Microwave Properties and Applications of High Temperature Superconductors

Abstract

High temperature superconductors and microwave devices form the ideal partnership. The application of superconductors in microwave devices, components and systems allows of a reduction in size, power consumption and insertion loss. The latter is of particular importance in complicated structures based on tapped delay lines, such as correlators and chirp filters, which cannot be implemented in normal conductor as the insertion losses are too great. A further feature of superconductors is that they are non-dispersive; information can be transmitted without any separation of frequencies. High temperature superconductor devices can operate in a more accessible and benign temperature regime, around that of the boiling point of liquid nitrogen, 77K, and not too far below the ambient in a satellite, which is about 100K. The reduction in size and power requirements, which together both lead to a reduction in system mass, coupled with the reasonably accessible operating temperature, suggest that HTS microwave components should find ready application in satellite communications systems. The general application of HTS has been inhibited by the difficulty of producing materials in bulk or over large areas with adequate properties. Microwave devices are fabricated from HTS thin films with dimensions of a few square centimetres. These films are just of the form and size which give the highest values of superconducting properties, such as citical temperature, critical current density and microwave surface conductance. This is another happy circumstance which further strengthens the belief that the first commercial applications of HTS will be found in microwave systems.