report doordarshan lucknow

7/31/2019 Report Doordarshan lucknow

1/27

2012

DOORDARSHAN

LUCKNOW

Aditi singhL.I.T. LUCKNOW

[SATELLITE COMMUNICATION]ORBITAL ASPECTS,WORKING OF SATELLITE,BASIC TRANSMISSION THEORY,LINK BUDGET

Under The Guidance of :

Mr. R. NAITHANI


2/27

CERTIFICATE

This is to satisfy that this project report

SATELLITE COMMUNICATION

Is a bonafied record of the work done by

Aditi singh student of ims engineering college

In practical fulfillment of requirement for the award of the degree of

Bachelor Technology in Electronics & communication.

DATE: 23/07/12 Mr. R.Naithani

Training head

( )


3/27

Acknowledgement

At the outset, I would like to express my

gratitude toDOORDARSHAN LUCKNOW who

gave me this opportunity to learn something new

and related to our branch that will be useful in my

academics and career.

A very special vote of thanks to Mr. R.Naithani sir for

guiding us through our training period.


4/27

CONTENTS1.HISTORY

2.ORBITAL ASPECT OF SATELLITECOMMUNICATION

3.WORKING OF SATELLITE

4.SATELLITE LINK DESIGN

5.BIBLIOGRAPHY


5/27

HISTORY

A satellite is an object which has been placed into orbit by humanendeavor. Such objects are sometimes called artificial satellites to.distinguish them from natural satellites such as moon .The worlds firstartificial satellite, the SPUTNIK 1, was launched by soviet union in 1957.

Satellites are used for a large number of purposes. Common types includemilitary and civilian Earth observation satellites, communications satellites,

navigation satellites, weather satellites, and research satellites. Spacestations and human spacecraft in orbit are also satellites. Satellite orbitsvary greatly, depending on the purpose of the satellite, and are classified ina number of ways. Well-known (overlapping) classes include low Earthorbit, polar orbit, and geostationary orbit.

Satellites are usually semi-independent computer-controlled systems.Satellite subsystems attend many tasks, such as power generation, thermalcontrol, telemetry, altitude control and orbit control.

Sputnik 2 was launched on November 3, 1957 and carried the first living

passenger into orbit, a dog named Laika.

'First launch by country

Order Country Year of first launch Rocket Satellite

1 Soviet Union 1957 Sputnik-PS Sputnik 1

2 United States 1958 Juno I Explorer 1
http://en.wikipedia.org/wiki/Communications_satellitehttp://en.wikipedia.org/wiki/Space_stationhttp://en.wikipedia.org/wiki/Space_stationhttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Low_Earth_orbithttp://en.wikipedia.org/wiki/Low_Earth_orbithttp://en.wikipedia.org/wiki/Polar_orbithttp://en.wikipedia.org/wiki/Geostationary_orbithttp://en.wikipedia.org/wiki/Attitude_controlhttp://en.wikipedia.org/wiki/Sputnik_2http://en.wikipedia.org/wiki/Laikahttp://en.wikipedia.org/wiki/Soviet_Unionhttp://en.wikipedia.org/wiki/Soviet_Unionhttp://en.wikipedia.org/wiki/Sputnik_(rocket)http://en.wikipedia.org/wiki/Sputnik_(rocket)http://en.wikipedia.org/wiki/Sputnik_1http://en.wikipedia.org/wiki/Sputnik_1http://en.wikipedia.org/wiki/United_Stateshttp://en.wikipedia.org/wiki/United_Stateshttp://en.wikipedia.org/wiki/Juno_Ihttp://en.wikipedia.org/wiki/Juno_Ihttp://en.wikipedia.org/wiki/Explorer_1http://en.wikipedia.org/wiki/Explorer_1http://en.wikipedia.org/wiki/Explorer_1http://en.wikipedia.org/wiki/Juno_Ihttp://en.wikipedia.org/wiki/United_Stateshttp://en.wikipedia.org/wiki/Sputnik_1http://en.wikipedia.org/wiki/Sputnik_(rocket)http://en.wikipedia.org/wiki/Soviet_Unionhttp://en.wikipedia.org/wiki/Laikahttp://en.wikipedia.org/wiki/Sputnik_2http://en.wikipedia.org/wiki/Attitude_controlhttp://en.wikipedia.org/wiki/Geostationary_orbithttp://en.wikipedia.org/wiki/Polar_orbithttp://en.wikipedia.org/wiki/Low_Earth_orbithttp://en.wikipedia.org/wiki/Low_Earth_orbithttp://en.wikipedia.org/wiki/Spacecrafthttp://en.wikipedia.org/wiki/Space_stationhttp://en.wikipedia.org/wiki/Space_stationhttp://en.wikipedia.org/wiki/Communications_satellite


