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For other uses, see Radar (disambiguation).
This long-range radar antenna, known as ALTAIR, is used to detect and track space objects in conjunction with ABM testing at the Ronald Reagan Test Site on the Kwajalein atoll.
This long-range radar antenna, known as ALTAIR, is used to detect and track space objects in conjunction with ABM testing at the Ronald Reagan Test Site on the Kwajalein atoll. An antenna is a Transducer designed to transmit or Receive electromagnetic waves In other words antennas convert electromagnetic waves into An anti-ballistic missile (ABM is a Missile designed to counter Ballistic missiles (a missile for Missile defense) The Ronald Reagan Ballistic Missile Defense Test Site, commonly referred to as the Reagan Test Site, is a Missile test range in the Pacific Ocean. Kwajalein Atoll ( Marshallese: Kuwajleen; kʷuwːɔ͡ɛt̪ʲl̪ʲɪn̪ʲ common English pronunciation ˈkwɑːʤəlɨ̞n often nicknamed Kwaj An atoll (pronounced /ˈætʌl/ is an island of Coral that encircles a Lagoon partially or completely [1]

Radar is a system that uses electromagnetic waves to identify the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, motor vehicles, weather formations, and terrain. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. The term RADAR was coined in 1941 as an acronym for Radio Detection and Ranging. Acronyms, initialisms, and alphabetisms are Abbreviations that are formed using the initial components in a phrase or name The term has since entered the English language as a standard word, radar, losing the capitalization. Radar was originally called RDF (Radio Direction Finder) in the United Kingdom.

A radar system has a transmitter that emits either radio waves or (more usually these days) microwaves that are reflected by the target and detected by a receiver, typically in the same location as the transmitter. Radio waves are electromagnetic waves occurring on the Radio frequency portion of the Electromagnetic spectrum. Microwaves are electromagnetic waves with Wavelengths ranging from 1 mm to 1 m or frequencies between 0 Although the signal returned is usually very weak, the signal can be amplified. This enables radar to detect objects at ranges where other emissions, such as sound or visible light, would be too weak to detect. Sound' is Vibration transmitted through a Solid, Liquid, or Gas; particularly sound means those vibrations composed of Frequencies Radar is used in many contexts, including meteorological detection of precipitation, measuring ocean surface waves, air traffic control, police detection of speeding traffic, and by the military. Meteorology (from Greek grc μετέωρος metéōros, "high in the sky" and grc -λογία -logia) is the Interdisciplinary In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric Ocean surface waves can be measured by several Radar Remote sensing techniques Air traffic control ( ATC) is a service provided by ground-based controllers who direct Aircraft on the ground and in the air Police are agents or agencies usually of the executive, empowered to enforce the law and to effect public and social order through the legitimatized use of force For a discussion of the maximum speed possible in the universe see Speed of light and Special relativity. Traffic on Roads may consist of Pedestrians ridden or herded Animals Vehicles Streetcars and other Conveyances either singly

Contents

History

Main article: History of radar

Several inventors, scientists, and engineers contributed to the development of radar. The history of radar began in the 1900s when engineers invented simple uni-directional ranging devices An inventor is a person who creates or discovers a new method form device or other useful means An engineer is a person professionally engaged in a field of Engineering. The history of radar began in the 1900s when engineers invented simple uni-directional ranging devices The first to use radio waves to detect "the presence of distant metallic objects" was Christian Hülsmeyer, who in 1904 demonstrated the feasibility of detecting the presence of a ship in dense fog, but not its distance. [2][3] He received Reichspatent Nr. 165546[4] for his pre-radar device in April 1904, and later patent 169154[5] for a related amendment for ranging. He also received a patent [6] in England for his telemobiloscope on September 22, 1904. Events 66 - Emperor Nero creates the Legion I Italica. 1236 - The Lithuanians Year 1904 ( MCMIV) was a Leap year starting on Friday (link will display calendar of the Gregorian calendar (or a Leap year starting on [2][7]

Nikola Tesla, in August 1917, first established principles regarding frequency and power level for the first primitive radar units. There have already been discussions about Tesla's ethnicity on the talk page [8] He stated, "[. . . ] by their [standing electromagnetic waves] use we may produce at will, from a sending station, an electrical effect in any particular region of the globe; [with which] we may determine the relative position or course of a moving object, such as a vessel at sea, the distance traversed by the same, or its speed. "

Before the Second World War, developments by the Americans (Dr. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including Robert M. Page tested the first monopulse radar in 1934),[9] the Germans, the French (French Patent n° 788795 in 1934)[10][11] and mainly the British who were the first to fully exploit it as a defence against aircraft attack (British Patent GB593017 by Robert Watson-Watt in 1935)[11][12][13] led to the first real radars. Monopulse radar is an adaptation of Conical scanning radar which sends additional information in the Radar signal in order to avoid problems caused by rapid changes Sir Robert Alexander Watson-Watt, FRS FRAeS ( 13 April 1892 &ndash 5 December 1973) is considered by many to be the " Hungarian Zoltán Bay produced a working model by 1936 at the Tungsram laboratory in the same vein. Zoltán Lajos Bay (1900-1992 was a Hungarian physicist professor and engineer who developed Microwave technology including Tungsten lamps Tungsram is a Hungarian manufacturer of Light bulbs and Vacuum tubes since 1896.

