TF/SF formulation for plane wave scattering from infinite dielectric

Does anyone know how to write a 2D FDFD (or FDTD) matlab code for scattering from infinite dielectric slab ? this is supposed to be a simple problem !
I managed to code scattering from finite objects but I cannot make it work for the simplest scattering problem (to compare with analytical solution) !
It seems there is a problem with the TF/SF formulation when the object is infinite since the scattered field region now is not homogeneous.
Please guys, I am desperate and have a deadline within a few days ! Any help is appreciated