RFID ID 20 or 12 with an external antenna?

Is it possible to connect a self build antenna to the RFID ID-20 module?

Is it possible to disconnect the build in antenna in this case or is it only possible to connect two antennas to one module when using the antenna pins of a RFID ID-20 or -12?

Does anybody already tried to connect a self build antenna to one of those RFID modules?

What was the maximum size of your antenna and what was the maximum reading range of this antenna when you connected it to a ID-12 or ID-20 module?

Thanks a lot for your help.