6/27

'First launch by country

Order Country Year of first launch Rocket Satellite

3 France 1965 Diamant Astrix

4 Japan 1970 Lambda-4S sumi

5 China 1970 Long March 1 Dong Fang Hong I

6 United Kingdom 1971 Black Arrow Prospero X-3

7 India 1980 SLV Rohini

8 Israel 1988 Shavit Ofeq 1

_ Russia[1]

1992 Soyuz-U Kosmos 2175

_ Ukraine[1]

1992 Tsyklon-3 Strela

11 Iran 2009 Safir-2 Omid
http://en.wikipedia.org/wiki/Francehttp://en.wikipedia.org/wiki/Francehttp://en.wikipedia.org/wiki/Diamanthttp://en.wikipedia.org/wiki/Diamanthttp://en.wikipedia.org/wiki/Ast%C3%A9rix_(satellite)http://en.wikipedia.org/wiki/Ast%C3%A9rix_(satellite)http://en.wikipedia.org/wiki/Japanhttp://en.wikipedia.org/wiki/Japanhttp://en.wikipedia.org/wiki/Lambda_(rocket)http://en.wikipedia.org/wiki/Lambda_(rocket)http://en.wikipedia.org/wiki/%C5%8Csumi_(satellite)http://en.wikipedia.org/wiki/%C5%8Csumi_(satellite)http://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/Long_March_1http://en.wikipedia.org/wiki/Long_March_1http://en.wikipedia.org/wiki/Dong_Fang_Hong_Ihttp://en.wikipedia.org/wiki/Dong_Fang_Hong_Ihttp://en.wikipedia.org/wiki/United_Kingdomhttp://en.wikipedia.org/wiki/United_Kingdomhttp://en.wikipedia.org/wiki/Black_Arrowhttp://en.wikipedia.org/wiki/Black_Arrowhttp://en.wikipedia.org/wiki/Prospero_X-3http://en.wikipedia.org/wiki/Prospero_X-3http://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Satellite_Launch_Vehiclehttp://en.wikipedia.org/wiki/Satellite_Launch_Vehiclehttp://en.wikipedia.org/wiki/Rohini_(satellite)http://en.wikipedia.org/wiki/Rohini_(satellite)http://en.wikipedia.org/wiki/Israelhttp://en.wikipedia.org/wiki/Israelhttp://en.wikipedia.org/wiki/Shavithttp://en.wikipedia.org/wiki/Shavithttp://en.wikipedia.org/wiki/Ofeqhttp://en.wikipedia.org/wiki/Ofeqhttp://en.wikipedia.org/wiki/Russiahttp://en.wikipedia