Mitigating the effect of direct signal interference in passive bistatic radar

Passive bistatic radar uses target illuminations by transmitters of opportunity (often commercial broadcasts). Unfortunately, the strength of the direct signal interference (DSI) can often be so strong as to mask target returns. Furthermore, when illumination is provided by a DAB (Digital Audio Broadcasting) network, the problem can be exacerbated by several transmitters operating on the same frequency. The present paper discusses strategies for reducing DSI and, in particular, the use of array nulls, cross polarization and shielding by topography. The effectiveness of these strategies is investigated through modelling.