A Yagi antenna has several elements arranged in echelon. They are connected together by a long element, called the boom. The boom carries no current. If the boom is an insulator, the antenna works the same. The rear-most element is called the reflector. The next element is called the driven element. All the remaining elements are called directors.
[img]http://www.hdtvprimer.com/ANTENNAS/yagi.gif[/img]
The directors are about 5% shorter than the driven element. The reflector is about 5% longer than the driven element. The driven element is usually a folded dipole or a loop. It is the only element connected to the cable. Yet the other elements carry almost as much current. The more directors you add, the higher the gain becomes. Gains above 20 dBi are possible. But the Yagi is a narrowband antenna, often intended for a single frequency. Yagi antennas are described in more detail at http://www.hdtvprimer.com/ANTENNAS/types.html .
Yagi antenna
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