THE INTRODUCION TO RADAR SYSTEMS
The active radars are those radars which are traditional radar that uses a transmitter, which radiates a (usually) narrow beam of radio waves, and a receiver, which detects the reflected signal.While passive radars areradar system which uses one (or more) receiver(s), but which has no active transmitter. The system detects ambient radio signals, emanating from nearby radio transmitters. Potential sources of electromagnetic radiation that can be exploited by a passive radar system include*Commercial radio and television signals,
*Signals from cell telephone towers,
*Sources from space-borne platforms, and others.
Passive radar systems also referred to as passive coherent location and passive covert radar comprises 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. In a passive radar system, there is no dedicated transmitter. Instead, the receiver uses third-party transmitters in the environment, and measures the time difference of arrival between the signal arriving directly from the transmitter and the signal arriving via reflection from the object. This allows the bistatic range of the object to be determined. In addition to bistatic range, a passive radar will typically also measure the bistatic Doppler shift of the echo and also its direction of arrival. These allow the location, heading and speed of the object to be calculated.
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