A comparison of two different ray based methods for analyzing large convex conformal antenna arrays

Abstract

A uniform geometrical theory of diffraction ray based approach is employed in two different ways to describe the radiation by large, flush mounted antenna arrays that are conformal to a larger complex metallic platform which is treated here as a perfect electric conductor. The platform is assumed to be locally convex in the neighbourhood of the array. First the array aperture surface field distribution is obtained numerically via, for example, the finite element method by solving only the local array problem excluding the remaining part of the platform outside the neighbourhood of the array. An equivalence theorem allows one to define equivalent magnetic surface current sources in terms of these numerically obtained array aperture surface fields that radiate the original fields with the aperture now closed by a conducting surface. Rays are then launched from these equivalent surface sources. In the first method, the rays are launched from only a few special flash points in the aperture interior, and from points on the aperture boundary, to provide a collective description for array aperture radiation fields. In the second method, the array aperture is decomposed into an appropriate but relatively small set of subaperture domains, and an equivalent ray based point magnetic current is defined at the centres of each subaperture from which rays are launched onto the array platform with the aperture again closed by a conductor as specified by the equivalence theorem. Both these methods for launching rays from the array aperture are far more efficient than the conventional approach of quantizing the equivalent magnetic surface current distribution into a set of sufficiently dense set of equivalent infinitesimal magnetic current sources, and then launching rays from this very large set of quantized sources. In all the methods, namely the conventional, the collective and the subaperture methods, respectively, the rays once launched from the corresponding equivalent sources then undergo interactions with the rest of the complex array platform to generate the near and far zone radiation field at any external observation point. It is seen that the collective ray method is more efficient, but the subaperture ray method is more robust; also, both are far more efficient than the conventional approach.