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

It is well known that high temperature superconductors (HTS) generally reveal a nonlinear dependence of the surface impedance on the input microwave power Zs(Pin) [1,2] unlike to normal metals behavior. This leads to undesirable nonlinear effects (such as: intermodulation distortions, generation of higher harmonics) in HTS passive microwave devices and strongly limits possibilities of their application even for weak microwave signals. On the other hand, strong nonlinear effects in HTS materials can be used for design of active devices, such as microwave power limitters. Similar devices have been elaborated already for application as dc and low-frequency ac current limitters in electric cirquits.