1. Satellite Communications*
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Satellite Communications
Introduction
General concepts
Satellite characteristics
System components
Orbits
Power sources
Communications
Frequencies
Path losses
GPS Satellite - NASA
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2. © 2010 Raymond P. Jefferis III*
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Text
Text
Satellite Communications, Second Edition, T. Pratt, C. Bostian, and J. Allnut, John Wilen & Sons, 2003.
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3. Other Useful References
Ippolito, Louis J., Jr., Satellite Communications Systems Engineering, John Wiley, 2008.
Kraus, J. D., Electromagnetics, McGraw-Hill, 1953. 
Kraus, J. D., and Marhefka, R. J., Antennas for All Applications, Third Edition, McGraw-Hill, 2002. 
Morgan, W. L. , and Gordon, G. D., Communications Satellite Handbook, John Wiley & Sons, 1989.
Proakis, J. G., and Salehi, M., Communication Systems Engineering, Second Edition, Prentice-Hall, 2002.
Roddy, D, Satellite Communications, Fourth Edition, Mc Graw-Hill, 1989.
Stark, H., Tuteur, F. B., and Anderson, J. B., Modern Electrical Communications, Second Edition, Prentice-Hall, 1988.
Tomasi, W., Advanced Electronic Communications Systems, Fifth Edition, Prentice-Hall, 2001.
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4. © 2010 Raymond P. Jefferis III*
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General Concepts
Satellite is in (earth) orbit
Special orbits have particularly useful properties
Carries its own source of power
Communications possible with:
Ground station fixed on earth surface
Moving platform (Non-orbital)
Another orbiting satellite
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5. Satellite Communications*
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Satellite Communications
• Advantages
Disadvantages
What is involved
Why use space
• Frequency spectrum
• Satellite components and systems
• System design considerations
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6. Advantages of Satellites
High channel capacity (>100 Mb/s)
Low error rates (Pe ~ 10-6)
Stable cost environment (no long-distance cables or national boundaries)
Wide area coverage (whole North America, for instance)
Coverage can be shaped by antenna patterns
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7. Disadvantages of Satellites
Expensive to launch
Expensive ground stations required
Cannot be maintained
Limited frequency spectrum
Limited orbital space (geosynchronous)
Constant ground monitoring required for positioning and operational control
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© 2010 Raymond P. Jefferis III

8. Satellite Communications Needs
Space vehicle used as communications platform
(Earth-Space-Earth, Space-Earth, Space-Space)
Space vehicle used as sensor platform with communications
Ground station(s) (Tx/Rx)
Ground receivers (Rx only)
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9. Satellite Characteristics
Orbital parameters
Height (velocity & period related to this)
Orientation (determined by application)
Location (especially for geostationary orbits)
Power sources
Principally solar power
Stored gas/ion sources for position adjustment
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10. Satellite Characteristics*
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Satellite Characteristics
Orbiting platforms for data gathering and communications – position holding/tracking
VHF, UHF, and microwave radiation used for communications with Ground Station(s)
Signal path losses - power limitations
Systems difficult to repair and maintain
Sensitive political environment, with competing interests and relatively limited preferred space
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11. © 2010 Raymond P. Jefferis III*
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Application Examples
Telecommunications
Military communications
Navigation systems
Remote sensing and surveillance
Radio / Television Broadcasting
Astronomical research
Weather observation
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12. © 2010 Raymond P. Jefferis III
Orbits
Have particular advantages and disadvantages
Are determined by satellite mission
Obey Keppler’s Laws
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13. © 2010 Raymond P. Jefferis III
Types of Orbit
Dr. Leila Z. Ribeiro, George Mason University
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14. Orbital Altitudes and Problems*
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Orbital Altitudes and Problems
Low Earth Orbit (LEO)
km altitude
Atmospheric drag below 300 km
Medium Earth Orbit (MEO)
km altitude
Van Allen radiation between km
Geostationary Orbit (GEO)
35,786 km altitude (42, km radius)
Difficult orbital insertion and maintenance
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15. © 2010 Raymond P. Jefferis III
LEO and MEO Features
Earth coverage requires multiple passes
Typical pass requires about 90 minutes
Signal paths relatively short (lower losses)
Small area, high resolution ground image
Earth station tracking required
Multiple satellites for continuous coverage (Decreases with increasing altitude - “Telstar”)
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16. © 2010 Raymond P. Jefferis III
The Clarke Orbit
Arthur C. Clarke, Wireless World, February, 1945, p58.
