Reflection characteristics of twisted component in rectangular waveguides

Abstract

AbstractTo develop a design theory for rectangular twisted waveguide components, the reflection characteristics at the junction to a straight waveguide are studied theoretically. First, a perturbation method and a modal analysis are applied to the hybrid mode field inside the twisted waveguide. In addition to the terms of the second perturbation for the twist constant, we derived analytical expressions for the reflection coefficient and the normalized admittance at the junction. It was found that the reflected wave caused by the higher‐order mode components generated at the junction is equivalent to that caused by the capacitive susceptance inserted in parallel in the transmission line. Also, the difference in the phase constant between the straight and twisted waveguides is due to discontinuity in the characteristic impedance. Next, a theoretical formula containing the effect of multiple reflection has been derived for the overall VSWR of the twisted component inserted in a straight waveguide. the validity of this formula has been confirmed by experiments in the 10‐ GHz band with specially manufactured twisted waveguides. Further, a design chart for a practical 90‐degree twist has been presented and a design method has been given for a broadband transmission characteristic with restricted maximum VSWR values.