ECE-D Antenna 2

8/14/2019 ECE-D Antenna 2

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Radiation from

Half Wave Dipole


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Half wave dipole

Its the simplest and fundamentalantenna, has length of Halfwavelength, ie /2.

Otherwise called Dipole antennaor /2 antenna.

Two metal rods or wires havephysical length of /4 withopposite polarity will act assimple dipole.


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Radiation Fields

We already developed the expressions forCurrent element or Unit lengthelement

A dipole of length /2 can be said as

continuously distributed current element,in other words, A dipole antenna is sub-divided into multiple current element.

E and H fields of a dipole we can derivefrom current element itself, howeverthese multiple current elements willcreate a phase shift between them

Such mechanism is modeled as:Total field =(Element Field)(space factor)

This spacer factor will give the phasedifference conce t, it takes a len th


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A dipole antenna isplaced at origin of3-d space

At a point p, located a(r,,)

From the origin,consider a currentelement is located

a height of z. The field created by

the currentelement will createa phase shift with

respect to origin byzcos

cos'zrR =


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Over all phase shift created by all currentelement is referred as Spacer factor

So the total field can be expressed as

Total field =(Element Field) (space factor)

=

sin

2coscos

2cos

factorSpacer

klkl

sin

2coscos

2cos

2E

klkl

r

eIj

jkro

sin

2coscos

2cos

2H

klkl

r

eIj

jkro

These equations are approximate

- for Far Field conditions

by single current element


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Power density, Radiationdensity

Powerdensity

Radiation

density


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For dipole: l=/2

sin

cos2

cos

2E

r

eIj

jkro

sin

cos2

cos

2H

r

eIj

jkro


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Radiated power density, Radiationresistance

Total radiated power

435.2)2( inC

Radiationresistance .Appr 75will match the 50

,Line to air medium for this reaso/ 2 dipole antenna

become much famous


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l>/2

While antenna length is greater than /2, theSpacer factor changes and creatingconstruction and destructions

destructionsConstructions

Side lob

For l=1.25


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l>>/2, for example: 2 or 5


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Assignment-1

Should be in IEEE format

Clear Reference

Plagiarism

Intro + Literature 3marks

Road map 2marks Conclusion 4marks

Earlier submission(before Feb-5) 1mark.

Two Quizzes 10 marks. First quiz on 28-01-2010.Propagation mechanism + Radiation Mechanism

Last date: Fab 12, 5.30pm.

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ECE-D Antenna 2

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