Improving Isolation in a dual fed air dielectric patch.

Hello everyone,
I'm designing a dual probe fed patch antenna with air dielectric for the lower GSM band. Although I get a very good radiation pattern and decent return loss, the isolation between the two ports is only about 12 dB at the higher end of the frequency range. The ports are at a distance of 73 mm from each and are a little bit on inside of adjacent edges of the antenna.

I've tried finding literature about the same but couldn't find a dedicated paper or article about improving isolation in dual fed patches.

Any help is appreciated..
Thanks,
Ananth.

Hello everybody..
Wow.. Nobody's got any ideas on how to improve isolation on a dual probe fed patch!

hi
u can use photonic crystals between them, like:
DGS, PBG, EBG, or use high impedance surface as your ground plane, or
use cavity beneath the patches, or as the simplest way, you can remove the substrate between the patches.
best of all is DGS.

Hey Hamid,
Thanks for the ideas, but since I've got air as the dielectric, the cavity and removal of substrate is out of question. I'll check into the high impedance ground plane idea and the photonic crystals idea..

Thanks a lot..
Ananth.

Added after 27 minutes:

Hi Hamid,
I've been checking the DGS structures but it seems like the structures are mainly on t-line fed antennas. Is there a way to implement this on probe fed antennas?