Adaptive mtd digital processor for surveillance radar

Abstract

A digital MTD processor interposed between a coherent video detector and a signal extractor of a surveillance radar comprises a plurality of Doppler filters connected in parallel to the video-detector output, including a zero filter, working into respective modulus extractors connected by way of respective threshold circuits to a common OR gate. Each threshold circuit includes a fixed-threshold comparator and an adaptive-threshold comparator with inputs connected in parallel to the output of the associated modulus extractor, either of these comparators being connectable to the OR gate via a switch controlled with the aid of a rain-clutter map so that the adaptive threshold is used only during exploration of regions with heavy rain. A ground-clutter map, which can be updated on the basis of level measurements performed on the output of the zero filter, controls the selective loading of each Doppler filter with one of three preselected sets of weights depending on the intensity of the ground clutter in the region being explored. Where ground clutter is heavy, the threshold circuit of the zero filter may be cut off from the OR gate. Both the fixed and the adaptive thresholds can be incremented in response to a command from the signal extractor generated upon the occurrence of an excessive number of false alarms.