Yagi - Uda Antenna

 Goals

            The main purpose of this experiment is to design a Yagi-Uda antenna using CST studio. To do this, how components of antenna are structured and how varying the lengths and positions of these components changes the characteristics of the antenna should be properly researched and understood. In addition, determining the antenna’s radiation pattern, gain and directivity are also aimed.

Introduction

Antennas are electric wave transmitting and receiving instruments. When an antenna receives a signal, it transforms the incident electromagnetic waves into electrical currents; when it transmits, it converts the incident electromagnetic waves into electrical currents. Antennas are made to radiate (or receive) electromagnetic energy with various radiation and polarization properties that are tailored to the device [3]. Shintaro Uda of Tohoku Imperial University in Japan invented it in 1926, with support from his colleague Hidetsugu Yagi [4]. They discovered the Yagi - Uda antenna, which was originally known as the Yagi antenna [1]. Yagi antennas were first extensively used in radar systems by the Japanese, Germans, British, and Americans during World War II.  They saw a lot of growth after the war as home television antennas [4].

It's a strongly directional antenna made up of an array of dipoles (Driven Element) and a group of parasitic elements (more than one director and a reflector) behind the driven element that increases the antenna's radiation properties when correctly positioned. It's a strongly directional antenna so it radiates more power in one direction, eliminating interference from all other sources. The Yagi - Uda antenna is commonly used for a variety of reasons, including low cost, high gain, and ease of construction. The antenna was first used in televisions, but later saw use in other areas such as radars, RFID, satellites, and so on. The Yagi - Uda antenna may also be used for radio frequency detection, which involves identifying a tag connected to an item using radio frequencies. Microwave or ultra - high frequency waves may be emitted by such tags, which may provide a wealth of valuable knowledge [1].

Figure 1. A modern high-gain UHF Yagi [4]

The point where the feeding is delivered is called a driven part or a dipole. The feeding is normally directed towards the dipole's core, allowing for optimum power transmission from transmitters to antennas. When the length of a dipole is half the wavelength of activity, it is assumed to be resonant. The arrangement of the dipoles does not have to be linear; it can also be folded. The gain of the antenna in both forward and backward directions is heavily influenced by the dipole's geometry. Any of these dipole elements is supported by a boom structure.

By reciprocal coupling, the powered element's field causes currents in the parasitic elements of the array, determining the majority of the antenna's parameters. A director is the smallest parasitic element. It's a resonant structure that runs at a lower frequency than the driven part. The arrangement is given a directional role by the directors, who have a high gain. A director's length is less than that of a guided element, and it varies depending on the spacing between the directors, which ranges from 0.1 to 0.5 λ. The number of directors used can be determined by the antenna's physical size, and increasing the number of directors can improve the antenna's directivity (gain). The length and spacing of a director have a major impact on forward and backward gain, as well as providing a directional radiation pattern to the antenna. The array's directors are the most critical elements [1].

At the ends of the powered part, a reflector is normally used. A reflector has a longer range than a driven element, but it operates at a lower frequency than the driven element. The length of a reflector is determined by the dimensions of each array unit, while the distance between reflectors would be on the order of 0.1-0.25 λ. The gain and input impedance of an antenna are both affected by the length and spacing of a reflector [1].

Since no feeding is given to these components, the reflector and director are engineered to be parasitic. These elements will change the powered element's radiation properties. The radiation pattern in the array is inverted as the duration between the guided and parasitic elements is changed [1].

1.1.Antenna Arrays

Parasitic components are antenna elements that are not electrically attached to the rest of the antenna. Consider the half-wave dipole below, which has only one half-wave parasitic portion. The radiation pattern with and without the reflector is seen.

Figure 2. Parasitic Element and Radiation Pattern with and without the reflector

1.1.1.      Parasitic Elements

The parasitic elements are excited by the radiation from the powered element. There are two types which are reflectors and directors.

1.1.1.1. Reflectors

The reflector element is approximately 5% longer than the powered element. In most cases, the Yagi antenna would only have one reflector. This is the side opposite the direction of highest sensitivity, and it is behind the key powered feature.

Additional reflectors behind the first have no discernible effect on the antenna's output. Many prototypes, however, employ reflectors made up of a reflecting plate or a sequence of parallel rods that simulate a reflecting plate. This improves results somewhat by lowering the amount of radiation or pick-up from behind the antenna, i.e. in the backwards direction. This will assist in lowering the rate of received intervention. In the forward direction, a reflector usually adds 4 to 5 dB of lift [5].

