about 900MHz RFID antenna

hello, guys!
now i have a RFID card encapsulated with PVC, antenna is located on PET. i want to know what value of dielectric constant of PET is? and i will simulate it with ADS momentum, this structure is on the following figure:
////dielectric PVC///
////strip cond/////
////PET////
////dielectric PVC///

is the definition of structure right? because i want to calculate the input impedance of it.
thanks!

could the thin paper of PET be considered identification with the dielectric PVC? then i can set the dielectric depth as the depth of card? does PVC have significant effect on the antenna's impedance?
i use ADS momentum simulating @900MHz!

could anyone help me?
thanks!