.org/wiki/Russiahttp://en.wikipedia.org/wiki/Russiahttp://en.wikipedia.org/wiki/Soyuz-Uhttp://en.wikipedia.org/wiki/Soyuz-Uhttp://en.wikipedia.org/wiki/Kosmos_2175http://en.wikipedia.org/wiki/Kosmos_2175http://en.wikipedia.org/wiki/Ukrainehttp://en.wikipedia.org/wiki/Ukrainehttp://en.wikipedia.org/wiki/Ukrainehttp://en.wikipedia.org/wiki/Tsyklon-3http://en.wikipedia.org/wiki/Tsyklon-3http://en.wikipedia.org/wiki/Strela_(satellite)http://en.wikipedia.org/wiki/Strela_(satellite)http://en.wikipedia.org/wiki/Iranhttp://en.wikipedia.org/wiki/Iranhttp://en.wikipedia.org/wiki/Safir_(rocket)http://en.wikipedia.org/wiki/Omid_(satellite)http://en.wikipedia.org/wiki/Omid_(satellite)http://en.wikipedia.org/wiki/Omid_(satellite)http://en.wikipedia.org/wiki/Safir_(rocket)http://en.wikipedia.org/wiki/Iranhttp://en.wikipedia.org/wiki/Strela_(satellite)http://en.wikipedia.org/wiki/Tsyklon-3http://en.wikipedia.org/wiki/Ukrainehttp://en.wikipedia.org/wiki/Ukrainehttp://en.wikipedia.org/wiki/Kosmos_2175http://en.wikipedia.org/wiki/Soyuz-Uhttp://en.wikipedia.org/wiki/Russiahttp://en.wikipedia.org/wiki/Russiahttp://en.wikipedia.org/wiki/Ofeqhttp://en.wikipedia.org/wiki/Shavithttp://en.wikipedia.org/wiki/Israelhttp://en.wikipedia.org/wiki/Rohini_(satellite)http://en.wikipedia.org/wiki/Satellite_Launch_Vehiclehttp://en.wikipedia.org/wiki/Indiahttp://en.wikipedia.org/wiki/Prospero_X-3http://en.wikipedia.org/wiki/Black_Arrowhttp://en.wikipedia.org/wiki/United_Kingdomhttp://en.wikipedia.org/wiki/Dong_Fang_Hong_Ihttp://en.wikipedia.org/wiki/Long_March_1http://en.wikipedia.org/wiki/Chinahttp://en.wikipedia.org/wiki/%C5%8Csumi_(satellite)http://en.wikipedia.org/wiki/Lambda_(rocket)http://en.wikipedia.org/wiki/Japanhttp://en.wikipedia.org/wiki/Ast%C3%A9rix_(satellite)http://en.wikipedia.org/wiki/Diamanthttp://en.wikipedia.org/wiki/France


