Exact Cutoff Wavenumbers of Composite Elliptical Metallic Waveguides

The cutoff wavenumbers of eccentric nonconfocal elliptical metallic waveguides are calculated in this paper. The solution is obtained using expansions in terms of the elliptical wave functions, in combination with the related addition theorem. The method presented here is exact, and allows the study of more complex elliptical waveguide geometries, like rotated elliptical interfaces arbitrarily placed inside the outer elliptical interface, or studies for possible change of the operational bandwidth. The solution is validated compared with other published results from the literature. The known problem of an elliptical metallic waveguide loaded by a concentric nonconfocal strip is revisited and discrepancies noticed by other authors are justified. Numerical results are presented for the cutoff wavenumbers for various composite elliptical waveguides for both TM and TE modes.