Modeling Electromagnetic Field Coupling Through Apertures for Radio-Frequency Interference Applications

Electromagnetic field coupling between a digital platform and a radio-frequency antenna through an aperture represents one of the typical coupling paths responsible for radio-frequency interference (RFI) issues in mixed-signal systems. Conventional approaches of modeling radiation through an aperture and evaluating the shielding effectiveness of a metallic enclosure with apertures for classic electromagnetic interference (EMI) applications are not sufficient to handle modern RFI challenges. This paper discusses a segmentation method, together with impedance network representation, employed to divide the enclosure EMI problem into exterior and interior problems. With a port definition based on the vector roof-top basis function, the impedance network for the exterior domain was rigorously formulated using a method of moments solution for mixed potential integral equations. The impedance network for the interior domain was computed using the cavity method based on the analytical formula of 3-D Green´s functions in a rectangular cavity. Connecting a pair of impedance networks yielded the overall impedance relationship between the interior port and the exterior port. Ewald´s transform was used to accelerate the computation of Green´s functions in a cavity with metallic walls, which yielded fast convergence of the series summation in Green´s functions. Good agreement with a commercial full-wave tool validated the proposed approach.