The performance of adaptive beamforming degrades dramatically in practice due to steering vector mismatches.As a solution

diagonal loading is usually used to improve its robustness.However

how to select the loading level remains an open problem.In this paper

the robust adaptive beamforming (RABF) which determines the loading level based on worst-case performance optimization is investigated and a simple closed-form solution to the optimal loading is derived after some approximations

revealing how different factors affect the optimal loading.On the basis of this solution

a performance analysis is carried out

focusing mainly on the source power estimation and signal-to-interference-plus-noise ratio (SINR).The corresponding analytical results are presented for performance prediction.Finally

numerical examples demonstrate the correctness of the analysis in this paper.