Proc. IEEE International Microwave Symposium, June 2006. IEEE Copyright © A Small Electromagnetic Bandgap Structure R. B. Waterhouse and D. Novak Pharad, Glen Burnie, MD 21061, USA Abstract — We present a small Electromagnetic Bandgap (EBG) cell which is easy to fabricate on standard PCB material and can be used where space is a premium. The EBG structure is an extension of the classical uni-planar structure where the inductance due to the thin transmission line sections is increased by meandering these microstrip lines within the EBG cell itself. We demonstrate the concept with an EBG surface that was designed and developed at 300 MHz on standard FR4. The size of a 3  3 structure is only 7.53 cm  7.53 cm and provides 10 dB attenuation across the surface. Index Terms — Electromagnetic Bandgap structures, artificial magnetic conductors, high impedance ground planes. I. INTRODUCTION Electromagnetic Bandgap (EBG) structures, artificial magnetic conductors, metamaterials, or high impedance ground planes [1 – 4] have received much attention due to their interesting electromagnetic properties. These structures can prevent the propagation of electromagnetic energy along their surface over a band of frequencies and therefore can be used to reduce electromagnetic interference in circuits [5], or even reduce radiation in a particular direction when coupled to an antenna [6]. One potential issue related to an EBG structure is the overall size required to make these surfaces effective; essentially the behavior of the EBG structure in based on the interactions between adjacent cells and therefore the larger the number of cells, the more effective the structure. This can be a problem when there is limited real-estate for the structure, especially when trying to integrate EBG surfaces with wireless communication devices/radiators that operate in the lower microwave frequency spectrum (less than 1 GHz). Having said this, the structure presented in [6] was only three cells wide and was still able to operate effectively over the band of interest at 2.4 GHz. However the size of the cell is a critical issue if EBG structures are to be integrated with other RF components for applications below 1 GHz. Recently there has been research into making the cell of an EBG structure smaller. For example, in the work presented in [7, 8] significant element size reduction was achieved for structures operating above 1 GHz, albeit at the expense of bandwidth which is consistent with fundamental electromagnetic theory [9]. The reduction in operating bandwidth is not a problem for most low microwave frequency wireless applications as the transmission bandwidths are usually less than 10 % of the carrier frequency. In this paper we present a new small EBG cell that can be used in applications where there is only a limited space available for the EBG structure. The concept is an extrapolation of the EBG structure presented in [2] and is relatively straightforward to design. We will present the design philosophy and equations used to create the new structure. We will also give an example of the EBG structure designed and realized at 300 MHz using low cost FR4 as the substrate. Although the overall structure of this new EBG is only 7.53 cm  7.53 cm in size, it can still provide 10 dB attenuation of power across its surface. II. CONFIGURATION AND DESIGN As described earlier, the design of the proposed EBG structure is based on the uni-planar surface presented in [2]. There are several advantages of the uni-planar EBG structure compared to the ‘mushroom’ version created by Sievenpiper [1]. Firstly, no vias are required for the uni-planar version which dramatically simplifies the fabrication process. Also, the uni-planar geometry can operate on electrically thin materials, which is important when investigating applications in the low microwave frequency spectrum [10]. Unfortunately the unit cell of the uni-planar EBG structure is typically larger than the ‘mushroom’ version and therefore for a given number of cells, these surfaces are larger. A photograph of a conventional uni-planar EBG structure designed for operation at 1 GHz is shown in Fig.1 highlighting the unit cell of the surface. Fig. 1. Photograph of a uni-planar EBG structure. For the EBG cells in [2], the gap between adjacent cells effectively provides the necessary capacitance for the