Research On Spatial Jamming Cancellation In Mutifunction Digital Array Radar

As the core equipment of the detection system,multifunction phased array radar can realize multiple functions such as search,tracking,imaging,and recognition for multiple targets,and undertake various tasks such as air defense and antimissile.Therefore it becomes the primary target of active electronic interference.With fully adaptive array,digital array radar has achieved high flexibility in beamforming and superior performance of jamming cancellation.This has enable good surveillance and tracking ability for the radar system operated in real-word electronic warfare.Among all the interference,the mainlobe jamming signal is one of the most serious threat to modern radar.It impinges on the array and comes within mainlobe.As it has high spatial correlation to the target signal,applying mainlobe jamming cancelltion techniques in a digital array system would also suppress target signal.In other words,target detection and tracking would suffer from mainlobe jamming cancellation.Moreover,wideband digital array radar which has been devloped for high-resolution application,is faced with more complex jamming scenario.Specifically,wideband and/or narrowband jamming which is received by mainlobe and/or sidelobe would degrade target resolution and recognition.In summary,it is of great difficulty and significance to maintain radar performance while applying jamming cancellation.This dissertation focus on adaptive beamforming to obtain high performance in target detection,angle estimation and high resolustion in the presence of jamming.Main contributions are as follows.1.In order to reduce the loss of monopulse angle estimation caused by the mainlobe jamming cancellation in a digital array radar system,a two-dimensional orthogonal anti-jamming and angle estimation method is proposed to solve the interference inter-connection in elevation and azimuth when applying adaptive beamforming and sumdelta beamforming.The propsed method has effectively suppressed multiple mainlobe and sidelobe jammings while maintaining accurate angle estimation.First of all,the analysis of the angle estimation accuracy degradation in both azimuth and elevation dimension is given by conventional two-dimensional adaptive beamforming.Then,based on the independence of beamforming in azimuth and elevation,a two-dimensional orthogonal beamforming method is proposed.The orthogonal operation has made that the adaptive beamforming for jamming cancellation in azimuth(elevation)does not affect the sum-delta beamforming for angle estimation in elevation(azimuth);In addition,the proposed method is extended in a two-dimensional rectangular array with digital sub-arrays,which further reduces the complexity of adaptive computation;Finally,it is verified by simulation that the proposed method can effectively suppress multiple mainlobe and sidelobe jammings and increase the accuracy of angle estimation.2.So as to reduce the target signal loss due to the high correlation between the target and the mainlobe jamming when applying mainlobe jammging cancellation in the digital array radar system,a two-stage beam fusion method is proposed for a distributed digital array radar.It has effectively suppressed multiple mainlobe and side lobe jammings while improving mainlobe gain for target detection.First,through the eigenvalue analysis,the reason of the target signal suppression when applying the main lobe jamming cancellation is revealed.The upper bound of the target detection performance in a array radar system when appling jamming cancellation is given.Then,a two-stage beam fusion jamming cancellation method is proposed for the distributed digital array radar.In the first step,the multipoint constraint LCMV method is employed in each radar station to avoid the problems of high correlation between the target and the mainlobe jamming so that only the multiple side lobe jammings are cancelled;In the second step,a high-resolution auxiliary beam is formed in central processing station.The beam is capable of accurately distinguishing the main lobe jamming from the target in the main beam.The MMSE method is therefore applied to estimate and cancel the main lobe jamming in the mainlobe whereas reduceing target signal loss;Finally,it is verified by simulation that the proposed method has obtained high mainlobe gain for target detection while resisting mainlobe and sidelobe jamming at low computation complexity.The method has shown great potential of jamming cancellation in a distributed array radar system.3.Wideband digital array radar has been faced with complex combined jamming characteristics of frequency domain and space domain in electronic warfare.First,based subband decomposition method for wideband jamming cancellation,the key parameters of the jamming dispersion residue in each subband are given by eigenvalue decompostion of the jamming correlation matrix.To this end,a baseband architecture for subband decomposition with high-performance filter is developed,and key parameters are optimized.Simulation results validate that the proposed method significantly mitigate the dispersion residue and improves the jamming cancellation performance.Then,for the combined scenario of wideband and narrowband,mainlobe and sidelobe jammings,a joint jamming cancellation method using multiple beams based on subband decomposition is further introduced.The adaptive sensing of the main and sidelobe jamming in the main beam by multiple auxiliary beams deals with the difference of jammging scenario in subbands.Simulation has shown good performance and verified effective jamming cancellation by applying the presented method in different jamming scenarios accross subband.Finally,with the airborne radar's sea detection experiment in multi-jamming environment,the high range resolution profile of the ship as a target has been obtained through the processing measured data,which has illustrated the superior performance of the proposed method.