An Extended Cavity Method to Analyze Slot Coupling Between Printed Circuit Board Cavities

In high-speed multilayer printed circuit boards, gaps are commonly used in planes, where different areas are utilized for different logic levels or where noise isolation from one area to another is necessary. However, these gap structures could present serious signal integrity and electromagnetic interference issues. In this paper, an extended cavity method is developed to characterize noise coupling caused by slots or gaps in the middle plane of a three-plane structure. According to the equivalence principle, the entire structure can be divided into two plane pairs without any slot in the middle plane, and then, equivalent magnetic currents are needed in both plane pairs in the slot region to retain the same field distributions. Dyadic Green´s functions of a rectangular cavity with perfect electric conductor top and bottom surfaces and perfect magnetic conductor sidewalls are derived for both electric and magnetic current excitations. Magnetic auxiliary ports with “magnetic voltage” and “magnetic current” are defined in the slot region to enable vertical connections of two plane pair. The conventional cavity model and segmentation technique are extended in this paper to handle such magnetic auxiliary ports. The proposed method can be used to effectively analyze the apertures with arbitrary shapes and is validated by full-wave simulations.