This was a BMEWS program surveillance radar that used a large, fixed-antenna fence system. Two beams were projected from the antenna array. Objects passing through the lower-angled beam provided initial data and warning for the North American Air Defense Command (NORAD). Data produced when the object passed through the upper beam allowed computation of trajectories on launch and target points. The radar operated in the UHF range at 425 MHz. General Electric, Heavy Military Electronics Department, installed these systems at Clear, Alaska, and Thule, Greenland, during the early 1960s.
Just to get an idea of the size of this antenna
Additional notes on the AN/FPS-50