[MOVED]Annular ring patch antenna optimization

I want to design an annular ring patch antenna for UWB application (3.1 - 10.6 GHz). Now i am facing a problem. I can't find how to optimize width of the annular ring. Everywhere I got all they are taking outer radius/ inner radius = 2. I want to optimize this width to get a broad band characteristic. Please tell me the necessary equation for calculating this width.