Waveguides: characteristic modes of hollow rectangular dielectric waveguides

Abstract

The field configurations and propagation constants of the normal modes of a hollow rectangular dielectric waveguide have been determined. In addition, the coupling coefficients of a Gaussian free-space mode into the normal modes of a square guide were calculated. The attenuation of each mode is found to be inversely proportional to the cube of the guide aperture 2alpha and proportional to the square of the free-space wavelength lambda. For a hollow dielectric square guide with 2alpha = 1 mm and lambda = 10.6 microm, an attenuation of 0.140 dB/m is predicted for SiO(2) and 0.032 dB/m for BeO. All modes are found to be hybrid modes, although they very closely approximate linearly polarized TEM modes.