Radio Propagation at 90 GHz

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

2
Overview

• Propagation effects and 90 GHz
• Dry air atmosphere
• Water vapor
• Fog and clouds
• Rain
• Other effects
• Summary

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

4
Atmospheric AttenuationVersus Frequency
oxygen H2O
High Attenuation (gt1 dB/km)
Low Attenuation (lt1 dB/km)
fog clouds
IR
Visible
W-Band
rain
Ka-Band
0.4- 10 GHz
3000- 1000000 GHz
10-3000 GHz
Microwave
mm-wave
IR and Visible
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

6
Dry Atmosphere Attenuation atLow 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)
7
Dry Atmosphere AttenuationLow Altitude - 2
100
50
20
10
5
2
1
Specific Attenuation - g (dB/km)
0.5
0.2
0.1
Dry Air
0.05
0.02
0.01
50
60
70
80
90
100
110
120
130
140
150
Frequency - f (GHz)
8
Water Vapor Characterization
Standard Definition

• Temperature (T C)
• Relative humidity (RH )

g/m3
10
What really matters
RH100

• Water vapor concentration in g/m3

1
RH5
0.1
-10 0 10 20 30 40 C
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
1
Specific Attenuation - ? (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)
10
Specific Attenuation Due toOxygen and Water Vapor
100
Sea Level (1013 mB)
10
1
Specific Attenuation - g (dB/km)
T20ºC and RH50
0.1
0.01
T20ºC and RH0
0.001
0
20
40
60
80
100
120
140
160
180
200
Frequency - f (GHz)
11
Attenuation vs. Frequency50 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
T 5ºC
0.2
T 0ºC
0
90
91
92
93
94
95
96
97
98
99
100
Frequency - f (GHz)
12
Water Vapor Contents vs Altitude

• Water vapor content decreases rapidly with
  altitude due to decreasing temperature (4-6 ºC/km)

ImportantRangeat 90 GHz
Ref Kulpa et al, 1979
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)
14
Visibility due to Fog

• 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

15
Attenuation due to Fog
T15 C
100
50
20
Fog 0.1 g/m3 100 m Visibility RH100
10
5
2
H2O RH100
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)
16
W-Band Performance in Clouds/ Fog
1000
100
(dB/km)
10
g
94 GHz

1
Clouds or Fog 0.1 g/m3 Visibility 50 m
0.1
Specific Attenuation -
0.01
-3
10
mm
Sub-mm
MicroW
IR
Visible
-4
10
-5
10
1
10
100
1000
10000
100000
1000000
Frequency - f (GHz)
17
Rain Characteristics
Basic Definition

• 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
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)
19
Rain Attenuation at 95 GHz
Heavy Rain
Light Rain
Moderate Rain
6
5
Hor Pol
4
Vert Pol
Specific Attenuation - g (dB/km)
3
Tropics
Temperate
2
Probability
1
gt 1
1
lt 1
0
0
1
2
3
4
5
6
7
8
Rain Rate - r (mm/h)
20
Some References
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 87-224, Oct. 1987. 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. 1979 (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.
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