Help needed with RFID design with CST Microwave studio

Hello everyone! I am new with cst and I have to use it to design an RFID tag for my project. The problem is that I have not been able to see a specific example for rfid tag design so it is really giving me a problem trying to understand the concept of RFID tag design using CST. can anyone provide me with a source for the examples of just give me ideas. The tag should operate at UHF 867 MHz.
Thanks

look at the pdf's in this link
Alien Technology - Products - RFID Tags