15 Feb 2001Property of R. Struzak1 Antenna Fundamentals (2) R. Struzak [email protected]...
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Transcript of 15 Feb 2001Property of R. Struzak1 Antenna Fundamentals (2) R. Struzak [email protected]...
15 Feb 2001 Property of R. Struzak 1
Antenna Fundamentals (2)
School on Digital and Multimedia Communications Using Terrestrial and Satellite Radio LinksThe Abdus Salam International Centre for Theoretical Physics ICTP Trieste (Italy) 12 February – 2 March 2001
15 Feb 2001 Property of R. Struzak 2
• Note: These materials may be used for study, research, and education in not-for-profit applications. If you link to or cite these materials, please credit the author, Ryszard Struzak. These materials may not be published, copied to or issued from another Web server without the author's express permission. Copyright © 2001 Ryszard Struzak. All commercial rights are reserved. If you have comments or suggestions, please contact the author at [email protected].
15 Feb 2001 Property of R. Struzak 3
Summary Slide
• Power Transfer
• EM Field
• Linear Antenna
• Radiation Resistance
• Radiation Pattern
15 Feb 2001 Property of R. Struzak 5
Antenna Effective Area
• Measure of the effective absorption area presented by an antenna to an incident plane wave.
• Depends on the antenna gain and wavelength
][m ),(4
22
GAe
Aperture efficiency: a = Ae / AA: physical area of antenna’s aperture, square meters
15 Feb 2001 Property of R. Struzak 6
Power Transfer in Free Space
: wavelength [m]
• PR: power available at the receiving antenna
• PT: power delivered to the transmitting antenna
• GR: gain of the transmitting antenna in the direction of the receiving antenna
• GT: gain of the receiving antenna in the direction of the transmitting antenna
• Matched polarizations
2
2
2
4
44
rGGP
G
r
PG
APFDP
RTT
RTT
eR
15 Feb 2001 Property of R. Struzak 7
Power Transfer: Example 1
• What is the power received from GEO satellite (=0.1m, PT =440 W, GT=1000) at Trieste (distance ~38'000 km, GR=1)?
• Free spacedB(W) 150
W101
104.4
10104.4
10384
1.010104.4
4
15
18
25
2
632
2
r
GGPP RTTR
15 Feb 2001 Property of R. Struzak 8
Power Transfer: Example 2
• What is the power from a transmitter (=0.1m, PT=440 mW, GT=1) received at distance of 3.8 cm (GR=1)?
• Free space )dB(W 50
W10
104.4
104.4
108.34
1.011104.4
4
5
8
3
2
21
2
r
GGPP RTTR
15 Feb 2001 Property of R. Struzak 10
EM Field of Linear Current Element
x
y
z
OP
r
ErE
E
HHHH
EEEE
r
r
dz: electric current element (short electrical dipole)
dz222
222
HHHH
EEEE
r
r
15 Feb 2001 Property of R. Struzak 11
EM Field of Current Element
2
0
)(sin120
)(cos2
)(sin
HHE
eQFFjA
H
eCQAE
eCjQFFjAE
r
rj
rjr
rj
3
2
2
)(
1
)(
1
1
30
rC
rQ
rFF
IdzA
Johnson & Jasik: Antenna Engineering Handbook; T. Dvorak: Basics of Radiation Measurements, EMC Zurich 1991; J. Dunlop, D. Smith Telecommunications Engineering1995, p. 216
Idz: “moment of linear current element”
15 Feb 2001 Property of R. Struzak 12
Field Components
0.001
0.01
0.1
1
10
100
1000
0.1 1 10
Relative distance
Rel
ativ
e fi
eld
stre
ng
th
FF
FF
Q
Q
C
C
15 Feb 2001 Property of R. Struzak 13
Field ImpedanceField impedance
Z = E/H depends
on the antenna type and on distance
0.01
0.1
1
10
100
0.01 0.1 1 10 100
Distance / (lambda/ 2Pi)
Z /
377
Short dipole
Small loop
15 Feb 2001 Property of R. Struzak 14
Far-Field, Near-Field • Near-field region:
– Angular distribution of energy depends on distance from the antenna;
– Reactive field components dominate (L, C)
• Far-field region: – Angular distribution of energy is independent on
distance;
– Radiating field component dominates (R)
15 Feb 2001 Property of R. Struzak 15
EM Field: Elementary Current Loop
2
0
)(sin
)(cos2
)(sin120
EEH
eQFFBE
eCQBH
eCjQFFBH
r
rj
rjr
rj
LoopAreaIdm
dmB
4
3
dm: “magnetic dipole moment”
15 Feb 2001 Property of R. Struzak 17
Arbitrary Linear Antenna
• I(z): antenna current • r: distance
2
2
)()(sin60
l
l
zrjdzezIr
jE
15 Feb 2001 Property of R. Struzak 18
EM Field of Linear Antennas
• Summation of vector components E (or H) produced by every antenna element
• In the far-field region, the vector componentsare parallel to each other
...
