What do you suppose this is for:
Here is the larger context:
This is Joint Base Elmendorf-Richardson outside of Anchorage, Alaska.
The answer to this mystery? Such rings, dubbed “elephant cages” or “turkey farms,” were antenna arrays set up around the world during the Cold War for High-Frequency Direction Finding (HF/DF, or “Huff-Duff.”) The general principle was to rotate a directional aerial and note where the detected radio signal was strongest. Using a simple aerial design, the signal would be strongest when pointing directly towards and directly away from the source. Once detected from two points, the signal’s source could be located by triangulation. “Elephant cages” have since been surpassed by more advanced technologies.