Published in IET Microwaves, Antennas & Propagation Received on 29th April 2009 Revised on 15th September 2009 doi: 10.1049/iet-map.2009.0224 In Special Issue on Asia-Pacific Microwave Conference ISSN 1751-8725 Narrow-beam azimuthally omni-directional millimetre-wave antenna using freeformed cylindrical woodpile cavity Y. Lee 1 X. Lu 3 Y. Hao 2 S. Yang 4 J.R.G. Evans 3 C.G. Parini 2 1 Space Science and Technology Department, STFC Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, UK 2 Antennas and Electromagnetics Group, School of Electronic Engineering and Computer Science, Queen Mary University of London, Mile End Road, London E1 4NS, UK 3 Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, UK 4 School of Engineering Science, University of Southampton, Southampton SO17 1BJ, UK E-mail: yoonjae.lee@stfc.ac.uk Abstract: A freeformed cylindrical electromagnetic bandgap (EBG) structure and its application for millimetre- wave antennas are presented. The cylindrical EBG structure is fabricated using the extrusion freeforming technique in which the design is downloaded directly to a building platform. The fabricated cylindrical woodpile exhibits bandgap characteristics around 95 GHz and is used for realising a resonant cavity antenna. The fabricated antenna achieves a narrow beam with 6.58 measured half-power beam-width in the elevation plane without using an array configuration. The overall antenna gain is approximately 5 dBi at 94.2 GHz, suitable for future short-range gigabit wireless communications. 1 Introduction Wireless personal area networking is one of the most promising future high data-rate wireless communication schemes [1]. The frequency spectrum around 60 GHz is of special interest because of the high atmospheric absorption making this frequency band suitable for communications at close distance, for example, indoors. Whereas, at the frequency band around 95 GHz, where the atmospheric absorption is much lower than at 60 GHz, data transmission rates of more than 1 Gbps are possible at ranges of several miles during normal weather conditions using a point-to-point wireless communication link, which could be a subsidiary to current fibre-optic networks in several areas for reduced cost and flexibilities. At this frequency the monolithic microwave integrated circuit high electron mobility transistor technology [2–4] can be adopted in transceiver blocks and the self-heterodyne detection scheme is a simple and low-cost solution for mobile units [5]. Antenna technologies at this frequency are mostly based on waveguide horns [6] and integrated patch types [7], which are unidirectional. The proposed antenna described in this paper using the current design of cylindrical woodpile can provide up to 9 – 10 dBi gain (using an ideal feeding) for omni-directional service area; thus it can be very well suited for in/outdoor wireless link for broadcast-type applications for larger numbers of users with an extended service range. Recently, a design of cylindrical cavity antenna using ceramic materials has been reported [8]. In this paper, we present a cylindrical resonant cavity using a woodpile bandgap structure and its application for realising a narrow-beam azimuthally omni- directional antenna for short-range communications at millimetre-wave bands. The characteristics of the cylindrical woodpile cavity and the resonator antenna are further investigated and analysed based on previous experience with cavity antennas with planar woodpile electromagnetic bandgaps (EBGs) [9–13]. The proposed antenna has superior properties over conventional conformal antenna arrays because of its low profile, easy to feed and cost-effectiveness. Similar configurations using metallic elements for EBG structures have been studied and tested at microwave frequencies [10, 11]; however, metallic elements are not preferred at millimetre-wave IET Microw. Antennas Propag., 2010, Vol. 4, Iss. 10, pp. 1491–1499 1491 doi: 10.1049/iet-map.2009.0224 & The Institution of Engineering and Technology 2010 www.ietdl.org