Abstract:
Highly directive antenna systems are being sought to address the perceived needs of FutureG wireless systems and their applications. Practical alternatives to complex, power-hungry phased arrays for space-limited applications are truly desired. A potential approach is to develop and employ compact superdirective systems.
The concept of “needle” radiation was introduced by Oseen over 100 years ago. A number of theoretical papers then followed over the last half of the last century that discussed the interesting attributes of unlimited directivity, i.e., superdirectivity, from arbitrarily small source regions. Recent explicit solutions of Maxwell’s equations based upon vector spherical wave expansions confirm this notion. Unfortunately, the consensus in the electromagnetics (EM) community generally has been that superdirective systems are impractical for reasons such as very low radiation resistance/efficiency; very large sensitivity to fabrication and component tolerances; and extremely narrow bandwidths. Nevertheless, a turning point in the history of superdirectivity occurred early this century with a set of successes in which electrically small, superdirective two-element endfire arrays of electric elements were demonstrated. Several superdirective multi-element endfire arrays of a similar nature have been demonstrated using electric or magnetic dipoles in the last decade. Their basic approaches follow from the theoretical demonstration that a densely packed linear array of M isotropic radiators can yield a directivity of M 2 in its endfire direction.
A more recent strategy to achieve superdirective performance has been to exploit mixtures of electric and magnetic multipoles. This multipole engineering paradigm has yielded unidirectional mixed-multipole antennas (MMAs) consisting of combinations of near-field resonant parasitic (NFRP) elements that are excited by simple driven dipoles and that exhibit multipole performance yielding directivities that exceed known bounds. Their practical realizations address the concerns of efficiency, bandwidth, and fabrication/assembly tolerances. Superdirective endfire and broadside radiating systems have been demonstrated. Most recently, highly efficient, superdirective uniform circular arrays of unidirectional MMAs and MMA-excited multilayered-spherical dielectric lens antennas have also been realized.
The historical aspects of superdirective systems from the 20th century and the electromagnetics – both physics and engineering features – of the 21st century innovative realizations of practical superdirective systems will be reviewed. They encourage further superdirective research activities since they demonstrate that practical superdirective radiating systems are, in fact, achievable.
Biography:
Richard W. Ziolkowski received the B. Sc. (magna cum laude) degree (Hons.) in physics from Brown University, Providence, RI, USA, in 1974; the M.S. and Ph.D. degrees in physics from the University of Illinois at Urbana-Champaign, Urbana, IL, USA, in 1975 and 1980, respectively; and an Honorary Doctorate degree from the Technical University of Denmark (DTU), Kongens Lyngby, Denmark in 2012.
He is currently a Professor Emeritus with the Department of Electrical and Computer Engineering at The University of Arizona, Tucson, AZ, USA. He was a Litton Industries John M. Leonis Distinguished Professor in the College of Engineering and was also a Professor in the College of Optical Sciences until his retirement in 2018. He was also a Distinguished Professor in the Global Big Data Technologies Centre in the Faculty of Engineering and Information Technologies (FEIT) at the University of Technology Sydney, Ultimo NSW Australia from 2016 until 2023. He was the Computational Electronics and Electromagnetics Thrust Area Leader with the Engineering Research Division of the Lawrence Livermore National Laboratory before joining The University of Arizona in 1990.
Prof. Ziolkowski was the recipient of the 2019 IEEE Electromagnetics Award (IEEE Technical Field Award). He is an IEEE Life Fellow, as well as a Fellow of OPTICA (previously the Optical Society of America, OSA) and the American Physical Society (APS). He was the 2014-2015 Fulbright Distinguished Chair in Advanced Science and Technology (sponsored by DSTO, the Australian Defence Science and Technology Organisation). He served as the President of the IEEE Antennas and Propagation Society (AP-S) in 2005 and has had many other AP-S leadership roles. He is also actively involved with the URSI (International Union of Radio Science) Commission B and the European Association on Antennas and Propagation (EurAAP). He is the co-Editor of the best-selling 2006 IEEE-Wiley book, Metamaterials: Physics and Engineering Explorations, as well as an author and co-Editor, respectively, of the recent Wiley-IEEE books: Advanced Antenna Array Engineering for 6G and Beyond Wireless Communications (2022) and Antenna and Array Technologies for Future Wireless Ecosystems (2022).
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