1

Introduction • General concepts• Needs, advantages, and

disadvantages• Satellite characteristics• Orbits• Earth coverage• System components and design• Power sources• Communication characteristics

Spectrum and Bandwidth Channel capacity Frequency and Wavelength Path losses

Antennas and beam shapingTextbook: Satellite Technology: Principles & Applications, Third Edition, Anil. K. Maini. V. Agrawal, John Wilen & Sons, 2014.

Satellite CommunicationsGeneral concept

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.

Lect 01 2

General Concepts of Satellites:

• They orbit around the earth– Have various orbital paths (to be discussed)

• They carry their own source of power• They can communicate with:

– Ground stations fixed on earth surface– Moving platforms (Non-orbital)– Other orbiting satellites

Lect 01 3

Needs, Advantages & Disadvantages

Lect 01 4

• Communications needs• Advantages of using satellites• Disadvantages of using satellites

Satellite Communications Needs

• Space vehicle to be used as communications platform(Earth-Space-Earth, Space-Earth, Space-Space)

• Space vehicle to be used as sensor platform with communications

• Ground station(s) (Tx/Rx)• Ground receivers (Rx only)•

Lect 01 5

Advantages of Using 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

Lect 01 6

Disadvantages of Using 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

Lect 01 7

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

Lect 01 11

Mission Dependent Characteristics

• Orbital parameters– Height (velocity & period related to this)– Orientation (determined by application)– Location (especially for geostationary orbits)

• Power sources– Solar (principal), nuclear, chemical power– Stored gas/ion sources for position adjustment

Lect 01 9

Satellite Application Examples

• Telecommunications• Military communications• Navigation systems • Remote sensing and surveillance• Radio / Television Broadcasting• Astronomical research• Weather observation

Lect 01 10

Orbits

• Have particular advantages and disadvantages (See text Chapter 1)

• Are determined by satellite mission• Keppler’s Laws of planetary motion describe

certain orbital properties (Covered in Lecture 2)

Lect 01 11

Orbital Properties

• Altitude (radius to center of the earth)• Inclination with respect to the earth axis• Period of rotation about the earth• Ground coverage by the satellite• Communications path length(s)

Lect 01 12

Types of Orbit

Lect 01 13Dr. Leila Z. Ribeiro, George Mason University

Missions Associated with Orbit Types

• GEO– Primarily commercial communications

• MEO– Military and research uses

• LEO– Remote sensing– Global Positioning Systems

Lect 01 14

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”)

Lect 01 15

The Geostationary (Clarke) Orbit

• Arthur C. Clarke, Wireless World, February, 1945, p58.

Lect 01 16

Geo-Synchronous Satellite (GEO) Features

• Appears fixed over point on earth equator • Each satellite can cover 120 degrees latitude• Orbital Radius = 42,164.17 km• Earth Radius = 6,378.137 km (avg)• Period (Sidereal Day) = 23.9344696 hr

(86164.090530833 seconds)• Long signal path - large path losses

Lect 01 17

GEO Features (continued)

• Ground image area (instantaneous)• Ground track coverage (multiple orbits)• Stationarity (geostationary orbit)• Space coverage (satellite-satellite)

Lect 01 18

Orbital Altitudes and Problems

• Low Earth Orbit (LEO)– 80 - 500 km altitude– Atmospheric drag below 300 km

• Medium Earth Orbit (MEO)– 2000 - 35000 km altitude– Van Allen radiation between 200 - 1000 km

• Geostationary Orbit (GEO)– 35,786 km altitude (42,164.57 km radius)– Difficult orbital insertion and maintenance

Lect 01 19

Orbital Inclinations

• Equatorial– Prograde – inclined toward the east – Retrograde – inclined toward the west

• Inclined– Various inclination angles with respect to the

spin axis of the earth, including polar

• Geostationary (on equator; no inclination)• Sun synchronous

Lect 01 20

Earth Coverage Calculation

Lect 01 21

By the Law of Sines:

and,

rs

sin()

d

sin( )

90

The elevation angle is approximately,

Earth Coverage Calculation (continued)

• The total coverage area on the surface of the earth, using the previously calculated value of δ) is given by the equation,

Lect 01 22

A 2re2 (1 Cos[ ])

Alternate Earth Coverage Calculation

• Coverage variation as a function of satellite altitude (rsat)

