Research On Anti-jamming Algorithm Of Adaptive Antenna Beamforming

With the rapid development of wireless communication technology and antenna technology,adaptive antenna arrays are widely used in wireless communication systems.Adaptive beamforming technology is the key technology of array signal processing for adaptive antenna array.Under the premise of the maximum beam gain pointing to the desired signal,zero notch can be formed adaptively in the angle position of sidelobe interferences to achieve the effect of spatial filtering.However,with the increasingly advanced jamming technology,the space electromagnetic environment is becoming more and more complex.The mainlobe jamming falling into the mainlobe region and the relative moving sidelobe jamming appear.The traditional adaptive beamforming technology can not effectively combat these two forms of interferences,resulting in a serious deterioration of the output performance.Therefore,how to effectively suppress mainlobe interference and offset sidelobe interference has become research hotspots in recent years.This paper mainly studies suppression methods of these two forms of interferences,and the research content is summarized as follows:1.In order to solve the problem of beampattern distortion caused by preprocessor-like adaptive beamforming algorithm,this paper introduces conformal algorithms for blocking matrix preprocessing algorithm and eigen-projection matrix preprocessing algorithm respectively.In this paper,the covariance matrix noise whitening method,diagonal loading method and linear constraint combined with diagonal loading technique are introduced to carry out the beam conformal of the blocking matrix preprocessing algorithm respectively.The covariance matrix noise whitening method can effectively improve the bad disturbance of small eigenvalues and reduce the offset angle of the maximum gain of the mainlobe beam to a certain extent.When the value of diagonal loading is selected properly,the diagonal loading method and the conformal method combined with linear constraint and diagonal loading technique can not only further improve the problem of mainlobe migration,but also obtain relatively lower sidelobe level.The preprocessing method of eigen-projection matrix has the advantage of freedom of lossless array antenna,but the preprocessing operation also causes the distortion of beam pattern.In this paper,the method of covariance matrix reconstruction and similarity constraint of the preprocessed training data is introduced to conformal the orientation pattern.The reconstruction of covariance matrix includes two different construction methods,namely ordinary reconstruction and integral reconstruction.The mainlobe conformal of beampattern is realized by using the reconstructed covariance matrix for beamforming.The conformal method with similarity constraint is more effective.The sidelobe level obtained by this method is close to that of static directional graph,which further improves the system’s ability to suppress interference and noise.2.Aiming at the problems of error in screening of the mainlobe interference eigen-vector and change in training data after eigen-projection preprocessing,an improved adaptive beamforming algorithm based on eigen-projection matrix preprocessing against mainlobe interference is proposed in this paper.Firstly,the selection process of mainlobe interference eigen-vectors is combined with spatial spectral angle estimation and maximum correlation coefficient matching method,which effectively avoids the error caused by improper selection of constant factors.Then,the power of noise and sidelobe interferences are estimated by the fast power estimation method,and the power matching of sidelobe interference is realized by the correlation coefficient method,and the modified covariance matrix of sidelobe interference plus noise is constructed for beamforming.By comparing the proposed algorithm with the existing excellent algorithms,the proposed algorithm can effectively avoid the complex iterative process and greatly reduce the computational complexity caused by the power estimation process.In addition,the proposed algorithm can effectively suppress the offset sidelobe interference caused by the pre-processing,and has a more ideal output effect.3.Aiming at the problem that the offset sidelobe interference can not be suppressed effectively due to the array platform jitter or the sidelobe interference motion,a null broadening beamforming algorithm based on virtual antenna technology and covariance matrix reconstruction is proposed in this paper.In the case of unknown interference information,the covariance matrix of sidelobe interference plus noise is reconstructed by interference power estimation and matching.Then,the correlation matrix is constructed by using the direction information that needs to be broadened,and the virtual interference information is constructed by sharpening and projection processing.In addition,the beam pattern effect is improved by diagonal loading technology.Finally,the fourth order cumulant in virtual antenna technology is introduced to carry out null broadening beamforming.The algorithm proposed in this paper guarantees sufficient array freedom.Compared with other null broadening algorithms,the range and number of null broadening of this algorithm are more flexible,and the algorithm is basically not affected by the number of sampling fast beats,so the output performance is better.