Research On Group Target Discrimination For High Frequency Surface Wave Radar

High-frequency surface wave radar(HFSWR)plays an essential role in civilian business and military security,with its unique advantages of over-the-horizon,antistealth,all-weather and real-time surveillance.The compact HFSWR reduces the coastal resource footprint and increases system flexibility,it is more convenient for system configuration and engineering applications.However,the azimuthal resolution of the compact system is decreased,which leads to a larger spatial resolution cell and the coexistence of multiple targets in one cell.Meanwhile,due the target maneuvering in the integration time,the two-dimensional coupling of range-doppler causes blurring of the discrimination in close targets.Therefore,group target discrimination is a critical issue to be addressed in HFSWR.In this thesis,the cross-range imaging and virtual array synthesis methods are proposed.The former applies the inverse synthetic aperture approach to HFSWR,which discriminates formation group targets in the cross-range domain.The latter is originated from the virtual array concept,which can enhance the resolution performance in the azimuthal domain and discriminate two-dimensional coupled group targets.The main achievements of this thesis are as follows:1.For the problem of formation group target discrimination,the HFSWR crossrange imaging method is proposed.The imaging principle and resolution are first derived based on the established signal model of formation targets.The core steps of the proposed method include motion compensation and cross-range scaling.The motion compensation equates the formation motion to a rotation model,and then uses the rotation-induced doppler shift to discriminate sub-targets.Based on the rotation angle,the cross-range scaling processing converts the doppler image into a cross-range image,whereby the sub-target spacing estimation is achieved.Simulation experiments show that the resolution of the proposed method is in the range of 0.5 to 4 km.Its target resolution and spacing estimation capabilities are verified by the imaging results of single column and V-formation,which is still robust under motion error scenarios.2.To solve the problems of motion parameter estimation,rotation angle estimation,and longer coherent accumulation time(CIT)limitation,the cross-range imaging method is improved.In the modified motion model,motion compensation is first performed based on the parameter estimation method of the minimum entropy criterion,which establishes compensation factors by estimating radial velocity and acceleration.Then,based on the fragment digital beamforming(DBF)rotation angle estimation,the cross-range scaling method is proposed,which derives the rotation angle by two times angle of arrival(DOA)estimation and avoids the chance error by using fragment occupancy ratio and mean value processing.Finally,the overlapping coherent integration method is proposed to improve the doppler resolution by data multiplexing approach,which alleviates the requirement of CIT.The simulation target is added to the measured data,and the experimental results show that the minimum entropy method achieves the doppler profile focusing;the spacing estimation of the cross-range image verifies the effectiveness of fragment DBF;the overlapping coherent integration can improve the imaging effect.The experimental results have reference value for engineering applications.3.The virtual array synthesis method is proposed for the non-formation group target discrimination.This method uses the target motion to synthesize virtual arrays,and improves the azimuthal resolution by increasing the array aperture.The virtual array synthesis principle and synthesis conditions are derived first.Then the unknown speed in the synthesis condition is considered,and the optimal DOA estimation result is found by using the maximum peak side-lobe ratio(PSLR)criterion.Compared with the real array,the virtual array improves the azimuth resolution performance,and the proposed method achieves the discriminate of two-dimensional coupled group targets and has anti-interference capability.