An attempt to 3D Capon beamforming

With growing interest in three-dimensional (3D) beamforming, this paper analyzes the standard Capon method in the 3D case with a planar array configuration, in which the direction of arrival is characterized by both horizontal and vertical angles. While simulations show a bad performance of the standard Capon method, theoretical and experimental analysis indicate the perturbation of small eigenvalues of estimated autocorrelation matrix and the increment of array element number are responsible for the performance degradation in the 3D case. Then an eigenvalue modified method is adopted to repair this drawback, and a decomposition method is also proposed to reduce the complexity brought by the increased array scale. Simulations show that the decomposition method outperforms the standard Capon method, but has a moderate performance degradation compared with the eigen-based method, demonstrating its possibility of implementing in the practical downlink beamforming weight calculation.