antenna2-140117111353-phpapp02.pptx

AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
RADIATION & PROPOGATION
-Fundamental Parameters ofAntennas
AJAL.A.J
Assistant Professor –Dept of ECE,
UNIVERSAL ENGINEERING COLLEGE
Mob: 8907305642 MAIL: ec2reach@gmail.com

An antenna is away of converting the guided waves
present in a waveguide,feeder cable or transmission line
into radiating waves travelling in free space, or vice
versa.

Radiation Pattern Lobes
Main lobe
Full Null Beamwidth
Between
1st NULLS
Side lobes
Back lobes

O nly accelerating charges produce radiation.
Idealized
Point Radiator Vertical Dipole Radar Dish
Isotropic Omnidirectional Directional

Two fields regions:
oNear field or Fresnel region: The region within the
radius of the smallest sphere which completely encloses
the antenna is called Fresnel region.
In sitting an antenna ,it’
s crucial to keep objects out of
the near field region to avoid coupling the currents in the
antenna with objects.
oFar Field or Fraunhofer region:The region beyond
Fresnel region is called Fraunhofer region

Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.EffectiveAperture
8.Beamwidth and Directivity
9.The Friis Formula:Antennas in Free Space
10.Polarisation Matching

The radiation pattern of an antenna is a plot of the far-
field radiation from the antenna.More specifically
,it is a
plot of the power radiated from an antenna per unit solid
angle,or its radiation intensity U [watts per unit solid
angle].This is arrived at by simply multiplying the power
density at a given distance by the square of the distance r
,
where the power density S [watts per square metre] is
given by the magnitude of the time-averaged Poynting
vector:
U=r^²S

Radiation Intensity
Aside on Solid Angles
arclength  

 1.0rad
r
 1.0sr
surfacearea  r2
total circumfrance  2 radians o
total surface area  S  4 r2
 r2

So
sr
r2
ds  r2
sin()d d
infinitesimal area
of surface of sphere
r2
d 
ds
 sin()d d

The directivity D of an antenna,a function of direction
is defined by the ratio of radiation intensity of antenna in
direction to the mean radiation intensity in all
directions

The resistive part of the antenna impedance is split into two parts,a
radiation resistance Rr and a loss resistance Rl.The power dissipated in
the radiation resistance is the power actually radiated by the antenna,and
the loss resistance is power lost within the antenna itself.This may be due
to losses in either the conducting or the dielectric parts of the antenna.
Radiation efficiency e of the antenna as e is the ratio of power radiated
to the power accepted by antenna
antenna with high radiation efficiency therefore has high associated
radiation resistance compared with the losses.The antenna is said to be
resonant if its input reactance Xa =0.

The power gain G,or simply the gain,of an antenna is
the ratio of its radiation intensity to that
of an isotropic antenna radiating the same total power
as accepted by the real antenna.When
antenna manufacturers specify simply the gain of an
antenna they are usually referring to the
maximum value of G.

Antenna Gain
G(,)  4
U(,)
Pinput
POWERDENSITYINACERTAINDIRECTION
DIVIDEDBYTHETOTALPOWERRADIATED
POWERDENSITYINACERTAINDIRECTION
DIVIDEDBYTHETOTALINPUTPOWER
TOTHEANTENNATERMINALS(FEEDPOINTS)
IFANTENNAHASOHMICLOSS…
THEN, GAIN <DIRECTIVITY
DIRECTIVITY
GAIN

The bandwidth of an antenna expresses its ability to
operate over awide frequency range. It is often defined
as the range over which the power gain is maintained to
within 3dB of its maximum value,or the range over
which the VSWR is no greater than 2:1,whichever is
smaller.The bandwidth is usually given as a percentage of
the nominal operating frequency
.The radiation
pattern of an antenna may change dramatically outside
its specified operating bandwidth

Reciprocity theorem:
Ifa voltageisappliedtotheterminalsof an antennaAand
the current measured at the terminals of another antenna B
thenan equalcurrentwillbeobtainedattheterminalsof
antennaAifthesamevoltageisappliedtotheterminalsof
antenna B.

EffectiveAperture
If an antenna is used to receive a wave with a power density S [W m2],it will produce a
power in its terminating impedance (usually a receiver input impedance) of Pr watts.The
constant of proportionality between Pr and S isAe,the effective aperture of the antenna in
square metres:
Pr = AeS
For some antennas,such as horn or dish antennas,the aperture has an obvious physical
interpretation,being almost the same as the physical area of the antenna,but the concept is
just as valid for all antennas.The effective aperture may often be very much larger than the
physical area,especially in the case of wire antennas.Note, however
,that the effective
aperture will reduce as the efficiency of an antenna decreases.
The antenna gain G is related to the effective aperture as follows
G=4pi/ (lamda)2Ae

Effective Aperture
planewave
incident
Aphysical
Pload
?
Pload  AphysicalWinc
Question:
Answer: UsuallyNOT
inc
W

Pload
Poad
l  Aeff Winc  Aeff

The directivity of an antenna increases as its beamwidth is
made smaller,as the energy
radiated is concentrated into a smaller solid angle

