Propagation behaviour of slotted inhomogeneous circular waveguides

By employing an approximate transverse-equivalent-network representation, the propagation behaviour of a slotted circular waveguide containing an axial dielectric rod is investigated. The complex transverseresonance equation is solved for E and Htype modes possessing an azimuthal dependence of zero and unity. The behaviour of both fast-wave and slow-wave regions is considered, and it is shown that, whereas the E mode propagation coefficient is a continuous function of frequency when the normalised phase-change coefficient passes through unity, the H mode propagation coefficient is discontinuous. The theoretical results for the slotted cylinder also demonstrate the form of the transition between the slow-wave behaviour of completely closed and completely open dielectric-rod structures. Theoretical phase-change coefficients in the fast-wave region are compared with those previously obtained from measurements of leaky-wave radiation patterns. Although good agreement is obtained, it is concluded that the perturbation caused by the introduction of a slot can be quite large in certain cases. A method is proposed whereby the perturbation might be reduced for modes with an azimuthal dependence of unity. it is suggested that the technique could prove useful in determining the fast-wave propagation characteristics of those asymmetric inhomogeneous-waveguide structures that are unamenable to analysis.