Non-linear microwave effects in thin superconducting films

The available experimental data on non-linear microwave effects in superconductors and some theoretical explanations of these, published since 1964, are reviewed. Various mechanisms of non-linearity observed under a wide variety of external conditions and in a broad spectrum of materials are discussed. Some examples of application of the non-linearity to frequency mixing are considered and analysed in the framework of a simple model of a fast-response resistive mixer.