, day of year, phase of the sunspot cycle and geomagnetic activity.

Geophysically, the state of the ionospheric plasma may be described by four parameters: electron density, electron and ion temperature and, since several species of ions are present, ionic composition.

Radio propagation depends uniquely on electron density. Models are usually expressed as computer programs. The model may be based on basic physics of the interactions of the ions and electrons with the neutral atmosphere and sunlight, or it may be a statistical description based on a large number of observations or a combination of physics and observations.

One of the most widely used models is the International Reference Ionosphere (IRI), [10] which is based on data and specifies the four parameters just mentioned.

The IRI is an international project sponsored by the Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI). [11] The major data sources are the worldwide network of ionosondes, the powerful incoherent scatter radars (Jicamarca, Arecibo, Millstone Hill, Malvern, St Santin), the ISIS and Alouette topside sounders, and in situ instruments on several satellites and rockets.

IRI is updated yearly. IRI is more accurate in describing the variation of the electron density from bottom of the ionosphere to the altitude of maximum density than in describing the total electron content (TEC). Since 1999 this model is ""International Standard"" for the terrestrial ionosphere (standard TS16457). Persistent anomalies to the idealized model [ edit]Ionograms allow deducing, via computation, the true shape of the different layers.

Nonhomogeneous structure of the electron / ion - plasma produces rough echo traces, seen predominantly at night and at higher latitudes, and during disturbed conditions. Winter anomaly [ edit]At mid-latitudes, the F 2 layer daytime ion production is higher in the summer, as expected, since the Sun shines more directly on the Earth.

However, there are seasonal changes in the molecular-to-atomic ratio of the neutral atmosphere that cause the summer ion loss rate to be even higher. The result is that the increase in the summertime loss overwhelms the increase in summertime production, and total F 2 ionization is actually lower in the local summer months.

This effect is known as the winter anomaly. The anomaly is always present in the northern hemisphere, but is usually absent in the southern hemisphere during periods of low solar activity. Equatorial anomaly [ edit]Electric currents created in sunward ionosphere. Within approximately ± 20 degrees of the magnetic equator, is the equatorial anomaly.

It is the occurrence of a trough in the ionization in the F 2 layer at the equator and crests at about 17 degrees in magnetic latitude.

The Earth's magnetic field lines are horizontal at the magnetic equator. Solar heating and tidal oscillations in the lower ionosphere move plasma up and across the magnetic field lines.

This sets up a sheet of electric current in the E region which, with the horizontal magnetic field, forces ionization up into the F layer, concentrating at ± 20 degrees from the magnetic equator. This phenomenon is known as the equatorial fountain. Equatorial electrojet [ edit]The worldwide solar-driven wind results in the so-called Sq (solar quiet) current system in the E region of the Earth's ionosphere ( ionospheric dynamo region) (100–130 km (62–81 mi) altitude).

Resulting from this current is an electrostatic field directed west–east (dawn–dusk) in the equatorial day side of the ionosphere.

At the magnetic dip equator, where the geomagnetic field is horizontal, this electric field results in an enhanced eastward current flow within ± 3 degrees of the magnetic equator, known as the equatorial electrojet. Ephemeral ionospheric perturbations [ edit]X-rays: sudden ionospheric disturbances (SID) [ edit]When the Sun is active, strong solar flares can occur that will hit the sunlit side of Earth with hard X-rays.

The X-rays will penetrate to the D-region, releasing electrons that will rapidly increase absorption, causing a high frequency (3–30 MHz) radio blackout. During this time very low frequency (3–30 k Hz) signals will be reflected by the D layer instead of the E layer, where the increased atmospheric density will usually increase the absorption of the wave and thus dampen it.

As soon as the X-rays end, the sudden ionospheric disturbance (SID) or radio black-out ends as the electrons in the D-region recombine rapidly and signal strengths return to normal. Protons: polar cap absorption (PCA) [ edit]Associated with solar flares is a release of high-energy protons.

These particles can hit the Earth within 15 minutes to 2 hours of the solar flare. The protons spiral around and down the magnetic field lines of the Earth and penetrate into the atmosphere near the magnetic poles increasing the ionization of the D and E layers. PCA's typically last anywhere from about an hour to several days, with an average of around 24 to 36 hours.

Coronal mass ejections can also release energetic protons that enhance D-region absorption in the polar regions. Geomagnetic storms [ edit]A geomagnetic storm is a temporary intense disturbance of the Earth's magnetosphere. During a geomagnetic storm the F₂ layer will become unstable, fragment, and may even disappear completely.

In the Northern and Southern pole regions of the Earth aurorae will be observable in the sky. Lightning [ edit]Lightning can cause ionospheric perturbations in the D-region in one of two ways.

The first is through VLF (very low frequency) radio waves launched into the magnetosphere. These so-called ""whistler"" mode waves can interact with radiation belt particles and cause them to precipitate onto the ionosphere, adding ionization to the D-region. These disturbances are called ""lightning-induced electron precipitation "" (LEP) events. Additional ionization can also occur from direct heating/ionization as a result of huge motions of charge in lightning strikes.

These events are called early/fast. In 1925, C. T. R. Wilson proposed a mechanism by which electrical discharge from lightning storms could propagate upwards from clouds to the ionosphere. Around the same time, Robert Watson-Watt, working at the Radio Research Station in Slough, UK, suggested that the ionospheric sporadic E layer (E s) appeared to be enhanced as a result of lightning but that more work was needed.

In 2005, C. Davis and C. Johnson, working at the Rutherford Appleton Laboratory in Oxfordshire, UK, demonstrated that the E s layer was indeed enhanced as a result of lightning activity.

Their subsequent research has focused on the mechanism by which this process can occur. Applications [ edit]Radio communication [ edit]Due to the ability of ionized atmospheric gases to refract high frequency (HF, or shortwave) radio waves, the ionosphere can reflect radio waves directed into the sky back toward the Earth.

Radio waves directed at an angle into the sky can return to Earth beyond the horizon. This technique, called ""skip"" or "" skywave "" propagation, has been used since the 1920s to communicate at international or intercontinental distances.

The returning radio waves can reflect off the Earth's surface into the sky again, allowing greater ranges to be achieved with multiple hops. This communication method is variable and unreliable, with reception over a given path depending on time of day or night, the seasons, weather, and the 11-year sunspot cycle. During the first half of the 20th century it was widely used for transoceanic telephone and telegraph service, and business and diplomatic communication. Due to its relative unreliability, shortwave radio communication has been mostly abandoned by the telecommunications industry, though it remains important for high-latitude communication where satellite-based radio communication is not possible. Some broadcasting stations and automated services still use shortwave radio frequencies, as do radio amateur hobbyists for private recreational contacts. Mechanism of refraction [ edit]

When a radio wave reaches the ionosphere, the electric field in the wave forces the electrons in the ionosphere into oscillation at the same frequency as the radio wave. Some of the radio-frequency energy is given up to this resonant oscillation.

The ionosphere is a region of the upper atmosphere where there are large concentrations of free ions and electrons. While the ions give the ionosphere its name, but it is the free electrons that affect the radio waves and radio communications.

Ionosphere & Radiowave Propagation

"Ionosphere & Radiowave Propagation The ionosphere is the key area for HF propagation - take a look at this page to find out what it is; how it becomes ionised; why does it support HF radio communications & how why does it support radiowave propagation.

Ionospheric propagation tutorial includes . . . . Ionospheric propagation Ionosphere Ionospheric layers Skywaves & skip Critical frequency, MUF, LUF & OWF Ionospheric absorption Solar indices Propagation software NVIS Transequatorial propagation Sporadic EAs electromagnetic waves, and in this case, radio signals travel, they interact with objects and the media in which they travel.

As they do this the radio signals can be reflected, refracted or diffracted. These interactions cause the radio signals to change direction, and to reach areas which would not be possible if the radio signals travelled in a direct line. The ionosphere is a particularly important region with regards to radio signal propagation and radio communications in general. Its properties govern the ways in which radio communications, particularly in the HF radio communications bands take place.

In particular the ionosphere is widely known for affecting signals on the short wave radio bands where it ""reflects"" signals enabling these radio communications signals to be heard over vast distances. Radio stations have long used the properties of the ionosphere to enable them to provide worldwide radio communications coverage. Although today, satellites are widely used, HF radio communications using the ionosphere still plays a major role in providing worldwide radio coverage.

The ionosphere extends over more than one of the meteorological areas, encompassing the mesosphere and the thermosphere, it is an area that is characterised by the existence of positive ions (and more importantly for radio signals free electrons) and it is from the existence of the ions that it gains its name.

Basics The free electrons do not appear over the whole of the atmosphere. Instead it is found that the number of free electrons starts to rise at altitudes of approximately 30 kilometres.

However it is not until altitudes of around 60 to 90 kilometres are reached that the concentration is sufficiently high to start to have a noticeable effect on radio signals and hence on radio communications systems. It is at this level that the ionosphere can be said to start. The ionisation in the ionosphere is caused mainly by radiation from the Sun.

In addition to this, the very high temperatures and the low pressure result in the gases in the upper reaches of the atmosphere existing mainly in a monatomic form rather than existing as molecules. At lower altitudes, the gases are in the normal molecular form, but as the altitude increases the monatomic forms are more in abundance, and at altitudes of around 150 kilometres, most of the gases are in a monatomic form.

This is very important because it is found that the monatomic forms of the gases are very much easier to ionise than the molecular forms.

Ionisation The Sun emits vast quantities of radiation of all wavelengths and this travels towards the Earth, first reaching the outer areas of the atmosphere. In creating the ionisation it is found that when radiation of sufficient intensity strikes an atom or a molecule, energy may be removed from the radiation and an electron removed, producing a free electron and a positive ion. In the example given below, the simple example of a helium atom is give, although other gases including oxygen and nitrogen are far more common.

Ionisation process in the ionosphere The radiation from the Sun covers a vast spectrum of wavelengths. However in terms of the effect it has on the atoms of molecules it can be considered as photons. The electrons in the atoms or molecules can be considered as orbiting the central nucleus consisting of protons and neutrons. Electrons are tied or bound to their orbit around the nucleus by electro-static forces, the electron is negatively charged and the nucleus is positively charged.

There are equal numbers of electrons and protons in any molecule and as a result it is electro-statically neutral. When a photon strikes the atom, or molecule, the photon transfers its energy to the electron as excess kinetic energy. Under some circumstances this excess energy may exceed the binding energy in the atom or molecule and the electron escapes the influence of the positive charge of the nucleus.

This leaves a positively charged nucleus or ions and a negatively charged electron, although as there are the same number of positive ions and negative electrons the whole gas still remains with an overall neutral charge. Most of the ionisation in the ionosphere results from ultraviolet light, although this does not mean that other wavelengths do not have some effect.

Additionally, each time an atom or molecule is ionised a small amount of energy is used. This means that as the radiation passes further into the atmosphere, its intensity reduces. It is for this reason that the ultraviolet radiation causes most of the ionisation in the upper reaches of the ionosphere, but at lower altitudes the radiation that is able to penetrate further cause more of the ionisation. Accordingly, extreme ultra-violet and X-Rays give rise to most of the ionisation at lower altitudes.

This reduction in these forms of radiation protects us on the surface of the Earth from the harmful effects of these rays.

The level of ionisation varies over the extent of the ionosphere, being far from constant. One reason is that the level of radiation reduces with decreasing altitude. Also the density of the gases varies. In addition to this there is a variation in the proportions of monatomic and molecular forms of the gases, the monatomic forms of gases being far greater at higher altitudes. These and a variety of other phenomena mean that there are variations in the level of ionisation with altitude.

The level of ionisation in the ionosphere also changes with time. It varies with the time of day, time of year, and according to many other external influences. One of the main reasons why the electron density varies is that the Sun, which gives rise to the ionisation is only visible during the day. While the radiation from the Sun causes the atoms and molecules to split into free electrons and positive ions. The reverse effect also occurs. When a negative electron meets a positive ion, the fact that dissimilar charges attract means that they will be pulled towards one another and they may combine.

This means that two opposite effects of splitting and recombination are taking place. This is known as a state of dynamic equilibrium.

Accordingly the level of ionisation is dependent upon the rate of ionisation and recombination. This has a significant effect on radio communications. Simplified view of the layers in the ionosphere over the period of a day Other effects like the season and the state of the Sun also have a major effect.

Sunspots and solar disturbances have a major impact on the level of radiation received, and these effects are covered in other articles on this website on Sunspots and Solar Disturbances.

The season also has an effect. Again this is covered in other articles on the Radio-Electronics. Com website. However very briefly, the radiation received from the Sun varies in the same way that heat from the Sun varies according to the season, and accordingly the level of ionisation and free electrons changes.

However this is a very simplified view as other facts also come into play. The ionosphere is a continually changing area. It is obviously affected by radiation from the Sun, and this changes as a result aspects including of the time of day, the geographical area of the world, and the state of the Sun.

As a result radio communications using the ionosphere change from one day to the next, and even one hour to the next. Predicting how what radio communications will be possible and radio signals may propagate is of great interest to a variety of radio communications users ranging from broadcasters to radio amateurs and two way radio communications systems users to those with maritime mobile radio communications systems and many more.

By Ian Poole Previous page Next page More Antenna & Propagation Topics: EM waves Radio propagation Ionospheric propagation Ground wave Meteor scatter Tropospheric propagation Cubical quad Dipole Discone Ferrite rod Log periodic antenna Parabolic reflector antenna Vertical antennas Yagi Antenna grounding Coax cable Waveguide Return to Antennas & Propagation menu . . . "

In free space the propagation speed of radio waves is the same as that of light, at approximately 300,000 km, so they would arrive there in about 1.3 seconds. The speed falls slightly when passing through a conductor such as an antenna or cable.

RF design guide Introduction What is a radio module? What are radio waves? What is an antenna? Radio control Knowledge required for design Radio transmission terminology What are radio waves? Here we will look at the characteristics of radio waves as far as is required for the design of radio communication equipment.

We will explain the methods of processing radio waves and the thinking behind it, and gain an perspective on the subject. People and radio waves Classification of radio waves What are the physical properties of radio waves?

The generation of radio waves Longitudinal waves and transverse waves The qualities of radio waves The speed and the wave length of radio waves Electric field intensity at an arbitrary location Electric field intensity and received power Propagation loss What happens to received power?

Fading Why do communication errors occur? Is there any impact on the human body or other equipment? People and radio waves As of technology has developed, equipment that utilizes radio waves such as television, mobile phones and so on has been introduced, and now radio waves are present all around us.

Radio waves themselves are not something that humans invented. They have existed since the moment when the universe came into being. Presently in the natural world radio waves are radiated onto the surface of the earth from the sun and the other stars, and electromagnetic waves (radio waves) also arise from movement of the earth's crust and from lightening and so on. However humans discovered radio waves, and have invented devices for generating them. Radio waves are currently used in all sorts of fields.

