feed calculation for dual band patch antenna

Hai
I want to design a square patch....
But i dont understand how to place the feed.........
can anyone help me in calculating the feed location for dual band patch antenna
I have searched many papers, but i dnt get any particular equation to calculate coax probe feed location.

So if you know any method, please explain me in detail.....

check out this pdf. they tried a bunch of feed points on the patch.

hai
thankq for your reply
First thing, i found some basics for your attachment regarding feed point location
Second thing,I tried your paper
but i thing it will not produce circular polarisation
but i want circular polarisation that to conical radiation........
Anyways, i got some useful points........
Thankq once again