1. Satellite Communications
Jayson P. Rogelio, E.C.E.
JPRogelio
Communications 5

2. Objectives Define satellite communications
Describe the history of satellite communications
Explain Kepler’s laws and how they relate to satellite communications
Define and describe satellite orbital patterns and elevation categories
Explain satellite look angles
Define and describe satellite system parameters
Explain satellite system link equations
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3. Introduction Satellite
In astronomical terms, it is a celestial body that orbits around a planet.
In aerospace terms, it is a space vehicle launched by humans and orbits Earth or another celestial body.
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4. Introduction Communication Satellite Transponder
Is a microwave repeater in the sky that consists of a diverse combination of one or more of the following:
Transponder
A satellite repeater radio repeater of which a satellite may have many.
Repeater
Transmitter
Amplifier
Regenerator
Filter
Onboard Computer
Multiplexer
Demultiplexer
Antenna
Waveguide
Other electronic communications circuits
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5. Satellite Communications
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6. History of Satellites
The first artificial earth satellite, SPUTNIK I, was launched in 1957.
1962 Telstar I (AT&T) – operated for only a few weeks due to radiation damage
1963 Telstar II (AT&T) – first transatlantic video transmission
1963 Syncom II – (Syncom I was lost)
1964 Syncom III – used to transmit 1964 Olympics from Tokyo
1965 Early Bird I – first Intelsat satellite
1969 Intelsat Satellites – placed over the Atlantic, Pacific, and Indian Oceans, allowing worldwide satellite communications
1972 Anik A-1 (Canada) – first commercial domestic communications satellite
1972 Westar 1 and 2 (Western Union) – first commercial United States domestic communications satellites
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7. KEPLER’s LAW Johannes Kepler (1571-1630) Kepler’s Law
German Astronomer discovered the laws that govern satellite motion.
Kepler’s Law
The planets move in ellipses with the sun at one focus
The line joining the sun and a planet sweeps out equal areas in equal interval of time
The square of the time of revolution of a planet divided by the cube of its mean distance from the sun gives a number that is the same for all planets
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8. Kepler’s First Law Where:  = semi-major axis  = semi-minor axis
 = eccentricity
Major
Axis
Minor F1 F2
Center
of Ellipse
Semi-Major Axis
Semi-Minor
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9. Kepler’s Second Law Law of Areas
States that equal intervals of time a satellite will sweep out equal areas in the orbital plane, focused at the barycenter
Earth A1 A2
Orbit
Satellite D1 V1 D2 V2
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10. Kepler’s Third Law Harmonic Law Where:
States that the square of the periodic time of orbit is proportional to the cube of the mean distance between the primary and the satellite
Where:
A = constant (unitless) =
 = semi-major axis (kilometers)
µ = Earth’s Gravitational Constant
= x 1014 m3/s2
ω = velocity of the satellite in radian per second
P = mean solar earth days
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11. Satellite Elevation Categories Satellite Orbital Patterns
Satellite Orbits
Satellite Elevation Categories
Satellite Orbital Patterns
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12. Satellite Orbits Orbital Satellites circular elliptical ccw cw ccw cw
Direction of Rotation
ccw cw
ccw rotation
(ωe)
circular
Earth
North
Pole
ccw cw
Direction of Rotation
ccw rotation (ωe)
elliptical
North Pole
Earth
Satellite (ωs)
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13. Elliptical Orbits
Earth
Apogee
Perigee

14. Circular Orbits Polar Orbit Equatorial Orbit Orbit Inclined
At 45O to Equator

15. Satellite Orbital Patterns
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16. Satellite Elevation Categories
LEO (low earth orbit)
1.0 GHz to 2.5 GHz ; 480 ,miles
MEO (medium earth orbit)
1.2 GHz to 1.66 GHz ; 6000 – 12, 000 miles
GEO (geosynchronous earth orbit)
2 GHz to 18 GHz ; 23, 000 miles
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17. Geosynchronous Satellites
Satellite Orbital Velocity
Round-Trip Time Delay
Clarke Orbit
Advantages and Disadvantages
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18. Geosynchronous Satellites
Geosynchronous satellites orbit Earth above the equator with the same angular velocity as Earth
Sometimes called stationary or Geostationary satellites appear to remain in a fixed location above one spot on Earth’s surface.
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19. Direction of Satellite Motion
Geostationary Orbit
6400 km
North Pole
Satellite
Earth
36, 000 km
Direction of Satellite Motion
Direction of
Rotation
Satellite Orbit
Footprint – Depiction of the signal strength contours from a satellite transmitter on the earth

20. Satellite Orbits
Perigee – The point closest to Earth in a Satellite Orbit
Apogee – The point farthest from earth in a Satellite Orbit
v = x 1011
(d )
where: v = velocity in meter per second
d = distance above earth’s surface in km

21. Path Loss Calculations
= GT (dBi) + GR (dBi)
– ( log d + 20 log f)
PR PT
(dB)
Where:
PR/PT (dB) = ratio of received to transmitted power, expressed in decibels
GT (dBi) = gain of transmitting antenna in decibels with respect to an isotropic radiator
GR (dBi) = gain of receiving antenna in decibels with respect to an isotropic radiator)
d = distance between transmitter and receiver in kilometers
f = frequency in megahertz