1.1.1.2.Directors

Directors are electrically shortened by 5% compared to the powered part. Their energy from the front of the antenna is reinforced and focused.

More parasitic elements equal more cost. Adding more directors is more efficient than adding more reflectors. The larger the number of directors, the higher the gain and the narrower the beam angle [2].

Figure 3. Dipole without reflector and Dipole with reflector [2]

As compared to a halfwave dipole antenna, Figure 3 represents doubling results in a 3 dB gain. The guided element radiates normally, allowing voltages and currents to be induced in the parasitic element, causing it to also radiate. Reflection causes a 180° phase transition, since the radiation that returns to the dipole is in phase.

1.2.Antenna Design

A proper understanding of how the components are structured and how changing the lengths and positions of these components affects the antenna's characteristics is needed for the design of a Yagi (Yagi - Uda) antenna. A driver, reflector(s), and a number of directors are among the components. The driver is the single active entity that is excited by a signal, while the reflectors and directors re-radiate by reflecting and directing the signal, respectively. As a result, both the reflector(s) and the directors are regarded as parasitic components. The length of the director should be marginally less than one-half of the expected operational wavelength, which is a standard starting point for a design [3]. Figure 1 depicts the proposed antenna's geometry. It is claimed to be horizontally polarized and consists of a dipole, reflector, and three directors configured to run at a resonant frequency of 400 MHz. A voltage source feeds a port connected to the center of the dipole element [1].

The following are the general specification principles for a 400 MHz Yagi - Uda antenna.

Reflector length is

L_R = 0.477*λ

Active element length is

L_i = 0.451*λ

Director length is       

L_D = 0.422*λ

Spacing between elements is

d = 0.25* λ

where

λ = c / f                                                                        (1)

Where “w” is the wavelength in meters, “c” is the speed of light in free space (3*10⁸ meters per second), and “f” is the operating frequency in megahertz.

Figure 5. The Final Example Design of Yagi Antenna [3]

Aluminum sheet was used to build the Yagi antenna for this example. Using pliers, the aluminum sheet was cut out and filed down to the necessary dimensions. A thin plastic sheet was used to form the driving part, which was then wrapped in copper tape. The Yagi antenna was constructed in this manner for two reasons: aluminum sheet and copper tape were both inexpensive and simple to deal with. The disadvantage of removing the Yagi antenna from an aluminum sheet was that the pattern was finalized at the time of cutting, and no further modifications could be made.

Figure 6. Construction Principles of Example Design [3]

A general schematic of the Yagi antenna that was installed is seen in Figure 6. The six lengths described in the schematic correspond to the previously explained individual lengths. These lengths are summarized in the table below.

In our design, frequency will be between 500 - 800 MHz band. 

Parameters	LR	LA	S1	S2
Value(mm)	250	225	160	70

Table 1.Our Example Design of Yagi Antenna

The length of the director should increase as it gets closer to the guided aspect, but it should not decrease as it gets farther away. The length of the sequence is regarded as more significant than the amount of elements included within it. The Yagi's matching is determined by the position of the first director element and the spacing of the reflectors. The number of array components determines the antenna gain. The advantage increases as the number of elements increases, as long as the elements are not too far apart and are of equal length [1].

1.3.Yagi Antenna Advantages

In certain applications, the Yagi antenna has many benefits over other types of antennas, but all advantages and drawbacks must be considered to ensure that the right antenna is selected.

·         Directivity: Since the Yagi antenna is directional, interference levels for receiving and transmitting are kept to a minimum.

·         Gain: The Yagi antenna has gain, which allows it to absorb weaker signals.

·         Straightforward construction: When opposed to other antenna architectures, the Yagi antenna has a comparatively simple mechanical architecture. Straight rods, which are easy to use and durable in most cases, may be used to build it.

·         Polarisation: The antenna's design allows it to be conveniently fixed on vertical and other poles using regular mechanical fasteners.

 

1.4.Yagi Antenna Disadvantages

The Yagi antenna has a host of drawbacks that must be considered as well.

·         Max gain ~20 dB: For a single antenna, gain is limited to about 20dB or so, otherwise the antenna becomes too wide and the beamwidth narrows. The physical size of low frequency antennas means that the overall number of components, and hence the gain, is much smaller than 20 dB.

·         Long for high gain:  The antenna becomes very long at high gain speeds.

To conclude this part, the Yagi antenna is a very practical RF antenna architecture that is well-suited to applications requiring gain and directivity. The Yagi is also the most cost-effective solution for gain and directivity, despite its higher cost than more basic antennas [5].

