The radiation field from the dielectric-rod antenna with two-layered, rectangular cross section

Abstract

It is difficult to operate a single-layered dielectric waveguide for the millimeter-wave frequency range in a single mode with a small dielectric loss while the electromagnetic field is sufficiently trapped in the guide. On the other hand, this becomes possible in a two-layered dielectric waveguide if the dimensions of the core and the clad are appropriately well chosen. In this paper, the electric field distributions of the amplitude and phase on the truncated plane and the radiation pattern of a two-layered dielectric rod antenna with a rectangular cross section are analyzed theoretically. By the “generalized effective dielectric constant method” [2], the electromagnetic field distribution on the truncated plane of the waveguide cross section is derived. The boundary conditions at the discontinuity are Fourier transformed in the x and y directions. The results are multiplied to compute the electromagnetic field distributions. In comparison with the two-dimensional Fourier transformation, this method has an advantage in that the computation time is shorter and the method can be applied to more complicated geometries. The results are compared with the assumption that the electromagnetic field on the cross section is identical to the one propagating in the waveguide. As for the electromagnetic amplitude distribution, the discontinuities of the electric field amplitude distributions are smaller at the boundary between the core and the clad in the present method. In regard to the phase distribution, the variation of the phase is smaller near the center axis so that the effect on the radiation pattern is negligible. The present method can be applied to analyze the problem of the discontinuities and truncations of a multilayered dielectric waveguide in the millimeter-wave and submillimeter-waves and of the radiation from an optical source.