7/27


8/27

Eccentricity classifications

Circular orbit: An orbit that has an eccentricity of 0 and whose pathtraces a circle

Hohmann transfer orbit:An orbital maneuver that moves aspacecraft from one circular orbit to another using two engine impulses.This maneuver was named afterWalter Hohmann

Elliptic orbit: An orbit with an eccentricity greater than 0 and lessthan 1 whose orbit traces the path of an ellipse.

Geosynchronous transfer orbit: An elliptic orbit wherethe perigee is at the altitude of a Low Earth orbit (LEO) and the apogeeat the altitude of a geosynchronous orbit.

Geostationary transfer orbit: An elliptic orbit where theperigee is at the altitude of a Low Earth orbit (LEO) and the apogee atthe altitude of a geostationary orbit.

Molniya orbit: A highly elliptic orbit with inclination of 63.4and orbital period of half of a sidereal day (roughly 12 hours). Such asatellite spends most of its time over two designated areas ofthe planet (specifically Russia and the United States).

Tundra orbit: A highly elliptic orbit with inclination of 63.4 andorbital period of one sidereal day (roughly 24 hours). Such a satellitespends most of its time over a single designated area of the planet.
http://en.wikipedia.org/wiki/Circular_orbithttp://en.wikipedia.org/wiki/Circular_orbithttp://en.wikipedia.org/wiki/Orbital_eccentricityhttp://en.wikipedia.org/wiki/Circlehttp://en.wikipedia.org/wiki/Hohmann_transfer_orbithttp://en.wikipedia.org/wiki/Hohmann_transfer_orbithttp://en.wikipedia.org/wiki/Impulse_(physics)http://en.wikipedia.org/wiki/Walter_Hohmannhttp://en.wikipedia.org/wiki/Elliptic_orbithttp://en.wikipedia.org/wiki/Elliptic_orbithttp://en.wikipedia.org/wiki/Ellipsehttp://en.wikipedia.org/wiki/Geosynchronous_transfer_orbithttp://en.wikipedia.org/wiki/Geosynchronous_transfer_orbithttp://en.wikipedia.org/wiki/Perigeehttp://en.wikipedia.org/wiki/Low_Earth_orbithttp://en.wikipedia.org/wiki/Apogeehttp://en.wikipedia.org/wiki/Geostationary_transfer_orbithttp://en.wikipedia.org/wiki/Geostationary_transfer_orbithttp://en.wikipedia.org/wiki/Molniya_orbithttp://en.wikipedia.org/wiki/Molniya_orbithttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Sidereal_dayhttp://en.wikipedia.org/wiki/Planethttp://en.wikipedia.org/wiki/Tundra_orbithttp://en.wikipedia.org/wiki/Tundra_orbithttp://en.wikipedia.org/wiki/Tundra_orbithttp://en.wikipedia.org/wiki/Planethttp://en.wikipedia.org/wiki/Sidereal_dayhttp://en.wikipedia.org/wiki/Orbital_periodhttp://en.wikipedia.org/wiki/Molniya_orbithttp://en.wikipedia.org/wiki/Geostationary_transfer_orbithttp://en.wikipedia.org/wiki/Apogeehttp://en.wikipedia.org/wiki/Low_Earth_orbithttp://en.wikipedia.org/wiki/Perigeehttp://en.wikipedia.org/wiki/Geosynchronous_transfer_orbithttp://en.wikipedia.org/wiki/Ellipsehttp://en.wikipedia.org/wiki/Elliptic_orbithttp://en.wikipedia.org/wiki/Walter_Hohmannhttp://en.wikipedia.org/wiki/Impulse_(physics)http://en.wikipedia.org/wiki/Hohmann_transfer_orbithttp://en.wikipedia.org/wiki/Circlehttp://en.wikipedia.org/wiki/Orbital_eccentricityhttp://en.wikipedia.org/wiki/Circular_orbit


9/27

Look Angle Of Satellite Communication

The coordinates to which the earth station antennas must be pointedto communicate with the satellite is called Look angles.

There r 2 types of look angles:

1. Azimuth angle:Measured eastward from geographic northto the projection of satellite path on the local horizontal plane at

the earth station.

2. Elevation Angle:Measured upward from local horizontalplane at the earth station to the satellite path.

Azimuth and Elevation Calculations

The azimuth and elevation angles for our earth station antenna must becalculated so that the correct satellite can be seen. The azimuth is thehorizontal pointing angle of the earth station antenna. The elevation is theangle we look up into the sky to see the satellite. To calculate the azimuthand elevation of a ground station antenna requires that the ground stationlatitude and longitude be known as well as the longitude of the satellite.The longitude of the satellite can be obtained from charts such as the

WESTSAT. The latitude and longitude of the ground station can beobtained from U.S. Geological Survey maps of the region you are in. Moreadvanced methods of locating the exact ground station are availablethrough the use of the Global Positioning Satellite (GPS). Once the actuallocation is known the elevation angle of the earth station antenna can becalculated using equation 1.


10/27

[Eq. 1]

Next the azimuth can be calculated using equation 2.

[Eq. 2]


11/27

Parking slot of a satellite:

Latitude and longitude of a sub-satellite point are called as parking slot ofthe satellite where sub-satellite point stands for a point where a straight linedrawn from a satellite to the center of the Earth intersects the Earth'ssurface.

parking slot is the longitudinal co-ordinates in case of geo-stationarysatellites .