22. Global Coverage
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23. Clarke Orbits
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24. Satellites in Geosynchronous Orbits
COMSTAR I
128°
WESTAR II
123.5°
WESTAR V
119.5°
SATCOM II
119°
ANIK III
114°
ANIK II
109°
ANIK I
104°
WESTAR I
99°
WESTAR IV
98.5°
TELESTAR
96°
COMSTAR II
95°
WESTAR III
91°
SATCOM V
143°
SATCOM I
135°
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25. Angle of Elevation Azimuth Angle Limits of Visibility
Antenna Look Angles
Angle of Elevation
Azimuth Angle
Limits of Visibility
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26. Antenna Look Angles Angle of Elevation (Elevation Angle) Azimuth Angle
the vertical angle formed between the direction of travel of an electromagnetic wave radiated from an earth station antenna pointing directly toward a satellite and the horizontal plane
Azimuth Angle
Azimuth is the horizontal angular distance from a reference direction, either the southern or northern most point of the horizon. Azimuth angle is defined as the horizontal pointing angle of an earth station antenna.
Engr DF de Bien
Communications 5

27. LOOKANGLES North (0°) West Azimuth East referred to 180°
South (180°)
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28. Geostationary Satellites
Propagation Time – The time taken for a signal to travel through space from transmitter to receiver
Inclinometer – is a device incorporating a level that can measure the angle of antenna axis from the horizontal.
Declination – The amount by which the antenna axis is offset from the earth’s axis

29. Θ = arctan R sin L H + R (1-cosL)
Geostationary Satellites
Angle of Declination
Θ = arctan R sin L H + R (1-cosL)
Where
R = Radius of the Earth (6400 km)
H = Height of the Satellite above the Earth (36 x 103 km)
L = Earth Station latitude

30. Geostationary Satellites
Slant Distance / Path Length
Where
d = distance to the satellite in km
r = radius of the earth in km (6400 km)
h = Height of the Satellite above the Earth (36 x 103 km)
θ = Angle of Elevation

31. Example Problems
Calculate the angle of declination for an antenna using a polar mount at a latitude of 45°. (Ans. = 6.81°)
Calculate the length of the path to a geostationary satellite from an earth station where the angle of elevation is 30°. (Ans. = 39 x 103 km)

32. Variation in Antenna Elevation Angle with Latitude
EQUATOR
North Pole
South Pole
Satellite
Faraday Rotation – The change in the direction of polarization of signals passing through the ionosphere

33. Spreading of Satellite Beam at High Frequencies
Diameter
Earth
Beam at Equator

34. Beam at Northern Latitude
Incremented Beam
Diameter
Beam at Northern Latitude

35. Subsatellite Point GEOCENTER Earth Station SUBSATELLITE POINT
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36. Transponder Transponder Type Satellite Frequencies Block Diagram
Digital Transponder
Beam Switching
Cross Link
Earth Station
TVRO
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37. Satellite and Transponder Type
Frequency Translation
And Amplification
Receiving Antenna
Transmitting Antenna
Bent – Pipe Satellite Transponder

38. Figure of Merit (G/T)dB G/T (dB) = GR (dBI) – 10log (Ta + T eq)
Ta = noise temp. of antenna and feedline, referenced to receiver antenna input in K
L = loss in feedline and antenna as a ratio of input to output power
Teq = the equivalent noise temp of the receiver
Engr DF de Bien
Communications 5

39. Losses in Antenna System Ta = {(L-1) 290K + T sky}/L
Ta = effective noise temp. of antenna and feedline, referenced to receiver antenna input in K
L = loss in feedline and antenna as a ratio of input to output power
Tsky = effective sky temperature (K)
Engr DF de Bien
Communications 5

40. Sample Problem
A receiving antenna with a gain of 40dbi looks at a sky with a noise temperature of 15K, the loss between the antenna and the LNA input, due to the feedhorn is 0.4db and the LNA has a noise temperature of 40K. Calculate the G/T. (20.6dB)
Engr DF de Bien
Communications 5

41. Commonly-Used Geostationary Satellite Frequencies
Band
Uplink (GHz)
Downlink (GHz)
Use S –
1.53 – 1.559
Marine (Inmarsat) C
5.925 – 6.425
3.7 – 4.2
Commercial X
7.9 – 8.4
7.25 – 7.75
Military Ku
14 – 14.5
11.7 – 12.2 K
27.5 – 30.5
17.7 – 20.2
30 – 31
20.2 – 21.2

42. Transponder Block Diagram (C Band)
Local Oscillator
2 GHz
Mixer
LNA
BPF
4 GHz
P.A. (TWT)
Receiving
Antenna
6 GHz
Transmitting

43. Digital Transponder Block Diagram
Decoder
Receiver/
Demodulator
Encoder
Modulator/
Transmitter
Receiving
Antenna
Transmitting

44. Beam Switching
Satellite
Alternate
Downlink
Uplink
Earth

45. Cross-Links
Satellite
Satellite
Cross-Link
Uplink
Down Link
Earth

46. Earth Stations

47. TVRO Block Diagram Antenna LNA Mixer Local Oscillator 950 – 1450 MHz
First
IF Amp
70 MHz
Second
Video
Detector
Sub carrier
Out
Audio
Receiver
Block Downconverter

48. Thank You
"Somewhere in me is a curiosity sensor. I want to know what's over the next hill. You know, people can live longer without food than without information. Without information, you'd go crazy"
-Arthur C. Clarke
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