Radar is an object-detection system that uses to determine the range, angle, or velocity of objects. It can be used to detect,,,,,, and.

A radar system consists of a producing in the or domain, a transmitting, a receiving antenna (often the same antenna is used for transmitting and receiving) and a and 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. A key development was the in the UK, which allowed the creation of relatively small systems with sub-meter resolution. The term RADAR was coined in 1940 by the as an for RAdio Detection And Ranging or RAdio Direction And Ranging.

The term radar has since entered and other languages as a common noun,. The modern uses of radar are highly diverse, including air and terrestrial traffic control,,,, to locate landmarks and other ships, aircraft anticollision systems, systems, outer space surveillance and systems, precipitation monitoring, altimetry and, target locating systems, for geological observations, and range-controlled radar for. High tech radar systems are associated with, and are capable of extracting useful information from very high levels. Other systems similar to radar make use of other parts of the. One example is ', which uses predominantly from rather than radio waves.

Main article: First experiments [ ] As early as 1886, German physicist showed that radio waves could be reflected from solid objects. In 1895,, a physics instructor at the school in, developed an apparatus using a tube for detecting distant lightning strikes. The next year, he added a. In 1897, while testing this equipment for communicating between two ships in the, he took note of an 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. Download Video Dragon Ball Z Sub Indo Mp4.

The principles of engineering materials /​ [by] Craig R. Barrett, William D. Nix [and] Alan S. Barrett, Craig R., 1939. Other Authors. Nix, William D. [Englewood Cliffs, N.J.]: [Prentice-Hall], [[1973]. Content Types. Carrier Types. Physical Description. Xiv, 554 pages.

The German inventor 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.

He obtained a patent for his detection device in April 1904 and later a patent for a related amendment for estimating the distance to the ship. He also got a British patent on September 23, 1904 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 and harbour but was rejected. In 1915, used radio technology to provide advance warning to airmen 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 and the detection of at long distances. Through his lightning experiments, Watson-Watt became an expert on the use of before turning his inquiry to transmission. Requiring a suitable receiver for such studies, he told the 'new boy' to conduct an extensive review of available shortwave units. Wilkins would select a 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, U.S. Navy researchers and 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, at the (NRL) observed similar fading effects from passing aircraft; this revelation led to a patent application 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.

Just before World War II [ ]. Experimental radar antenna, US, Anacostia, D. C., late 1930s Before the, researchers in the,,,,, the, the, and the, independently and in great secrecy, developed technologies that led to the modern version of radar.,,, and followed prewar Great Britain's radar development, and generated its radar technology during the war. In France in 1934, following systematic studies on the, the research branch of the (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 in 1935. During the same period, Soviet military engineer, in collaboration with, produced an experimental apparatus, RAPID, capable of detecting an aircraft within 3 km of a receiver. 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 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 fighters.

More than 230 Gneiss-2 stations were produced by the end of 1944. 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, working at the. The following year, the successfully tested a primitive surface-to-surface radar to aim at night.

This design was followed by a pulsed system demonstrated in May 1935 by and the firm in Germany and then another in June 1935 by an team led by in Great Britain. Memorial plaque commemorating Robert Watson-Watt and In 1935, Watson-Watt was asked to judge recent reports of a German radio-based 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 of 26 February 1935, using a powerful 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,, the was very impressed with their system's potential and funds were immediately provided for further operational development. Watson-Watt's team patented the device in GB593017.

Development of radar greatly expanded on 1 September 1936 when Watson-Watt became Superintendent of a new establishment under the British, Bawdsey Research Station located in, near Felixstowe, Suffolk. Work there resulted in the design and installation of aircraft detection and tracking stations called ' 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; 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 ' of reporting and coordination to make best use of the radar information during tests of early 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 (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 [ ]. Main article: A key development was the 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.

In April 1940, showed an example of a radar unit using the Watson-Watt patent in an article on air defence. 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. Watson-Watt was sent to the U.S. In 1941 to advise on air defense after Japan’s.

