Direct-path suppression by spatial filtering in digital television terrestrial broadcasting-based passive radar

The signal model of digital television terrestrial broadcasting (DTTB) is introduced and its ambiguity function is analysed here. In order to suppress the direct-path (and multipath) interference generated by single frequency network in DTTB-based passive radar, the corresponding spatial filtering methods are designed according to the feature of each channel. In the echo channel, the interference is suppressed by discarding the signal-subspace. The noise-subspace can be estimated from the power of the covariance matrix to avoid the eigen-decomposition and to eliminate the need to obtain the corresponding dimension. In the reference channel, the transmitting signal of a certain transmitter is regarded as the desired signal. The desired signal will be cancelled by conventional spatial filtering algorithms for the high signal-to-noise ratio case, which will also result in a distorted pattern and high side-lobes. To solve this problem, an improved general side-lobe canceller structure is proposed to realise the adaptive beamformer. To improve the robustness of the proposed methods and suppress the distributed clutter, the 'broad null' algorithm is combined with the beamformer. The simulation results show that the proposed methods are effective to suppress the interference in DTTB-based passive radar.