Nonlinear model of coupled Superconducting lines

High Temperature Superconductor materials are known to produce intermodulation and other nonlinear effects. In planar structures, these nonlinearities depend on the field configuration on the strip, which in turn strongly depends on the device structure and therefore on the coupling between the strips. In this work we present an equivalent circuit that models the linear and nonlinear effects in coupled transmission lines. Numerical techniques based on Harmonic Balance are used to solve the equivalent circuit. We validate the equivalent circuit model by fitting measurements of a superconducting hairpin notch resonator. Examples of several coupled transmission line structures are given.