Wojciech Gwarek

Wojciech Gwarek graduated from Warsaw Univ. Tech. (WUT) in Poland in 1970 and received Ph.D. from there in 1974. He also received M.Sc. from Mass. Inst. Tech in 1974. He continued his academic career at WUT as a head of Microwave Laboratory there until his retirement in 2017 His academic activities included co-operation with several foreign institutions in USA, Canada, France, Germany and RSA. In 1992-93 he was a co-organiser of the Franco-Polish School of New Information and Telecommunication Technologies in Poznan, directing the Electronics and Physics department there. He is a co-author of “Theory of Electromagnetic Field” (WNT 1978, 1985,1990) – a textbook used by most Polish universities until now. He has also acted as an industrial consultant for several leading companies in US and Europe. He was a TPC member of many leading conferences since 1997 and chaired the TPC of MIKON Conference in 2008 and 2010. He served as IEEE Distinguished Microwave Lecturer in the years 2003-2005. In 2001 he was elevated to the rank of IEEE Fellow and is now a Life Fellow. In 2011 he received IEEE Microwave Pioneer Award for his seminal publications on electromagnetic simulations published more than 20 years earlier. In 1997 he co-founded QWED company and served as its President until 2017. The company introduced on the World’s market the electromagnetic software tools of Quick Wave series and established a strong international position in the domain of microwave material measurements.

Title of the presentation:
Mode-Selective Boundary Conditions and their Application to Novel Types of Microwave Resonators

Abstract:
Classical electromagnetics (EM) distinguishes two basic types of boundary conditions, Perfect Electric Conductor (PEC) and Perfect Magnetic Conductor (PMC), which are both “polarisation-dependent”. For example, at a PEC boundary the tangential component of E-field is zero, while the normal component has zero normal derivative. In the context of antenna technology, excellent contributions were made [1] to develop “polarisation-independent” boundaries, corresponding to the soft and hard surfaces in acoustics. For example, corrugated “soft” antenna horns produce beams of the same width of the radiation patterns in both E- and H-plane.

In this presentation, we explore a new type of artificial boundary conditions, which we shall call “mode-selective”, as they impose nearly-zero or nearly-unity reflection coefficient, depending on the incident mode. We focus on their use in high-Q resonators, as elaborated in the recent patent application [2]. It has been shown there, that with such boundary conditions (which is practically realized with a combination of corrugations and lossy inserts) we can filter-out a class of unwanted modes while keeping the wanted ones unaffected. Thereby, the spectrum of modes inside the resonator is “cleaned” to contain the desired modes only.

When applied in a high-Q resonator, the “mode-selective” surface is named Q-Choke [2]. Its design is performed with full-wave EM simulations, which will be used to illustrate this talk. Two examples of application to microwave material measurements will be discussed, by reference to two resonators manufactured and measured at QWED: Q-SCR (Q-choked Split Cylinder Resonator [3]) and Q-SSR (Q-Choked Sandwiched Sapphire Resonator [4]). We hope that the presented idea will inspire members of the Microwave Community to extend the concept of “mode-selective boundaries” to other types of resonators and their applications.

[1] P.-S. Kildal, “Artificially soft and hard surfaces in electromagnetics,” IEEE Trans. Antennas Propag., Oct. 1990, doi: 10.1109/8.59765
[2] W. Gwarek, Electromagnetic Resonating Structure and a Method of Measuring a Material Parameter of a Flat Sample, European Patent Application no., EP23461651.4, of 2023-09-18, published as EP4524554A1, EP Bulletin 2025/12.
[3] M. Celuch et al. “A Novel Q-Choked Resonator for Microwave Material Measurements Alleviating Sample Thickness Limitations of Existing Techniques,” IEEE Microw. Wireless Technol. Lett., June 2024, doi:10.1109/LMWT.2024.3397912.
[4] W. Gwarek, M. Celuch and L. Nowicki, “A Novel Q-Choked Sapphire Sandwiched Resonator for Wideband Measurements of Flat Dielectric Samples,” IEEE Microw. Wireless Technol. Lett., June 2025, doi: 10.1109/LMWT.2025.3568534.