Performance and modeling of superconducting ring resonators at millimeter-wave frequencies

Microstrip ring resonators operating at 35 GHz have been fabricated from laser-ablated YBCO thin films deposited on lanthanum aluminate substrates. They were measured over a range of temperatures, and their performance was compared to that of identical resonators made of evaporated gold. Below 60 K the superconducting strip performed better than the gold, reaching an unloaded Q approximately 1.5 times that of gold at 25 K. A shift in the resonant frequency follows the form predicted by the London equations. The phenomenological loss equivalence method is applied to the ring resonator, and the theoretically calculated Q values are compared to the experimental results.<>