The outboard antenna structure was connected to the end of the mast. It contained two antennas, C-Band and X-Band, two Global Positioning System (GPS) antennas, Light Emitting Diode (LED) targets, and a corner-cube reflector. Both outboard antennas only received radar signals. Transmitting of radar signals was done by the main antenna.
One outboard antenna received radar signals in the C-Band where the radar wavelength is equal to 5.6 centimeters. The other radar antenna received radar signals in the X-band where the radar wavelength is equal to 3 centimeters.
The GPS antennas were used to gather accurate position information for the Space Shuttle.
The LED targets were used by the Target Tracker on the Attitude and Orbit Determination Avionics (AODA) to measure the position of the outboard antenna relative to the main antenna.
The corner-cube reflector was used by the Electronic Distance Measurement unit on the AODA to measure the length of the mast to within 3 millimeters.