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Introduction to Satellite

Communications

Joe Montana

IT 488 - Fall 2003

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The class notes used in this course are based on two different sets of class notes provided by Dr. Jeremy Allnutt and Dr.

James W. LaPean when teaching Satellite Communications courses. Material from Leila Ribeiro is also used. All

material is used with the permission of the author.

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Agenda

History

Overview and Basic concepts of Satel l i teCommunications

Spectrum Al location

Satel l i te Systems Applications

System Elements

System Design Considerations

Current Developments and Future Trends

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Important M ilestones (before 1950)Putting the concepts together

1600 Tycho Braches experimental observations on planetary motion.

1609-1619 Keplers laws on planetary motion

1926 First liquid propellant rocket lauched by R.H. Goddard in the US.

1927 First transatlantic radio link communication

1942 First successful launch of a V-2 rocket in Germany.

1945 Arthur Clarke publishes his ideas on geostationary satellites for

worldwide communications (GEO concept).

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Rocket motors produce thrust in a process which can be explained by Newton's third law (for every action there is an equal but opposite reaction). In the case of

rocket engines, the reactionary force is produced by the combustion of fuel in a combustion chamber. This force then acts upon the rocket nozzle, causing the

reaction which propels the vehicle. Since rocket motors are designed to operate in space, they require an oxidizer in order for combustion to take place. Thisoxidizer is, in many cases, liquid oxygen. There are three different types of rocket engines:

1. Solid propelled rockets

2. Liquid propelled rockets

3. Nuclear rockets

The advantages and disadvantages of each type are shown below.

Solid Fueled RocketsIn solid fueled rockets, the fuel and oxidizer both in solid form and thoroughly mixed during manufacture. The section where the fuel is stored is also the combustion

chamber. One end of the chamber is closed (the payload of the rocket would be attached to this end) and the other end of the chamber is a rocket nozzle.

Advantages of solid fuel rockets include simplicity and reliability, since there are no moving parts and high propellant density, which results in a smaller sized

rocket. Among the disadvantages are these: once you turn on a solid rocket motor, you can't shut it off. You have to wait for the fuel to run out. Also, the thrust of a

solid fuel rocket decreases greatly during its burn time.

Liquid Fueled RocketsIn liquid fueled rockets the fuel and oxidizer are stored in liquid form and pumped into the combustion chamber. There are two types of liquid propellent rockets; bi-

propellant rockets, which have separate fuel and oxidizer, and mono-propellant rockets, which have their fuel and oxidizer combined into a single liquid. Liquid

fueled rockets are superior to solid fuel rockets in many respects; they can be shut off and subsequently restarted, they generally have a higher exhaust velocity,

which means lower burn times are required, and they can be throttled to produce more or less thrust, as needed. However, liquid fuel rockets are highly complex,

and therefore have a lower rate of reliability.

Nuclear RocketsNuclear rockets work by routing hydrogen through a nuclear reactor. The reactor is at a high temperature, which causes the hydrogen fuel to expand as it leaves

the nozzle, producing a high amount of thrust. Nuclear rockets do not need an oxidizer, and they require much less fuel per pound of payload than liquid or solid

fuel rockets. This allows a vehicle using a nuclear rocket to be more versatile than one which uses chemical rockets. Disadvantages of nuclear rockets include

radiation effects caused by the nuclear reactor, and the high weight of the engine assembly.

OdysseusRecent studies have shown nuclear propulsion for Mars missions offers several major advantages over all-chemical propulsion systems. Therefore, a nuclear

engine was selected for the Odysseus program. The Oddyseus II engine will produce 1,112,500 Newtons of thrust at a weight of 9100 kg. The engine will be

approximately 3m in diameter and 6 meters long.

Propulsion

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V2 Rocket

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Important Milestones (1950s)Putting the pieces together

1956 - Trans-Atlantic cable opened (about 12 telephone channels

operator).

1957 First man-made satellite launched by former USSR (Sputnik,

LEO).1958 First US satellite launched (SCORE). First voice communication

established via satellite (LEO, lasted 35 days in orbit after batteries

failed).

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Sputnik - I

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Explorer - I

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Important Milestones (1960s)

First satellite communications

1960 First passive communication satellite launched into space (Large

balloons, Echo I and II).

1962: First non-government active communication satellite launchedTelstar I (MEO).

1963: First satellite launched into geostationary orbit Syncom 1

(comms. failed).

1964: International Telecomm. Satellite Organization (INTELSAT)created.

