Linköping Studies in Science and Technology Dissertations No. 1146 Ultra-wideband Antenna and Radio Front-end Systems Magnus Karlsson Department of Science and Technology Linköping University, SE-601 74 Norrköping, Sweden Norrköping 2007 Ultra-wideband Antenna and Radio Front-end Systems A dissertation submitted to the Institute of Technology, Linköping University, Sweden for the degree of Doctor of Technology. ISBN: 978-91-85895-36-6 ISSN: 0345-7524 http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-10338 Copyright © 2007, Magnus Karlsson, unless otherwise noted Linköping University Department of Science and Technology SE-601 74 Norrköping Sweden Printed by LiU-Tryck, Linköping 2007 Abstract Abstract The number of wireless communication applications increase steadily, leading to the competition for currently allocated frequency bands. Pressure on authorities around the world to permit communications in higher and wider frequency ranges to achieve higher wireless capacity than those existed in the past has resulted in several new specifications. The federal communication commission (FCC) in USA has unleashed the band 3.1-10.6 GHz for ultra- wideband radio (UWB) communications. The release has triggered a worldwide interest for UWB. Other regulatory authorities throughout the world have issued use of UWB techniques as well. Capacity issues in form of data rate and latency have always been a bottleneck for broadened wireless-communication usages. New communication systems like UWB require larger bandwidth than what is normally utilized with traditional antenna techniques. The interest for compact consumer electronics is growing in the meantime, creating a demand on efficient and low profile antennas which can be integrated on a printed circuit board. In this thesis, some methods to extend the bandwidth and other antenna parameters associated with wideband usages are studied. Furthermore, methods on how to enhance the performance when one antenna-element is not enough are studied as well. The principle of antenna parallelism is demonstrated using both microstrip patch antennas and inverted-F antennas. Several techniques to combine the antennas in parallel have been evaluated. Firstly, a solution using power-splitters to form sub-arrays that covers one 500-MHz multi-band orthogonal frequency division multiplexing (OFDM) UWB is shown in Paper I. It is then proposed that the sub-bands are selected with a switch network. A more convenient method is to use the later developed frequency multiplexing technique as described in Papers V and VIII. Using the frequency multiplexing technique, selective connection of a number of antennas to a common junction is possible. The characteristic impedance is chosen freely, typically using a 50-Ω feed-line. Secondly, in Paper VIII a frequency-triplexed inverted-F antenna system is investigated to cover the Mode 1 multi-band UWB bandwidth 3.1-4.8 GHz. The i Abstract antenna system is composed of three inverted-F antennas and a frequency triplexer including three 5th order bandpass filters. In Papers VI and X a triplexer without and with low noise amplifier (LNA) integrated in a printed circuit board for multi-band UWB radio is presented. The triplexer utilizes a microstrip network and three combined broadside- and edge-coupled filters. The triplexer is fully integrated in a four metal-layer printed circuit board with the minimum requirement on process tolerances. Furthermore, the system is built completely with distributed microstrips, i.e., no discrete component except the LNA. Using the proposed solution an equal performance in the sub-bands is obtained. Finally suitable monopoles and dipoles are discussed and evaluated for UWB. In Paper XI circular monopole and dipole antennas for UWB utilizing the flex-rigid concept are proposed. The flex-rigid concept combines flexible polyimide material with the regular printed circuit board material. The antennas are placed entirely on the flexible part while the antenna ground plane and the dipole antenna balun are placed in the rigid part. ii Populärvetenskaplig sammanfattning Populärvetenskaplig sammanfattning Antalet trådlösa radioapplikationer bara ökar, vilket medför att konkurrensen om tillgängliga frekvensband hårdnar. År 2002 öppnade federal communication commission (FCC) i USA frekvensbandet 3.1-10.6 GHz för ultra bredbandskommunikation. Det här frisläppandet av bandbredd utlöste en våg av förnyat intresse för bredbandiga radiosystem bland forskare världen över. Konstruktion av ultra bredbandsradio (UWB) ställer nya hårdare krav på kompetens och designmetodik. Kapacitetsbegränsningar i form av fördröjning och datakapacitet har alltid varit ett problem för trådlösa överföringstekniker. Bandbreddskravet för ett typiskt UWB-system är mycket högre än vad som traditionellt har krävts av en antenn i ett kommunikationssystem. Detta samtidigt som man eftersträvar att bygga små, kompakta system som kan integreras i alla möjliga sammanhang. I den här avhandlingen har olika metoder för att kontrollera viktiga parametrar i bredbandskommunikation, som till exempel att öka antennens impedansbandbredd. Förutom det har olika lösningar för att kombinera flera antenner studerats, det vill säga att effektivt koppla samman flera radiatorer parallellt när en antenn inte räcker till. Principen för antennparallellism demonstreras både med microstrip patch- antenner och med inverterade-F antenner. En teknisk lösning baserad på switchar och delare har utvärderats. Ytterligare en teknisk lösning som studerats ingående för antennparallellism är frekvensmultiplexning. Med frekvensmultiplexning kan varje antenn täcka en del av det totala frekvensbandet, vilket kan vara ett 500 MHz frekvensband i UWB sammanhang. Förutom multiantennlösningar har även bredbandiga antennelement och möjliga integrationslösningar studerats. Speciellt intressant är antennintegration på så kallat ”flex-rigid” substrat som är en kombination av traditionellt (icke böjbart) och mjukt böjbart mönsterkortsmaterial. Det flexibla substratet är större och sticker ut från det hårda, således får man en fast (eng. rigid) och en flexibel (eng. flex) del. Den