How to calculate band diagrams using HFSS?

I am trying to calculate the band diagrams of certain structures, such as photonic crystals, by using HFSS. I was able to do so by using periodic boundary conditions in CST. But I can not figure out how to do it in HFSS. Does anyone have experience in such calculations by using HFSS?

This may help

http://www.ansoft.com/news/articles/...p_surfaces.pdf

unfortunatley my only practical experience of PBGs is with CST also

Sorry, forgot to mention that this was the article I used when getting a model running in CST!! (so should be good for HFSS)

why HFSS has to be so counterintuitive? I set up a unit cell as I did in CST, applied master-slave boundary conditions. And the result is not even close to CST. The band diagram I got from CST is almost identical to the band diagram obtained from a plane wave expansion method. I know, I am doing something wrong in HFSS. But I can not figure it out.