Joint-modal beamformer for acoustic vector circular array

To address the issue of reduced robustness caused by eigenbeam nulls in the traditional circular array modal-domain beamformer, a null-free modal-domain beamforming method based on pressure-velocity joint modes is proposed. By exploiting vector signal processing techniques, null-free eigenbeams are constructed, and a pressure-velocity joint modal-domain model is established. Within this model, delay-and-sum, phase-mode, and frequency-dependent multi-constraint beamforming methods are developed. In particular, the frequency-dependent multi-constraint method adaptively adjusts design parameters with frequency, thereby achieving a balance between robustness and array gain. Simulation and experimental results demonstrate that the proposed method effectively eliminates eigenbeam nulls and significantly improves broadband robustness. Compared with the conventional multi-constraint method, the proposed frequency-dependent design improves the white noise gain by more than 3 dB at the cost of less than 0.3 dB in array gain.