over-the-horizon radar

…the first successful demonstration of high-frequency over-the-horizon (HF OTH) radar, whose propagating waves are refracted by the Earth’s ionosphere. The detection of ships, aircraft, and ballistic missiles was thereby extended out to about 3,200 km (2,000 miles), approximately 10 times the range of microwave radars, which are limited to the…

Frequencies lower than about 100 MHz usually are not desirable for radar applications. An example where lower frequencies can provide a unique and important capability is in the shortwave, or high-frequency (HF), portion of the radio band (from 3 to 30 MHz). The…

For earlier warning, over-the-horizon radars or satellite-borne infrared detectors can be used.