Nonlinear microwave effects in superconducting microstrip resonators basedon YBCO thin films

Linear microstrip resonators based on YBaCuO thin films made by RF magnetro n sputtering on Mgo substrates have been characterized with transmission mi crowave measurements as a function of temperature (from 10 K to T-C) and th e incident microwave power (from -30 to 10 dBm), The variation of the reson ant frequency with temperature has been used to determine the intrinsic par ameters (lambda (0), T-C) of the thin film using a fitting procedure and ap propriate models, For low microwave powers (< -18 dBm), the variation of th e quality factor, the insertion loss and the surface resistance do not exhi bit any nonlinear effect, For higher microwave powers nonlinear effects app ear and the variation of the quality factor has shown that they vary in a d ifferent way according to three temperature zones. Various theoretical mode ls have been used to discuss the experimental results. These zones can be c orrelated to the temperature dependence of the surface resistance, in parti cular to grain boundaries resistance and to penetration of microwave Joseph son vortices into the weak links. Moreover, the variation of the measured s urface resistance as a function of the RF surface magnetic field is discuss ed considering different models.