Winding Tolerances in Helix Waveguide

Abstract

In a perfect helix waveguide the circular electric wave loss is increased by eddy currents, finite pitch of the helix, radiation through the wire spacing and effects of the wire coating. Only the contributions from eddy currents and pitch are large enough to limit wire size and spacing. Experimental helix waveguides have tilted turns. These tilts cause coupling between circular electric and unwanted modes. From the coupling between modes in curved and in offset helix waveguide, the coupling in a helix waveguide with tilted turns is found. For helix waveguide with slightly irregular winding of arbitrary form, generalized telegraphist's equations are derived. Tilts and other irregularities in the winding increase the circular electric wave loss. The average increase is a function of the covariance of irregularities. Winding tilts with an exponential covariance and an rms value of 0.6° increase the TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">01</inf> loss in 2-inch inside diameter waveguide at 55 kmc at the most by 10 per cent of the loss in a perfect copper pipe with smooth walls. Present fabrication procedures insure a smaller wire tilt than this.