A communication satellite receives radio signals from earth stations, amplifies them, and redirects them back to earth. It acts as a radio relay in space, allowing signals to be transmitted over greater distances than would be possible with terrestrial communication methods alone. A satellite's transponder receives uplink signals, amplifies them using a low-noise amplifier, down converts the frequency, filters it, amplifies it again using a power amplifier, and retransmits it back to earth on the downlink frequency. This allows the satellite to receive and redirect communications between various earth stations.

2. A Satellite is a solid object which revolves
around some heavenly body due to the effect of
gravitational forces which are mutual in nature.
COMMUNICATION SATELLITE-
A communication satellite is an artificial satellite
that act as a radio relay station in orbit above the
earth that receives, amplifies, and redirects
analog and digital signals carried on a specific
radio frequency. It act as a repeater in long
distance communication path.

3. •Natural Satellite
 E.g. moon
•Artificial Satellite
 E.g. Aryabhata, INSAT..
•Active Satellite
•Passive Satellite

4. ACTIVE SATELLITE
It is a functioning satellite that receives and transmits or
retransmits radio-communication signals to or from a base
station.
They have more complicated structures having a processing
equipment called Transponder which is very vital for
functioning of the satellite. These transponders serve dual
purpose i.e. provides amplification of the incoming and
performs the frequency translation of the incoming signal to
avoid interference between the incoming and outgoing
signals.
PASSIVE SATELLITE
Passive satellites are relay stations in space. It simply reflects
light or radio waves transmitted from one ground terminal to
another without amplification or retransmission.

5. Satellite
communication is
simply the
communication of the
satellite in space with
large number of earth
stations on the
ground.
A Communication
Satellite can be
looked upon as a
large microwave
repeater.

6. Users are connected to the earth station via some
telephone switch or some dedicated link. They
generate baseband signals, which is processed at
the earth station and then transmitted to the
satellite through dish antennas. The satellite
receives the uplink frequency and the transponder
present inside the satellite does the processing
function and frequency down conversion and then
transmit the downlink signal at different
frequency. The earth station then receives the
signal from the satellite through parabolic dish
antenna and processes it to get back the
baseband signal. This baseband signal is then
transmitted to the respective user via dedicated
link or other terrestrial system.

7. DownlinkUplink

8. Long distance communication beyond 10 – 20
MHz in three modes failed:-
Ground wave due to conduction losses
Space wave due to limited line of sight
Sky wave due to penetration of the ionosphere
by the higher frequencies beyond critical
frequency.
And thus, there came the need of satellite
communication.
We have seen that the waves of freq.> 30MHz can
not propagate by conventional modes due to
penetration of frequencies beyond 30MHz
through ionosphere.

9. A single satellite can provide coverage to over
30% of Earth’s surface and thus was adopted
for long distance communication.
Communication links could be setup through
out the entire world using satellites. This can’t
be done with other modes of communication
due to some severe limitations. It is often the
only solution for some isolated areas.
And a new concept of communication, the
communication through a Satellite
revolutionized communication technology.

10. Frequency Band Range
L-Band 1 to 1.5 GHz
S-Band 1 to 3 GHz
C-Band 3 to 8 GHz
X-Band 8 to 12GHz
Ku-Band 10 to 18 GHz
Ka-Band 18 to 22 GHz

11. FREQUENCY BAND UPLINK DOWNLINK
C-Band 6.00GHz 4.00GHz
X-Band 8.00GHz 7.00GHz
Ku-Band 14.00GHz 11.00GHz
Ka-Band 30.00GHz 20.00GHz

12. C-Band
Adv. : Broad Footprint, little rain fade
Disadv. : Weak signals, interference, large antenna sizes
and amplifiers
Ku-Band
Adv. : Focused Foot prints, no terrestrial interference small
antenna and amplifier
Disadv. : Interference to rain.
Ka-Band
Adv. : Focused Foot prints, large unused bandwidths
Disadv. : Interference to rain.

13. Space Segment
1. The Satellite
2. Tracking, Telemetry and
Telecommand
The Ground Segment
1. Earth Stations

15. Ground segment is basically consist of an
earth station.
An earth station provides a complete uplink
and downlink chain for the signal. It transmits
and receives the signal to and from the
satellite. It is also consist of an antenna. Since
the user baseband signal cannot be
transmitted directly, it is also consist of
amplifiers, modulators and demodulators,
frequency up- and down- converters.

