Waves on Inhomogeneous Cylindrical Structures

Abstract

An analysis is given of some of the basic properties of exponential modes on passive cylindrical structures in which the material constants of the medium vary over the cross section. The bounding surface is assumed to be opaque, in the form of an electric or a magnetic wall; it is therefore always nondissipative. Major consideration is given to structures in which the internal medium is also nondissipative. Each mode is usually a TE = TM mixture. Some of the conventional orthogonality conditions no longer remain valid. In certain circumstances, however, the instantaneous and vector power that flow along the system are still additive among the various modes. Stored and dissipated energies per unit length generally are not additive. The propagation constant for modes on a nondissipative structure cannot be complex. The relation between the direction of the time-average Poynting vector at any point of the cross section, and that of the phase and group velocities, is no longer necessarily conventional, and the space angle between the transverse electric and magnetic fields may vary over the cross section. The field distribution of each mode varies with frequency in a manner which is clarified by physical interpretation.