Working of PBG structure on ground plane of patch antenna

Can anyone tell me the working of pbg structure on gnd plane of patch antenna? pbg structures are employed for redcing backlobe & increasing gain. but how is it doing it? plzz help

The PBG structure on the ground plane doesn't permit the propagation of the wave in the substrate/laminate. So it is radiated, instead of being trapped in the laminate, reducing efficiency and generating side lobes. Perhaps someone can comment in a more professional and scientific manner?

why this name photonic band gap? actually what is it? & also is there any relation b/w EBG(electronic bandgap)?

- - - Updated - - -

can any1 suggest any gud IEEE paper containing the detailed working of PBG? or any gud link...plzz help