In this letter we investigate the leaky modes supported by a M type slab weveguide which is made of three dielectric layers imbeded in a cladding. Some numerical results are shown.

In this letter, we investigated in detail the basic characteristics of W type slab waveguide in the vicinity of the cutoff frequency. Concerning with the leaky mode, we obtained some interesting results.

We discussed the cutoff characteristics of slab waveguide, and showed some numerical examples. We used the approximate dispersion equation which is valid in the frequency region near the cutoff, and is applicable not only to the lower modes but also to the higher modes.

In this paper, we developed the analytical method for the radiation field from a line current source placed in a stratified slab waveguide. This method is applicable to the analysis of excitation problem of inhomogeneous slab waveguide by increasing the number of layers. The numerical results are given for the cases of five layers, such as W and M type waveguides, and the inhomogeneous slab waveguide. The influence of guided and leaky modes on the radiation field are studied.