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

Objectives Define satellite communications Describe the history of satellite communications Explain Kepler’s laws and how they relate to satellite communications Define and describe satellite orbital patterns and elevation categories Explain satellite look angles Define and describe satellite system parameters Explain satellite system link equations JPRogelio Communications 5

Introduction Satellite In astronomical terms, it is a celestial body that orbits around a planet. In aerospace terms, it is a space vehicle launched by humans and orbits Earth or another celestial body. JPRogelio Communications 5

Introduction Communication Satellite Transponder Is a microwave repeater in the sky that consists of a diverse combination of one or more of the following: Transponder A satellite repeater radio repeater of which a satellite may have many. Repeater Transmitter Amplifier Regenerator Filter Onboard Computer Multiplexer Demultiplexer Antenna Waveguide Other electronic communications circuits JPRogelio Communications 5

Satellite Communications JPRogelio Communications 5

History of Satellites The first artificial earth satellite, SPUTNIK I, was launched in 1957. 1962 Telstar I (AT&T) – operated for only a few weeks due to radiation damage 1963 Telstar II (AT&T) – first transatlantic video transmission 1963 Syncom II – (Syncom I was lost) 1964 Syncom III – used to transmit 1964 Olympics from Tokyo 1965 Early Bird I – first Intelsat satellite 1969 Intelsat Satellites – placed over the Atlantic, Pacific, and Indian Oceans, allowing worldwide satellite communications 1972 Anik A-1 (Canada) – first commercial domestic communications satellite 1972 Westar 1 and 2 (Western Union) – first commercial United States domestic communications satellites JPRogelio Communications 5

KEPLER’s LAW Johannes Kepler (1571-1630) Kepler’s Law German Astronomer discovered the laws that govern satellite motion. Kepler’s Law The planets move in ellipses with the sun at one focus The line joining the sun and a planet sweeps out equal areas in equal interval of time The square of the time of revolution of a planet divided by the cube of its mean distance from the sun gives a number that is the same for all planets JPRogelio Communications 5

Kepler’s First Law Where:  = semi-major axis  = semi-minor axis  = eccentricity Major Axis Minor F1 F2 Center of Ellipse Semi-Major Axis Semi-Minor JPRogelio Communications 5

Kepler’s Second Law Law of Areas States that equal intervals of time a satellite will sweep out equal areas in the orbital plane, focused at the barycenter Earth A1 A2 Orbit Satellite D1 V1 D2 V2 JPRogelio Communications 5

Kepler’s Third Law Harmonic Law Where: States that the square of the periodic time of orbit is proportional to the cube of the mean distance between the primary and the satellite Where: A = constant (unitless) =  = semi-major axis (kilometers) µ = Earth’s Gravitational Constant = 3.986005 x 1014 m3/s2 ω = velocity of the satellite in radian per second P = mean solar earth days JPRogelio Communications 5

Satellite Elevation Categories Satellite Orbital Patterns Satellite Orbits Satellite Elevation Categories Satellite Orbital Patterns JPRogelio Communications 5

Satellite Orbits Orbital Satellites circular elliptical ccw cw ccw cw Direction of Rotation ccw cw ccw rotation (ωe) circular Earth North Pole ccw cw Direction of Rotation ccw rotation (ωe) elliptical North Pole Earth Satellite (ωs) Communications 5

Elliptical Orbits Earth Apogee Perigee

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

Satellite Orbital Patterns Communications 5

Satellite Elevation Categories LEO (low earth orbit) 1.0 GHz to 2.5 GHz ; 480 ,miles MEO (medium earth orbit) 1.2 GHz to 1.66 GHz ; 6000 – 12, 000 miles GEO (geosynchronous earth orbit) 2 GHz to 18 GHz ; 23, 000 miles Communications 5

Geosynchronous Satellites Satellite Orbital Velocity Round-Trip Time Delay Clarke Orbit Advantages and Disadvantages Communications 5

