Attenuation in wedge and septate waveguides

Abstract

The wedge waveguide consists of a circular cylinder, a cross section of which has a sector occupied by a metal wedge. As the wedge angle approaches zero the wedge waveguide becomes a septate waveguide. The presence of the wedge permits a mode of lower cutoff frequency than the circular H 1.1 mode to propagate for a given-diameter waveguide, and the transverse fields associated with this mode become infinite at the tip of the wedge. Because of this, the standard impedance condition, used to calculate the flow of power into the waveguide walls, yields a coupled mode which does not satisfy the Meixner edge condition. This in turn yields extremely high values for the ohmic losses near the tip of the wedge and, as the wedge angle approaches zero, the integrals involved in calculating these losses fail to converge. In the present paper the results of a careful analysis (presented in an earlier paper) of the behaviour of fields near the tip of a metal wedge are presented. The surface impedance condition is modified to agree with this analysis and used to calculate the attenuation constant of wedge waveguides. Graphs of attenuation constant vs frequency and vs wedge angle are presented for the wedge waveguide operating in its lowest mode. The results of an experimental determination of the attenuation constant are also presented and found to be in agreement with the calculated value. The losses do not become large as the wedge angle is allowed to approach zero and the attenuation constant of the septate waveguide compares favorably with that of standard waveguides.