A residue-based robust adaptive beamforming with flexible null management

Abstract

Steering vector errors and interference nonstationarity are two main degrading factors of adaptive beamforming methods. The former can be mitigated by using the interference-plus-noise covariance matrix (INCM), instead of sample covariance matrix. An estimate of INCM can be obtained through the integration of the Capon spectrum, which usually approximated by a summation over a uniform grid points on the angular region of interference and noise. A simple technique to overcome the nonstationarity problem is the null widening technique using covariance matrix tapers (CMT). The first purpose of this paper is to introduce a gridless method to do the integration for calculating the INCM. The method, applicable for uniform linear arrays, applies the residue theorem to calculate the integral through converting it into an integral over a closed contour. The second purpose is to modify the beamformer such that each null can separately be widened and deepened to definitely mitigate the corresponding interference. This purpose is also attainable by the residue-based representation of INCM, which separates the contribution of each interference, based on which a flexible null widening and deepening technique is introduced by applying different CMTs on different contributions and by moving the corresponding singular point toward the unit circle.