[Untitled]

The nonlinear characteristics of YBCO (123) and TBCCO (2212) films were measured using the parallel plate resonator technique. The model approach has been developed as applied for this configuration. The current crowding at the edges of the rectangular structure is taken into consideration. A simple empirical model with few fitting parameters is used for a description of the surface impedance in linear and nonlinear mode. A suitable approximation has been found for the temperature dependence of the fitting parameter B0 corresponding to the threshold magnetic field for the onset of nonlinearity.