A Relation for the Loss Characteristics of Circular Electric and Magnetic Modes in Dielectric Lined Waveguide

Recent studies 1 indicate many modes not of the circular electric type may have very low loss in dielectric lined circular waveguide. In these studies the duality principle was used to explain the lowloss characteristics of circular magnetic modes for linings having thicknesses which are an odd multiple of a quarter wavelength. In this paper we extend this use of the duality principle and derive a simple relation between the loss characteristics of circular electric and magnetic modes in dielectric lined circular waveguide. In all cases, we find the minimum heat loss obtainable as the dielectric thickness varies is greater for circular magnetic modes in comparison with the minimum circular electric mode heat loss. 1639 1640 THE BELL SYSTEM TECHNICAL JOURNAL, MAY-JUNE 1971 The waveguide under consideration is shown in Fig. 1. It consists of a highly conducting outer wall to which a thin layer of dielectric (of relative permittivity e) is bonded. The liner is usually "electrically" thin and its sole function is to break the phase velocity degeneracy between the TE, n and T M n modes in hollow metal-walled waveguide. In this paper we are concerned with the effect of thicker linings (linings which are an integral multiple of a quarter wavelength thick) on the conducting wall losses of the waveguide. We will assume t h a t the dielectric is lossless in this study. The metal walls of the waveguide in Fig. la may be modeled 2 as a low-impedance termination (Z, « r?) for the fields interior to the walls.