A corner reflector is an antenna reflector that reflects electromagnetic waves in such a way that the reflected waves always leave the reflector in the same direction in which they hit it. Thus, the electromagnetic waves are reflected in the direction of their point of origin. They serve as radar targets or marker points.
Corner reflectors consist of three reflecting surfaces placed at right angles to each other. For vertically or horizontally polarized waves, two reflection surfaces at right angles to each other are also sufficient. In principle, the incident electromagnetic waves are reflected at the reflection surface they hit, at the angle corresponding to the angle of incidence.
The same happens at the second reflection surface. The sum of all reflection angles is thus always 180 degrees, which means that the waves leave the reflector in the same direction in which they hit it.