Helix waveguide theory and application

Generalized telegraphist's equations have been derived for curved helix waveguide and coefficients obtained for conversion from normal modes of the helix waveguide to normal modes of the metallic waveguide. A radial wave impedance at the helix interface is used to calculate the effect of composite jacket structures. Three different applications of the helix waveguide for circular electric wave transmission are discussed: As a mode filter, the helix waveguide should have a lossy jacket which causes a high transmission loss for all unwanted modes. For sharp intentional bends with tapered curvature, the helix waveguide should have a jacket of low-loss dielectric material surrounded by a highly conducting coaxial shield. For an all-helix waveguide, in order to reduce both mode conversion-reconversion effects at imperfections and loss in curvature the jacket should be medium lossy and also surrounded by a metallic shield. The distance between helix ami shield should in all applications be about a quarter of the radial wavelength in the material. Measurements on unwanted mode transmission and TE01 curvature loss confirm the analysis.