Friend-foe detection

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A friend-foe recognition ( English identification friend or foe (IFF) ) is an electronic system that enables the identification of a recognized object. It is mostly used in military radar systems to detect enemy fighter planes . However, it is also increasingly being used for land vehicles and ships.

How radar works

A friend-foe recognition is based on the communication of a query device (interrogator) on the ground or on board an aircraft with a response device ( transponder ) on board another aircraft. Its transponder must be loaded with a corresponding cryptographic key and an individual code. The interrogator sends an encrypted request to the transponder of the aircraft, which responds with the programmed key, which must match that of the interrogator, and its own code. In this way, the answering aircraft is successfully recognized as a friend and identified via the code or classified as an enemy.

Technically, the military IFF method is based on the same principle as the civil secondary radar . Both use the same NATO-wide harmonized frequencies (1030 and 1090 MHz; with a defined safety distance) for transmission and reception. The military IFF system is compatible with the civilian SSR (Secondary Surveillance Radar) system ; see also radio transponder .


Air Force

Hawk: Platoon Command Post (PCP) trailer with fire control computer and IFF system

The system is used in most military air surveillance radar systems, in anti-aircraft and anti-aircraft missile systems (see HAWK and Patriot ), on ships and in most airborne weapon systems. An IFF system is also used with the shoulder-supported FlaRak system FIM-92 Stinger .

Ground forces

When ground forces such as infantry and armored troop optical be retroreflectors used. These are in a fixed position on the uniforms and vehicles. They reflect infrared light and thus enable identification in the dark when using night vision devices.

An active IFF system for infantry was developed by Rheinmetall Defense in the 2000s . As part of the ZEFF basic demonstrator soldier , a system consisting of an active transponder on the soldier and an interrogation unit on the rifle was presented in 2005. The dismounted soldier identification device (DSID) should enable a more reliable identification of own soldiers than previous passive systems. The maximum range is 3000 m.


The first IFF devices were developed during World War II. In Great Britain, dipole antennas were used in aircraft from the beginning of the war, later the more sophisticated systems IFF Mark I to IFF Mark III . German fighters chased British bombers back to England to shoot them down shortly before landing. The British air defense now had the problem of distinguishing enemy aircraft from its own. The system was codenamed Parrot (parrot) - and when controllers asked the aircraft crew to switch on this “original IFF” for identification purposes, they transmitted: “Squawk your parrot”, something like: “Let your parrot screech!” The name Squawk is still used today in aviation for the transponder code . In the winter of 1941/42 it was possible for the British to fight the enemy with precision, even with several aircraft.

On the German side, GEMA developed an IFF system. The on-board devices “Erstling” (FuG 25a) worked in the VHF band with the frequencies 168 MHz (responder / transmitter) and 117–133 MHz (interrogator). The technical code name was: 300 W VHF interrogation pulse repeater.

Web links

Individual evidence

  1. ↑ For frequency availability for IFF systems, see NATO Joint Civil / Military Frequency Agreement (NJFA) frequency range 960–1215 MHz
  3. Hubregt J. Visser: Array and Phased Array Antenna Basics. John Wiley & Sons Publisher, 2006, ISBN 9780470871188
  4. Fliegermagazin 08/2005.
  5. The indirect distance measurement with radar. Engineer, Transmission Force Magazine, Number 1, January 1949