15 Feb 2001 Property of R. Struzak 1 Antenna Fundamentals (1) Prof. R. Struzak [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 February – 2 March 2001
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15 Feb 2001Property of R. Struzak1 Antenna Fundamentals (1) Prof. R. Struzak [email protected] School on Digital and Multimedia Communications.
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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
• Transmitting antenna transforms power in the form of time-dependent electrical currentinto time-and-space-dependent electro-magnetic (EM) wave.
15 Feb 2001 Property of R. Struzak 8
R-Antenna
• Receiving antenna transforms time-and-space-dependent EM wave into time-dependent electrical current (power)
15 Feb 2001 Property of R. Struzak 9
Intended Antennas
• Radiocommunication antennas– Transmitting
– Receiving
• EM applicators– Industrial
– Medical
• Measuring antennas
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)
15 Feb 2001 Property of R. Struzak 11
PFD
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
PPFD T
r
Power Flux Density (PFD)
15 Feb 2001 Property of R. Struzak 13
PFD: Distance Dependence
0.01
0.1
1
10
100
0.1 1 10
Distance
PFD
15 Feb 2001 Property of R. Struzak 14
PFD: Example 1
• What is the PFD from TV broadcast GEO satellite at Trieste?
• EIRP = 180 kW (52.5 dB(W))
• Distance: ~38'000 km• Free space )dB(Wm 100
Wm101
108.1
108.1
)1038(4
10108.1
2
2-11
16
5
26
32
PFD
15 Feb 2001 Property of R. Struzak 15
PFD: Example 2
• What is the PFD from a hand-held phone at the head?
• EIRP = 180 mW• Distance = ~3.8 cm• Free space
)dB(Wm 10
Wm10
108.1
108.1
)108.3(4
108.1
2-
2-
2
1
22
1
PFD
15 Feb 2001 Property of R. Struzak 16
PFD: Example 3
• What is the ratio of the powers required to produce the same power 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
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 on radiocommunication systems
• To assure electromagnetic compatibility • Relates to the field-strength of plane wave
15 Feb 2001 Property of R. Struzak 18
PFD Limits
• The WRC 2000 decided that the PFD at the Earth’s surface produced by emission from a space station in Fixed-satellite service shall not exceed the limit 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
[d
B(W
m^
2)]
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 ()
15 Feb 2001 Property of R. Struzak 20
Directivity and Gain
15 Feb 2001 Property of R. Struzak 21
Radiation Intensity
• Radiation intensity = Power per steradian = = (,) [watts/steradian]x
y
z
OP
Transmitting antenna r
Distance (r) is very large
• measure of the ability of an antenna to concentrate radiated power in a particular direction
15 Feb 2001 Property of R. Struzak 22
Antenna Directivity
• D Has no units• Note:
P0 = power radiated
4
),(),(),(
0PD
avg
4
intensityradiation Average
sin),(
radiatedpower Total
0avg
0
2
00
P
ddP
15 Feb 2001 Property of R. Struzak 23
Antenna Gain
• The directivity and gain are measures of the ability of an antenna to concentrate power in a particular direction.
• Directivity – power radiated by antenna (P0 )
• Gain – power delivered to antenna (PT)
: radiation efficiency (50% - 75%)
• G has no units – Usually relates to the peak
directivity of the main radiation lobe
– Often expressed in dB– Known as “Absolute Gain”
or “Isotropic Gain”
0
),(),(
P
P
DG
T
15 Feb 2001 Property of R. Struzak 24
PFD vs. Antenna Gain
S0 = PFD produced by a loss-less isotropic radiator
0
20
2
),(4
),(
),(
))((
),(),(
SGr
PG
rrrS
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]
15 Feb 2001 Property of R. Struzak 26
Antenna Gain
Actual antenna
P = Power Delivered to the antenna
S = Power receivedat a great distance
Measuring equipment
Reference antenna
Po = Power Delivered to the antenna
S = Power receivedat a great distance
Measuring equipment
Antenna Gain (in the specific direction) = P / Po
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)
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 patternin vertical plane
Radiation patternIn horizontal plane
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) in the orthogonal plan
Radiation patternin vertical plane
Radiation patternIn horizontal plane
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
15 Feb 2001 Property of R. Struzak 31
Typical Gain and Beam-widthType 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
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.
15 Feb 2001 Property of R. Struzak 33
EIRP
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
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 RR impose PFD limits of (-160) dB (W/(m2*4kHz)) at the earth surface in Equator (distance 35900 km) ?
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