Improvement of Broadband Characterization of Dielectric Waveguide at the $Ka$ -Band by Using TRL Calibration Method

When evaluating a dielectric waveguide, it is necessary to convert it into a metallic coaxial line or a metallic waveguide in order to connect it to a measurement port of a vector network analyzer (VNA). Mismatches in connections of different types of cables lead to an error in measurements, which have been a serious problem in the characterization of dielectric waveguides. To this end, we propose the use of two-line standards and a reflect standard made of dielectric waveguides as thru-reflect-line (TRL) calibration devices in order to ensure the accuracy of measurement of the propagation characteristics of dielectric waveguides. By using the developed TRL calibration devices, the calibration planes in VNA measurements are extended to the cross sections of the dielectric waveguide, which makes it possible to perform accurate measurements of the dielectric waveguide without the influence of mismatches between different types of cables. To demonstrate the usefulness of the proposed approach, we performed numerical calculations to investigate the robustness of the proposed method against dimensional variations in the calibration devices. Furthermore, we experimentally verified the method by applying it to measurements on circular dielectric waveguides made of polytetrafluoroethylene in the 28-GHz band, which has been planned to be implemented in the next-generation wireless communications.