Reactive power radiated from the planar electromagnetic bandgap structures, a source of EMI in high speed packages

Electromagnetic bandgap structures are frontrunners in solving GHz switching noise in printed circuit boards and packages. However, less attention 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 typically generated using S-parameters. We show that the reactive near fields radiating from openings within the EBG layer can be substantial and are present in the frequency band including propagating and non-propagating mode regions. These fields decay fast with distance, however, they can couple significant energy to adjacent layers and to signal lines. 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 and insuring signal integrity.