Elliptical boundary arrays for coherent and incoherent imaging

In the imaging of far-field source distributions by a planar array of antenna elements, the quality of the image is determined by the beam pattern of the array. The physical size of the aperture ultimately determines its resolution capability, and the excitation or weighting imparted to the aperture controls the sidelobe characteristics. For a given number and spacing of antenna elements, the largest physical apertures are formed if the elements are distributed only around the boundaries of the apertures. This, however, results in beam patterns with rather high sidelobes. Thus it is of clear practical advantage to have available a technique for effectively filling in the interior of such a boundary aperture through appropriate signal processing applied to the boundary element signals. The paper builds on early results concerning such a technique, which made use of incoherent (receive-only) imaging systems. It is shown that for both incoherent imaging, the latter implemented using a transmit/receive scheme, it is possible to obtain such a filling-in or interpolation effect when imaging with an array composed of an elliptical (or circular) arrangement of array elements. Explicit synthesis theorems which give a specific constructive approach to implementing this effective interpolation to any desired degree of accuracy are given, and this approach is illustrated by giving the results of simulations, both with and without element location errors.