In 1934, Émile Girardeau, working with the first French radar systems, stated he was building radar systems "conceived according to the principles stated by Tesla". [1]

The war precipitated research to find better resolution, more portability and more features for the new defence technology. Post-war years have seen the use of radar in fields as diverse as air traffic control, weather monitoring, astrometry and road speed control. Air traffic control ( ATC) is a service provided by ground-based controllers who direct Aircraft on the ground and in the air Astrometry is the branch of Astronomy that relates to precise measurements and explanations of the positions and movements of Stars and other celestial bodies

Principles

Reflection

Brightness can indicate reflectivity as in this 1960 weather radar image. The radar's frequency, pulse form, and antenna largely determine what it can observe.
Brightness can indicate reflectivity as in this 1960 weather radar image. The radar's frequency, pulse form, and antenna largely determine what it can observe.

Electromagnetic waves reflect (scatter) from any large change in the dielectric or diamagnetic constants. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of A dielectric is a nonconducting substance ie an insulator. The term was coined by William Whewell in response to a request from Michael Faraday. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied Magnetic field, thus causing a repulsive effect This means that a solid object in air or a vacuum, or other significant change in atomic density between the object and what's surrounding it, will usually scatter radar (radio) waves. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. This is particularly true for electrically conductive materials, such as metal and carbon fiber, making radar particularly well suited to the detection of aircraft and ships. Electrical conduction is the movement of electrically charged particles through a Transmission medium ( Electrical conductor) Radar absorbing material, containing resistive and sometimes magnetic substances, is used on military vehicles to reduce radar reflection. Radar absorbent material, or RAM, is a class of materials used in Stealth technology to disguise a vehicle or structure from radar detection Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. This is the radio equivalent of painting something a dark color.

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. A mirror is an object with a surface that has good Specular reflection; that is it is smooth enough to form an Image. If the wavelength is much longer than the size of the target, the target is polarized (positive and negative charges are separated), like a dipole antenna. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations A dipole antenna, developed by Heinrich Rudolph Hertz around 1886, is an antenna with a center- fed Driven element for transmitting This is described by Rayleigh scattering, an effect that creates the Earth's blue sky and red sunsets. Rayleigh scattering (named after Lord Rayleigh) is the elastic Scattering of Light or other electromagnetic radiation by particles much smaller Sunset, also called sundown in some American English Dialects is the instant when the trailing edge of the Sun 's disk disappears below When the two length scales are comparable, there may be resonances. In Physics, resonance is the tendency of a system to Oscillate at maximum Amplitude at certain frequencies, known as the system's Early radars used very long wavelengths that were larger than the targets and received a vague signal, whereas some modern systems use shorter wavelengths (a few centimeters or shorter) that can image objects as small as a loaf of bread. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth

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. Reflection is the change in direction of a Wave front at an interface between two different media so that the wave front returns into the medium from which A structure consisting of three flat surfaces meeting at a single corner, like the corner on a box, will always reflect waves entering its opening directly back at the source. These so-called corner reflectors are commonly used as radar reflectors to make otherwise difficult-to-detect objects easier to detect, and are often found on boats in order to improve their detection in a rescue situation and to reduce collisions. A corner reflector is a Retroreflector consisting of three mutually perpendicular intersecting flat surfaces which reflects Electromagnetic waves back towards the For similar reasons, objects attempting to avoid detection will angle their surfaces in a way to eliminate inside corners and avoid surfaces and edges perpendicular to likely detection directions, which leads to "odd" looking stealth aircraft. Stealth aircraft are Aircraft that use Stealth technology to make it harder to be detected by radar and other means than conventional aircraft by employing a These precautions do not completely eliminate reflection because of diffraction, especially at longer wavelengths. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle 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. Chaff, originally called Window by the British, and Düppel by the World War II era German Luftwaffe, is a The extent to which an object reflects or scatters radio waves is called its radar cross section. Radar cross section (RCS is a measure of how detectable an object is with a Radar.

Radar equation

The amount of power Pr returning to the receiving antenna is given by the radar equation:

P_r = {{P_t G_t A_r \sigma F^4}\over{{(4\pi)}^2 R_t^2R_r^2}}

where

In the common case where the transmitter and the receiver are at the same location, Rt = Rr and the term Rt² Rr² can be replaced by R4, where R is the range. This yields:

P_r = {{P_t G_t A_r \sigma F^4}\over{{(4\pi)}^2 R^4}}

This shows that the received power declines as the fourth power of the range, which means that the reflected power from distant targets is very, very small.

The equation above with F = 1 is a simplification for vacuum without interference. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. The propagation factor accounts for the effects of multipath and shadowing and depends on the details of the environment. In Wireless Telecommunications multipath is the propagation phenomenon that results in Radio signals reaching the receiving In a real-world situation, pathloss effects should also be considered. Path loss (or path attenuation) is the reduction in power density ( attenuation) of an Electromagnetic wave as it propagates through space

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 fact that radar returns from moving targets typically "chirp" (change their frequency as a function of time, as does the sound of a bird or bat). Time-frequency analysis is a body of techniques for characterizing and manipulating signals whose component frequencies vary in time such as transient signals A wavelet is a mathematical function used to divide a given function or continuous-time signal into different frequency components and study each component with a resolution In Signal processing, the chirplet transform is an Inner product of an input signal with a family of analysis primitives called chirplets.

Polarization

In the transmitted radar signal, the electric field is perpendicular to the direction of propagation, and this direction of the electric field is the polarization of the wave. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations 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. In Electrodynamics, circular polarization (also circular polarisation) of Electromagnetic radiation is a Polarization such that the tip of the Linear polarization returns usually indicate metal surfaces. In Electrodynamics, linear polarization or plane polarization of Electromagnetic radiation is a confinement of the Electric field vector or Random polarization returns usually indicate a fractal surface, such as rocks or soil, and are used by navigation radars. Randomness is a lack of order Purpose, cause, or predictability A fractal is generally "a rough or fragmented geometric shape that can be split into parts each of which is (at least approximately a reduced-size copy of the whole" Navigation is the process of reading and controlling the movement of a craft or vehicle from one place to another

Interference

Radar systems must overcome several different sources of 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). Signal-to-noise ratio (often abbreviated SNR or S/N) is an Electrical engineering concept also used in other fields (such as scientific Measurements SNR is defined as the ratio of a signal power to the noise power within the desired signal.

