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2001 APCO/NENA State Training Conference
January 19, 2001
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An Antenna is :An Antenna is :
An An effective interface between the radio and free space:
Radio Antenna
Free space
For Terrestrial Communications, a antennas must be directional:
Radio
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Terrestrial Microwave Antennas for Point-To-Point Communication
• Terrestrial microwave antennas generate a beam of RF signal to communicate between two locations.
• Point-To-Point communication depends upon a clear line of sight between two microwave antennas.
• Obstructions, such as buildings, trees or terrain interfere with the signal.
• Depending upon the location, usage and frequency, different types can be utilized.
• We will address the basic characteristics of these various types…
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Gain
Front to Back Ratio (F/B)
Radiation Pattern Envelope
Cross-Polar Discrimination (XPD)
Return Loss (VSWR)
Interport Isolation (IPI)
Electrical Performance Parameters
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Ga (dBi) = 10 log10 [ 4Aa /
Where:
Ga = Antenna Directive Gain (Catalog spec)
= Aperture Efficiency (50-55%)
Aa = Antenna Aperture Area
= Wavelength (speed of light / frequency)
Parabolic AntennaDirective Gain
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Typical ParabolicTypical ParabolicAntenna Gain in dBiAntenna Gain in dBi
Antenna Diameter
Fre
qu
ency
2 ft(0.6m)
4 ft(1.2m)
6 ft(1.8m)
8 ft(2.4m)
10 ft(3.0m)
12 ft(3.7m)
15 ft(4.5m)
2 GHz 19.5 25.5 29.1 31.6 33.5 35.1 37
4 GHz 25.5 31.6 35.1 37.6 39.5 41.1 43.1
6 GHz 29.1 35.1 38.6 41.1 43.1 44.6 46.6
8 GHz 31.6 37.6 41.1 43.6 45.5 47.1 49.1
11 GHz 34.3 40.4 43.9 46.4 48.3 49.9 51.8
15 GHz 37 43.1 46.6 49.1 51 52.6 N A
18 GHz 38.6 44.6 48.2 50.7 N A N A N A
22 GHz 40.4 46.4 49.9 N A N A N A N A
38 GHz 45.1 51.1 N A N A N A N A N A
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Radiation Pattern ConceptRadiation Pattern Concept
Antenna Under Test
Source Antenna
Antenna Test Range
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Radiation PatternRadiation Patternabout Bore sightabout Bore sight
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Cut Through Radiation Pattern at Cut Through Radiation Pattern at BoresightBoresight
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Front to Back RatioFront to Back Ratio
• Ratio of the signal level at beam peak to that directed behind the antenna
• Considered in intra-system interference calculation (hop overreach)
• Expressed in dB
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Co-Polarization and Co-Polarization and Cross-Polarization Cross-Polarization
Co-polarized antenna pattern
Azimuth AngleR
ela
tiv
e P
ow
er
X-polarized patttern
• Co-Polarization
– Where Transmit & Receive Antennas have the Same Polarization
– Either Horizontal or Vertical (HH or VV)
– In your System, The Wanted Signal
• Cross-Polarization– Where Transmit & Receive Antennas
have Different Polarizations
– Either HV or VH.
