Non-linear microwave response of HTS thin films: a comparison of intermodulation and conventional measurements

The non-linear microwave response of HTS thin films is a crucial issue for applications of the cuprates in future communications technologies. We report comparisons of nonlinear characterisation measurements made by two different techniques. The first involves two-tone intermodulation measurements, for which the HTS thin films are incorporated into a high Q resonant structure and two spectrally pure tones are injected within the resonator bandwidth. The second consists of a conventional high power steady-state parallel-plate resonator measurement of the non-linear response of Z_s(H_rf). Two very different HTS thin film samples are examined and simple physical models, involving grain boundary effects or film heating, are used to relate the intermodulation and power dependent impedance results to properties of the HTS thin film