17. The user generates the signal to be
transmitted known as baseband signal. This
baseband signal is consist of video(5MHz),2
audio subcarriers(5.5MHz and 5.75MHz) and
energy dispersal signal(25 MHz). After
modulation(70 MHz) and up conversion(6
GHz),the carrier is amplified and uplinked
through solid parabolic dish antenna(PDA).
Downlink signal can be received through same
PDA using trans-receive filter (TRF) and low
noise amplifier(LNA). After down conversion to
70 MHz it is demodulated to get audio and
video signal.

18. •Parabolic dish
antenna
•Diameter - gain (as a
function of frequency)
•Noise - temperature
(as a function of
elevation)
•Cross-polarisation
isolation
•Wind resistance
•Temperature
variations tolerance
•Tracking...

19. Prime Focus Antenna
• Single Reflector Antenna.
• Feed horn is placed at
the Focal point of the
Reflector.
• Antenna Electronics are
placed on Feed.
• More susceptible to
Interference from Low
elevation sources.
• More Blockage because
feed.
• Antenna Efficiency is in
the range of 60%.
• Low Cost Antenna.
• Primarily Used for
Receive only
applications.

20. Cassagrain Antenna
• Main reflector is
Parabolic
• Sub-Reflector is
hyperboloid and placed
at Prime Focus
• Feed is Corrugated Horn
and is placed at Center
of the Main Reflectors.
• The paraboloid
converges towards the
Sub Reflector ( prime
focus), which is then
reflected by Sub-
Reflector to form a
Spherical Wave
converging on the Feed.

21. Gregarion Antenna
• Main reflector is
Parabolic
• Sub-Reflector is
Parabolic and placed at
Prime Focus
• Feed is Corrugated Horn
and is placed at Center
of the Main Reflectors.
• The paraboloid
converges towards the
Sub Reflector (prime
focus), which is then
reflected by Sub-
Reflector to form a
Spherical Wave
converging on the Feed.

22. Offset Fed Antenna
• Used for Smaller Earth
Stations.
• Main Reflector is a
section of Parabolic,
cutoff above the axis.
• Feed is located below the
axis giving a completely
unblocked Aperture.
• High Antenna efficiency

23.  LNA - amplifies RF signal from the antenna
and feeds it into frequency converter
(typically IF of 70/140 MHz)
 LNB - amplifies RF signal from the antenna
and converts it to an L-band signal (950-2100
MHz)
 LNA is more precise and stable but more
expensive than LNB (LO stability).
 Transmit power amplifiers provide
amplification of signals to be transmitted to
the satellite
 Transceiver takes 70/140 MHz signal and
amplifies it to either C or Ku-band final
frequency.
 Block Up-Converter takes L-band signal

24. The space segment is
consist of the satellite
itself.
A satellite has various
transmitting and receiving
antenna, transponders
and other control systems
like temperature control,
power supply control,
orbit and altitude control,
tracking, telemetry and
command equipment etc..

25. An orbit is the path that a satellite
follows as it revolves around
Earth. In terms of commercial
satellites, there are three main
categories of orbits:
1. LEO( Low Earth Orbit)
• 500-2,000 km above the earth
• These orbits are much closer
to the Earth, requiring
satellites to travel at a very
high speed in order to avoid
being pulled out of orbit by
Earth's gravity
• At LEO, a satellite can circle
the Earth in approximately
one and a half hours

26. 2. MEO( Medium Earth Orbit)
• 8,000-20,000 km above the earth
• These orbits are primarily reserved for
communications satellites that cover the
North and South Pole
• MEO's are placed in an elliptical (oval-
shaped) orbit

27. 3. GEO ( Geosynchronous Orbit)
• 35,786 km above the earth
• Orbiting at the height of 22,282 miles above the equator
(35,786 km), the satellite travels in the same direction and
at the same speed as the Earth's rotation on its axis,
taking 24 hours to complete a full trip around the globe.
Thus, as long as a satellite is positioned over the equator
in an assigned orbital location, it will appear to be
"stationary" with respect to a specific location on the
Earth.
• A single geostationary satellite can view approximately
one third of the Earth's surface.
If three satellites are placed at the proper longitude, the
height of this orbit allows almost all of the Earth's surface to
be covered by the satellites.

