Propagation of a plane electromagnetic wave through a planar inhomogeneous
layer of an isotropic medium with a positive permittivity is studied. A sol
ution method is proposed that enables one to reduce the number of independe
nt parameters of the layer. The convergence and stability of the solution a
re analyzed for the normal incidence of a wave. The applicability criterion
is formulated for the normal incidence model. Fields are estimated in the
vicinity of the turning point.