Microwave Characterization of Dielectric Sheets in a Plano-Concave Fabry-Perot Open Resonator

Despite its long history, a double-concave (DC) Fabry-Perot open resonator (FPOR) has recently gained popularity in the characterization of dielectrics in the 20–110 GHz range, mainly due to such novel accomplishments as full automation of the measurement process and the development of even more accurate and computationally efficient electromagnetic model. However, it has been discovered that such a DC resonator suffers from unwanted mode coupling present for electrically thick samples. Such limitations are missing in a plano-concave (PC) FPOR. For those reasons, the aim in this article is to apply the newly proposed scattering matrix method in the study of major properties of that kind of a resonator and, subsequently, to propose a new tool dedicated to the measurement of dielectrics without the aforementioned limits. For the first time in the literature, major properties of the PC FPOR with and without the sample, such as resonance frequencies, geometric factors, energy filling factors, and the resulting quality factor, are rigorously computed. Moreover, their impact on the accuracy of the loss tangent extraction is investigated. Such a study, which opens the way for accurate microwave characterization of electrically thick dielectric sheets above 20 GHz, has never been performed before. The whole complex permittivity extraction algorithm presented in this article is validated experimentally by measuring well-known materials, namely, C-plane sapphire, silicon, and Z-cut monocrystalline quartz.