Poly-frequency cw doppler radar system with leakage cancellation and

Abstract

A single antenna poly-frequency Continuous Wave (CW) Doppler radar system having leakage cancellation. The system provides for transmitting a plurality of carrier frequency signals and receiving the return signals by means of a single antenna coupled to an antenna interface through which a portion of the transmitted signal may leak. The signal appearing on an output port of the antenna interface is then down-converted to an intermediate frequency (IF) signal by a stable mixing signal. The IF signal is coupled to an adder which in turn is coupled to an output. The IF signal is further split into a pair of cancellation loops for each carrier frequency signal. Each cancellation loop includes a correlator and provides for processing the IF signal with an in-phase or a quadrature-phase signal associated with the carrier frequency signal so that each pair of cancellation loops outputs a feedback signal representative of and equal to the amplitude of the leakage signal only, which feedback signal then being subtracted from the IF signal with the resultant return signal less the leakage signal then being transmitted for further processing. Preferably, a second order linear feedback circuit and phase compensation circuit is provided in each cancellation loop for processing of the IF signal. The disclosed system does not require high precision, high cost oscillators and has particular application in military radars, navigation radars and vehicular collision warning radars.