Buoy in San Diego Harbor. Note metal plates near the top configured at right angles to reflect radar signals.

In optics and telecommunication, the term corner reflector has the following meanings:

1. A reflector consisting of three mutually perpendicular intersecting conducting flat surfaces, which returns a reflected electromagnetic wave to its point of origin. The three intersecting surfaces usually have square shapes.

One such device, normally consisting of three metallic surfaces or screens perpendicular to one another, is designed to act as a radar target or marker. Another such device uses passive optical mirrors which returns an incident light beam in the opposite direction. Arrays of such retroreflectors are used in bicycle reflectors, automobile tail lights and as targets for laser range finding. Microscopic corner reflector structures can be incorporated into reflective paint for increased visibility at night.

2. A directional antenna using two mutually intersecting conducting flat surfaces.

3. In radar interpretation, an object that, by means of multiple reflections from smooth surfaces, produces a radar return of greater magnitude than might be expected from the physical size of the object.

Source: from Federal Standard 1037C in support of MIL-STD-188 and from the Department of Defense Dictionary of Military and Associated Terms