Modes on elliptical cross-section dielectric-tube waveguides

The problem of electromagnetic-wave propagation along a dielectric-tube waveguide of elliptical cross-section is considered. The characteristic equations for odd and even hybrid modes are derived in the form of two infinite determinants, which degenerate to the well-known characteristic equation for hybrid modes on circular tubes as the eccentricity tends to zero. The characteristic roots are computed for various eccentricities and tube thicknesses. It is found that there exist two dominant modes which possess zero cutoff frequencies. The modes on the elliptical tube waveguide are designated by observing computer plots of the radial variation of the field components. The phase velocity is shown to be dependent more upon dielectric area than eccentricity. Thin-walled tubes exhibit less dispersion while thick-walled guides behave as solid dielectric rods. Experimental results on zero-eccentricity tubes agree well with theory.