Closed-form expressions for determining approximate PMC boundaries around an aperture in a metal cavity wall

Modern electronic systems may use mixed RF/digital technologies to achieve various functionalities, which leads to various intra-system interference problems including the RF interference from noisy digital circuits to sensitive RF receivers, especially when the overall system is contained in a metal enclosure. A fast method based on a cavity formulation can be used to estimate the internal noise coupling mechanisms inside the enclosure. This method assumes that only the TM_z0 mode exists inside the enclosure, i.e., the electric field along the z-direction is constant. The cavity formulation fails in the region adjacent to an aperture in an enclosure wall, since the aperture introduces higher order modes. The developed closed-form expressions compute the Ez-field variation along the z-direction. Thus, they can be used to estimate the breakpoint where the cavity method is no longer effective.