  In this work, we demonstrate that the interaction of electromagnetic waves
with a microstructured material formed by metallic wires connected to a
metallic surface can be described using homogenization methods provided an
additional boundary condition is considered. The additional boundary condition
is derived by taking into account the specific microstructure of the wire
medium. To illustrate the application of the result, we characterize a
substrate formed by an array of tilted metallic wires connected to a ground
plane, demonstrating that in such configuration the wire medium behaves
essentially as a material with extreme optical anisotropy and that in some
circumstances the substrate can be seen as an impedance surface.