Geosynchronous Satellites Geosynchronous satellites orbit Earth above the equator with the same angular velocity as Earth Sometimes called stationary or Geostationary satellites appear to remain in a fixed location above one spot on Earth’s surface. Communications 5

Direction of Satellite Motion Geostationary Orbit 6400 km North Pole Satellite Earth 36, 000 km Direction of Satellite Motion Direction of Rotation Satellite Orbit Footprint – Depiction of the signal strength contours from a satellite transmitter on the earth

Satellite Orbits Perigee – The point closest to Earth in a Satellite Orbit Apogee – The point farthest from earth in a Satellite Orbit v = 4 x 1011 (d + 6400) where: v = velocity in meter per second d = distance above earth’s surface in km

Path Loss Calculations = GT (dBi) + GR (dBi) – (32.44 + 20 log d + 20 log f) PR PT (dB) Where: PR/PT (dB) = ratio of received to transmitted power, expressed in decibels GT (dBi) = gain of transmitting antenna in decibels with respect to an isotropic radiator GR (dBi) = gain of receiving antenna in decibels with respect to an isotropic radiator) d = distance between transmitter and receiver in kilometers f = frequency in megahertz

Global Coverage Communications 5

Clarke Orbits Communications 5

Satellites in Geosynchronous Orbits COMSTAR I 128° WESTAR II 123.5° WESTAR V 119.5° SATCOM II 119° ANIK III 114° ANIK II 109° ANIK I 104° WESTAR I 99° WESTAR IV 98.5° TELESTAR 96° COMSTAR II 95° WESTAR III 91° SATCOM V 143° SATCOM I 135° Communications 5

Angle of Elevation Azimuth Angle Limits of Visibility Antenna Look Angles Angle of Elevation Azimuth Angle Limits of Visibility Communications 5

Antenna Look Angles Angle of Elevation (Elevation Angle) Azimuth Angle the vertical angle formed between the direction of travel of an electromagnetic wave radiated from an earth station antenna pointing directly toward a satellite and the horizontal plane Azimuth Angle Azimuth is the horizontal angular distance from a reference direction, either the southern or northern most point of the horizon. Azimuth angle is defined as the horizontal pointing angle of an earth station antenna. Engr DF de Bien Communications 5

LOOKANGLES North (0°) West Azimuth East referred to 180° South (180°) Communications 5

Geostationary Satellites Propagation Time – The time taken for a signal to travel through space from transmitter to receiver Inclinometer – is a device incorporating a level that can measure the angle of antenna axis from the horizontal. Declination – The amount by which the antenna axis is offset from the earth’s axis

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

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

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

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

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

Beam at Northern Latitude Incremented Beam Diameter Beam at Northern Latitude

Subsatellite Point GEOCENTER Earth Station SUBSATELLITE POINT Communications 5

Transponder Transponder Type Satellite Frequencies Block Diagram Digital Transponder Beam Switching Cross Link Earth Station TVRO Communications 5

Satellite and Transponder Type Frequency Translation And Amplification Receiving Antenna Transmitting Antenna Bent – Pipe Satellite Transponder

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

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

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

Commonly-Used Geostationary Satellite Frequencies Band Uplink (GHz) Downlink (GHz) Use S 1.6265 – 1.6605 1.53 – 1.559 Marine (Inmarsat) C 5.925 – 6.425 3.7 – 4.2 Commercial X 7.9 – 8.4 7.25 – 7.75 Military Ku 14 – 14.5 11.7 – 12.2 K 27.5 – 30.5 17.7 – 20.2 30 – 31 20.2 – 21.2

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

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

Beam Switching Satellite Alternate Downlink Uplink Earth

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

Earth Stations

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

Thank You "Somewhere in me is a curiosity sensor. I want to know what's over the next hill. You know, people can live longer without food than without information. Without information, you'd go crazy" -Arthur C. Clarke Communications 5