Beam output interference cancellation for line arrays

Broadband multibeam line array systems are increasingly used for initial detection in underwater acoustics. Beams with power significantly greater than the average indicate directional sources. Strong sources can corrupt the spatial normalization by leaking through the sidelobes of the beam pattern and causing beam to beam imbalance. This imbalance can obscure the detection of weaker contacts. This paper discusses a beam output approach to minimize the impact of strong interference. The technique uses an adaptive filter to subtract from the beam under test a weighted linear combination of samples of a beam pointed at the interference. The weights adapt to force the correlation between the filtered output and the reference beam to zero. We analyze the effectiveness of interference suppression by calculating the spatial variation of the beam output power before and after filtering, for a variety of geometries, and as a function of interference of noise ratio. Our results indicate reductions of average spatial bias levels by amounts greater than 5dB for interference to noise ratios greater than -10 dB at the beamformer input. Our results indicate the advantages of beam output interference suppression and suggest a potentially effective implementation.