12/27


13/27

Communication Satellite:

Communication satellites are very complex and extremely expensive toprocure & launch.

The communication satellites are now designed for 12 to 15 years of lifeduring which the communication capability of the satellite earns revenue, torecover the initial and operating costs. Since the satellite has to operateover a long period out in the space the subsystems of the satellite are

required to be very reliable. Major subsystems of a satellite are:

Satellite Bus Subsystems Satellite Payloads


14/27

Satellite Bus subsystems:

Mechanical structure Attitude and orbit control system

Propulsion System Electrical Power System Tracking Telemetry and Command System Thermal Control System

Satellite Payloads

Communication transponders Communication Antennas

Since the communications capacity earns revenue, the satellite must carryas many communications channels as possible. However, the largecommunications channel capacity requires large electrical power from largesolar arrays and battery, resulting in large mass and volume. Putting aheavy satellite in geosynchronous orbit being very expensive, it is logical to

keep the size and mass of the satellite small. Lightweight material optimallydesigned to carry the load and withstand vibration & large temperaturecycles are selected for the structure of the satellite.

Attitude and orbit control system maintains the orbital location of thesatellite and controls the attitude of the satellite by using different sensorsand firing small thrusters located in different sides of the satellite. Liquidfuel and oxidizer are carried in the satellite as part of the propulsion systemfor firing the thrusters in order to maintain the satellite attitude and orbit.The amount of fuel and oxidizer carried by the satellite also determines the

effective life of satellite.

The electrical power in the satellite is derived mainly from the solar cells.The power is used by the communications payloads and also by all otherelectrical subsystems in the satellite for housekeeping. Rechargeablebattery is used for supplying electrical power during ellipse of the satellite.


15/27

Telemetry, Tracking and Command system of the satellite works along withits counterparts located in the satellite control earth station. The telemetrysystem collects data from sensors on board the satellite and sends thesedata via telemetry link to the satellite control centre which monitors thehealth of the satellite. Tracking and ranging system located in the earthstation provides the information related to the range and location of thesatellite in its orbit. The command system is used for switching on/off ofdifferent subsystems in the satellite based on the telemetry and trackingdata.

The thermal control system maintains the temperature of different parts ofthe satellite within the operating temperature limits and thus protects thesatellite subsystems from the extreme temperature conditions of the outerspace.

The communications subsystems are the major elements of acommunication satellite and the rest of the space craft is there solely tosupport it. Quite often it is only a small part of the mass and volume of thesatellite. The communications subsystem consists of one or more antennasand communications receiver - transmitter units known as transponders.Transponders are of two types, Repeater or Bent pipe and processing orregenerative. In Repeater type, communications transponder receives thesignals at microwave frequencies and amplifies the RF carrier afterfrequency conversion, whereas in processing type of transponder in

addition to frequency translation and amplification, the RF carrier isdemodulated to baseband and the signals are regenerated and modulatedin the transponder. Analog communication systems are exclusivelyrepeater type. Digital communication system may use either variety. Fig.3(a) and 3(b) show the schematic diagrams of repeater type andregenerative type transponders respectivelyregenerative typetransponders respectively.


16/27


17/27

GROUND SEGMENT:

The ground segment of satellite communications system establishes thecommunications links with the satellite and the user. In large and mediumsystems the terrestrial microwave link interfaces with the user and the earthstation. However, in the case of small systems, this interface is eliminatedand the user interface can be located at the earth station. The earth stationconsists of

Transmit equipment.

Receive equipment. Antenna system.

Fig. 4 shows the schematic block diagram of an earth station.


18/27

In the earth station the base band signal received directly from userspremises or from terrestrial network are appropriately modulated and thentransmitted at RF frequency to the satellite. The receiving earth station afterdemodulating the carrier transmits the base band signal to the user directlyor through the terrestrial link.

