The directivity of a compact antenna: an unforgettable figure of merit
University of Technology Sydney (UTS), Global Big Data Technologies Centre,
2 The University of Arizona, Department of Electrical and Computer Engineering, Tucson, AZ 85721, USA
* e-mail: Richard.Ziolkowski@uts.edu.au
Received in final form: 28 July 2017
Accepted: 25 August 2017
Published online: 11 October 2017
When an electrically small antenna is conceived, designed, simulated, and tested, the main emphasis is usually placed immediately on its impedance bandwidth and radiation efficiency. All too often it is assumed that its directivity will only be that of a Hertzian dipole and, hence, its directivity becomes a minor consideration. This is particularly true if such a compact antenna radiates in the presence of a large ground plane. Attention is typically focused on the radiator and its size, while the ground plane is forgotten. This has become a too frequent occurrence when antennas, such as patch antennas that have been augmented with metamaterial structures, are explored. In this paper, it is demonstrated that while the ground plane has little impact on the resonance frequency and impedance bandwidth of patch antennas or metamaterial-inspired three-dimensional magnetic EZ antennas, it has a huge impact on their directivity performance. Moreover, it is demonstrated that with both a metamaterial-inspired two-element array and a related Huygens dipole antenna, one can achieve broadside-radiating electrically small systems that have high directivities. Several common and original designs are used to highlight these issues and to emphasize why a fundamental figure of merit such as directivity should never be overlooked.
Key words: Directivity / Electrically small antennas / Huygens source / Metamaterial-inspired antennas / Patch antennas
© R.W. Ziolkowski, published by EDP Sciences, 2017
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.