Two stage computation of apertures in finite screens

Large, finite screens containing smaller apertures with a variety of geometries are addressed. Owing to the large size of the finite screen it is assumed that matrix methods would not be applicable for the problem in its entirety. The use of the conjugate gradient (CG) algorithm may not provide the most efficient approach either, for the following reasons: each configuration requires a separate computation; a separate computation is needed for each excitation; it has been shown in the past that intricate geometries may inhibit convergence. The solution process is separated into two distinct stages: (a) Green's function for the unperturbed, short circuited finite screen structure is evaluated numerically. At this stage the CG is applicable with good and predictable convergence characteristics and no large matrix needs to be stored. (b) This Green's function is subsequently used with a new magnetic field integral equation for the aperture region, solved by the moment method. Most of the matrix elements are useful for aperture configurations, hence computation time for each configuration is greatly reduced. The scheme thus combines the two methods in a way that utilises their advantages where they are most applicable.