Continuously transmitting and receiving radar

Abstract

A continuously transmitting and receiving radar comprises a transmitter (10), a receiver (16), an antenna (12) and a circulator (14) for effecting communication between the transmitter and the antenna and between the antenna and the receiver. A reflected power canceller is provided for suppressing the effects of leakage between the transmitter and receiver. The reflected power canceller comprises a directional coupler (20) for supplying a part of the transmitted signal to a modulator (22) which forms a cancelling signal by adjusting the phase and amplitude of the sampled signal. The cancelling signal is applied to another directional coupler (24) which subtracts the cancelling signal from the leakage and wanted signals. A narrowband control path is connected between the output of the receiver (16) and the modulator (22). The reduction in carrier leakage and AM noise sidebands is made more effective by providing a time delay device (21) in the signal path from the coupler (20) to the modulator (22). The time delay introduced by the device (21) is set so that the propagation times between the transmitter (10) and the directional coupler (24) via the circulator (14) and via the modulator (22) are the same. Optionally FM noise can be reduced by ensuring the propagation time of the local oscillator signal applied to a mixer in the receiver (16) is the same as that of the leakage path between the transmitter and receiver.