AMCs can be made of using different structures, and corrugated surfaces is one of them as well. AMC, EBG (electromagnetic band-gaps) are general terms used for surfaces which have high impedance behavior.
I couldn't figure exactly what kind is your EBG from your posts. Can you give the citation of the paper that you are using? Also, I still don't know what kind of antenna is your antenna.
In any case, you need to scale and recheck for the behavior of AMC at your own frequency. It is not like "one design works for all frequencies". It is very likely it only has some certain bandwidth that it is useful for.
You can use CST's built in corrugated wall materials (it uses homogenization) as a first trial. Go to materials, hit new material, there choose "corrugated walls". Make sure your corrugations depths are lambda/4 at the frequency of interest. You have to also set tooth and gap widths. You can start with lambda/10 for both. Don't forget that if you use corrugated walls, it uses some equivalent values, not the actual corrugated surface. So once you see your improvement, you can built the actual corrugated surface of yours...
Google corrugated horns, or corrugated surfaces, you will find plenty of references. Also you will have some insight about the shape, how to place it etc...