Lect 01 23

Sin 1 re

rsat

Sin 1 rsat

re

Sin[ ]

A 2re2 (1 Cos[ ])

rsat is the radius to the satellite from the center of the earth

Calculation: CoverageArea.nbre = 6378.137; (* km *)rs = re + hs; alpha = ArcSin[re/rs]ad = alpha/Degreedelta = ArcSin[(rs/re)*Sin[alpha]] - alphadd = delta/DegreeA = 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]"}]

Lect 01 24

Advanced Earth Coverage Calculations

In: Orbital Mechanics with MATLABhttp://www.cdeagle.com/html/ommatlab.html

Recommended download:Coverage Characteristics of Earth Satellites

http://www.cdeagle.com/ommatlab/coverage.pdf

Lect 01 Lect 01 - 25

“Satellite System” Components

• Satellite(s)• Earth station(s)• Computer systems• Information network

(Example: Internet)

Lect 01 26

Satellite System Design

Lect 01 27

Satellite network with earth stations.

Satellite Components• Receiver (receives on an uplink)• Receiving antenna• Signal processing (decode, security, encode, other)• Transmitter (transmits on a downlink)• Transmitting antenna (beam shaping)• Power and environmental control systems• Attitude control• (De)multiplexing (used in rotating satellites)• Position holding (mission dependent option)

Lect 01 28

Satellite Power Sources

• Solar power panels (near-earth satellites)– Power degrades over time - relatively long

• Radioactive isotopes (deep space probes)– Lower power over very long life, rarely used.

• Fuel cells (space stations with resupply)– High power but need maintenance and chemical

resupply, rarely used.– Example: International Space Station

Lect 01 29

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: 2 - 75 kW• Photocell output degrades over time

Lect 01 30

Typical Solar Power Panel Example

Lect 01 31

Geostationary Operational Environmental Satellites (GOES) - Ground testing of solar panels, NASA

Type: GaAs/GeVoltage: 53.1 VoltsPower: 1940 Watts( Effective Load + Source Resistance: 1.45341 Ω )

Satellite Communication Characteristics

• 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”) to make up for path loss

and noise• Spectrum and Bandwidth• Channel capacity• Frequency and Wavelength• Path losses

Lect 01 32

Spectrum and Bandwidth

Lect 01 33

• Electromagnetic spectrum allocations (“DC to light” – see next slide)

• Bandwidth: the size or “width” (in Hertz) of a spectrum frequency band

• Frequency band: a range of frequencies in the available spectrum.

• Channel capacity increases with the bandwidth (see Slide 42)

Electromagnetic Spectrum

Lect 01 34

Wikipedia

Channel Capacity

• The number of error free bits of information transmitted and received per second

• Shannon (BSTJ, Vol. 27,1938)

The capacity C [bits/s] of a channel with bandwidth W, and signal/noise power ratio S/N is

Lect 01 35

C W log2 1S

N

Frequency and Wavelength Formula

• Microwave energy, at a given frequency, f [Hz]

• Moves at a velocity, v [m/s]• And has a 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 = 299 792 458 [m/s]

Lect 01 36

Frequencies of Interest for Satellites

Lect 01 37

• Generally between 300 MHz and 300 GHz. The microwave spectrum Allows efficient generation of signal power

Energy radiated into space Energy may be focused (beam shaping)

Efficient reception over a specified area.• Properties vary according to the frequency used: Propagation effects (diffraction, noise, fading) Antenna Sizes

Microwaves

Lect 01 38

• Include 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)

Designated Microwave Bands

Lect 01 39

Wikipedia

Standard designationsFor microwave bands

Common bands for satellite communication are the L, C and Ku bands.

Common Microwave Frequency Allocations

• L band 0.950 - 1.450 GHz Note: GPS at 1.57542 GHz

• C band 3.7 - 4.2 GHz (Downlink) 5.925 - 6.425 GHz (Uplink)

• Ku band 11.7 - 12.2 GHz (Downlink) 14 - 14.5 GHz (Uplink)

Lect 01 40

Common Microwave Frequency Allocations

• Ka band 18.3 - 18.8, 19.7 - 20.2 GHz (Downlink) 30 GHz (Uplink)

• V band 40 - 75 GHz 60 GHz allocated for unlicensed (WiFi) use 70, 80, and 90 GHz for other wireless

Lect 01 41

L-Band

• Frequencies: 0.950 – 1.450 GHz (λ ~30cm)• Uses:

