Antenna Basics 1
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Transcript of Antenna Basics 1
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15 Feb 2001 Property of R. Struzak 1
Antenna Fundamentals (1)
Prof. R. [email protected]
School on Digital and Multimedia Communications Using Terrestrial and Satellite Radio Links
The Abdus Salam International Centre for Theoretical Physics ICTP Trieste (Italy) 12 February2 March 2001
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15 Feb 2001 Property of R. Struzak 2
Note: These materials may be used for study,research, and education in not-for-profitapplications. If you link to or cite these materials,please credit the author, Ryszard Struzak. Thesematerials may not be published, copied to orissued from another Web server without theauthor's express permission. Copyright 2001
Ryszard Struzak. All commercial rights arereserved. If you have comments or suggestions,please contact the author [email protected].
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15 Feb 2001 Property of R. Struzak 3
Summary Slide
Introduction
PFD
Directivity and Gain
EIRP
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15 Feb 2001 Property of R. Struzak 4
Introduction
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15 Feb 2001 Property of R. Struzak 5
Radio Link
Antenna
Transmitter
Antenna
Receiver
Antennas: important elements of any radio link
Radio wave
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15 Feb 2001 Property of R. Struzak 6
Photographs
ofVarious Antenna Types
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15 Feb 2001 Property of R. Struzak 7
T-Antenna
Transmitting antenna transforms
power in the form of time-dependent electrical current
intotime-and-space-dependent electro-magnetic (EM)
wave.
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15 Feb 2001 Property of R. Struzak 8
R-Antenna
Receiving antenna transformstime-and-space-dependent EM wave
intotime-dependent electrical current (power)
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15 Feb 2001 Property of R. Struzak 9
Intended Antennas
Radiocommunication antennas
Transmitting
Receiving EM applicators
Industrial
Medical
Measuring antennas
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15 Feb 2001 Property of R. Struzak 10
Unintended Antennas
Any conductor/ installation carrying electrical
current
(e.g. electrical installation of vehicles) Any conducting structure/ installation irradiated by
EM waves
Permanent (e.g. Antenna masts, or power network)
Time-varying (e.g. Windmills, or helicopter propellers)
Transient (e.g. Re-radiating aeroplane)
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15 Feb 2001 Property of R. Struzak 11
PFD
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15 Feb 2001 Property of R. Struzak 12
PFD: Isotropic Radiator
Notes
Loss-less propagation medium
assumed Isotropic radiator cannot be
physically realized
PFD does not depend on
frequency/ wavelength
24 r
P
PFDT
r
Power Flux Density (PFD)
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15 Feb 2001 Property of R. Struzak 13
PFD: Distance Dependence
0.01
0.1
1
10
100
0.1 1 10
Distance
PFD
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15 Feb 2001 Property of R. Struzak 14
PFD: Example 1
What is the PFD fromTV broadcast GEOsatellite at Trieste?
EIRP = 180 kW(52.5 dB(W))
Distance: ~38'000 km Free space
)dB(Wm100
Wm101
108.1
108.1
)1038(4
10108.1
2
2-11
16
5
26
32
PFD
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15 Feb 2001 Property of R. Struzak 15
PFD: Example 2
What is the PFDfrom a hand-held
phone at the head?
EIRP = 180 mW
Distance = ~3.8 cm
Free space)dB(Wm10
Wm10
108.1
108.1
)108.3(4
108.1
2-
2-
2
1
22
1
PFD
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15 Feb 2001 Property of R. Struzak 16
PFD: Example 3
What is the ratio of the
powers required to
produce the samepower flux density at a
GEO- satellite and at a
LEO-satellite.?
Distances: GEO: 38 000 km
LEO: 1 000 km
14441000
380002
2
LEO
GEO
GEO
LEO
LEO
GEO
LEO
GEO
P
P
Dist
Dist
P
P
PFD
PFD
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15 Feb 2001 Property of R. Struzak 17
PFD concept
Used often in the management/ regulating the use
of the radio frequency spectrum
To define the restrictions imposed onradiocommunication systems
To assure electromagnetic compatibility
Relates to the field-strength of plane wave
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15 Feb 2001 Property of R. Struzak 18
PFD Limits
The WRC 2000 decided that the
PFD at the Earths surface
produced by emission from a
space station in Fixed-satellite
service shall not exceed thelimit shown in the figure.
The figure is valid for stations
at the geostationary orbit in
frequency band 10.7-11.7 GHz
and reference band 4 kHz. For
other cases see RR Table S21-4. -152
-150
-148
-146
-144
-142
-140
-138
0 10 20 30 40 50 60 70 80 90
Angle of arrival (above the horizontal plane)
PFD[dB(Wm^2)]
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15 Feb 2001 Property of R. Struzak 19
PFD: Real Antenna
PFD produced by physically realizable
antennas depends on
power and distance (as isotropic source)
horizontal direction angle ()
vertical direction angle ()
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15 Feb 2001 Property of R. Struzak 20
Directivity and Gain
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15 Feb 2001 Property of R. Struzak 21
Radiation Intensity
Radiation intensity =Power
per steradian ==(,) [watts/steradian]
x
y
z
OPTransmitting
antennar
Distance (r) is very large
measure of the ability
of an antenna to
concentrate radiated
power in a particular
direction
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15 Feb 2001 Property of R. Struzak 22
Antenna Directivity
D Has no units
Note:
P0 = power radiated
4
),(),(),(
0P
Davg
4
intensityradiationAverage
sin),(
radiatedpowerTotal
0avg
0
2
00
P
ddP
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15 Feb 2001 Property of R. Struzak 23
Antenna Gain
The directivity and gain
are measures of the ability
of an antenna toconcentrate power in a
particular direction.