Familiar items include mobile phones, televisions, radios, amateur radio equipment and the like. There has been an explosive spread of mobile phones, allowing people to contact each other wherever they go.

Exchanging email is also a very popular function. Television images are sent from countries on the other side of the earth, and for people who are not really interested in technology and the like, the technology behind these communications is not important.

What is important is the content of the communication. Although we will consider the design of equipment using radio modules, it is not necessary for us to inquire particularly deeply into the physical characteristics of radio waves. Just a little knowledge of the subject is sufficient for designing radio equipment. For detailed information on the physical properties of radio waves, please refer to the relevant literature.

First we will cover the basic information. This refers to radio modules, and communication range is up to several kilometers, while the frequency of the radio waves is in a range of from several hundred MHz to several tens of GHz.

Classification of radio waves Radio waves are electromagnetic waves. Electromagnetic waves include waves such as X rays, ultraviolet light, visible light, infrared rays and so on, but you probably imagine radio waves to be quite different from these waves. Of the various kinds of electromagnetic waves, radio waves have a longer wave length than infrared rays, and are defined by the Radio Law as 'electromagnetic waves with a frequency of less than 3,000 GHz (3 THz)'.

Ultralow frequency radio waves below 3k Hzradio waves 3k Hz~ 3THzinfrared rays 3THz~ 380THz visible light 380THz~ 790THz ultraviolet light 790THz~ 10 5 THz X rays 10 5 THz~ 10 7 THz γ rays above 10 7 THz*K:kilo 1*10 3, M:mega 1*10 6, G:giga 1*10 9, T:tera 1*10 12Names of radio waves Frequency Wave length Principal applications VLF (Very Low Frequency) 3k Hz ~ 30k Hz 100km ~ 10km LF (Low Frequency) 30k Hz ~ 300k Hz 10km ~ 1km Vessel / Airplane beacon MF (Medium Frequency) 300k Hz ~ 3MHz 1km ~ 100m AM radio, Marine radio, Amateur radio HF (High Frequency) 3MHz ~ 30MHz 100m ~ 10m Shortwave broadcasting, Marine / Air radio, Amateur radio VHF (Very High Frequency) 30MHz ~ 300MHz 10m ~ 1m TV, FM, Fire radio, Police radio, Disaster PA radio network UHF (Ultra High Frequency) 300MHz ~ 3GHz 1m ~ 10cm Low power radio, Mobile-phone, Taxi radio, Amateur radio, TV, Wireless LANSHF (Super High Frequency) 3GHz ~ 30GHz 10cm ~ 1cm Satellite broadcasting, Radar EHF (Extremely High Frequency) 30GHz ~ 300GHz 1cm ~ 1mm Satellite broadcasting, Radio astronomy, Radarsubmillimeter waves300GHz ~ 3THz 1mm ~ 0.1mm What are the physical properties of radio waves?

Radio waves are electromagnetic waves. Electromagnetic waves include waves such as X rays, ultraviolet light, visible light, infrared rays and so on, but you probably imagine radio waves to be quite different from these waves.

Among the kinds of electromagnetic waves, radio waves have a longer wave length than infrared rays, and are defined as electromagnetic waves with a frequency of less than 3,000 GHz.

In free space their propagation velocity is the same as that of light, at approximately 300,000 km in 1 second. The distance from the earth to the moon is about 390,000 km, so from the moon, a signal would arrive in about 1.3 seconds.

The generation of radio waves Recall the scientific experiments you did at school. When a copper wire was placed on top of a compass and a current was applied from a battery, the needle of the compass shook. Next, when a bar magnet was moved quickly through the middle of a coil made of copper wire, the needle of the ammeter connected to the coil shook. In the former case, a magnetic field was generated by the change in the current (electric field), and in the latter case, a current (electric field) was generated by the change in the magnetic field.

When a high frequency current flows in an antenna, the electric field changes acutely and a magnetic field is generated in the vicinity.

Then due to this magnetic field, an electric field is generated. This process is repeated and matter flying in space moves perpendicularly (at right angles) to the direction of vibration of the electric field and magnetic field according to the form of the radio wave.

The electric field (E) and magnetic field (H) vibrate at right angles to each other. In this way, electric fields and magnetic fields have an integral relationship in radio waves, and neither one exists independently of the other. The qualities of radio waves are often compared to those of sound waves, but the definitive difference is that radio waves are transmitted even in the absence of matter (a medium).

(For sound waves to be transmitted air is required.) In other words, radio waves can even be transmitted in a vacuum. In fact, radio waves are transmitted from communications satellites. Longitudinal waves and transverse waves You may have heard the words 'longitudinal wave' and 'transverse wave'. Waves that, like sound, vibrate in the same direction as their direction of propagation are longitudinal waves, while waves that vibrate at right angles to their direction of propagation are transverse waves.

Radio waves are one kind of transverse wave. The qualities of radio waves The shorter the wave length of radio waves becomes, the more they take on the qualities of light, and the greater their straightness becomes.

In other words, their energy is concentrated in one direction, and they are said to have strong directivity.

Furthermore, the higher the frequency, the more acute is the attenuation of the wave's energy. In general, radio waves are considered to propagate in a straight line, but what happens if there are various physical obstacles in their path such as mountains, buildings, walls, or people and so on?

If we consider an example of an urban area where there are many buildings, there are direct waves that arrive directly, reflected waves that arrive after hitting buildings and the like, diffracted waves that circumvent the shadows of buildings, transmitted waves that arrive by passing through the glass or walls of buildings, and so on. The kinds of wave differs according to type (material) of obstacle. Radio waves can pass through glass and ceramics (permeation), but they are reflected by metal and concrete. Furthermore, waves with frequencies higher than several GHz are scattered and absorbed by rain, snow, fog and the like, and their power tends to attenuate. The speed and the wavelength of radio waves

In free space the propagation speed of radio waves is the same as that of light, at approximately 300,000 km, so they would arrive there in about 1.3 seconds. The speed falls slightly when passing through a conductor such as an antenna or cable.

The wave length λ (lambda) of radio waves is as follows; If the frequency of the radio wave is f, and the speed of the radio wave in a vacuum is C, then As the speed per second of radio waves in a vacuum is about 300,000 km (about 3×10 8 [m/sec]), at 433 MHz the wave length λ is< Click to move to the calculation window >There is a close relationship between the wave length of the radio wave and the characteristics of the antenna.

Electric field intensity at an arbitrary location It should be obvious that to receive another party's voice by mobile phone, there must be radio waves in that location. Although whether or not there are radio waves is to a large extent related to the distance from the transmitting antenna, it is the electric field intensity that indicates the strength of the radio waves there.

Electric field intensity at an arbitrary location When considering the characteristics of radio waves and antennas theoretically, a method taking a virtual antenna as a reference is used. This theoretical antenna is called an isotropic antenna. Isotropic antennas are point-like antennas, that can emit and receive radio waves in all directions with a certain field strength.

As in the diagram below, the power per unit area at a location D [m] distant from an isotropic antenna with P [W] power, is called power density PD [W/m2], and is the value shown in (2).

In addition, the value for the Poynting vector PV [W/m2] at that location is (1) assuming electric field intensity E [V/m]. Since the power density and Poynting vector are equal, assuming (1) = (2), the electric field intensity of the location at distance D [m] is (3).

* Poynting vector: A theorem identified by John Henry Poynting Electric field intensity at an arbitrary location with an absolute gain Gi antenna As the formulae above suggest, the general form for finding the electric field intensity of the location d [m] is with an antenna with absolute gain Gi is (4).

Replace Gi with the true value. Electric field intensity and received power It is possible to find the received power of an antenna from the electric field intensity at the location where the antenna is placed.

The following is the calculation of received power in free space. Actually, there are a variety of propagation loss factors, and it is not possible simply to calculate it, but it is possible to find approximate values and tendencies.

In addition, since there are many mobile radio devices in use at a height of about 1 m above ground level, we present propagation loss calculations for two simple wave models over flat terrain. Calculation of received power with the Friis transmission formula The Friis transmission formula shows the relationship between transmitted power and antenna received power at the location D [m].

It is possible to find the received power from the power density PD (1) of the receiving location and the effective area AR (2) of the receiving antenna. Since PR = PD*AR, received power is found as shown in (3). Calculation of received power with the Poynting vector and antenna effective area It is possible to find the received power from the Poynting vector PV (1) of the receiving location and the effective area of the receiving antenna AR (2) as shown in (3).

If the field strength of the receiving location and the receiving antenna absolute gain is known, it is possible to find the received power.

Calculation of the electric field intensity and received power in free space. The approximate value of the electric field intensity and received power in free space can be found with using the following calculation tool.< Click to move to the calculation window >Calculation of the electric field intensity and received power over flat terrain.

The approximate value of the electric field intensity and received power over flat terrain can be found with using the following calculation tool.< Click to move to the calculation window >Propagation loss In free space (space in which there is nothing to obstruct the progress of the radio waves), radio waves decay proportionally at the square of the distance, and in inverse proportion to the square of the wave length of the radio waves.

If we call the ratio of effective received power Wr and transmitted power Wt free space propagation loss L, and we call frequency f [Hz], distance d [m], wave length λ [m], and the absolute gain of the transmitting and receiving antennas Gt and Gr shown in decibels, we get If the transmitting and receiving antennas used are isotropic antennas, the free space propagation loss is called free space basic propagation loss LB.

Since the decibel value found is a loss calculation, its code is minus. Example: If we try a frequency of 400 MHz and distance of 500 m, we get LB [d B] = 78.5 d B.

With a frequency of 2,400 MHz and distance of 500 m, we get LB [d B] = 94.0 d B. It is easy to see the difference in decay due to frequency.< Click to move to the calculation window >What happens to received power?

If assumed there is no loss other than free space basic propagation loss, to calculate in decibels the received power at the receiving antenna, we use the following formula. Note however, that the transmitted power is power applied directly to the antenna. When thinking about the output terminals or input terminals of radio equipment, consideration must be given to connection loss from cables, connectors and the like.

PR [d Bm] = PT [d Bm] + (GTA [d Bi] + GRA [d Bi]) – LB [d B]Propagation loss not covered by the calculation This free space propagation loss can be applied with slight correction in the case of transmission from the earth to a communications satellite, or two way, line of sight communication between two high locations. However, in the environments in which radio modules are used, there is an impact from the terrain and buildings and so on, and the weather conditions and the like has an effect.

Also, the conditions of use at a ground level of about 1 m are greatly affected by the environment, and the calculations do not necessarily apply.

Data is available for a location in the suburbs where line of sight is possible that shows actual differences in decay of 20 d B with the free space propagation loss at a frequency of 400 MHz due to the installed height and surroundings, so it is necessary to carry out actual tests. Example: Although there are several formulae for propagation loss over flat terrain, we present the following formula. With this formula, if the communication distance is sufficiently far with regard to the installed height, the following approximation results.

With the following conditions we will obtain the received power [d Bm] at the receiver. Conditions: h T and h R are the height of the transmitting and receiving antennas, and h T = h R = 1.2 m. d is the communication distance and d = 500 m. Transmitted power PT = 10 m W. Transmitting antenna gain is GTA = 0 d Bi.

Receiving antenna gain is GRA = 0 d Bi. Transmitting frequency is 400 MHz. If transmitted power is expressed in decibels, PT = 10 m W so PT = 10 d Bm The received power received by the antenna is very low at –95 d Bm, or 0.316 p W (picowatts)< Click to move to the calculation window >Fading You have no doubt heard the words multipath and fading, but what do they actually mean?

The radio waves emitted by the transmitter arrive at the receiver by a variety of paths, and at that time, the received field strength varies due to the effects of the different routes taken and differences in distance.

This phenomenon is called fading. There are many kinds of fading depending on the causes, but a representative kind is multipath fading. Multipath means that the radio waves reach the receiver by various paths, and the aggregate radio wave received by the antenna may experience interference and may fluctuate widely. If the signals are in phase, the field strength is high, but when they are out of phase, it gets weak.

The wave length of microwaves is particularly short so the impact of multipath is especially acute. Why do communication errors occur? There are a variety of causes of interference to transmissions in the space in which radio communication occurs. Some slight errors may occur with images and sound due to noise and the like, and the data may not reach the receiver correctly, but this is not a problem. In fact, we are not bothered by a slight ghost when we watch television, and with mobile phones it is not much of a problem if the sound is interrupted or distorted.

However, when we consider controlling machinery and the like using radio waves in the industrial sector, if control of the machinery is incapacitated due to data error caused by noise, a major accident could result.

Or if we were transmitting an execution file to a computer, executing the application with that file containing an error of even 1 bit might cause the system to freeze with the loss of important internal data. The causes of these issues are problems such as noise and interference. We will next look at a summary of the possible causes.

Noise from the environment Noise is emitted from the engines of trains and automobiles, from industrial equipment such as power lines and industrial plants, and also from consumer appliances. Furthermore, microwave ovens and fluorescent lighting in the home create noise, and radio wave noise is emitted simply by operating power switches fixed to the wall. Noise from the natural world There are radio disturbances on earth from atmospheric noise and sun flares, and electromagnetic noise caused by natural phenomena such as cosmic noise, movement of the earth's crust and so on.

Interference from other radio equipment This is interference from radio equipment or appliances using the same frequency or a close frequency. With narrowband radio equipment, only one piece of equipment can be used in the same area, at the same frequency, and at the same time.

Noise from the device itself When you come to design your radio equipment, there is a high possibility of errors occurring due to the proximity to noise emanating from around the power supply, the CPU, and from other components.

Causes due to the physical properties of radio waves In the path of the radio waves between the transmitter and the receiver, there may be several kinds of obstacle such as mountains and buildings, walls, people and so on.

If we consider an example involving buildings, there are direct waves that arrive directly, reflected waves that arrive after hitting buildings and the like, diffracted waves that circumvent the shadows of buildings, transmitted waves that arrive by passing through the glass or walls of buildings, and so on. These radio waves arrive after a longer delay than direct waves and reach the receiver with different phases. When these are combined, the received signal level becomes variously stronger or weaker, and this causes errors to occur.

This phenomenon is called multipath fading. Many problems can be anticipated particularly when moving around with the radio equipment during telecontrol. But even with systems involving fixed equipment, the same issue may occur if there are moving obstacles such as cars and people in the vicinity, and if it happens to be located in the valley of the radio wave or 'dead spot', communication will be unreliable.

Is there any impact on the human body or other equipment? With the spread of mobile phones, there is a lot of attention being given to the impact of radio waves on the human body and the effects on other equipment.

Naturally there is also concern from this point of view when designing radio equipment using radio modules.

Direct impact of radio waves on the human body Radio waves are electromagnetic waves, and the types of electromagnetic waves include ultraviolet light and the radio waves that are used in microwave ovens. The chemical action of ultraviolet light is very strong and it is used for the purpose of sterilization in fields related to foods.

