Research On Key Technologies Of Passive Target Detection In Mutipath Environment

Research on passive target detection technology has always been a hot topic in radar target detection area.In recent years,under the trend of paying more and more attention to the complex electromagnetic environment and effectively implementing the covert attack and defense of weapon systems,the passive detection system application using non-cooperative illuminators can offer the advantages of low cost,covert detection,anti-electromagnetic interference and anti-stealth.Therefore,these researches have received widespread attention in academic and industrial area.Compared with traditional FM radio,TV,navigation satellite and other non-cooperative illuminators,the use of non-cooperative radar illuminators has the characteristics of farther detection distance and higher resolution,which is very important for improving target detection performance.However,the research on passive target detection technology based on frequency agile phased array radar illuminator is more representative and challenging.The use of frequency agile phased array radar illuminator can not only enrich the types of non-cooperative illuminators,but also exploit the advantages of advanced radar system.However,the non-cooperative working mode is subject to the characteristics of non-cooperative illuminator,thus the passive target detection system applications also face the other technical problems in signal processing.On one hand,since the passive detection system application works in a non-cooperative mode,there is a problem that the instantaneous parameters of transmitting signal are unknown at the receiver,the frequency agility technology destroys the coherency between pulses and the ability of rapidly changing beam scanning makes it difficult for PBR to realize space synchronization.On the other hand,the exploited non-cooperative illuminator works in the low frequency band,and the multipath propagation effect is very serious.The desired signal in the target echo is strongly correlated with the multipath signal,or even completely coherent,and they are always closely spaced in the mainlobe.In addition,the direct waves from the non-cooperative illuminator may be intercepted by the reference antenna at the same time.The energies of these transmitting signals are high,and they may come from the same direction as the direct signalBased on the analysis of the above problems,the dissertation closely focuses on the actual needs of non-cooperative target passive detection system application,and carries out the research on the key technologies of non-cooperative target passive detection based on frequency agile phased array radar illuminator.The aim of the dissertation is to solve the problems of direct wave parameter estimation,direction of arrival(DOA)estimation,and engineering implementation in mutipath environment.The research results obtained in the dissertation can effectively compensate for the shortcomings of conventional radar target detection in complex electromagnetic environment,provide powerful technical supplement for active and passive integrated aerospace situational awareness,and promote the engineering and practicality of passive detection technology with reference values.The specific work of the dissertation is summarized as follows:The second chapter analyzes the theories and problems of passive target detection using non-cooperative illuminators.Firstly,based on the basic structure of passive target detection system application,the radar distance equation and radar power coverage are analyzed.Then the passive target localization principle is given and analyzed with bistatic distance error and target viewing angle error.Finally,the characteristics of the exploited non-cooperative illuminator and multipath propagation characteristics are both analyzed,and the main problems in passive target detection are clarified.These provide a solution and theoretical basis for direct wave parameter estimation and direction of arrival estimation algorithm,and engineering implementation research in the later chapters.In the third chapter,the problems of direct wave parameter estimation for passive target detection in multipath environment are studied.A novel direct wave parameter estimation method based on fractional Fourier domain sparse reconstruction is proposed to solve the problem caused by multipath component.Afterwards,a new direct wave parameter estimation algorithm based on nearest neighbor Kalman filter is proposed to solve the problems in the complex electromagnetic environment,which not only contains multipath components,but also has multiple illuminator signals.Simulation experiments and measured data processing verify the effectiveness of the proposed algorithms.In the fourth chapter,the problems of DOA estimation for passive target detection in multipath environment are studied and a novel spatial difference iterative adaptive DOA estimation algorithm is proposed.The algorithm firstly distinguishes the uncorrelated signals from the coherent signals based on the eigenvalues of the uncorrelated and coherent signals,and then acquire their DOA estimation.Then,the spatial difference technique is used to eliminate the contribution of the uncorrelated signals in the array covariance matrix.Finally,the reconstructed covariance matrix is processed by the Iterative adaptive algorithm(IAA)to complete the coherent signal DOA estimation.The proposed algorithm fully combines the advantages of spatial difference technology and IAA algorithm while avoiding their shortcomings.The simulation results show that the proposed algorithm has super-resolution DOA estimation performance,and still works well in the scenario of low signal-to-noise ratio and limited sample snapshot.The fifth chapter first introduces the overall architecture of the passive target detection system application,which mainly includes the direct wave processing subsystem and the target echo processing subsystem and their engineering platforms.Then,a novel passive target detection signal processing scheme is proposed.By using simultaneous multi-beamforming method to cover the observation area to achieve spatial synchronization,and using the direct wave parameter estimation method to achieve time-frequency synchronization.Then,a novel probability statistical histogram method is used to detect the weak target,which is used as a priori information.The bistatic range and time echo plane is then used for moving target detection,and then the bistatic range and angle localization method is used to achieve passive target localization.Finally,the feasibility and effectiveness of the proposed scheme in the passive target detection and location are proved by conducting numerous non-cooperative target detection field trails.