Loaded reciprocal filter for OFDM-based passive radar signal processing

The Range-Doppler maps of Passive Bistatic Radar (PBR) are often evaluated by means of the suboptimal batches algorithm. For OFDM waveforms of opportunity, a typical choice is to fragment the signal in batches length equal to the OFDM symbol length. This is shown to provide Signal-to-Noise Ratio (SNR) losses for both Matched Filter (MF) and Reciprocal Filter (RF), especially for long target ranges. We investigate the case of “non-OFDM fragmentation”, with special attention to the case of batch length much longer than a single OFDM symbol that can potentially reduce the losses at long ranges. While this is effective for the MF, we show that the RF filter in this case still provides high Peak-to-Sidelobes Ratio (PSLR) values but at the expense of significant SNR losses. Therefore, we propose the Loaded Reciprocal Filter (LRF) as a modified version of the RF for the non-OFDM fragmentation case, which is shown to provide a trade-off between SNR losses and PSLR. Finally, a simulated case study is presented for a DVB-T-based PBR, which clearly shows the effectiveness of the proposed LRF scheme when using the non-OFDM fragmentation.