Beamforming with nonsinusoidal signal for grating lobes suppression in underwater acoustic imaging

Suppression of grating lobes caused by spatial aliasing should be considered in array design for underwater acoustic imaging. To address this problem, a different approach to beamform with nonsinusoidal signal for grating lobes suppression is proposed in this paper. The desirable nonsinusoidal signal can be obtained by exacting the envelopes of the received signals. The reception of the envelopes with short time duration is identical to weak signal detection and matched filtering is employed to enhance the signal-noise-ratio (SNR). And then beamforming with signal envelopes in time domain is investigated. As the signal envelope is nonperiodic, grating lobes can be eliminated from the beam pattern and the element spacing is not restricted by half of the wavelength. The array designed with the proposed method is a kind of sparse arrays. Such an array with only a few elements leads to low-complexity and low-cost imaging system. The validity of the proposed method is verified by numerical simulations and the results show the proposed method can achieve a better performance of beam pattern than the conventional method with sinusoidal signals.