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.