Organized the at Cambridge, Massachusetts which developed the technology in the years 1941–45. Later, in 1943, Page greatly improved radar with the that was used for many years in most radar applications. The war precipitated research to find better resolution, more portability, and more features for radar, including complementary navigation systems like used by the. Applications [ ]. 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, 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 aircraft.

Aircraft can land in fog at airports equipped with radar-assisted 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.

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, radar systems are used to monitor and regulate ship movements in busy waters. Meteorologists use radar to monitor and wind. It has become the primary tool for short-term and watching for such as,,, precipitation types, etc.

Use specialized to map the composition of. Police forces use to monitor vehicle speeds on the roads.

Smaller radar systems are used to. Examples are breathing pattern detection for sleep monitoring and hand and finger gesture detection for computer interaction.

Automatic door opening, light activation and intruder sensing are also common. Principles [ ] Radar signal [ ]. Further information: A radar system has a that emits called radar signals in predetermined directions. When these come into contact with an object they are usually or 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 —especially by most metals, by and by wet ground.

Some of these make the use of 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 of the radio waves, caused by the. 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.

More sophisticated methods of 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,, and, 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 [ ] Radar relies on its own transmissions rather than light from the or the, or from 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 [ ]. Further information: In all, the electric field is perpendicular to the direction of propagation, and the electric field direction is the 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, is used to minimize the interference caused by rain. Returns usually indicate metal surfaces. Random polarization returns usually indicate a surface, such as rocks or soil, and are used by navigation radars. Limiting factors [ ] Beam path and range [ ].

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 of air, that is called the. Even when the beam is emitted parallel to the ground, it will rise above it as the 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.

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.

Main article: 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 (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. Main article: 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, (such as rain, snow or hail),, animals (especially birds), atmospheric, and other atmospheric effects, such as reflections, trails, and.

Clutter may also be returned from man-made objects such as buildings and, intentionally, by radar countermeasures such as. Some clutter may also be caused by a long radar between the radar transceiver and the antenna. In a typical (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 (note that meteorological radars wish for the opposite effect, and therefore use 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 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. Doppler separates clutter from aircraft and spacecraft using a, 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 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., a form of (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 from a target cause ghosts to appear. Clutter may also originate from multipath echoes from valid targets caused by ground reflection, or / (e.g., ). 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 or a physical impossibility.

Terrain bounce jamming exploits this response by amplifying the radar signal and directing it downward. 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. Main article: 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 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 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 ( sidelobe jamming).

Mainlobe jamming can generally only be reduced by narrowing the mainlobe 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 to detect and disregard non-mainlobe signals. Radar signal processing [ ] Distance measurement [ ] Transit time [ ]. Continuous wave (CW) radar One way to obtain a is based on the: 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, 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 and the characteristics of the received signal as compared to noise depends on the shape of the pulse. The pulse is often to achieve better performance using a technique known 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, 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 [ ]. Main article: 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 and is often found in aircraft. In these systems a 'carrier' radar signal is frequency modulated in a predictable way, typically varying up and down with a 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 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 travelled. That distance can be displayed on an instrument, and it may also be available via the. This signal processing is similar to that used in speed detecting Doppler radar.

Example systems using this approach are,, and. 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 [ ] 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 marks on the radar screen and then calculating the speed using a. 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.

Most modern radar systems use this principle into and systems (, 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 over time. It is possible to make a Doppler radar without any pulsing, known as a (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 (Weyl Heisenberg or ), as well as the which makes use of the change of frequency of returns from moving targets ('chirp'). 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 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 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. 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 ' capability required to improve military air combat survivability. Pulse-Doppler is also used for ground based surveillance radar required to defend personnel and vehicles.

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 flying techniques and 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 which prevents range from being determined directly, and 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. Reduction of interference effects [ ] is employed in radar systems to reduce the. Signal processing techniques include,, moving target detection processors, correlation with targets,, and.

