Need Help with 13.56Mhz PA and coupling

I am trying to increase the read range of MCRF355 reader to around 60 cm. The PA design given in the circuit will not work more than 12cms, can use the same circuit and provide 12 or 24 volts so that, it provides more wattage?
Also I have designed a antenna of around 1000mmX600 mm so for the same propose, how do I couple it to the circuit.It made of 15mm dia copper pipe.
Any ideas guys.