Microwave power dependence of HTS thin film transmission lines

Stripline resonator measurements indicate nonlinear response in thin film YBa/sub 2/Cu/sub 3/O/sub 7-x/ transmission lines when microwave power levels exceed a certain critical level. The nonlinearities likely originate in the intergranular junctions of the c-axis epitaxial films. An effective medium approach is used here to model the series impedance of the grain junctions. The field dependence of the surface resistance and penetration depth in the junctions are modeled at low fields with a Ginzburg-Landau type response, at intermediate fields by an intergranular fluxoid state, and at high fields by a flux flow shielding state which occurs at a frequency and temperature dependent transition field H/sub trJ/. Comparisons are made with measured data over a range of frequencies and power levels.