Robust Null Broadening Beamforming Based on Adaptive Diagonal Loading for Look Direction Mismatch

The error in the look direction estimate can cause the mismatch between the actual and presumed steering vector. With this imprecise knowledge, the mainbeam is shifted leading to the self-null phenomenon of the desired signal and resulting in the performance degradation. In order to be robust against direction of arrival (DOA) mismatch, an adaptive diagonal loading technique is proposed and applied to the minimum variance distortionless response (MVDR) beamformer and the covariance matrix taper (CMT) null broadening beamforming. The adaptation is terminated by convergence of an indicator for the updated presumed DOA. The simulation results in comparison between a fixed diagonal loading and the proposed diagonal loading technique exhibits enhanced robustness and increased output signal to interference plus noise ratio (SINR).