Anten

1.4.3 RaWith this Mathemat

Fig. 15: C

Note: Forequation i

1.4.4 Ra

Radiationspace coo

A

fi

H A

fa

nna pa

adiated Poinformation,

tically it can b

Calculation of

r antennas, mis over a close

adiation P

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A field pattern

ixed distance

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A power patterar-field with d

ramete

ower , now we arebe written as

f radiated pow

mostly we areed surface wi

Pattern

graphical rep

n is a graph t

from the ante

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rn is a graph tdirection at a

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ers: (Co

in a position

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enna. A field

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d radiation. Sthe surface is

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e far field val

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adiated power

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nitude (amplit

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ration in the afar from anten

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of the

A typical antenna radiation pattern is shown in Fig. 16 (a). The characteristics to note down from this pattern are:

(i) Main (major) lobe (ii) Minor lobe (includes side lobes and back lobe) (iii) Half-power beamwidth (HPBW) (iv) Beamwidth between first nulls (BWFN)

Note: A radiation pattern shows only the relative values but not the absolute values of the field or power quantity. Hence the values are usually normalized (i.e., divided) by the maximum value. [In Fig. 16, mark the maximum of the main lobe that is 1)

The size of the minor lobes is much smaller than that of the major lobe. In order to clearly visualize the minor lobes, sometimes the scales of the radiation pattern are expressed in dB, as shown in Fig. 16 (b).

The calculation procedure of the beamwidths from the radiation pattern is shown in Fig. 17.

Note: By the reciprocity theorem, the radiation pattern of an antenna in the transmitting mode is same as those for the antenna in the receiving mode.

(a)

Minor lobes

Main lobe

1.0

0.5

Half-power Beamwidth

(HPBW)

Beamwidth between first nulls (BWFN)

Main lobe maximum direction

0 dB

- 3 dB

- 10 dB

Main lobe

(b)

Fig. 16: Antenna radiation pattern

Fig. 17: C

Is

O

Calculation of

sotropic Rado Charac

o Exists o Used a

Omnidirectiono Along o Maximo Somet

f beamwidths

diation Pattercteristics

CompletelyRadiates anRadiation p

only as a maas a referencenal Radiatiothe ends of th

mum radiationtimes used a r

from the radi

rn: It is the pa

y non-directiond receives eqpattern is sphethematical co

e n Pattern: Ithe dipole thern is along the reference

iation pattern

attern of a po

onal antenna qually well inerical oncept

t is the patternre is no radiatbroadside dir

.

oint source.

n all directions

n of a Hertziation (nulls) rection

s

an dipole. [seee Fig. 18]

x

y

(b)

z

090HPBW

sin

(c)

(a)

x

z

y

Fig. 18: Omnidirectional radiation pattern.

Example:

The step-by-step procedure of drawing the radiation pattern of a Hertzian dipole is as follows:

Step – 1

Step – 2

Step – 3

Step – 4

Step – 5

1.4.5 Fi

The spacefield regio

Far field independe

than 2D2/as the Fradistributio

The field This regioaccording

ield Regio

e surroundingon. (See Fig.

is defined aent of the dist

from the anaunhofer region is independ

immediately on is again dg to their char

ns

g an antenna 19)

as that regiontance from th

ntenna, whereon. In this redent of the ra

surrounding divided into twacteristics. (S

is usually di

n of the fieldhe antenna. Th

e D is the ovegion, the fieldial distance

the antenna awo sub regio

See Fig. 19).

ivided into tw

d of an antenhis region is c

erall dimensild componenwhere the me

and the far fiens as (a) reac

wo regions: (

nna where thcommonly ta

ion of the antnts are essentieasurements a

eld region is ctive near fie

(i) near field

he angular fiaken to exist a

tenna. This reially transverare made.

known as theeld and (b) ra

region and (

ield distributiat distances g

egion is also crse and the an

e near field readiating near

ii) far

ion is greater

called ngular

egion. field,

362.0 D 22D

D

Reactive region

Radiating region

Near field region Far field region

Fig. 19: Near field and far field regions of an antenna.