Also there are many reports of examples of skin cancer caused by absorbing large quantities of ultraviolet light from the sun. Microwave ovens make the water molecules in food vibrate using the energy of radio waves, to heat the food with this frictional heat. On the same principle, it may be thought that radio waves cause the same heating effect with regard to the human body.

But these cases involve extremely large amounts of energy. However, the power output of mobile phones is quite large (output power: about 1,000 m W), and it is said that using them close to your head is not good for you.

Similarly, there are people who have reported various effects from proximity to high powered radio stations. The radio waves that we are going to use with our modules are quite weak in comparison to the examples above (output power: about less than 10 m W).

However, there are people who are concerned that absorbing even weak radio waves over a long period of time is not good for the body. Unfortunately we cannot provide any clear answers to this problem. While there have been a range of reports on this issue, at the present time there is no definitive study report available.

We believe that prudence is required concerning this issue, and that it is necessary for users to be aware of it when using the products. Effect on medical equipment and Pacemakers Some people may be aware of the fact that the PHS (Personal Handy Phone) used by medical personnel inside hospitals is understood to have no impact on medical equipment.

The power output of PHS is 10 m W, and the power output of SRD (Short Range Device) used in the ISM band is also less than 10 m W, so it is thought not to have any impact, although unfortunately, we do not have any actual proof of this.

Please carry out sufficient practical testing with regard to medical equipment before deciding on the propriety of implementing these products. Inside hospitals, use of ordinary PHS and mobile phones is forbidden. (In Japan)Effect on other equipment When entering an aircraft, you are required to turn off the power of mobile phones and electronic equipment.

This is because it may affect the radio traffic between the electronic equipment of the aircraft and the control tower.

Although the frequencies used for control and the frequencies of mobile phones are different, radio waves are emitted from the mobile phone for the purpose of positioning even when it is not being used, and this has adverse effects on control. Furthermore, the electronic equipment such as computers and digital videos players built into mobile phones emit a wide range of RF noise and the combination of all of these has adverse effects.

This is not only a problem in aircraft; it is the same on the ground too. Electronic equipment must be used so as not to inconvenience others. Effect on equipment in the same waveband Between radio equipment that uses a certain frequency, if communications from another piece of radio equipment on the same waveband interrupt communications, the original two way communication becomes impossible. For this reason, there is a procedure called carrier sensing that senses whether or not the frequency channel to be used is being used by other equipment before starting transmission. In Japan carrier sensing is laid down in the Wireless Telegraphy Act as an essential function that equipment must have, although there is no similar regulation as such in Europe.

est Best Answer: longest wave Radio waves are electromagnetic waves occurring on the radio frequency portion of the electromagnetic spectrum. A common use is to transport information through the atmosphere or outer space without wires.

Which is the longest wave and highest frequency from the electromagnetic waves ?

"Science & Mathematics Physics Which is the longest wave and highest frequency from the electromagnetic waves ?1 following 7 answers Answers Relevance Rating Newest Old

Radio waves are distinguished from other kinds of electromagnetic waves by their wavelength, a relatively long wavelength in the electromagnetic spectrum. Propagation is a term that describes the travel of electromagnetic waves, there being three main modes of propagation. The first is a straight line travel: the manner that radio waves travel through deep space (ignoring the slight deviations caused by gravity under the theory of relativity).

A second way is skip, which is bouncing between the surface of the earth and the ionosphere. Frequencies between 3 MHz and 30 MHz are most reliable for this kind of propagation, called High Frequency (see image at right).

The third way is to hug the surface of the earth as it curves around. Radio waves of very low frequency most often travel this way. Radio signals can also enter two ionospheric layers of differing electron densities and duct between them. The image at the right illustrates this. Two radio signals of differing elevation angles are broadcast into the ionosphere, where they split into ordinary (red) and extraordinary (green) components.

In this example, the ordinary component began ducting between the E and F ionospheric regions. Although this mode of radio wave propagation is less common than the skip mode, it is nonetheless an important mode because it permits radio signals to travel significant distances with little attenuation.

Radio waves were first predicted by mathematical work done in 1865 by James Clerk Maxwell. Maxwell noticed wave-like properties of light and similarities in electrical and magnetic observations and proposed equations that described light waves and radio waves as waves of electromagnetism that travel in space. In 1887 Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory. Many inventions followed, making practical use of radio waves to transfer information through space.

Nikola Tesla and Guglielmo Marconi are credited with inventing systems to allow radio waves to be used for communication. highest frequency Gamma rays (denoted as γ) are a form of electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions, such as electron-positron annihilation or radioactive dec

ay. Gamma rays are generally characterized as electromagnetic radiation having the highest frequency and energy, and also the shortest wavelength (below about 10 picometer), within the electromagnetic spectrum. Gamma rays consist of high energy photons with energies above about 100 ke V.

d. The speed of light is constant in space. All forms of light have the same speed of 299,800 kilometers/second in space (often abbreviated as c ). From highest energy to lowest energy the forms of light are Gamma rays, X-rays, Ultraviolet, Visible, Infrared, Radio. (Microwaves are high-energy radio waves.

Properties of Light

Properties of Light Chapter index in this window — — Chapter index in separate window -- Please support this website This material (including images) is copyrighted! . See my copyright notice for fair use practices. Select the photographs to display the original source in another window.

Electric and magnetic fields oscillate together but perpendicular to each other and the electromagnetic wave moves in a direction perpendicular to both of the fields. Light, electricity, and magnetism are manifestations of the same thing called electromagnetic radiation.

The energy you see coming out of the computer screen you are using to read this page is made of fluctuating electric and magnetic energy fields. The electric and magnetic fields oscillate at right angles to each other and the combined wave moves in a direction perpendicular to both of the electric and magnetic field oscillations.

This energy also comes in many forms that are not detectable with our eyes such as infrared (IR), radio, X-rays, ultraviolet (UV), and gamma rays.

We feel infrared light as heat and our radios pick up the messages encoded in radio waves emitted by radio stations. Ultraviolet light has high enough energy to damage our skin cells, so our bodies will produce a darker pigment in our skin to prevent exposure of the deeper skin cells to the UV (we tan as a defense mechanism).

The special bulbs called ``black lights'' produce a lot of UV and were used by hospitals to kill bacteria, amoebas, and other micro-organisms. X-rays are produced by very hot things in space. X-rays have more energy than UV, so they can pass through skin, muscles, and organs.

They are blocked by bones, so when the doctor takes your X-ray, the picture that results is the shadow image of the X-rays that passed through your body.

Because X-rays have such high energy, they can damage or kill cells. A few brief exposures to low-intensity X-rays is okay. The X-ray technician would be exposed to thousands of X-ray exposures if s/he did not use some sort of shielding. Gamma rays are the most energetic form of electromagnetic radiation and are produced in nuclear reactions.

The form of electromagnetic radiation your eyes can detect is called ``visible'' or ``optical''. Astronomers have only recently (within the past few decades) been able to use the other forms of electromagnetic radiation or light. Every time technology has been developed to detect another form of light, a revolution in our understanding of the universe has occurred.

The figure above shows all of the forms of electromagnetic radiation in order of INcreasing wavelength (given in nanometers (nm)) and DEcreasing energy. Notice how tiny the visible band is!There are some general properties shared by all forms of electromagnetic radiation: It can travel through empty space. Other types of waves need some sort of medium to move through: water waves need liquid water and sound waves need some gas, liquid, or solid material to be hear

)A wavelength of light is defined similarly to that of water waves---distance between crests or between troughs. Visible light (what your eye detects) has wavelengths 4000-8000 Ångstroms. 1 Ångstrom = 10 -10 meter. Visible light is sometimes also measured in nanometers (``nm'' in the figure above): 1 nanometer = 10 -9 meter = 10 Ångstroms, so in nanometers, the visible band is from 400 to 800 nanometers.

Radio wavelengths are often measured in centimeters: 1 centimeter = 10 -2 meter = 0.01 meter. The abbreviation used for wavelength is the greek letter lambda: . White light is made of different colors (wavelengths). When white light is passed through a prism or diffraction grating, it is spread out into all of its different colors.

You see this happen every time you see a rainbow. Not all wavelengths of light from space make it to the surface.

Only long-wave UV, Visible, parts of the IR and radio bands make it to surface. More IR reaches elevations above 9,000 feet (2765 meters) elevation. That is one reason why modern observatories are built on top of very high mountains. Fortunately, as far as life is concerned, our atmosphere shields us from the gamma rays, X-rays, and most of the UV.

It also blocks most of the IR and parts of the radio. Astronomers were not able to detect these forms of energy from celestial objects until the space age, when they could put satellite observatories in orbit. Besides using wavelength to describe the form of light, you can also use the frequency --the number of crests of the wave that pass by a point every second.

Frequency is measured in units of hertz (Hz): 1 hertz = 1 wave crest/second. For light there is a simple relation between the speed of light ( c ), wavelength ( ), and frequency ( f ):f = c/ .

Since the wavelength is in the bottom of the fraction, the frequency is inversely proportional to the wavelength. This means that light with a smaller wavelength has a higher (larger) frequency. Light with a longer wavelength has a lower (smaller) frequency. The animation shows waves with different wavelengths moving to the right with the same speed. The bottom wave has a wavelength = 3× (wavelength of the top wave).

The counter shows how many wavelengths of the top wave have passed the dashed line. In one second, the top wave moves three wavelengths to the right so its frequency is 3 Hz.

The bottom wave moves one of its wavelengths in one second so its frequency is 1 Hz (= 1/3×top wave frequency). Some colors and their approximate wavelength, frequency and energy ranges are given in the table below.

The unit of energy is the Joule (J). A Joule is how much energy you expend when you lift an object with 1 kilogram of mass (for example, a liter of water) about 10 centimeters above the ground.

If you then let it go, the object hits the ground with that much energy. Sometimes light energy is also measured in ``ergs'', where 1 erg = 10 -7 Joule.color (Å) f (*10 14 Hz) Energy (*10 -19 J)violet 4000 4600 7.5 6.5 5.0 4.3indigo 4600 4750 6.5 6.3 4.3 4.2blue 4750 4900 6.3 6.1 4.2 4.1green 4900 5650 6.1 5.3 4.1 3.5yellow 5650 5750 5.3 5.2 3.5 3.45orange 5750 6000 5.2 5.0 3.45 3.3red 6000 8000 5.0 3.7 3.3 2.5Note the trends: bluer light has shorter, higher f, and more energy.

Redder light has longer, lower f, and less energy. At the beginning of the 20th century Max Planck (lived 1858--1947) suggested that atoms can absorb and emit energy in only discrete chunks (called quanta). This quantum behavior of atoms could explain the drop-off of a continuous spectrum's shape at the short wavelength end.

A few years after Planck's discovery Albert Einstein (lived 1879--1955) discovered that the quantum of energy was not due to the atoms but, rather, a property of the energy itself.

You can consider light as packets of energy called photons. A photon is a particle of electromagnetic radiation. Bizarre though it may be, light is both a particle and a wave. Whether light behaves like a wave or like a particle depends on how the light is observed (it depends on the experimental setup)!

Einstein found a very simple relationship between the energy of a light wave (photon) and its frequency: Energy of light = h × f Energy of light = (h × c)/,where h is a universal constant of nature called ``Planck's constant'' = 6.63 × 10 -34 J·sec.

Light can also behave as a particle and a wave at the same time. An example of light acting as both a particle and a wave is the digital camera---the lens refracts (bends and focusses) waves of light that hit a charge-coupled device (CCD).

The photons kick electrons out of the silicon in the CCD. The electrons are detected by electronics that interpret the number of electrons released and their position of release from the silicon to create an image. Another example is when you observe the build-up of the alternating light and dark pattern from diffraction (a wave phenomenon) from light passing through a narrow slit. You see one bright spot (a photon), then another bright spot (another photon), then another... until the diffraction pattern is created from all of the accumulated photons.

This happens so quickly that it is undetectable to the human eye. To decode the information stored in light, you pass the light through a prism or diffraction grating to create a spectrum ---any display of the intensity of light (EM radiation) at different wavelengths or frequencies (a picture or a graph of intensity vs. either wavelength or frequency).

If white light is examined, then the spectrum will be a rainbow. The term intensity has a particular meaning here: it is the number of waves or photons of light reaching your detector; a brighter object is more intense but not necessarily more energetic.

Remember that a photon's energy depends on the wavelength (or frequency) only, not the intensity. The photons in a dim beam of X-ray light are much more energetic than the photons in an intense beam of infrared light. The type of light produced by an object will depend on its temperature, so let's digress slightly to investigate what ``temperature'' is.

Temperature is a measure of the random motion (or energy) of a group of particles. Higher temperature (T) means more random motion (or energy). A natural scale would have zero motion at zero degrees (absolute zero). This scale is the Kelvin scale.

It scales exactly like the Celsius system, but it is offset by 273 degrees. Here is a comparison of the Kelvin, Celsius, and Fahrenheit temperature scales: K C F0 -273 -459 absolute zero100 -173 -279.4273 0 32 water freezes310 37 98.6 human temperature373 100 212 water boils (STP)755 482 900 oven on ``clean'' setting5840 5567 10053 Sun's temperature Vocabularyelectromagnetic radiation frequency hertzintensity Kelvin photonspectroscopy spectrum temperaturewavelength Formulae Frequency and wavelength relation: f = c/ .

Energy of a photon: E = h×f, where h is a constant of nature. Energy of a photon: E = (h×c)/ . Review Questions Why is light so very important to astronomy? What kinds of information can you get from it? Why is light called electromagnetic radiation? Is radio a form of light?

Put the following forms of light in order of increasing frequency (lowest frequency first): ultraviolet, infrared, gamma rays, visible, radio, X-rays. Put them in order of increasing wavelength (shortest wavelength first). Put them in order of increasing energy (lowest energy first). Do all forms of light travel at the same speed in a vacuum (empty space)? Why is it important that light can travel through empty space?

What forms of light can be observed from the ground (including high mountains)? What forms can be observed at high altitudes in our atmosphere? What forms must be observed in space? Is electromagnetic radiation a wave or a particle? What determines if you will see light as a wave or a photon ? Which of these are a spectrum: plot of intensity vs. wavelength, plot of intensity vs. brightness, plot of frequency vs. wavelength, rainbow, plot of acceleration vs. time, plot of energy vs. frequency. What is the difference between intensity and energy? If a particular CCD chip requires light energies of 4.2 × 10 -19 J to release electrons from the silicon, which will produce more electrons (and hence, a brighter computer image): an intense beam of yellow light or a dim beam of UV light? Explain your answer!Why is the Kelvin scale preferred over the Celsius or the Fahrenheit scales? Where is absolute zero on the three temperature scales? Where is the Sun's temperature on the three temperature scales? Go back to previous section -- Go to next section Go to Astronomy Notes home -- Please support this websitelast updated: January 8, 2013Is this page a copy of Strobel's Astronomy Notes? Author of original content: Nick Strobel

Below 30 MHz, the ionosphere, at altitudes from around 100 to 500 km, absorbs and reflects signals. Above 30 GHz, the lower atmosphere or troposphere, below 10 km, absorbs radio signals due to oxygen and water vapour.