1965 First communications satellite launched into geostationary orbit

for commercial use Early Bird (re-named INTELSAT 1).

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ECHO I

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Telstar I

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Intelsat I

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Important Milestones (1970s)GEO applications development

1972 First domestic satellite system operational (Canada).

INTERSPUTNIK founded.

1975 First successful direct broadcast experiment (one year duration;USA-India).

1977 A plan for direct-to-home satellite broadcasting assigned by the

ITU in regions 1 and 3 (most of the world except the Americas).

1979 International Mobile Satellite Organization (Inmarsat) established.

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Important Milestones (1980s)GEO applications expanded

1981 First reusable launch vehicle flight.

1982 International maritime communications made operational.

1983 ITU direct broadcast plan extended to region 2.

1984 First direct-to-home broadcast system operational (Japan).

1987 Successful trials of land-mobile communications (Inmarsat).

1989-90 Global mobile communication service extended to land mobile

and aeronautical use (Inmarsat)

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Important Milestones (1990s)

1990-95:

- Several organizations propose the use of non-geostationary (NGSO)satellite systems for mobile communications.

- Continuing growth of VSATs around the world.- Spectrum allocation for non-GEO systems.- Continuing growth of direct broadcast systems. DirectTV created.

1997:

- Launch of first batch of LEO for hand-held terminals (Iridium).

- Voice service telephone-sized desktop and paging service pocket sizemobile terminals launched (Inmarsat).1998: Iridium initiates services.1999: Globalstar Initiates Service.2000: ICO initiates Service. Iridium fails and system is sold to Boeing.

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Iridium

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Overview and Basic concepts ofSatellite Communications

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Main orbit types:

LEO 500 -1000 km

GEO 36,000 km

MEO 5,00015,000 km

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USEFUL ORBITS 1:

GEOSTATIONARY ORBIT

In the equatorial plane

Orbital Period = 23 h 56 min. 4.091 s

= one Sidereal Day(definedas one complete rotation relative to the fixedstars)

Satellite appears to be stationary over a

point on the equator to an observerRadius of orbit, r, = 42,164.57 km

NOTE: Radius = orbital height + radius of the earth

Average radius of earth = 6,378.14 km

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USEFUL ORBITS 2:

Low Earth Orbit (>250 km); T 92 minutes

Polar (Low Earth) Orbit; earth rotates about23o each orbit; useful for surveillance

Sun Synchronous Orbit(example, Tiros-N/NOAA satellites used for search and rescueoperations)

8-hour and 12-hour orbits

Molniya orbit (Highly Elliptical Orbit (HEO); T 11h 38 min; highly eccentric orbit;inclination 63.4 degrees

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MOLNIYA VIEW OF THE EARTH

(Apogee remains over the northern hemisphere)

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Molniya Variants (HEOs)

Tundra Orbit Lies entirely above the Van Allen

belts.The Russian Tundra system, which employstwo satellites in two 24-hour orbits separatedby 180 deg around the Earth, with an apogee

of 53,622 km and a perigee of 17,951 km.The Molniya orbit crosses the Van Allen belts twicefor each revolution, resulting in a reduction ofsatellite life due to impact on electronics

the Russian Molniya system employs threesatellites in three 12-hour orbits separated by120 deg around the Earth, with an apogee of39,354 km and a perigee of 1000 km.

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Molniya Variants (HEOs)

The LOOPUS orbit.The LOOPUSsystem employs three satellites inthree eight-hour orbits separatedby 120 deg around the Earth, with

an apogee of 39,117 km and aperigee of 1238 km.

The ELLIPSO orbit

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A Highly Elliptical Orbit (HEO)

A satellite in HEO typically has a perigee at about 500 km above the surfaceof the Earth and an apogee as high as 50,000 km. The orbit is usuallyinclined at 63.4 deg to provide communications services to locations at highnorthern latitudes. This inclination value is selected to avoid rotation of theapses; thus, a line from the Earth's center to the apogee always intersects

the Earth's surface at a latitude of 63.4 deg North. Orbit period varies fromeight to 24 hours. Owing to the high eccentricity of the orbit, a satellitespends about two-thirds of the orbital period near apogee, during which timeit appears to be almost stationary to an observer on the Earth (aphenomenon known as `apogee dwell'). During the brief time the satellite isbelow the local horizon, a hand-off to another satellite in the same orbit is

required in order to avoid loss of communications. Free space loss andpropagation delay for this type of orbit are comparable to that ofgeosynchronous satellites. However, due to the comparatively greatmovement of a satellite in HEO relative to an observer on the Earth, satellitesystems using this type of orbit must cope with large Doppler shifts.

