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The radar horizon with an antenna height of 75 feet (23 m) over the ocean is 10-mile (16 km). However, since the pressure and water vapor content of the atmosphere varies with height, the path used by the radar beam is refracted by the change in density. With a standard atmosphere, electromagnetic waves are generally bent or refracted downward.
MADRE over-the-horizon radar at the NRL's Chesapeake Bay Detachment U.S. Navy Relocatable Over-the-Horizon Radar station. The most common type of OTH radar, OTH-B (backscatter), [3] uses skywave or "skip" propagation, in which shortwave radio waves are refracted off an ionized layer in the atmosphere, the ionosphere, and return to Earth some distance away.
The radar mile is the time it takes for a radar pulse to travel one nautical mile, reflect off a target, and return to the radar antenna. Since a nautical mile is defined as 1,852 m, then dividing this distance by the speed of light (299,792,458 m/s), and then multiplying the result by 2 yields a result of 12.36 μs in duration.
For radar (e.g. for wavelengths 300 to 3 mm i.e. frequencies between 1 and 100 GHz) the radius of the Earth may be multiplied by 4/3 to obtain an effective radius giving a factor of 4.12 in the metric formula i.e. the radar horizon will be 15% beyond the geometrical horizon or 7% beyond the visual. The 4/3 factor is not exact, as in the visual ...
RAF Boeing E-3 Sentry AEW1 with rotating radar dome. The dome is 30 ft (10 m) across. The E-3 is accompanied by two Panavia Tornado F3. Early Warning (EW) Radar Radar Systems Ground Control Intercept (GCI) Radar; Airborne Early Warning (AEW) Airborne ground surveillance (AGS) Over-the-Horizon (OTH) Radar; Target Acquisition (TA, TAR) Radar Systems
AN/SPS-2 Long range height finding radar by General Electric. [53] AN/SPS-3 Also known as XDK, 3D target designator/rapid volume search radar jointly developed by MIT Radiation Laboratory and Naval Research Laboratory. [53] AN/SPS-4 Surface and low altitude air search radar by Raytheon. [53] AN/SPS-6 2D air search radar; AN/SPS-8 2D height ...
Both radar types can be triggered with either equal or opposed phases. Both antenna types can optionally be mounted on a standard 50 m pylon. This arrangement causes a displacement of the radar horizon which in turn increases the detection altitude up to 6 km at a distance of 150 km.
An over-the-horizon radar sited in the USSR would help solve this problem, and work on such a system for this associated role started in the late 1960s. The first experimental system, Duga, was built outside Mykolaiv in Ukraine , successfully detecting rocket launches from Baikonur Cosmodrome at 2,500 kilometres (1,600 mi).