RADIO FREQUENCIES FOR SPACE COMMUNICATIONINTRODUCTIONTo be useful satellites and spacecraft must communicate, sometimes to relay communications between two points, sometimes to transmit data they have collected. Although there have been some experiments in optical communications using lasers, most satellite communication is accomplished by radio, one part of the electromagnetic spectrum. Radio frequencies must be shared with terrestrial radio services, and international frequency assignment is essential to avoid interference between all the different uses made of the radio spectrum.

The International Telecommunications Union (ITU) is the global body that assigns radio frequency allocations. In doing this they divide the world into three regions, regions I, II and III. Australian lies in region III. The general frequency assignments may be found at the ITU web site, and Australian allocations may be seen at the ACMA web site. The ITU unfortunately, charges horrendous prices for any of its publications. However, the Australian Communications and Media Authority (ACMA) makes all spectral allocation information available for free download.

This includes a book, an attractive wall poster and a simplified spectrum graphic. This note discusses the frequencies that are used for space communications.

THE ELECTROMAGNETIC SPECTRUMThere are four, and only four known forces in the universe (although the so-called dark energy hints at another). These are, in order of strength, the nuclear strong force, the electromagnetic force, the nuclear weak force and the gravitational force. The two nuclear forces exert their influence over only very very short (nuclear) distances, and apart from holding all matter together do not directly influence us in everyday life.

It is gravity and particularly electromagnetism that are of direct concern to us in our daily interactions. Gravity springs from the property of matter we call mass, while electromagnetic effects derive from the property we call charge.

When a charge is stationary, it has around it an electrostatic field. If it moves with a constant velocity it produces a magnetic field, and when it accelerates or declerates it generates electromagnetic radiation. Electromagnetic radiation is a coupled oscillation of electric and magnetic fields that propagates through space with a velocity of about 3 x 10 8 metres per second.

The properties of this electromagnetic radiation vary markedly depending on the frequency of the oscillation. This gives rise to what we know as the electromagnetic spectrum. The chart below shows the major divisions of the electromagnetic spectrum.

An electromagnetic wave may be characterised by its frequency f (the number of times per second the signal undergoes a complete oscillation at a specified point in space) or its wavelength λ (the distance between successive extremal values of the wave at a specified time). Note:1 For clarity the bands are not shown with uniform frequency or wavelength spacing 2 The visible spectrum occupies only a very small part of the total EM spectrum 3 Bands also have subdivisions (this is particularly true of the radio spectrum) 4 The band divisions are not as sharp as shown, but rather fuzzy, merging into one another 5 In the frequency scale T=10 12, P=10 15, E=10 18 6 In the wavelength scale μ=10 -6, n=10 -9, p=10 -12THE RADIO SPECTRUMThe radio spectrum is a subset of the electromagnetic spectrum.

It extends from frequencies below 1 Hz up to around 3000 GHz or 3 THz, where it gives way to the infrared spectrum. Different frequencies have different uses because of different propagation, generation and general properties. The radio spectrum is divided into many different bands. This table shows the usually accepted division of the radio spectrum.

The left hand column lists the frequency (f), the centre column the band designator and the right column the wavelength (λ).

The relationship between frequency and wavelength is given by the expression:f = c / λwhere c = 3 x 10 8 metres per second is the speed of light (and other EM radiation) in free space. In the above relation, frequency is given in Hertz (Hz) when wavelength is specified in metres (m). Note that the designated band qualifiers are not in the same order going toward lower frequencies as they are going toward higher frequencies.

Also note that the division between ELF and ULF is not universally agreed. It can be placed anywhere from 1 Hz to 100 Hz. The one shown (1 Hz) is that employed by geophysicists. There is no lower limit to the ULF band and magnetic signals with periods of years can be identified.

Microwave is a term that was historically applied to signals with wavelengths less than one foot (30 cm), and this region has been subdivided into letter bands. However, there are several schemes of designation for microwave bands. Two of these, which we shall call traditional and new, are given below.

Despite the efforts of many engineers to have the 'new' division adopted, the 'traditional' scheme seems to be firmly entrenched among space communicators.

WINDOWS TO SPACENot all of the electromagnetic spectrum can pass through the Earth's atmosphere. Obviously, visible light can - we can see the stars at night, at least when there is no cloud. However, ultraviolet and higher frequencies are mostly absorbed by different components of the atmosphere. There are in fact only two main windows of the EM spectrum that are open to space. One is the visible spectrum, as mentioned above, and the other is the radio spectrum. However, not all of the radio spectrum is useable for space communication. The available window spans from about 30 MHz to 30 GHz, although these are not absolute end frequencies.

Even between 20 and 30 GHz, there are some absorption bands that must be avoided. HISTORICAL SPACE FREQUENCIESThe first satellite to orbit the Earth was Sputnik 1, launched by the Soviets in October 1957. It carried two radio beacons on frequencies of 20.005 and 40.01 MHz. The Soviets continued to use frequencies around 20 MHz and even some around 15 MHz for many subsequent missions.

The first satellite launched by the USA (Explorer 1) carried beacons on 108.00 and 108.03 MHz. This lay just above the terrestrial FM broadcast band (from 88 to 108 MHz) and just inside the civil aviation band which extends from 108 to 136 MHz.

This frequency had been specified by an international committee for the International Geophysical Year (IGY - 1957/8) as the one to be used for all scientific satellites launched in pursuit of IGY objectives. The Soviets had chosen to ignore this recommendation and use the much lower frequencies previously mentioned.

SPACE COMMUNICATION BANDSThe following is a list of some of the more heavily used frequency bands for space communication. Specific frequencies may be found in the links provided at the end of this note. VHF Band136 - 138 MHz This band was used heavily by many different types of satellites in the past.

Today (2012), most activity is restricted to 137-138 MHz (which is the current allocation) and consists of meteorological satellites transmitting data and low resolution images, together with low data rate mobile satellite downlinks (eg Orbcomm)144 - 146 MHz One of the most popular bands for amateur satellite activity.

Most of the links are found in the upper half of the band (145 - 146 MHz).148 - 150 MHz This tends to be used for uplinks of the satellites that downlink in the 137 - 138 MHz band.149.95 - 150.05 MHz This is used by satellites providing positioning, time and frequency services, by ionospheric research and other satellites.

Before the advent of GPS it was home to large constellations of US and Russian satellites that provided positioning information (mainly to marine vessels) by use of the Doppler effect).

Many satellites transmitting on this band also transmit a signal on 400 MHz.240 - 270 MHz Military satellites, communications. This band lies in the wider frequency allocation (225 - 380 MHz) assigned for military aviation. UHF Band399.9 - 403 MHz This band includes navigation, positioning, time and frequency standard, mobile communication, and meteorological satellites.

Around 400 MHz is a companion band for satellites transmitting on 150 MHz.432 - 438 MHz This range includes a popular amateur satellite band as well as a few Earth resources satellites.460 - 470 MHz Meteorological and environmental satellites, includes uplink frequencies for remote environmental data sensors. L Band1.2 - 1.8 GHz This frequency range includes a very diverse range of satellites and encompasses many sub-allocations. This range includes the GPS and other GNSS (Global Navigation Satellite Systems - Russian Glonass, European Galileo, Chinese Beidou).

It also hosts SARSAT/COSPAS search and rescue satellites which are carried on board US and Russian meteorological satellites. It also includes a mobile satellite communication band.1.67 - 1.71 GHz This is one of the primary bands for high resolution meteorological satellite downlinks of data and imagery.

S Band2.025 - 2.3 GHz Space operations and research, including 'deep space' links from beyond Earth orbit. This encompasses the Unified S-band (USB) plan which is used by many spacecraft, and which was also used by the Apollo lunar missions. It also includes military space links including the US Defense Meteorological Satellite Program (DMSP). Many Earth resources (remote sensing) satellites downlink in this band.2.5 - 2.67 GHz Fixed (point-to-point) communication and broadcast satellites, although the broadcast allocation is only used in some Asian and Middle-eastern countries.

C Band3.4 - 4.2 GHz Fixed satellite service (FSS) and broadcast satellite service (BSS) downlinks. International TV broadcast uses this allocation heavily.5.9 - 6.4 GHz This is the FSS/BSS uplink for the 3.4-4.2 GHz downlink band.

X band8 - 9 GHz This is used heavily for space research, deep space operations, environmental and military communication satellites. Many satellites/spacecraft carry complementary S and X band transmitters. Ku band10.7 - 11.7 GHz Fixed satellite services (FSS)11.7 - 12.2 GHz Broadcast satellite service (BSS) downlinks.

This band is used for domestic TV programs.14.5 - 14.8 GHz The uplink for the previous Ku downlink band.17.3 - 18.1 GHz An alternate 'Ku' band BSS uplink. 'Ka' band23 - 27 GHz A region that will be used increasingly by a variety of fixed link, broadcast, environmental and space operations satellites in the future as more bandwidth is required than can be provided in the lower bands.

The disadvantage of this band is the increased absorption due to water vapour and rain. Not very useful for tropical regions of the Earth.

SPECIFIC SPACE COMMUNICATION FREQUENCIESRussia Russian manned spacecraft use 143.625 and 121.5 MHz FM for voice communications. Other frequencies used on manned missions include 166 and 923 MHz. The Russian ISS (International Space Station) module uses the band from 628 - 632 MHz. China China uses 180 MHz for weather satellite downlinks, and possibly for manned missions. Meteorological satellites also use 480 MHz for downlink. North Korea North Korea has now (May 2012) made three unsuccessful attempts to launch an orbiting satellite.

They have stated that communications will be on 27 MHz (morse code slogan), 470 MHz (propaganda song) and 8 GHz (imagery). Amateur Satellites Many satellites have been launched which use the amateur radio bands for downlinking data, telemetry and imagery, and for providing relay communications and store and forward communications.

Most of the amateur radio frequency bands have a satellite allocation sub-band. The most popular bands for these satellites are the 144-146 and 435-438 MHz bands. The Russians have often used the HF bands at 21 and 29 MHz for amateur communications. A very popular frequency for many amateur satellites is 145.825 MHz.

ARISS (Amateur Radio on the International Space Station) typically uses frequencies in the 144 - 146 band. NASA Deep Space Network Three NASA ground stations in the Deep Space Network, Goldstone (California), Tidbinbilla (Canberra) and Madrid (Spain) provide data and tracking services for all NASA spacecraft outside of Earth orbit. These use S, X and Ka bands. Band Uplink Frequency (MHz) Downlink Frequency (MHz)S 2110 - 2120 2290 - 2300X 7145 - 7190 8400 -8450Ka 34200 - 34700 31800 - 32300The earliest DSN spacecraft used S-band (1960s), then in the 1990s moved to X-band, and Ka-band started to be used in the 21st century. Many spacecraft have dual frequency capability (S/X and lately X/Ka). The use of higher frequencies allows larger bandwidths, better tracking capability and minimises ionospheric effects. It also requires greater pointing accuracy. LINKSThe links here provide detailed information about specific frequencies of various types of satellites. COMMERCIAL SATELLITE COMMUNICATIONS (BROADCAST)Lyngsat METEOROLOGICAL SATELLITESMetsat AMATEUR SATELLITESAmsat MONITORED SATELLITESZarya Australian Space Academy

Radio waves, visible light waves, gamma rays, x-rays, infrared light, and ultraviolet light are all types of electromagmetic radiation. They all travel at the same speed, being the speed of light. All these waves travel fastest in a vacuum and travel only slightly slower in the atmosphere.

Do radio waves travel at the speed of light?

"Science & Mathematics Other - Science Do radio waves travel at the speed of light?1 following 20 answers Answers Relevance Rating Newest Oldest Best Answer: They CAN travel at the speed of light. Radio waves are an example of electromagnetic waves (other examples include light, microwaves and x-rays) can all travel at the speed of light.

However, their actual speed (called the propagation velocity) depends on two variables. One is called permeability and the other is called permittivity. Each variable's value depends on the material that the waves are traveling through. Basically, you can think of the variables as how ""easy"" it is for electic fields and magnetic fields to travel through the medium.

If the waves are traveling in free space, they will always travel at the speed of light. Otherwise, the waves will travel slower.

Source (s):3 years of electrical engineering courses in collegesteve23063 · 1 decade ago4 0 Comment Asker's rating Radio Wave Speed Source (s):https://shrinks.im/a8PEPErika · 1 year ago0 0 Comment Speed Of Radio Waves Source (s):https://shrink.im/a8Eancris · 2 years ago0 0 Comment Radio waves, like all forms of electromagnetic waves, travel at the speed of light.

Unlike the speed of sound that changes depending on the substance through which the sound wave travels, the speed of light is a constant Source (s):http://www.aerospaceweb.org/question/ast... Derek · 1 decade ago2 0 Comment Radio waves are electromagnetic waves with frequencies ranging from 3Hz to 3GHz (3,000,000,000Hz).

Their speed of propagation in vacuum is equal to the speed of light ""c"" and this speed is the same for all electromagnetic waves including microwaves, infrared, ultravioler and visible light. However the propagation velocity changes according to the material that the radio wave is travelling through. Thus every material has a velocity factor eg. a standard coaxial radio transmission line used to connect a radio transmitter with the antenna is around 0.66.

Thus the radio wave would travel inside this cable 44% slower than the speed of light. Source (s): I am an electronics engineer now employeed in the mobile communications sector.

Sporadic · 1 decade ago2 0 Comment This Site Might Help You. RE: Do radio waves travel at the speed of light? Source (s):radio waves travel speed light: https://tr.im/JObfr Anonymous · 3 years ago0 0 Comment Both radio waves and light are electromagnetic waves.

So they travel in the same speed. The product of the frequency and wavelength of electromagnetic waves is a constant. Though both light and radio waves have different wavelength and frequencies,their product is always the same,which is equal to the sped of light.

So not just radio waves,all the electromagnetic waves travel in the speed of light. Anonymous · 1 decade ago1 0 Comment Radio waves constitute a narrow band within the Electromagnetic Spectrum ES that includes light, radio, TV, cell phones, xrays, microwave and many others. The entire ES travels at the ""speed of light"" 186,000 miles per second. As the attached article explains, the difference is in the wavelength, frequency and energy. Source (s):http://imagine.gsfc.nasa.gov/docs/scienc... Jim · 1 decade ago1 0 Comment Radio waves and light are parts of the electromagnetic spectrum. They travel at the same speed. RG · 1 decade ago0 0 Comment

The variation in speed in differing media is what causes refraction. Pretzels · 1 decade ago0 0 Comment1 2 3 next Maybe you would like to learn more about one of these? Try for your MBA online? Get a Master's Degreee Online Interested in dating sites? Can cloud services help you? "

Answer Electromagnetic energy is a form of energy that can be reflected or emitted from objects through electrical or magnetic waves traveling through space. Electromagnetic energy comes in many examples including gamma rays, X-rays, ultraviolet radiation, visible light, microwaves, radio waves and infrared radiation.

