Passive ranging with focusing beamformers and shaded arrays

Abstract

We consider focused beamforming using passive arrays as a means of achieving rapid range solutions and demonstrate that a new class of geometry‐dependent amplitude shading distributions can improve range resolution. The distribution is determined by treating the array as if it were a set of samples distributed in a hypothetical curved wave front originating from the array focus and by projecting the hydrophone coordinates onto the spherical surface along radii emanating from the focus. We define a continuous shading distribution on this surface to assign weights to each hydrophone input and divide the shading distribution by the wave front sample density. This technique is called “wave front sample density compensated (WSDC) shading.” Simulated performance is presented for a large surveillance towed array with a target whose signature contains a characteristic tonal and is located broadside to the array. A comparison among unit shading, a simple element placement scheme, and the WSDC method shows that, although there is some loss in gain, the focused beamforming method with the WSDC shading provides greater resolution and computational speed and lower side‐lobe levels than the other methods. [Work supported by ONR.]