The Delay-Lock Discriminator-An Optimum Tracking Device

The delay-lock discriminator described in this paper is a statistically optimum device for the measurement of the delay between two correlated waveforms. This new device seems to have important potential in tracking targets and measuring distance, depth, or altitude. It operates by comparing the transmitted and reflected versions of a wide-bandwidth, random signal. The discriminator is superior to FM radars in that it can operate at lower power levels; it avoids the so-called "fixed error," and it is free of much of the ambiguity inherent in such periodically modulated systems. It can also operate as a tracking interferometer. The discriminator is a nonlinear feedback system and can be thought of as employing a form of cross-correlation along with feedback. The basic theory of operation is presented, and a comparison is made with the phase-lock FM discriminator. Variations of performance with respect to signal spectrum choice, target velocity, and signal and interference power levels are discussed quantitatively. The nonlinear, "lock-on" transient and the threshold behavior of the discriminator are described. Performance relations are given for tracking both passive and actively transmitting targets. Results of some experimental measurements made on a laboratory version of the discriminator are presented.