Abstract: The robustness of the Polynomial Broadband BeamFormers(PBBF)is theoretically studied.Based on the statistical analysis of beampattern distortion in the presence of microphone mismatches and the analysis of white noise gain,the inherent properties on the robustness of the PBBF are revealed.It is shown that,when the main lobe of the beam is steered to the edge of look direction range,the robust performance of PBBF is worse than that when steered to the center.Moreover,the main factors affecting the directivity index of the PBBF are also studied.It is pointed out that the truncation error of the polynomial structure may lead to large deviation of the main lobe orientation,which can significantly deteriorate the directivity index as a result.In order to overcome the drawback of the existing design,we then present an improved design structure with a self-calibration capability.Compared with the existing design,the steering module used in the proposed structure can fully reflect the nonlinear relationship between the expected and the actual beam orientation,thus avoiding the large steering deviation caused by the linear steering module used in the existing structure,which can effectively improve the performance of the PBBF.