High-Q open resonant structures with a sparse spectrum

The possibility of developing high Q, coaxial, open resonant structures for waveguides in the electromagnetic millimeter, submillimeter, and optical ranges using surface magnetic modes with a unit radial index is discussed. The H(miq), with q being the longitudinal index of the mode, is possible due to the descending region present in the dispersion characteristics of H(mi) waves. Since the transverse eigenvalue for H(mi) magnetic waves is unaffected by the ratio of the inner and outer radii of coaxial structures, the structure profile can be tailored to yield one mode per octave, with the higher Q obtainable from larger structures.