MOMENT METHOD ANALYSIS OF ARBITRARY SHAPED APERTURES IN WAVEGUIDES AND CONDUCTING SCREENS

Abstract

Aperture coupling is an important boundary-value problem in electromagnetics. Practical applications ofaperture coupling can be found in slotted antenna arrays, directional couplers, cavity resonators, radiating slots in screens, microstrip-patch antennas etc. Besides, undesirable coupling of electromagnetic energy may occur ifthere is an inadvertent crack/slit in the applicator/RF equipment leading to electromagnetic compatibility (EMC) and electromagnetic interference (EMI) problems. In this study, we have developed a moment method solution procedure for the general problem of apertures of arbitrary shape coupling arbitrary regions. Appropriate modelling of the aperture surface has been carried out using triangular patch modelling, proposed by Rao et al. [82] for scattering from bodies of arbitrary shape. Suitably defined set of basis functions has been integrated into the formulation which is capable of accurately evaluating fields of apertures of arbitrary shape. The problem has been formulated by invoking equivalence theorem [46] and utilizing boundary conditions on the aperture to derive an integro-differential equation. This equation has been transformed into amatrix equation via the method of moments and solved numerically by simulation on adigital computer. Easy-to-use expressions for numerical integration over a triangular domain have been developed. Further, careful treatment of singular integrals which arise due to the use of Green's funct.on of free space has been performed. Explicit expressions for evaluating various matrices and parameters of interest have been developed. Extensive computation of various parameters for apertures of various shapes, based on the preceding expressions, has been done and results presented. Also, comparative studies for the various parameters of different aperture shapes have been undertaken. Specifically, the four main classes of problems treated in this study comprise apertures of arbitrary shape coupling two half spaces via a conducting screen, waveguide-backed apertures of arbitrary shape in a ground plane radiating into halfspace, apertures of arbitrary shape in the transverse cross-section of a uniform rectangular waveguide and broadwall radiating apertures and slots of arbitrary shape in a rectangular waveguide.