A fast nonlinear method for the harmonic effects analysis of a HTS stripline structure

Nonlinear resistivity of the high temperature superconducting (HTS) thin films generates harmonic effects at medium and high power levels. These effects in general and the intermodulation products in particular limit the power handling capability of the HTS microwave circuits and antennas in many communication systems where the co-channel and adjacent channel distortion and interference are of major concern. An experimental study has shown that the dominant low order harmonics can be modeled by the following nonlinear relation between the surface resistance, R/sub s/, and the RF magnetic field intensity, H/sub RF/, at the temperature T and the frequency: R/sub s/(f,T,H/sub RF/)=a(f,T)+b(f,T)H/sup 2//sub RF/. This is also consistent with the Ginzburg-Landau (G-L) theory. For the theoretical study of the harmonic effects it is possible to apply directly the (G-L) theory to the fields inside the HTS medium. This makes the computation very intense both in time and memory. By considering each segment in the thin film circuit as a dipole, a lumped circuit model under harmonic voltage excitation has been constructed for a microwave HTS planar circuit. We have applied the harmonic balance method to this circuit model of a distributed field structure and thus avoided the time consuming direct solution of the G-L theory.