Dielectric resonators as microwave characterization tools

Dielectric resonators, formed by sandwiching a cylindrical piece of polished dielectric material (sapphire) between two planar endplates, offer an attractive platform for microwave testing of HTS films. Each resonator is tested as a two-port system, by exciting and detecting the modal fields with loop-terminated coaxial cables. The observed quality factor of the resonator is a gauge of the surface resistance of the endplates. We discuss utilization of this method as a tool for testing /spl sim/1 cm/sup 2/ areas, at frequencies in the 20-40 GHz range, and at cryogenic temperatures, using field analysis to explore trade-offs involving cylinder geometry, field confinement, and miniaturization. An improved method for analyzing two-port data eases the difficulties associated with testing the resonator in a cryogenic environment.