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A Yagi antenna is a directional antenna consisting of a driven element such as dipole or folded dipole and additional parasitic elements, typically a reflector and one or more directors. It radiates in only one direction and is most commonly used in point-to-point communications.
A Yagi antenna is used for communications in a medium range of three to five miles between two points. It can also be used as a bridge antenna to connect clients to an access point.
This term is also known as a Yagi-Uda array or patch antenna.
The Yagi antenna was invented by Shintaro Uda and his colleague Hidetsugu Yagi in 1926. A similar design to the Yagi antenna is found all over the United States and is referred to as a log-periodic antenna.
A Yagi antenna has two to three straight antenna elements, which are set to a length of roughly half the electrical wavelength they are designed to support. It is considered a balanced type but can also be unbalanced depending on whether it is used with a balun at the feed line joint, which joins the drive element of the antenna.
The benefits of the Yagi antenna include good range and ease of aiming the antenna compared to other directional dishes and designs. Since the Yagi antenna is directional, it focuses its entire signal in a cardinal direction. This results in increased gain over an antenna dispersing energy in a 360-degree circle, such as the omni-directional model of other antenna designs.
One disadvantage of the Yagi design is its large size, especially for the range achieved.