Parallel plate resonator for accurate RF surface loss measurements

This paper reports on a resonator structure for measuring RF surface losses in superconductive materials developed and an absolute accuracy of 20% verified by measurements on copper films. The test structure utilizes two unpatterned, rectangular substrates which are pressed together by a spring-pressure arrangement, providing for short measurement turn-a-round times and rapid assessment of the microwave quality of HTS films. The unbalanced, parallel-plate transmission line structure is capacitively coupled to a pari of input/output leads. With 1-inch-long MgO substrates the fundamental resonance is at about 2 GHz. An rms accuracy of several percent has been confirmed by a series of measurements on thick, copper films. Data is provided on measurement results obtained with this structure on high-quality, superconducting films developed at Du Pont