In less technical terms, signal-to-noise ratio (SNR), compares the level of a desired signal (such as targets) to the level of background noise. The higher a system's SNR, the better it is in isolating actual targets from the surrounding noise signals.

Noise

Signal noise is an internal source of random variations in the signal, which is inherently generated to some degree by all electronic components. In Science, and especially in Physics and Telecommunication, noise is fluctuations in and the addition of external factors to the stream of target 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 (similar to trying to hear a whisper while standing near a busy road). Therefore, the most important noise sources appear in the receiver and much effort is made to minimize these factors. Noise figure is a measure of the noise produced by a receiver compared to an ideal receiver, and this needs to be minimized. In Telecommunication, noise figure ( NF) is a measure of degradation of the signal to noise ratio ( SNR) caused by components in the RF signal chain

Noise is also generated by external sources, most importantly the natural thermal radiation of the background scene surrounding the target of interest. In modern radar systems, due to the high performance of their receivers, the internal noise is typically about equal to or lower than the external scene 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. Johnson–Nyquist noise ( thermal noise, Johnson noise, or Nyquist noise) is the electronic noise generated by the thermal agitation

There will be also Flicker noise due to electrons transit, but depending on 1/f, will be much lower than thermal noise when the frequency is high. Flicker noise is a type of Electronic noise with a 1/f or pink spectrum Hence, in pulse radar, the system will be always heterodyne. In Radio and Signal processing, heterodyning is the generation of new frequencies by mixing or multiplying two Oscillating waveforms See intermediate frequency. In communications and Electronic engineering, an intermediate frequency ( IF) is a Frequency to which a carrier frequency is shifted as an

Clutter

Clutter refers to actual radio frequency (RF) echoes returned from targets which are by definition uninteresting to the radar operators in general. Such targets mostly 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 and meteor trails. In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric In Fluid dynamics, turbulence or turbulent flow is a fluid regime characterized by chaotic Stochastic property changes The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation Clutter may also be returned from man-made objects such as buildings and, intentionally, by radar countermeasures such as chaff. Chaff, originally called Window by the British, and Düppel by the World War II era German Luftwaffe, is a

Some clutter may also be caused by a long radar waveguide between the radar transceiver and the antenna. A waveguide is a structure which guides waves such as Electromagnetic waves Light, or Sound waves 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. The plan position indicator (PPI, is the most common type of Radar display. 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.

While some clutter sources may be undesirable for some radar applications (such as storm clouds for air-defence radars), they may be desirable for others (meteorological radars in this example). Meteorology (from Greek grc μετέωρος metéōros, "high in the sky" and grc -λογία -logia) is the Interdisciplinary Clutter is considered a passive interference source, since it only appears in response to radar signals sent by the radar.

There are several methods of detecting and neutralizing clutter. Many of these methods rely on the fact that clutter tends to appear static between radar scans. Therefore, when comparing subsequent scans 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, therefore using linear polarization the better to detect precipitation). In Electrodynamics, circular polarization (also circular polarisation) of Electromagnetic radiation is a Polarization such that the tip of the In Electrodynamics, linear polarization or plane polarization of Electromagnetic radiation is a confinement of the Electric field vector or Other methods attempt to increase the signal-to-clutter ratio.

CFAR (Constant False-Alarm Rate, a form of Automatic Gain Control, or AGC) is a method relying on the fact that clutter returns far outnumber echoes from targets of interest. Constant false alarm rate (CFAR detection refers to a common form of adaptive algorithm used in Radar systems to detect target returns against a background of noise Automatic gain control (AGC is an adaptive System found in many electronic devices 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 an actual target cause ghosts to appear.
Radar multipath echoes from an actual target cause ghosts to appear. In Wireless Telecommunications multipath is the propagation phenomenon that results in Radio signals reaching the receiving A light echo is a phenomenon observed in Astronomy. Analogous to an echo of Sound, a Light echo is produced when a sudden flash or burst A ghost is said to be the apparition of a Deceased person frequently similar in appearance to that person and usually encountered in places she or he frequented

Clutter may also originate from multipath echoes from valid targets due to ground reflection, atmospheric ducting or ionospheric reflection/refraction. In Wireless Telecommunications multipath is the propagation phenomenon that results in Radio signals reaching the receiving In Telecommunication, an atmospheric duct is a horizontal Layer in the lower atmosphere in which the vertical Refractive index gradients are such that Ionospheric reflection: Of electromagnetic waves propagating in the Ionosphere, a redirection i Refraction is the change in direction of a Wave due to a change in its Speed. This specific clutter type is especially bothersome, since it appears to move and behave like other normal (point) targets of interest, thereby creating a ghost. In a typical scenario, an aircraft echo is multipath-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 - worse - eliminating it on the basis of jitter or a physical impossibility. Jitter is an unwanted variation of one or more characteristics of a periodic signal in Electronics and Telecommunications. 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. In newer ATC 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 due to calculated height, distance, and radar timing.

