Note: The 1988 model Reatta did not have Remote Keyless Entry nor did they have an antenna in the back window.

It appears there was a mid-year change in the RKE antennas in 1989.

Some '89s had the antenna fully horizontal in the blacked out area at the top of the glass. This must not have been ideal as some '89s and all '90s had a loop antenna bonded to the glass similar to the rear window defrosters.

The button connectors are similar to that of a 9V battery but both are the same and they are soldered to the black area on the glass.

I am attaching some pictures of the straight and loop style antennas.

The early style antenna, I am guessing, is just two bars going away from the buttons of  the connector. They appear to be not a loop but an antenna going each way and not connected to each other. The loop style on the late '89s and '90s appear to be a complete loop. Antenna dimensions are in the last photo.

Thanks to Jim Finn, member of the Reatta forums, for this information.