More than one hundred years ago, two men invented Yagi antenna. Have you ever heard of this antenna? It was invented back n 1926 in the Tohoku Imperial University by Shintaro Uda with Kiyoshi Kawakami, and Hidetsugu Yagi, as well as other colleagues present at the same university.
This antenna became the first designed antenna to be able to exploit the benefits of having to receive multiple direction signals to remove jamming or noise wit high directionality, high gain, as well as a continuous line of sight. This pair Uda and Yagi were now referred to as “fathers of antennas.” Our article will be explaining the basics of Yagi antenna, its component, design considerations, applications, and more.
What is Yagi Antenna?
Yagi antenna can also be called Yagi Uda Antenna. This can be described as a directional antenna which has at least two resonant parallel components that acts as half wave dipoles. The antenna is mainly formed from three components.
These include directors, driven element, and reflector, whereby one driven component forms connectivity with either the receiver or transmitter through the transmission lines or with other types of parasitic components. Generally, parasitic elements can be described as the reflector as well as some directors (the longer element).
The shorter elements (parasitic elements) aren’t connected electrically to the receiver or transmitter. However, they serve as passive resonators that work with these driven elements. Generally, Yagi antennas are created to work effectively In UHF and HF ranges and they offer functional frequency that falls within 30 MHz and 3 GHz, even when its bandwidth is small or very minimal. The unique design of these antennas is done to have great gain values that are higher than 10 decibels.
Components of the Yagi Antenna
Yagi antenna are composed of three main components
Reflector
The reflector’s length is usually 5% higher compared to the driven element. Most times, every Yagi antenna is made up of a reflector element present at the backside of a driven element. This means it’s at sideways from the area the greatest sensitivity will happen.
Furthermore, reflectors present at the back region of driven elements reveals no obvious difference to the antenna’s performance. Whereas that are designs that employ reflectors with some parallel rods or reflecting plate, which resembles the reflecting plate. When this happens, there would be a little increase in the performance of the device and therefore reduce the level of radiation. In addition, the pattern of the design will reduce the interference range.
Driven Element
Driven element offers the required current needed for the radiation of electromagnetic energy in space. Usually, they have similar strength as half wavelength at intended operating frequencies. Other elements can be described as electrical multiples of the half length of a wavelength ensuring their resonation at one frequency as its driven element. This additional length or a multiple of the half wavelength can be achieved through the insertion of a capacitance or inductance in every parasitic element that can increase the electrical length without having to change the physical length.
Director
Whenever there are more directors or just one direction, the directors’ length is shorter compared to driven components. Also, the directions’ positioning will stay in-front of a driven component, meaning it stays in a direction having a high sensitivity level.
Most times, there’s a gain of about 1 dB across every director element in a forward path even when this level is decreased in cases where we have more directors. The directors present will determine the number of lobes that appear on this antenna’s radiation pattern. The more the love present, then narrower they would become. This means it is possible for them to focus on just one specific direction
The Working and Construction of the Yagi Antenna
This section will be explaining the design of Yagi Antenna as well as its mode of operation.
The Design of Yagi Antenna
In the past decades, you can find Yagi antennas most times on roof of houses. The parasitic dipoles and components form the Yagi antenna collectively. The antenna could have more directors and it helps in enhancing the directionality of the antenna. You can consider the feeder to be a folded dipole, and then the reflector has an additional length which is usually situated at the end parts of the antenna.
For the Yagi antenna design, its structure takes the form of center rod whereby the components can be placed. Its active components are referred to as driven component whereby the transmission line features an internal connection via a black stud. These single materials found at the driven component’s back end is referred to as the reflector whereby it reflects the full energy present in the radiation pattern’s direction. The remaining components present before thee driven components are referred to as directors that help to reflect beams in the required angle’s direction
Working Principle of the Yagi Antenna
Before you get into operating the Yagi antennas, let us first consider how the antenna works. Antennas can be described as devices which receive as well as send signals. Whenever these incoming signals get to the antenna’s input terminal, the AC (alternating current) will be created across the terminals to respond to incoming waves.
The alternating current (AC) is usually coupled with the receiver’s input terminal through a waveguide or coaxial cable. In summary, this receiver antenna will receive electromagnetic waves, which it then converts to electrical signals. The transmitter antennas, on the other hand, help in converting the electrical signals in to the electromagnetic waves.
The antennas come with different sizes and shapes. This depends on the application. For typical design for antennas, its conductors are usually bent in at least one geometric shape like folded dipoles or horizontal dipoles.
Yagi antennas are mostly folded dipole antennas. Whenever, there is a supply or extrinsic excitation into the dipole, the flow of current across active components help in creating the voltage across the parasitic components that ensures the current flow across it.
Furthermore, the component having more length compared to the wavelength/2 reveals inductive features ensuring the reflector component’s current lags its induced voltage. Also, the component or director’s short length induces the capacitive features ensuring that the flow of current across this director leads its induced voltage.
Transmission of Yagi antenna
As the director’s position is found in-front of that driven component, the director includes the field of the driven component in an opposite direction (which is away from its position). Whenever multiple directors are available, then each director will provide an excitation to the subsequent one.
Furthermore, the reflector helps to add the field of the driven component in its direction (near it). This takes place to reduce losses as a result of backward radiated signals. In order to achieve extra gain, employ additional directors in the direction of the beam.
Fundamentally, this induced current and voltage flow as a result of an induced voltage passing across this component usually differs relating to the distance between the active and parasitic components altogether with reactance phenomenon that is linked to these components.
What has to be observed here is that during the operation of Yagi antenna, if there is an increase in the spacing present between the driven component and director, then there is an increase n the need for capacitive reactance ensuring that correct and precise phasing is offered at the director. This is why the length of the component director is usually maintained a little in order to achieve the capacitive reactance.
What are the Advantages and Disadvantages of the Yagi Antenna?
Advantages
- With the Yagi antenna, you can be sure of high gain
- Because directors are utilized, it possesses high directional function and features
- Yagi antennas are very power efficient
- Constructing and maintaining them isn’t complex
- Its pricing is inexpensive
- Great sustainable levels for different high frequency activities
Disadvantages
- To get high gains while using the Yagi antenna, this antenna will be lengthier
- For one antenna, the gain level must limit to 20 decibels or else that device would become extremely large and its beamwidth would become reduced
- This antenna is very prone to interference, noise, as well as atmospheric conditions therefore the device’s performance becomes reduced.
What are the Applications of the Yagi Antenna?
Yagi antennas have a few applications. These are
- Defense applications
- TV signal reception because the antenna has great receiving capability
- Serves the astronomical domain effectively
- Utilized in radio astronomy
Conclusion
In summary, Yagi antenna can be described as a directional antenna which has at least two resonant parallel components that acts as half wave dipoles. The antenna is mainly formed from three components. These include directors, driven element, and reflector. In the past decades, you can find Yagi antennas most times on roof of houses. The parasitic dipoles and components form the Yagi antenna collectively. For the Yagi antenna design, its structure takes the form of a center rod whereby the components can be placed.