29. Three geosynchronous satellite covering entire earth

30. •R=6400 km T=84 minutes
• R=7100 km T=99 minutes (LEO)
• R=11400 km T=201 minutes (MEO)
• R=42350 km T=24 hrs (GEO)
So, an object placed at the orbit approx. 36 000
km above the equator will be seen at the same
position in the sky from Earth.

31. 1. Circular orbit: An orbit that has an eccentricity of 0 and
whose path traces a circle.
2. Elliptic orbit: An orbit with an eccentricity greater than
0 and less than 1 whose orbit traces the path of an
ellipse.
3. Hyperbolic orbit: An orbit with the eccentricity greater
than 1. Such an orbit also has a velocity in excess of
the escape velocity and as such, will escape the
gravitational pull of the planet and continue to travel
infinitely.
4. Parabolic orbit: An orbit with the eccentricity equal to
1. Such an orbit also has a velocity equal to the escape
velocity and therefore will escape the gravitational pull
of the planet and travel until its velocity relative to the
planet is 0. If the speed of such an orbit is increased it

32. 1. Equatorial orbit: An orbit whose inclination in
reference to the equatorial plane is zero degrees.
2. Polar orbit: An orbit that passes above or nearly
above both poles of the planet on each revolution.
Therefore it has an inclination of (or very close to)
90 degrees
3. Inclined orbit: An orbit whose inclination in
reference to the equatorial plane is not zero degrees.

34. The choice of orbit depends upon the nature of
mission, the acceptable interference and the
performance of the launcher:
The extent and latitude of the area covered.
The elevation angle for earth station.
Transmission duration and delay.
Interference.
The performance of launcher.

35. Geo-Synchronous Satellite
• Orbit on the equatorial plane - appears stationary
• Altitude of 36000 Kms.
• Circular orbit around earth with period of 24 hours.
• Coverage of about 1/3 of Earth.
• 2 deg. apart. Identified by Longitudinal position with
ref. to Greenwich.
Advantage Of Geostationary Satellite
• Simple ground station tracking requirements.
• Removes Satellite hand-over problems.
• Negligible Doppler shift

36. Polar Orbiting Satellite
• These satellites orbit the earth in such a
way as to cover the north and south
polar regions.
• These satellites if in a low earth orbit
have to travel at a very high speed.
• These satellites can be kept in low earth
orbit (800 -900 km) or at 36000km apart.

37. Inclined Orbit Satellite
• A disadvantage of Geostationary satellites
is that points on Earth beyond about 80
deg latitude are not visible.
• Inclined orbits, on the other hand can
provide visibility to the higher northern
and southern latitudes, although they
require earth stations to continually track
the satellite

38. Geosynchronous
Geosynchronous means that the satellite is
synchronized with the earth in time and
direction. It means that is time taken by a
satellite to complete its orbit around earth is
equal to the time taken by to earth rotates
around its own axis
Satellite Footprint
Coverage of entire surface of earth that is visible
by the satellite.

39. A communications satellite’s transponder, is the series
of interconnected units which form a communications
channel between the receiving and the transmitting
antennas .
A transponder is consist of:
An input band limiting device (a band pass filter).
An Input low-noise amplifier (LNA) to amplify the
(normally very weak, because of the large distances
involved) signals received from the earth station.
A frequency translator (normally composed of an
oscillator and a frequency mixer )used to convert the
frequency of the received signal to the frequency
required for the transmitted signal.

40. A output band pass filter.
A power amplifier (this can be a TWT or a solid
state amplifier).
Frequency band on the satellite is divided into
several channels. Each channels are called
transponder Each transponder have 40 MHz .

41. BLOCK DIAGRAM OF A
SATELLITE TRANSPONDER
LOW NOISE
AMPLIFIER(L.N.A)
DOWN
CONVERTER
POWER
AMPLIFIER(P.A)
FILTER
6GHz
4GHz

42. The uplinked signal to satellite is 6GHz.it is
received at the satellite and then amplified
using a Low Noise Amplifier(L.N.A). This
amplified signal is then down converted at
4GHz. It is sent through a filter and then power
amplifier(TWT). The local oscillator frequency
of the down converter is 2225MHz for C band
and Ex-C band. This signal is then
retransmitted at earth ground station.