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A Medium-Earth Orbit (MEO)By setting the altitude parameters at 10,000 km, you generated a medium-Earth orbit (MEO). This one happens to

be an Intermediate Circular Orbit (ICO), since the apogee and perigee are equal. Its orbit period measures aboutseven hours. The maximum time during which a satellite in MEO orbit is above the local horizon for an observer onthe Earth is a few hours. A global communications system using this type of orbit requires relatively few satellites intwo to three orbital planes to achieve global coverage. MEO systems operate similarly to LEO systems. In MEOsystems, however, hand-over is less frequent, and propagation delay and free space loss are greater. Examples ofMEO (specifically ICO) systems are Inmarsat-P (10 satellites in 2 inclined planes at 10,355 km), and Odyssey (12satellites in 3 inclined planes, also at 10,355 km).

A Low-Earth Orbit (LEO)By selecting a relatively short period (90 minutes), we have generated a satellite in low-Earth orbit(LEO). A typical LEO is elliptical or, more often, circular, with a height of less than 2000 km abovethe surface of the Earth. The orbit period at those altitudes ranges between 90 minutes and twohours. The radius of the footprint of a communications satellite in LEO ranges between 3000 and4000 km. The maximum time during which a satellite in LEO is above the local horizon for anobserver on the Earth is 20 minutes. A global communications system using this type of orbitrequires a large number of satellites, in a number of different orbital planes. When a satellite

serving a particular user moves below the local horizon, it must hand over its duties to asucceeding one in the same orbit or in an adjacent one. Due to the comparatively great movementof a satellite in LEO relative to an observer on the Earth, satellite systems using this type of orbitmust cope with large Doppler shifts. Satellites in LEO are also affected by atmospheric drag thatcauses the orbit to gradually deteriorate.Examples of major LEO systems are GlobalstarTM (48+8 satellites in 8 orbital planes at 1400 km)and Iridium (66+6 satellites in 6 orbital planes at 780 km). There are also a number of small LEO

systems, such as PoSat, built by SSTL in 1993 and launched into an 822 by 800 km orbit, inclinedat 98.6 deg.

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Geosynchronous & Geostationary OrbitsA geosynchronous orbit is defined as an orbit with a period of one sidereal day (1436.1 minutes). A geostationary orbit is a special case ofa geosynchronous orbit with zero inclination and zero eccentricity, i.e., an equatorial, circular orbit. A satellite in a geostationary orbitappears fixed above a location on the surface of the Earth. In practice, a geosynchronous orbit typically has small non-zero values forinclination and eccentricity, causing the satellite to trace out a small figure eight in the sky. The footprint or service area of ageosynchronous satellite covers almost one-third of the Earth's surface (from about 75 deg South to about 75 deg North latitude), so thatnear-global coverage can be achieved with as few as three satellites in orbit. A disadvantage of a geosynchronous satellite in a voicecommunication system is the round-trip delay of approximately 250 milliseconds.

A Polar OrbitThe plane of a polar orbit is inclined at about 90 deg to the equatorial plane, intersecting the North and South poles. The orbit is fixed inspace, and the Earth rotates underneath. Thus, in principle, the coverage of a single satellite in a polar orbit encompasses the entireglobe, although there are long periods during which the satellite is out of view of a particular ground station. This gap in coverage may beacceptable for a store-and-forward communications system. Accessibility can, of course, be improved through the deployment of two ormore satellites in different polar orbits.Most small LEO systems employ polar or near-polar orbits. An example is the COSPAS-SARSAT Maritime Search and Rescue system, whichuses eight satellites in near polar orbits: four SARSAT satellites moving in 860 km orbits inclined at 99 deg (which makes them Sun-synchronous) and four COSPAS satellites moving in 1000 km orbits inclined at 82 deg.

A Sun-Synchronous OrbitIn a Sun-synchronous or helio-synchronous orbit, the angle between the orbital plane and Sun remains constant, resulting in consistentlight conditions for the satellite. This can be achieved by careful selection of orbital altitude, eccentricity and inclination, producing aprecession of the orbit (node rotation) of approximately 1 deg eastward each day, equal to the apparent motion of the Sun. This conditioncan be achieved only for a satellite in a retrograde orbit. A satellite in Sun-synchronous orbit crosses the equator and each latitude at thesame time each day. This type of orbit is therefore advantageous for an Earth observation satellite, since it provides constant lightingconditions.

