Range resolution improvement in passive bistatic radars using deconvolution

Abstract

Passive radar (PR) systems attract interests in radar community due to its lower cost and power consumption over conventional radars. However, one of the main disadvantages of a PR system is its low range resolution. The reason for this is, the range resolution depends on the bandwidth of the transmitted waveform and in a PR scenario, it is impossible to change transmitted waveform properties of a commercial broadcast. In this thesis, a post processing scheme is proposed to improve the range resolution of an FM broadcast based PR system. In the post processing scheme, the output of the ambiguity function is re-expressed as convolution of the autocorrelation of the transmitted signal and a channel impulse response. Therefore, it is shown that it is possible to use deconvolution methods to compute the channel impulse response using the output of the ambiguity function and the autocorrelation of the transmitted signal. Thus, using deconvolution to solve the channel impulse response provides an increase in the range resolution of the PR system. The method successfully increases the target separation distance and range resolution of a PR system using single FM channel signal. The conventional ambiguity function is able to separate two targets when the targets have about 17 km between each other where as the deconvolution based post processing method can decrease this to about 10 km. The deconvolution based post processing methods also decreases the side lobes around the target when the system uses multi channel FM signals. For a scenario in which three FM channels are employed, the highest side lobe is 1.2 dB below the main target peak and after deconvolution, this highest side lobe decreases to about 10 dB below the main target peak.