1. Radio Propagation at 90 GHz
Vilhelm Gregers-Hansen
Radar Division
Naval Research Laboratory
Presented at FCC Forum:
“New Horizons : 90 GHz Technologies”
July 14, 2000
07/12/2000
FCC Forum 90 GHz.PPT

2. Overview Propagation effects and 90 GHz Dry air atmosphere Water vapor
Fog and clouds
Rain
Other effects
Summary
07/12/2000
FCC Forum 90 GHz.PPT

3. Propagation Effects Molecular absorption in gas
Oxygen, water vapor
Extinction due to particles
Clouds, fog
Rain, snow, hail
Dust, sand
Refraction
Anomalous propagation
Fading along propagation path
07/12/2000
FCC Forum 90 GHz.PPT

4. Atmospheric Attenuation Versus Frequency
oxygen & H2O
High Attenuation (>1 dB/km)
Low Attenuation (<1 dB/km)
fog & clouds IR
Visible
W-Band
rain
Ka-Band
GHz
GHz
GHz
Microwave
mm-wave
IR and Visible
07/12/2000
FCC Forum 90 GHz.PPT

5. Dry Atmosphere at Low Altitude
Barometric pressure ~ 1013 mB
Temperature -30 to +35 C
Relative humidity RH= 0%
Nitrogen 78%
Oxygen 21%
Other 1%
07/12/2000
FCC Forum 90 GHz.PPT

6. Dry Atmosphere Attenuation at Low Altitude - 1
100 50 20 10 5 2
Specific Attenuation - g (dB/km) 1
0.5
0.2
0.1
0.05
Dry Air
0.02
0.01 10 20 40 70
100
200
400
700
1000
Frequency - f (GHz)
07/12/2000
FCC Forum 90 GHz.PPT

7. Dry Atmosphere Attenuation Low Altitude - 2
100 50 20 10 5 2 1
Specific Attenuation - g (dB/km)
0.5
0.2
0.1
0.05
Dry Air
0.02
0.01 50 60 70 80 90
100
110
120
130
140
150
Frequency - f (GHz)
07/12/2000
FCC Forum 90 GHz.PPT

8. Water Vapor Characterization
Standard Definition:
Temperature (T C)
Relative humidity (RH %)
g/m3 10
What really matters:
RH=100%
Water vapor concentration in g/m3 1
RH=5%
0.1 C
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FCC Forum 90 GHz.PPT

9. Effect of Water Vapor and Oxygen
RH= 50%
100
T= 40ºC
T= 30ºC
T= 20ºC
T= 10ºC
T= 0ºC 50 20 10 5 2
Specific Attenuation -  (dB/km) 1
0.5
0.2
0.1
0.05
Dry Air
0.02
0.01 10 20 40 70
100
200
400
700
1000
Frequency - f (GHz)
07/12/2000
FCC Forum 90 GHz.PPT

10. Specific Attenuation Due to Oxygen and Water Vapor
100
Sea Level (1013 mB) 10 1
Specific Attenuation - g (dB/km)
T=20ºC and RH=50%
0.1
0.01
T=20ºC and RH=0%
0.001 20 40 60 80
100
120
140
160
180
200
Frequency - f (GHz)
07/12/2000
FCC Forum 90 GHz.PPT

11. Attenuation vs. Frequency 50 % Relative Humidity
1.4
1.2
T= 35ºC 1
T= 30ºC
0.8
Specific Attenuation- g (dB/km)
T= 25ºC
0.6
T= 20ºC
0.4
T= 15ºC
T= 10ºC
0.2
T= 5ºC
T= 0ºC 90 91 92 93 94 95 96 97 98 99
100
Frequency - f (GHz)
07/12/2000
FCC Forum 90 GHz.PPT

12. Water Vapor Contents vs Altitude
Water vapor content decreases rapidly with altitude due to decreasing temperature (4-6 ºC/km)
Important Range at 90 GHz
Ref: Kulpa et al, 1979
07/12/2000
FCC Forum 90 GHz.PPT

