Research Models of Helix Waveguides

A cylindrical metallic waveguide provides a unique transmission line for a circular electric wave having a wavelength less than one third the inside diameter of the waveguide. Under such conditions the lowest circular electric wave, TE 0 i , has less loss than any other mode. Furthermore, for perfectly round straight pipe, the losses for this mode decrease indefinitely as the frequency increases. Unlike all other modes, the circular electric modes induce no longitudinal wall currents. The currents which do flow are in the circumferential direction and result from the action of the pipe in restricting and directing the propagating energy. Rigorous theory and experimental d a t a substantiating the validity of the above statements have been presented elsewhere. (Refs. 1 through 6). T h e usefulness of these properties has provided the stimulus for a comprehensive study by Bell Telephone Laboratories at Ilolmdel, N. J. For this purpose, a round waveguide having a 2-inch inside diameter has been selected, and it is anticipated t h a t its transmission will be useful over the band from 35,000 to 75,000 megacycles. Aside from economic considerations, the penalty for using a larger diameter is t h a t the number of parasitic modes which may propagate is greatly increased and the physical tolerances become more critical. 679