What Is Electromagnetic Energy?

Science Physics Electricity Q: What Is Electromagnetic Energy? A: Quick

Continue Reading Keep Learning What Is Electromagnetic Radiation? What Is Transferred by Electromagnetic Waves? What Does a Sound Source of High Energy Emit? Credit: Chip Somodevilla Getty Images News Getty Images Full Answer The electromagnetic spectrum is the range of all types of electromagnetic radiation (electromagnetic radiation being a type of electromagnetic energy).

Electromagnetic radiation is a kind of energy that travels and spreads outward as it goes, such as the lamp sending visible light in a person's home or the radio waves coming from the radio station. People encounter electromagnetic spectrum energy all the time. Radio electromagnetic energy can be seen not only in the radio waves captured and emitted by radio stations, but also in the radio waves emitted by gases in space and stars in space.

The microwave radiation cooks popcorn and is also used by astronomers to discover the structures of nearby galaxies. Infrared energy can be seen through night vision goggles and in space it helps astronomers map the dust found between the stars. Visible light is an energy that humans can detect on their own with their naked eye. Light bulbs, stars and fireflies all emit visible light.

Ultraviolet radiation is emitted by the sun and is what gives humans skin burns or tans. Learn more about Electricity Sources: reference.com nasa.gov Related Questions Q: What Are Different Types of Electromagnetic Radiation? A: The spectrum of electromagnetic radiation is comprised of waves or particles that carry different amounts of energy. The visible spectrum is what humans an... Full Answer >Filed Under: Magnetism Q: How Is Electrical Energy Generated?

A: Electrical energy in the form of electricity is primarily manufactured by using massive generators equipped with turbines. It can also be generated by tran... Full Answer >Filed Under: Electricity Q: What Is Wind Energy? A: Wind energy is a form of renewable energy produced through machines that use wind as their power source. Wind energy is only possible because of the sun. Full Answer >Filed Under: Electricity Q: What Is Geothermal Power?

A: Geothermal power is a form of renewable energy generated from heat that naturally occurs within the Earth. Radioactive materials, such as uranium and potas... Full Answer >Filed Under: Electricity You May Also Like Q: What Are Some Non-Conductive Metals? Q: Why Is Copper a Good Conductor of Electricity? Q: Does Wood Conduct Electricity? Q: What Is Three-Phase Power? Q: How Does an Electric Motor Work? Q: What Is a PAR Light Bulb?

ce For three of the four, you have named the medium ... rope, slinky, and tuning fork. In each case, there would be no wave without it. The radio wave, as well as all other electromagnetic waves, can travel through material media, but don't need one in order to propagate.

Which type of wave does not require a medium to travel through? A. rope wave B. radio wave C. slinky wave D. tuning fork wave

High School Physics 5 points Which type of wave does not require a medium to travel through? A. rope wave B. radio wave C. slinky wave D. tuning fork wave Ask for details Follow Reportby Tabitha Bencosme964 09/30/2014Verified answer What is a Verified Answer? Log in to view the full answer. Unlock Verified Answers and get help from subject experts. Unlock verified answer Answersbookwormrds Ambitious The answer is radio wave, waves on the electromagnetic spectrum don't need a medium Comments Report4.7 23 votes Thanks 43AL2006 A

Comments Report4.8 21 votes Thanks 33

Now, like you've said, there are indeed light waves and radio waves in space, but these waves are not sound, but light. Light does not need air to travel, but then you don't hear it; you see it, or it is interpreted by your radio set and then translated into sound.

Can you hear sounds in space?  (Beginner)

"Can you hear sounds in space? (Beginner)A few friends and I are currently in debate about space. They say that there is no sound in space and that it is because there is no air in space. For instance if someone were talking to you, you couldn't hear what they were saying. I found it hard to believe either of those claims.

I argued that there has to be air out there and that even if there was no air, there would still be sound because things like radio waves and light waves travel through space.

Could you please clear us up on this argument. Answer by Dave: I'm afraid that your friends are right. In empty space, there is no air, and what we call ""sound"" is actually vibrations in the air.

Astronauts in space do talk to each other. In the spacecraft, there is plenty of air, so they just talk normally. When they are spacewalking, they talk by means of radios in their helmets. The radio waves, again, have no problem in space, but they're not sound. They're radio, which has to be converted into sound by the astronauts' headsets. But can't there be vibrations in matter that isn't air?

And if there are gases in space, then why can't sounds move through them? Answer by Lynn: You're right that there are gases in space, and it's true that these gasses can propagate sound waves just like Earth's air allows sound to travel.

The difference is that interstellar gas clouds are much less dense than the Earth's atmosphere. (They have fewer atoms per cubic foot.) So if a sound wave was traveling through a big gas cloud in space and we were out there listening, only a few atoms per second would impact our eardrum, and we wouldn't be able to hear the sound because our ears aren't sensitive enough.

Maybe if we had an amazingly large and sensitive microphone we could detect these sounds, but to our human ear it would be silent.

There can also be vibrations in matter that's not gaseous: for example, the solid Earth or even the Sun (see the related link below). But although sound can travel through Earth, it can't travel from Earth to Mars because there's essentially no matter (gases, liquids, solids) in between the two planets for it to travel through. So it's not strictly true that no sound vibrations can travel through space at all, but it is true that humans would not be able to hear any sounds in space.

But in movies when they show a large space ship exploding and another spaceship nearby they often play a large exploding sound.

I'm wondering in large explosions (maybe not as small as a spaceship exploding, but say in a supernova) could a person hear the sound because possibly the explosion releases gases in which the acoustic energy is transported through the vacuum between the explosion and some observer in a spaceship (or possibly on earth) if the supernova or spaceship explosion was relatively nearby? Answer by Lynn: I know in movies a lot of times they play sounds when things explode, but I don't know of any cases where this would actually be realistic.

Because space is a vacuum, gases released into space expand very quickly, and as they expand their density decreases. So say you were in a spaceship in the middle of a big space battle and a nearby ship exploded. The exploding ship would release gases and technically sound could travel along with them. However, since space is a vacuum, these gases will spread out very rapidly and the density will drop off very fast with distance from the explosion.

(If you think about it, the amount of air in the ship is probably not very large compared to the volume of space between two ships.) So by the time the explosion reached your ship nearby, any sounds carried by the gas would still be too faint to hear.

It seems more likely to me that what you would hear would be the shrapnel from the explosion banging into the hull of your ship.

As you point out, it depends on distance. If the your ship was directly next to the exploding ship, you would be more likely to hear something, but it would also be bad news for your ship and crew!It's pretty much the same for a supernova.

The gases from a supernova explosion expand rapidly, and the density will drop off fast. I'm not sure how close you would have to be to hear a supernova, because I'm not sure where you would have to be to get densities close to Earth atmospheric values, and you might need a computer simulation to tell exactly. But to get some idea of how the density of gas would drop off as you expand the material of a star, I did a really simple calculation.

If you took a star 50 times the mass of the sun and distributed its mass over a sphere of space with a radius equal to the planet Mercury's orbital distance, the density would already be 10 times less than atmospheric density at sea level on Earth. Mercury is pretty close to the sun, and you wouldn't be able to hear sounds even at that distance!

In reality, not all the star's mass is ejected into space, and the gas that is expelled has shock waves, which are compressed. But the basic idea is that you would have to be extremely close to get densities high enough to hear anything.

So we won't ever hear a supernova explosion on Earth, for example. It's a little sad, but space really is silent. Page last updated on June 22, 2015. Space Exploration Sound Supernovae Explosion Waves Interstellar Medium Vacuum Dave Kornreich Dave was the founder of Ask an Astronomer.

He got his Ph D from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question. "

Now, like you've said, there are indeed light waves and radio waves in space, but these waves are not sound, but light. Light does not need air to travel, but then you don't hear it; you see it, or it is interpreted by your radio set and then translated into sound. Astronauts in space do talk to each other. In the spacecraft, there is plenty of air, so they just talk normally.

"Can you hear sounds in space? (Beginner)Friday, 16 April 1999 18:50Answered by Dave Kornreich Views: 504504A few friends and I are currently in debate about space. They say that there is no sound in space and that it is because there is no air in space. For instance if someone were talking to you, you couldn't hear what they were saying.

I found it hard to believe either of those claims. I argued that there has to be air out there and that even if there was no air, there would still be sound because things like radio waves and light waves travel through space.

Could you please clear us up on this argument. Answer by Dave: I'm afraid that your friends are right. In empty space, there is no air, and what we call ""sound"" is actually vibrations in the air.

When they are spacewalking, they talk by means of radios in their helmets. The radio waves, again, have no problem in space, but they're not sound. They're radio, which has to be converted into sound by the astronauts' headsets. But can't there be vibrations in matter that isn't air? And if there are gases in space, then why can't sounds move through them? Answer by Lynn: You're right that there are gases in space, and it's true that these gasses can propagate sound waves just like Earth's air allows sound to travel.

The difference is that interstellar gas clouds are much less dense than the Earth's atmosphere. (They have fewer atoms per cubic foot.) So if a sound wave was traveling through a big gas cloud in space and we were out there listening, only a few atoms per second would impact our eardrum, and we wouldn't be able to hear the sound because our ears aren't sensitive enough.

Maybe if we had an amazingly large and sensitive microphone we could detect these sounds, but to our human ear it would be silent.

There can also be vibrations in matter that's not gaseous: for example, the solid Earth or even the Sun (see the related link below). But although sound can travel through Earth, it can't travel from Earth to Mars because there's essentially no matter (gases, liquids, solids) in between the two planets for it to travel through.

So it's not strictly true that no sound vibrations can travel through space at all, but it is true that humans would not be able to hear any sounds in space.

But in movies when they show a large space ship exploding and another spaceship nearby they often play a large exploding sound.

I'm wondering in large explosions (maybe not as small as a spaceship exploding, but say in a supernova) could a person hear the sound because possibly the explosion releases gases in which the acoustic energy is transported through the vacuum between the explosion and some observer in a spaceship (or possibly on earth) if the supernova or spaceship explosion was relatively nearby? Answer by Lynn: I know in movies a lot of times they play sounds when things explode, but I don't know of any cases where this would actually be realistic.

Because space is a vacuum, gases released into space expand very quickly, and as they expand their density decreases. So say you were in a spaceship in the middle of a big space battle and a nearby ship exploded. The exploding ship would release gases and technically sound could travel along with them. However, since space is a vacuum, these gases will spread out very rapidly and the density will drop off very fast with distance from the explosion.

(If you think about it, the amount of air in the ship is probably not very large compared to the volume of space between two ships.) So by the time the explosion reached your ship nearby, any sounds carried by the gas would still be too faint to hear. It seems more likely to me that what you would hear would be the shrapnel from the explosion banging into the hull of your ship.

As you point out, it depends on distance. If the your ship was directly next to the exploding ship, you would be more likely to hear something, but it would also be bad news for your ship and crew!It's pretty much the same for a supernova.

The gases from a supernova explosion expand rapidly, and the density will drop off fast. I'm not sure how close you would have to be to hear a supernova, because I'm not sure where you would have to be to get densities close to Earth atmospheric values, and you might need a computer simulation to tell exactly.

But to get some idea of how the density of gas would drop off as you expand the material of a star, I did a really simple calculation.

If you took a star 50 times the mass of the sun and distributed its mass over a sphere of space with a radius equal to the planet Mercury's orbital distance, the density would already be 10 times less than atmospheric density at sea level on Earth. Mercury is pretty close to the sun, and you wouldn't be able to hear sounds even at that distance!

In reality, not all the star's mass is ejected into space, and the gas that is expelled has shock waves, which are compressed. But the basic idea is that you would have to be extremely close to get densities high enough to hear anything.

So we won't ever hear a supernova explosion on Earth, for example. It's a little sad, but space really is silent. Page last updated on June 22, 2015. Space Exploration Sound Supernovae Explosion Waves Interstellar Medium Vacuum Dave Kornreich Dave was the founder of Ask an Astronomer.

He got his Ph D from Cornell in 2001 and is now an assistant professor in the Department of Physics and Physical Science at Humboldt State University in California. There he runs his own version of Ask the Astronomer. He also helps us out with the odd cosmology question. "

Radars do not use sound as a signal, but the Electromagnetic waves (EM) called the Radio waves and microwaves. Radio waves and Micro waves are two different types of electromagnetic waves. EM waves, like all waves, transport energy and can do so through vacuum.

What are the different uses of Radar?

"What are the different uses of Radar? Print Email Save Image Credit: windows2universe.org Radar is an object-detection system which utilizes Electromagnetic waves, specifically radio waves to determine the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations.

The radar dish, or antenna, transmits pulses of radio waves or micro waves which bounce off any object in their path.

The object returns a tiny part of the wave ’s energy back to the dish or antenna which is usually located at the same site as the transmitter. The full expansion of the term “Radar” is “ Ra dio D etection a nd R anging”, although the term is now used as a single word rather than an abbreviation.

The term RADAR was coined in 1940 by the U. S. Navy. Content What is the History of Radar? How Radar works? What are the Applications of Radar? What is the History of Radar? History of Radar begins in 1886 when Heinrich Hertz, a German Physicist, demonstrated that radio / electromagnetic waves can be reflected off solid objects.

In 1895 Alexander Popov, a physics instructor at the Imperial Russian Navy School in Kronstadt (Russian town), developed an apparatus using a tube that could detect distant lightening strikes. Christian Hulsmeyer, a German researcher, was the first to use radio waves to detect “the presence of distant metallic objects”.

In 1904, he built an experimental device that could detect nearby ships in a dense fog, that were otherwise completely invisible to the naked eye. He received a British patent on September 23, 1904 for full Radar application, which he called “ Telemobiloscope ”. Practical radar was developed in secrecy during World War II by Britain and other nations. How Radar works?

Most Radars now a days have a video monitor that shows the location of all the ""detected"" objects within the range of the radar device. A computer measures the time it takes for the signal to reflect off the target and then calculates how far it is. The basic idea behind radar is very simple: a signal is transmitted, it bounces off an object and it is later received by some type of receiver.

Sound waves and ocean waves require matter to transport energy but EM waves can do so without the presence of matter. Due to this, satellites can use radars to work on projects outside of the Earth’s atmosphere and on other planets.

A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come in contact with an object they are usually reflected and or scattered in many directions. Radar signals are reflected well by most metals, by sea water, by wet lands since all of them has considerable electrical conductivity.

