Oops. I thought it was a defrost. I read somewhere it was a good idea to put a defrost in the right rear so to increase visibility for the driver. it sure looks like a defrost. i can see the one on the left panel is an antennae, but the one on the right had me fooled.
Both rear side windows have antenna grids in them, not defrosters. There is an antenna control module, which monitors the signals from each side, and automatically selects the one with the better reception signal for the radio to use.