Similarities in the electromagnetic behaviour of optical waveguides and corrugated feeds

Important similarities are described in the electromagnetic behaviour of optical waveguides, comprising concentric dielectric cylinders of slightly different refractive index, and corrugated circular waveguide feeds for microwave antennas. It is shown that, subject to approximations, which are justified in many applications, the eigenvalue equations for the two structures have the same form. Similarities in their radiation characteristics are discussed, also in the excitation efficiencies of focusing systems employing either type of structure at the focus.