Since the discovery of efficient leaky-wave radiation from a slot in a wave guide by Oliner, leaky-wave antennas have attracted a lot of interest in applications that require beam scanning. Printed planar configurations of LWAs have become very popular, due to low cost. Half-width LWAs based on microstrip lines and substrate-integrated-wave guides have provided an additional advantage of narrow footprint. Professor Christophe Caloz (AP-S Distinguished Lecturer 2014-16) has brilliantly summarised in his distinguished lectures and illustrated how the problem of massive drop of antenna efficiency, when the beam is attempted to steer in the broadside direction, has been solved using Composite Right/Left-Handed (CRLH) structures and other methods. After briefly reviewing such crucial historical milestones in LWAs, this presentation will focus on recent developments in LWA antenna research and practical outcomes, including some that have the potential to further extend applications of LWAs from current niche scanning applications to mass communication applications such as wireless local area networks and emerging 5G mobile communications. One of them is fixed-frequency beam steering using only two values of bias voltages, for applications where sweeping the operating frequency is not possible. Several methods of LWA fixed-frequency beam steering has been demonstrated, including one recently developed by the speaker’s team that requires only two bias voltage values to steer the beam. This is very promising for millimetre-wave communication systems such as Wi-Gig and potential millimetre-wave modes of 5G. The principle underlying these LWAs is formation of a multi-state radiating structure by cascading several binary reconfigurable unit cells. Thus the basic building block of the antenna is a reconfigurable binary unit cell, switchable between two states. A macro cell is created by combining several reconfigurable unit cells and the periodic LWA is formed by cascading identical macro cells. Antenna beam is digitally steered in small steps by switching to different macro-cell states. Microwave prototypes based on this concept have demonstrated excellent beam steering over 30 degrees with negligible gain variation (of about 1 dB) and good input matching. As all switches in the antenna are binary, only two bias voltage values are required for beam steering, and the antenna sub-system can be controlled easily using digital electronics. Other recent developments presented in the lecture include (i) steering two side beams simultaneously by sweeping the operating frequency, using the second higher order mode of a microstrip, and (ii) dual-band beam scanning by frequency sweeping, with one beam scanning forward directions and the other one scanning backward directions. At the end, selected topics suitable to future research in this area will be discussed.
Professor Karu Esselle, IEEE ‘M (1992), SM (1996), F (2016), received BSc degree in electronic and telecommunication engineering with First Class Honours from the University of Moratuwa, Sri Lanka, and MASc and PhD degrees in electrical engineering from the University of Ottawa, Canada. He is a Professor of Electronic Engineering, Macquarie University, Sydney, Director of WiMed Research Centre (one of the two) and the Past Associate Dean – Higher Degree Research (HDR) of the Division of Information and Communication Sciences. He has also served as a member of the Dean’s Advisory Council and the Division Executive and as the Head of the Department several times. After two stages in the selection process, Karu was selected by IEEE Antennas and Propagation (AP) Society as one of two candidates in the ballot for 2019 President of the Society, which has over 8,000 members worldwide. Only three people from Asia or Pacific have received this honour (one from Australia and two from Japan) in the 68-year history of this Society – the premier global organisation dedicated for antennas and propagation. Karu has also been selected as one of the three Distinguished Lecturers of IEEE AP Society for 2017-2019. He is the only Australian AP Distinguished Lecturer (DL) in almost two decades, and second Australian AP DL ever. When Karu was elected to the IEEE AP Society Administrative Committee for a three-year term in 2014, he became the only person residing in the Asia-Pacific Region (IEEE Region 10) to be elected to this highly competitive position over a period of at least six years (2010-2015). Karu is also the chair of the Board of management of Australian Antenna Measurement Facility, and elected Chair of both IEEE New South Wales (NSW) Section, and IEEE NSW AP/MTT Chapter, in 2016 and 2017. He directs the Centre for Collaboration in Electromagnetic and Antenna Engineering. Karu was elevated to prestigious IEEE Fellow grade for his contributions to resonance-based antennas. He is also a Fellow of Engineers Australia. Karu has authored over 500 research publications. He is the first Australian antenna researcher ever to reach Google Scholar h-index of 30 and his current h-index of 36 is the highest among Australian antenna researchers. Since 2002, his research team has been involved with research grants, contracts and PhD scholarships worth over 16 million dollars. His multi-award-winning research has been funded by many national and international organisations. Karu has been invited to serve as an international expert/ research grant assessor by several nationwide research funding bodies overseas. In addition to the large number of invited conference speeches he has given, he has been an invited keynote speaker of IEEE workshops and conferences. Thirty-eight international experts who examined the theses of his recent PhD graduates ranked them in the top 5% or 10%. Karu has provided expert assistance to more than a dozen companies. He is an Associate Editor of IEEE Transactions on Antennas and Propagation and IEEE Access. Karu is the General Co-Chair of TENSYMP 2018. His research activities are at http://web.science.mq.edu.au/~esselle/