Parameters that need to connect the power amplifier between rfid reader and antenna

Hi To All
I am New to this portal, I am a Fresher.
Now i am working in a java card / Smart Card development project.
I have a question what are the Parameters that need to consider to connect the power amplifier between Rfid reader and Rfid Antenna.
Which Power amplifier is Best suited for UHF.
I have no Idea about what is APDU Command,
We are using VisionTek 92 POS,Works on Linux.
ISO 7816 standard.
Can any one Guide me...........

Thanks in Advance.

Hema Krishna