What is a Yagi Antenna?

A Yagi antenna or a Yagi-Uda antenna, is a directional antenna that radiates signals in one main direction. It consists of a long transmission line with a single driven element consisting of two rods connected on either side of the transmission line. It also consists of a single reflector on one side of the transmission line and a number of parasitic elements which act as directors. The driven element of a Yagi is equivalent of a center-fed, half-wave dipole antenna. Parallel to the driven element are straight rods or wires called reflectors and directors. A reflector is placed behind the driven element and is slightly longer than driven element; a director is placed in front of the driven element and is slightly shorter than driven element. A typical Yagi antenna has one reflector and one or more directors.

The Yagi antenna propagates electromagnetic field energy in the direction running from the driven element toward the director(s), and is most sensitive to incoming electromagnetic field energy in this same direction. The more directors a Yagi has, the greater the forward gain and the longer the antenna becomes. This type of antenna has become particularly popular for television reception, but it is also used in a number of other domestic and commercial applications where an RF antenna with high gain and directivity is needed.

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