Tunable microwave characteristics of a superconducting planar transmission line by using a nonlinear dielectric thin film

A field solution for a planar type-II superconducting transmission line made of two high-temperature superconducting films and a nonlinear dielectric thin film is derived. The combined effects of the nonlinear dielectric permittivity as well as of vortices inside the superconductors on the attenuation constant and phase velocity are numerically investigated. Variation in temperature-dependent phase velocity due to the dielectric nonlinearity is lowered pronouncedly in the presence of vortices. In addition, variation in phase velocity versus dc electric field is also reduced in the case of more vortices. The role played by the nonlinear dielectric as well as the vortices in such a tunable microwave component are thus demonstrated.