A microwave broadband technique to measure the complex resistivity of HTS thin films

We propose a new broadband swept frequency technique to measure the complex resistivity of high T_c superconducting thin films in the microwave range (from a few GHz up to 50 GHz). A coaxial cable connects the sample to a vector network analyzer which performs reflection measurements; the film and the coaxial end are separated by a short section of circular waveguide. The absence of direct electrical contact between the sample and the coaxial core simplifies realization and avoids contact instability with large temperature variations. We provide an electromagnetic analysis of the coaxial to cylindrical transition (CCT) and find a closed form relation between the measured quantities and the film resistivity. Finally, we present some experimental results obtained for an YBa₂Cu₃O_7-δ thin film using the described method