Analysis of the digital MTI filter with random PRI

Modulation of the radar pulse repetition interval (PRI) is a conventional technique to improve the target velocity coverage in a moving target indicator (MTI) filter. Typically, a given pattern of interpulse intervals is periodically repeated (staggered PRI). Additionally, the staggered PRI gives us some protection against PRI analysis in an electronic intelligence environment. Nevertheless, this protection is limited by the repetitive character of the PRI modulation pattern. Much greater protection can be achieved by means of a random selection of the PRI between fixed bounds.This paper presents an analysis of the digital MTI for two types of PRI random generation. In the first type, small deviations with respect to a mean PRI are randomly generated (random deviation method, RDM). In the second type, the intervals themselves are randomly selected random interval method, RIM). We derive for both cases the relationship between the velocitydependent gain factor and the probability density function (PDF) of the corresponding random variables. This allows us to predict the influence of the PDF in the expected performance. Specific design strategies that take into account practical constraints, like the maximum unambiguous range and the dwell time, are also proposed for each method.