Research On Optimal Robust Beamforming Algorithm Of Digital Array

Adaptive beamforming has been widely used in many fields due to its advantage of adaptively adjusting the weight vector.In practical applications,the performance of classical beamformers is degraded because of many non-ideal factors,such as direction-of-arrival error,steering vector mismatch,excessive snapshots number and the exists of desired signal in the sample covariance matrix.Many robust beamforming algorithms have been proposed in recent years.This paper focuses on the optimal robust beamforming algorithm for the case of unknown mutual coupling in the uniform linear array,as well as robust adaptive beamforming of coherent signals in the presence of the unknown mutual coupling.The main work and research contents are as follows:1.Two optimal beamforming criteria are introduced.Three classical beamforming algorithms are discussed.The performance of these algorithms are analyzed through simulation results.2.For the case that the desired signal exists in the covariance matrix,three kinds of algorithms based on covariance matrix reconstruction are studied and analyzed.Because these algorithms simultaneously re-estimate the steering vector of the desired signal,the robustness of these algorithms have been greatly improved.3.In most cases,it is assumed that the array elements are independent of each other,but in practical applications,there exists mutual coupling effect due to the small spacing between the array elements.The data matrix structure is distorted.For this case,two optimal robust adaptive beamforming algorithms for unknown mutual coupling are proposed.Using the Toeplitz property of the mutual matrix of the uniform linear array,a signal complex envelope containing mutual coupling information is obtained,and the desired signal’s covariance matrix and the interference-plus-noise covariance matrix including the mutual coupling information are reconstructed.Finally,robust beamforming is obtained by using the criterion of maximizing the output signal-to-interference-plus-noise ratio and the matrix reconstruction criterion based on power sampling.The proposed two algorithms are effective for DOA mismatch,steering vector mismatch,as well as the mutual coupling without introducing any iterative process.The output performance is very close to the optimal beamforming performance.4.The existence of a coherent signals causes the data covariance matrix to be out of rank,and the conventional beamforming algorithm loses its ability to suppress interferences.Therefore,a new method based on the matrices reconstruction is proposed to deal with coherent signals in the presence of the unknown mutual coupling.Based on an iterative adaptive method,the coherent interference-plus-noise covariance matrix can be reconstructed.Finally,based on the maximum output signal-to-interference-plus-noise ratio criterion,a beamformer which is robust against mutual coupling and coherent signals is obtained.The algorithm is robust to large DOA mismatches,and the output SINR is very close to the optimal beamforming algorithm over a large range of SNR,and converges fast.