The approach of wideband robust adaptive beamforming （RABF） for speech enhancement based on micro-phone arrays was investigated. It combined the technologies of frequency focusing and diagonal loading

with the former aiming at frequency domain consistency of the beampattern

whereas the latter at robustness against steering vector mis-matches. The loading level was determined based on worst-case performance optimization and a simple closed-form so-lution to the optimal loading was derived after some approximations. Compared with many existing methods in this field

the one with the proposed analytical solution is computationally less demanding and achieves better performance in speech enhancement. Moreover

the analytical solution reveals how different factors affect the optimal loading. Numeri-cal examples confirm its correctness and effectiveness.