Passive Radar Signal Processing in the Presence of Sample Clock Offset

Passive radar signal processing is hindered by the need to sample a reference signal from the chosen illuminator, which is subject to sensor noise and interference from clutter returns. The reference signal may be demodulated and reconstructed to remove artifacts. However, without accounting for the transmitter's clock offset, the remodulated reference signal will be a poor match for the surveillance signal. This article evaluates clock offset estimation methods in terms of the radar ambiguity surface, thereby appraising them specifically for passive radar applications. Existing offset estimation methods are shown to meet variance bounds; however, these bounds worsen with increased clock offset. Ambiguity surfaces constructed from signals reconstructed with poor clock offsets exhibit power leakage. A new clock offset estimator is proposed, which refines coarse estimates made by an existing method. The new estimator is demonstrated to achieve accurate estimation of clock offset. Reference signals reconstructed with these estimates produce ambiguity surfaces with no significant power leakage.

I. Introduction

Passive bistatic radar (PBR) performs detection and state estimation of targets without use of a dedicated radar transmitter [1]. Instead an ambient source of RF energy, such as a radio or television transmitter, is exploited as an illuminator of opportunity (IOO). Benefits of PBR include less hardware expense, stealthy operation, and the ability to exploit bands of the spectrum, which are not otherwise available to radar [2].