Antenna Applications Corner
Sudhakar Rao Northrop Grumman Aerospace Systems One Spacepark Redondo Beach, CA 90278 USA Tel: +1 (310) 813-5405 E-mail:
[email protected]
Nuria Llombart EEMCS, Delft University of Technology Mekelweg 4, 2628 CD, Delft, The Netherlands E-mail:
[email protected]
An Overview of Tuning Techniques for Frequency-Agile Antennas Aldo Petosa Communications Research Centre Canada 3701 Carling Avenue Ottawa, Ontario Canada, K2H 8S2 Tel: +1 (613) 991-9352; Fax: +1 (613) 990-8369; E-mail:
[email protected]
Abstract Frequency-agile antennas can be designed to switch between a set of discrete frequencies, or to be tuned over a continuous range of frequencies. Methods for achieving discrete or continuous frequency tuning can be grouped into three categories: mechanical actuation, tunable materials, and integrated electronic devices. Example tuning techniques in each class are presented, highlighting strengths and weaknesses of each method. Keywords: Frequency agility; reconfigurable; tunable antennas; reconfigurable antennas
W
1. Introduction
ith the rapid increase in the number of hand-held wireless devices, new services, and applications, the current allocated frequency spectrum is being quickly filled. This has led to the study of various methods for improving channel capacity, such as multiple-input multiple-output (MIMO) systems, polarization and spatial-diversity techniques, ultra-wideband (UWB) systems, and cognitive radios. Many of these approaches involve the use of multiple antennas and/or antennas with wideband or multi-band performance. For handsets or compact portable devices, the limited real estate available may preclude the use of wideband or UWB antennas. These antennas could also have a negative impact on the signal-to-noise ratio, and may require additional filtering
to suppress unwanted interference. A potential alternative for these applications is a reconfigurable antenna, the pattern shape, polarization, or frequency of which can be dynamically controlled. Although this paper focuses on frequency-agile antennas, many of the tuning techniques described herein could also potentially be used to reconfigure pattern shape or polarization. By designing antennas with frequency agility, small antennas with narrow instantaneous bandwidths can be tuned to operate over a larger range of frequencies, resulting in an effectively larger-bandwidth performance. Over the last few years, a large number of frequency-agile antenna configurations has been considered, where various antenna elements (such as microstrip patches, PIFAs, printed dipoles, slot antennas, helices, and dielectric resonator antennas)
IEEE Antennas and Propagation Magazine, Vol. 54, No. 5, October 2012
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