Array optimization applied in the near field of a microphone array
James G. Ryan, Rafik A Goubran · IEEE Transactions on Speech and Audio Processing · 2000
This paper describes the application of array optimization techniques in the near-field of a microphone array. It is shown that the optimum weights obtained for microphone spacing equal to a half wavelength are real, aside from the propagation delay, and inversely proportional to the distance from each microphone to the focal point. When the microphone spacing is less than a half wavelength, the optimum weights are super-directive requiring both an amplitude and phase adjustment in addition to delay-and-sum beamforming. In the super directive regime, the maximum array gain increases as the distance to the focal points decreases. The technique is suitable for applications where the source of interest is located in the near-field region but interfering sources are located farther from the array.