Intermodulation Distortion in Coupled-Resonator Filters With Nonuniformly Distributed Nonlinear Properties—Use in HTS IMD Compensation

We present a general procedure for calculating intermodulation distortion in coupled-resonator filters that allows one to predict the performance of a nonlinear filter as a function of the general nodal matrix defining the filter and the material parameters that cause the nonlinear behavior. It is valid for almost any type of nonlinear distributed effects, including those produced by high-temperature superconductors, nonlinear dielectrics such as ferroelectrics, or superconductor/ferroelectric bilayers, and it is valid when the spatial distribution of nonlinearities is not uniform. The procedure has been validated with experimental measurements in an eight-pole quasi-elliptic superconducting filter. Using this procedure, we have assessed a combination of materials with different types of nonlinear effects to partially or completely mitigate the filter´s nonlinear response. This includes superconducting filters with a ferroelectric pre- or post-distorter stage or even with intermediate ferroelectric compensation stages