Multiple FM-Based Passive Bistatic Pairs for Robust Target Detection with Improved Position Accuracy

High-power FM transmitters are often employed for passive detection of long-range targets. However, higher bandwidth digital modulations (e.g. DAB, DVB-T) are preferred at shorter target ranges due to their improved range resolutions and their content agnostic ambiguity functions. Modern multi-channel, high-bandwidth, and wide-band software defined radios (SDRs) now make possible the simultaneous reception of reflections from multiple transmitters of opportunity using a single commercial off-the-shelf (COTS) appliance. Sophisticated and highly diverse passive radars employing multiple transmitter technologies can now be implemented using COTS equipment. The diversity advantage of multistatic FM-based passive radar are not often demonstrated. This paper demonstrates how transmitter and channel diversity can improve both 2D target detection and range resolution for such multistatic FM-based passive radars. Moreover, a single airborne target was simultaneously tracked using four FM bistatic pairs. These FM bistatic pairs were formed using various remote transmitters and a single four-channel COTS SDR receiver. The diversity advantage offered by the separate transmitters, different channels, and varying radio content is analysed for an increasing number of redundant bistatic pairs. These redundant bistatic pairs allowed for a more robust and reliable target detection that is less dependent on the channel content. A range cell area reduction of approximately 37% was calculated when using four instead of only two bistatic pairs.