Antenna PARAMETERS

Antenna PARAMETERS

1. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
RADIATION & PROPOGATIONRADIATION & PROPOGATION
--Fundamental Parameters of AntennasFundamental Parameters of Antennas
AJAL.A.J
Assistant Professor –Dept of ECE,
UNIVERSAL ENGINEERING COLLEGE

Mob: [phone] MAIL: [email protected]

2. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
An antenna is a way of converting the guided waves
present in a waveguide, feeder cable or transmission line
into radiating waves travelling in free space, or vice
versa.

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

4. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Only accelerating charges produce radiation.


Idealized
Point Radiator Vertical Dipole Radar Dish
Isotropic
Omnidirectional Directional

5. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
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

6. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

7. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
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

8. Radiation IntensityRadiation Intensity
Aside on Solid Angles
r
r=lengtharc
rad0.1=q
r
sr0.1=W
2
rareasurface=
radianscecircumfrantotal p2=
22
4 rrSareasurfacetotal
o
W=== p
sr
r
S
o
2
=W
fqqddrds )sin(
2
=
infinitesimal area
of surface of sphere
fqqdd
r
ds
d )sin(
2
==W

9. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

10. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
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.

11. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

12. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
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.

13. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

14. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
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.

15. Antenna GainAntenna Gain
input
P
U
G
),(
4),(
jq
pjq=
POWER DENSITY IN A CERTAIN DIRECTION
DIVIDED BY THE TOTAL POWER RADIATED
POWER DENSITY IN A CERTAIN DIRECTION
DIVIDED BY THE TOTAL INPUT POWER
TO THE ANTENNA TERMINALS (FEED POINTS)
IF ANTENNA HAS OHMIC LOSS…
THEN, GAIN < DIRECTIVITY
DIRECTIVITY
GAIN

16. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

17. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
The bandwidth of an antenna expresses its ability to
operate over a wide 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.

18. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

19. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Reciprocity theorem:
If a voltage is applied to the terminals of an antenna A and
the current measured at the terminals of another antenna B
then an equal current will be obtained at the terminals of
antenna A if the same voltage is applied to the terminals of
antenna B.

20. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

21. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Effective ApertureEffective Aperture
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 is Ae, 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

22. Effective ApertureEffective Aperture
plane wave
incident
A
physicalP
load
incphysicalload WAP
?
=Question:
Answer: Usually NOT
inc
load
effinceffload
W
P
AWAP =Þ=

23. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

24. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
The directivity of an antenna increases as its beamwidth is
made smaller, as the energy
radiated is concentrated into a smaller solid angle

25. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

26. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
roto
t
r
DD
RP
P
2
4
÷
÷
ø
ö
ç
ç
è
æ
=
p
l

27. Directivity and Maximum Effective Aperture Directivity and Maximum Effective Aperture
(no losses)(no losses)
Antenna #2
transmit
receiver
R
Direction of wave propagation
Antenna #1
A
tm
, D
t
A
rm
, D
r
oem
DA
p
l
4
2
=

28. Directivity and Maximum Effective Aperture Directivity and Maximum Effective Aperture
(include losses)(include losses)
Antenna #2
transmit
receiver
R
Direction of wave propagation
Antenna #1
A
tm
, D
t
A
rm
, D
r
2
*
2
2
ˆˆ
4
)1(
awocdem DeA rr
p
l
×G-=
conductor and
dielectric losses
reflection losses
(impedance mismatch)
polarization mismatch

29. Friis Transmission Equation (no loss)Friis Transmission Equation (no loss)
Antenna #2
Antenna #1
R
tra
n
sm
it
A
tm, D
t
receiver
A
rm, D
r
The transmitted power density supplied by Antenna #1
at a distance R and direction (q
r
,f
r
) is given by:
2
4
),(
R
DP
W
ttgtt
t
p
jq
=
(q
t
,f
t
)
(q
r
,f
r
)
The power collected (received) by Antenna #2 is given by:
),(),(
4
4
),(
4
),(
4
),(
2
2
22
rrgrttgt
t
r
rrgrttgtt
r
ttgtt
rtr
DD
RP
P
D
R
DP
A
R
DP
AWP
jqjq
p
l
p
ljq
p
jq
p
jq
÷
÷
ø
ö
ç
ç
è
æ
=
===

