Problems designing a circularly polarized patch antenna

Hi, I'm trying to design a circularly polarized antenna at 1.7 GHz, using a substrate with Er=2.2 and 31 mils. I need to enhance the bandwidth of the antenna, which is a patch antenna with edge feed and a lambda/4 transformer, and I don't know which technique is most effective.

Also I need that the polarization was circular, and I cut the corners of the patch, but I don't know how much should be. Just trial and error?