P t D t i i O bit Si d

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Parameters Determining Orbit Size and

Shape

Parameter Definition

Semimajor Axis Half the distance between the two points in the orbit that are farthest apart

Apogee/PerigeeRadius

Measured from the center of the Earth to the points of maximum and minimum radius in the orbit

Apogee/PerigeeAltitude

Measured from the "surface" of the Earth (a theoretical sphere with a radius equal to the equatorial radiusof the Earth) to the points of maximum and minimum radius in the orbit

Period The duration of one orbit, based on assumed two-body motion

Mean Motion The number of orbits per solar day (86,400 sec/24 hour), based on assumed two-body motion

Eccentricity The shape of the ellipse comprising the orbit, ranging between a perfect circle (eccentricity = 0) and aparabola (eccentricity = 1)

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Orientation of Orbital Plane in SpaceParameter Definition

Inclination The angle between the orbital plane and the Earth's equatorial plane (commonly used as areference plane for Earth satellites)

Right Ascension of theAscending Node

The angle in the Earth's equatorial plane measured eastward from the vernal equinox to theascending node of the orbit

Argument of Perigee The angle, in the plane of the satellite's orbit, between the ascending node and the perigee of theorbit, measured in the direction of the satellite's motion

Longitude of theAscending Node

The Earth-fixed longitude of the ascending node

The ascending node (referenced in three of the above definitions) is the point in the satellite's orbit where it crosses the Earth's equatorial

plane going from south to north.

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Parameters determining orbit orientation

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Satellite Location parametersTo specify the satellite's location within its orbit at epoch.

Parameter Definition

True Anomaly The angle from the eccentricity vector (points toward perigee) to the satellite position vector, measured inthe direction of satellite motion and in the orbit plane.

Mean Anomaly The angle from the eccentricity vector to a position vector where the satellite would be if it were alwaysmoving at its angular rate.

Eccentric Anomaly An angle measured with an origin at the center of an ellipse from the direction of perigee to a point on acircumscribing circle from which a line perpendicular to the semimajor axis intersects the position of thesatellite on the ellipse.

Argument ofLatitude

The sum of the True Anomaly and the Argument of Perigee.

Time PastAscending Node

The elapsed time since the last ascending node crossing.

Time Past Perigee The elapsed time since last perigee passage.

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Parameters determining satellite position

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Orbital Velocities and Periods

Satellite Orbital Orbital Orbital

System Height (km) Velocity (km/s) Period

h min s

INTELSAT 35,786.43 3.0747 23 56 4.091

ICO-Global 10,255 4.8954 5 55 48.4

Skybridge 1,469 7.1272 1 55 17.8

Iridium 780 7.4624 1 40 27.0

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GSO AND NGSO FACTORSNGSO OPTIONS:

LEO

MEO

HEO

AVOID

RADIATION

BELTS IF

POSSIBLE

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Coverage vs. Altitude

Satellite Altitude (km)

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LEO, MEO and GEO Orbit Per iods

0.0

5.0

10.0

15.0

20.0

25.0

30.0

0 5000 10000 15000 20000 25000 30000 35000 40000

Altitude [km]

Hours

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Minimum Delay for two hops

0.0

50.0

100.0

150.0

200.0

250.0

300.0

0 5000 10000 15000 20000 25000 30000 35000 40000

Altitude [km]

Delay[ms]

Wh d lli i

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F1(Gravitational

Force)

v(velocity)

Why do satellites stay moving

and in orbit?

F2(Inertial-Centrifugal

Force)

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Spectrum Allocation

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Frequency Spectrum concepts:

Frequency: Rate at which an electromagnetic wave reverts its

polarity (oscillates) in cycles per second or Hertz (Hz).

Wavelength: distance between wavefronts in space. Given in

meters as: = c/fWhere: c = speed of light (3x108 m/s in vacuum)

f = frequency in Hertz

Frequency band: range of frequencies.

Bandwidth: Size or width (in Hertz) or a frequency band.

Electromagnetic Spectrum: full extent of all frequencies from

zero to infinity.

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Radio Frequencies (RF)RF Frequencies: Part of the electromagnetic spectrumranging between 300 MHz and 300 GHz. Interestingproperties:

Efficient generation of signal power

Radiates into free space

Efficient reception at a different point.

