Estimation of common-mode EMI caused by a signal line in the vicinity of ground edge on a PCB

The authors have developed an estimation method of common mode radiation from a PCB. A parameter named ´current division factor´ explains a generation mechanism of the common mode. Rigorous analysis, instead of rough approximation, is required to calculate the factor for an asymmetric structure. A 2-dimensional static electric field analysis by the boundary element method (BEM) is applied to this calculation, which requires less time than 3-dimensional simulations. EMI increases when the signal line comes close to the edge of ground pattern. The effect is evaluated with the simulation of the factor. The estimation agrees well with measurement within 1 dB.