EXPERIMENT NO.14

Simulate Yagi-Uda antenna

 Time ( min) Content Learning Aid / Methodology Faculty Approach Typical Student Activity Skill / Competency Developed 10 Relevance and significance of experiment Chalk & Talk , Presentation Introduces, Facilitates, Monitors Listens, Participates, Discusses Knowledge, Communication, intrapersonal 20 Explanation of experiment Chalk & Talk , Presentation Introduces, Facilitates, Explains Listens Knowledge, Communication, intrapersonal, Application 60 Reading Demonstration Explains, Monitors Participates, Discusses comprehension, Hands on experiment 20 Calculations N/A Explains, Monitors Participates, Discusses Knowledge, Communication, Intrapersonal, Application 10 Results and conclusions Keywords Lists, Facilitates Listens, Participates, Discusses Knowledge, Communication, intrapersonal, Comprehension

Practical Session Plan

Title: Analysis of Parabolic Reflector

Objectives: Model the Yagi-Uda antenna to analyze the performance parameters

Aim:

Â· To model the Yagi-Uda antenna

Â· To compute gain, beam width, return loss & impedance of Yagi-Uda antenna

Apparatus: Antenna Simulation software

Theory:

An antenna array is a group of radiators whose currents are of different amplitudes and phases. They use electromagnetic wave interference phenomena to enhance the radiative signal in the desired direction and diminish it in the non-desired direction. Antenna arrays are the solution to the problem defined as the limitations of operating a single antenna.

A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element (typically a dipole or folded dipole) and additional parasitic elements (usually a so-called directors and one or more reflector). The name stems from its inventors, as the Yagi-Uda array was invented in 1926 by Shintaro Uda of Tohoku Imperial University, Japan, with a lesser role played by his colleague Hidetsugu Yagi. The reflector element is slightly longer (typically 5% longer) than the driven dipole, whereas the so-called directors are a little shorter. This design achieves a very substantial increase in the antenna's directionality and gain compared to a simple dipole.

Highly directional antennas such as the Yagi-Uda are commonly referred to as "beam antennas" due to their high gain. However the Yagi-Uda design only achieves this high gain over a rather narrow bandwidth, making it more useful for various communications bands (including amateur radio).

Fig. 1: Three elements Yagi-Uda Antenna

Yagi-Uda antennas are routinely made with rather high gains (over 10dB) making them a common choice for directional antennas especially in VHF and UHF communications systems where a narrowband antenna is acceptable

Problem Statement:

Design a 3 element Yagi Uda array operated at a frequency of 50MHz. The length of reflector element is 2.921m, length of active element is 2.788 m & length of director is 2.758 m.

Procedure:

1. Click anywhere on the information window title bar and enter name of antenna you want to design and simulate then click Ok or press the <Enter> key

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2. Click anywhere on the selection button to its left. Enter desire frequency in the dialog text box, and click Ok or press <Enter>. It will automatically calculate wavelength and get displayed into wavelength menu.

3. Open the Wires Window by clicking on the Control Center "Wires" line, or the selection button to its left. Position the Wires and View Antenna Windows for convenient viewing. The position of each wire in space is specified by giving its x, y, and z coordinates. These coordinates represent distances from the origin.

e.g. for dipole that lies along X-axis at origin of length 0.5m has its X=0.25,Y=0,Z=0 (for end-1); X=-0.25,Y=0,Z=0 (for end-2). The last column is to define the number of segments for the wire. Total 20 segments are allowed for EZNEC-Demo version. As number of segments increases, accuracy of current distribution and thereby radiation pattern increases.

4. In the Sources Window grid, you can see that there's one source (source no. 1), which is placed on wire #1, 50% from end 1. This is where we want the source to be. However, this is a good time to practice a little with the Sources Window. The source type, shown in the Type column, is a current source. The Sources Window also shows the source amplitude and phase, in this case one ampere at zero degrees. When a model contains only a single source, the magnitude, phase, or type have no effect on the pattern or source impedance.

5. Click on the Ground Type line, and select real. The height of the antenna will determine which ground model we use. If you have a fast computer, you can always choose High Accuracy analysis unless you need to make a connection to ground. When we changed the ground type to Real, one ground medium was created. The conductivity and dielectric constant of newly-created grounds can be set for your local ground conditions by means of the Control Center Options menu Default Ground Const selection. The values initially used by EZNEC are those of "average" or "good" ground (conductivity of 0.005 S/m, dielectric constant of 13).

6. Click on the Units line or the selection button to its left, then select meter, and Ok.

7. Click on the Plot Type row in the Control Center and select either of elevation, azimuth or 3D-pattern.

8. Save the antenna description by clicking the Save As action button.

9. Click the action button. FF Plot; it will show you the radiation pattern and beam width, gain etc. Under view option of 3D plot it is also possible to see 2D pattern of radiation.

Calculations:

1. Calculate wavelength=>

2. Length of antenna=> meter.

Conclusion:

Upon completion of experiment students will be able to:

Oral Question Bank

Theory Question Bank

 Q. No Description 1 What is Yagi-uda antenna? 2 What are factors affecting yagi-uda antenna gain? 3 What are factors affecting yagi-uda antenna beam width? 4 What are factors affecting yagi-uda antenna impedance and return loss? 5 List the formulae for a) Reflection coefficient b) VSWR c) Return loss Of Yagi-uda Antenna 6 Yagi antenna is generally used for which frequency range? 7 What are the parameters to be considered for the design of a Yagi-uda antenna? 8 Explain the special features of Yagi-uda antenna? 9 What is the main advantage of Yagi-uda antenna? 10 Draw the radiation pattern for Yagi-Uda antenna? 11 List application of Yagi-uda antenna