Technique for determination of RF-magnetic field dependence of the HTS surface impedance by microwave resonators

The investigations of nonlinear electromagnetic properties of high-temperature superconductors (HTS) in the last years arouse active interest in connection with the prospects of HTS application in various microwave devices (resonators, filters, antennas etc.), with the problems of quality control of these materials, and with the fundamental problems of the physics of superconductors. The nonlinearity of HTS is usually characterized by the dependence of a surface impedance Z_s on the amplitude of a variable magnetic field H on the HTS surface, i.e. Z_s(H). This dependence is determined by using microwave resonators of various designs. For all resonator types there is a strong inhomogeneity of the field H distribution on the HTS surface. It is shown that the HTS nonlinearity and fields inhomogeneity lead to essential errors in conventional techniques, and a new approach to the problem of diagnostics of nonlinear microwave properties of HTS is advanced