Spatially resolved measurements of HTS microwave surface impedence

We describe further development of a novel technique for the characterizati on of microwave properties of HTS films which allows the spatial variation of this important physical parameter to be measured [1], The method employs a dielectric puck system that can be moved over the surface of a large BTS wafer, sampling the surface impedance at a number of discrete frequencies between 5 and 15 GHz. The surface impedance can also be rapidly measured as a function of microwave magnetic field strength. Spatial resolution for th e prototype system is as small as 1-2 mm. The surface resistance and the sh ift in surface reactance can be measured by using a loop oscillator which c an be interrupted by a fast microwave switch. The decay of microwave power in the resonator is then monitored as a function of time to determine the p ower dependent surface impedance parameters. This process is extremely fast and straight-forward and the loop oscillator configuration permits only re latively inexpensive components to be used. We describe measurements made a t 11.5 GHz of the spatial variation of the non-linear surface impedance of a number of HTS films at 77 Ii.