Designing patch antenna fed through SMA cable

I am feeding my patch through coax cable. I understand I will have to do so using an SMA Cable. My question is that how do I know which 50 ohm SMA to use. And also when I make the design in hfss should I make the hexagonal ring that most connectors seem to have? In all the figures I have seen the connector pin goes through the substrate and the plate touches the substrate instead of the ground plate. How do they fabricate that. Please respond soon