Abstract
This is an IEEE Distinguished Lecture from Antennas and Propagation Society. 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 (APS 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 [1]. 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 multistate 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 [2], (ii) dual-band beam scanning by frequency sweeping, with one beam scanning forward directions and the other one scanning backward directions [3], (iii) arrays of leaky-wave antennas with a combined beam in broadside direction [4], and (iv) tri-band leaky wave antennas. At the end, selected topics suitable to future research in this area will be discussed.
Published Version
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