Jamming

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. Radar jamming and deception is the intentional emission of Radio Frequency signals to interfere with the operation of a radar by saturating its receiver Jamming may be intentional, as with an electronic warfare (EW) tactic, or unintentional, as with friendly forces operating equipment that transmits using the same frequency range. Electronic warfare ( EW) is the use of the Electromagnetic spectrum to effectively deny the use of this medium by an adversary while optimizing its use by friendly 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 line-of-sights, due to the radar receiver's sidelobes (Sidelobe Jamming). In antenna engineering side lobes are the lobes of the far field Radiation pattern that are not the main beam, where the terms "beam"

Mainlobe jamming can generally only be reduced by narrowing the mainlobe solid angle, and can never fully be eliminated when directly facing a jammer which uses the same frequency and polarization as the radar. The solid angle, Ω, is the angle in three-dimensional space that an object Subtends at a point 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. An omnidirectional antenna is an antenna system which radiates power uniformly in one plane with a directive pattern shape in a perpendicular plane Other anti-jamming techniques are frequency hopping and polarization. Frequency-hopping spread spectrum ( FHSS) is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations See Electronic counter-counter-measures for details. Electronic counter-countermeasures (ECCM describes a variety of practices which attempt to reduce or eliminate the effect of Electronic countermeasures (ECM on electronic

Interference has recently become a problem for C-band (5. C band is a name given to certain portions of the Electromagnetic spectrum, as well as a range of Wavelengths of Light, used for communications 66 GHz) meteorological radars with the proliferation of 5. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. 4 GHz band WiFi equipment. Wi-Fi (ˈwaɪfaɪ is the trade name for the popular wireless technology used [14]

Radar signal processing

Distance measurement

Transit time

Pulse radar
Pulse radar

One way to measure the distance to an object is to 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 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 (186,000 miles per second or 300,000,000 meters per second), 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 device called a duplexer, the radar switches between transmitting and receiving at a predetermined rate. The minimum range is calculated by measuring the length of the pulse multiplied by the speed of light, divided by two. In order to detect closer targets one must use a shorter pulse length.

A similar effect imposes a maximum range as well. If the return from the target comes in when the next pulse is being sent out, once again the receiver cannot tell the difference. In order to maximize range, one wants to use longer times between pulses, or commonly referred to as a pulse repetition time (PRT).

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 again. 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. This pattern of pulses and pauses is known as the pulse repetition frequency (or PRF), and is one of the main ways to characterize a radar. A Radar System uses a Radio Frequency electromagnetic signal reflected from a target to determine information about that target As electronics have improved many radars now can change their PRF thereby changing their range. The newest radars actually fire 2 pulses during one cell, one for short range (~6 miles) and a separate signal for longer ranges (~60 miles).

The distance resolution and the characteristics of the received signal as compared to noise depends heavily on the shape of the pulse. Optical resolution describes the ability of an imaging system to resolve detail in the object that is being imaged The pulse is often modulated to achieve better performance thanks to a technique known as pulse compression. In Telecommunications, modulation is the process of varying a periodic Waveform, i Pulse compression is a Signal processing technique mainly used in Radar, Sonar and Echography to augment the range resolution as

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 exactly 1,852 meters, then dividing this distance by the speed of light (exactly 299,792,458 meters per second), and then multiplying the result by 2 (round trip = twice the distance), yields a result of approximately 12. 36 microseconds in duration.

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 changing 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. Continuous-wave radar system is a Radar system where a known stable frequency Continuous wave Radio energy is transmitted and then received from any reflecting A radar altimeter, radio altimeter, low range radio altimeter (LRRA or simply RA measures Altitude above the Terrain presently beneath 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 broadcast has shifted to some other frequency. The amount of that shift is greater over longer times, so greater frequency differences mean a longer distance, the exact amount being the "ramp speed" selected by the electronics. The amount of shift is therefore directly related to the distance traveled, and can be displayed on an instrument. This signal processing is similar to that used in speed detecting Doppler radar. The Doppler effect (or Doppler shift) named after Christian Doppler, is the change in Frequency and Wavelength of a Wave for Example systems using this approach are AZUSA, MISTRAM, and UDOP. AZUSA refers to a ground-based Radar tracking system installed at Cape Canaveral, Florida and the NASA Kennedy Space Center. MISTRAM ( MISsile TRAjectory Measurement) was a high-resolution tracking system used by the United States Air Force (and later NASA) to provide highly The UDOP (UHF Doppler multistatic radar and multiradar system (MSRS utilizes Doppler radar for missile tracking and trajectory measurement

A further advantage is that the radar can operate effectively at relatively low frequencies, comparable to that used by UHF television. This was important in the early development of this type when high frequency signal generation was difficult or expensive.

Speed measurement

Speed is the change in distance to an object with respect to time. Speed is the rate of motion, or equivalently the rate of change in position often expressed as Distance d traveled per unit of Distance is a numerical description of how far apart objects are Thus the existing system for measuring distance, combined with a memory capacity to see where the target last was, is enough to measure speed. In Psychology, memory is an organism's ability to store retain and subsequently retrieve information 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. A crayon is a stick of colored Wax, Charcoal, Chalk, or other materials used for writing and Drawing. The slide rule, also known as a slipstick, is a mechanical Analog computer. Modern radar systems perform the equivalent operation faster and more accurately using computers.

