Efficient Implementation of Broadband Beamformers Using Nested Hexagonal Arrays and Frustum Filters

A broadband beamformer is proposed based on nested hexagonal arrays, hexagonal frustum filters and multirate techniques. The nested hexagonal arrays used here consist of several hexagonal arrays of increasing size in the x-y plane (each one called subarray) where the distance between elements in each subarray is two times larger than in the previous one. The proposed beamformer consists of subarray beamformers, each one using the signals obtained from one of the nested hexagonal arrays as the input. These signals are filtered and downsampled so that the Region of Support (ROS) of the resulting 3D signals in the 3D frequency domain are the same for all subbands. The same hexagonal frustum filter design can therefore be used for all subarray beamformers to pass the desired signal and eliminate interferences. The use of nested arrays leads to larger effective aperture at low temporal frequencies and thus, better selectivity for low frequencies. Further, hexagonal arrays are known to require a lower sensor density for alias free sampling than rectangular arrays. Examples illustrate the performance of the proposed beamformer with respect to beampattern and computational complexity.