From what I've read so far, you want to look into getting the non-metallic tint, ie. ceramic tint. You can ask the tint installer to use ceramic tint or at least test it out by taking a sheet of the tint that's going to be used and place it over the nav antenna in the rear window.
I was worried about the same thing & ended up getting High Performance tint from Llumar. They assured me that it would not affect reception even tho it had metal in it. She not only said they would redo it w/ the cheaper non-metal tint if I had problems but there is a lifetime guarantee on it that I can take to any Llumar dealer to get fixed.
Nav still works fine but far away radio stations that I used to be able to get now have some static but I think that that is a small price to pay.
This cost me $160 but if you got the extra funds, Ceramic is the best tint to get for your car but I was quoted upwards of $400.