Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. A radar system consists of a transmitter producing electromagnetic waves in the radio or microwaves domain, a transmitting antenna, a receiving antenna and a receiver and processor to determine properties of the object(s). Radio waves from the transmitter reflect off the object and return to the receiver, giving information about the object's location and speed.
A Doppler radar is a specialized radar that uses the Doppler effect to produce velocity data about objects at a distance. It does this by bouncing a microwave signal off a desired target and analyzing how the object's motion has altered the frequency of the returned signal. This variation gives direct and highly accurate measurements of the radial component of a target's velocity relative to the radar. Doppler radars are used in aviation, sounding satellites, Major League Baseball's StatCast system, meteorology, radar guns, radiology and healthcare, and bistatic radar.
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.
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. Continuous wave is also the name given to an early method of radio transmission, in which a sinusoidal carrier wave is switched on and off. Information is carried in the varying duration of the on and off periods of the signal, for example by Morse code in early radio. In early wireless telegraphy radio transmission, CW waves were also known as "undamped waves", to distinguish this method from damped wave signals produced by earlier spark gap type transmitters.
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 less-advanced Pinetree Line, which was located further 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 more capable DEW Line further north.
Radar cross-section (RCS) is a measure of how detectable an object is by radar. Therefore, it is called electromagnetic signature of the object. A larger RCS indicates that an object is more easily detected.
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 are detected using the Doppler effect, which causes the received signal to have a different frequency than the transmission, allowing it to be detected by filtering out the transmitted frequency.
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.
The Medicina Radio Observatory is an astronomical observatory located 30 km from Bologna, Italy. It is operated by the Institute for Radio Astronomy of the National Institute for Astrophysics (INAF) of the government of Italy.
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. The Doppler shift is due to the component of motion of the object in the direction of the transmitter, plus the component of motion of the object in the direction of the receiver. Equivalently, it can be considered as proportional to the rate of change of bistatic range.
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 radar in which the transmitter and receiver are collocated is called a monostatic radar. A system containing multiple spatially diverse monostatic radar 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.
The bistatic angle is the angle subtended between the transmitter, target and receiver in a bistatic radar. When it is exactly zero the radar is a monostatic radar, when it is close to zero the radar is pseudo-monostatic, and when it is close to 180 degrees the radar is a forward scatter radar. Elsewhere, the radar is simply described as a bistatic radar. The bistatic angle is an important factor in determining the radar cross section of the target.
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.
Radar MASINT is a subdiscipline of measurement and signature intelligence (MASINT) and refers to intelligence gathering activities that bring together disparate elements that do not fit within the definitions of signals intelligence (SIGINT), imagery intelligence (IMINT), or human intelligence (HUMINT).
Most sonar systems are monostatic, in that the transmitter and receiver are in the same place. Bistatic sonar describes when the transmitter and receiver(s) are separated by a distance large enough to be comparable to the distance to the target.
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".
Sugar Tree is the name of a bistatic radar Over-the-horizon radar built by the US in the 1960s. The key idea in Sugar Tree was a reinvention of Klein Heidelberg Nazi German radar system developed for use in the Second World War. Sugar Tree was a "covert hitchhiker using Soviet, surface-wave HF radio broadcast signals and a remote sky-wave receiver to detect Soviet ballistic missile launches". The key idea, in other words, is to receive radar reflexions without oneself transmitting a radar signal by using instead some other signal, typically one that originates from the adversary.
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.
