Spangles of jamming

The spangles are metal filaments used for to scramble a Radar. They are ineffective against the missiles with infra-red guidance of " type; car-and-oublie". They can be appeared as needles, strips or ribbons.

Compared etymology

The armies of the various countries developed them quasi at the same moment but did not want to employ them immediately not to reveal the secrecy. In the Royal Air Force they were indicated code name window and in the USA have calls them chaff (Ivraie). The German term used is " Düppel" name of the district of Berlin - Düppel where they were used for the first time at the time of an air attack.

Composition and physical principle

" paillettes" consist of conducting wire different lengths. In the beginning, one had used tinfoil ribbons (stanniol). One employs today synthetic fibers covered with a metal film applied in vapor phase or carbon fibers conducting. There exist several processes to disperse them in the air.

When the spangles are illuminated by the beam of a radar, they function like antenna S dipoles and reflect part of the energy radiated in so far as their length corresponds to the Wavelength of the radar, i.e. in fact a multiple of the half-length of wave. The receiver of the radar receives an erroneous echo then.

The current fighters use spangles of which the length was given according to the wavelength of the unfavourable radars. The modern radars are not however also any more easy to scramble owing to the fact that they measure by the Effect Doppler the speed of the detected objects and are thus able to filter the very slow spangles and to dépacement insulate the aircraft in dépacement fast.

Various types of implementation

A Aéronef can eject definite quantities of spangles and leave them behind him as a smoke screen which the radar cannot bore. This can make it possible to mask certain activities. A method of defensive use of the spangles consists, in the event of attack by a Missile or an unfavourable aircraft, to eject small clouds of spangles using mini-rockets or other projectiles in order to delude the attacker and to divert the threat. During the Cold war, the American heavy bombers were equipped with receivers which measured the wavelength of the enemy radars installations and with machines which could cut spangles to the length wished starting from a tinfoil ribbon of several kilometers length rolled up on an embarked reel.

Today, the spangles belong to the standard equipment of Contre-mesure with the lures.

Signals of echoes of rain recorded by the radars weather per good weather in the absence of any nebulosity are most probably the trace of military tests. This is sometimes the case above the American military zones in Germany () in particular in the zone " Temporary Restricted Airspace" (TRA LAUTER) above the forest in the border zone being next to France opposite Lorraine.

The echo (blip) of a spangle is presented in the form of a point located at 1 or 2 km above the ground. The spangles move with the wind and disperse before falling on the ground.

Meteorology

The use of the spangles is not solely reserved for the military field. They are also employed in meteorology to study the displacement of the airstreams into high atmosphere. For this purpose, they are placed using fused of research in the zone to study and their displacement is then followed by radar what makes it possible to determine the direction and the speed of the Vent S.

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