A Yagi beam antenna has a driven element and one (or more) additional parallel elements attached to a boom. This antenna produces a directional pattern that is popular for spanning long distances. A rooftop television antenna, for example, is a horizontally-polarized type of Yagi.

Most Yagi antennas have at least three elements attached to the boom: The driven element, director element, and reflector element. The driven element is one-half wavelength long while the director elements are a little shorter and the reflector element is a little longer. The arrangement causes radiofrequency energy (RF) to radiate forward and, to a much lesser extent, behind the Yagi. There is very little RF energy radiated to the sides. Yagi beams vary from just a few elements to nearly a dozen or more!