GB764737A - Improvements in or relating to electromagnetic wave transmission systems - Google Patents

Abstract

764,737. Waveguides. WESTERN ELECTRIC CO., Inc. March 11, 1955 [March 15, 1954; March 15, 1954], No. 7235/55. Class 40 (8). In order to prevent mode degeneracy in a waveguide transmission system utilizing the H01 mode of propagation the waveguide wall is formed from a helical conductor whose pitch is less than a quarter wavelength of the propagated energy. The helix is electrically discontinuous for longitudinal currents associated with the undesired dominant E mode. The turns of the helix 61, Fig. 6, may be spaced from each other or, if the helix is formed from a conductor having an insulating layer of enamel 62, they may be contiguous. If the helix is formed from aluminium wire 52, Fig. 5, the surface layer of oxide provides the insulation. In order to damp longitudinal currents the helix is surrounded by a layer 63 of lossy material, e.g. polyethylene containing ion dust or carbon black. The guide is encased in protective casing 64 of conductive material. Where the helix 52, Fig. 5, is formed from aluminium it is necessary to maintain its circularity by providing a winding 51 of spring steel between the lossy layer 53 and the casing 55. The lossy layer may be formed from a continuous ribbon which is wound with adjacent turns overlapping around the helix. The turns are fused together by heat. The helix may be formed from a wire of rectangular section with the wide dimension arranged parallel to the guide axis. The guide may be filled with lowloss dielectric material.