Yagi antennas are also known to the industry by another name, Yagi-Uda. Some would simply call it Yagi. Commonly used in communications, Yagis are a qualified directional antenna with frequencies above 10 MHz.
The antenna of this type are popular among Citizens Band and Amateur Radio operators and are utilized at satellite communications systems for their surface installations.
Components of a Yagi System
A Yagi system is usually comprised of 2 – 3 straight elements. Each of which is approximately ½ electrical wavelengths. There are 2 classifications for these antennas, they can be balanced or unbalanced. As for the Yagi type of antenna, they are usually considered as a balanced antenna. And yet you can feed them with coaxial cable together with another device referred to as a balun. This is the point where the driven element would be joining the feed line.
The Yagi driven element is comparable to the half-wave, center-fed dipole antenna. At approximately 0.2 to 0.5 wavelength on both sides of the parallel driven element, are straight wires or rods known as reflectors and directors. Reflectors, slightly shorter by ½ wavelength, are installed fronting the driven element.
It is quite typical for Yagis to come with one reflector but with plenty of directors. The antenna will propagate the electromagnetic field energy from the driven element direction toward the director(s). It is also very sensitive to incoming electromagnetic field energy from the exact, same direction.
High quality yagi antennas are not just going to have a response pattern and unidirectional radiation, they can also concentrate response and the radiation. If a Yagi system has more directors, the greater is this so-called forward gain. If more directors would be added to a Yagi, its natural response or tendency is to become even longer.
Some Yagis have plenty of directors, from 10 or even 12, which is on top of one reflector and the driven element. You seldom use long Yagis that are below 50 MHz. The underlying reason behind this is that these frequencies would render the structure to become physically unwieldy.
The Name Behind Yagi Antennas
Shintaru Uda, together with a colleague, Hidetsugu Yagi, conceptualized and invented the Yagi system of an antenna from a very long time ago, in 1926. In almost every part of the United States, there was a similar design and was called a log-periodic antenna.
A Yagi system of antenna usually comes with 2-3 straight antenna elements. They are set to a length at least half the electrical wavelength they are intended to provide support. We qualify them as a balanced type, but this would depend if they are used with a balun, then they can be unbalanced, joining the antenna’s driven element.
One of the many benefits of the Yagi system of the antenna would include the ease of aiming the antenna and its range as opposed to many other directional designs.
A Yagi antenna is a qualified directional type, and for this reason, it will center the entirety of its signal to just a cardinal direction. This measure helps in making it possible to have increased gain over the omnidirectional models of other designs of the antenna.