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On the Design of Robust Steerable Frequency-Invariant Beampatterns with Concentric Circular Microphone Arrays

This paper studies the problem of frequency-invariant beamforming with concentric circular microphone arrays (CCMAs). We develop a beamforming algorithm based on an optimal approximation of the beamformer's beampattern with the Jacobi-Anger expansion. In comparison with the existing frequency-invariant beamformers with either circular microphone arrays (CMAs) or CCMAs, the developed algorithm offers the following advantages: 1) it can mitigate the deep-null problem encountered in CMAs and therefore has a consistent directivity factor over the frequency range of speech signals; 2) it is more flexible in terms of steering flexibility and the resulting beampattern can be steered to any direction; and 3) it does not require the microphones in different rings of the CCMA to be aligned, which is very useful in practice, particularly when microphone arrays with small and compact apertures have to be used.