However, 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. The Doppler effect (or Doppler shift) named after Christian Doppler, is the change in Frequency and Wavelength of a Wave for Most modern radar systems use this principle in the pulse-doppler radar system. Pulse-Doppler is a Radar system capable of not only detecting target location (bearing range and altitude but also measuring its radial velocity (range-rate Return signals from targets are shifted away from this base frequency via the Doppler effect enabling the calculation of the speed of the object relative to the 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. Azimuth ( is a mathematical concept defined as the angle usually measured in degrees (° between a reference plane and a point. Additional information of the nature of the Doppler returns may be found in the radar signal characteristics article. A Radar System uses a Radio Frequency electromagnetic signal reflected from a target to determine information about that target

It is also possible to make a radar without any pulsing, known as a continuous-wave radar (CW radar), by sending out a very pure signal of a known frequency. Continuous-wave radar system is a Radar system where a known stable frequency Continuous wave Radio energy is transmitted and then received from any reflecting CW radar is ideal for determining the radial component of a target's velocity, but it cannot determine the target's range. CW radar is typically used by traffic enforcement to measure vehicle speed quickly and accurately where range is not important.

Reduction of interference effects

Signal processing is employed in radar systems to reduce the radar interference effects. Signal processing is the analysis interpretation and manipulation of signals Signals of interest include sound, images, biological signals such as Signal processing techniques include moving target indication (MTI), pulse doppler, moving target detection (MTD) processors, correlation with secondary surveillance radar (SSR) targets, space-time adaptive processing (STAP), and track-before-detect (TBD). Moving target indication ( MTI) is a mode of operation of a Radar to discriminate a target against clutter. Pulse-Doppler is a Radar system capable of not only detecting target location (bearing range and altitude but also measuring its radial velocity (range-rate Secondary Surveillance Radar ( SSR) is a Radar system used in Air traffic control (ATC which not only detects and measures the position of aircraft Space-time Adaptive Processing (STAP is a signal processing technique most commonly used in Radar systems In Radar technology and similar fields track-before-detect ( TBD) is a concept according to which a signal is tracked before declaring it a target Constant false alarm rate (CFAR) and digital terrain model (DTM) processing are also used in clutter environments. Constant false alarm rate (CFAR detection refers to a common form of adaptive algorithm used in Radar systems to detect target returns against a background of noise A digital elevation model ( DEM) is a Digital representation of ground Surface Topography or Terrain.

Plot And Track Extraction

Radar video returns on 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. A sequence of plots can then be monitored and a 'track' formed, thus easing the identification of a genuine aircraft target through unwanted and non relevant radar returns.

Radar engineering

Radar components
Radar components

A radar has different components:

Antenna design

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 omni-directional broadcast antennas, with directional receiver antennas which were pointed in various directions. An omnidirectional antenna is an antenna system which radiates power uniformly in one plane with a directive pattern shape in a perpendicular plane For instance the first system to be deployed, Chain Home, used two straight antennas at right angles for reception, each on a different display. Chain Home was the codename for the ring of coastal Radar stations built by the British before and during World War II. In Geometry and Trigonometry, a right angle is an angle of 90 degrees corresponding to a quarter turn (that is a quarter of a full circle 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 shows a minimum. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation

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. In Physics, an inverse-square law is any Physical law stating that some physical Quantity or strength is inversely proportional To get a reasonable amount of power on the "target", the transmitting aerial should also be directional.

Parabolic reflector

More modern systems use a steerable parabolic "dish" to create a tight broadcast beam, typically using the same dish as the receiver. In Mathematics, the parabola (pəˈræbələ from the Greek παραβολή) is a Conic section, the intersection of a right circular 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 symetric parabolas or spoiled parabolas:

Types of scan

  1. Primary Scan: A scanning technique where the main antenna aerial is moved to produce a scanning beam, examples include circular scan, sector scan etc
  2. Secondary Scan: A scanning technique where the antenna feed is moved to produce a scanning beam, example include conical scan, unidirectional sector scan, lobe switching etc.
  3. 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.
Phased array: Not all radar antennas must rotate to scan the sky.
Phased array: Not all radar antennas must rotate to scan the sky. This article is about general theory and electromagnetic phased array

Slotted waveguide

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. slotted waveguide is a Waveguide that is used as an antenna in microwave Radar applications Owing to lower cost and less wind exposure, shipboard, airport surface, and harbour surveillance radars now use this in preference to the parabolic antenna.

Phased array

Main article: Phased array

Another method of steering is used in a phased array radar. This article is about general theory and electromagnetic phased array This uses an array of similar aerials suitably spaced, the phase of the signal to each individual aerial being controlled so that the signal is reinforced in the desired direction and cancels in other directions. In Computer science an array is a Data structure consisting of a group of elements that are accessed by indexing. If the individual aerials are in one plane and the signal is fed to each aerial in phase with all others then the signal will reinforce in a direction perpendicular to that plane. By altering the relative phase of the signal fed to each aerial the direction of the beam can be moved because the direction of constructive interference will move. Because phased array radars require no physical movement the beam can scan at thousands of degrees per second, fast enough to irradiate and track many individual targets, and still run a wide-ranging search periodically. In Physics, motion means a constant change in the location of a body By simply turning some of the antennas on or off, the beam can be spread for searching, narrowed for tracking, or even split into two or more virtual radars. However, the beam cannot be effectively steered at small angles to the plane of the array, so for full coverage multiple arrays are required, typically disposed on the faces of a triangular pyramid (see picture).