30. Friis Transmission Equation (no loss)Friis Transmission Equation (no loss)
Antenna #2
Antenna #1
R
tra
n
sm
it
A
tm, D
t
receiver
A
rm, D
r
(q
t
,f
t
)
(q
r
,f
r
)
),(),(
4
2
rrgrttgt
t
r
DD
RP
P
jqjq
p
l
÷
÷
ø
ö
ç
ç
è
æ
=
If both antennas are pointing in the direction of their maximum radiation pattern:
roto
t
r
DD
RP
P
2
4
÷
÷
ø
ö
ç
ç
è
æ
=
p
l

31. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
Antenna parameters are:
1.Radiation Pattern
2.Directivity
3.Radiation Resistance and Efficiency
4.Power Gain
5.Bandwidth
6.Reciprocity
7.Effective Aperture
8.Beamwidth and Directivity
9.The Friis Formula: Antennas in Free Space
10.Polarisation Matching

32. AJAL.A.J- AP ECE UNIVERSAL ENGG COLLEGE
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

33. AppendicesAppendices

34. Friis Transmission Equation: Example #1Friis Transmission Equation: Example #1
A typical analog cell phone antenna has a directivity of 3 dBi at its operating frequency of
800.0 MHz. The cell tower is 1 mile away and has an antenna with a directivity of 6 dBi.
Assuming that the power at the input terminals of the transmitting antenna is 0.6 W, and
the antennas are aligned for maximum radiation between them and the polarizations are
matched, find the power delivered to the receiver. Assume the two antennas are well
matched with a negligible amount of loss.
nWwattsP
r
65.142
609.344 14
375.0
6.0
2
=××÷
ø
ö
ç
è
æ
×
×=
p
2
*maxmax
2
22
ˆˆ
4
)1)(1(
awrttrcdrcdt
t
r
DD
R
ee
P
P
rr
p
l
×
÷
÷
ø
ö
ç
ç
è
æ
G-G-=
= 0
= 0
= 1
= 1
= 1
0.410
0.210
375.0
6800
83
10/6max
10/3max
==
==
===
r
t
D
D
m
e
e
f
c
l

35. Friis Transmission Equation: Example #2Friis Transmission Equation: Example #2
A half wavelength dipole antenna (max gain = 2.14 dBi) is used to communicate from an
old satellite phone to a low orbiting Iridium communication satellite in the L band (~ 1.6
GHz). Assume the communication satellite has antenna that has a maximum directivity of
24 dBi and is orbiting at a distance of 781 km above the earth. Assuming that the power at
the input terminals of the transmitting antenna is 1.0 W, and the antennas are aligned for
maximum radiation between them and the polarizations are matched, find the power
delivered to the receiver. Assume the two antennas are well matched with a negligible
amount of loss.
pWwattsP
r 15.025164.1
781,0004
1875.0
0.1
2
=××÷
ø
ö
ç
è
æ
×
×=
p
2
*maxmax
2
22
ˆˆ
4
)1)(1(
awrttrcdrcdt
t
r
DD
R
ee
P
P
rr
p
l
×
÷
÷
ø
ö
ç
ç
è
æ
G-G-=
= 0
= 0
= 1
= 1
= 1
0.25110
64.110
1875.0
6800
83
10/24max
10/14.2max
==
==
===
r
t
D
D
m
e
e
f
c
l

36. Friis Transmission Equation: Example #2Friis Transmission Equation: Example #2
A roof-top dish antenna (max gain = 40.0 dBi) is used to communicate from an old satellite
phone to a low orbiting Iridium communication satellite in the Ku band (~ 12 GHz).
Assume the communication satellite has antenna that has a maximum directivity of 30 dBi
and is orbiting at a distance of 36,000 km above the earth. How much transmitter power is
required to receive 100 pW of power at your home. Assume the antennas are aligned for
maximum radiation between them and the polarizations are matched, find the power
delivered to the receiver. Assume the two antennas are well matched with a negligible
amount of loss.
W
watts
P
t 82
1000000,10
36,000,0004
025.0
10100
2
12
=
××÷
ø
ö
ç
è
æ
×
×
=
-
p
2
*maxmax
2
22
ˆˆ
4
)1)(1(
awrttrcdrcdt
t
r
DD
R
ee
P
P
rr
p
l
×
÷
÷
ø
ö
ç
ç
è
æ
G-G-=
= 0
= 0
= 1
= 1
= 1
0.100010
000,1010
025.0
6800
83
10/30max
10/40max
==
==
===
t
r
D
D
m
e
e
f
c
l