If the object is moving either closer or farther away, there is a slight change in the frequency of the radio waves, as explained by the “ Doppler Effect ”. What are the Applications of Radar? There are many different types of Radars and their uses are as follows. The modern uses of radar are highly diverse. They include Air traffic control, Air-defense systems, and Antimissile systems.

Nautical Radars: it is used to locate landmarks and other ships; ocean-surveillance systems, outer space surveillance, etc.,Aviation Radars: Aircrafts are equipped with radar devices that warn of obstacles in or approaching their path and give accurate altitude readings Marine Radars: They are used to measure the bearing and distance of ships to prevent collision with other ships, to navigate and fix their positions at sea when within range of shore or other fixed references such as islands, buoys and light ships Weather-sensing Radars: It is an important tool in weather forecasting and helps make the forecasts more accurate Detection and search Radar: It is the “early warning radar”, which is used for long-range detection of objects Target Acquisition (TA) Radar systems: It is used to locate surface-to-air-missiles (SAM).

These types of radar are often used in the military and in coastal surveillance, as well as for detecting car speed in high way patrol.

Missile Guidance Systems: This radar is used to locate the target of missile often present in Military aircraft Radar for Biological Research : : Bird and Insect radar are used frequently by scientists to track the migration patterns of animals. Bird radar is also being used in NASA’s Kennedy Space Center in Florida to track the presence of birds, especially Vultures, near launching pads.

Air traffic control and navigation Radar: This radar is used by airport to ensure the safety of planes. This type of radar detects the proximity of an aircraft and identifies the identity and altitude of the plane. External References Wikipedia: Radar Windows 2 Universe.org: How Radar Works Scholastic.com: Radar and Sonar "

Electromagnetic energy is familiar to most people as light and heat, but it can take many other forms, such as radio waves and X-rays. These are all types of radiation originating from the electromagnetic force, which is responsible for all electrical and magnetic phenomena. The radiation travels at the speed of light in a manner resembling waves. Unlike sound waves, electromagnetic waves do not require a medium through which to move and can travel across empty space.

What is Electromagnetic Energy?

The length of the wave can vary from hundreds of yards (meters) down to subatomic scales. The full range of wavelengths is known as the electromagnetic spectrum, of which visible light forms only a small part. Despite the observed wave-like character of electromagnetic radiation (EMR), it can also behave as if it's composed of tiny particles, known as photons.

Light, Electricity, and Magnetism The connection between light and electromagnetism was revealed in the 19th century by physicist James Clerk Maxwell's work on electric and magnetic fields. Using equations he developed, he found that the speed at which the fields move through space was exactly the speed of light and concluded that light was a disturbance of these fields, traveling in the form of waves.

His equations also showed that other forms of EMR with longer and shorter wavelengths were possible; these were later identified. Maxwell's findings gave rise to the study of electrodynamics, according to which EMR consists of oscillating electric and magnetic fields at right angles to one another and to the direction of motion.

This explained the wave-like nature of light, as observed in many experiments. Wavelength, Frequency and Energy Electromagnetic radiation can be described in terms of its wavelength — the distance between the crests of the waves — or its frequency — the number of crests that pass by a fixed point during a fixed time interval.

When moving through a vacuum, EMR always travels at light speed; therefore, the rate at which the crests travel does not vary and the frequency depends only on the length of the wave. A shorter wavelength indicates a higher frequency and a higher energy. This means that high energy gamma rays do not travel any faster than low energy radio waves; instead, they have much shorter wavelengths and much higher frequencies.

The Wave-Particle Duality Electrodynamics was very successful in describing electromagnetic energy in terms of fields and waves, but early in the 20th century, Albert Einstein 's investigation of the photoelectric effect, in which light dislodges electrons from a metal surface, raised a problem. He found that the energy of the electrons was entirely dependent on the frequency, and not the intensity, of the light. An increase in frequency produced higher energy electrons, but an increase in brightness made no difference.

The results could only be explained if the light consisted of discrete particles — later named photons — that transferred their energy to the electrons. This created a puzzle: observed over large scales, EMR behaves as waves, but its interactions with matter at the smallest scales can only be explained in terms of particles.

This is known as the wave-particle duality. It emerged during the development of quantum theory and applies to everything at the subatomic scale; electrons, for example, can behave as waves as well as particles.

There is no overall consensus among scientists as to what this duality actually means about the nature of electromagnetic energy. Quantum Electrodynamics A new theory, known as quantum electrodynamics (QED), eventually emerged to explain the particle-like behavior of EMR. According to QED, photons are the particles that carry the electromagnetic force, and the interactions of electrically charged objects are explained in terms of the production and absorption of these particles, which themselves carry no charge.

QED is considered one of the most successful theories ever developed. How Electromagnetic Energy is Produced Classical electrodynamics described the production of EMR in terms of the movement of electrical charges, but a more modern explanation — in line with quantum theory — is based on the idea that the subatomic particles of which matter is composed can only occupy certain fixed energy levels.

Electromagnetic radiation is released by the change from a higher to a lower energy state. Left to itself, matter will always try to reach its lowest level of energy. EMR can be produced when matter temporarily absorbs energy — for example, when it is heated — then releases it to drop to a lower level.

A lower energy state can also be achieved when atoms or molecules combine with one another in a chemical reaction. Combustion is a familiar example: typically, a molecule combines with oxygen from the air, forming products that collectively have less energy than the original molecule. This causes electromagnetic energy to be released in the form of flame. In the Sun's core, four hydrogen nuclei combine, in a series of steps, to form a helium nucleus that has slightly less mass, and therefore less energy.

This process is known as nuclear fusion. The excess energy is released as high frequency gamma rays that are absorbed by matter further out, which then emits this energy, mostly in the form of visible light and heat. Electromagnetic Energy, Life, and Technology Energy from the Sun is crucial to life on Earth. Sunlight heats the Earth's surface, which in turn heats the atmosphere, maintaining temperatures suitable for life and driving the planet's weather systems.

Plants make use of the Sun's electromagnetic energy for photosynthesis, the method by which they produce food.

Solar energy is converted to chemical energy that powers the processes that allow plants to make the glucose they need to survive from carbon dioxide and water. The by-product of this reaction is oxygen, so photosynthesis is responsible for maintaining the planet's oxygen levels. Most forms of technology rely largely on electromagnetic energy. The Industrial Revolution was powered by heat generated by the combustion of fossil fuels, and more recently, solar radiation has been used directly to provide ""clean"" and renewable power.

Modern communication, broadcasting, and the Internet depend heavily on radio waves and on light channeled through fiber optic cables.

Laser technology uses light to read from and write to CDs and DVDs. Most of what scientists know about the universe comes from the analysis of EMR of various wavelengths from distant stars and galaxies. Effects on Health High frequency EMR, such as gamma rays, X-rays, and ultraviolet light, carries enough energy to cause chemical changes in biological molecules.

It may break chemical bonds or remove electrons from atoms, forming ions. This can damage cells and alter DNA, increasing the risk of cancer. Concerns have also been expressed about the health effects of lower frequency EMR, such as the radio waves and microwaves used by cell phones and other communication devices.

Although these forms of radiation appear to have no direct effect on the chemistry of life, they may cause tissue to be heated in localized areas with prolonged exposure. There does not, so far, appear to be any conclusive evidence that this can make people ill. Ad "

The electromagnetic spectrum includes gamma rays, X-rays, ultraviolet, visible, infrared, microwaves, and radio waves. The only difference between these different types of radiation is their wavelength or frequency. Wavelength increases and frequency (as well as energy and temperature) decreases from gamma rays to radio waves. All of these forms of radiation travel at the speed of light (186,000 miles or 300,000,000 meters per second in a vacuum).

What is Infrared? Our eyes are detectors which are designed to detect visible light waves (or visible radiation). Visible light is one of the few types of radiation that can penetrate our atmosphere and be detected on the Earth's surface.

There are many forms of light (or radiation) which we cannot see with our eyes. Actually we can only see a very small part of the entire range of radiation called the electromagnetic spectrum.

Infrared radiation lies between the visible and microwave portions of the electromagnetic spectrum. Infrared waves have wavelengths longer than visible and shorter than microwaves, and have frequencies which are lower than visible and higher than microwaves. Infrared is broken into three categories: near, mid and far-infrared . Near-infrared refers to the part of the infrared spectrum that is closest to visible light and far-infrared refers to the part that is closer to the microwave region.

Mid-infrared is the region between these two. Infrared view of a melting ice cube Infrared view of a microwaved burrito Old Faithful in the infrared The primary source of infrared radiation is heat or thermal radiation.

This is the radiation produced by the motion of atoms and molecules in an object. The higher the temperature, the more the atoms and molecules move and the more infrared radiation they produce. Any object which has a temperature i.e. anything above absolute zero (-459.67 degrees Fahrenheit or -273.15 degrees Celsius or 0 degrees Kelvin), radiates in the infrared.

Absolute zero is the temperature at which all atomic and molecular motion ceases. Even objects that we think of as being very cold, such as an ice cube, emit infrared. When an object is not quite hot enough to radiate visible light, it will emit most of its energy in the infrared.

For example, hot charcoal may not give off light but it does emit infrared radiation which we feel as heat. The warmer the object, the more infrared radiation it emits. Courtesy of Meditherm Humans, at normal body temperature, radiate most strongly in the infrared at a wavelength of about 10 microns (A micron is the term commonly used in astronomy for a micrometer or one millionth of a meter).

This is the case for most warm-blooded animals. Cold-blooded animals, such as reptiles, will take on the temperature of their environment and are more difficult to detect in the infrared, unless compared to a cooler or warmer background.

Cold-blooded lizard in a warm human hand We experience infrared radiation every day. The heat that we feel from sunlight, a fire, a radiator or a warm sidewalk is infrared.

Although our eyes cannot see it, the nerves in our skin can feel it as heat. The temperature-sensitive nerve endings in your skin can detect the difference between your inside body temperature and your outside skin temperature. We also commonly use infrared rays when we operate a television remote.

RF (radio frequency) is in a portion of the electromagnetic spectrum with such things as xrays, gamma rays, visible, uv and ir light. These waves (and particles) may move through a vacuum. Ultrasound is at a frequency above ordinary audible sound. Sound is a mechanical wave that requires a medium.

What is the major difference between RF and ultrasound rathar than frequency?

"Science & Mathematics Engineering What is the major difference between RF and ultrasound rathar than frequency?i know that the frequency is different and the following Ultrasound is narrow pulses rf carries location data ultrasonic signals reflects heavily ultrasonic signals are pulses Follow 6 answers Answers Relevance Rating Newest Oldest Best Answer: we5yuwr s doesnt know what he (she) is talking about!

RF no matter what the frequency, is an electromagnetic wave, where ultrasound is (as the name implies) a SOUND wave.justme · 1 decade ago1 0 Comm

ent RF (radio frequency) is an electromagnetic wave form that can be distorted by metal and magnetic fields but can travel in a vacuum ultrasound is a physical wave form that requires a medium to travel in (solid or liquid) and will not travel in a vacuum.

Actually, all of the things you list in your added part apply to both rf and ultrasound (narrow pulses - if used for location, timing for location, reflection. )Mike1942f · 1 decade ago2 0 Comment Ultrasonic Vs Ultrasound Source (s):https://shrinkurl.im/a7U3hhannaford · 1 year ago0 0 Comment

If the material (walls) is a dielectric (insulator, not metal), some of the power is reflected at the surface and some of the power travels through the material. As radio waves travel through the dielectric material, some of the power is absorbed generating heat and some of the power travels through and comes out of the other side.

Why do radio waves and gamma rays pass through walls but visible light does not?

"Raj Doshi, Procastinator Answered Feb 17, 2015Simple Answer: For the same reason that a fired bullet can pass through your body while a rock cannot.

Technical Answer: (Source: http://www.physlink.com/Educatio...) Goldilocks and the Three Bears example of this radiation is too big and slow and this radiation is too small and fast. Gamma rays, visible light, and radio waves are all examples of electromagnetic radiation, and radio waves are on one end of the spectrum (with a wavelength of meters), gamma rays are on the other end (with a wavelength of about 10-12 meters) and visible light is somewhere in between (with a wavelength of around 5 x 10-7 meters).

Three things happen to EM radiation when it encounters a barrier. It can bounce (reflectance or scattering), pass through (transmittance), or just plain stop (absorbance).

The intensity of radiation transmitted depends on several things: The wavelength of the radiation The intensity of the radiation hitting the barrier The chemical composition of the barrier The physical microstructure of the barrier The thickness of the barrier Your question has to do with #1, but keep in mind that powerful enough visible light (many times brighter than sunlight) would be able to pass through the walls of your home so you could see it, and even a weak light can shine through a paper-thin wall or a wall made of glass. EM waves interact with matter on their own scale of size and time.

The reason why visible light can't travel through walls as easily as gamma rays or radio waves is because, to the visible light, there's something 'there' on a similar scale of length (wavelength) and time (frequency) that the gamma rays are too small and fast to interact with and the radio waves are too large and slow to interact with.

The gamma rays just pass through the spaces between and within atoms and molecules. They're small enough to do that. If your walls were made of pure lead, they'd have a little more trouble. The radio waves on the other hand are large enough to ignore the walls because they're too thin. But if you've ever tried to listen to a radio in a tunnel or a cave, you know that radio waves have trouble penetrating through meters of earth.

Visible light interacts with many solid materials because the wavelengths are the right size to be scattered by structural elements within those materials like microfibers and cracks and porous spaces. Well-cut glass or diamond don't have these structural elements at this length scale so they look clear unless they're shattered or rough.

So scattering due to physical elements of the right size is a major reason, but another factor contributes too. Visible light also interacts with pigments in the paint on surface of your wall. This occurs because the pigment molecules have chemical bonds within them that only vibrate at certain frequencies.

When visible light at that frequency hits the molecule, it's absorbed. The frequency of gamma rays is far too high and that of radio waves is far too low to interact with these kinds of vibrations. Thanks for A2A :)23k Views · View Upvoters · Answer requested by Dheeraj M Pai Your response is private.

Is this answer still relevant and up to date?promoted by UC Berkeley Extension Organic chemistry course at UC Berkeley Extension. Prepare for grad school & health careers with courses from UC Berkeley Extension. Learn More at extension.berkeley.edu Related Questions More Answers Below How is it that radio waves can go through concrete and x-rays through muscle?

What determines whether photons will pass through without intera... How does a radio wave pass right through a human while X-rays, gamma rays are absorbed?

Why can't gamma rays pass through concrete? Why can't light go through a brick wall, but sound waves can if loud enough?

What can radio waves pass through? Ask New Question Klara Theophilo, Ph D, atom's trapper. Answered Mar 8, 2015 · Author has 83 answers and 54k answer views Originally Answered: If we check the electromagnetic spectrum, it has radio waves on the lower side and x-rays and other such wavelengths on upper side. All the other electromagnetic wavelengths seem to penetrate walls, so why can't visible light? Because a medium is transparent to a wavelength it cannot absorb.

