  We bring forward rather simple algorithm allowing us to calculate the
effective impedance of inhomogeneous metals in the frequency region where the
local Leontovich (the impedance) boundary conditions are justified. The
inhomogeneity is due to the properties of the metal or/and the surface
roughness. Our results are nonperturbative ones with respect to the
inhomogeneity amplitude. They are based on the recently obtained exact result
for the effective impedance of inhomogeneous metals with flat surfaces.
One-dimension surfaces inhomogeneities are examined. Particular attention is
paid to the influence of generated evanescent waves on the reflection
characteristics. We show that if the surface roughness is rather strong, the
element of the effective impedance tensor relating to the p- polarization state
is much greater than the input local impedance. As examples, we calculate: i)
the effective impedance for a flat surface with strongly nonhomogeneous
periodic strip-like local impedance; ii) the effective impedance associated
with one-dimensional lamellar grating. For the problem (i) we also present
equations for the forth lines of the Pointing vector in the vicinity of the
surface.
