How to determine bandgap of EBG structures?

I want to know how to determine the bandgap of an EBG structure (by which parameters)
Anybody helps me!
Thank you.

I am also new in this field, so just provide some suggestions.

EBG generally can be implemented in following ways:
1) drilling a periodic pattern of holes in the substrate
2) etching a periodic pattern of circles in the ground plane
3) adding a periodic pattern of metallic pads which are shorted to the ground by vias
4) Uniplanar EBG

There is some rough relation between the geometrical paramters of the periodic pattern and the stopband frequency. Up to now, I decide the stopband by simulation.