High gain beamforming method in low-frequency band using virtual array migration

Abstract

When measuring the low-frequency radiated noise of underwater low-noise targets, a conflict arises between the large-scale array’s ability to achieve low-frequency gain and the reduction of propagation loss at a fixed measurement distance. This paper presents a method for virtual array element migration, based on the measured phase modulation of array elements. By increasing the phase differences between adjacent elements and further enhancing the phase differences between steering vectors in different directions, the proposed method improves the suppression of undesired directional interference signals, thereby enabling high-gain measurements under limited aperture conditions. To mitigate the reduction in robustness associated with virtual array construction, a virtual array factor is introduced for analysis. The results demonstrate that when the virtual array factor is set to 1, the proposed method performs comparably to conventional beamforming. When the virtual array factor exceeds 1, it can effectively enhance the suppression of interference signals in the low-frequency range. The optimal value of this factor should be selected based on the signal-to-noise ratio of the data to ensure the robustness of the algorithm. Both simulation and lake test data demonstrate that the proposed algorithm significantly outperforms conventional methods in terms of its ability to reject interference in low-frequency radiated noise measurements.