The baseband signals received at the earth stations are mostly of thefollowing types.

Groups of voice band analog or digital signals

Analog or digital video signals

Single channel analog or digital signal

Wide band digital signal.

In satellite communications, in early days FM modulation scheme was mostfrequently used for analog voice and video signal transmission. However,the trend is now to use digital signals for both voice and video. Variousdigital modulation schemes like Phase Shift Keying (PSK) and FrequencyShift Keying (FSK) are adopted for transmission of digital signals.

The network operations and control centre for the communications networkmonitors the network operations by different users, distribution of differentcarriers within a transponder and allocation of bandwidth & EIRP ofdifferent carriers. Proper functioning of Network operations and controlcentre is essential where the number of users in the network is large.

Network operations & control centre is also responsible for giving clearanceto the ground system in respect of antenna radiation pattern, EIRP etc.


19/27

SATELLITE LINK DESIGN

Basic transmission theory:

A link budget is the accounting of all of the gains and losses from thetransmitter, through the medium (free space, cable, waveguide, fiber, etc.)to the receiver in a telecommunication system. It accounts for theattenuation of the transmitted signal due to propagation, as well asthe antenna gains, feed line and miscellaneous losses. Randomly varyingchannel gains such as fading are taken into account by adding some

margin depending on the anticipated severity of its effects. The amount ofmargin required can be reduced by the use of mitigating techniques suchas antenna diversity orfrequency hopping.

A simple link budget equation looks like this:

Received Power(dBm) = Transmitted Power (dBm) + Gains (dB) Losses

(dB)

Note that decibels are logarithmic measurements, so adding decibels isequivalent to multiplying the actual numeric ratios.

Link Budget Parameters:

Transmitter power at the antenna

Antenna gain compared to isotropic radiator

EIRP

Flux density at receiver

Free space path loss System noise temperature

Figure of merit for receiving system

Carrier to thermal noise ratio

Carrier to noise density ratio

Carrier to noise ratio
http://en.wikipedia.org/wiki/Telecommunicationhttp://en.wikipedia.org/wiki/Antenna_gainhttp://en.wikipedia.org/wiki/Feedlinehttp://en.wikipedia.org/wiki/Fadinghttp://en.wikipedia.org/wiki/Antenna_diversityhttp://en.wikipedia.org/wiki/Frequency_hoppinghttp://en.wikipedia.org/wiki/DBmhttp://en.wikipedia.org/wiki/Decibelhttp://en.wikipedia.org/wiki/Decibelshttp://en.wikipedia.org/wiki/Decibelshttp://en.wikipedia.org/wiki/Decibelhttp://en.wikipedia.org/wiki/DBmhttp://en.wikipedia.org/wiki/Frequency_hoppinghttp://en.wikipedia.org/wiki/Antenna_diversityhttp://en.wikipedia.org/wiki/Fadinghttp://en.wikipedia.org/wiki/Feedlinehttp://en.wikipedia.org/wiki/Antenna_gainhttp://en.wikipedia.org/wiki/Telecommunication


20/27

ISOTOPIC RADIATOR: An isotropic radiator is a theoretical pointsource ofelectromagnetic orsound waves which radiates the sameintensity of radiation in all directions. It has no preferred

direction of radiation. It radiates uniformly in all directions over a sphere

centered on the source. Isotropic radiators are used as reference radiatorswith which other sources are compared.

Whether a radiator is isotropic is independent of whether it obeys Lambert'slaw. As radiators, a spherical black body is both, a flat black body isLambertian but not isotropic, a flat chrome sheet is neither, and bysymmetry the Sun is isotropic, but not Lambertian on account oflimbdarkening.

