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Radar is a detection system that uses radio waves to determine the distance (ranging), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the objects. Radio waves from the transmitter reflect off the objects and return to the receiver, giving information about the objects' locations and speeds.
A multistatic radar system contains multiple spatially diverse monostatic radar or bistatic radar components with a shared area of coverage. An important distinction of systems based on these individual radar geometries is the added requirement for some level of data fusion to take place between component parts. The spatial diversity afforded by multistatic systems allows different aspects of a target to be viewed simultaneously. The potential for information gain can give rise to a number of advantages over conventional systems.
Stealth technology, also termed low observable technology, is a sub-discipline of military tactics and passive and active electronic countermeasures, which covers a range of methods used to make personnel, aircraft, ships, submarines, missiles, satellites, and ground vehicles less visible to radar, infrared, sonar and other detection methods. It corresponds to military camouflage for these parts of the electromagnetic spectrum.
A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or particle accelerator having a continuous output, as opposed to a pulsed output.
Semi-active radar homing (SARH) is a common type of missile guidance system, perhaps the most common type for longer-range air-to-air and surface-to-air missile systems. The name refers to the fact that the missile itself is only a passive detector of a radar signal—provided by an external ("offboard") source—as it reflects off the target. Semi-active missile systems use bistatic continuous-wave radar.
The Mid-Canada Line (MCL), also known as the McGill Fence, was a line of radar stations running east–west across the middle of Canada, used to provide early warning of a Soviet bomber attack on North America. It was built to supplement the Pinetree Line, which was located farther south. The majority of Mid-Canada Line stations were used only briefly from the late 1950s to the mid-1960s, as the attack threat changed from bombers to ICBMs. As the MCL was closed down, the early warning role passed almost entirely to the newer and more capable DEW Line farther north.
The Kolchuga passive sensor is an electronic-warfare support measures system developed in the Soviet Union and manufactured in Ukraine. Its detection range is limited by line-of-sight but may be up to 800 km (500 mi) for very high altitude, very powerful emitters. Frequently referred to as Kolchuga Radar, the system is not really a radar, but an ESM system comprising three or four receivers, deployed tens of kilometres apart, which detect and track aircraft by triangulation and multilateration of their RF emissions.
Continuous-wave radar is a type of radar system where a known stable frequency continuous wave radio energy is transmitted and then received from any reflecting objects. Individual objects can be detected using the Doppler effect, which causes the received signal to have a different frequency from the transmitted signal, allowing it to be detected by filtering out the transmitted frequency.
Over-the-horizon radar (OTH), sometimes called beyond the horizon (BTH), is a type of radar system with the ability to detect targets at very long ranges, typically hundreds to thousands of kilometres, beyond the radar horizon, which is the distance limit for ordinary radar. Several OTH radar systems were deployed starting in the 1950s and 1960s as part of early warning radar systems, but these have generally been replaced by airborne early warning systems. OTH radars have recently been making a comeback, as the need for accurate long-range tracking becomes less important with the ending of the Cold War, and less-expensive ground-based radars are once again being considered for roles such as maritime reconnaissance and drug enforcement.
Passive radar systems encompass a class of radar systems that detect and track objects by processing reflections from non-cooperative sources of illumination in the environment, such as commercial broadcast and communications signals. It is a specific case of bistatic radar, the latter also including the exploitation of cooperative and non-cooperative radar transmitters.
GNSS reflectometry involves making measurements from the reflections from the Earth of navigation signals from Global Navigation Satellite Systems such as GPS. The idea of using reflected GNSS signal for earth observation became more and more popular in the mid-1990s at NASA Langley Research Center and is also known as GPS reflectometry. Research applications of GNSS-R are found in
Project Diana, named for the Roman moon goddess Diana, was an experimental project of the US Army Signal Corps in 1946 to bounce radar signals off the Moon and receive the reflected signals. This was the first experiment in radar astronomy and the first active attempt to probe another celestial body. It was the inspiration for later EME (Earth-Moon-Earth) communication techniques.
Bistatic radar is a radar system comprising a transmitter and receiver that are separated by a distance comparable to the expected target distance. Conversely, a conventional radar in which the transmitter and receiver are co-located is called a monostatic radar. A system containing multiple spatially diverse monostatic or bistatic radar components with a shared area of coverage is called multistatic radar. Many long-range air-to-air and surface-to-air missile systems use semi-active radar homing, which is a form of bistatic radar.
Radar engineering details are technical details pertaining to the components of a radar and their ability to detect the return energy from moving scatterers — determining an object's position or obstruction in the environment. This includes field of view in terms of solid angle and maximum unambiguous range and velocity, as well as angular, range and velocity resolution. Radar sensors are classified by application, architecture, radar mode, platform, and propagation window.
The Dish, also known as the Stanford Dish, is a radio antenna in the Stanford foothills. The 150-foot-diameter (46 m) dish was built in 1961 by the Stanford Research Institute. The cost to construct the antenna was $4.5 million, and was funded by the United States Air Force. In the 1960s the Dish was used to provide information on Soviet radar installations by detecting radio signals bounced off the moon.
Bistatic sonar is a sonar configuration in which transmitter and receiver are separated by a distance large enough to be comparable to the distance to the target. Most sonar systems are monostatic, in that the transmitter and receiver are located in the same place. A configuration with multiple receivers is called multistatic.
The Motorola AN/FPS-23 was a short-range early warning radar deployed on the Distant Early Warning Line. It was used as a "gap filler", looking for aircraft attempting to sneak by the DEW line by flying between the main AN/FPS-19 stations at low altitude. It could detect aircraft flying at 200 feet over land or 50 feet over water. The system was known as Fluttar during its development at the Lincoln Laboratory, and this name was widely used for the production units as well. It was also sometimes known as "Type F".
Laus was the name for a series of German ECCM equipment during World War II. They were additions to German radar equipment in order to counteract the Allied use of 'Window', a chaff radar countermeasure.
Klein Heidelberg (KH) was a passive radar system deployed by the Germans during World War II. It used the signals broadcast by the British Chain Home system as its transmitter, and a series of six stations along the western coast of continental Europe as passive receivers. In modern terminology, the system was a bistatic radar. Because the system sent no signals of its own, the allies were unaware of its presence, and did not learn of the system until well after the D-Day invasion. The system is referred to as Klein Heidelberg Parasit in some references.
Radar angels are an effect seen on radar displays when there is a periodic structure in the view of the radar that is roughly the same length as the signal's wavelength. The angel appears to be a physically huge object on the display, often miles across, that can obscure real targets. These were first noticed in the 1940s and were a topic of considerable study in the 1950s. The underlying mechanism is due to Bragg's law.
References
- ↑ Willis, Nicholas J.; Griffiths, Hugh (2007). Advances in Bistatic Radar. SciTech Publishing. pp. 54–55. ISBN 9781891121487.
- ↑ Chong Sze Sing, 2014. Thesis submitted to the Naval Postgraduate School, Monterey, CA. "Passive multistatic detection of maritime targets using opportunistic radar".
- ↑ Willis, N & Griffiths, H (eds), Advances in Bistatic Radar, SciTech Publishing, Raleigh, NC 2007, cited in Willis & Griffiths " Klein Heidelberg – a WW2 bistatic radar system that was decades ahead of its time". http://www.cdvandt.org/K-H%20final.pdf
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