An organ-pipe scanner is a system used in some

radar Radar is a system that uses radio waves to determine the distance ('' ranging''), direction ( azimuth and elevation angles), and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track ...

systems to provide scanning in azimuth or elevation without moving the antenna. It consists of a series of

waveguide A waveguide is a structure that guides waves by restricting the transmission of energy to one direction. Common types of waveguides include acoustic waveguides which direct sound, optical waveguides which direct light, and radio-frequency w ...

s and

feed horn A feed horn (or feedhorn) is a small horn antenna used to couple a waveguide to e.g. a parabolic dish antenna or offset dish antenna for reception or transmission of microwaves. A typical application is the use for satellite television rec ...

s arranged in front of a shaped reflector, each one positioned to reflect the beam in a different direction. The wave guides meet at a central point where a small rotating waveguide feeds the

microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...

signal into each of the horns in turn as it rotates past them. The system was found in a number of 1950s and 60's era radars, notably the US's AN/FPS-50 radar used in the

BMEWS The RCA 474L Ballistic Missile Early Warning System (BMEWS, 474L System, Project 474L) was a United States Air Force Cold War early warning radar, computer, and communications system, for ballistic missile detection. The network of twelve radar ...

network, and the High Speed Aerial of the UK's

RX12874 RX12874, also known as the Passive Detection System (PDS) and by its nickname "Winkle", was a radar detector system used as part of the Royal Air Force's Linesman/Mediator radar network until the early 1980s. Winkle passed out of service along wi ...

Passive Detection System. The concept fell from use with the increasing use of

phased array In antenna (radio), antenna theory, a phased array usually means an electronically scanned array, a computer-controlled Antenna array, array of antennas which creates a radio beam, beam of radio waves that can be electronically steered to point ...

, which provided a similar steering mechanism in purely electronic form with no moving parts. A similar concept is the

Foster scanner {{Short description, Type of radar system The Foster scanner, or Variable Path scanner, is a type of radar system that produces a narrow beam that rapidly scans an area in front of it. Foster scanners were widely used in post-World War II radar sy ...

, which is typically found on lower-power systems like

counter-battery radar A counter-battery radar or weapon tracking radar is a radar system that detects artillery projectiles fired by one or more guns, howitzers, Mortar (weapon), mortars or rocket launchers and, from their trajectories, locates the position on the g ...

References

* {{cite web , url=http://www.radartutorial.eu/06.antennas/an66.en.html , title=Organ-Pipe Scanner , website=Radar Tutorial Radar