Impedece measurement of the antenna

hai all ..

I saw a construction of a simple patch antenna.....the feed point of the antenna is located with a perfect impedance match position of the patch ....
I need to know how to select a perfect position for feeding the signal in patch in order to match the impedance of the coax line(50 ohm)..?

There is a Video lecture on this in Youtube by Antenna Theory Which uses Voltage to Current distribution ratio at individual points to find a position for 50 ohms.. U'L get better idea watching it . !