Improvements in or relating to coaxial transmission lines for high frequency electromagnetic waves

摘要

771,670. High-frequency cables. WESTERN ELECTRIC CO., Inc. Dec. 30, 1955 [Dec. 31, 1954], No. 37430/55. Class 36. In a high-frequency transmission line comprising three coaxial conducting members 1, 2, 3, separated by insulation 4, 5, the intermediate member 2 has a thickness of less than one " skin-depth " at the predetermined operating frequency, the insulating materials 4, 5 have different wave-propagation properties and the nature of the insulating materials, the thicknesses of the members 1, 3 and the distances between the members 1, 2, 3 are so chosen that. the line has a relatively low power loss and a more uniform attenuation over a range of operating frequencies including the predetermined frequency than that of a comparable twoconductor cable of like external diameter operating over the same frequency range. The insulating material 4, 5 may have different dielectric constants and/or different permeabilities and may comprise polyethylene and polystyrene respectively. The member 2 may be nearer to the member 1 than it is to the member 3 and the member 1 may be solid or hollow. Where the member 1 is hollow, the thickness both of this member and of the member 3 may be between one and two " skin-depths ", the thickness of the member 2 being between half and one " skindepth ". The members 1 and 3 may comprise coatings of the required thickness of a relatively highly conducting material such as copper on the outer and inner surfaces respectively of inner and outer cylindrical supporting members of less conductive material such as iron. The " skin-depth " # is given by: where f is the operating frequency, Á the permeability of the conductor and g its conductivity. The Specification indicates the manner in which the optimum values for the different variables may be calculated. Specification 715,359 is referred to.