A Lossy Coplanar EBG Structure for Anti-Resonance Suppression and Stopband Extension

In this paper, a lossy coplanar electromagnetic bandgap (EBG) structure embedded with periodic resistors is proposed for anti-resonance suppression and stopband extension. With the aid of the resistors, anti-resonance formed by the capacitance of the unit cell and the parasitic interconnect inductance of the decoupling capacitor is mitigated, the lower cutoff frequency is shifted below 1 MHz, three orders of magnitude reduction compared to the conventional coplanar EBG structures and two orders of magnitude reduction compared to the current stopband enhanced coplanar EBG structures. An equivalent circuit model is developed and the effect of parameters of capacitance, inductance and resistance of the lossy components is analyzed. To verify the effectiveness of the structure, test boards are fabricated and measured both in the high and low-frequency range. Measurements and full-wave simulation results are in good agreement, showing that the proposed structure creates a stopband from 0.63 MHz to 9.91 GHz under the suppression level of -30 dB. The lower cutoff frequency falls in the effective frequency range of the lossy RC components and becomes insensitive to the bridge inductance, so the bridges between neighboring EBG cells can be shortened and widened, which will mitigate the degradation of signal integrity. Eye diagram results show the maximum eye open has a 25% improvement by the lossy components.