Study On Target Detection And Interference Suppression For Passive Bistatic Radar

As a new type of radar with great potential in application,passive bistatic radar(PBR)detects targets passively by applying the external electromagnetic radiation source as radar sources.Due to the low frequency band and the bistatic/multistatic working pattern,passive bistatic radar has advantages in detecting the low altitude and stealth targets.Besides,as a supplement to the existing detection method,passive bistatic radar also has the advantage of flexible structure,strong survivability and high cost-effectiveness ratio which has important practical value in ground-based intelligence radar,early warning and surveillance radar and space target monitoring system.Despite the advantages of passive bistatic radar system,it still has a series of new problems in the practical application compared with the traditional active radar due to the particularity of the system.From the point of view of solving the engineering application problem in passive bistatic radar,this dissertation carries out the relevant research work for the problems of reference signal purification,reference signal preprocessing,clutter and interference suppression and long-time coherent integration.The research contents of this dissertation can be summarized as follows: 1.The reference signal purification method in passive bistatic radar is studied.Usually,a separate channel is set to receive the direct-path signal.But in reality,except the direct-path signal,the multipath signal may also be received by the reference antenna which will lower the parameter estimation performance of the radar system.Aiming at this problem,a reference signal purification method based on double-channel processing in passive bistatic radar is proposed.In this method,the echo signal is firstly projected to the subspace which only consists of the reference signal to obtain the direct-path signal in the echo channel.Next,the direct-path signal obtained in the previous step is used to remove the multipath signal in the reference channel to obtain the pure reference signal.Since the multipath is suppressed,there is no extra peaks when Range-Doppler correlation between the reference signal and echo signal is applied.Simulation result and the performance analysis verify that the proposed reference signal purification method can suppress the multipath signal in the reference channel and realize the reference signal purification.2.The reference signal preprocessing method in passive bistatic radar is studied.Since the opportunistic source signal in passive bistatic radar is not designed for radars,there may exist the ambiguity range and Doppler sidelobes in the ambiguity function,which will seriously influence the detection performance of the radar system.Aiming at the ambiguity sidelobe suppression problem,a two-dimensional sidelobe suppression method is proposed.By constructing a new cost function to constrain the energy of the two-dimensional sidelobes,the novel method can reduce the energy loss while suppressing the ambiguity range and Doppler sidelobes.Besides,to deal with ambiguity sidelobes suppression problem when a low signal-to-noise ratio in reference signal is given,a robust sidelobe suppression method is proposed.Based on the idea of the worst performance optimization,a new optimization model is built up.By solving the optimization problem,the optimal solution is obtained to achieve the sidelobe suppression in the case of the low signal-to-noise ratio in reference signal.Furthermore,aiming at the sidelobe residual problem,target detection method after sidelobe suppression is proposed.In this novel method,the influence of the sidelobe residual on target detection is reduced through preprocessing.Then,constant false alarm ratio detection method is used to further process the remaining sidelobes.The effectiveness of the above methods is verified by simulation test and measured data.3.Clutter and interference cancellation method in passive bistatic radar is studied.Firstly,the existing clutter and interference cancellation method is studied.In the existing methods,performance and computation cannot be considered simultaneously.Aiming at this problem,clutter and interference cancellation method based on three-step cascade processing is proposed.Through dividing the antenna array into several parts,low sidelobe spatial filtering,temporal adaptive cancellation and robust spatial filtering method are used in series to suppress the clutter echo and interference in this method.The effectiveness of the proposed method is verified by simulation test.However,the antenna array usually does not have the ability of adaptive processing in a real situation.Thus,the methods mentioned above lose its ability in clutter and interference suppression.Aiming at this problem,a multistage clutter and interference suppression method is proposed.In this method,the direction of the interference is determined by comparing the energy level of the residual signals in each beam channel after clutter cancellation,and the samples of the interference are obtained.Then,interference signals mixed in the echo signal are suppressed sequentially according to the energy level in each beam channel by using the temporal adaptive cancellation method.The effectiveness of the proposed method is verified by the simulation test and the measured data.4.Long time coherent integration method in passive bistatic radar is studied.Firstly,the influence of long time integration on target detection is studied.Aiming at the range migration problem in Doppler frequency sensitive signal,a long time coherent integration method based on multi Range-Doppler processing is proposed.In this novel method,the received signal is firstly segmented into several parts.Then the Range-Doppler processing is performed in each part of the signal.At the same time,the offset of the range walks and the inherent phase relationship between each part of the signal are estimated.The final processing result is obtained by synthesizing each Range-Doppler result through the estimated offset of range walk and the phase relationship.Simulation results show that the method can correct the range migration when the Doppler frequency sensitive signal is given.Besides,the carrier frequency of the radar sources may not always remain unchanged in practice.The frequency hopping characteristic of the transmitting signal makes the signal unable to accumulate coherently.Aiming at this problem,long time coherent integration method based phase compensation is proposed.In the proposed method,the frequency difference in each Doppler channel for different carrier frequency is estimated according to the corresponding relationship between each Doppler channel and the velocity,firstly.Next,the phase error is compensated according to the Doppler channel by the estimated frequency difference.Then the long time coherent integration for the frequency hopping signal can be achieved.Simulation results show that the proposed method can achieve long time coherent integration in the case of carrier frequency hopping.