Compressive sensing for passive surveillance radar using DAB signals

Bistatic/passive radars offer several advantages over monostatic radars. One of them is that the separation of transmitter and receiver opens the possibility to illuminate the targets from different aspect angels compared to the receiver. This spatial diversity can enhance the capability of target detection, parameter estimation, and identification, especially for stealth objects with low monostatic radar cross sections. Another benefit for passive radar is the lower cost of production and operation as existing transmitters are used as illuminators of opportunity. Accordingly the power maintenance is much lower compared to an active radar system. However, there are two main challenges linked to bistatic/passive radars: the high dynamic range of the receiver due to the very strong direct signal, in particular if the illuminator transmits continuously as it is the case for broadcast stations, and the required high integration gain to detect manoeuvring objects. The first issue is part of the analog processing chain and has to be taken into account during the design stage of the receiver. The second challenge is to collect enough signal energy to detect weak target signals covered by a strong direct and multi-path signals. A requirement to achieve this is a clean reference signal for pulse compression. In case of orthogonal frequency division multiplex (OFDM) waveforms this reference signal can be exactly reconstructed even from a distorted signal. This paper presents the results from an investigation applying compressive sensing techniques to improve the signal processing of passive radar systems using a digital audio broadcast station as an illuminator of opportunity.