Study On Deceptive Jammer Suppression With Waveform Diversity Array Radars

The environment of the modern electronic warfare is becoming more and more complex,where both the electronic countermeasures(ECM)and electronic counter-counter measures(ECCM)are constantly evolving in the struggle.Among various types of ECM,the deceptive jammer,especially from the mainlobe,poses a significant threat to existing radar systems.Moreover,the deception capability has been significantly enhanced with the development of digital radio frequency memory(DRFM)technology.Usually,the probing waveform is replicated and delayed by the false target generator(FTG)to produce false targets after modulation,making it difficult for the radar to distinguish the true target from the false ones and suppress deceptive jammers.The radar system has been constantly developed,progressing from the mechanical scanned radar to phased array radar as well as the multiple-input multiple-output(MIMO)radar.In this respect,the controllable degrees-of-freedom(DOFs)have been increased,enhancing the ability to acquire information of targets from the surroundings for the radar systems.Particularly,innovative waveform diverse array radars,represented by the frequency diversity array(FDA)radar,have sparked intense interest from the research community in recent years,enriching the MIMO techniques.The FDA can generate a range-angle-timedependent beampattern by modulating the frequencies across adjacent array elements,increasing the flexibility of system design and signal processing.Combined with transmitted waveform separation,the extra DOFs in the range domain can be obtained,providing an effective way to solve the problem of mainlobe deceptive jammer suppression.In this dissertation,aimed at solving the worldwide problem of mainlobe deceptive jammer suppression in modern complex electromagnetic environment,supported by national nature science fund,i.e.,“Research on frequency diverse array: basic theory,key techniques and radar applications”,I have conducted a throughout study on deceptive jammer suppression in waveform diverse array radars.In specific,methods are proposed to reveal the principle of separating target and jammers using angle and range information.Furthermore,the performance of deceptive jammer suppression using the controllable DOFs are corroborated.Main contributions are summarized as follows:1.Focused on the problem of mainlobe deceptive jammer suppression,the method based on data-dependent beamforming is proposed in FDA-MIMO radar to distinguish the true and false targets in the joint transmit-receive spatial frequency domain,where non-perfectly orthogonal waveforms,which are suitable for engineering applications,are utilized.Furthermore,due to the pseudo-random distribution of false targets,a robust nonhomogeneous sample detection(NSD)method is proposed to obtain the jamming-plus-noise covariance matrix with high accuracy,where two steps are involved,i.e.,1)selecting the nonhomogeneous samples including signal and/or jammer;2)rejecting the samples including signal by virtue of spatial smoothing.2.Focused on the problem of nonhomogeneous sample selection with data-dependent beamforming for jammer suppression in FDA-MIMO radar,a method to suppress mainlobe deceptive jammers is proposed based on data-independent beamforming.By designing an appropriate frequency increment,false targets can be suppressed by nulling of the dataindependent beampattern.However,in practice,the false targets may deviate the presumed directions owing to the range quantization error,angle estimation error and frequency increment error.In this respect,the proposed method based on data-independent beamforming fails to adjust such mismatches adaptively.3.Focused on the problem of suppression performance degradation in the presence of mismatches for false targets using data-independent beamforming,an approach of precisely controlling the beampattern based on artificial interferences is proposed to enhance the robustness of the method based data-independent beamforming.In specific,the method is implemented by assigning artificial interferences with prescribed powers around the nulls of the beampattern corresponding to the false targets.Furthermore,a preset broadened nulling beamformer(PBN-BF)algorithm is developed to design the optimal weight vector of the transmit-receive two-dimensional(2-D)beamformer,improving the performance of false targets suppression.4.Focused on the problem of suppression performance degradation in the presence of mismatches existing both for the true and false targets,an approach of precisely controlling the beampattern based on the weight vector orthogonal decomposition and oblique projection techniques is proposed to enhance the robustness of the method based data-independent beamforming.Firstly,the sub-weight vector for a single region of the beampattern is devised by performing the orthogonal decomposition technique.Then,a “filtering matrix”is constructed using the oblique projection operator to synthesize sub-weight vectors from different regions.As a result,a range-angle-dependent 2-D transceive beampattern can be formed with a flat-top mainlobe,multiple broadened quasi-nulls,and low sidelobes,improving the gain of the beampattern response of the true target and the performance of false targets suppression.5.Focused on the problem of mainlobe deceptive jammer suppression,a method based on data-independent beamforming is proposed in element-pulse coding(EPC)-MIMO radar to distinguish the true and false targets in the joint transmit-receive spatial frequency-pulse three-dimensional(3-D)domain.Specifically,the true and false targets are distinguished by using beampointing directions of the equivalent transmit beampatterns from different range ambiguity regions.Moreover,by properly designing the coding coefficients,the false targets,which correspond to specific range ambiguity regions,can be suppressed by nulling of the data-independent beampattern.Furthermore,when the angle mismatch exists both for the true and false targets,a preset beampattern synthesis(PBPS)method proposed by orthogonally decompositing the weight vector.Hence,a 2-D transceive beampattern with a flat-top mainlobe,broadened nulls,and low sidelobes can be designed,improving the gain of the beampattern response of the true target and the performance of false targets suppression.