HTSC inverted and conventional geometry microstrip resonator for UHF frequencies

HTSC (high-temperature superconductor) planar resonators may be used to replace voluminous normal conductivity high-Q resonators by miniaturized ones at UHF frequencies (0.3-3 GHz). Therefore an inverted microstrip resonator has been investigated. Both electrodes of the resonator are made of epitaxial films of YBa₂ Cu₃O_7-δ, and one of them is structured into a meander-type stripline. The distance between stripline and ground plane is held by a 50-μm-thick spacer foil which also carries the resonator feeding lines in conventional microstrip design. The small distance between both electrodes ensures that only a small amount of electrical energy is located in the LaAlO₃ substrates and that the effective dielectric loss factor is low. At 77 K and at a resonant frequency of 700 MHz the measured unloaded Q was 2800. During improving the structuring process and reoptimizing the resonator design, the unloaded Q of the conventional geometry microstrip resonator has been increased to Q₀=25000. The use of the inverted microstrip resonator design will improve the Q values beyond that