The Yagi-Uda antenna consists of a driven element connected to a transmission line and one or more passive parasitic elements. The reflector element is longer than the driven element to make it inductive, while the director elements are shorter than the driven element to make them capacitive. Together the elements produce a unidirectional beam with moderate directivity and gains of around 8dB. Adding more director elements increases the directivity. It has advantages of simple construction, low cost, and ease of feeding but has limitations of limited bandwidth and requiring additional elements for higher gains over longer distances.

1. By
V.D.SRINIVAS
(17304008)

3. 1.INTRODUCTION
2.STRUCTURE
3.ELEMENTS
4.WORKING
5.DESIGN
6.CHARACTERISTICS
7.DISADVANTAGES
8.APPLICATIONS

4. In the 1926,Dr.Shintaro Uda and Dr.Hidetsugu Yagi of the Tohoku imperial
university invented a directional antenna system consisting of an array of coupled
parallel diploes.
Most high Gain Antennas.
Yagi-Uda antenna is familiar as the commonest kind of triennial tv antenna to be
found on the rooftops of houses
It is usually used at frequencies between 30Mhz to 3Ghz to cover 40 to 60 Km.

6. 1.REFLECTOR
Passive element
It adds up the fields of driven element in the direction from reflector
towards driven element
2.DRIVEN ELEMENT
Active element
It is a resonant half wave dipole or metallic rod
The element was feeder ,supplied the charge
3.DIRECTORS
Passive element
It can be one or more for increasing the directivity
Size: 5% less than the Driven element

7. YAGI-UDA ANTENNA
Combining the effect of reflectors and directors elements, a highly
directional antenna is obtained: the Yagi.

8. 1.Yagi Uda antenna is an array of a driven element and one or more parasitic
elements
2.They are not connected directly to Tx line but Electrically coupled
3.Parasitic elements are arranged collinearly and parallel to each other elements
4.Current flow in the driven element induces voltage in parasitic elements.
5.The phase and current flows depends up on the spacing and reactance of the
elements
6.Spacing are in order of 0.1λ to 0.15λ.

9. 1.The REFLECTOR length is 5% more than the Driven element (≥ λ/2)
---- Leads to Inductive
2.The DIRECTOR length is 5% less than the Driven element (≤ λ/2)
-----Leads to Capacitive

10. Reflector Length = 500/f(Mhz)
Driven element Length=475/f(Mhz)
Director Length =455/f(Mhz)
Feet
Feet
Feet

13. 1.Unidirectional beam of moderate Directivity
2.Gain of order of 8db or front to back ratio of about 20 db
3. Beam antenna—3 element config,
4. Super directivity or gain antenna due to its high gain and beam width per unit area of array
5. Further elements increase ---directivity increases
6.Construction is simple
7.Less cost and simple to feed

15. 1.Gain is not much more
2.Need more driven elements for longer distances
3.Bandwidth is Limited