Britannica Sources used in this answer

How do parabolic reflectors focus parallel rays of light or signals?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram showing a double cone intersected by planes at different angles, producing the conic sections: a horizontal plane creates a circle, a tilted plane creates an ellipse, a plane parallel to the cone's side forms a parabola, and a steep plane produces a hyperbola. Each section is labeled, with the axis and apex of the cone indicated. — analytic geometry The conic sections result from intersecting a plane with a double cone, as shown in the figure. There are three distinct families of conic sections: the ellipse (including the circle), the parabola (with one branch), and the hyperbola (with two branches).

A parabolic reflector, or parabolic mirror, is a concave surface formed by rotating a parabola about its axis of symmetry, creating a paraboloid of revolution.12

This shape possesses a unique geometric property that allows it to focus energy. When incoming rays of light, sound, or radio waves arrive from a distant source parallel to the reflector's axis of symmetry, they strike the curved surface and are reflected to converge at a single, fixed point known as the focus. Conversely, if a source is placed at the focus, rays emanating from that point will reflect off the surface to travel outward in a beam parallel to the axis.13

This principle is fundamental to the design of various technologies, including reflecting telescopes, satellite dishes, radar systems, and headlights, where the precise control of incoming or outgoing waves is required for effective communication or observation.12