 

1.5.Yagi Gain / Beamwidth Factor

The average Yagi antenna gain is influenced by a number of factors. There is a relationship between gain and beamwidth. The beamwidth reduces as the Yagi gain increases. This can be explained by considering the transmit power available. Since there is a finite amount of power available, in order to generate gain, power must be taken from one direction and directed into the main beam.

Very high gain antennas are also very directive. As a result, high gain and narrow beamwidth must often be matched to achieve optimal efficiency [6].

Figure 7. Yagi Antenna Gain and Beamwidth Options [6]

1.6.Yagi - Uda Antenna Gain Considerations

A Yagi antenna's gain is influenced by a number of factors, including:

1.6.1.      Number of elements in the Yagi

The number of elements in the antenna is the most apparent aspect that affects the Yagi antenna gain. A reflector is usually the first component applied to any Yagi design because it provides the most additional gain, usually about 4 to 5 dB. Following that, directors are added. Each director offers approximately 1 dB of gain for mid-ranges of the number of directors.

1.6.2.      Element spacing

But not as much as the number of components, the spacing will affect the Yagi benefit. A wide-spaced beam, or one with a large spacing between the components, usually has more benefit than a compact beam. The reflector and first director are the most important element positions because their spacing determines the spacing of all other elements that might be inserted.

1.6.3.      Antenna length

In a multi-element Yagi array, the advantage is usually proportional to the length of the array when calculating the optimum positions for the different elements. The element places have a certain amount of leeway.

Therefore, the number of elements in the Yagi antenna configuration is one of the most important factors influencing the antenna gain. The spacing between the items, on the other hand, has an effect. The overall efficiency of an RF antenna is influenced by a number of interconnected factors, and as a result, many early designs failed to achieve their maximum potential [6]. Today, computer programs are used to optimize prototypes before they are manufactured, resulting in improved performance over earlier designs.

Method

Table 2. Yagi Antennas of Six Different Lengths with Optimized Parasitic Element Lengths [7]

The antenna's basic configuration is modeled using the construction parameters seen in Table 1 from Peter P. Viez Bicke of the National Bureau of Standards' "Yagi Antenna Design." standards were established in 1968. The "boom," which is the long feature to which the directors, reflectors, and feed components are physically connected, determines the antenna's length. Boom is not used in this style because it is unnecessary. It's believed that the developers of the aforementioned paper experimented with spacing before they reached an optimal range and released it. The spacing between the directors is consistent and is mentioned in the table's second-to-last row. d = 0.0085*λ gives the diameter of the elements. The table above provides a good starting point for estimating the antenna's necessary length (the boom length), as well as a range of lengths and spacing that achieve the desired gain. All spacing, distances, and diameters, in general, are design variables that can be constantly optimized to change efficiency.

Figure 8 shows Yagi - Uda antenna designed in CST program. The antenna consists of 6 parts in total. There are 1 reflector, 1 driven and 4 directors. λ is accepted 500 mm. Driven has a length of 0.45 * λ and is accepted as the origin in driven positioning. A 6 mm gap was created at the center of the driven, and this gap and a discrete port were defined. The reflector is positioned 0.32 * λ (to the left) from the driven and its size is 0.5 * λ. The defined directors were placed at 0.14 * λ distances both among themselves and with driven, and length of directors were 0.2 * λ, 0.17 * λ, 0.14 * λ and 0.11 * λ, respectively.

Figure 8.Designed Yagi - Uda antenna in CST program

Results

The S-parameter graph of the designed Yagi-Uda antenna between 0 - 2 GHz is shown in Figure 9. In Figure 10, it is seen that the Yagi-Uda antenna is between 500 - 800 MHz at -3 dB. 

Figure 9. S-parameter of designed Yagi-Uda antenna

Figure 10. Detailed S-parameter of designed Yagi-Uda antenna at -3 dB

Resonance Frequency is 0.564 GHz and resonance value of it is -13.46 dB, according to Figure 11. 

Figure 11. Resonance frequency and value Yagi-Uda antenna

        Figure12 shows the efficiency graph of the Yagi - Uda antenna. According to the graph, the antenna works with 95% efficiency about at 570 MHz.

Figure 12. Efficiency of Yagi - Uda Antenna

Figure 13, Figure 14, Figure 15 show the farfield results of the Yagi - Uda antenna at 0.56 GHz, 0.65 GHz, 0.7 GHz, respectively. It is understood from the graph that the violence towards the right of driven is more. The reason for this is that the height of the directors is shorter than the reflector. 

