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Surface impedance boundary conditions (SIBC) for superconductor layers are provided. These can be used for arbitrary thick conductors from very thin to very thick. A superconducting 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 microstrip line and a coplanar waveguide made of Niobium on a LaAlO3 substrate.

A new 3D hybrid finite-difference (FD) method is presented that accounts for finite conductivity. The field gradients inside conductors and structural details are treated combining quasi-static field solutions with the fullwave analysis. In the quasi-static regime, the magnetic field computations and the corresponding source formulation needs special consideration The hybrid method reduces computational efforts while maintaining accuracy of the conventional FD scheme. The new approach is verified for a MMIC coplanar short stub and airbridges.