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We report on a general procedure to calculate intermodulation distortion in cavities with superconducting endplates that is applicable to the dielectric-loaded cavities currently used for measurement of surface resistance in high-temperature superconductors. The procedure would enable the use such cavities for intermodulation characterization of unpatterned superconducting films, and would remove the uncertainty of measuring intermodulation on patterned devices, in which the effect of patterning damage might influence the outcome of the measurements. We have verified the calculation method by combining superconducting and copper endplates in a rutile-loaded cavity. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1535742͔Microwave nonlinearities are important features of superconducting thin films that might limit their applicability. This is the case in high-temperature superconductors ͑HTS͒, whose use in wireless and other communication systems is limited, among other factors, by this type of nonlinearity. 1Microwave nonlinearities are enhanced when there are high current densities in the superconductor, and are most prominent in planar resonators in which magnetic field wraps around a thin superconducting film.2 There is a widespread agreement to attribute the nonlinearities to a dependence of the surface impedance on the local magnetic field or, equivalently, on the surface current density. 3There is concern regarding the possible effects of patterning superconducting films on the nonlinear behavior of the resulting planar devices, especially when considering intermodulation distortion ͑IMD͒. Besides the obvious technological implications in device fabrication, this could also affect basic studies that use the IMD of patterned resonators to probe the properties of superconductors. 4 Measurements of third-harmonic generation made on planar HTS lines of various cross sections 5 suggest that etching in HTS has a limited effect on IMD, but to completely rule out these effects, a study similar to Ref. 6 should be made. That work compares nonlinear measurements of cavities with superconducting films used as endplates with measurements of planar devices fabricated with the same films, and finds that the power dependence of the microwave surface resistance is unaffected by the patterning process. To extend such work to IMD and rule out the effects of patterning on this type of distortion, it is necessary to relate the results of a cavity IMD measurement with the properties of the superconducting film. In this letter, we address this by describing a method to calculate the power of the intermodulation products coupled out of a cavity with one or two superconducting endplates, and show experimental results that verify the method.We assume that we have a cavity, which might be dielectric-loaded as those in Refs. 6 and 7, in which one of the endplates is made of a superconducting material and the other is a normal metal. We also assume that the electric field on the superconducting endplate will be a superposition ...

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In this work we predict the nonlinear behaviour of an eight-pole quasi-elliptic bandpass high temperature superconducting (HTS) filter with an equivalent circuit extracted from intermodulation measurements performed at the centre of the filter passband. We present measurements that show that the equivalent circuit is able to predict the intermodulation products produced by the filter when driven by two in-band or out-of-band sinusoidal signals. Numerical techniques based on harmonic balance are used to extract the elements of the equivalent circuit and to simulate its nonlinear performance.

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