Yagiantenna

A Yagi-Uda antenna, commonly known as a Yagi antenna or simply a Yagi, is a highly directional antenna that consists of a driven element and one or more parasitic elements. It was invented by Shintaro Uda and Hidetsugu Yagi in 1926. The antenna is typically composed of a single straight conductive rod, known as the driven element, which is connected to a source of radio frequency power. Adjacent to the driven element are one or more additional conductive rods, called parasitic elements. These parasitic elements are not electrically connected to the transmitter or receiver but are designed to resonate at the operating frequency.

The parasitic elements are strategically spaced and sized relative to the driven element to influence the antenna's radiation pattern. One type of parasitic element is the reflector, which is slightly longer than the driven element and is placed behind it. The reflector's purpose is to reflect radio waves back towards the front of the antenna, thereby increasing the forward gain. Another type of parasitic element is the director, which is slightly shorter than the driven element and is placed in front of it. Directors help to focus the radio waves in the forward direction, further enhancing the antenna's gain and directivity.

The gain of a Yagi antenna increases with the number of parasitic elements. By adding more directors, the antenna can achieve higher directivity and a narrower beamwidth. This makes Yagi antennas well-suited for applications where a strong, focused signal is required in a specific direction, such as long-distance communication, amateur radio, television reception, and point-to-point wireless links. The performance of a Yagi antenna is sensitive to the dimensions and spacing of its elements, requiring precise construction for optimal results.

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