periodic boundary conditions cst

Does anybody have idea on the calculation transmission under the plane-wave
incidence and periodic boundary conditions in cst?
I am trying to repeat Fig. 3(b) in a paper published in Phys. Rev. Lett. 101, 047401 (2008) entitled "plasmon-induced transparency in metamaterials". But what I got isn't the exactly same as this figure.

Hi everyone,
I have a problem. I am simulating a FSS cell in CST Studio and I want to calculate the reflection coefficient in a frequency range with a plane wave (TEM mode). I am using a waveguide, but I am not sure which mode I am exciting with a waveguide. Any of you can you tell me how to excite a TEM mode with a waveguide port.
Thanks in advance,
David