Phased array radars have been in use since the earliest years of radar use in World War II, but limitations of the electronics led to fairly poor accuracy. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including Phased array radars were originally used for missile defense. A missile (see also pronunciation differences) is a self-propelled explosive Projectile used as a weapon towards a target Defence They are the heart of the ship-borne Aegis combat system, and the Patriot Missile System, and are increasingly used in other areas because the lack of moving parts makes them more reliable, and sometimes permits a much larger effective antenna, useful in fighter aircraft applications that offer only confined space for mechanical scanning. The Aegis combat system is an integrated weapons system used by the United States Navy. The MIM-104 Patriot is a Surface-to-air missile (SAM system the primary of its kind used by the United States Army and several allied nations

As the price of electronics has fallen, phased array radars have become more and more common. Almost all modern military radar systems are based on phased arrays, where the small additional cost is far 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 also valued for use in aircraft, since they can track multiple targets. The first aircraft to use a phased array radar is the B-1B Lancer. The first aircraft fighter to use phased array radar was the Mikoyan MiG-31. For the fictional aircraft of the novel and movie "Firefox", see Mikoyan MiG-31 (fictional. The MiG-31M's SBI-16 Zaslon phased array radar is considered to be the world's most powerful fighter radar [2]. For the fictional aircraft of the novel and movie "Firefox", see Mikoyan MiG-31 (fictional. Phased-array interferometry or, aperture synthesis techniques, using an array of separate dishes that are phased into a single effective aperture, are not typically used for radar applications, although they are widely used in radio astronomy. Interferometry is the technique of using the pattern of Interference created by the superposition of two or more Waves to diagnose the properties of Radio astronomy is a subfield of Astronomy that studies celestial objects at radio frequencies. Because of the Thinned array curse, such arrays of multiple apertures, when used in transmitters, result in narrow beams at the expense of reducing the total power transmitted to the target. The thinned array curse (sometimes sparse array curse) is a theorem in electromagnetic theory of Transmitters It states that a transmitting aperture In principle, such techniques used could increase the spatial resolution, but the lower power means that this is generally not effective. Aperture synthesis by post-processing of motion data from a single moving source, on the other hand, is widely used in space and airborne radar systems (see Synthetic aperture radar). Synthetic-aperture radar (SAR is a form of Radar in which the highly-directional (and thus very large rotating antenna used by conventional radar is replaced with many low-directivity

Frequency bands

The traditional band names originated as code-names during World War II and are still in military and aviation use throughout the world in the 21st century. World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including They have been adopted in the United States by the IEEE, and internationally by the ITU. The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization 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 (ECM) industries, have replaced the traditional military designations with their own systems. For the band see Broadcast (band Broadcasting is the distribution of audio and/or Video signals which transmit Electronic Countermeasures ( ECM') are a subsection of Electronic warfare which includes any sort of electrical or electronic device designed to trick

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'
P < 300 MHz 1 m+ 'P' for 'previous', applied retrospectively to early radar systems
VHF 50–330 MHz 0. High frequency (HF radio frequencies are between 3 and 30 MHz. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. The metre or meter is a unit of Length. It is the basic unit of Length in the Metric system and in the International Over-the-horizon radar, or OTH (sometimes also beyond the horizon, or BTH) is a design concept for Radar systems to allow them to detect targets Very high frequency (VHF is the Radio frequency range from 30 MHz to 300 MHz. 9–6 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'
S 2–4 GHz 7. The United States Air Force Ballistic Missile Early Warning System ( BMEWS) was the first operational Ballistic missile detection Radar. NATO L band The NATO L band is defined as the frequency band between 40 and 60  G[[Hertz Hz]] (5–7 The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth Air traffic control ( ATC) is a service provided by ground-based controllers who direct Aircraft on the ground and in the air Surveillance is the monitoring of Behavior. Systems surveillance is the process of monitoring the behavior of people objects or processes within systems for conformity The S band ranges from 2 to 4  GHz, crossing the (artificial boundary between UHF and SHF at 3 5–15 cm terminal air traffic control, long-range weather, marine radar; 'S' for 'short'
C 4–8 GHz 3. C band is a name given to certain portions of the Electromagnetic spectrum, as well as a range of Wavelengths of Light, used for communications 75–7. 5 cm Satellite transponders; a compromise (hence 'C') between X and S bands; weather
X 8–12 GHz 2. The X band is part of the Microwave region of the Electromagnetic spectrum. 5–3. 75 cm missile guidance, marine radar, weather, medium-resolution mapping and ground surveillance; in the USA the narrow range 10. A missile (see also pronunciation differences) is a self-propelled explosive Projectile used as a weapon towards a target The United States of America —commonly referred to as the 525 GHz ±25 MHz is used for airport radar. An airport is a location where Aircraft such as airplanes, Helicopters and blimps take off and land Named X band because the frequency was a secret during WW2.
Ku 12–18 GHz 1. The Ku band ( pronounced "kay-yoo") is a portion of the Electromagnetic spectrum in the Microwave range of frequencies 67–2. 5 cm high-resolution mapping, satellite altimetry; frequency just under K band (hence 'u')
K 18–27 GHz 1. NATO K band The NATO K band is defined as a frequency band between 20 and 40 GHz (7 11–1. 67 cm from German kurz, meaning 'short'; limited use due to absorption by water vapour, so Ku and Ka were used instead for surveillance. The German language (de ''Deutsch'') is a West Germanic language and one of the world's major languages. General properties of water vapor Evaporation/sublimation Whenever a water molecule leaves a surface it is said to have evaporated 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.
Ka 27–40 GHz 0. The Ka band (Pronounced "Kay-A Band" covers the frequencies of 26 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. Extremely high frequency is the highest Radio frequency band. 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.
Q 40–60 GHz 7. 5 mm – 5 mm Used for Military communication.
V 50–75 GHz 6. The V band (vee-band of the Electromagnetic spectrum ranges from 40 to 75 GHz 0–4 mm Very strongly absorbed by the atmosphere.
E 60–90 GHz 6. 0–3. 33 mm
W 75–110 GHz 2. The W band of the Microwave part of the Electromagnetic spectrum ranges from 75 to 111  GHz. 7 – 4. 0 mm used as a visual sensor for experimental autonomous vehicles, high-resolution meteorological observation, and imaging.

