Broadband nearfield beamforming using a radial beampattern transformation

Abstract

This paper presents a new method of designing a beamformer having a desired nearfleld broadband beampattern. The methodology uses the spherical harmonic solution to the wave equation to transform the desired nearfleld beampattern to an equivalent farfleld beampattern. A farfleld beamformer is then designed for a transformed farfleld beampattern, which, if achieved, gives the desired nearfleld pattern exactly. Salient features of the new method are as follows: i) The nearfleld patterns can be achieved for all angles and not just the primary look direction. ii) There is no theoretical restriction on the bandwidth. iii) General array geometries may be used. As an illustration, we apply the method to the problem of producing a practical array design that achieves a nearfleld beampattern that is frequency invariant over an octave bandwidth, where at the lowest frequency, the array-source separation is three wavelengths. Show more