From the RC OPtion Data (SDU-906)
The SDU receives airplane heading and attitude data from the inertial reference unit (IRU). The SDU system processor determines the elevation and azimuth angle necessary to point the high gain antenna beam at the applicable satellite. The SDU sends this data to the beam steering unit (BSU).
The Anetnna is a phased arraray type It needs to know which Active elements to activate to 'Steer the beam; ( done electronically, no moving components)
If anyone knows AF's fit Manufacturer &/or High Gain/Low Gain Antenna(s) please let me know