What is a Yagi-Uda antenna?

The Yagi-Uda antenna is a directional antenna designed to maximize reception over long distances. Generating a much higher signal-to-noise ratio than other antenna designs, the Yagi-Uda antenna has become the de facto standard in antenna applications in almost all stationary applications utilizing frequencies above 10 MHz. Amateur radio operators often fashion homemade Yagi antennas from everyday items, and more recently wifi enthusiasts have taken up the hobby as well. Yagi antenna design has become an art in and of itself in some communities.

Although often simply referred to as the Yagi antenna, homage to the electrical engineer Hidetsugu Yagi, the antenna was actually invented by Shintaro Uda. Uda had been studying wireless energy transfer, and demonstrated his unique antenna for the first time in 1926. The Tohoku Imperial University of Sendai, Japan, in which both Uda and Yagi were employed, took little interest in further developing the design. Two years later, Yagi translated Uda's research and publish much of it in English-language publications. Despite the fact that Hidetsugu Yagi never took credit for the antenna's design, it was his name that the American press used to refer to the concept. The Yagi antenna's popularity soared in the rapidly growing US radio field, despite the lack of attention given to it in Japan. In fact, Japanese engineers only became aware of the antenna's strong points while fighting the US Navy in World War II. By this time, the Germans had also begun widespread use of the design, especially on fighter aircraft. The Yagi-Uda antenna had seen little development since World War II until the early years of the 21st century, when wifi use had renewed interest in wireless technology.

The advent of affordable wifi communications has seen a renewed interest in homemade Yagi antenna construction. While early antennas were designed to receive a wide range of frequencies, wifi-specific designs are very focused. Many Internet websites have detailed plans for Yagi antennas made from household materials that are specially tuned for the 2.4 GHz band in which wifi operates. Tested plans ranging from as simple as converted Pringles chips cans to complex 2 meter Yagi monsters are available. Online Yagi antenna calculators are available for computing the size and power needed for various scenarios, from simply connecting to a remote access point to wardriving. Although most of these designs are very simple and inexpensive to construct, they may be against the law in some areas. Untrained and unlicensed use could be disruptive at best, and dangerous at worse.