AN/FPS-118

The AN/FPS-118 was an Over-the-Horizon Backscatter (OTH-B) early warning radar system, developed by Lockheed Martin in the United States during the 1970s and 1980s. Operating in the HF band (5-28 MHz) as a bistatic, Frequency Modulated Continuous Wave (FMCW) Doppler radar, it was designed for long-range, all-altitude surveillance of aerial approaches to the United States, detecting low-flying enemy aircraft. Each system comprised geographically separated transmit and receive sites, along with an operations center, to prevent interference; for example, a transmit site was located near Moscow, Maine, and its associated receive site near Columbia Falls, Maine. The radar utilized large transmitter arrays to bounce signals off the ionosphere, which were then backscattered by aircraft and detected by equally large receiver arrays, covering a 60-degree arc with an instrumented range of 900 to 3,333 km (1,800 NM) and an average power of 1 MW. All AN/FPS-118 OTH-B radar transmitter and receiver facilities have since been demolished.

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