13. Attenuation Calculated From Persian Gulf Radiosonde Measurements
10000
94 GHz
1000
Height - H (m)
100
USS Arkansas CG-34
August 24, 1991 10
0.001
0.01
0.1 1
Specific Attenuation - g (dB/km)
07/12/2000
FCC Forum 90 GHz.PPT

14. Visibility due to Fog 07/12/2000 FCC Forum 90 GHz.PPT
Density of fog usually described in terms of visibility range
Related to water content in g/m3
Particle size affects attenuation
Radiation fog : Cooling after sunset
Advection fog: Humid air and low surface temperature
07/12/2000
FCC Forum 90 GHz.PPT

15. Attenuation due to Fog T=15 C 100 50 20 10 Fog 0.1 g/m3
100 m Visibility
& RH=100% 5 2
H2O
RH=100% 1
Specific Attenuation - g (dB/km)
0.5
0.2
0.1
0.05
Dry Air
0.02
0.01 10 20 40 70
100
200
400
700
1000
Frequency - f (GHz)
07/12/2000
FCC Forum 90 GHz.PPT

16. W-Band Performance in Clouds/ Fog
1000
(dB/km)
100 10 g 1
94 GHz
Clouds or Fog 0.1 g/m3
Visibility 50 m
0.1
Specific Attenuation -
0.01 10 -3
MicroW mm
Sub-mm IR
Visible 10 -4 -5 10 1 10
100
1000
10000
100000
Frequency - f (GHz)
07/12/2000
FCC Forum 90 GHz.PPT

17. Rain Characteristics Basic Definition: Meteorology:
Rain rate r (mm/hr)
Drop size distribution
Probability of precipitation at rate r
Height distribution of precipitation
Rain cell diameter
Thunderstorm cell diameter
Meteorology:
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FCC Forum 90 GHz.PPT

18. Effect of Rain 2.5, 5 , 10 mm/hr
100 50 20 10
10 mm/hr 5
5 mm/hr 2
2.5 mm/hr 1
Specific Attenuation - g (dB/km)
0.5
0.2
0.1
0.05
Dry Air
0.02
0.01 10 20 40 70
100
200
400
700
1000
Frequency - f (GHz)
07/12/2000
FCC Forum 90 GHz.PPT

19. Rain Attenuation at 95 GHz
Light Rain
Moderate Rain
Heavy Rain 6 5
Hor Pol 4
Vert Pol
Specific Attenuation - g (dB/km) 3
Temperate
Tropics 2 1
Probability
> 1% 1%
< 1% 1 2 3 4 5 6 7 8
Rain Rate - r (mm/h)
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FCC Forum 90 GHz.PPT

20. Some References 07/12/2000 FCC Forum 90 GHz.PPT
R.K. Crane, Electromagnetic Wave Propagation Through Rain, John Wiley.
L.J. Ippolito, “Propagation Effects Handbook for Satellite Systems Design”, NASA Reference Publication 1082(04), 1989.
H.J. Liebe, “Millimeter-Wave Properties of the Atmosphere: Laboratory Studies and Propagation Modeling”, US Department of Commerce, NTIA Report , Oct
S.M. Kulpa and E.A. Brown, “Near-Millimeter Wave Technology Base Study, Volume I : Propagation and Target/Background Characteristics”, Report HDL-SR-79-8, US Army Materiel Development and Readiness Command and Defense Advanced Project Agency, Nov (Approved for public release).
H.J. Liebe, G.A. Hufford, and M.G. Cotton, “Propagation modeling of moist air and suspended water/ice particles at frequencies below 1000 GHz”, AGARD Meeting on Atmospheric Propagation Effects through Natural and Man-Made Obscurants for Visible to MM-Wave Radiation, May 1993.
07/12/2000
FCC Forum 90 GHz.PPT

21. Summary Standard dry atmosphere has a small effect at 90 GHz
High humidity at elevated temperatures introduces significant loss (up to 1 dB/km) but only at low altitude. Higher elevation paths suffer loss of only a few dB
Effects of fog and clouds quite modest
Rain is the most important factor in the design of 90 GHz communication and radar systems
07/12/2000
FCC Forum 90 GHz.PPT