Yagi

Another antenna design that uses passive elements is the Yagi antenna. This antenna, illustrated in figure 15, is inexpensive and effective. It can be constructed with one or more (usually one or two) reflector elements and one or more (usually two or more) director elements. Figure 16 shows a Yagi antenna with one reflector, a folded-dipole active element, and seven directors, mounted for horizontal polarization.

Figure 15. The Yagi antenna — (a) three elements and (b) multiple elements

Figure 16. A typical Yagi antenna

Figure 17 is a typical pattern for a threeelement (one reflector, one active element, and one director) Yagi antenna. Generally, the more elements a Yagi has, the higher the gain, and the narrower the beamwidth. This antenna can be mounted to support either horizontal or vertical polarization and is often used for point-to-point applications, as between a base station and repeater-station sites.

Figure 17. A Yagi antenna horizontalplane pattern