Nearfield broadband adaptive beamforming

A nearfield broadband adaptive beamforming approach based on the modal expansion of the solution to the spherical wave equation is formulated. It provides an efficient parameterization for the nearfield beamforming problem with a single parameter to focus the beamformer to a desired operating radius and a set of modal coefficients to control the angular response. As a consequence, the adaptive beamformer has a frequency invariant response for nearfield sources, decorrelates coherent interferers (thus combating signal cancellation) and has a smaller number of parameters to be adapted compared to a conventional beamformer. A simulation example is presented to demonstrate the use of the proposed method in microphone array applications in speech acquisition systems.