Effect Of Image Plane Dimensions On Radiated Emissions

The effect of finite dimensions of an image plane on the reduction of radiated emissions is investigated numerically. The applications are important in the reduction of the radiated fields from common-mode currents on Printed Circuit Board (PCB) conductors (lands). Earlier experimental results showed that common-mode currents tend to be the dominant contributors to the emissions from PCB lands [1,2]. Additional experimental results showed that placement of a metallic plane beneath the PCB could dramatically reduce the emissions [3]. The numerical results presented in this paper are intended to confirm these observations and are obtained for a ground plane of infinite length but finite width (2D) and for a ground plane (and current) of finite width and length (3D). These results show that reductions of radiated emissions of the isolated current of around lOdB are obtained when a finite ground plane is placed beneath it. It is also shown that as long as the ground plane dimensions are larger than approximately one wavelength, the height of the current above the ground plane is electrically small and the current is not too close to the edges of the ground plane, image theory provides an adequate characterization of the problem even though the ground plane dimensions are finite.