Direct signal suppression schemes for passive radar

Passive radar systems must detect the presence of a target response many orders of magnitude weaker than the direct signal interference. Even when digitally modulated waveforms with favorable ambiguity surfaces are employed, the floor of the ambiguity surface sets significant limitations on the minimum detectable signal. Suppression of this direct path and close-in clutter from the surveillance waveform is crucial for maximizing the dynamic range which increases the useful detection range of the system. Presented here is an evaluation of various direct signal suppression schemes - both block and adaptive filtering - tested against various metrics on experimental collected passive radar data using North American digital television (DTV) waveforms. Results show the fast block least-mean squares adaptive filter to be significantly faster than existing algorithms with superior suppression performance. Strategies for selecting filtering schemes depending on the task at hand are also discussed.