. The Bell System technical journal . paced-ring structure does present some difficultproblems with regard to fabrication. An analogous structure composed of a continuous helical conductorsupported within a lossy housing has electrical properties which approxi-mate of the spaced-ring .structure, and the helix should be con-siderably easier to manufacture in long lengths. The helix might beexpected to support a wave-type approximating the circular electricwave both from the standpoint of field distribution and loss when oneobserves that a helix of very small pitch presents almost circumf
. The Bell System technical journal . paced-ring structure does present some difficultproblems with regard to fabrication. An analogous structure composed of a continuous helical conductorsupported within a lossy housing has electrical properties which approxi-mate of the spaced-ring .structure, and the helix should be con-siderably easier to manufacture in long lengths. The helix might beexpected to support a wave-type approximating the circular electricwave both from the standpoint of field distribution and loss when oneobserves that a helix of very small pitch presents almost circumferentialconductivity as required by the circular-electric wave, and the very smalllongitudinal component necessary due to the finite wire size tends towardzero as the helix pitch tends toward zero. James A. Young of theselaboratories has constructed helices in the 2 db/mile waveguide size ( at 9,000 mc) and found a heat-loss coefficient on the order times the theoretical value for ideal copper pipe. These large ex-. B-B A-A Fig. 26 ■— Spaced-ring circuhir electric wtivoguide. 1252 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1954 perimental helices were known to be impei-fect, and in a smaller diameterof helix, losses within 15 per cent of the theoretical values for perfectcopper pipe were achieved. These results lead us to regard the helicalline as a verj- promising medium for circular electric waves. SURFACE ROUGHNESS Since frequencies on the order of 50,000 mc are desirable for low-losswaveguide use, it was recognized that roughness of the surface at thewaveguide walls might appreciabh^ increase the heat loss in a practicalwaveguide. The first approach to this problem was made by VV. using sections of 5 diameter copper pipe from the experimentalline. Tyrrell measured the heat-loss coefficients of the pipe when used asa resonant cavity at 9,000 mc in lengths on the order of 4 to 8 feet. Care-fully selected resonant conditions were employed to a
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