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.
5.
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
11.
12.
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
14.
15. 1.Gain is not much more
2.Need more driven elements for longer distances
3.Bandwidth is Limited