flexibla delen lämpar sig för att placera själva antennen som sen kan böjas åt olika håll. I rigid delen kan man placera övriga transceiverkomponenter som till exempel en balun. iii Acknowledgements Acknowledgements First of all I would like to express my gratitude to my supervisor, Professor Shaofang Gong, for providing guidance through the years, and not least the opportunity of doing research in this interesting and challenging field. Furthermore, I want to thank all the personell at the Department of Science and Technology who in various ways have supported me in my work. Many thanks are to the teachers in various postgraduate and graduate courses that have given me the foundation to do this work. Furthermore I want to thank remaining teachers in my previous educations that have improved my theoretical knowledge and technological skills. Moreover, I would like to thank Acreo AB for support with measurements, especially Patrick Blomqvist and Magnus Svensson. Furthermore, Ericsson AB in Sweden is acknowledged for financial support. Last but not least, I would like to express my deepest gratitude to my parents Bo and Gunilla Karlsson. Without their support, it would be impossible for me to achieve what I have done. v List of Publications List of Publications Papers included in the thesis: [I] M. Karlsson, and S. Gong, “Wideband patch antenna array for multi-band UWB,” Proc. IEEE 11th Symp. on Communications and Vehicular Tech., Ghent, Belgium, Nov. 2004. [II] M. Karlsson, and S. Gong, “An integrated spiral antenna system for UWB,” Proc. IEEE 35th European Microwave Conf., Paris, France, Oct. 2005, pp 2007-2010. [III] M. Karlsson, and S. Gong, “Monofilar spiral antennas for UWB with and without air core,” ISAST Transactions on Electronics and Signal Processing, 2007. [IV] M. Karlsson, and S. Gong, “Air core patch antennas suitable for multi-band UWB,” Proc. GigaHertz 2005, Uppsala, Sweden, Nov. 2005. [V] M. Karlsson, P. Håkansson, A. Huynh, and S. Gong, “Frequency-multiplexed Inverted-F Antennas for Multi-band UWB,” IEEE Wireless and Microwave Technology Conf. WAMICON 2006, pp. FF-2-1 - FF-2-3, Dec. 2006. [VI] A. Serban, M. Karlsson, and S. Gong, “All-Microstrip Design of Three Multiplexed Antennas and LNA for UWB Systems,” Proc. Asia-Pacific Microwave Conf., 2006, pp. 1109-1112, Dec. 2006. [VII] M. Karlsson, P. Håkansson, S. Gong, “A Frequency Triplexer for Ultra-wideband Systems Utilizing Combined Broadside- and Edge-coupled Filters,” Manuscript submitted to IEEE Transactions on Advanced Packaging, 2007. vi List of Publications [VIII] M. Karlsson, and S. Gong, “A Frequency-Triplexed Inverted-F Antenna System for Ultra-wide Multi-band Systems 3.1-4.8 GHz,” ISAST Transactions on Electronics and Signal Processing, 2007. [IX] A. Serban, M. Karlsson, and S. Gong, “Microstrip Bias Networks for Ultra-Wideband Systems,” ISAST Transactions on Electronics and Signal Processing, 2007. [X] A. Serban, M. Karlsson, and S. Gong, “A Frequency-triplexed RF Front-end for Ultra-wideband Systems 3.1-4.8 GHz,” Manuscript, submitted to ISAST Transactions on Electronics and Signal Processing, 2007. [XI] M. Karlsson, S. Gong, “Mono- and Di-pole Antennas for UWB Utilizing Flex-rigid Technology,” ISAST Transactions on Electronics and Signal Processing, 2007. vii Contents Contents Preface: Abstract....................................................................................................i 0H 187H Populärvetenskaplig sammanfattning (in Swedish).........................iii 1H 188H Acknowledgements................................................................................v 2H 189H List of Publications..............................................................................vi 3H 190H Contents..............................................................................................viii 4H 191H List of Abbreviations.........................................................................xvi 5H 192H Chapters: 1. Introduction........................................................................................1 6H 193H 1.1. Background and Motivation..........................................................1 7H 194H 1.2. Objectives.......................................................................................2 8H 195H 1.3. Outline of the Thesis......................................................................2 9H 196H 2. Ultra-wideband Radio Antennas......................................................5 10H 197H 2.1. Antenna History.............................................................................5 11H 198H 2.2. Theory and Techniques..................................................................6 12H 199H 2.2.1. Antenna Principles and Printed Circuit Board Integration.....7 13H 200H 2.2.2. Parasitics, and Resistive Loading...........................................12 14H 201H 2.2.3. Multi- Band and Resonance Antenna Systems.......................15 15H 202H 2.2.4. Wideband Impedance Matching Through Geometrical 16H Control....................................................................................20 203H 2.3. A Summary of UWB Antenna Technologies..............................22 17H 204H 2.3.1. Frequency-independent Antennas..........................................22 18H 205H 2.3.2. Electrical Antennas (Small Element)......................................24 19H 206H 2.3.3. Magnetic and Slot Antennas (Small Element)........................29 20H 207H 2.3.4. Horn and Reflector Antennas.................................................31 21H 208H 2.4. UWB antenna considerations.......................................................32 22H 209H 3. Types of Antennas Used in This Work..........................................35 23H 210H 3.1. Patch Antenna..............................................................................35 24H 211H 3.2. Spiral Antenna..............................................................................41 25H 212H 3.3. Inverted-F Antenna......................................................................44 26H 213H 3.4. Monopole and Dipole Antennas..................................................45 27H 214H viii