Flexible Robust Adaptive Beamforming Method With Null Widening

The nonstationarity of interferences and array errors may bring fatal degradation to the interference cancellation performance of an adaptive beamformer. Covariance matrix tapering (CMT) can produce wide troughs in receiving pattern and becomes a promising solution. However, not only the full adaption methods but also the robust sidelobe canceller widen all nulls symmetrically to the original directions of arrival (DOAs) with the same width. In fact, in most cases, the adaptive pattern does not need symmetrical and equivalent-width nulls since it is of little possibility that different interference poses the same nonstationarity. To cover the worst nonstationarity, traditional CMT methods need to produce a widest null and will suffer a waste of degrees of freedom (DOFs). In this paper, a flexible method for null widening is proposed which can produce wide null with different desired width and asymmetry. The asymmetry is developed from the spatial asymmetrical interference cluster, and the unequal null width is produced by disturbing different interference space with different tapering matrix. Computer simulation result corroborate the feasibility and merits of the proposed method.