Statistics of Clutter Residue in MTI Radars with IF Limiting

Abstract

In an MTI (moving target indicator) radar, when the received signal from clutter exceeds the IF (intermediate frequency) dynamic range, i.e., limits in the IF bandpass limiter, the radar literature states that good MTI performance cannot be achieved. Close examination of clutter sequences shows that when the dynamic range of the radar is exceeded, occasional large spikes of clutter residue do occur but good clutter rejection is obtained in most of the clutter cells. This paper provides insight into the cause of the spikes of clutter residue and presents the statistics of the residue for two-pulse, three-pulse, and four-pulse MTI filters. The percentage of clutter-limited cells with good MTI performance supports the conclusion that most of the clutter-limited cells do exhibit good MTI performance. The infrequent residue spikes have a distinct pattern at the output of the clutter filter that is markedly different from targets. With the insight of the time domain view, this paper suggests that false alarms can be avoided with the use of a binary detection scheme and that by using an m-out-of-n detection criteria, clutter rejection performance can be as good as that for linearly processed signals.