Differences depending on the RF frequency used:

- Signal Bandwidth

- Propagation effects (diffraction, noise, fading)

- Antenna Sizes

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Microwave Frequencies Sub-range of the RF frequencies approximately from1GHz to 30GHz. Main properties:

- 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 power amplification as frequency grows:

Radio Frequency Power OUTDirect Current Power IN

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Spectrum Regulation

International Telecommunication Union (ITU): Members from

practically all countries around the world.

Allocates frequency bands for different purposes and distribute

them around the planet.

Creates rules to limit RF Interference (RFI) between countries

that reuse same RF bands.

Mediates disputes and creates rules to deal with harmful

interference when it occurs.

Meets bi-annually with its members, to review rules and

allocations: World Radio Communication Conference (WRC).

There are also the Regional Radio Communication

Conferences (RCC), which happen less often.

R di F S

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Radio Frequency SpectrumCommonly Used Bands

AM HF VHF UHF L S C X KuKa V Q

1 10 100 1

MHz GHz

Terrestrial Bands

Space Bands

Shared (Terrestrial and Space)

SHF

0.1 10010

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Space-Earth Frequency Usabil i ty

Atmospheric attenuation effects for Space-to-Earth as a function of frequency (clear air conditions).

(a) Oxygen; (b) Water vapor. [Source: ITU 1988]

Resonance frequencies

below 100GHz:

22.2GHz (H20)

53.5-65.2 GHz (Oxygen)

I i h F S l i

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LEO satellites need lower RF frequencies:

Omni-directional antennas on handsets have low gain- typically G = 0 db = 1

Flux density F in W/m2at the earths surface in anybeam is independent of frequency

Received power is F x A watts , where A is effectivearea of antenna in square meters

For an omni-directional antenna A = G 2/ 4 =2/ 4

At 450 MHz, A = 353 cm2, at 20 GHz, A =0.18 cm2

Difference is 33 dB - so dont use 20 GHz with an

Insights on Frequency Selection:(Part 1: Lower frequencies, stronger links)

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GEO satellites need more RF frequencies

High speed data links on GEO satellites need about 0.8

Hz of RF bandwidth per bit/sec.

A 155 Mbps data link requires 125 MHz bandwidth

Available RF bandwidth:

C band 500 MHz (All GEO slots

occupied) Ku band 750 MHz (Most GEO

slots occupied) Ka band 2000 MHz

(proliferating)

Q/V band ?

Insights on Frequency Selection:

(Part 2: Higher frequencies, higher capacity)

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Satellite Systems Applications

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Initial application of GEO Satellites:

Telephony

1965 Early Bird 34 kg 240 telephonecircuits

1968 Intelsat III 152 kg 1500 circuits

1986 Intelsat VI 1,800 kg 33,000 circuits

2000 Large GEO 3000 kg 8 - 15 kW power1,200 kg payload

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Current GEO Satellite Applications:

Broadcasting - mainly TV at presentDirecTV, PrimeStar, etc.

Point to Multi-point communicationsVSAT, Video distribution for Cable TV

Mobile ServicesMotient (former American Mobile Satellite),INMARSAT, etc.

S t llit N i ti

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GPS is a medium earth orbit (MEO) satellite system

GPS satellites broadcast pulse trains with very

accurate time signalsA receiver able to see four GPS satellites cancalculate its position within 30 m anywhere in world

24 satellites in clusters of four, 12 hour orbital period

You never need be lost againEvery automobile and cellular phone will eventuallyhave a GPS location read-out

Satellite Navigation:

GPS and GLONASS

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LEO Satellites in year 2000

Several new systems are just starting service

Circular or inclined orbit with < 1400 km altitude

Satellite travels across sky from horizon to horizon in5 - 15 minutes

Earth stations must track satellite or have omni-

directional antennas

Constellation of satellites is needed for continuous

communication.

Handoff needed.

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System Elements

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Space Segment

Satellite

TT&C Ground Station

Satellite System Elements

Ground Segment

EarthStations

Coverage Region

SCC

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Space Segment

Satellite Launching Phase Transfer Orbit Phase Deployment Operation

TT&C - Tracking Telemetry and Command Station:Establishes a control and monitoring link with satellite. Tracks orbitdistortions and allows correction planning. Distortions caused byirregular gravitational forces from non-spherical Earth and due tothe influence of Sun and Moon forces.SSC - Satellite Control Center, a.k.a.: OCC - Operations Control Center

SCF - Satellite Control FacilityProvides link signal monitoring for Link Maintenance andInterference monitoring.

Retirement Phase

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Types of Satellite StabilizationSpin Stabilization

Satellite is spun about the axis on which

the moment of inertia is maximum (ex., HS376, most purchased commercialcommunications satellite; first satelliteplaced in orbit by the Space Shuttle.)

