2006 INTERNATIONAL RF AND MICROWAVE CONFERENCE PROCEEDINGS, SEPTEMBER 12 - 14, 2006, PUTRAJAYA, MALAYSIA Bandwidth Enhancement of a Narrowband Rectangular Microstrip Antenna on a Spiral Fan-Shape Electromagnetic Band-Gap (EBG) Patch Structure T. Masri, M. K. A. Rahim, M. H. Jamaluddin and A. Asrokin Wireless Communication Centre, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia ithelaha@yahoo.com.my, mkamal@fke.utm.my, haizal@fke.utm.my, awil982@yahoo.com Abstract - An innovative and novel technique has been explored in enhancing the bandwidth of a rectangular patch antenna by introducing a spiral fan-shape Electromagnetic Band Gap (EBG) structure between a narrowband patch antenna and its ground plane. Measured result shows an excellent return loss and good impedance matching which resulted in an increment of the bandwidth from about 4 % for a single layered narrow band rectangular microstrip patch, to more than 17 % after the EBG structure was introduced. This paper present the methodology, simulations and experimental works carried out in accomplishing the objective above. Microwave Office 2006 software has been used to initially simulate and find the optimum design and results. Keywords: Microstrip, Antenna, electromagnetic Band-Gap, Narrow Ban & Broad band Antenna 1. Introduction Electromagnetic band-gap (EBG) structures have two commonly employed configurations, namely the perforated dielectric and the metallodielectric structures. The perforated EBG structures consists of a periodically arranged air-columns, which effectively suppress unwanted substrate modes commonly exist in microstrip antennas, but it also creates disadvantageous in terms of fabrication. On the other hand, the metallodielectric EBG structures consists of printed array of metallized elements, used to suppressed substrate modes [1]. The later was more practical and proofed to exhibits an attractive reflection phase future where the reflected field changes continuously from 180° to -180° versus frequency. It allows a low profile wire antenna to radiate efficiently with enhance bore sight gain, reduced back radiation and side lobes levels [2]. EBG substrates have found possible applications in the antenna technology to improve performance like reducing mutual coupling between antennas on the same substrate or reduce side lobe effects due to truncated surface waves that would be excited in a standard antenna substrate [3]. EBG substrates can also be used to eliminate scan blindness phenomena presented in array antennas. EBG layers have also been used as a top cover of a Fabry-Perot Cavities to produce highly-directive radiators [4]. Recently, EBG structures have been used to mimic perfect magnetic conductors (PMC) over a narrow frequency range, for use as a ground plane in a low- profile antenna configuration [5]. In this research, we focus our study on the effect of introducing an EBG structures in the form of periodic spiral fan-shape patches between a narrow band resonator, a rectangular patch for this case, and the ground plane. A parametric study on the performance of the antenna, especially on enhancing the bandwidth was done using AWR simulation software and the optimum results was confirmed through fabrication of a model of the antenna. It was found that the results were excellent. 2. Parametric Study A spiral fan-shape EBG patch structure was introduced between a narrowband; coaxial feed rectangular patch and its ground plane. This structure was chosen due to its simplicity of design and less time consuming when simulated using the AWR software. Figure 1 show the geometry of the antenna involves, which consist of two 1.6 mm thick FR4 substrate with an gr of 4.6, one with a rectangular resonator patch on the top plane and the other, with the spiral fan-shape EBG patch structure, on top of a ground plane. The width and length of the rectangular patch was calculated to resonate at 2.4 GHz while the width and radius of the spiral fan-shape EBG patch structure was varied proportionally (Figure l.b) to obtain the optimum results, as mentioned above. 0-7803-9745-2/06/$20.00 (©)2006 IEEE. 225