Directivitypower
radiated by antenna (P0 ) Gainpower delivered to
antenna (PT)
: radiation efficiency(50% - 75%)
G has no units
Usually relates to the peakdirectivity of the mainradiation lobe
Often expressed in dB
Known as AbsoluteGain or Isotropic Gain
0
),(),(
P
P
DG
T
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15 Feb 2001 Property of R. Struzak 24
PFD vs. Antenna Gain
S0 = PFD produced by a loss-less isotropic radiator
0
2
0
2
),(
4),(
),(
))((
),(),(
SG
r
PG
rrrS
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15 Feb 2001 Property of R. Struzak 25
Other Definitions of Gain
For practical purposes, the antenna gain is defined as the
ratio (usually in dB), of the power required at the input of a
loss-free reference antenna to the power supplied to the
input of the given antenna to produce, in a given direction,the same field strength or the same power flux-density at
the same distance.
When not specified otherwise, the gain refers to the
direction of maximum radiation. The gain may be considered for a specified polarization.
[RR 154]
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15 Feb 2001 Property of R. Struzak 26
Antenna Gain
Actual
antenna
P = Power
Delivered to
the antenna
S = Power
received
at a great
distance
Measuring
equipment
Reference
antenna
Po = Power
Delivered to
the antenna
S = Power
received
at a great
distance
Measuring
equipment
Antenna Gain (in the specific direction) = P / Po
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15 Feb 2001 Property of R. Struzak 27
Reference Antennas
Isotropic radiator
isolated in space (Gi, absolute gain, or isotropic gain)
Half-wave dipole isolated in space, whose equatorial plane of symmetry
contains the given direction (Gd)
Short vertical antenna
(much shorter than /4), close to, and normal to a
perfectly conducting plane which contains the given
direction (Gv)
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15 Feb 2001 Property of R. Struzak 28
Reference Antennas (1)
Isotropic antenna
Sends (receives) energy
equally in (from) all
directions
Gain = 1 (= 0 dB)
When supplied by P,
produces at distance r power
flux density = P /(4r2)
Theoretical concept, cannot
be physically realized
Radiation pattern
in vertical plane
Radiation pattern
In horizontal plane
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15 Feb 2001 Property of R. Struzak 29
Reference Antennas (2)
Half-Wave Dipole
Linear antenna, realizable
Gain = 1.64 (= 2,15 dB) in
the direction of maximum
radiation
Figure-eight-shaped radiation
pattern in the dipole plane,
omnidirectional (circular) inthe orthogonal plan
Radiation pattern
in vertical plane
Radiation pattern
In horizontal plane
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15 Feb 2001 Property of R. Struzak 30
Typical radiation pattern
Omnidirectional
Broadcasting
Mobile telephony Pencil-beam
Microwave links
Fan-beam (narrow in one plane, wide in the other)
Shaped-beam
Satellite antennas
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15 Feb 2001 Property of R. Struzak 31
Typical Gain and Beam-width
Type of antenna Gi[dB] HPBW [0]
Isotropic 0 360x360
Dipole 2 360x120
Helix (10 turn) 14 35x35
Small dish 16 30x30
Large dish 45 1x1
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15 Feb 2001 Property of R. Struzak 32
Gain and Beam-width
Gain and beam-width of directive antennas are
inter-related
G ~ 30000 / (1*2)
1 and 2 are the 3-dB beam-widths (in degrees)in the two orthogonal principal planes of antenna
radiation pattern.
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15 Feb 2001 Property of R. Struzak 33
EIRP
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15 Feb 2001 Property of R. Struzak 34
e.i.r.p.
Equivalent Isotropically Radiated
Power (in a given direction):
The product of the power supplied to the
antenna and the antenna gain relative to
an isotropic antenna in a given direction
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15 Feb 2001 Property of R. Struzak 35
e.i.r.p.: Example 1
PFD = e.i.r.p./(4d2)
e.i.r.p. = PFD*(4d2)
-160 dB 10-16 W/(m2*4kHz)
d2 ~ 1.29*1015m2
4d2 ~ 4*1015m2
e.i.r.p. ~ 0.4 W/4kHz
What is the maximum
e.i.r.p. of a GEO
satellite station if RRimpose PFD limits of
(-160) dB
(W/(m2*4kHz)) at the
earth surface inEquator (distance
35900 km) ?
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15 Feb 2001 Property of R Struzak 36
e.r.p.
Effective Radiated Power (in a given
direction):
The product of the power supplied to the
antenna and its gain relative to a half-wave
dipole in a given direction