A Three-Conductor Elementary Clogston Coaxial Transmission Line --- Calculation, Fabrication and Experiment

A three-conductor coaxial cable, in which the locations of the two inner conductors are transposed at regular intervals, was built and shown to have about 20 per cent lower attenuation over a certain frequency interval than a two-conductor coaxial of the same size. 1 This is because the eddy current losses are smaller, and this in t u r n is a result of the normal central conductor having been divided into two and the normal central current having been divided nearly evenly between these two. 2551 2552 T H E B E L L SYSTEM TECHNICAL J O U R N A L , N O V E M B E R 19G3 It is possible to do this so t h a t the two conductors occupy approximately the same space as the single one did before, since the skin effect causes most of the current to flow in a thin shell at the outer periphery of the inner conductor over a certain frequency interval. Dividing the central conductor provides two shells for current flow. One way to achieve equal currents in the two inner shells is to transpose the two inner conductors frequently enough in the manner of litz wire and so force the even division. This is the method used in the project described in Ref. 1. Another method is to so choose the dimensions and properties of the two dielectric spaces t h a t the line has a natural mode of propagation with approximately the desired current distribution. This is a special case of the method suggested by Clogston a number of years ago, 2 namely, t h a t the conductors of a transmission line be made of many laminations with proper dielectric separation.