MTI Radar adaptable to different environmental conditions

Claim 1

In a radar having antenna means for the emission of outgoing pulses of different carrier frequencies on a radar beam of predetermined effective width and for the reception of echoes thereof reflected by outlying targets during a range sweep initiated by any outgoing pulse, frequency-generating and pulse-forming means provided with a timer operable to randomly select any one of a predetermined number of available carrier frequencies for emission at any sweep, transmitting means inserted between said pulse-forming means and said antenna means, receiving means connected to said antenna means, and gating means controlled by the timer for sampling incoming echoes, the combination therewith of: memory means connected to said gating means for storing samples of echoes incoming during each sweep for n consecutive sweeps at locations whose relationship with the carrier frequencies of the respective echoes is memorized by said timer, the number j of available carrier frequencies being less than the number n of outgoing pulses accommodated within the width of the radar beam whereby at least some carrier frequencies randomly recur during any scan of a target, with no carrier frequency occurring more than m<n times during n successive sweeps, said frequency-generating means maintaining phase coherence of each carrier frequency for at least said n sweeps; multiplexer means connected to said memory means and controlled by said timer for concurrently reading out, in the course of each sweep, up to m correlated samples of echoes of identical carrier frequency stored during n preceding sweeps; and m-weight Doppler-filter means connected to said multiplexer means for evaluating the correlated samples concurrently read out from said memory means to distinguish moving targets from clutter.