...
321
321
HHHH
EEEE
O
15 Feb 2001 Property of R. Struzak 19
Very Short Antenna
• r: distance• Le: effective length of antenna
2
20
)(0
2
2
)(
)(1
sin60
)(sin60
l
l
e
zrje
l
l
zrj
dzzII
L
eLIr
jE
dzezIr
jE
15 Feb 2001 Property of R. Struzak 21
Self- Impedance
• Transmitting antenna • Receiving antenna
jX: energy stored in near-field components (E C, H L)
Rrad: energy radiated
Rlos: energy loss
ZZ
E
E = Electromotive force (open-circuit voltage) induced by radio wave
15 Feb 2001 Property of R. Struzak 22
Short Antenna Radiation Resistance • The PFD in the far
field is given by the Poynting’s vector = |= E|2/(120)
• Antenna radiation resistance = = 802(Le/)2
– For other antennas it is much easier to measure the antenna impedance. 2
0
22
0
320
22
2
2
0
80
sin60
sin2
120
sin60
IL
P
dIL
P
drdS
dSE
P
r
LIE
e
e
S
e
15 Feb 2001 Property of R. Struzak 25
Radiation Pattern
• Radiation Intensity = Power per steradian radiated in a given direction
• Radiation Pattern = Radiation Intensity as function of the azimuth/ elevation angles
• Generally 3 dimensional
15 Feb 2001 Property of R. Struzak 26
Short Dipole in Free Space FF
0
1
0 90 180 270 360
Degrees
Re
lati
ve G
ain
H
V
Horizontal plane: GVi /GVimax = 1
Vertical plane: GHi /GHimax = |sin |
-11
15 Feb 2001 Property of R. Struzak 27
Elements of Radiation Pattern
0-180 180
Emax
Emax /2
Beamwidth
Sidelobes
Nulls
Main lobe • Gain
• Beam width
• Nulls (positions)
• Side-lobe levels (envelope)
• Front-to-back ratio
15 Feb 2001 Property of R. Struzak 28
Long Antenna with Sinusoidal Current Distribution
r: distance
sin2
coscos2
cos60
cossin60
cos)(
cos)(
0
2
2
cos0
0
ll
r
eIjE
dzzeeIr
jE
zrzr
zIzI
rj
l
l
zjrjz
z cos
r(z)
r
15 Feb 2001 Property of R. Struzak 29
Demonstration (Simulation)
LinAntLongThis program simulates radiation pattern of
linear antenna of arbitrary length. It produces 2D radiation diagrams that
show how the positions and magnitudes of radiation lobes, and positions of zeros
depend on the antenna length
15 Feb 2001 Property of R. Struzak 30
Half-wave Dipole (l = /2)
• Radiation resistance = 73.1 ohm
sin
cos2
cos60 0
r
eIjE
rj
15 Feb 2001 Property of R. Struzak 31
Half-wave Dipole at Harmonics
0
0.5
1
1.5
-180 -90 0 90 180
Elevation angle, degrees
Re
lati
ve F
ield
-str
en
gth
3rd harmonic
Fundamental
).1,...(1,0);12/(2cos
cos)2/)(12(max)(
.,...1,0);12/()12(cos
)2/)(12(
cos)2/)(12(0)(sin
cos)2/)(12(cos)(
)12()2/(
sin
coscoscos)(
nknk
knf
nknk
k
nf
nf
nL
LL
f
Odd harmonics
15 Feb 2001 Property of R. Struzak 32
Antenna Mask (Example 1)• Typical
relative directivity- mask of receiving antenna (Yagi ant., TV dcm waves)
[CCIR doc. 11/645, 17-Oct 1989)
-20
-15
-10
-5
0
-18
0
-12
0
-60 0
60
12
0
18
0
Azimith angle, degrees
Iso
tro
pic
gai
n, d
B
15 Feb 2001 Property of R. Struzak 33
Antenna Mask (Example 2)
-50
-40
-30
-20
-10
0
0.1 1 10 100
Phi/Phi0
Re
lati
ve g
ain
(d
B)
RR/1998 APS30 Fig.9
COPOLAR
CROSSPOLAR
Reference pattern for co-polar and cross-polar components for satellite transmitting antennas in Regions 1 and 3 (Broadcasting ~12 GHz)
0dB
-3dB
Phi0/2
Phi