Yagi Antennas

Yagi Antennas

HAM RADIO PRO ARTICLE SERIES

Yagi antennas are directional antennas that were invented by Hidetsugu Yagi and Shintaro Uda in 1926. They are also known as Yagi-Uda antennas, after their inventors. Yagi antennas are widely used in many applications such as broadcasting, wireless communication, satellite communication, and amateur radio.

They are popular because they are easy to construct and provide high gain, which makes them ideal for long-range communication. In this article, we will explore the basics of Yagi antennas, how they work, their design, and applications.

Basic Principles of Yagi Antennas

 

Yagi antennas are based on the concept of a resonant dipole antenna. A dipole antenna is a simple antenna that consists of two metal rods of equal length and parallel to each other. When a dipole antenna is excited with an alternating current, it generates electromagnetic waves that radiate into free space. However, a dipole antenna is omnidirectional, meaning it radiates equally in all directions. This is where Yagi antennas come into play. They use a technique called “directivity” to make the antenna directional.

 

Directivity is achieved by adding one or more parasitic elements to the dipole antenna. These elements are typically thin, metal rods placed parallel to the dipole. They do not connect to the feed line and are not excited directly. Instead, they rely on the electromagnetic field of the driven element to create their own currents. By adjusting the length and spacing of these parasitic elements, the radiation pattern of the antenna can be shaped.

 

The Yagi antenna consists of a single driven element and one or more parasitic elements. The driven element is typically a half-wave dipole, and the parasitic elements are shorter or longer than the driven element. The parasitic elements are placed a specific distance from the driven element, and their lengths and spacing are adjusted to maximize the gain and directivity of the antenna.

 

Yagi Antenna Design

 

The design of a Yagi antenna involves several key parameters that determine its performance. These include the length and diameter of the elements, the spacing between the elements, the feed point location, and the reflector and director element lengths. These parameters are interdependent, and changing one will affect the others.

 

The length of the elements is determined by the operating frequency of the antenna. The driven element is typically a half-wave dipole, which means it is half the wavelength of the operating frequency. The parasitic elements are shorter or longer than the driven element and are spaced a specific distance from the driven element.

 

The spacing between the elements also affects the performance of the antenna. The spacing between the driven element and the reflector should be approximately 0.2 wavelengths, while the spacing between the driven element and the director should be approximately 0.15 wavelengths.

 

The feed point location is also critical to the performance of the antenna. The feed point is where the signal is applied to the driven element, and it should be located at the point of maximum voltage on the dipole. This is typically at the center of the dipole.

 

The reflector and director element lengths are also important parameters in Yagi antenna design. The reflector is typically longer than the driven element, while the director is shorter than the driven element. These elements are positioned a specific distance from the driven element to create the desired radiation pattern.

 

Applications of Yagi Antennas

 

Yagi antennas are widely used in many applications, including

 

Broadcasting: Yagi antennas are used to transmit and receive radio and TV signals over long distances. They are commonly used by TV stations to transmit their signals to remote areas.

 

Wireless Communication: Yagi antennas are used in wireless communication systems such as Wi-Fi and cellular networks. They provide directional coverage, which makes

 

Yagi antennas are commonly used in Ham Radio for HF (High-Frequency) Bands, which range from 1.8 MHz to 30 MHz. HF bands are popular among amateur radio enthusiasts because they allow for long-distance communication with relatively low power levels. Yagi antennas are ideal for HF bands because they can provide high gain and directivity, which allows for efficient and effective long-range communication.

 

One of the most popular uses of Yagi antennas in Ham Radio is for directional communication. Ham Radio enthusiasts often use Yagi antennas to communicate with other operators over long distances. By pointing the Yagi antenna in the direction of the desired station, the operator can increase the strength of the signal and reduce interference from other directions.

 

Yagi antennas are also used for contesting, which is a popular activity among Ham Radio operators. Contesting involves making as many contacts as possible in a set amount of time. Yagi antennas are ideal for contesting because they allow operators to quickly and efficiently make contacts with other stations over long distances.

 

Another use of Yagi antennas in Ham Radio is for DXing, which involves communicating with stations in distant locations. DXing is a popular activity among Ham Radio operators because it allows them to test their equipment and skills. Yagi antennas are ideal for DXing because they can provide high gain and directivity, which allows for efficient communication over long distances.

 

Overall, Yagi antennas are an essential tool for Ham Radio enthusiasts operating on HF bands. They provide high gain and directivity, which makes them ideal for long-range communication, contesting, and DXing. By using a Yagi antenna, Ham Radio operators can efficiently and effectively communicate with other stations over long distances.

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