Method of tracking target in presence of clutter

Claim 1

In the operation of a pulse Doppler radar responsive to clutter and a target wherein a frequency tracking loop is incorporated, such loop including an oscillator operating at an adjustable frequency to provide a frequency tracking capability whereby only target return signals are tracked, the method of generating a control signal for the oscillator, such method comprising the steps of: (a) forming, from all signal returns received during a predetermined period of time, a range/Doppler matrix having N×M cells, where N equals the number of range bins and M equals the number of Doppler bins at each range, a digital one in any one of the cells indicating a return signal and a digital zero indicating absence of a return signal; (b) sequentially reading, in accordance with a predetermined program, the content of each one of the cells successively to form digital numbers from 4 M sequentially read cells, each digit in each one of such digital numbers being indicative of the presence, or absence, of reutrn signals in four successive range bins; (c) comparing each five successively formed digits with a five digit reference digital number having a digital one as the center digit and a digital zero as the first and fifth digits to produce a gating signal only when the first, center and fifth of five successively formed digits in the successively formed digital numbers correspond with the five digit reference digital number; (d) generating, in synchronism with each successively formed digital number, a frequency control signal representative of the Doppler frequency of a selected cell; and (e) passing the frequency control signal extant with the gating signal to the oscillator to control the frequency thereof.