Figure 13. Farfield results of the Yagi - Uda antenna at 0.56 GHz

Figure 14.Farfield results of the Yagi - Uda antenna at 0.65 GHz

Figure 15.Farfield results of the Yagi - Uda antenna at 0.7 GHz 

It can be understood from the graphs above that as the frequency increases, the directivity of the antenna decreases after 0.56 GHz.

In Figure 16, the radiation pattern outputs of the Yagi - Uda antenna at 0.56 GHz was seen.

Figure 16. Radiation pattern outputs of the Yagi - Uda antenna at 0.56 GHz 

In Figures 17 and 18, the effect of the length of the driven on the s-parameter is observed.

Figure 17. S - Parameters of Yagi - Uda antenna with changing length of driven

Figure 18.S - Parameters of Yagi - Uda antenna with changing length of driven 

        There is an inverse relationship between the driven length and the resonance frequency. When the length of the driven decreases, the resonance frequency of the S parameter increases.

        As can be seen from the Figure 19, as the length of driven increases, the gain frequency shifts to the left. So as the length increases, the center frequency decreases for gain. In addition, the amount of gain changes differently for each length. This reason that general comments cannot be made.

Figure 19. Efficiency of S - Parameters of Yagi - Uda antenna with changing length of driven

        In Figure 20, the effect of changing length of the reflector on the s-parameter can be seen. Orange, green, blue and red in Figure 20 represent 0.2 * λ, 0.3 * λ, 0.4 * λ and 0.5 * λ, respectively. 0.35 * λ is a critical value for this s-parameter. This is because that the gain of the antenna increases up to 0.35 * λ. However, if this value is exceeded, the capacity of the antenna suddenly decreases.

Figure 20.S - Parameters of Yagi - Uda antenna with changing length of reflector 

        In Figure 21, to interpret the change in gain with the change in the length of the reflector, radiation efficiency is constantly moving in a more way if the length of the reflector decreases. This is evidence of the change in total efficiency.

Figure 21. Efficiency of S - Parameters of Yagi - Uda antenna with changing length of reflector

        Figure 22 shows the effect of the changing in distance between reflector and driven on the s-parameter. This graph shows the s-parameters of the 0.2 * λ, 0.35 * λ and 0.5 * λ distances, respectively. The variation of distance clearly affects the gain of the antenna. 

Figure 22. S - Parameters of Yagi - Uda antenna with changing distance of reflector and driven

        To interpret the Figure 23, a general inference cannot be made from these graphs, but the gain is affected by each length of the reflector. Graphical results were obtained with a continuous change around a point.

Figure 23.Efficiency of S - Parameters of Yagi - Uda antenna with changing distance of reflector and driven

        Figure 24 shows the effect of changing length of director 1 (leftmost) on the s-parameter. This graph shows the s-parameters of the 0.1 * λ, 0.175 * λ and 0.25 * λ lengths, respectively. As the length of director 1 increases, the resonance frequency and gain of the antenna increase.

Figure 24. S - Parameters of Yagi - Uda antenna with changing length of director 1 (leftmost)

Looking at this Figure 25, it is difficult to make a general statement, but as the length of director 1 increased, the efficiency of the antenna increased. 

Figure 25.Efficiency of S - Parameters of Yagi - Uda antenna with changing length of director 1 

        Figure 26 shows the effect of changing the distance of director 1 (leftmost) as regard driven on the s-parameter. As the distance of director 1 increases according to driven, the antenna's bandwidth increases.

Figure 26. S - Parameters of Yagi - Uda antenna with changing distance between Director 1 (leftmost) and Driven

        In Figure 27, to interpret the change in gain with the change in the distance between director 1 and driven, radiation efficiency is constantly moving in a more way if the distance of the director 1 decreases. 

Figure 27. Efficiency of S - Parameters of Yagi - Uda antenna with changing distance between Director 1 (leftmost) and Driven 

        Figure 28 shows the effect of changing the length of director 2 as regard driven on the s-parameter. This graph shows the s-parameters of the 0.1 * λ, 0.175 * λ and 0.25 * λ lengths, respectively. As the length of director 2 increases according to driven, the antenna's gain increases.

Figure 28.S - Parameters of Yagi - Uda antenna with changing length of director 2 

        Looking at Figure 29, it is hard to decide a general statement, but as the length of director 2 increased, the efficiency of the antenna increased.

Figure 29. Efficiency of S - Parameters of Yagi - Uda antenna with changing length of director 2 

        Figure 30 shows the effect of changing the distance of director 2 as regard driven on the s-parameter. This graph shows the s-parameters of the 0.2 * λ, 0.275 * λ and 0.35 * λ distances, respectively. As the distance of Director 2 increases according to driven, the antenna's gain decreases.

