Direct signal cancellation in passive bistatic DVB-T based radar

Passive radars receive target reflections from transmitters of opportunity. They do not emit any radiation, which makes them harder to find. A challenge with the passive radar is to suppress the strong direct signal incoming at the surveillance antenna, emitted from the transmitter, in order to be able to detect weaker targets. A direct signal cancellation method called ”Extensive Cancellation Algorithm” is the focus of this report. The algorithm minimizes the contribution of the direct signal to the surveillance signal, by means of a least mean squares method. We demonstrate the use of this cancellation algorithm on real data, and give an estimate on how much the signal to noise ratio of a target can be increased. Two different antenna configurations are used. Antenna configuration A has an angle of about 90◦ between the direction to the transmitter and the surveillance antenna main lobe. In configuration B, the surveillance antenna is pointing towards the transmitter, which should maximize the direct signal interference. The target signal to noise ratio of ten targets observed with antenna configuration A experience an average increase of about 10dB after direct signal cancellation. The average increase is about 20dB for configuration B. Some targets from this configuration had initially a signal level lower than the estimated noise floor. After cancellation, the SNR had increased such that they were able to be detected as a target. The corresponding reduction in noise floor level are about 10dB and 14dB for configuration A and B, respectively. The result show that the effect of direct signal cancellation depends on where the direct signal interferes in the surveillance antennas antenna pattern.