WT4 Millimeter Waveguide: TE01Transmission in Waveguide with Axial Curvature

Abstract

In this paper we examine the relationship between the loss of the TE 01 mode in a multimode circular waveguide and the waveguide geometry. First-order perturbation theory solutions of the coupled line equations were used to predict the loss from measurements of the waveguide geometry. The predicted loss disagreed with the measured loss for the 14 km long waveguide line in the WT4 field evaluation test. An analysis of the coupled line equations which considers the effects of both first- and second-order mode conversion is described. The appropriate coupling coefficients are derived and discussed. Second-order perturbation theory solutions of the coupled line equations are developed and examined. Losses predicted from the measured waveguide curvature and the second-order theory agree well with measured loss data. The results indicate that axial curvature leads to significant mode conversion-reconversion effects between the TE 01 –TM 11 , TM 01 –TE 12 , TM 11 –TM 21 , TE 12 –TM 21 modes in the installed waveguide of the WT4 field evaluation test. The TM 21 conversion is due to curvature fluctuations with a characteristic wavelength of 10 to 30 m.