design of yagi antenna

2. CONTENT
 INDRODUCTION
 PRINCIPLE
 CONSTRUCTION
 WORKING.
 PICTURE OF ANTENNA.
 ADVANTAGES
 DISADVANTAGES.
 INTRODUCTION.
 APPLICATIONS.

3. INTRODUCTION
 The Yagi-Uda antenna or Yagi Antenna is one of the most brilliant
antenna designs. It is simple to construct and has a high gain
typically greater than 10 dB.
 The Yagi-Uda antennas typically operate in the HF to UHF bands
(about 3 MHz to 3 GHz) and Covers 40 to 60 Km.
 A Directional Antenna System Consisting of an array of Coupled
Parallel Dipoles. This is commonly known as Yagi-uda or Simply
Yagi Antenna.
 Yagi-uda Antenna is familiar as the Commonest kind Of
Terrestrial TV Antenna to be found on the Roof tops of houses.

5. PRINCIPLE
• Yagi-uda antenna is an electromagnetic device that collects radio
waves.
• An antenna tuned to a particular frequency will resonate to a radio
signal of the same frequency

6. CONSTRUCTION
THERE ARE THREE TYPES OF ELEMENTS:
 THE REFLECTOR (R)
 THE DRIVEN ELEMENT (D)
 THE DIRECTORS (DI)

7. CONSTRUCTION
DRIVEN ELEMENT :
• The driven element of a Yagi is the feed point where the feed line is
attached from the transmitter to the Yagi to perform the transfer of
power from the transmitter to the antenna.
• A dipole driven element will be "resonant" when its electrical
length is 1/2 of the wavelength of the frequency applied to its feed
point.
• The feed point in the picture above is on the center of the driven
element.

8. CONSTRUCTION
DIRECTOR :
• The director is the shortest of the parasitic elements and this end of
the Yagi is aimed at the receiving station. It is resonant slightly higher
in frequency than the driven element, and its length will be about 5%
shorter, progressively than the driven element.
• The directors lengths can vary, depending upon the director spacing,
the number of directors used in the antenna, the desired pattern,
pattern bandwidth and element diameter.
• The amount of gain is directly proportional to the length of the
antenna array and not by the number of directors used.

9. CONSTRUCTION
REFLECTOR
• The reflector is the element that is placed at the rear of the driven
element (The dipole).
• It's resonant frequency is lower, and its length is approximately 5%
longer than the driven element. It's length will vary depending on the
spacing and the element diameter
• The spacing of the reflector will be between .1 wavelength and .25
wavelength. It's spacing will depend upon the gain, bandwidth, F/B
ratio, and side lobe pattern requirements of the final antenna design.

10. Working
• Reflector here derives it’s main Power from a driver , it reduces the
signal strength in it’s own direction and thus reflectes the radiation
towardes the driver and directors.
• The driven element is where the signal is intercpeted by the receiving
equipment and has the cable attached that takes the recevied signal
to the receiver
• The radiator and driver can be placed more closer to increase the
radiation length towards the directors.

11. Director length 0.4λ
Feeder length 0.45λ
Reflector length 0.482λ
Reflector feeder spacing 0.2λ
Director spacing 0.2λ
Director feeder spacing 0.2λ

12. FIVE ELEMENT YAGI-UDA
REFLECTOR
DRIVER

13. Radiation pattern formed
bY the directional antenna
jack

14. Radiation pattern formed
bY the directional antenna
The antenna exhibits a directional pattern consisting of a
main forward lobe and a number of spurious side lobes.
The main one of these is the reverse lobe caused by
radiation in the direction of the reflector.
The antenna can be optimised to either reduce this or
produce the maximum level of forward gain.
jack

15. PICTURE OF ANTENNA
ELEVEN ELEMENT’S OF YAGI-UDA ANTENNA
FORWARD
DIRECTION

16. PICTURE OF ANTENNA for TV
SIGNAL RECEPTION
The Yagi antenna is a particularly useful form of RF antenna
design. It is widely used in applications where an RF antenna
design is required to provide gain and directivity. In this way the
optimum transmission and reception conditions can be obtained.

17. ADVANTAGES
It has a Moderate Gain Of About 7 (dB).
It is a Directional Antenna.
Can be used at High Frequency.
Adjustable front to Back Ratio.

18. DISADVANTAGES
The Gain is not Very High.
Needs a large number of Elements to be used.

19. APPLICATIONS
 Yagi-uda antenna is a unidirectional antenna. Used for
television recivers.They provide better tunning because
of large bandwidth and has decent gain.