Improving beamwidth of a patch antenna array.

Hi everyone,
I've designed a patch antenna array for the 1710-2170 MHz band.
I'm able to meet all other specifications other than the Azimuthal beamwidth (needs to be 65 degrees but i get about 52 degrees) at the center frequency of the band. Obviously, the gain of the antenna is maximum at the center frequency (although not too much over the requirement but lets just say its better) which in turn is reducing the Azimuthal beamwidth. Any ideas on what could be done to increase the beamwidth. Problem is that anything I do needs to be concentrated on the mid frequency otherwise the patterns at other frequencies get squints, tilt over so on nand so forth.

Will a further reduction in substrate height (currently air) increase the beamwidth?

I've tried playing with the patch sizes, using rectangular patches etc etc. Its a probe fed array.

Thanks,
Ananth.

Hi
you can find good things about that at "Handbook of microstrip antenna" by Clarricoats and Rahmat-sami

Thanks for the information, Ali. I'll try and find the book..

Ananth.