Stopband Prediction with Dispersion Diagram for Electromagnetic Bandgap Structures in Printed Circuit Boards Yoshitaka Toyota Department of Communication Network Engineering Okayama University Okayama 700–8530 Japan Email: toyota@cne.okayama-u.ac.jp Arif Ege Engin, Tae Hong Kim, and Madhavan Swaminathan Packaging Research Center School of Electrical and Computer Engineering Georgia Institute of Technology Email: engin@ece.gatech.edu Kazuhide Uriu EMC Design Group System Engineering Center Matsushita Electric Industrial Co., Ltd. Abstract— Electromagnetic bandgap (EBG) structures that prevent propagation of electromagnetic waves within a given frequency range are quite effective in suppressing simultaneous switching noise on parallel power planes. However, it is quite time consuming to compute the stopband frequencies of interest using full-wave electromagnetic simulation of the entire structure. In contrast, using dispersion-diagram analysis based on a unit- cell network of EBG structures is more efficient and less time consuming. This paper presents an approach for two-dimensional EBG structures by extending a well-known dispersion-diagram analysis of one-dimensional infinite periodic structures. The stopbands predicted with the proposed analysis were compared with good agreement to measured and simulated results. In addition, the concept was applied to test the stopband range of EBG structures formed on an actual printed circuit board with a test coupon of an EBG unit cell placed on the same board. I. I NTRODUCTION Electromagnetic interference (EMI) has become a critical performance issue in recent mixed-signal systems because of the dense packaging of digital and RF/analog circuits. To iso- late sensitive RF/analog signals from simultaneous switching noise (SSN), electromagnetic bandgap (EBG) structures that prevent propagation of electromagnetic waves within a given frequency range are quite effective in suppressing SSN on parallel power planes. The EBG structure that we have proposed provides an excel- lent isolation of more than 60 dB within the stopband [1], [2]. Fig. 1 illustrates two examples of the proposed EBG pattern, which consists of a lattice with large metal patches and small metal branches connecting adjacent large patches. This pattern is assigned to either the power plane or the ground plane depending on the design. Since this EBG structure requires no additional vias that are essential to the other EBG structures [3], [4], a standard printed circuit board (PCB) fabrication technique is easily applicable for this EBG structure, which is a cost-effective solution. To meet the general demand for more compact wireless devices, furthermore, a size reduction of the EBG structure has been achieved by improving the geometries and materials of the structure [5]. To apply these EBG structures to actual PCBs, it is necessary to quickly and accurately compute the stopband frequencies of interest in the design stage. Since a full-wave electromagnetic (EM) simulation for the entire structure is quite time consuming, a more realistic option is to use a wave analysis that focuses on a unit cell in infinite periodic structures. In previous studies, there have mainly been two kinds of approaches used. One of the approaches is the eigen- mode analysis with a full-wave EM solver [4]. In this case, a high-frequency structure simulator (HFSS) is commonly used because it originally included an eigenmode calculation tool for a unit cell with periodic boundaries. However, a HFSS is also time consuming. On the other hand, the other wave analysis, which uses a transmission-line circuit model [6]–[8], is expected to reduce the computational time, but this model needs to be modified whenever the geometrical features of a unit cell change. x y (0, 0) (0, 0) Port 1 (1, 7) Port 2 (58, 7) Port 1 (1, 22) Port 2 (58, 22) a p a b O (a) (b) Fig. 1. Examples of EBG lattice combining large square patches with small square branches (unit in mm). (a) 1-D lattice (4×1 unit cells). (b) 2-D lattice (4×2 unit cells). 1-4244-0293-X/06/$20.00 (c)2006 IEEE 807