Consider an Isotropic Source (punctual radiator) radiating Pt Wattsuniformly into free space. At distance R, the area of the spherical shell withcenter at the source is 4pR2 Flux density at distance R is given by Eq. 4.1

W/m224 R

PF

t
http://en.wikipedia.org/wiki/Point_sourcehttp://en.wikipedia.org/wiki/Point_sourcehttp://en.wikipedia.org/wiki/Electromagnetic_wavehttp://en.wikipedia.org/wiki/Sound_wavehttp://en.wikipedia.org/wiki/Lambert%27s_lawhttp://en.wikipedia.org/wiki/Lambert%27s_lawhttp://en.wikipedia.org/wiki/Lambert%27s_lawhttp://en.wikipedia.org/wiki/Limb_darkeninghttp://en.wikipedia.org/wiki/Limb_darkeninghttp://en.wikipedia.org/wiki/Limb_darkeninghttp://en.wikipedia.org/wiki/Limb_darkeninghttp://en.wikipedia.org/wiki/Limb_darkeninghttp://en.wikipedia.org/wiki/Lambert%27s_lawhttp://en.wikipedia.org/wiki/Lambert%27s_lawhttp://en.wikipedia.org/wiki/Sound_wavehttp://en.wikipedia.org/wiki/Electromagnetic_wavehttp://en.wikipedia.org/wiki/Point_sourcehttp://en.wikipedia.org/wiki/Point_source


21/27

Antenna Gain: In electromagnetics, an antenna's power gain orsimply gain is a key performance figure which combinesthe antenna's directivity and electrical efficiency. As a transmitting antenna,the figure describes how well the antenna converts input power into radio

waves headed in a specified direction. As a receiving antenna, the figuredescribes how well the antenna converts radio waves arriving from aspecified direction into electrical power. When no direction is specified,"gain" is understood to refer to the peak value of the gain. A plot of the gainas a function of direction is called the radiation pattern.

Antenna gain is usually defined as the ratio of the power produced by theantenna from a far-field source on the antenna's beam axis to the powerproduced by a hypothetical lossless isotropic antenna, which is equallysensitive to signals from all directions. Usually this ratio is expressed

in decibels, and these units are referred to as "decibels-isotropic" (dBi).Antenna has gain in every direction! Term gain may be confusingsometimes. Usually Gain denotes the maximum gain of the antenna. Thedirection of maximum gain is called boresight.

G [dB] = 10 log10 (G ratio)

Antenna gain is relative to this standard. Antennas are fundamentallypassive:

No additional power is generated

Gain is realized by focusing power

Similar to the difference between a lantern and a flashlight

Effective Isotropic Radiated Power (EIRP):

EIRP is the amount of power the transmitter would have to produce if itwas radiating to all directions equally

Note that EIRP may vary as a function of direction because of changesin the antenna gain vs. angle

The output power of a transmitter HPA is Pout watts
http://en.wikipedia.org/wiki/Electromagneticshttp://en.wikipedia.org/wiki/Antenna_(radio)http://en.wikipedia.org/wiki/Directivityhttp://en.wikipedia.org/wiki/Antenna_efficiencyhttp://en.wikipedia.org/wiki/Radio_wavehttp://en.wikipedia.org/wiki/Radio_wavehttp://en.wikipedia.org/wiki/Radiation_patternhttp://en.wikipedia.org/wiki/Isotropic_antennahttp://en.wikipedia.org/wiki/Decibelshttp://en.wikipedia.org/wiki/Decibelshttp://en.wikipedia.org/wiki/Isotropic_antennahttp://en.wikipedia.org/wiki/Radiation_patternhttp://en.wikipedia.org/wiki/Radio_wavehttp://en.wikipedia.org/wiki/Radio_wavehttp://en.wikipedia.org/wiki/Antenna_efficiencyhttp://en.wikipedia.org/wiki/Directivityhttp://en.wikipedia.org/wiki/Antenna_(radio)http://en.wikipedia.org/wiki/Electromagnetics


22/27

Some power is lost before the antenna Pt =Pout /Lt watts reaches theantenna( Pt = Power into antenna)

The antenna has a gain of Gt relative to an isotropic radiator

This gives an effective isotropic radiated power of EIRP = Pt Gt wattsrelative to a 1 watt isotropic radiator.

