Research On The Weak Target Detection In Passive Radar Systems

Passive radar systems use illuminators of opportunity presented in environment fortargets detecting, locating and tracking. Due to covert operation, low weight, low cost,anti-elint and anti-stealth, passive radar systems have better performance than conventionalradar systems in national defence area. However, weak-targets echoes are stronglyinterferenced because both transmitted waveform and directions are uncontrollable. Thereforeproposing effective interference suppression methods is the key point of solving the difficultfor weak-targets detection in passive radar systems.This paper focuses on techniques of weak-targets detection in passive radar systems. Inreference channel, blind equalization method is studied. In echo channel, both existence andinexistence of strong-targets interference are discussed. The main works are as follows:Both basic principle of passive radar systems and detection capability of illumanitors areanalyzed. The structure of passive radar systems is summarized, then geometry and powerrelation are analyzed. Ambiguity function is applied to examine the range and Dopplerresolution of common illuminators, including digital broadcasting, global television terrestrialbroadcasting, global navigation satellite systems and wireless communication.The modified steepest descent constant modulus algorithm (MSD-CMA) is proposed forblind equalization in reference channel. Based on the steepest descent constant modulusalgorithm (SD-CMA), MSD-CMA brings former error vectors into current error vectoriteration. Lyapunov function is used to select the appropriate algorithm step-size and erroradjustment step-size. Convergence rate and stable performance of MSD-CMA arecodetermined by algorithm step-size and error adjustment step-size. With both quickconvergence rate and excellent stable performance, MSD-CMA effectively solves the problemwhich SD-CMA is disabled in the condition of high power noise.In the condition of stong-targets interference inexistence, an interference suppressionmethod is developed by applying correlation subtraction algorithm multistage Wiener filter(CSA-MWF) into range-Doppler domain. According to the characteristics of interference, anew initialization method is presented in echo channel. The echoes are processed throughforward recursion and backward error recursion. Finally, the output errors are targets echoeswith multipath-interference suppressed. Subsequently iterative Householder transform-MWF(IHT-MWF) is proposed for multipath-interference suppression. IHT-MWF algorithmimproves the robustness and reduces the filter rank.In the condition of stong-targets interference existence, the effect which strong-targets echoes to weak-targets echoes is discussed and subspace projection based interferencesuppression method is proposed. Firstly, the optimal subspace projection method is presented.It has the optimal performance in suppression of both multipath-interference andstrong-targets interference. But the prior information of stong-targets which algorithmrequires is hard to obtain. Suboptimal subspace projection method is proposed to make up theshortage of optimal method. The suboptimal method replaces the large size projection matrixwith several small size projection matrices. It extends applied area and improves running ratewithout prior information. Finally, a blocking suboptimal subspace projection method isintroduced. In both the reference and echo channel, the received signal is divided into severalconsecutive blocks and processed in parallel.The theory analysis and simulation results demonstrate that both blind equalization ofreference channel and interference suppression method of echo channel can meet the need ofpassive radar systems and improve the capability of weak-targets detection.