FDTD coding for perioc boundary condition(PBC)

Hi,

I try to use Sin-Cosine method on Taflove's book to implement PBC with a plane wave excitation by TF/SF method.

But the result seems to be failed!

1. I wonder that if iterating the PBC on the total-field is correct, or else on the scattered-field?

2. Do you guys know how to implement PBC with TS/SF, or I need try another plane wave excitation method(ex. pure scattered field method)?

Thanks a lot!