Yagi-Uda Aerial Antennas
A Yagi-Uda antenna is a unidirectional antenna mainly used in communications. It is mostly used when a frequency above 10MHz is required. This frequency makes this antenna applicable in Citizen Band radio operators and also among Amateur Radio stations. The antenna is also quite popular among TV stations and can be found among house rooftops. Here is a brief description of this antenna; how it works, its basic elements, its basic structure and design, and how it can be useful to a designer.
Invented in 1926, the basic Yagi-Uda antenna is made of about three elements, each of these elements measure about half of electrical wavelength. This antenna can further be made balanced or unbalanced; it is naturally made balanced but can be made unbalanced when fed with a coaxial cable.
Elements of the yadi-uda Antenna
The three types of elements that make up the antenna are; the director, the reflector and the driving element. When using this antenna, only its driving element is connected directly to a feeder, the other elements are connected to the transmitter power through electromagnetic fields. This assists to induce currents within transmission.
It is important to note that the driving element is frequently made of a folded dipole. Since it is connected directly to the feeder, it has a driving point impedance of about 300 ohms. However, this large resistance is reduced to about 50 ohms due to the shunting effect produced by the other elements.
How it works
While the operation of the antenna could seem sophisticated, it is simple and straightforward operation principle. The driving element i.e. the feeder is composed of normal plastic element that has a gap at its centre. Unlike other loads like a receiver, the feeder is connected to a short circuit.
After connection, the short circuit the power is transmitted through 180 degrees out of phase. To achieve this out of phase degree, the wave of the transmitter should always be made shorted at the feeder location. This means that the driving element should be made of a solid element.
Use to a designer
The antenna is applied in satellite communications systems. It works well at frequencies that range from 30MHz to 3GHz, its wavelength range is from 10cm to 10 meters. However, there are some radio enthusiasts that take this wavelength to 80 meters.
The antenna comes with some benefits to the designer. The gain of the antenna is quite moderate and stable. It is further cheap, simple to build and is tolerant to variations in constructions. Any designer will thus find great ease with designing the Yagi-Uda antenna.