Chaff (countermeasure)
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Chaff, originally called Window or Düppel, is a radar countermeasure involving the dispersal of thin strips of aluminium, metallized glass fiber, or plastic. Dispersed chaff produces a large radar cross section intended to blind or disrupt radar systems.
Modern US Navy RR-144 (top) and RR-129 (bottom) chaff countermeasures and containers. Note how the strips of the RR-129 chaff (bottom) are of different widths, while those of the RR-144 (top) are all the same width. The RR-144 is designed to prevent interference with civil ATC radar systems.
A Lancaster dropping chaff (the crescent-shaped white cloud on the left of the picture) over Essen during a thousand-bomber raid
Two forms of RAF "Window" radar countermeasure: chopped aluminium wire and paper backed with aluminium foil
The effect of chaff on the display of a Würzburg Riese radar. The effect of jamming appears in the left "jagged" half of the circular ring, contrasting with the normal "smooth" (unjammed) display on the right half of the circle with a real target at the 3 o'clock position – on the jammed left side, the real target "blip" would have been indistinguishable from the jamming.
Radar
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Radar is a system that uses radio waves to determine the distance (ranging), direction, and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track aircraft, ships, spacecraft, guided missiles, motor vehicles, map weather formations, and terrain.
Radar of the type used for detection of aircraft. It rotates steadily, sweeping the airspace with a narrow beam.
Experimental radar antenna, US Naval Research Laboratory, Anacostia, D. C., from the late 1930s (photo taken in 1945)
The first workable unit built by Robert Watson-Watt and his team