Applications of high-T/sub c/ superconductors in sub-Gigahertz r.f. cavity resonators

The size of cavity resonators below 1 GHz may be reduced by using dielectric or helical loading. With normal conductors, such electrically small resonators suffer problems of losses and inadequate Q-factor. However, by using superconductor in the portions with the highest current density, very good performance may be obtained with very electrically-small cavities. A cylindrical dielectric resonator was used to load a corrugated cavity, having YBaCuO thick-film end plates, and operated at VHF. The results showed a significant improvement over corrugated cavities with copper end plates. Investigations have also been undertaken with high-T/sub c/ superconductor helical loading. The size of the cavities was electrically very small (about 0.02 of free space wavelength), and results with both bulk and thick-film helical loading elements were obtained. The results showed a significant improvement over a similar copper helically-loaded cavity resonator.>