– Amateur radio communications– GPS devices

• Features:– Patch antenna used for GPS receivers– Low rain fade - Low atmospheric atten. (long paths)– Low power– Small receiver configurations

Lect 01 42

C-Band

• Frequencies: 3.7 - 6.425 GHz (λ ~5cm)• Uses:

– TV reception (motels)– IEEE-802.11 WiFi– VSAT

• Features:– Large dish antenna needed (3m diameter)– Low rain fade - Low atmospheric atten. (long paths)– Low power - terrestrial microwave interferences

Lect 01 43

Ku-Band

• Frequencies: 12 - 18 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

Lect 01 44

Ka-Band

• Frequencies: 18 - 40 GHz (λ ~ 1cm)• Uses:

– High-resolution radar– Communications systems– Deep space communications

• Features:– Obstacles interfere (buildings, vegetation, etc.)– Atmospheric absorption

Lect 01 45

V-Band

• Frequencies: 40 to 75 GHz. (λ ~ 5 mm)• Uses:

– Millimeter wave radar research (very expensive!)– High capacity millimeter wave communications– Point-to-point fixed wireless systems (WiFi)

• Features:– Rain fade– Obstacles block path– Atmospheric absorption– Expensive equipment

Lect 01 46

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 addressed– Some of its detectors operate at minus 273.05C

Lect 01 47

Path Losses

• The loss of a radiated signal with distance• Losses increase with frequency• Satellites typically require long path lengths

( Path lengths can be over 42,000 km )

Lect 01 48

Causes of Path Loss

• Dispersion with distance• Atmospheric absorption (Calculated in Lecture

11)• Rain, snow, ice, & cloud attenuation

(Calculated in Lecture 12)• Atmospheric noise effects resulting in

increased Bit Error Rate (BER) (Calculated in Lecture 6)

Lect 01 Lect 01 - 49

Simple Path Loss Model

• Free-space power loss = (4πd / λ)2

In dB this becomes,

Lect 01 50

LossdB 32.44 20 log10 (d) 20 log10 ( f )

where:d is the path distance in kmf is the frequency in MHz

Calculation of Sample Path Loss Model

• Ku band geosynchronous satellite:f = 15,000 MHzd = 42,000 km

• LossdB = 32.44 + 20 log10(40,000) + 20 log10(15,000) = 208 dB

• Atmospheric losses must be added to this

Lect 01 51

Atmospheric Attenuation (Loss)

Lect 01 52

Microwave Attenuation [dB/km] vs Frequency [GHz], Wikipedia

O2

53.5 - 65.2 GHz

H2O

22.2 GHz

H2O vs Dry Air Absorption (Loss)

Lect 01 53

Remedies for Path Loss

• High gain antennas• High transmitter power• Low-noise receivers• Tracking of steered antennas• Modulation techniques• Error correcting codes• Frequency selection• Beam shaping to focus energy

Lect 01 54

Constraints Limiting Path Loss Remedies

• 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)

Lect 01 55

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 = 15775

GdB = 10 log10[Power Gain ] = 40 dB

Note: Losses and sidelobe effects can reduce this gain to 60% or less of its possible value.

Lect 01 56

Antenna Gain Efficiency Loss

• From text, p115d / λ = 5.6 (4GHz), η = 0.35GaindB = 10 log10η(πd/λ)2 = 20.9 dB

• From text, p116d = 9m, λ = 0.075m (4GHz), η = 0.6GaindB = 10 log10η (πd/λ)2 = 49.3 dB

Note: Smaller antenna has lower efficiency.

Lect 01 57

Beam Shaping through Antenna Design

• Antenna radiation patterns (the beam) can be shaped to redistribute the radiated energy, by antenna design

• Shaping radiation patterns can increase signal strength in selected areas– Allows for more signal energy where higher

noise levels are expected– Allows energy to be conserved for areas of low

noise or low economic concern

Lect 01 58

Intelsat Galaxy-11 Example

• 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)

Lect 01 59

Intelsat Galaxy-11 C-Band Coverage

Lect 01 60

Intelsat Galaxy-11 Ku-Band Coverage

Lect 01 61

Conclusions

• Design constraints limit the power avaiable to satellite communications equipment

• Path losses limit communication capacity• High gain antennas can overcome some

limitations• Antenna patterns can be shaped to favor

desired locations on the earth

Lect 01 62