P
 Dto Dro

2

r
 
Pt  4 R 


DirectivityandMaximumEffectiveAperture
(nolosses)
Antenna#2
transmit receiver
R
Directionof wavepropagation
Antenna#1
Atm, Dt
Arm, Dr

2
Aem
4
Do

DirectivityandMaximumEffectiveAperture
(includelosses)
Antenna#2
transmit receiver
R
Directionof wavepropagation
Antenna#1
Atm, Dt
Arm, Dr
* 2
a
o w
cd
em
4
D ̂  ̂
A  e (1 
2
)

2
conductorand
dielectriclosses
reflectionlosses
(impedancemismatch)
polarizationmismatch

FriisTransmissionEquation(noloss)
Antenna#2
Antenna#1
t
Pt Dgt (t ,t )
4 R2
W 
rr)
tt)
R
ThetransmittedpowerdensitysuppliedbyAntenna#1
at adistance Randdirection rr) is givenby:
Thepowercollected(received)byAntenna#2is givenby:
r
gr r r
4
( , )2
t gt t t
4 R2
t gt t t
4 R2
PD ( , ) PD ( , ) D
 Dgt (t ,t )Dgr (r ,r )

2
Pt  4 R 
P  
r
 
A 
Pr Wt Ar 

FriisTransmissionEquation(noloss)
Antenna#2
Antenna#1
rr)
tt)
R
 Dgt (t ,t )Dgr (r ,r )

2
Pt  4 R 
P  
r
 
If bothantennasarepointingin the directionof theirmaximumradiation pattern:
 DtoDro

2
r
 
Pt  4 R 
P  

The polarisation mismatch loss is the ratio between
the power received by the antenna and the power
which would be received by an antenna perfectly
matched to the incident wave

FriisTransmissionEquation: Example#1
Atypical analogcellphoneantenna hasadirectivity of3dBi atits operatingfrequencyof
800.0MHz. Thecelltoweris1mileawayandhasanantennawithadirectivity of6dBi.
Assumingthatthepowerattheinputterminalsofthetransmittingantennais0.6W,and
theantennas arealignedfor maximumradiation betweenthemandthepolarizations are
matched,findthepowerdeliveredtothereceiver.Assumethetwoantennasarewell
matchedwithanegligibleamount of loss.
r
0.375
24 1.65nW



2



P  0.6 watts
4 1609.344
* 2
2
2 2
ˆa
w
t
r
cdt cdr
t
P
max max
ˆ
4 R
Dr  
 D


Pr   
 e e (1  )(1 t )
= 0 = 0
= 1
= 1 = 1
r
t
Dmax
106/10
 4.0
Dmax
103/10
 2.0
 0.375m
3e8
f 800e6
 
c


Ahalfwavelengthdipoleantenna(max gain= 2.14dBi)isused tocommunicate froman
oldsatellitephonetoaloworbitingIridiumcommunicationsatelliteintheLband (~1.6
GHz).Assumethecommunicationsatellitehasantennathathas amaximum directivity of
24dBiandisorbiting atadistanceof 781kmabovetheearth.Assumingthatthepowerat
theinputterminalsof thetransmitting antennais 1.0W,andtheantennas arealignedfor
maximumradiationbetweenthemandthepolarizationsarematched,findthepower
deliveredtothereceiver.Assumethetwoantennasarewellmatchedwithanegligible
amountofloss.
r
 1.64251 0.15 pW


2

 0.1875
P 1.0 watts
4 781,000
* 2
2
2 2
ˆa
w
t
r
cdt cdr
t
P
max max
ˆ
4 R
Dr  
 D


Pr   
 e e (1  )(1 t )
= 0 = 0
= 1
= 1 = 1
r
t
Dmax
1024/10
 251.0
Dmax
102.14/10
1.64
 0.1875m
3e8
f 800e6
 
c


Aroof-top dishantenna(maxgain=40.0dBi) is usedtocommunicate fromanoldsatellite
phonetoaloworbiting Iridiumcommunicationsatellite in theKuband(~ 12GHz).
Assumethecommunicationsatellitehasantennathathasamaximumdirectivity of30dBi
andisorbiting atadistance of36,000kmabovetheearth. Howmuchtransmitter poweris
requiredtoreceive100pWofpoweratyourhome.Assumetheantennasarealignedfor
maximumradiationbetweenthemandthepolarizationsarematched,findthepower
deliveredtothereceiver.Assumethetwoantennasarewellmatchedwithanegligible
amountofloss.
t  82 W


 0.025 
2
P 
100 1012
watts
  10,0001000
4 36,000,000
* 2
2
2 2
ˆa
w
t
r
cdt cdr
t
P
max max
ˆ
4 R
Dr  
 D


Pr   
 e e (1  )(1 t )
= 0 = 0
= 1
= 1 = 1
t
r
Dmax
1030/10
1000.0
Dmax
1040/10
10,000
3e8
f 800e6
 
c
  0.025m

antenna2-140117111353-phpapp02.pptx

Recommended

Recommended

More Related Content

Similar to antenna2-140117111353-phpapp02.pptx

Similar to antenna2-140117111353-phpapp02.pptx (20)

More from tahaniali27

More from tahaniali27 (20)

Recently uploaded

Recently uploaded (20)

antenna2-140117111353-phpapp02.pptx