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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 EngineeringPAF-Karachi Institute of Economics & Technology Karachi
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 andencouragement to pursue my interests, even when the interest went beyond the boundaries offield and scope. Without their support and kindness this work would not have been possible.
ACKNOWLEDEMENT Praise to Allah the most beneficent and the most mercifulWe are grateful to our project advisor Mr. Abbas, for enlightening us with his preciousknowledge and vast experience to benefit us in the future. We also like to thank to our teachersand lab assistants for their assistance and support.We would also thank with all gratitude and depth of our hearts to our parents who helped usnot only financially but with integrity too and support us in all our hardships. Finally our sincerethanks to our institute PAF-KIET, College of Engineering, for providing us the opportunity togave 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 andTechnology may make great progress in Pakistan and Pakistan may become a part of thedeveloped nations.Thank you.
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 simpleto construct and has a high gain, typically greater than 10 dB. The Yagi-Uda antennas typicallyoperate in the HF to UHF bands (about 3 MHz to 3 GHz), although their bandwidth is typicallysmall, on the order of a few percent of the center frequency. We are probably familiar with thisantenna, 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 onthe rooftops of houses. It is usually used at frequencies between about 30MHz and 3GHz, or awavelength range of 10 metres to 10 cm. (There are some obsessional amateur radioenthusiasts who construct Yagi-Uda antennas for the 80 metre wavelength band. This is ratherimpractical as spacing them from the ground by more than half a wavelength is difficult.) Therod lengths in a Yagi-Uda are about a half wavelength each, and the spacings of the elementsare about 1/3 of a wavelength. This puts the overall sizes of Yagi-Udas in the rangesfreq transverse length length length dimension 3 elements 5 elements 15 elements (lambda/2) 30MHz 5 metres 6 metres 13 metres 47 metres100MHz 1.5 metres 1.8 metres 3.9 metres 14 metres300MHz 50 cm 60 cm 1.3 metres 4.7 metres1GHz 15 cm 18 cm 39 cm 1.4 metres3GHz 5 cm 6 cm 13 cm 47 cmA 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 (parallelLC circuit) inserted along their conductors on each side, allowing the antenna to be used at twodifferent frequency bands.
The first step in modeling an antenna is to determine what frequency range it will cover. Ourtarget frequency is going to be Hz(a common commercial wireless frequency). Using thewavelength - frequency equation it is discovered that the wavelength of a this signal is roughlycm. This tells us that if the antenna were a single dipole, it would have to be at least half thislength to receive the signal, because otherwise the antenna is not able to tell what kind ofsignals it is picking up. This is due to the fact that the antenna would have no zero referencepoint from which to continue propagating. Since a Yagi-Uda antenna is being constructedinstead, it can be seen that it differs in that an array of dipoles is used. With only one elementactive (usually the second to last), the remaining elements, referred to as directors, guide andfocus the signal toward the active element.As a basic rule, the directors should be roughly 1/4 a wavelength apart. This makes sure thatwhen a signal is picked up in the outermost element, and is induced in each element down theline toward the driven element, the signal remains in phase. In fact this mutual inductance ofthe multiple directors has an adding affect on the signal, boosting its strength, which isresponsible for the antennas characteristically high gain factor (to an extent, the number ofdirectors dictate how high the gain factor is). Now that the signal has been passed down theline of directors, it induces current in the driven element and the reflector, which should bepositioned 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 anengineered antenna, but it would still work.
Radiation pattern:Advantages: Easy to design Have high gain Low costReferences:http://www.cisco.com/en/US/prod/collateral/wireless/ps7183/ps469/images/0900aecd806a1a3e_null_null_null_08_07_07-11.jpghttp://yagi-uda.com/http://www.antenna-theory.com/antennas/travelling/yagi3.phphttp://www.oh1sa.net/data/antenna/XE1MEX-yagi/