Three-Axis StabilizationBias momentum type (ex., INTELSAT V)

Zero momentum type (ex., Yuri)

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Satellite SubsystemsCommunications

Antennas

TranspondersCommon Subsystem (Bus Subsystem)

Telemetry/Command (TT&C)

Satellite Control (antenna pointing,attitude)

PropulsionElectrical Power

Structure

Thermal Control

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Ground Segment

Earth Station = Satellite Communication Station (air, ground or sea, fixed or mobile).

FSSFixed Satellite Service MSSMobile Satellite Service

Collection of facilities, users and applications.

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System Design Considerations

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Basic Principles Satellite

Uplink

Earth

Station

Downlink

TxSource

Information RxOutput

Information

Earth

Station

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SignalsSignals:

Carried by wires as voltage or current

Transmitted through space as electromagnetic waves.

Analog: Voltage or Current proportional to signal; e.g., Telephone.

Digital: Generated by computers.

Ex. Binary = 1 or 0 corresponding to +1V or1V.

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Separating SignalsUp and Down:

FDD: Frequency Division Duplexing.

f1 = Uplink

f2 = Downlink

TDD: Time Division Duplexing.

t1=Up, t2=Down, t3=Up, t4=Down,.

Polarization

V & H linear polarization

RH & LH circular polarizations

S ti Si l

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Separating Signals(so that many transmitters can use the same transponder simultaneously)

Between Users or Channels (Multiple Access):FDMA: Frequency Division Multiple Access; assignseach transmitter its own carrier frequency

f1 = User 1; f2 = User 2; f3 = User 3,

TDMA: Time Division Multiple Access; eachtransmitter is given its own time slot

t1=User_1, t2=User_2, t3=User_3, t4 = User_1, ...

CDMA: Code Division Multiple Access; eachtransmitter transmits simultaneously and at the samefrequency and each transmission is modulated by itsown pseudo randomly coded bit stream

Code 1 = User 1; Code 2 = User 2; Code 3 = User 3

l C S

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Digital Communication System

RECEIVER

RF

Channel

Output

Data

Source

Decoding

Channel

Decoder

Demodulator

Source

Data

Source

Coding

Channel

Coding

Modulator

TRANSMITTER

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Current Developments andFuture Trends

C T d i S lli

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Bigger, heavier, GEO satellites with multiple roles

More direct broadcast TV and Radio satellitesExpansion into Ka, Q, V bands (20/30, 40/50 GHz)

Massive growth in data services fueled by Internet

Mobile services:May be broadcast services rather than point to point

Make mobile services a successful business?

Current Trends in Satellite

Communications

Th F f S lli

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Growth requires new frequency bands

Propagation through rain and clouds becomes a problem

as RF frequency is increased

C-band (6/4 GHz) Rain has little impact

99.99% availability is possible

Ku-band (10-12 GHz) Link margin of 3 dB needed

for 99.8% availabilityKa-band (20 - 30 GHz) Link margin of 6 dB needed

for 99.6% availability

The Future for Satellite

Communications1

The Future for Satellite

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Low cost phased array antennas for mobiles areneeded

Mobile systems are limited by use of omni-directional

antennas

A self-phasing, self-steering phased array antenna with

6 dB gain can quadruple the capacity of a system

Directional antennas allow frequency re-use

The Future for Satellite

Communications - 2

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Homework #1

Answer the questions below for Dish Networks direct-to-home digital television broadcasting.

Reference the text pages 7, 443, 445 and Dish Networks Web site, and section 11.2 page 441.

1) How many satellites does Dish Network have in the sky? Name them?

2) How many transponders are on each of these satellites? What frequency band is used?

3) What orbit are these satellites in (LEO, MEO, GEO)?

4) Why are two heads used on the Dish Network antenna (text page 445)?

5) On what date was Echostar I launched? Echostar V?

6) Are these satellites spin or three axis stabilized? See page 443

7) Go to the Website and download the azimuth and elevation application( productsinstallation)

and follow the directions to aim the dish antenna to receive a signal for the zip code where you live.State the azimuth, elevation and skew angles and longitude for each satellite.

8) See page 443. If the frequency band were C rather than Ku, how would this affect the size of the

receive antenna you would need on your rooftop?

9) What is a transponder? Why does a satellite have multiple transponders and not just one?

10) Extra credit Go to the Air & Space Museum and view Explorer I Sputnik I the V2 rocket