Standard Capon beamformer is sensitive to steering vector error and diagonal loading is an efficient approach to improve its robustness. Based on maximization of the output power, a varying diagonal loading algorithm has been proposed by Jian Li et al (2003). By analysis of this paper, it shows that the effect of antenna amplitude, phase and position errors to steering vector is generally less serious than that due to steering angle errors. For large steering angle error case, we propose to use pipe constraint instead of sphere one. Because optimization over a pipe is difficult, we propose to let a sequence of spheres overlay the pipe and Li's algorithm is subsequently applied to every sphere constraint. Simulation results demonstrate its superior performance.
['Changzheng Ma', 'Boon Poh Ng', 'Haoji Bao', 'Xuebin. Yang']
Robust adaptive beamforming for large steering angle error