Winding Tolerances in Helix Waveguide

Helix waveguide consisting of closely wound insulated copper wire covered with an electrically absorbing or reactive jacket is a good transmission medium for circular electric waves. 1 In long distance communica tion with circular electric waves it is useful as a mode filter, for negotiating bends or particularly as transmission line proper instead of a plain metallic waveguide. As in metallic waveguide, the loss of circular electric waves decreases steadily with frequency only in a perfect helix waveguide. Any deviations from a round and straight guide and from a uniform and low pitch will add to the loss of circular electric waves. Deviations from straightness and deformations of the cross section of helix waveguide have been analyzed before and their effect on circular electric wave transmission has been determined. 2 . When these imperfec627 (330 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1961 tions are caused in the manufacturing process they are statistically distributed over the guide length with a small correlation distance. Then they add nearly the same average loss to the circular electric wave as they do in a plain metallic waveguide. 4 M a n u f a c t u r i n g tolerances for straightness and for cross-sectional deformations are therefore the same for helix waveguide as they are for metallic waveguide. Deviations of the winding from a low-pitch uniform spiral are imperfections peculiar to the helix waveguide. Their effect on circular electric wave transmission will be analyzed here and tolerances on the winding of the helix waveguide for low-loss transmission will be determined.