Lined Waveguide

Round waveguide with dielectric lining shows promise as a communication medium.1 The circular electric wave loss in perfectly straight and round metallic waveguide decreases steadily with frequency. Any deformations of the cross section or curvature of the guide axis degrade these ideal transmission characteristics. The TMin waves in particular are coupled by curvature to TE0n , and since they propagate with nearly equal phase velocity, there will he large mode conversion. A dielectric lining close to the wall changes the TMi n waves appreciably with almost no change to TEon . The phase velocities are now different and, despite curvature coupling, mode conversion stays small. When the lining is made lossy it will serve still another purpose.2 Circular electric wave loss is increased only very little, while all other waves suffer an effective dielectric loss. This mode filtering loss will reduce the degrading effects of mode conversion and reconversion. * This work was performed under a Letter Contract with Bell Telephone Laboratories at the Institut fuer Hoecbstfrequenztechnik, Technische Hochschule Braunschweig. 745