cst ebg band

Hello friends. I am trying to find out the surface wave band-gap of EBG using direct transmission method. I am using semi-infinite structure which is having 6 ebg cells and two ports on both the ends. I made periodic bounderies on two sides and Electric elsewhere. Is there any method that I can get TE and TM mode stopbands seperately using same method? And finally how can we apply the same method for finite EBG structure say 6X6 EBG. I seem to get wrong answers. I am using CST 2009 version. Any help would be greatly appreciated.

Thanks & Regards
Praful