Nonlinear attenuation in a long YBCO coplanar transmission line in the vicinity of Tc.

The segments of coplanar transmission lines, fabricated from HTS (YBCO) thin films, can be used as superconducting microwave power limiters. The choice of coplanar lines for HTS thin film limiters is conditioned by simplicity of the 50 Ohm line fabrication accompanied with a possibility of strip width variation, determining the limit power level. Usage of transmission lines, in contrast to the lumped elements, results in enhanced linearization of AFC in a wide frequency range starting from radio frequencies and up to 20 GHz. Certainly, there is a perspective for usage of such kind limiters in microwave circuits, containing passive HTS thin film devices (filters) and low temperature low-noise amplifiers. So, the present work is devoted to experimental study of inserted nonlinear attenuation (insertion losses -IL) in a long coplanar transmission line, fabricated from HTS (YBCO) thin film. In particular, dependencies of insertion losses on the temperature and input power values IL(Pin,T) were measured for this type of transmission lines.