Per-Unit-Length Matrixes of Shielded Coupled Microstrip Lines With Different Grounds

This paper addresses the problem of intentional electromagnetic interference (IEMI) that affects grounding circuits in critical equipment. As a test structure, we use a structure that approximates a printed circuit board (PCB) of a simple electromagnetic interference (EMI) filter. This structure includes two coupled microstrip lines that represent the Line and Neutral conductors, the finite ground plane of these microstrips that represents the Earth conductor, and a rectangular shield (case). To simulate IEMI excitation of grounding circuits, the structure is modeled as a section of a 3-conductor transmission line (with the 4th conductor as the circuit ground). Two grounding options are examined: the first features the finite ground plane that serves as the circuit ground and the shield that acts as the signal conductor, and the second has the shield as the circuit ground and the finite ground plane as the signal conductor. The paper presents preliminary results due to significant computational errors that could impact subsequent simulations. Specifically, per-unit-Iength matrices for both options were carefully calculated using the method of moments implemented in the new TUSUR.EMC domestic software to ensure accurate simulations of time and frequency responses. The segmentation of conductor-dielectric and dielectric-dielectric boundaries in the cross-section was improved to obtain more accurate matrices suitable for reliable subsequent simulations. Furthermore, differences between matrices for the two grounding options were analyzed.