Echo ranging system for detecting velocity of targets using composite

Abstract

Target velocity and range are measured with high resolution in an echo ranging system (sonar or radar) using composite Doppler invariant signals consisting of at least two segments, such as 'rooftop' or 'vee' HFM signals, such composite signals having ambiguity functions that intersect along the zero-velocity time axis with ridge lines slanted in different directions. A single correlator is used for each segment wherein returns from the target are correlated with replicas of each segment of the composite signal to separately transform the Doppler frequency shifts of the target return into outputs whose time relationship provides a frame of reference for high resolution measurement of the velocity of the target. The time relationship measurement is implemented by a set of tapped delay lines and coherent summers which output a coherent correlation-like detection peak in a bin which corresponds to the target's velocity. Thus, one correlator for each transmission segment together with a tapped delay line and summer network may be used for velocity detection, with high precision range detection, based upon the timing of the detection peak with respect to the transmitted signal, also being implemented at the same time, thereby avoiding the classical need for an expensive bank of correlators (one for each velocity bin) and yielding significant economies for the simultaneous high resolution measurement of range and velocity for a target by means of echo ranging.