Power flux density:We now want to find the power density atthe receiver. We know that power is conserved in a lossless mediumThe power radiated from a transmitter must pass through a sphericalshell on the surface of which is the receiver. The area of this sphericalshell is 4pR2 .Therefore spherical spreading loss is 1/4pR2 .

Power flux density (p.f.d.) is a measure of the power per unit area. Thisis a regulated parameter of the system. CCIR regulations limit the p.f.d.of any satellite system. CCIR regulations are enforced by signatorynations. Allowable p.f.d. varies w.r.t. elevation angle. It also allowscontrol of interference. There is increasing importance with proliferationof LEO systems.

Effective aperture: Real antennas have effective flux collectingareas which are LESS than the physical aperture area.

Effective Aperture Area Ae is where Aphy is actual

physical aperture area and = aperture efficiency .

Aperture antennas: (horns and reflectors) have a physicalcollecting area that can be easily calculated from their dimensions.

xe phyAA

4

2

2 DrAphy


23/27

WHY db is used as a unit for calculations?

There is a large dynamic range of parameters in satellitecommunications. A typical satellite antenna has a gain of >500.Receivedpower flux is about one part in 100,000,000,000,000,000,000of thetransmitted power.

Wouldnt it be nice to have a better way to write these large numbers? dB also lets many calculations be addition or subtraction!Decibel (dB) isthe unit for 10 times the base 10 logarithmic ratio of two powers Forinstance: gain is defined as Pout/Pin (where Pout is usually greater thanPin)

In db Gain is expressed as

Similarly loss can be expressed as

dBlog10

in

out

P

P

G

dBlog10

out

in

P

PL


24/27

LINK BUDGET:

Transmission:

RECEP

TX

+ HPA Power

Transmission Losses

(cables &

connectors)

+ Antenna Gain

Antenna Pointing

Loss

Free Space Loss

Atmospheric

Loss (gaseous,

clouds, rain)

- Rx Antenna

Pointin Loss

+ Antenna gain

Reception Losses

(cables & connectors)

+ Noise Temperature

Contribution

Rx


25/27

Need for calculation of a Link Budget

System performance is tied to operation thresholds .Operation thresholdsCmin tell the minimum power that should be received at the demodulator inorder for communications to work properly.

Operation thresholds depend on:

Modulation scheme being used.

Desired communication quality.

Coding gain.

Additional overheads.

Channel Bandwidth. Thermal Noise power.

System figure of merit:

G/Ts: RX antenna gain/system temperature which is also called the SystemFigure of Merit, G/Ts . It easily describes the sensitivity of a receive system.It must be used with caution:

Some (most) vendors measure G/Ts under ideal conditions only. G/Tsdegrades for most systems when rain loss increases. This is caused by theincrease in the sky noise component. This is in addition to the loss ofreceived power flux density.

System noise power:

Performance of system is determined by C/N ratio.

Most systems require C/N > 10 dB. (Remember, in dBs: C - N > 10 dB)

Hence usually: C > N + 10 dB

We need to know the noise temperature of our receiver so that wecan calculate N, the noise power (N = Pn).

Tn (noise temperature) is in Kelvins (symbol K):

2730 CTKT 2739

532

0 FTKT


26/27


27/27

Bibliography

Wikipedia

Satellite communication book by DennisRoddy

www.satcoms.org.uk

technologyinterface.nmsu.edu

www.meteor.iastate.edu

www.cosmic.ucar.edu
http://www.satcoms.org.uk/http://www.satcoms.org.uk/http://www.meteor.iastate.edu/http://www.meteor.iastate.edu/http://www.meteor.iastate.edu/http://www.satcoms.org.uk/

report doordarshan lucknow

Documents