Radiating emissions from the planar electromagnetic bandgap (EBG) structures

Electromagnetic bandgap (EBG) structures are considered as a viable solution for the problem of switching noise in printed circuit boards and packages. Less attention, however, has been given to whether or not the introduction of EBGs affect the EMI potential of the circuit to couple unwanted energy to neighboring layers or interconnects. In this paper, we show that the bandgap of EBG structures, as generated using the Brillouin diagram, does not necessarily correspond to the suppression bandwidth generated using S-parameters. In fact, we show that the slow modes which typically exist at the edges of the bandgap of periodic structures contribute to increased radiation, even within the suppression band obtained from the S-parameters. We validate this finding using numerical simulation. Based on this work, design guidelines for EBG structures can be drawn to insure not only suppression of switching noise but also minimization of EMI.