Mode Conversion in Metallic and Helix Waveguide

Helix waveguide consisting of closely wound insulated copper wire covered with an electrically absorptive or reactive jacket (Fig. 1) is a good transmission medium for circular electric waves.1 In long distance communication with waveguides it is useful as a mode filter, for negotiating bends or particularly as the transmission line proper instead of a metallic waveguide." The loss of circular electric waves decreases steadily with frequency only in a perfect metallic waveguide.3,4 A similar situation prevails for helix waveguide. Any deviations from a round and straight guide will add to the transmission loss. At such imperfections power is converted from the circular electric wave into other propagating modes and reconverted. The mode conversion-reconversion effects increase the loss and degrade the transmission characteristics. * Parts of this paper were presented at the I . R . E . Professional Group on Microwave Theory and Techniques Symposium, San Diego, California, 1960. 613 G14