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17. Geostationary Orbit (GEO)
Appears fixed over point on earth equator
Each satellite can cover 120 degrees latitude
Orbital Radius = 42, km
Earth Radius = 6, km (avg)
Period (Sidereal Day) = hr
( seconds)
Long signal path - large path losses
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18. © 2010 Raymond P. Jefferis III
Orbital Features
Ground image area (instantaneous)
Ground track coverage (multiple orbits)
Stationarity (geostationary orbit)
Space coverage (satellite-satellite)
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19. Orbital Inclination Angles
Equatorial
Prograde - toward the east
Retrograde - toward the west
Inclined
Various inclination angles, including polar
Geostationary
Sun synchronous
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20. © 2010 Raymond P. Jefferis III
Earth Coverage
By the Law of Sines:
and,
The elevation angle is approximately,
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21. Earth Coverage (continued)
The total coverage area on the surface of the earth is given by,
Ref:
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22. Sample Calculation [Mathematica®]
re = ; (* km *) delta = ; (* degrees *) area = 2 p re^2 (1 - Cos[delta Degree]); Print["Area = ", area, “[km^2]"] Area = *10^7 [km^2]
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23. © 2010 Raymond P. Jefferis III
Ground Coverage Area
Coverage with satellite altitude,
For satellite radius rsat
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24. Coverage vs Satellite Altitude
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25. Mathematica® Notebook
re = ; (* km *) rs = re + hs; alpha = ArcSin[re/rs] ad = alpha/Degree delta = ArcSin[(rs/re)*Sin[alpha]] - alpha dd = delta/Degree A = 2 p re^2 (1.0 - Cos[delta]) Plot[A, {hs, 1000, 2000}, AxesLabel -> "Coverage [km^2]", Frame -> True, FrameLabel -> {"Altitude [km]", "Coverage [km^2]"}]
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26. © 2010 Raymond P. Jefferis III*
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System Components
Satellite(s)
Ground station(s)
Computer systems
Information network
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27. Basic Satellite Network*
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Basic Satellite Network
Satellite network with earth stations.
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28. © 2010 Raymond P. Jefferis III*
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Satellite Components
Receiving antenna
Receiver (uplink)
Processing (decode, security, encode, other)
Transmitter (downlink)
Transmitting antenna (beam shaping)
Possible (de)multiplexing (for rotating satellites)
Power and environmental control systems
Attitude control
Possible position holding (geosynchronous)
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29. Simple Satellite Schematic*
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Simple Satellite Schematic
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30. Telemetry Block Diagram*
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Telemetry Block Diagram
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31. Satellite Power Sources
Solar panels (near-earth satellites)
Power degrades over time - relatively long
Radioactive isotopes (deep space probes)
Lower power over very long life
Fuel cells (space stations with resupply)
High power but need maintenance and chemical resupply
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32. © 2010 Raymond P. Jefferis III
Solar Panels
Type: GaAs/Ge
Voltage: 53.1 Volts
Power: 1940 Watts
( Effective Load + Source Resistance: Ω )
Geostationary Operational Environmental Satellites (GOES) - Ground testing of solar panels, NASA
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33. © 2010 Raymond P. Jefferis III
Solar Power
Power available in orbit: ~1400 watts of sunlight per square meter
Conversion efficiency: ~25%
Useful power: ~350 Watts/square meter
Panel steering required for maximum power
Typical power levels: kW
Photocell output degrades over time
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34. © 2010 Raymond P. Jefferis III
Communications Links
Via electromagnetic waves (“radio”)
Typically at microwave frequencies
High losses due to path length
Many interference sources
Attenuation due to atmosphere and weather
High-gain antennas needed (“dish”)
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35. © 2010 Raymond P. Jefferis III
Bandwidth/Spectrum
Frequency band: range of frequencies
• Bandwidth: size or “width” (in Hertz) of a frequency band
Channel capacity increases with bandwidth (see next slide – Slide 29)
• Electromagnetic spectrum: all frequencies
(“DC to light” – see Slide 30)
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36. © 2010 Raymond P. Jefferis III
Cnannel Capacity
Shannon (BSTJ, Vol. 27,1938)
The capacity C [bits/s] of a channel with bandwidth W, and signal/noise power ratio S/N is
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37. Frequency and Wavelength
Velocity = Frequency * Wavelength
Wavelength = Velocity/Frequency
where,
velocity ≈ velocity of light in vacuum ( about 3 x 108 meters/sec)
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38. Satellite Communications Frequencies
Generally between 300 MHz and 300 GHz.
