Analysis of Sidelobe Level Spread Due to Sonar Array Distortion: A Comparison of Beamformers

Sonar arrays are extensively utilized in maritime surveillance and for the safe navigation of passing vessels in the ocean. The characteristic of the beam pattern is one of the most vital properties of a soanr array. A directional main lobe with low sidelobe levels (SLLs) efficiently improve the sonar performance and reduce the interferences. Beamformers have been employed for forming the beam pattern and controlling the lobes of the beam. They are intended to filter out noises and other incoherent signals from all directions while boosting the signal-to-noise ratio from the desired direction essentially to detect targets and estimate their location. Both pre-formed beams in all directions or beam steering are usually followed during a sonar operation. Such pre-formed beams are required to be identical and undistorted. Diverse beams produce errors in the bearing, resolution and judgement of target detection, etc. Beamwidth, SLLs, beam sensitivity and tolerance to the array distortion are the key factors of beam identicality. They can be regulated by optimizing the individual elements of the array with a proper weighting factor called windowing. These optimizations are often complex and sensitive to mismatches in individual sensors, namely variations in receiving sensitivity, error in sensor location, failure of sensors, and acoustic centre, etc. and hence distort the beam pattern and introduce spread in lobes. This paper presents an investigation on the SLL spread due to array distortions. The four most commonly used standard beamformers and a novel product beamformer are chosen for the comparative analysis. The presented results suggest that the product beamformer is more robust with less SLL spread than the traditional beamformers.