Hybrid phase shift and shifted sideband beamforming for large-aperture MIMO sonar imaging

A multiple-input multiple-output (MIMO) sonar can form a large-aperture virtual uniform linear array (ULA) from a small number of physical elements. However, the large-aperture MIMO sonar encounters a dilemma between the computation load and the imaging performance. Since the traditional phase-shift beamformer (PSBF) and shifted sideband beamformer (SSBF) cannot solve the dilemma individually, the authors proposed a hybrid beamformer (HBF) which combines PSBF and SSBF together. Specifically, the proposed HBF contains the off- and on-line processing. In the off-line processing SSBF is applied to the transmitting ULA to process transmitting waveforms. In the on-line processing PSBF is applied to the receiving ULA, and outputs of off-line SSBFs are utilised to matched filter outputs of PSBFs. Thus, in the proposed HBF the time delays of SSBF is calculated off-line; and the multi-beam processing is simplified as PSBFs on the receiving ULA. Consequently, the proposed HBF can reduce the computation load of the large-aperture MIMO sonar effectively while obtaining a fine imaging performance. Numerical simulations show the effectiveness of the proposed HBF.