Study On Interference And Clutter Suppression Algorithm In Passive Bistatic Radar

With the development of anti-radar technology,the traditional radar is faced to four kinds of challenges which include the electromagnetic interference,the low altitude penetration,the anti-radiation missile and the invisible plane.For meeting four kinds of threatening challenges,the research institutions of various countries continue to develop the new radar technology.The passive bistatic radar(PBR)is just one of the new radar systems with the great development potential.The PBR which is also named as the passive radar doesn't transmit the electromagnetic wave and applies the existing non-cooperative signals in the space to detect passively the potential targets.With the characteristics of the bistatic system and the receiving silently,the PBR owns the great advantages of against interference and anti-radiation missile,anti-invisible plane,against low altitude penetration and no electromagnetic pollution.Therefore,the target detection technology of the PBR system attracts the great research interests.Because the PBR applies the non-cooperative illuminator to detect the targets passively,the electromagnetic environment where the PBR locates is very complex.In the real scenario,the signal processing in the PBR system is faced with the tough issues of the mainlobe common-frequency interference and the multipath clutter in the reference signal.The mainlobe common-frequency interference and the target echo signal are undistinguished in the time domain,the frequency domain and the space domain.The traditional methods cannot suppress the mainlobe common-frequency interference effectively.There will be the blind zone of detection in this beam mainlobe of PBR system.Moreover,the signal processing of PBR system is also faced with the issue of the multipath clutter in the reference signal.The direct-path signal is reflected by the near surface features and propagates along the multipath channel,so the reference signal received by the PBR system includes not only the direct-path signal but also the multipath clutter components.The contaminated reference signal with the multipath clutter brings the serious impact to the performance of signal processing.Aiming at these mentioned issues,this dissertation researches the detailed issues of the mainlobe common-frequency interference and the multipath clutter in reference signal in the PBR system.The detailed research work of the dissertation is arranged as follows.1.Firstly,the dissertation researches and analyzes the issue models of the blind separation processing and the blind equalization processing.With the theoretical analysis,the tough issues of the mainlobe common-frequency interference and the multipath clutter in the reference signal are matched with the issue models of the blind signal processing.Then,the joint point between the blind signal processing and the signal processing of PBR is found on this basis.The dissertation applies the vital principle of blind signal processing in the communication field into the interference and clutter suppression processing in the PBR field.The research work in the dissertation can solve the suppression issue of the mainlobe common-frequency interference and the multipath clutter in the reference signal.2.Because the mainlobe common-frequency interference and the target echo signal are undistinguished in the time domain,the frequency domain and the space domain,the mainlobe common-frequency interference can hardly be suppressed effectively by the conventional method.Aiming at the issue of the mainlobe common-frequency interference in the PBR system,the dissertation shows the mixed signal model of the mainlobe commonfrequency interference and the target echoes,and proposes the mainlobe common-frequency interference suppression algorithm based on the independent component analysis(ICA).Firstly,the proposed algorithm applies the method of eigen-beam to determine the mainlobe common-frequency interference.Then,the proposed algorithm applies the principal component analysis to compress and whiten the echo signal,and the principal component of interference is extracted.Then,the proposed algorithm applies the ICA to separate the principal component of interference for the mainlobe common-frequency interference samples in the time domain.Finally,the proposed algorithm applies the ECA to construct the rectangular projection matrix and cannel the mainlobe common-frequency interference.The simulation experiments are used to prove the performance of the proposed mainlobe common frequency interference suppression algorithm in this dissertation.3.When the reference signal includes the multipath clutter in the PBR,the contaminated reference signal is matched with the target echoes and causes the false targets,resulting in the false alarm probability rises.According to the constant modulus feature of the opportunity illuminator signal,this dissertation utilizes the constant modulus algorithm to blind equalize the reference signal,and suppress the multipath clutter without any training sequence.When the multipath clutter owns the great time delay,the suppression performance of traditional CMA is worse.Thus,the dissertation proposes the modified constant modulus algorithm(CMA)based on the higher-order statistics.The dissertation introduces the higherordar statistics to improve the cost function and optimizes the iteration processing of the weight,and the convergence performance of proposed algorithm is improved.The simulation experiments are used to prove the performance of the proposed multipath clutter suppression algorithm in this dissertation.4.Because of the airborne received platform moving,the multipath clutter in the airborne PBR owns not only the time delay but also the Doppler frequency,the traditional blind equalization algorithm is unavailable for the signal processing in airborne PBR system.Aiming at the issue of the contaminated reference signal in the airborne PBR system,the dissertation proposes the modified blind equalization algorithm based on the cyclostationarity to suppress the multipath clutter with the Doppler frequency in the contaminated reference signal.To restrain the Doppler frequency of equalization fiter output,the proposed algorithm in the dissertation applies the cyclostationarity to construct the new cost function,and applies the complex value BP network to solve the constraint optimization problem.The simulation experiments are used to prove the performance of the proposed modified blind equalization algorithm in this dissertation.