Design and Analysis of Dual-Band EBG Resonator Antennas Using Millimetre-Wave EBG Structures for Improved Directivity and Radiation Bandwidth Basit A. Zeb 1 , Karu P. Esselle 1 1 Centre for Microwave and Wireless Applications, Department of Electronic Engineering Macquarie University, Sydney, NSW 2109, Australia Fax: + 61(2)–98509128; email: basit.zeb@students.mq.edu.au, karu@ieee.org Abstract The design of a dual-band Electromagnetic Band Gap (EBG) resonator antenna using the defect- mode characteristics of a millimetre wave EBG superstrate is presented. The technique of multiple source excitations is used to increase the antenna directivity and 3-dB radiation bandwidth in two frequency bands. Computed radiation patterns confirm the dual-band directivity enhancement with a wider radiation bandwidth. By properly spacing the array feed elements, high directivity and low side-lobe levels are achieved without the appearance of grating lobes. 1. Introduction The use of Electromagnetic Band Gap (EBG) structures as antenna superstrates is a promising solution for enhancing the directivity of various antennas. One class of such antennas, also known as EBG resonator antennas or Fabry-Perot Resonator antennas, has the main advantages of design simplicity and low complexity as compared to the conventional planar antenna arrays. Various configurations of such EBG resonator antennas have been developed for use in single and multiple frequency bands us- ing single feed source [1-2]. The defect modes in these antennas have inherent narrow bandwidth that can be increased using dual EBG resonators in combination with multiple-feed sources which results in improved directivity [3]. In this work, the design of a dual-band EBG superstrate is presented to increase the antenna directivity and radiation bandwidth using an array of sources. The antenna is de- signed to operate in two frequency bands around 28 GHz and 38 GHz for point-to-point communica- tion links. CST Microwave Studio commercial software has been used for the design and analysis. 2. Dual-Band EBG Superstrate: Unit-Cell Design The proposed antenna configuration is shown in Fig. 1. When the antenna ground plane is replaced by the image of the antenna, the corresponding unit-cell geometry is as shown in Fig. 2. It consists of two-dielectric slabs ( r = 10.2) and a defect dielectric rod ( r = 2.2) placed in the air gap, quarter–free- space-wavelengths above the first slab. The model is excited by normally incident plane waves at port 1 and 2 with periodic boundary conditions on the four-walls, to observe the transmission through the structure. As seen from Fig. 2, the EBG structure exhibits two defect modes within a very wide band- gap. The first mode with a wide bandwidth (low Q) is due to the insertion of defect dielectric rods, while the second mode with a narrow bandwidth (high Q) is due to the cavity between the inner slabs. By controlling the thickness, periodicity of the square-shaped defect rod, and the location of dielectric slabs, defect frequencies have been tuned to 28.5 GHz and 38.9 GHz. The two defect-modes satisfy the necessary condition of directivity enhancement, i.e., they have vanishing tangential electrical fields at the structure’s symmetry plane, where a conducting ground plane will be positioned, and hence are useful to implement a dual-band EBG resonator antenna. Metamaterials '2011: The Fifth International Congress on Advanced Electromagnetic Materials in Microwaves and Optics ISBN 978-952-67611-0-7 - 715 - © 2011 Metamorphose-VI