Application of Negative/positive Impedance Converters in Electrically Small Antennas

The University of Michigan Radiation Lab and Trident Chapter are pleased to host Professor Silvio Hrabar from the University of Zagreb in Croatia. Prof. Hrabar will give a seminar, "Application of Negative/positive Impedance Converters in Electrically Small Antennas" at 3:00 pm ET on Tuesday, October 7. This talk is part of the Radlab Seminar Series.
The in-person seminar is free and open to the public and will be held in room GG Brown 1571 on the University of Michigan North Campus in Ann Arbor, MI.
UM Radiation Laboratory (https://radlab.engin.umich.edu/)
SEM Trident Chapter (AP03/ED15/MTT17/PHO36) (https://r4.ieee.org/sem/chapter-iv-trident/)
Speaker(s): Prof. Silvio Hrabar
Agenda:
Welcome: 3:00 pm
Presentation
Q&A
Closing
Application of Negative/positive Impedance Converters in Electrically Small Antennas
Radlab Seminar Series
Dr.sc. Silvio Hrabar
Professor
Faculty of Electrical Eng. and Comp., University of Zagreb,
Unska 3, Zagreb, HR-10000,Croatia
Abstract: Electrically small antennas (ESAs) are a very old but still highly challenging research topic. It is well known that classical passive resonant matching of an ESA is inherently limited by a very narrow bandwidth due to the inevitably high Q-factor. Alternatively, there are active approaches such as non-Foster-based matching. This method uses so-called Negative Impedance Converters (NICs), which convert ordinary reactive elements (capacitors and inductors) into their “negative images”: negative capacitors and negative inductors. The use of these negative elements theoretically offers an operating bandwidth of several octaves. Unfortunately, this method suffers from stability problems and limited power-handling capabilities when used in transmitting applications.
In the first part of this talk, various approaches to overcoming stability problems in general non-Foster-based antennas with NICs are discussed. It will be shown that the main problem is not, as commonly assumed, the limitations of the technology used (such as the occurrence of "parasitics"). Surprisingly, the issues stem from an insufficient understanding of the physical background and the "blind" use of commercial CAD tools for stability analysis. A simple design that leads to stable systems is explained for different types of actively matched small dipole and loop antennas. These designs use stability-robust band-pass negative capacitors and two-transmitter non-Foster-inspired matching.
The second part addresses the concept of widely tunable, perfectly matched self-oscillating and self-oscillating/amplifying ESAs based on NICs. The basic idea is to use two identical radiators, with one converted into its 'negative-impedance image.' Connecting a bare radiator and its 'negative image' creates a system that supports both widely tunable self-oscillations and non-Foster-based reflection amplification.
In the third part, it will be shown that Positive Impedance Converters (PICs or gyrators), which so far have been used very rarely in RF engineering, may lead to the design of ultra-broadband directional ESAs with a Huygens radiation pattern.
The discussion of the above methods will be complemented by examples of practical experimental demonstrators operating in the lower RF band (< 1 GHz), developed at the University of Zagreb. Finally, some unsolved problems and related future research directions will be highlighted.
Bio: Silvio Hrabar received Dipl. Ing. and M.S. degrees from University of Zagreb, Croatia and a Ph.D degree from Brunel University of West London, United Kingdom, all in electrical engineering. In the past, he was employed at various consulting, development, research and teaching positions both in industry and academia, in the fields of radio engineering, microwave electronics, antenna engineering, electromagnetic compatibility, electromagnetic metrology, computational electromagnetics and electrostatics. Currently, he is affiliated with University of Zagreb, Croatia, where he is a Professor of applied electromagnetics. His research interest includes applied electromagnetics, electromagnetic compatibility, antennas, microwave measurements and microwave engineering. He is the author and co-author of more than 200 technical papers in journals and conferences, many technical studies for government and industry, one textbook, and several book chapters. He also serves as a reviewer for a dozen of scientific journals in electrical engineering and applied physics. Professor Hrabar is a chair of Metamaterial group at Faculty of Electrical Engineering and Computing (FER), University of Zagreb. In 2012 he received ‘Award for exceptional achievements in research and innovations’ for ‘Contribution to the understanding of basic physics of electromagnetic metamaterials and development of their engineering applications’. In 2022, 2023 and 2024, Prof. Hrabar was ranked among the 2% most cited scientists in the world in the field of Information and communication technologies (Stanford University list).
Room: GGB 1571, Bldg: GG Brown Building, 2350 Hayward Street, University of Michigan North Campus, Ann Arbor, Michigan, United States, 48109