Lecture - 1.3 · 1.4.3 Ra With this Mathemat Fig. 15: C Note: For equation i 1.4.4 Ra Radiation...
Transcript of Lecture - 1.3 · 1.4.3 Ra With this Mathemat Fig. 15: C Note: For equation i 1.4.4 Ra Radiation...
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1.4.3 RaWith this Mathemat
Fig. 15: C
Note: Forequation i
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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
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iation pattern
attern of a po
onal antenna qually well inerical oncept
t is the patternre is no radiatbroadside dir
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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
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ield Regio
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is defined aent of the dist
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immediately on is again dg to their char
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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.
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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.