Precise microwave characterization of lanthanum aluminate and LSAT substrates for HTS circuits with superconducting post dielectric resonator

Accurate data of complex permittivity of dielectric substrates is needed for efficient design of HTS microwave planar circuits. We have used a recently developed resonator for precise microwave characterisation of LaAI03 and (La,Sr)(AI,Ta)03 substrates at cryogenic temperatures. The measurement fixture has been fabricated using a post dielectric resonator with superconducting (DyBa2Cu307) end plates and silver-plated copper sidewalls to achieve high sensitivity and resolution of loss tangent measurements. The post resonator together with an appropriate numerical\ud technique has been used to measure the complex permittivity of LAO and LSA T planar dielectrics and can be used for screening of HTS substrates before deposition of HTS films for microwave applications