Surface impedances for planar conductors in volume discretization methods without frequency limitations

Surface impedance boundary conditions (SIBC) for lossy metal layers are presented that are not limited to the frequency range in which a metal layer is thicker than several skin depth. A metal layer is considered as a TEM transmission line so that the SIBCs can be obtained as the input impedances of an open ended and a short circuited transmission line, respectively. The SIBCs are verified for a MMIC microstrip line and a coplanar waveguide.