Evaluation of Common-Mode Radiation from Printed Circuit Boards by Modelling Imperfect Ground Effect

I-Fong CHEN  Ching-Wen HSUE  

IEICE TRANSACTIONS on Communications   Vol.E85-B   No.12   pp.2924-2933
Publication Date: 2002/12/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Electromagnetic Compatibility(EMC)
common-mode radiation,  imperfect ground,  transmission line,  EMI,  wire antenna,  

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Fundamental EMI source that generates common-mode radiation from printed circuit boards (PCBs) is investigated here. It is done by modelling the ground lines of PCBs as imperfect ground. The radiation emission in the far zones from PCBs is obtained by regarding interconnects on PCBs as transmission lines and the far field emission is evaluated based on the current distribution of the lines. The finite size ground trace is defined as an imperfect ground, that can be viewed as an inductive reactance which, in turn, causes the ground return path to radiate as a wire antenna. For the accurate analysis of imperfect ground effect, we divide the equivalent circuit into N sections. In addition, based on transverse electromagnetic (TEM) assumption, we estimate the electromagnetic interference (EMI) of three typical PCB geometries, namely, coplanar strips, parallel-plate strips and microstrips. The quantitative value of induced current distribution along the ground return path depends on the physical size, geometry and length of ground traces. Measured data are presented to confirm the result of numerical analysis. A knowledge of EMI source mechanisms and their relationship to layout geometries is necessary to determine the essential features that must be taken into account to estimate emissions and provide direction for reducing EMI due to interconnects on PCBs.