Figure 30. S - Parameters of Yagi - Uda antenna with changing distance between Director 2 and Driven

        In Figure 31, to interpret the change in gain with the change in the distance between director 2 and driven, radiation efficiency is constantly moving in a more way if the distance of the director 2 decreases. 

Figure 31.Efficiency of S - Parameters of Yagi - Uda antenna with changing distance between Director 2  and Driven 

        Figure 32 shows the effect of changing the length of director 3 as regard driven on the s-parameter. This graph shows the s-parameters of the 0.1 * λ, 0.175 * λ and 0.25 * λ lengths, respectively. As the length of director 3 increases according to driven, the antenna's gain decreases.

Figure 32. S - Parameters of Yagi - Uda antenna with changing length of director 3

        Looking at Figure 33, it is difficult to decide on a general statement, but as the length of the director 3 increased, the efficiency of the antenna increased. 

Figure 33. Efficiency of S - Parameters of Yagi - Uda antenna with changing length of director 3 

        Figure 34 shows the effect of changing the distance of director 3 as regard driven on the s-parameter. This graph shows the s-parameters of the 0.3 * λ, 0.375 * λ and 0.45 * λ distances, respectively. As the distance of director 3 increases according to driven, the antenna's gain decreases insignificantly.

Figure 34. S - Parameters of Yagi - Uda antenna with changing distance between director 3 and Driven

        Looking at Figure 35, it is hard to decide on a general statement, but as the length of the director 3 increased, the efficiency of the antenna increased insignificantly. 

Figure 35. Efficiency of S - Parameters of Yagi - Uda antenna with changing distance between Director 3 and Driven 

        Figure 36 shows the effect of changing the length of director 4 as regard driven on the s-parameter. This graph shows the s-parameters of the 0.1 * λ, 0.175 * λ and 0.25 * λ lengths, respectively. As the length of director 4 increases according to driven, the antenna's gain increases.

Figure 36. S - Parameters of Yagi - Uda antenna with changing length of director 4 (rightmost)

        Looking at Figure 37, it is hard to decide on a general expression, but as the length of the director 4 increased, the efficiency of the antenna increased insignificantly.

Figure 37. Efficiency of S - Parameters of Yagi - Uda antenna with changing length of director 4 (rightmost) 

        Figure 38 shows the effect of changing the distance of director 4 as regard driven on the s-parameter. This graph shows the s-parameters of the 0.5 * λ, 0.575 * λ and 0.65 * λ distances, respectively. As the distance of Director 4 increases according to driven, the antenna's gain increases insignificantly.

Figure 38. S - Parameters of Yagi - Uda antenna with changing distance between Director 4 and Driven 

        In Figure 39, to interpret the change in gain with the change in the distance between director1 and driven, radiation efficiency is constantly moving in a more way if the distance of the director 4 decreases. 

Figure 39.Efficiency of S - Parameters of Yagi - Uda antenna with changing distance between Director 4 and Driven

Conclusion

        Yagi - Uda antenna was investigated, its characteristics and importance in daily life usage were learned. In order to realize the desired design, the mathematical calculations of this antenna were examined and our own design was made according to these calculations. Although mathematical operations were performed, the desired design was carried out by trial and error method in order to obtain the desired results. The effect of each parameter on the s-parameter and how it affects the efficiency of the antenna were examined. The results obtained were evaluated according to the specified parameter and discussed.

References

[1] MATHEW, Pristin K. A three element Yagi Uda antenna for RFID systems. Director, 2014, 50: 2.

[2] USNA, EE302 Lesson 14: Antennas Fundamentals, 2014, PowerPointSlide

[3] DELGADILLO, Mario; PANGGABEAN, Maringan Pardamean. 2.4 GHz Yagi-Uda Antenna.

[4] Wikipedia, Yagi–Uda antenna, 2021, the site is https://en.wikipedia.org/wiki/Yagi%E2%80%93Uda_antenna

[5] Electronicsnotes, Yagi Antenna / Yagi-Uda Aerial, 2021, with site of https://www.electronics-notes.com/articles/antennas-propagation/yagi-uda-antenna-aerial/basics-overview.php

[6] Electronicsnotes, Yagi Antenna Gain, Directivity & Front to Back Ratio, 2021, with the site of .

[7] VIEZBICKE, Peter P. Yagi antenna design. US Government Printing Office, 1976.