Aspects of Delay-Doppler Filtering in OFDM Passive Radar

Abstract

Delay-Doppler filtering enables the isolation of radar returns from a designated region of the ambiguity plane. Such returns can be cancelled from the surveillance signal, lowering the ambiguity floor and reducing demands on dynamic range. Modern passive radar systems frequently use OFDM-based illuminators of opportunity, and recent studies have demonstrated how the structure of OFDM signals can be exploited to perform delay-Doppler filtering in the frequency domain. In this study several aspects of one such algorithm are investigated: the ability to cancel returns when delay is not a whole number of samples; the ability to conserve computation by approximating a projection matrix; the effect of returns having delays exceeding the OFDM guard interval; and the application of the method to extended targets. The consideration of these aspects demonstrates the efficacy of the method in situations common to passive radar.