Comparison between linear FM and phase-coded CW radars

Abstract

The classical linear FM CW radar signal is compared with P3 and P4 phase-coded CW signals. The comparison covers the theoretical delay-Doppler response, the spectrum and the performances in digital receiver processors. The receivers produce a matrix of delay and Doppler cells. Three receiver approaches are considered: (a) Doppler compensation followed by a multicorrelation processor. This is a general and efficient implementation of many matched filters, which applies to any phase-coded signal. (b) A modification of (a), applicable to P3, P4 signals, in which the multicorrelators are efficiently replaced by FFTs, without altering the performances. (c) A single correlator followed by two levels of spectral analysis, for range and for Doppler. In the two matched filter implementations, (a) and (b), the P signals exhibit lower range sidelobes, due to their inherent property of perfect periodic autocorrelation. The LFM signal requires additional weighting (hence additional SNR loss) and even then does not approach the low range sidelobes of P signals. In the single correlator receiver, the two signals exhibit almost identical performances, which are similar to the performances of LFM in the matched receiver.