A Circularly Polarized Annular-ring Patch Antenna with a Groundplane EBG Annular-slot Array X.L. Bao, G. Ruvio and M. J. Ammann Centre for Telecommunications Value-chain Research, School of Electronic & Communications Engineering, Dublin Institute of Technology, Kevin Street, Dublin 8, Ireland Tel: +353 1 402 4716; E-mail: xbao@dit.ie Abstract—The effects of tuning the parameters of an annular-ring circular patch antenna with a cross-slot are analyzed and discussed. Then, based on this structure, a novel antenna with an electromagnetic bandgap cell system, which consists of a 4×4 annular-slot array in the groundplane, is designed and both numerically and experimentally evaluated. When compared to the annular-ring patch antenna on a groundplane of the same size without EBG structure, the proposed antenna presents a significant increase in the impedance bandwidth, axial-ratio bandwidth and gain. On the other hand, the insertion of the EBG structure allows a 10% reduction of the centre frequency when compared to the annular-ring patch antenna on a conventional groundplane. The simulated and measured results are in good agreement. Index Terms - Annular-ring patch antenna, Annular-slot, Electromagnetic Bandgap, Circular polarization. I.INTRODUCTION ∗ Electromagnetic Band Gap (EBG) structures are periodic complex cell systems, which present ∗ Preliminary report. X.L.Bao, G. Ruvio and M.J.Ammann, Circularly Polarized Annular-ring Patch Antenna with EBG Groundplane, European Conf. Antennas & Propagation, 2006, Nice, No. 349921. bandstop characteristics within a certain frequency range. They behave as filters that suppress within a certain frequency range surface waves, which 0 l1 l1 l2 l2 Feedpoint L1 L2 0 l1 l1 l2 l2 Feedpoint L1 L2 Fig. 1 The geometry of the proposed CP antenna. (a) Top view; (b) Side view; (c) Cross-slot in ground plane 69 IJMOT-2007-10-275 © 2008 ISRAMT INTERNATIONAL JOURNAL OF MICROWAVE AND OPTICAL TECHNOLOGY VOL. 3, NO. 2, APRIL 2008