Radar modulators

Modulators, also called pulse forming networks or line (PFNs) act to provide the short pulses of power to the magnetron. In Telecommunications, modulation is the process of varying a periodic Waveform, i A Pulse Forming Network (PFN accumulates Electrical energy over a comparatively long time then releases the stored energy in the form of a relatively square pulse A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various This technology is known as Pulsed power. Pulsed power is the term used to describe the science and technology of accumulating Energy over a relatively long period of time and releasing it very quickly thus increasing In this way, the transmitted pulse of RF radiation is kept to a defined, and usually, very short duration. Modulators consist of a high voltage pulse generator formed from an HV supply, and a high voltage switch such as a thyratron. A thyratron is a type of Gas filled tube used as a high Energy electrical Switch and controlled Rectifier.

A klystron tube may also be used as a modulator because it is an amplifier, so it can be modulated by its low power input signal. A klystron is a specialized linear-beam Vacuum tube (evacuated electron tube

Radar coolant

Coolanol and PAO (poly-alpha olefin) are the two main coolants used to cool airborne radar equipment today. Coolanol is a Trade name for a series of Silicate Ester industrial Coolants It is manufactured by Exxon Mobil Corporation A polyolefin is a Polymer produced from a simple Olefin (also called an Alkene with the general formula CnH2n as a Monomer.

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. Pollution prevention (P2 describes activities that reduce the amount of pollution generated by a process whether it is consumer consumption driving or industrial production Because of this Coolanol is used less often today.

PAO is a synthetic lubricant composition is a blend of a polyol ester admixed with effective amounts of an antioxidant, yellow metal pacifier and rust inhibitors. Esters are a class of Chemical compounds and Functional groups Esters consist of an inorganic or organic Acid in which at least An antioxidant is a Molecule capable of slowing or preventing the oxidation of other molecules The polyol ester blend includes a major proportion of poly (neopentyl polyol) ester blend formed by reacting poly(pentaerythritol) partial esters with at least one C7 to C12 carboxylic acid mixed with an ester formed by reacting a polyol having at least two hydroxyl groups and at least one C8-C10 carboxylic acid. Pentaerythritol is the Organic compound with the formula C(CH2OH4 Carboxylic acids are Organic acids characterized by the presence of a Carboxyl group, which has the formula -C(=OOH usually written -COOH or -CO2H Preferably, the acids are linear and avoid those which can cause odours during use. Effective additives include secondary arylamine antioxidants, triazole derivative yellow metal pacifier and an amino acid derivative and substituted primary and secondary amine and/or diamine rust inhibitor. Triazole (Htrz refers to either one of a pair of Isomeric Chemical compounds with Molecular formula C2H3N3 having a five-membered In Chemistry, an amino acid is a Molecule containing both Amine and Carboxyl Functional groups In Biochemistry, this Amines are Organic compounds and Functional groups that contain a basic Nitrogen Atom with a Lone pair.

A synthetic coolant/lubricant composition, comprising an ester mixture of 50 to 80 weight percent of poly (neopentyl polyol) ester formed by reacting a poly (neopentyl polyol) partial ester and at least one linear monocarboxylic acid having from 6 to 12 carbon atoms, and 20 to 50 weight percent of a polyol ester formed by reacting a polyol having 5 to 8 carbon atoms and at least two hydroxyl groups with at least one linear monocarboxylic acid having from 7 to 12 carbon atoms, the weight percents based on the total weight of the composition.

Radar functions and roles

Surface search radar display commonly found on ships
Surface search radar display commonly found on ships

Detection and search radars

Threat radars

Missile guidance systems

Battlefield and reconnaissance radar

Military map marking symbol Radar as of NATO standard APP-6a
Military map marking symbol Radar as of NATO standard APP-6a

Air Traffic Control and navigation

Air traffic control radar at London Heathrow Airport
Air traffic control radar at London Heathrow Airport

Space and range instrumentation radar systems

Weather-sensing Radar systems

Storm front reflectivities on a Weather radar screen (NOAA)

Wind profiling radar


Radars for biological research

Through The Wall Radar Systems

Radar systems which operate using Ultra Wideband technology can sense a human behind walls. Note the term " fire control " may also refer to means of stopping a fire such as sprinkler systems A fire-control system Ultra-wideband (aka UWB, ultra-wide band, ultraband, etc is a radio technology that can be used at very low energy levels for short-range high-bandwidth This is possible since the reflective characteristics of humans are generally greater than those of the typical materials used in construction. However, since humans reflect far less radar energy than metal does, these systems require sophisticated technology to isolate human targets and moreover to process any sort of detailed image.