The microwave spectrum
Allows efficient generation of signal power
Energy radiated into space
Energy may be focused
Efficient reception over a specified area.
Properties vary according to the frequency used:
Propagation effects (diffraction, noise, fading)
Antenna Sizes
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39. © 2010 Raymond P. Jefferis III
Millimeter Waves
Planck space exploration satellite
Planck is a flagship mission of the European Space Agency (Esa). It was launched in May 2009 and moved to an observing position more than a million km from Earth on its "night side".It carries two instruments that observe the sky across nine frequency bands. The High Frequency Instrument (HFI) operates between 100 and 857 GHz (wavelengths of 3mm to 0.35mm), and the Low Frequency Instrument (LFI) operates between 30 and 70 GHz (wavelengths of 10mm to 4mm).
Johnson noise problems
Some of its detectors operate at minus C
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40. Communications Channel
Microwave energy at frequency, f (Hertz)
Moves at velocity, v [m/s]
With wavelength (distance between peak intensities), λ [m]
Formula: λ = v / f (v = c for space) Note: The speed of light, c, in a vacuum (space) is fixed at, c = [m/s]
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41. © 2010 Raymond P. Jefferis III
Microwaves
Frequencies from 0.3 GHz to 300 GHz.
- Line of sight propagation (space and atmosphere).
- Blockage by dense media (hills, buildings, rain)
- Wide bandwidths compared to lower frequency bands.
- Compact antennas, directionality possible.
Reduced efficiency of generation
1 GHz to 170 GHZ spectrum divided into bands with letter designations (see next slide)
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42. Electromagnetic Spectrum
Wikipedia
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43. Designated Microwave Bands
Standard designations
For microwave bands
Common bands for satellite communication are the L, C and Ku bands.
Wikipedia
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© 2010 Raymond P. Jefferis III

44. Common Frequency Allocations
L band
GHz
Note: GPS at GHz
C band
GHz (Downlink)
GHz (Uplink)
Ku band
GHz (Downlink)
GHz (Uplink)
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45. Other Frequency Allocations
Ka band
, GHz (Downlink)
30 GHz (Uplink)
V band
GHz
60 GHz allocated for unlicensed (WiFi) use
70, 80, and 90 GHz for other wireless
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46. Wavelength/Antenna Constraints
Maximal antenna sizes push satellite radio wavelengths below 2m.
Requirements for antenna gain, due to communication path losses, reduce the practical wavelengths to below 20cm. (Diameter, d, of many wavelengths, λ)
Dish-Antenna Power Gain = η(πd/λ)2 (where η is antenna efficiency)
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47. Antenna Gain Calculation
Ku-Band antenna
Diameter 80 cm (d/λ = 40), η = 0.6 (about 40 wavelengths at 15GHz)
Power Gain = 0.6*(3.14*40)2 = GdB = 10 log10[Power Gain ] = 40 dB Note: Losses and sidelobe effects can reduce this gain to 60% or less of its possible value.
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48. Antenna Gain Efficiency
From text, p115 d / λ = 5.6 (4GHz), η = 0.35 GaindB = 10 log10η(πd/λ)2 = 20.9 dB
From text, p116 d = 9m, λ = 0.075m (4GHz), η = 0.6 GaindB = 10 log10η (πd/λ)2 = 49.3 dB Note: Smaller antenna has lower efficiency.
