I want to use the old apm flight controller to make an aat

I want to use the ancient flight control apm to do an automatic antenna tracking, but I don’t know how to communicate between the aat and the aircraft. At present, I test and use the digital mavlink to directly communicate with the aat, but the aat does not start tracking the aircraft. Doesn’t it have to be connected to a computer to make it work?

Comprehensive information can be found in the Wiki:
https://ardupilot.org/antennatracker/index.html