Antenna

1. Yagi Uda Antennea
B.E. PROJECT REPORT
Electronic Field & Waves (12814)
Prepared by
Salman Khaliq Bajwa (3746)
Mohammad Ghazanfar (4795)
Advisor
Asstt. Professor, Muhammad Abbas
College of Engineering
PAF-Karachi Institute of Economics & Technology
Karachi

2. DEDICATION
This report is dedicated to
Our Parents, Teachers & Friends,
Whose love, affection and support helped me in bringing our work to this level of
accomplishments; We are also thankful to them for their unconditional support and
encouragement to pursue my interests, even when the interest went beyond the boundaries of
field and scope. Without their support and kindness this work would not have been possible.

3. ACKNOWLEDEMENT
Praise to Allah the most beneficent and the most merciful
We are grateful to our project advisor Mr. Abbas, for enlightening us with his precious
knowledge and vast experience to benefit us in the future. We also like to thank to our teachers
and lab assistants for their assistance and support.
We would also thank with all gratitude and depth of our hearts to our parents who helped us
not only financially but with integrity too and support us in all our hardships. Finally our sincere
thanks to our institute PAF-KIET, College of Engineering, for providing us the opportunity to
gave us the strength to undertake this research.
Special thanks to all our fellows and friends who lend us a hand throughout this project.
We pray this effort may prove to be the beginning of new era, a era in which Science and
Technology may make great progress in Pakistan and Pakistan may become a part of the
developed nations.
Thank you.

4. Objective:
The main objective of this project is to understand the working and design of Yagi Uda Antenna.
Description:
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), although their bandwidth is typically
small, on the order of a few percent of the center frequency. We are probably familiar with this
antenna, as they sit on top of roofs everywhere.
Construction:
A Yagi-Uda antenna is familiar as the commonest kind of terrestrial TV antenna to be found on
the rooftops of houses. It is usually used at frequencies between about 30MHz and 3GHz, or a
wavelength range of 10 metres to 10 cm. (There are some obsessional amateur radio
enthusiasts who construct Yagi-Uda antennas for the 80 metre wavelength band. This is rather
impractical as spacing them from the ground by more than half a wavelength is difficult.) The
rod lengths in a Yagi-Uda are about a half wavelength each, and the spacings of the elements
are about 1/3 of a wavelength. This puts the overall sizes of Yagi-Udas in the ranges
freq transverse length length length
dimension 3 elements 5 elements 15 elements
(lambda/2)
30MHz 5 metres 6 metres 13 metres 47 metres
100MHz 1.5 metres 1.8 metres 3.9 metres 14 metres
300MHz 50 cm 60 cm 1.3 metres 4.7 metres
1GHz 15 cm 18 cm 39 cm 1.4 metres
3GHz 5 cm 6 cm 13 cm 47 cm
A three-element Yagi-Uda antenna used for amateur radio. The longer reflector element (left),
the driven element (center), and the shorter director (right) each have a so-called trap (parallel
LC circuit) inserted along their conductors on each side, allowing the antenna to be used at two
different frequency bands.

5. The first step in modeling an antenna is to determine what frequency range it will cover. Our
target frequency is going to be Hz(a common commercial wireless frequency). Using the
wavelength - frequency equation it is discovered that the wavelength of a this signal is roughly
cm. This tells us that if the antenna were a single dipole, it would have to be at least half this
length to receive the signal, because otherwise the antenna is not able to tell what kind of
signals it is picking up. This is due to the fact that the antenna would have no zero reference
point from which to continue propagating. Since a Yagi-Uda antenna is being constructed
instead, it can be seen that it differs in that an array of dipoles is used. With only one element
active (usually the second to last), the remaining elements, referred to as directors, guide and
focus the signal toward the active element.
As a basic rule, the directors should be roughly 1/4 a wavelength apart. This makes sure that
when a signal is picked up in the outermost element, and is induced in each element down the
line toward the driven element, the signal remains in phase. In fact this mutual inductance of
the multiple directors has an adding affect on the signal, boosting its strength, which is
responsible for the antennas characteristically high gain factor (to an extent, the number of
directors dictate how high the gain factor is). Now that the signal has been passed down the
line of directors, it induces current in the driven element and the reflector, which should be
positioned approximately 1/2 a wavelength behind the active element. The reflector picks up
"spare radiation," from both the directors and the driven element, further focusing it. Presto!
You have an antenna! Although this is a VERY simple design it would still work, not as well as an
engineered antenna, but it would still work.

7. Radiation pattern:
Advantages:
Easy to design
Have high gain
Low cost
References:
[1]
http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/images/0900aecd806a1a
3e_null_null_null_08_07_07-11.jpg
[2]
http://yagi-uda.com/
[3]
http://www.antenna-theory.com/antennas/travelling/yagi3.php
[4]
http://www.oh1sa.net/data/antenna/XE1MEX-yagi/