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49. © 2010 Raymond P. Jefferis III
C-Band
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50. © 2010 Raymond P. Jefferis III
C-Band
Frequencies: GHz (λ ~5cm)
Uses:
TV reception (motels)
IEEE WiFi
VSAT
Features:
Large dish antenna needed (3m diameter)
Low rain fade - Low atmospheric atten. (long paths)
Low power - terrestrial microwave interferences
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51. © 2010 Raymond P. Jefferis III*
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Ku-Band
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52. © 2010 Raymond P. Jefferis III
Ku-Band
Frequencies: GHz (λ ~ 2cm)
Uses:
Remote TV broadcasting
Satellite communications
VSAT
Features:
Rain, snow, ice (on dish) susceptibility
Small antenna size - high antenna gain
High power allowed
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53. © 2010 Raymond P. Jefferis III
Ka-Band
Frequencies: GHz (λ ~ 1cm)
Uses:
High-resolution radar
Communications systems
Deep space communications
Features:
Obstacles interfere
Atmospheric absorption
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54. © 2010 Raymond P. Jefferis III
V-Band
Frequencies: 40 to 75 GHz. (λ ~ 5 mm)
Uses:
Millimeter wave radar research (expensive!)
High capacity millimeter wave communications
Point-to-point fixed wireless systems (WiFi)
Features:
Rain fade
Obstacles block path
Atmospheric absorption
Expensive equipment
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55. © 2010 Raymond P. Jefferis III
Path Loss
Losses increase with frequency
Long path lengths (dispersion with distance)
( Path lengths can be over 42,000 km )
Atmospheric absorption
Rain, snow, ice, & cloud attenuation
Atmospheric noise effects that increase the Bit Error Rate (BER)
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56. Satellite Communications
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Satellite Communications
Link budget analysis
Overview
Antenna gain
Path loss
Obstacle loss
Atmospheric loss
Receiver gain
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© 2010 Raymond P. Jefferis III
© 2009 Raymond P. Jefferis III

57. Antenna Gain and Link Losses
Pt = transmitted power
Pr - received power
At = transmit antenna aperture
Ar = receive antenna aperture
Lp = path loss
La = atmospheric attenuation loss
Ld = diffraction losses
Antenna Gain (t or t):
Gt/r = 4π Ae t/r/λ2
Combined Antenna Gain (t + t):
G = GtGy
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58. © 2010 Raymond P. Jefferis III
Simple Path Loss Model
Free-space power loss = (4πd / λ)2 In dB this becomes,
where:
d is the path distance in km
f is the frequency in MHz
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59. Sample Path Loss Calculation
Ku band geosynchronous satellite: f = 15,000 MHz d = 42,000 km
LossdB = log10(40,000) log10(15,000) = 208 dB
Atmospheric losses must be added to this
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60. BPSK Bit Error Rate Graph
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61. Atmospheric Attenuation
GHz
H2O
22.2 GHz
Microwave Attenuation [dB/km] vs Frequency [GHz], Wikipedia
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62. H2O vs Dry Air Absorption
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63. © 2010 Raymond P. Jefferis III
Remedies for Path Loss
High gain antennas
High transmitter power
Low-noise receivers
Tracking of antennas
Modulation techniques
Error correcting codes
Frequency selection
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64. Radiation Pattern of Aperture
E-field for aperture with D/ = 10
The Mathematica® notebook follows, for D/λ = 10:
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65. © 2010 Raymond P. Jefferis III
System Example
Intelsat GALAXY-11 at 91W (NORAD 26038)
39.1 dBW on C-Band (20W, 24 ch, Bw: 36 MHz)
5945 (+n*20 MHz) MHz Uplink
3720 (+n*20 MHz) MHz Downlink
47.8 dBW on Ku-Band (75/140W, 40 ch, Bw: 36 MHz)
14020 (+n*20 MHz) MHz Uplink
11720 (+n*20 MHz) MHz Downlink
Power Supply: 10 kW (Xenon ion propulsion needs)
Polarization: v (odd), h (even) - Downlink opposite
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© 2010 Raymond P. Jefferis III

66. Intelsat Galaxy-11 Specifications
Location: 91W
Power: Solar, 10.4 KW
Antennas:
C-Band: 2.4m
Ku-Band: 1.8m
Transponders:
24 channels C-Band: 20W each
24 channels Ku-Band: 75W (data)
16 channels Ku-Band: 140W (TV video)
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67. Intelsat Galaxy-11 C-Band Coverage
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68. Intelsat Galaxy-11 Ku-Band Coverage
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69. © 2010 Raymond P. Jefferis III
Conclusions
Limited satellite transmitter power
Significant path losses
High gain antennas needed
Antenna patterns can be shaped as desired
Location and tracking necessary
Atmospheric effects can be significant
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70. © 2010 Raymond P. Jefferis III
End
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