And processing are also used in clutter environments. Plot and track extraction [ ]. Main article: 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. • • • 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 is used to associate the sequence of plots belonging to individual targets and estimate the targets' headings and speeds. Engineering [ ]. Radar components A radar's components are: • A that generates the radio signal with an oscillator such as a or a and controls its duration by a. • A that links the transmitter and the antenna. • A 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.

Knowing the shape of the desired received signal (a pulse), an optimal receiver can be designed using a. • A display processor to produce signals for human readable. • 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 [ ].

Main article: 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, 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 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 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 of that transmitted. To get a reasonable amount of power on the 'target', the transmitting aerial should also be directional. Parabolic reflector [ ].

Main article: More modern systems use a steerable '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 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 [ ] • 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. •: The radar beam is rotated in a small circle around the 'boresight' axis, which is pointed at the target. Slotted waveguide [ ].

Main article: Another method of steering is used in a 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.

The amount of cancellation is side-lobe suppression. 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 defence (see for example ). They are the heart of the ship-borne and the. 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. 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.

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. The first fighter aircraft to use phased array radar was the.

The MiG-31M's SBI-16 radar was considered to be the world's most powerful fighter radar, until the was introduced on the. Phased-array or 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.

Because of the, 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. By post-processing motion data from a single moving source, on the other hand, is widely used in space and. Frequency bands [ ]. Main article: The 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 and internationally by the. 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 and industries, have replaced the traditional military designations with their own systems. Radar frequency bands Band name Frequency range Wavelength range Notes 3–30 10–100 Coastal radar systems, (OTH) radars; 'high frequency' 30–300 MHz 1–10 m Very long range, ground penetrating; 'very high frequency' P 1 m 'P' for 'previous', applied retrospectively to early radar systems; essentially HF + VHF 300–1000 MHz 0.3–1 m Very long range (e.g. ), ground penetrating, foliage penetrating; 'ultra high frequency' 1–2 15–30 Long range air traffic control and; 'L' for 'long' 2–4 GHz 7.5–15 cm Moderate range surveillance, Terminal air traffic control, long-range weather, marine radar; 'S' for 'short' 4–8 GHz 3.75–7.5 cm Satellite transponders; a compromise (hence 'C') between X and S bands; weather; long range tracking 8–12 GHz 2.5–3.75 cm guidance,, weather, medium-resolution mapping and ground surveillance; in the United States the narrow range 10.525 GHz ±25 MHz is used for radar; short range tracking. Named X band because the frequency was a secret during WW2. 12–18 GHz 1.67–2.5 cm High-resolution, also used for satellite transponders, frequency under K band (hence 'u') 18–24 GHz 1.11–1.67 cm From kurz, meaning 'short'; limited use due to absorption by, 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.

24–40 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, 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. 40–75 GHz 4.0–7.5 mm Very strongly absorbed by atmospheric oxygen, which resonates at 60 GHz. 75–110 GHz 2.7–4.0 mm Used as a visual sensor for experimental autonomous vehicles, high-resolution meteorological observation, and imaging.

Radar 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 These modulators consist of a high voltage pulse generator formed from a high voltage supply, a, and a high voltage switch such as a.

They generate short pulses of power to feed, e.g. Techsatish Sun Tv Serials Nadhaswaram on this page. , the, a special type of vacuum tube that converts DC (usually pulsed) into microwaves. This technology is known as. In this way, the transmitted pulse of RF radiation is kept to a defined and usually very short duration. • Hybrid mixers, fed by a waveform generator and an exciter for a complex but 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 or a solid state transmitter. In this way, the transmitted pulse is intrapulse-modulated and the radar receiver must use techniques. Radar coolant [ ]. Main article: Coherent microwave amplifiers operating above 1,000 watts microwave output, like and, 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. ( ) was used in several military radars in the 1970s. However, it is, leading to and formation of highly flammable alcohol. The loss of a U.S. Navy aircraft in 1978 was attributed to a silicate ester fire. Coolanol is also expensive and toxic.

Navy has instituted a program named (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 [ ] Radar (also: RADAR) is defined by article 1.100 of the (ITU) (RR) as: A 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 and, these might operate in the or the. See also [ ].