Spatial aliasing-cancellation for circular microphone arrays

Circular microphone arrays facilitate spatial processing and analysis of sound fields in applications where the sound field sources are primarily expected from the azimuthal directions. The operating frequency bandwidth of the array depends on the array aperture and on the number of microphones. At high frequencies, spatial aliasing generates side-lobes in the array beam pattern, which limits array performance. One way to reduce the spatial aliasing effect and to extend the array operating bandwidth is to increase the number of microphones. In this paper, a novel method for designing beam-formers that overcome the effect of spatial aliasing is presented. The undesired side-lobes are suppressed through signal processing without increasing the number of microphones or physically modifying the array. This is achieved by taking into account the expected aliasing pattern in the beamformer design, leading to a higher directivity-index at frequencies previously considered to be beyond the microphone array frequency range of operation. A simulation example with a 15-element circular microphone array illustrates the performance of the proposed method.