yagi antenna class.ppt

design of yagi antenna

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

3. INTRODUCTION
TheYagi-UdaantennaorYagiAntennaisoneofthemostbrilliant
antennadesigns.Itissimpletoconstructandhasahighgain
typicallygreaterthan10dB.
TheYagi-UdaantennastypicallyoperateintheHFtoUHFbands
(about3MHzto3GHz)andCovers40to60Km.
ADirectionalAntennaSystemConsistingofanarrayofCoupled
ParallelDipoles.ThisiscommonlyknownasYagi-udaorSimply
YagiAntenna.
Yagi-udaAntennaisfamiliarasthe CommonestkindOf
TerrestrialTVAntennatobefoundontheRooftopsofhouses.

5. PRINCIPLE
•Yagi-udaantennaisanelectromagneticdevicethatcollectsradio
waves.
•Anantennatunedtoaparticularfrequencywillresonatetoaradio
signalofthesamefrequency

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

7. CONSTRUCTION
DRIVEN ELEMENT :
•ThedrivenelementofaYagiisthefeedpointwherethefeedlineis
attachedfromthetransmittertotheYagitoperformthetransferof
powerfromthetransmittertotheantenna.
•A dipole driven element will be "resonant" when its electrical
lengthis 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 :
•Thedirectoristheshortestoftheparasiticelementsandthisendof
theYagiisaimedatthereceivingstation.Itisresonantslightlyhigher
infrequencythanthedrivenelement,anditslengthwillbeabout5%
shorter,progressivelythanthedrivenelement.
•Thedirectorslengthscanvary,dependinguponthedirectorspacing,
thenumberofdirectorsusedintheantenna,thedesiredpattern,
patternbandwidthandelementdiameter.
•Theamountofgainisdirectlyproportionaltothelengthofthe
antennaarrayandnotbythenumberofdirectorsused.

9. CONSTRUCTION
REFLECTOR
•Thereflectoristheelementthatisplacedattherearofthedriven
element(Thedipole).
•It'sresonantfrequencyislower,anditslengthisapproximately5%
longerthanthedrivenelement.It'slengthwillvarydependingonthe
spacingandtheelementdiameter
•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
•Reflectorherederivesit’smainPowerfromadriver,itreducesthe
signalstrengthinit’sowndirectionandthusreflectestheradiation
towardesthedriveranddirectors.
•Thedrivenelementiswherethesignalisintercpetedbythereceiving
equipmentandhasthecableattachedthattakesthereceviedsignal
tothereceiver
•Theradiatoranddrivercanbeplacedmoreclosertoincreasethe
radiationlengthtowardsthedirectors.

11. Director length 0.4λ
Feeder length 0.45λ
Reflector length 0.482λ
Reflector feeder spacing 0.2λ
Director spacing 0.2λ
Director feeder spacing0.2λ

12. FIVE ELEMENT YAGI-UDA
REFLECTOR
DRIVER

13. Radiation pattern formed
bY the directional antenna
jack

14. Radiation pattern formed
bY the directional antenna
Theantennaexhibitsadirectionalpatternconsistingofa
mainforwardlobeandanumberofspurioussidelobes.
Themainoneoftheseisthereverselobecausedby
radiationinthedirectionofthereflector.
Theantennacanbeoptimisedtoeitherreducethisor
producethemaximumlevelofforwardgain.
jack

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

16. PICTURE OF ANTENNA for TV
SIGNAL RECEPTION
TheYagiantennaisaparticularlyusefulformofRFantenna
design.ItiswidelyusedinapplicationswhereanRFantenna
designisrequiredtoprovidegainanddirectivity.Inthiswaythe
optimumtransmissionandreceptionconditionscanbeobtained.

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-udaantennaisaunidirectionalantenna.Usedfor
televisionrecivers.Theyprovidebettertunningbecause
oflargebandwidthandhasdecentgain.