A Unique Ka-Band Measurement System Based on Quasi-Optical Dielectric Resonator Technology for Studying Small Superconducting Samples

A new measurement system for microwave property study has been developed. Modified from the standard quasi-optical dielectric resonator technique, the sapphire cylinder resonator excited with whispering gallery modes has a narrow slit along the radius, within which a piece of small-sized single crystal or thin film sample can be positioned. Sandwiched by two pieces of YBCO films, the resonator is sealed in a specially designed vacuum vessel, which is soaked in liquid ⁴He. A microwave signal is coupled to the vacuum vessel by stainless steel thin wall waveguides and then to the resonator by sapphire waveguides. Coupling between the resonator and the two sapphire waveguides can be controlled accurately during the measurement. Furthermore, a decompressed liquid ⁴He port has been designed in the vacuum vessel so as to extend the measurement to lower temperatures down to 2.6 K. A high-quality single crystal pnictide superconductor of BaFeNiAs was used for testing.