Miniature superconducting high frequency coaxial lines

The use of superconductors in coaxial cables designed for high frequency transmissions leads to an appreciable reduction of both the losses and physical dimensions. In this paper, after recalling the definition of the electrical parameters of the coaxial lines, theoretical and experimental studies of miniature superconducting coaxial lines are reviewed. An attenuation constant of 0.5 dBkm-1 has been achieved at 1 GHz and 4.2 K with a 2 mm external diameter line having lead-plated copper conductors and a fluoroethylene-propylene dielectric. Such performances can only be achieved with lines of high geometrical and structural qualities, having few physical irregularities and without periodic non-uniformities. The results are promising for a new teletransmission medium and may be compared with the two other challengers, guided waves and optic fibres. However, the need for a cryogenic environment has for the present hindered extensive industrial development. (author)