Theory of Azimuthally Propagating Electromagnetic Waves in Cylindrical Cavities

TL;DR

This paper develops a comprehensive theoretical framework for azimuthally propagating electromagnetic waves in cylindrical cavities, revealing new propagation behaviors, universal curves for mode analysis, and implications for microwave filter design.

Contribution

It introduces a detailed dispersion analysis, universal curves for mode determination, and compares propagation-based models with resonance-based models in cylindrical cavities.

Findings

Lowest TE mode propagates at a frequency depending only on cavity height.

Universal curves enable mode analysis without additional computation.

Propagation models can be more accurate than resonance models.

Abstract

The paper presents a detailed study of azimuthally propagating electromagnetic waves in cylindrical metallic cavities with circular cross section. Dispersion characteristics of these waves are determined from Maxwell's equations. Solutions are grouped into branches that account for all known results that are obtained from axial propagation. It is reported that the lowest TE mode starts propagating in the azimuthal direction at a frequency that depends only on the height of the cavity and may be much lower than the cutoff of the TE mode in the axial direction. Universal curves allow the determination of resonant frequencies and field distribution of TE and TM modes in circular cavities containing wedges of arbitrary angles and baffles, with no additional computation. It is shown that the frequency dependence of the propagation constant of a given branch determines all the resonant frequencies of the branch for arbitrary boundary conditions in the azimuthal direction. It is argued that propagation-based models, when applicable, are more accurate than resonance-based models. The lowest TE branch starts at a non-physical resonance. Applications to microwave dual-mode filter design are discussed briefly.