– In your System, The Unwanted Signal
XPD
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Inter-port Isolation (IPI)Inter-port Isolation (IPI)
• Leakage of Signal Between Antenna Ports
• Internal Noise
• Expressed in dBTowards Reflector
Transmit Signal
Leakage Signal
Feed Horn
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Voltage Standing Wave Ratio Voltage Standing Wave Ratio (VSWR)(VSWR)
• VSWR : 1.30 Reflection Coefficient : 13% (0.13)
• VSWR : 1.20 Reflection Coefficient : 9.1% (0.091)
• VSWR : 1.10 Reflection Coefficient : 4.7% (0.047)
• VSWR : 1.08 Reflection Coefficient : 3.8% (0.038)
• VSWR : 1.06 Reflection Coefficient : 2.9% (0.029)
VSWR = 1 + (Reflection Coefficient) 1 - (Reflection Coefficient)
Reflected Signal
Incident Signal
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Return Loss Return Loss The Amount of Energy The Amount of Energy LostLost due to Reflected ( due to Reflected (Returned) Returned) SignalSignal
• RL : 17.8dB Reflection : 13% (0.13) VSWR : 1.30
• RL : 20.8dB Reflection : 9.1% (0.091) VSWR : 1.20
• RL : 26.7dB Reflection : 4.7% (0.047) VSWR : 1.10
• RL : 28.4dB Reflection : 3.8% (0.038) VSWR : 1.08
• RL : 30.7dB Reflection : 2.9% (0.029) VSWR : 1.06
RL = -20 x log (Reflection Coefficient)
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Basic Antenna TypesBasic Antenna Types
Standard Standard Parabolic Parabolic AntennaAntenna
Shielded Shielded AntennaAntenna
GRIDPAKGRIDPAK®® AntennaAntenna
Focal Plane Focal Plane AntennaAntenna
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GRIDPAKGRIDPAK®® Antenna Antenna
• Grid Reflector
• Low Wind load
• Single Polarized
• Below 2.7GHz
• Shipped in Flat, Lightweight Package
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Standard Parabolic AntennaStandard Parabolic Antenna
• Basic Antenna
• Comprised of
– Reflector
– Feed Assembly
– Mount
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Focal Plane AntennaFocal Plane Antenna
• Deeper Reflector
• Edge Geometry
• Improved F/B Ratio
• Slightly Lower Gain
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Shielded AntennaShielded Antenna
• Absorber-Lined Shield
• Improved Feed System
• Planar Radome
• Improved RPE
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Antenna EfficiencyAntenna Efficiency
Well-designed antennas have efficiency ratings of 45 - 65%
Efficiency Factor Affected By :
• Feed Illumination
• Aperture Blockage
• Reflector Surface Tolerance
Efficiency can never be 100%
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f
D
f/D = 0.250
Antenna f/D RatioAntenna f/D Ratio
f
D
f/D = 0.333
Standard & Shielded Antennas
Focal Plane Antennas
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Unwanted SignalsUnwanted Signals
Scattering
Diffraction
Spillover
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Front to Back RatioFront to Back Ratio
Direction of Signal
Direction of Signal
Direction of Signal
Shielded Shielded AntennaAntenna
Focal Plane Focal Plane AntennaAntenna
Standard Parabolic Standard Parabolic Antenna Antenna
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Parabolic Reflector BeamwidthParabolic Reflector Beamwidth
0.3 m 0.6 m 1.2 m 1.8 m 2.4 m 3 m 3.7 m 4.5 m
2 GHz 35 17.5 8.75 5.83 4.38 3.5 2.84 2.33
6 GHz 11.67 5.83 2.92 1.94 1.46 1.17 0.95 0.78
8 GHz 8.75 4.38 2.19 1.46 1 0.88 0.71 0.58
11 GHz 6.36 3.18 1.59 1 0.8 0.64 0.52 0.42
14 GHz 5 2.5 1.25 0.83 0.63 0.5 0.41 0.33
18 GHz 3.89 1.94 0.97 0.65 0.49 0.39 0.32 0.26
23 GHz 3 1.52 0.76 0.51 0.38 0.3 0.25 0.2
38 GHz 1.84 0.92 0.46 0.31 0.23 0.18 0.15 0.12
Beamwidth in Degrees
Diameter
Fre
qu
en
cy
3dB
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0
10
20
30
40
50
60
70
80
90
100
0 10 15 205 4060 80 100 120 140 160 180
Azimuth - Degrees from Main Lobe
An
ten
na
Dir
ecti
vity
dB
do
wn
fro
m M
ain
Lo
be
Radiation Pattern Envelope
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Radomes
• Reduce Windloading on Tower
• Protection Against Ice, Snow and Dirt
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Other Antenna Options
High XPD antennas
Dual beam antennas
Dual band antennas
Low profile antennas
Integrated antennas