Tuning Patch Antenna for maximum BW.

Hi,
I'm going to design a simple rectangular patch antenna with HFSS,
The patch is feeded via slot coupling.
My parameters are the length And width of the patch And slot. Also The location of the slot under the patch. I think I can also change the two substrates thicknesses.

How should I tune these parameters for my frequency?
What do you suggest to obtain the best bandwidth?

Thanks in advance.
Cheers.