The Power Macintosh G5 from 2005 allowed a wireless network connection using an internal AirPort Extreme card. Since the Power Macintosh G5 had an external aluminum case, this external AirPort antenna was included.
The back of the Power Macintosh G5 included a proprietary port, the AirPort Extreme antenna port:
“AirPort Extreme antenna port—Connect the AirPort Extreme antenna to this port if your Macintosh has an optional AirPort Extreme Card installed.”
This AirPort Extreme antenna port is unopened in its original packaging.