Evaluation of direct signal suppression for passive radar

Passive radar (PR) systems must be able to detect the presence of a target signal many orders of magnitude weaker than the direct signal interference (DSI). Due to the continuous nature of most PR signals, this interference, rather than thermal noise, determines the sensitivity of the system. Suppression of DSI and clutter prior to range-Doppler processing is crucial for maximizing the effective dynamic range, to increase detection range and improve overall system performance. A number of time-domain adaptive filtering techniques have been proposed to mitigate the effects of DSI, with varying levels of success. As such, an investigation of the primary factors affecting suppression performance is presented, using Advanced Television Systems Committee digital television (DTV) waveforms as an example, through simulation and extensive experimental trials. A number of spectral and spatially diverse DTV signals are considered to analyze suppression performance under a wide range of realistic scenarios. In particular, the fast block least mean squares filter is shown to provide good suppression performance with low computational requirements. Results of this analysis can be used to predict PR performance and stability. Practical metrics, such as suppression runtime and ease of implementation, also serve to counsel selection of DSI mitigation algorithms for experimental systems.