Measured TE01 Attenuation in Helix Waveguide with Controlled Straightness Deviations

The added mode conversion loss in a circular waveguide due to random straightness deviations of the guide axis has been calculated by Rowe and Waiters. 1 These calculations show that if the mechanical spectrum of the axis wiggles has high density near the beat wavelengths of the coupling modes, then the transmission loss for a TEoi signal mode can be excessive for axis deviations of fractions of a mil. However, as emphasized in this paper and in other calculations,2-3 the requirement on the straightness depends strongly on the mechanical spectrum of the deviations. If the significant part of the mechanical spectrum is far from the beat wavelength of the coupling modes, then extremely large deviations (several feet) do not seriously affect the TE 0 i transmission. Here we offer experimental evidence of these facts for a 2-inch diameter helix waveguide, and associated theoretical calculations which agree favorably with the experimental results. In Section II we describe the experiment and discuss briefly the measured results of the experiment. Section III contains some theoretical calculations and, finally, in Section IV we discuss the comparison of experimental and theoretical results and some conclusions of the experiment. 273