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ANTENA DIPOLE

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ANTENA DIPOLE

Antena dipole dalam beberapa aspek miripdengan saluran transmisi yang open circuit.

Antena yang termasuk tertua, palingsederhana, paling murah dan banyakaplikasinya.

ANTENA DIPOLE

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(Hertz electric dipole, infinitesimal dipole and doublet)

zr

R

P

I

z

x

y

1. Write the expression of the current

zzyxzIzyxI )'()'()'()'()'( J

2. Construct vector potential A

)( 'r

zr

e

zIdvrr

e

'rzIzdvR

e

r

rjrrjRj

4''4)(

'4)'(v

'

v

JA

zr

ezI

rj

4

A'rr

so

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(Hertz electric dipole, infinitesimal dipole and doublet)

zr

R

P

I

z

x

y

3. Find H field:

4. Find E field:

)(11

zAz

AH

sin)1

1(

4 r

e

rj

jzI

rj

H

HE j

1

rr

e

rj

r

zI

re

rrjjzI

rj

rj

cos11

2

sin)(

1114

2

2

E

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Radiation is characterized by the field components decaying as

r

1

Radiation field of

an ideal dipole:

sin4 r

ej

zIrj

H

sin

4 r

ej

zI rjEPattern

z

x

y

E

H

ImportantObservations:

1. E & H fields are in phase

2. E & H fields are transverse to the direction of

propagation (no radial component)

3.The ratio of

4.The angular dependence defines radiation

pattern

5. E, H and r are orthogonal to each other

HE /

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0t

Tt8

1

Tt4

1

Tt 8

3

Tt2

1

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For ideal dipole, thenormalized pattern : sin),( F

Beam solid angle :

Directivity :

in dB :

3

42sinsin

0

2

0

2

ddA

3

8A

2

34

dipoleideal

ADD

75.12

3log10 dBD dB

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Macam-macam antena Dipole

Ada beberapa macam antena dipole yaitu :

Half wave Dipole

Short Dipole Antenna Antena Biconical

Cylindrical Antenna

Bow Tie Antenna Folded Dipole Antena

Antena Monopole

Antena Loop

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Current Density : zyxzIr )'()'()'()'(

J

A good approximation

for the current :

)'

2(sin)'( zl

IzI m

Note : Current goes to zero at the ends

For different length dipoles, current

distribution takes various distributions

For far field computation :

2/

2/

''')'(

4')'(

4

l

l

rrjrj

rrj

V

rj

dzezIr

edver

r

e

JA

Am

1

m

1

2mA

dipole along

Z axis

dipole length

z

mI2/l

2/l

2/l

l

for

for

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Among various length dipoles, half-wavelength ( ) dipoles

are the most popular ones. This is because of their goodinput impedance.

2/

Recall for oriented linear currentz )cos''( zrr

E-field: ')'(4

sinsincos'

dzezIr

ejAjAjE

zjrj

z

For2

l

')'2

sin(

')'2

sin(

cos'4/

0

cos'0

4/

dzezI

dzezIf

zj

m

zj

mun

z

yx

cos

sinsincossin

zz '

unf

We need evaluate

this integral !!

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Integral

Identity : )cos()sin()sin(

22

bxabbxaccb

edxebxa

cxcx

Then after some

manipulation :)cos

2cos(2

sin2

mun

If

2sin

)cos2

cos(

sin4

2

r

eIjE

jkr

m

2sin

)cos2cos(sin)( F

1)2/(;2

at

FNote:

Pattern :

Finally :

element pattern

pattern factor

radiation pattern

Each differential

current element

radiates sin

4/

4/

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Dipole Gelombang

Half-waveDipole

a. Currentdistribution

b. Radiationpattern

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Dipole Gelombang (samb)

Distribusi arus pada antena dipole 1/2 gelombang yangtipis dapat didekati dengan gelombang berdiri sinusdengan arus.

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Dipole Gelombang (samb)

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Tt8

10t

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Tt4

1 Tt

8

3

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Short Dipole Antenna

Antena dipole pendek digunakan pada frekuensirendah ketika besar. Konduktor linear pendeksering disebut dipole pendek.

d

I

+q

-q

Saluran Transmisi rangkaian ekivalen

L > d

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Short Dipole Antenna (samb)

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Short Dipole Antenna (samb)

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2/

Note: For an antenna of length L, that carriers an axial

uniform current

sohmic Ra

LR

2

fRs 2;2

Surface resistance

a2

L

frequency

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Biconical Antenna

Antena ini banyakdigunakan untuk antenamobil.