43. GEO 15 Yrs $2B
MEO 10 Yrs $2-3B
LEO 5 Yrs $1.5-3B
Lease 1 Yrs
Own 5-15 Yrs

44. LARGE >1000Kg
MEDIUM 500-1000Kg
MINI 100-500Kg
MICRO 10-100Kg
NANO 1-10Kg
PICO <1 Kg

45. 1. Can reach over large geographical area. A single
satellite can provide coverage to over 30% of Earth’s
surface. With just 3 geosynchronous satellite we can
cover the entire earth.
2. Point to Multi point communication is possible.
3. Only solution for developing and isolated areas.
4. Ideal for broadcast applications.
5. No need for the local loop.
6. Wide bandwidths (155 Mbps) are available now.
7. Transmission cost and quality of signal is
independent
of distances.
8. During critical condition earth stations can be
removed and relocated easily.

46. 1. Delay of 270+270 msec makes one feel annoying.
2. Delay reduces the of satellite in data transmission
during long file transfer.
3. Communication path between TX and RX is
approximately 75000 km.
4. High atmospheric losses above 30 GHz limit
carrier frequencies.
5. Large up front capital costs (space segment and
launch)
6. Terrestrial break even distance expanding (now
approx. size of Europe)
7. Congestion of frequencies and orbits

47. 1.Communication Satellite Services
2.Broadcasting Satellite Services [BSS]
3.Mobile Satellite Services
4.Navigational Satellite Services
5.Metrological Satellite Services.
6.Military Satellite Services.

48. 1. Positioning in orbit
This can be achieved by several methods
One method is to use small rocket motors.
These use fuel - over half of the weight of most
satellites is made up of fuel.
Often it is the fuel availability which
determines the lifetime of a satellite.
Commercial life of a satellite typically 10-15
years

49. 2. Stability
 It is vital that satellites are stabilised
•to ensure that solar panels are aligned
properly
•to ensure that communications antennae are
aligned properly
 Early satellites used spin stabilisation
•Either this required an inefficient omni-
directional aerial
•Or antennae were precisely counter-rotated in
order to provide stable communications
 Modern satellites use reaction wheel
stabilisation - a form of gyroscopic stabilisation
Other methods of stabilisation are also possible
 Including:
•eddy current stabilisation
•forces act on the satellite as it moves through
the earth’s magnetic field

50. 3. Reaction wheel stabilisation
Heavy wheels which rotate at
high speed - often in groups of 4.
3 are orthogonal, and the 4th (spare) is a
backup at an angle to the others.
Driven by electric motors - as they speed
up or slow down the satellite rotates.
If the speed of the wheels is inappropriate,
rocket motors must be used to stabilise the
satellite - which uses fuel

51. 4. Power
Modern satellites use a variety of power .
Solar panels are now quite efficient, so
solar power is used to generate electricity.
Batteries are needed as sometimes the
satellites are behind the earth - this
happens about half the time for a LEO
satellite.
Nuclear power has been used - but not
recommended

52. 5. Harsh Environment
Satellite components need to be specially
“hardened”
Circuits which work on the ground will fail
very rapidly in space
Temperature is also a problem - so
satellites use electric heaters to keep
circuits and other vital parts warmed up -
they also need to control the temperature
carefully

53. 6. Alignment
There are a number of components
which need alignment
•Solar panels
•Antennae
These have to point at different parts of
the sky at different times, so the problem
is not trivial

54. 7. Antennae alignment
A parabolic dish can be used which is
pointing in the correct general direction.
Different feeder “horns” can be used to
direct outgoing beams more precisely.
Similarly for incoming beams
A modern satellite should be capable of at
least 50 differently directed beams

55. 8. Rain fade
Above 10 GHz rain and other disturbances
can have a severe effect on reception.
This can be countered by using larger
receiver dishes so moderate rain will have
less effect.
In severe rainstorms reception can be lost
In some countries sandstorms can also be a
problem

60. 8/30/2017 60T.Shanmugaraju,ADE,STI[T],Delhi

64.  1990 – Insat-1D launched using the
American Delta launch vehicle.
 1988 – Insat-1C launched by Ariane space
from French Guyana in July.