Acorner reflector is aretroreflector consisting of three mutuallyperpendicular,intersecting flat reflective surfaces. It reverses the direction of an incoming wave with beingtranslated by reflections on the three orthogonal sides. The three intersecting surfaces often are triangles (forming atetrahedron) or may have square shapes. Radar corner reflectors made of metal are used to reflect radio waves fromradar sets. Optical corner reflectors, calledcorner cubes orcube corners, made of three-sided glassprisms, are used insurveying andlaser ranging.
The incoming ray is reflected three times, once by each surface, which results in a reversal of direction.[1][2] To see this, the three corresponding normal vectors of the corner's perpendicular sides can be considered to form abasis (arectangular coordinate system) (x,y,z) in which to represent the direction of an arbitrary incoming ray,[a, b, c]. When the ray reflects from the first side, sayx, the ray'sx component,a, is reversed to −a without changing they andz components, resulting in a direction of[−a, b, c]. Similarly, when reflected from sidey and finally from sidez, theb andc components are reversed. Therefore, the ray direction goes from[a, b, c] to[−a, b, c] to[−a, −b, c] to[−a, −b, −c], and it leaves the corner reflector with all three components of direction exactly reversed.
A roof mirror, sometimes called a roof prism mirror if two prisms are used to construct it[3], consisting of two flat reflection surfaces meeting together at the right angle, does retroreflection but only in the plane formed by the surfacenormals (e.g., a x-y plane if the normals are x and y axes, respectively) while the corner reflector dose full retroreflection.
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Radar corner reflectors are designed to reflect themicrowaveradio waves emitted byradar sets back toward the radar antenna. This causes them to show a strong "return" on radar screens. A simple corner reflector consists of three conducting sheet metal or screen surfaces at 90° angles to each other, attached to one another at the edges, forming a "corner". These reflect radio waves coming from in front of them back parallel to the incoming beam. To create a corner reflector that will reflect radar waves coming from any direction, 8 corner reflectors are placed back-to-back in anoctahedron (diamond) shape. The reflecting surfaces must be larger than severalwavelengths of the radio waves to function.[4]
In maritime navigation they are placed onbridge abutments,buoys,ships and, especially,lifeboats, to ensure that these show up strongly on ship radar screens. Corner reflectors are placed on the vessel's masts at a height of at least 4.6 m (15 feet) above sea level (giving them an approximate minimumhorizon distance of 8 kilometers or 4.5nautical miles).Marine radar usesX-band microwaves with wavelengths of 2.5–3.75 cm (1–1.5 inches), so small reflectors less than 30 cm (12 inches) across are used. In aircraft navigation, corner reflectors are installed on ruralrunways, to make them show up on aircraft radar.
An object that has multiple reflections from smooth surfaces produces a radar return of greater magnitude than might be expected from the physical size of the object. This effect was put to use on theADM-20 Quail, a small decoy missile which had the sameradar cross section as aB-52.
The corner reflector is not the only efficient radar reflector design; otherretroreflector designs have also seen use.Luneburg lens, for example, are used on theADM-141 TALD.[5]
Inoptics, corner reflectors typically consist of threemirrors or reflectiveprism faces which return an incidentlight beam in the opposite direction. Insurveying,retroreflector prisms are commonly used as targets for long-range electronic distance measurement using atotal station.
Five arrays of optical corner reflectors have been placed on theMoon for use byLunar Laser Ranging experiments observing alaser'stime-of-flight to measure the Moon's orbit more precisely than was possible before. The three largest were placed byNASA as part of theApollo program, and theSoviet Union built two smaller ones into theLunokhod rovers.
Automobile andbicycle tail lights are molded with arrays of small corner reflectors, with different sections oriented for viewing from different angles. Reflectivepaint for visibility at night usually containsretroreflective spherical beads.Thin plastic with microscopic corner reflector structures can be used astape, on signs, or sewn or molded ontoclothing.
Corner reflectors can also occur accidentally.Tower blocks withbalconies are often accidentalacoustic corner reflectors and return a distinctiveecho to an observer making a sharp sound noise, such as a hand clap, nearby.
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This article incorporatespublic domain material fromFederal Standard 1037C.General Services Administration. Archived fromthe original on 2022-01-22. (in support ofMIL-STD-188). This article incorporatespublic domain material fromDictionary of Military and Associated Terms.United States Department of Defense.