Berdasarkan Schelkunoff:

E = C+ e -jk0 r + C- e jk0 r

r sin r sin

H = C+ Y0 e

-jk0 r - C-YO ejk0 r

r sin r sin

Zc = 120 ln cot 0/2

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Cylindrical Antenna

Perbandingan BiconicalAntenna denganCylindrical Antenna:

Mudah difabrikasidibandingkan biconicalantenna

Bandwidth biconical lebihlebar (wide-angle)

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Folded DipoleAntena

Antena ini banyak digunakan sebagai antena TV

Daya pancarnya : Pr = 4x36,56 lo2

Resistansi Radiasi : Ra = 4x73,13 = 292,5

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Folded DipoleAntena (samb)

a. The Folded dipole antenna

b. Even Excitation

c. Odd Excitation

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Antena Monopole (Grounded Dipole)

Antena monopole merupakan setengah dariantena dipole yang berada di atas permukaanbumi

Banyak digunakan untuk :

* siaran komersial pada AM-band (500-1500 KHz)

* pelayanan komunikasi land mobile

Antena monopole terdiri dari 1/2 antena dipole

yang diletakkan di atas bumi (biasanya dimenara)dengan menggunakan 1/4 panjanggelombang(quarter wave antenna).

Resistansi radiasi ideal = 36,56

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Antena Monopole(samb)

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Antena Monopole(samb)

A monopole antenna withfour radial arm groundscreen

Ground Screen digunakanuntuk menghindari powerloss karena konduktivitaspentanahan yang buruk

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In the upper hemisphere, monopole creates exactly the same

electromagnetic fields as the dipole

Image theory allows one to

create equivalent known

problem

Infinite ground plane

monopole

antenna

P.E.C Equivalent

Ideal

monopole

dipole

dipoleAmonoA

mono DD 2

2

1

44

,,

Directivity of a

monopole is twice

of dipole

22

,, )(40

2

1

h

RR dipolermonor Length of monopole

dipole

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Antena Loop

Antena Loop ini terdiri dari berbagai konfigurasinamun karena konstruksi dan kesederhanaan dalamanalisis, loop berbentuk lingkaran paling populer danmenarik perhatian untuk ditelaah.

Disini diasumsi loop antenaekivalen dengan dipole pendekdalam menganalisa daerah E

dan H -nya.Pada antena loop, medan yangada E dan H

E = 0 dan Er = 0H = 0 dan Hr = 0

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Antena Loop (samb)

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Small loop

antennas :

It turns out that the radiation fields of small loops are

independent of the shape of the loop and depend only onthe area of the loop

Vector potential :

C

rrj

rj

rrj

V

rj

dcer

edver

e '4

'4

''

'

IJA

Note : It appears to be easier to construct for the square loop

Perimeter , uniform time varying current

current along the loop

along the loop

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Small square loop can be thought of as

combination of 4 ideal dipoles.

xI

#1

#2

#4

#3y

z 1R

r

4321 AyAxAyAx

squaresmall

A

or

42

31

42

31

4

4

R

e

R

eIlA

R

e

R

eIlA

RjRj

y

RjRj

x

Far field

approximation:

for amplitude term:

RRRRR 4321

for phase

term :

cossin2

cossin2

sinsin2

sinsin2

4

2

3

1

lrR

lrR

lrR

lrR

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Then :

sinsin)2/(sinsin)2/(

4

ljljrj

x eer

IleA

)(2

1sin

jj eej

Recall :

Finally :

sinsin2

sin4

2 lr

IlejArj

x

cossin

2sin

42

l

r

IlejA

rj

y

cossin2l

)(2

smallfor l

ll

or : )

cos

sin(sin4

2

yxr

Ie

ljyAxA

rj

yx

A

AEHE j:fields&

Note :

22

2 loop)of(area

lS

sin4

1

sin4

2

2

r

IeSr

r

IeS

rj

rj

EH

E

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x

I y

z

x

mI

y

z

x

Iy

zLoop

area S

z z

Ideal magnetic

dipole along z

axis

Ideal dipole

along z axissmall loop in x-y

planeISjzIm

Define

ohmS

R

dBD

HP

r

ezIj

rezIj

r

A

o

rj

m

rj

m

2

2

280

75.1or2

3

3

8

90

sin4

sin4

H

E

ohmz

R

dBD

HP

r

ezIj

rezIj

r

A

o

rj

rj

2

280

75.1or2

3

38

90

sin4

sin

4

H

E