Product beamforming and nested array in tandem for enhanced sonar performance

High-performance sonar systems mostly combine a large sensor array and an efficient beamformer for enhancing the overall detection capabilities and estimation of Direction of Arrival (DoA) of the acoustic signal released from underwater targets in the ocean. The array geometry and the number of elements have direct influences on the beam width and the signal to noise ratio but increase the complexity in terms of hardware and computational requirement. Even when such hardware complexities are accommodated in complex systems, the performance of such systems is often par below its expected level because of the limitations of the beamformer. The efficacy of the beamforming lies in obtaining a narrow beamwidth for the main lobe with minimum sidelobe levels (SLL) while keeping the element utilization factor as maximum as possible. This in turn demands proper optimization over array parameters and beamforming methods. Several optimization techniques have been established over the years and practised in a variety of sonar systems. Statistical array processing with nested and sparse array concepts with virtual elements offer effective solutions to these challenges. This article proposes an approach comprising a novel product beamforming concept that uses the idea of destructive interference in tandem with the nested array concept to demonstrate that better sonar performance can be achieved. The former helps to minimize the SLL without affecting the veracity of the main lobe, while the latter helps to reduce the requirement of a large number of sensors and thereby reduce the system complexity.