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What Is a Yagi Antenna?

Yagi, or Yagi-Uda antennas, are commonly used in narrow-band applications. A favorite antenna of ham radio operators, Yagis are inherently directional, with high gain within the band in which it broadcasts. Yagis come in a variety of elements and heights, and can be used as repeater antennas for wireless networks. Understanding the variety of uses and how they work reveals a peek into why the Yagi is so widely used.

Basic Construction
- Yagi antennas are made with a single drive element, from which protrude two to three elements. These elements are driven with a balanced signal line from the transmission source to the drive element. For convenience, coaxial cables are often used with a matching transformer as opposed to a ladder line. The Yagi antenna is typically suspended via a single support mast.
Reflectors and Directors
- Of the rods that protrude from the center drive element, the reflector is positioned behind the drive element. The reflector helps direct electromagnetic energy towards the directors, of which there is at least one and typically two or three. The reflectors focus the energy towards the directors based on the amount of energy needed to reach the required frequency. As such, the antenna becomes physically larger. For example, a 20 megahertz Yagi requires more reflectors and directors than one operating at 10 megahertz. Most Yagis do not exceed 50 megahertz due to size considerations.
Ham Radio
- Arguably the most common application for Yagi antennas, ham radio operators. The inherently low signal to noise ratio and high gain makes the antenna perfect for this application, operating above 10 megahertz. Additionally, Yagi antennas are compact and not difficult to build on the DIY level. Yagi antennas for this application can even be mounted in attics and on shallow peak rooftops, performing well without excessive boom height.
WiFi Applications
- Since Yagi antennas are fundamentally a feed, reflector, and director in its most basic form, these three elements can be configured in a variety of ways to collect and boost the signal. In wireless networking environments, Yagi antennas for wireless applications are as simple as a single drive element surrounded by a reflector, often tubular in appearance. The length of the reflector that the drive element is inserted into serves as the director. In these applications, Yagi WiFi antennas can be very compact, since they only must effectively operate in the 2.4 gigahertz range.

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