That said, an atom can absorb a photon of energy [math]\Delta E=\hbar \nu [/math], where [math]\nu [/math] is the frequency of the wave.

This energy is the Energy needed to go from one atomic state to another (more excited). Radiowaves are low frequency waves, so they pass through atoms without being noticed. X-ray are super-high frequency waves, so they can pass trough the material, because they're not in the usual range of absorption and have a high Penetration depth.

Although they CAN ionize atoms. In the end, visible and near infrared light are most likely to be absorb because atoms and molecules vibrations (resonances) are usually in this range.8.9k Views · View Upvoters Your response is private.

Is this answer still relevant and up to date? Shannon Oswald, 23+ years as a USAF RF Transmission Systems tech Answered Mar 31, 2016There are plenty of competent answers already (especially Raj Doshi's), but here goes. Let's see if I can add some additional understanding. So not all materials behave the same way at both light frequencies and radio frequencies due to their atomic structure.

If the material (walls) is a dielectric (insulator, not metal), some of the power is reflected at the surface and some of the power travels through the material. As radio waves travel through the dielectric material, some of the power is absorbed generating heat and some of the power travels through and comes out of the other side.

Absorption in a dielectric is called the attenuation coefficient of the material. How much power travels through a dielectric depends on both the thickness of the material and its attenuation coefficient (the walls in my home have a higher attenuation coefficient than notebook paper but definitely lower than steel reinforced concrete).

A small attenuation coefficient indicates that the material in question is relatively transparent, while a larger value indicates greater degrees of opacity. So lets bring light into this, light traveling through your sun glasses lens has a few percent reflected at the surface and between 10% and 90% of the light power absorbed through heating inside the glass (Tinting upps the absorption) and a few percent of the power comes out the other side.

Even through my 24+ years, I am still learning something new everyday. Honestly, I never really comprehended how the metal mesh antenna worked until I read the linked article and discovered that the holes in the metal mesh have to be 1/100 of the wavelength or smaller of the EM radiation you wish to reflect.

(Thanks to Mad Scientist Adrian Popa for the learning)See: Re: Which materials block radio waves the most (and why)?5.8k Views · View Upvoters Your response is private. Is this answer still relevant and up to date?promoted by Better Help Are you struggling emotionally? Chat with a therapist 24/7. Chat with a licensed therapist through your phone, computer or tablet. Starting at $36 a week. Start Now at betterhelp.go2cloud.org Jeremy Lee, B. Sc (Hons) Electronics Answered May 19, 2015 · Author has 192 answers and 90.6k answer views

Originally Answered: Why are radio waves (light) able to travel through buildings, but visible light is not? It all boils down to frequency which is proportional to energy. Wavelength of em wave is = c/f so as frequency changes, and c is constant, wavelength changes and the length of this wave dictates whether it interacts with atoms in a medium or not.

That in turn depends on the atoms and structure of the medium.

So visible light travels through glass, but not thick wood. Radio waves are long and pass through buildings because of this. Also, gamma rays are short and therefore very high energy which is another way to pass though materials. Interestingly, very long radio waves drag in the earth and water, slowing down and will hug the Earth...

"Raj Doshi, Procastinator Answered Feb 17, 2015Simple Answer: For the same reason that a fired bullet can pass through your body while a rock cannot.

Technical Answer: (Source: http://www.physlink.com/Educatio...) Goldilocks and the Three Bears example of this radiation is too big and slow and this radiation is too small and fast. Gamma rays, visible light, and radio waves are all examples of electromagnetic radiation, and radio waves are on one end of the spectrum (with a wavelength of meters), gamma rays are on the other end (with a wavelength of about 10-12 meters) and visible light is somewhere in between (with a wavelength of around 5 x 10-7 meters).

Three things happen to EM radiation when it encounters a barrier. It can bounce (reflectance or scattering), pass through (transmittance), or just plain stop (absorbance).

The reason why visible light can't travel through walls as easily as gamma rays or radio waves is because, to the visible light, there's something 'there' on a similar scale of length (wavelength) and time (frequency) that the gamma rays are too small and fast to interact with and the radio waves are too large and slow to interact with.

The gamma rays just pass through the spaces between and within atoms and molecules. They're small enough to do that. If your walls were made of pure lead, they'd have a little more trouble. The radio waves on the other hand are large enough to ignore the walls because they're too thin. But if you've ever tried to listen to a radio in a tunnel or a cave, you know that radio waves have trouble penetrating through meters of earth.

Visible light interacts with many solid materials because the wavelengths are the right size to be scattered by structural elements within those materials like microfibers and cracks and porous spaces. Well-cut glass or diamond don't have these structural elements at this length scale so they look clear unless they're shattered or rough.

So scattering due to physical elements of the right size is a major reason, but another factor contributes too. Visible light also interacts with pigments in the paint on surface of your wall. This occurs because the pigment molecules have chemical bonds within them that only vibrate at certain frequencies.

When visible light at that frequency hits the molecule, it's absorbed. The frequency of gamma rays is far too high and that of radio waves is far too low to interact with these kinds of vibrations. Thanks for A2A :)23k Views · View Upvoters · Answer requested by Dheeraj M Pai Your response is private.

Is this answer still relevant and up to date?promoted by UC Berkeley Extension Organic chemistry course at UC Berkeley Extension. Prepare for grad school & health careers with courses from UC Berkeley Extension. Learn More at extension.berkeley.edu Related Questions More Answers Below How is it that radio waves can go through concrete and x-rays through muscle?

What determines whether photons will pass through without intera... How does a radio wave pass right through a human while X-rays, gamma rays are absorbed?

Why can't gamma rays pass through concrete? Why can't light go through a brick wall, but sound waves can if loud enough?

What can radio waves pass through? Ask New Question Klara Theophilo, Ph D, atom's trapper. Answered Mar 8, 2015 · Author has 83 answers and 54k answer views Originally Answered: If we check the electromagnetic spectrum, it has radio waves on the lower side and x-rays and other such wavelengths on upper side. All the other electromagnetic wavelengths seem to penetrate walls, so why can't visible light? Because a medium is transparent to a wavelength it cannot absorb.

That said, an atom can absorb a photon of energy [math]\Delta E=\hbar \nu [/math], where [math]\nu [/math] is the frequency of the wave.

This energy is the Energy needed to go from one atomic state to another (more excited). Radiowaves are low frequency waves, so they pass through atoms without being noticed. X-ray are super-high frequency waves, so they can pass trough the material, because they're not in the usual range of absorption and have a high Penetration depth.

Although they CAN ionize atoms. In the end, visible and near infrared light are most likely to be absorb because atoms and molecules vibrations (resonances) are usually in this range.8.9k Views · View Upvoters Your response is private.

Is this answer still relevant and up to date? Shannon Oswald, 23+ years as a USAF RF Transmission Systems tech Answered Mar 31, 2016There are plenty of competent answers already (especially Raj Doshi's), but here goes. Let's see if I can add some additional understanding. So not all materials behave the same way at both light frequencies and radio frequencies due to their atomic structure.

If the material (walls) is a dielectric (insulator, not metal), some of the power is reflected at the surface and some of the power travels through the material. As radio waves travel through the dielectric material, some of the power is absorbed generating heat and some of the power travels through and comes out of the other side.

Absorption in a dielectric is called the attenuation coefficient of the material. How much power travels through a dielectric depends on both the thickness of the material and its attenuation coefficient (the walls in my home have a higher attenuation coefficient than notebook paper but definitely lower than steel reinforced concrete).

A small attenuation coefficient indicates that the material in question is relatively transparent, while a larger value indicates greater degrees of opacity. So lets bring light into this, light traveling through your sun glasses lens has a few percent reflected at the surface and between 10% and 90% of the light power absorbed through heating inside the glass (Tinting upps the absorption) and a few percent of the power comes out the other side.

Even through my 24+ years, I am still learning something new everyday. Honestly, I never really comprehended how the metal mesh antenna worked until I read the linked article and discovered that the holes in the metal mesh have to be 1/100 of the wavelength or smaller of the EM radiation you wish to reflect.

(Thanks to Mad Scientist Adrian Popa for the learning)See: Re: Which materials block radio waves the most (and why)?5.8k Views · View Upvoters Your response is private. Is this answer still relevant and up to date?promoted by Better Help Are you struggling emotionally? Chat with a therapist 24/7. Chat with a licensed therapist through your phone, computer or tablet. Starting at $36 a week. Start Now at betterhelp.go2cloud.org Jeremy Lee, B. Sc (Hons) Electronics Answered May 19, 2015 · Author has 192 answers and 90.6k answer views

Originally Answered: Why are radio waves (light) able to travel through buildings, but visible light is not? It all boils down to frequency which is proportional to energy. Wavelength of em wave is = c/f so as frequency changes, and c is constant, wavelength changes and the length of this wave dictates whether it interacts with atoms in a medium or not.

That in turn depends on the atoms and structure of the medium.

So visible light travels through glass, but not thick wood. Radio waves are long and pass through buildings because of this. Also, gamma rays are short and therefore very high energy which is another way to pass though materials. Interestingly, very long radio waves drag in the earth and water, slowing down and will hug the Earth...

The reason why visible light can't travel through walls as easily as gamma rays or radio waves is because, to the visible light, there's something 'there' on a similar scale of length (wavelength) and time (frequency) that the gamma rays are too small and fast to interact with and the radio waves are too large and slow to interact with.

"Raj Doshi, Procastinator Answered Feb 17, 2015Simple Answer: For the same reason that a fired bullet can pass through your body while a rock cannot.

Technical Answer: (Source: http://www.physlink.com/Educatio...) Goldilocks and the Three Bears example of this radiation is too big and slow and this radiation is too small and fast. Gamma rays, visible light, and radio waves are all examples of electromagnetic radiation, and radio waves are on one end of the spectrum (with a wavelength of meters), gamma rays are on the other end (with a wavelength of about 10-12 meters) and visible light is somewhere in between (with a wavelength of around 5 x 10-7 meters).

Three things happen to EM radiation when it encounters a barrier. It can bounce (reflectance or scattering), pass through (transmittance), or just plain stop (absorbance).

The gamma rays just pass through the spaces between and within atoms and molecules. They're small enough to do that. If your walls were made of pure lead, they'd have a little more trouble. The radio waves on the other hand are large enough to ignore the walls because they're too thin. But if you've ever tried to listen to a radio in a tunnel or a cave, you know that radio waves have trouble penetrating through meters of earth.

Visible light interacts with many solid materials because the wavelengths are the right size to be scattered by structural elements within those materials like microfibers and cracks and porous spaces. Well-cut glass or diamond don't have these structural elements at this length scale so they look clear unless they're shattered or rough.

So scattering due to physical elements of the right size is a major reason, but another factor contributes too. Visible light also interacts with pigments in the paint on surface of your wall. This occurs because the pigment molecules have chemical bonds within them that only vibrate at certain frequencies.

When visible light at that frequency hits the molecule, it's absorbed. The frequency of gamma rays is far too high and that of radio waves is far too low to interact with these kinds of vibrations. Thanks for A2A :)23k Views · View Upvoters · Answer requested by Dheeraj M Pai Your response is private.

Is this answer still relevant and up to date?promoted by UC Berkeley Extension Organic chemistry course at UC Berkeley Extension. Prepare for grad school & health careers with courses from UC Berkeley Extension. Learn More at extension.berkeley.edu Related Questions More Answers Below How is it that radio waves can go through concrete and x-rays through muscle?

What determines whether photons will pass through without intera... How does a radio wave pass right through a human while X-rays, gamma rays are absorbed?

Why can't gamma rays pass through concrete? Why can't light go through a brick wall, but sound waves can if loud enough?

What can radio waves pass through? Ask New Question Klara Theophilo, Ph D, atom's trapper. Answered Mar 8, 2015 · Author has 83 answers and 54k answer views Originally Answered: If we check the electromagnetic spectrum, it has radio waves on the lower side and x-rays and other such wavelengths on upper side. All the other electromagnetic wavelengths seem to penetrate walls, so why can't visible light? Because a medium is transparent to a wavelength it cannot absorb.

That said, an atom can absorb a photon of energy [math]\Delta E=\hbar \nu [/math], where [math]\nu [/math] is the frequency of the wave.

This energy is the Energy needed to go from one atomic state to another (more excited). Radiowaves are low frequency waves, so they pass through atoms without being noticed. X-ray are super-high frequency waves, so they can pass trough the material, because they're not in the usual range of absorption and have a high Penetration depth.

Although they CAN ionize atoms. In the end, visible and near infrared light are most likely to be absorb because atoms and molecules vibrations (resonances) are usually in this range.8.9k Views · View Upvoters Your response is private.

Is this answer still relevant and up to date? Shannon Oswald, 23+ years as a USAF RF Transmission Systems tech Answered Mar 31, 2016There are plenty of competent answers already (especially Raj Doshi's), but here goes. Let's see if I can add some additional understanding. So not all materials behave the same way at both light frequencies and radio frequencies due to their atomic structure.

If the material (walls) is a dielectric (insulator, not metal), some of the power is reflected at the surface and some of the power travels through the material. As radio waves travel through the dielectric material, some of the power is absorbed generating heat and some of the power travels through and comes out of the other side.

Absorption in a dielectric is called the attenuation coefficient of the material. How much power travels through a dielectric depends on both the thickness of the material and its attenuation coefficient (the walls in my home have a higher attenuation coefficient than notebook paper but definitely lower than steel reinforced concrete).

A small attenuation coefficient indicates that the material in question is relatively transparent, while a larger value indicates greater degrees of opacity. So lets bring light into this, light traveling through your sun glasses lens has a few percent reflected at the surface and between 10% and 90% of the light power absorbed through heating inside the glass (Tinting upps the absorption) and a few percent of the power comes out the other side.

Even through my 24+ years, I am still learning something new everyday. Honestly, I never really comprehended how the metal mesh antenna worked until I read the linked article and discovered that the holes in the metal mesh have to be 1/100 of the wavelength or smaller of the EM radiation you wish to reflect.

(Thanks to Mad Scientist Adrian Popa for the learning)See: Re: Which materials block radio waves the most (and why)?5.8k Views · View Upvoters Your response is private. Is this answer still relevant and up to date?promoted by Better Help Are you struggling emotionally? Chat with a therapist 24/7. Chat with a licensed therapist through your phone, computer or tablet. Starting at $36 a week. Start Now at betterhelp.go2cloud.org Jeremy Lee, B. Sc (Hons) Electronics Answered May 19, 2015 · Author has 192 answers and 90.6k answer views

Originally Answered: Why are radio waves (light) able to travel through buildings, but visible light is not? It all boils down to frequency which is proportional to energy. Wavelength of em wave is = c/f so as frequency changes, and c is constant, wavelength changes and the length of this wave dictates whether it interacts with atoms in a medium or not.

