I would like to obtain a good reference (or references) on the implementation of a wideband beamformer for a small planar (rectangular) array comprised of 4 rows by 6 columns, for 24 elements in total. This is a passive acoustic array with air-coupled microphones; the array does not transmit. Each element in the array has the same spacing distance. Given discrete input signals from each element, I would like to compute the beamformer/beamsteering output for a beam at a particular azimuth and elevation. I need to be able to compute multiple beams to electronically steer the array. Is it possible to compute multiple beams all at the same time?
I suppose that I might need to use Fourier-domain techniques involving the FFT. Are these techniques justified for my small array? I've found an IEEE conference paper (http://www.curtistech.co.uk/papers/wideband.pdf or http://dx.doi.org/10.1049/ic:19980121) that may deal with this technique, but how would I apply this to a 2D planar rectangular array? I am interested in the mathematics operating on discrete signals rather than descriptions of the process.
Since this is an acoustic array, the elements are evenly spaced on a 4 rows by 6 columns grid. The spacing between the elements is less than $\lambda/2$, where $\lambda$ is the minimum wavelength of the sound wave. The wavelength range is between 3.31 cm and 331 cm. This is a receiving array. The target area should be in the far field of the array, but I am also wondering if it is possible to resolve signals in the near-field as well.