Early-warning radar

This greatly reduces their interaction with rain and snow in the air, and therefore improves their performance in the long-range role where their coverage area will often include precipitation.

Since then, improvements in receiver electronics has greatly reduced the amount of signal needed to produce an accurate image, and in modern examples the transmitted power is much less; the AN/FPS-117 offers 250 nautical miles (460 km; 290 mi) range from 25 kW.

The first early-warning radars were the British Chain Home, the German Freya, the US CXAM (Navy) and SCR-270 (Army), and the Soviet Union RUS-2 [ru].

Although techniques for long-range propagation were known and widely used for shortwave radio, the ability to process the complex return signal was simply not possible at the time.

Starting in the 1950s, a number of over-the-horizon radars were developed that greatly extended detection ranges, generally by bouncing the signal off the ionosphere.