A model used for an analysis is a three-layered structure as shown in FIG. 7 as mentioned above wherein it is supposed that the medium M1 and medium M3 are isotropic media, the dielectric constant of the medium M1 is ??1 and the magnetic permeability of the medium M1 is ??1, while the dielectric constant of the medium M3 is ??3 and the magnetic permeability of the medium M3 is ??3.