Pulse compression radar

A bi-phase decoder comprising two phase-shift detectors each operative to measure the phase difference between each sub-pulse in a received bi-phase code relative to a respective one of two signals in phase quadrature with one another;

• two sampling circuits each operative to sample periodically the output of a respective one of the phase-shift detectors and to produce a first signal representative of the magnitude of the sampled output and a further signal representative of the sign of the sampled output;
• a combiner for combining the magnitude signals generated by the sampling circuit in such a manner as to render the sensitivity of the decoder substantially independent of the phase of the received code and an autocorrelator connected to receive the output signal of the combiner and the sign signal from one of the sampling circuits and to autocorrelate the signal from successive sub-pulses to effect pulse compression;
• the decoder further including signal modifying means for correcting errors in the sign signal derived from one of the sampling circuits resulting from Doppler shifting of the carrier frequency of the received bi-phase code, the signal modifying means being operative to detect such errors by detecting changes in the product of the sign signals derived from the separate sampling circuits at times when the value of the magnitude signal derived from a predetermined one of the sampling circuits is greater than the value of the magnitude signal derived from the other.