| Passive radar is a special bistatic radar that uses non-cooperative radiation sources for detection.It has the advantages of small size,low cost,strong anti-interference ability,and no additional spectrum occupation.At present,the commonly used external radiation sources include FM broadcasting,terrestrial digital TV broadcasting,Digital Radio Mondiale(DRM)and so on.Among them,the DRM signal is located in the short-wave band and is the only short-wave digital sound broadcasting system in the world.The DRM-based passive radar has outstanding advantages such as long range,over-thehorizon,and anti-stealth,and has important research value.But at the same time,passive radar also faces the problems of weak target echo,high power and widening of clutter and its side lobes.The target is easily submerged in the clutter and its side lobes.Therefore,how to suppress clutter quickly and effectively is a key problem to be solved in the signal processing of passive radar.This paper focuses on the DRM-based passive radar clutter suppression method.After the signal structure analyzing,the DRM signal is simulated and its ambiguity function is corrected during reconstruction.Then,after in depth analysis and comparison of the commonly used clutter suppression algorithms,the research focuses on the doppler spread clutter suppression and its rapid implementation.The main research contents are as follows:1.Research on the DRM-based passive radar system.The signal model of each channel is established based on the passive radar signal processing.Then,the DRM signal is simulated by studying its framing structure.After that,the feasibility of the DRM signal as the passive radar signal is verified based on the signal ambiguity function and pointed out that there are still some shortcomings such as fuzzy side peaks.2.Research on reference signal purification and clutter suppression technology.The reference signal is purified through signal reconstruction,and the fuzzy secondary peaks are eliminated through signal correction during the reconstruction process.After that,the time domain filtering method is used to suppress the strong clutter in the echo channel.The simulation and comparative analysis of various algorithms based on the least mean square error criterion and the least square criterion are carried out.3.Research on Fast Suppression of Doppler-Broadened Clutter.The properties of Doppler extended clutter are analyzed and the multi-channel filtering method for extended clutter is studied.It is pointed out that multi-channel filtering will greatly increase the amount of computation required for clutter suppression.Then,based on the performance simulation analysis of the algorithm,the extended least squares algorithm with good clutter suppression effect but large amount of calculation is selected.Obviously,the amount of computation depends on the filter order,in order to improve the algorithm's performance by reducing computation,two methods are adopted.First,the frequency dimension filtering order is reduced by the clutter frequency identification and extraction algorithm based on projection matrix decomposition.Then,the delay dimension filtering order is reduced by carrier conversion based on the multi-carrier modulation characteristics of DRM signals.The simulation verifies that the algorithm can reduce the calculation amount of the multi-channel filtering algorithm as much as possible at a small cost,which is beneficial to the real-time implementation of the clutter suppression algorithm under long-term signal processing. |
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