Intermodulation in a microwave resonator with a high-temperature superconductor

Intermodulation, or the generation of a combination-frequency signal, is studied theoretically in the case where the nonlinearity is provided by a high-temperature superconductor placed in a microwave resonator. A general formula that relates the power of an intermodulation signal to the electromagnetic performance of the resonator, the physical parameters of the superconductor, and the intensity of pump waves is derived. A parameter that characterizes the nonlinearity is evaluated from data available from the literature. The potentialities of various resonators for the microwave characterization of the nonlinearities in high-temperature superconductors are assessed.