See also

Notes

  1. ^ Ronald Reagan Test Site on the Kwajalein atoll
  2. ^ a b Christian Hülsmeyer by Radar World
  3. ^ (German) Christian Hülsmeyer Biografie
  4. ^ Patent DE165546; Verfahren, um metallische Gegenstände mittels elektrischer Wellen einem Beobachter zu melden.
  5. ^ Verfahren zur Bestimmung der Entfernung von metallischen Gegenständen (Schiffen o. dgl.), deren Gegenwart durch das Verfahren nach Patent 16556 festgestellt wird.
  6. ^ GB patent 13170 Telemobiloscope
  7. ^ (German) 100. Jahre Radar Improve­ment in Hertzian-wave Projecting and Receiving Apparatus for Locating the Position of Distant Metal Objects in 100 years of radar a German publication
  8. ^ The Electrical Experimenter, 1917
  9. ^ Goebel, Greg (2007-01-01). A crossed-field amplifier (CFA is a specialized Vacuum tube, first introduced in the mid-1950s and frequently used as a Microwave Amplifier in very-high-power Amplitude monopulse direction finding refers to a common technique employed in radar systems to improve the accuracy with which the direction of arrival of a pulse can be estimated Bistatic Doppler shift is a specific example of the Doppler effect that is observed by a radar or sonar system with a separated transmitter and receiver Bistatic range refers to the basic measurement of range made by a Radar or Sonar system with separated transmitter and receiver Constant false alarm rate (CFAR detection refers to a common form of adaptive algorithm used in Radar systems to detect target returns against a background of noise Gallium arsenide ( GaAs) is a compound of two elements Gallium and Arsenic. A klystron is a specialized linear-beam Vacuum tube (evacuated electron tube This is a list of radars. A Radar is an electronic system used to detect range (determine the distance of and map various types of targets A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various Over-the-horizon radar, or OTH (sometimes also beyond the horizon, or BTH) is a design concept for Radar systems to allow them to detect targets Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. The Secrets of Radar Museum is a small museum located near Parkwood Hospital in London Ontario, Canada. LIDAR ( Li ght D etection a nd R anging is an optical remote sensing technology that measures properties of scattered light to find range and/or LORAN ( LO ng R ange A id to N avigation is a terrestrial Radio navigation system using Low frequency Radio transmitters Sonar (which started as an Acronym for sound navigation and ranging) is a technique that uses Sound propagation (usually underwater to navigate A traveling-wave tube (TWT is an electronic device used to amplify Radio frequency signals to high power usually in an electronic assembly known as a traveling-wave Radar has many different types and applications " Search radars " scan a wide area with pulses of short radio waves 3D radar provides for Radar coverage on three dimensions unlike the more common 2D radar. An Electronically Scanned Array (AESA also known as active Phased array Radar is a type of Radar whose Transmitter and A maritime Radar with Automatic Radar Plotting Aid (ARPA capability can create tracks using radar Contacts The system can calculate the tracked object's Bistatic radar is the name given to a Radar system which comprises a transmitter and receiver which are separated by a distance that is comparable to the expected target distance Continuous-wave radar system is a Radar system where a known stable frequency Continuous wave Radio energy is transmitted and then received from any reflecting A doppler radar is a Radar using the Doppler effect of the returned echoes from targets to measure their Radial velocity. Frequency Modulated Continuous-wave radar (FM-CW is a Radar system where a known stable frequency Continuous wave Radio energy is modulated by a triangular Traditional Radar sends directional pulses of Electromagnetic energy and detects the presence position and motion of an object (such as an Aircraft) by analyzing Incoherent scatter refers to a ground-based technique for studying the earth's Ionosphere. Millimeter-wave cloud radar is a Radar system designed to monitor Cloud structure with Wavelengths about ten times shorter than those used in conventional Monopulse radar is an adaptation of Conical scanning radar which sends additional information in the Radar signal in order to avoid problems caused by rapid changes Passive radar systems (also referred to as passive coherent location and passive covert radar) encompass a class of Radar systems that detect and track The planar array radar is a type of radar that uses a high-gain Planar array antenna. Precision approach radar (PAR is a type of Radar guidance system designed to provide lateral and vertical guidance to an aircraft pilot for landing until the missed Pulse-Doppler is a Radar system capable of not only detecting target location (bearing range and altitude but also measuring its radial velocity (range-rate A radar gun or speed gun is a small Doppler radar used to detect the speed of objects SCR-270 ( Signal Corps Radio model 270 was one of the first operational Early warning radars It was the U The X band is part of the Microwave region of the Electromagnetic spectrum. The H2S Radar was used in bombers of RAF Bomber Command. It was designed to identify targets on the ground for night and all-weather bombing Chain Home was the codename for the ring of coastal Radar stations built by the British before and during World War II. A Radar System that is said to be portable by a person or a groups of people Kwajalein Atoll ( Marshallese: Kuwajleen; kʷuwːɔ͡ɛt̪ʲl̪ʲɪn̪ʲ common English pronunciation ˈkwɑːʤəlɨ̞n often nicknamed Kwaj An atoll (pronounced /ˈætʌl/ is an island of Coral that encircles a Lagoon partially or completely The Electrical Experimenter ( was a technical science magazine that was published monthly Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. New Year See also New Year The Ancient Romans began their consular year on January 1st since 153 BC The Wizard War: WW2 & The Origins Of Radar, Chapter 1: The British Invention of Radar. Retrieved on 2007-03-24. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 1401 - Mongol emperor Timur sacks Damascus. 1603 - James VI of Scotland
  10. ^ FR patent 788795 Nouveau système de repérage d'obstacles et ses applications
  11. ^ a b (French) Copy of Patents for the invention of radar on www. radar-france. fr
  12. ^ British man first to patent radar official site of the Patent Office
  13. ^ GB patent 593017 Improvements in or relating to wireless systems
  14. ^ Example of WiFi equipment jamming meteorological radars.

References

Further reading

External links

Dictionary

radar

-noun

  1. (uncountable) A method of detecting distant objects and determining their position, velocity, or other characteristics by analysis of sent radio waves (usually microwaves) reflected from their surfaces
  2. (countable) A type of system using such method, differentiated by platform, configuration, frequency, power, and other technical attributes.
  3. (countable) An installation of such a system or of the transmitting and receiving apparatus.
  4. (countable) An superior ability to detect something.

-verb

  1. To scan with radar, or as if with radar.
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