i worked with the CNT's in that band but for humidity, temperature and gaz sensing, the articals that i found are different from each other, every artical gives its own impedance and other caractrestics depends on the mesures that they used and the techniques of implementation, the number of layers and so many other parameters, i suggest that you searche for articals wher they used the CNT's for windshield RFID tags and you pick the values that they took, but nothing will help more then mesuring that or an artical that used the same thing as you will!
if it is not an obligation to use the CNT's, look for another material that will give you the results that you want, if you want to have an idea about what i said above, i can give you the articals so you can make the difference by your own