That in turn depends on the atoms and structure of the medium.

So visible light travels through glass, but not thick wood. Radio waves are long and pass through buildings because of this. Also, gamma rays are short and therefore very high energy which is another way to pass though materials. Interestingly, very long radio waves drag in the earth and water, slowing down and will hug the Earth...

"Raj Doshi, Procastinator Answered Feb 17, 2015Simple Answer: For the same reason that a fired bullet can pass through your body while a rock cannot.

Technical Answer: (Source: http://www.physlink.com/Educatio...) Goldilocks and the Three Bears example of this radiation is too big and slow and this radiation is too small and fast. Gamma rays, visible light, and radio waves are all examples of electromagnetic radiation, and radio waves are on one end of the spectrum (with a wavelength of meters), gamma rays are on the other end (with a wavelength of about 10-12 meters) and visible light is somewhere in between (with a wavelength of around 5 x 10-7 meters).

Three things happen to EM radiation when it encounters a barrier. It can bounce (reflectance or scattering), pass through (transmittance), or just plain stop (absorbance).

The reason why visible light can't travel through walls as easily as gamma rays or radio waves is because, to the visible light, there's something 'there' on a similar scale of length (wavelength) and time (frequency) that the gamma rays are too small and fast to interact with and the radio waves are too large and slow to interact with.

The gamma rays just pass through the spaces between and within atoms and molecules. They're small enough to do that. If your walls were made of pure lead, they'd have a little more trouble. The radio waves on the other hand are large enough to ignore the walls because they're too thin. But if you've ever tried to listen to a radio in a tunnel or a cave, you know that radio waves have trouble penetrating through meters of earth.

Visible light interacts with many solid materials because the wavelengths are the right size to be scattered by structural elements within those materials like microfibers and cracks and porous spaces. Well-cut glass or diamond don't have these structural elements at this length scale so they look clear unless they're shattered or rough.

So scattering due to physical elements of the right size is a major reason, but another factor contributes too. Visible light also interacts with pigments in the paint on surface of your wall. This occurs because the pigment molecules have chemical bonds within them that only vibrate at certain frequencies.

When visible light at that frequency hits the molecule, it's absorbed. The frequency of gamma rays is far too high and that of radio waves is far too low to interact with these kinds of vibrations. Thanks for A2A :)23k Views · View Upvoters · Answer requested by Dheeraj M Pai Your response is private.

Is this answer still relevant and up to date?promoted by UC Berkeley Extension Organic chemistry course at UC Berkeley Extension. Prepare for grad school & health careers with courses from UC Berkeley Extension. Learn More at extension.berkeley.edu Related Questions More Answers Below How is it that radio waves can go through concrete and x-rays through muscle?

What determines whether photons will pass through without intera... How does a radio wave pass right through a human while X-rays, gamma rays are absorbed?

Why can't gamma rays pass through concrete? Why can't light go through a brick wall, but sound waves can if loud enough?

What can radio waves pass through? Ask New Question Klara Theophilo, Ph D, atom's trapper. Answered Mar 8, 2015 · Author has 83 answers and 54k answer views Originally Answered: If we check the electromagnetic spectrum, it has radio waves on the lower side and x-rays and other such wavelengths on upper side. All the other electromagnetic wavelengths seem to penetrate walls, so why can't visible light? Because a medium is transparent to a wavelength it cannot absorb.

That said, an atom can absorb a photon of energy [math]\Delta E=\hbar \nu [/math], where [math]\nu [/math] is the frequency of the wave.

This energy is the Energy needed to go from one atomic state to another (more excited). Radiowaves are low frequency waves, so they pass through atoms without being noticed. X-ray are super-high frequency waves, so they can pass trough the material, because they're not in the usual range of absorption and have a high Penetration depth.

Although they CAN ionize atoms. In the end, visible and near infrared light are most likely to be absorb because atoms and molecules vibrations (resonances) are usually in this range.8.9k Views · View Upvoters Your response is private.

Is this answer still relevant and up to date? Shannon Oswald, 23+ years as a USAF RF Transmission Systems tech Answered Mar 31, 2016There are plenty of competent answers already (especially Raj Doshi's), but here goes. Let's see if I can add some additional understanding. So not all materials behave the same way at both light frequencies and radio frequencies due to their atomic structure.

If the material (walls) is a dielectric (insulator, not metal), some of the power is reflected at the surface and some of the power travels through the material. As radio waves travel through the dielectric material, some of the power is absorbed generating heat and some of the power travels through and comes out of the other side.

Absorption in a dielectric is called the attenuation coefficient of the material. How much power travels through a dielectric depends on both the thickness of the material and its attenuation coefficient (the walls in my home have a higher attenuation coefficient than notebook paper but definitely lower than steel reinforced concrete).

A small attenuation coefficient indicates that the material in question is relatively transparent, while a larger value indicates greater degrees of opacity. So lets bring light into this, light traveling through your sun glasses lens has a few percent reflected at the surface and between 10% and 90% of the light power absorbed through heating inside the glass (Tinting upps the absorption) and a few percent of the power comes out the other side.

Even through my 24+ years, I am still learning something new everyday. Honestly, I never really comprehended how the metal mesh antenna worked until I read the linked article and discovered that the holes in the metal mesh have to be 1/100 of the wavelength or smaller of the EM radiation you wish to reflect.

(Thanks to Mad Scientist Adrian Popa for the learning)See: Re: Which materials block radio waves the most (and why)?5.8k Views · View Upvoters Your response is private. Is this answer still relevant and up to date?promoted by Better Help Are you struggling emotionally? Chat with a therapist 24/7. Chat with a licensed therapist through your phone, computer or tablet. Starting at $36 a week. Start Now at betterhelp.go2cloud.org Jeremy Lee, B. Sc (Hons) Electronics Answered May 19, 2015 · Author has 192 answers and 90.6k answer views

Originally Answered: Why are radio waves (light) able to travel through buildings, but visible light is not? It all boils down to frequency which is proportional to energy. Wavelength of em wave is = c/f so as frequency changes, and c is constant, wavelength changes and the length of this wave dictates whether it interacts with atoms in a medium or not.

That in turn depends on the atoms and structure of the medium.

So visible light travels through glass, but not thick wood. Radio waves are long and pass through buildings because of this. Also, gamma rays are short and therefore very high energy which is another way to pass though materials. Interestingly, very long radio waves drag in the earth and water, slowing down and will hug the Earth...

Radio waves are the lowest-energy, lowest-frequency and longest-wavelength electromagnetic waves. They are produced when an alternating current flows in an aerial and they spread out and travel through the atmosphere. They are not strongly absorbed by the atmosphere.

Radio waves & microwaves

Radio waves & microwaves Quick revise The video and text below describes some of the characteristics and uses of Radio waves and Microwaves. Radio Waves

Another aerial is used as a detector and the waves produce an alternating current in it, with a frequency that matches that of the radio waves. Anyone with a receiver can tune it to this frequency to pick up the radio waves so they are suitable for broadcasting (for example, radio and TV programmes) to large numbers of people.

An advantage is that this method of communicating does not require wires to transmit information. A disadvantage is that radio stations using similar transmission frequencies sometimes interfere.

A common mistake is to think that we can hear radio waves. We cannot hear any electromagnetic radiation. The radiation is used to carry a signal that is converted into a sound wave by the receiver.

Medium wavelength radio waves are reflected from the ionosphere, a layer of charged particles in the upper atmosphere, so they can be used for long distance communication. Digital radio has better-quality reception as it uses digital signals and so does not have problems of noise and interference.

Radio waves & microwaves

One is because of what I described above; the wavelength is about the same as ordinary object. Radio waves tend to exhibit diffraction, that is they can bend around objects that are near the same size as their wavelength. So, radio waves can go around objects in general. The other way radio waves interact with objects is by reflection. Radio waves can bounce off objects. Often when radio waves hit an object like a building for example it will do both, refract around the building and reflect off of it as well. Now finally to your question. The main thing that makes radio waves go through an object or reflect off of it is the electromagnetic nature of object itself. Most common building materials like wood, plaster, glass, brick, stones, cement, etc are very poor conductors of electricity. These materials are referred to as dielectric materials.

Mad Sci Network: Physics Query: Re: Why do radio waves pass through some materials and not others? Date: Sat Feb 3 09:28:37 2007 Posted By: Tom Hancewicz, Staff, Advanced Imaging and Measurement, Unilever Research & Development Area of science: Physics ID: 1169422873.

Ph Message: It's actually a very complex process by which radio waves propagate from one point to another point on the earth. When you first think about it, it seems like it might be a relatively straight-forward process. However, there are so many factors that influence the process that it quickly becomes overwhelming.

I will give a very simple view of what happens but I would encourage you to search the web and your local library.

There are many sites and books that have very detailed explanations of the phenomenon. A good place to start on the web would be at: http://www.radio-electronics.com/info/propagation/index.php Or http://tpub.com/neets/book10/40.htm ===================================== Radio waves are a form of electromagnetic radiation just as like visible, UV, infrared and X-rays. What makes it very different and somewhat peculiar in its behavior is the frequency or wavelength of the radiation. All the other forms of radiation that I mentioned have wavelengths much much smaller than common objects we would know like a book, a house, a car, the window of your room, etc.

In many ways this makes them relatively easy to describe in terms of propagation. Radio waves on the other hand occur in a very large range of wavelengths (millimeters to thousands of meters). The wavelength of FM radio waves is on the order of 1-10 meters and AM radio waves are on the order of 100-1000 meters. Therefore they occur in a range of wavelengths about equal to common everyday objects. There are two main ways radio waves interact with objects.

Materials like metal, solutions of ions (like the ocean waters) have the ability disperse an electrical charge and so are good electrical conductors. Radio waves will reflect off of good conductors but can penetrate to varying degrees dielectric materials.

This is why radio waves can go through your house but not through metal doors or walls. This is the straight-forward part but what about buildings with steel frames or large amounts of metal reinforcement bars? Everyone knows that it is relatively easy to get a radio signal in your house but not in a large office building.

The reason is that the large metal interior skeleton of the building acts as a metal cage with distance between conducting elements (the steel) about the same or smaller than the wavelength of the radio waves. This is where refraction comes into play again. Each of the metal structural elements refracts the waves but because of the close the proximity of the elements to each other in the building skeleton and because the wavelength is just right, the waves refracting around the steel beams destructively interfere with each other.

This means the signal is either completely attenuates or substantially weakened to the point that reception is horrible.

I will stop here even though there are more details that could be explained regarding the different kinds of radio waves and reflection from other objects like the ground, the oceans and lakes, and interaction with the atmosphere (primarily the charged layer called the ionosphere), but I think this is enough to get you started.

The rest I will leave up to you to explore on your own. Current Queue | Current Queue for Physics | Physics archives Try the links in the Mad Sci Library for more information on Physics . Mad Sci Home | Information | Search | Random Knowledge Generator | Mad Sci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support Mad Sci Mad Sci Network, webadmin@madsci.org © 1995-2006. All rights reserved.

Various frequencies of radio waves are used for television and FM and AM radio broadcasts, military communications, mobile phones, ham radio, wireless computer networks, and numerous other communications applications. Most radio waves pass freely through Earth's atmosphere.

Radio Waves

"Various types (frequencies) of radio waves are used for communications. Click on image for full size Windows to the Universe original artwork.

Related links: Electricity and Magnetism Fundamental Physics relevant to Space Weather Space Weather Radio Waves Radio waves are a type of electromagnetic radiation. A radio wave has a much longer wavelength than does visible light. We use radio waves extensively for communications. Radio waves have wavelengths as short as a few millimeters (tenths of inches) and as long as hundreds of kilometers (hundreds of miles).

Visible light, for comparison, has wavelengths in the 400 to 700 nanometer range, about 5,000 times shorter than the shortest wavelength radio waves. Radio waves oscillate at frequencies between a few kilohertz (k Hz or thousands of hertz) and a few terahertz (THz or 10 12 hertz). ""Far infrared"" radiation borders radio waves on the electromagnetic spectrum; far IR is slightly higher energy and shorter wavelength radiation than radio.

Microwaves, which we use for cooking and for communication, are short wavelength radio waves with wavelengths between a few and a few hundred millimeters (tenths of inches to tens of inches).

However, some frequencies can be reflected or absorbed by the charged particles in the ionosphere. Last modified July 13, 2005 by Randy Russell. Shop Windows to the Universe Science Store!Our online store includes books on science education, classroom activities in The Earth Scientist, mineral and fossil specimens, and educational games! "

Best Answer: Anything that travels by waves or rays is considered radiation, like heat and light, and radio waves. Microwave radiation is small radio waves that are produced by a magnetron. They are reflected by the metal of the box. They are absorbed by the food causing the temperature to rise. They are transmitted by the glass, plastic or paper dishes.

Do old microwaves emit radiation?

"Science & Mathematics Other - Science Do old microwaves emit radiation? Like from the mid-late 80's. Follow 2 answers Answers

Older microwaves that have a door with a side hinge have been noted to leak more than the ones that have a hinge on the bottom. this is because someone could have leaned on the door while open and sprung it some or someone left a dishtowel half in the door while it was in operation.

Most seem to have the side open doors now. The parts of the body that are likely to be damaged by microwaves are the eyes an testes.

Do not stare into a microwave while it is running. Do not leave your hand on the opening seam. Just because it is old does not mean that it leaks, but does not mean that it does not. Source (s): I worked for Amana, the first microwve company who discovered the use for the waves, cooking, while working on RADAR during WW IIscience teacher · 9 years ago1 0 Comment Same as the new ones!

Microwaves are a form of RADIO WAVE. They are NOT ""radiation"" like something being radioactive, and microwave ovens do NOT make your food ""radioactive"" or ""glow in the dark"".

There are ""radiations"" because the radio wave ""radiate"" from a central location (like an antenna) inside the oven. Microwaves are very similar to radar waves. In fact, that was how microwaves ovens were discovered. In the late 1940s, US Army radio technicians were working on a then new technology called RADAR. In order to tell of the radar was working, the technicians would often climb up to the antenna and stand in front of it.

If they 'tingled"" then the radar was working. is is said that one technician had a Hershey Bar in his pocket.

Being full of chocolate fat, the candy bar melted! The technician performed some other experiments, and installed an old radar tube into a cabinet, and made it pop popcorn. The first ""microwave oven"" was about the size of a refrigerator, and was designed ONLY to pop popcorn!

The rest is history. Todays microwaves use radio frequencies different than radar, but the principal behind how they work has not changed in over 60 years. Gary B · 9 years ago2 0 Comment Maybe you would like to learn more about one of these? Try online nursing courses? Time for a Caribbean cruise? Hard drive full? Cloud storage Looking for a new chandelier? "