Jean P. Feuillet
Space and Naval Warfare Systems Command, Washington, DC 20999
Walter S. Allensworth
Appl. Hydro-acoustic Res., Inc., Rockville, MD 20850
Bruce K. Newhall
Johns Hopkins Univ., Laurel, MD 20723
Technology of towed line arrays and associated signal processing has progressed in recent years to the point that wideband multiline array coherent signal processing can now be performed in real time. Earlier implementation (1993) of a multiline array beamformer centered around the ability to convolve a conventional line array beam response with that of an orthogonal dipole. Performance of this implementation provided a unique nonambiguous right/left beam with roughly -20-dB energy rejection in the null steered direction over a significant range of vertical arrival angles. However, performance suffered significantly with other than straight and parallel towed lines. Recent (1994) implementation of a beamformer for a twin-line towed array has shown the ability to form deep backlobe nulls (-37 dB). Implementation of this beamformer is similar to the MVDR method except an isotropic noise field is assumed in the horizontal plane. This technique allows for uniform suppression of sidelobes at all off-MRA azimuth directions while maintaining backlobe rejection and MRA shape. Spatial weights are adaptively calculated based on the estimate of the twin-line array shape. This method has been shown to be robust for nonparallel and dissimilar shapes.