Chapter 5

1

Introduction

2

Satellite Communication Systems

3

Basic operation of a communication satellite

between two earth stations

4

Satellite System Links

5

Satellite Transponder

6

Satellite Frequency Bands

7

Satellite Bandwidth

8

• Bandwidth of the satellite will determine the number of signals that can be transmitted • Wider bandwidth can allow many signals to be carried at a time • C-band has different frequencies for uplink≈ 500 MHz • Each transponder is assigned a bandwidth, eg : MEASAT-1 has a bandwidth of 36 MHz for each transponder (total of 12 transponders) • There are 4 MHz guard bands between channels that are used to minimize adjacent channel interference

Increasing Channel Capacity

9

• There is not enough spectrum space for satellite to use all the transponders unless some form of frequency reuse is employed • This method determined that half of the transponders use vertical polarization and another half uses horizontal polarization, with overlapping frequencies

Satellite Orbits

10

Satellite Orbits

11

Satellite Orbits – Orbital Path

12

• There are an infinite number of orbital paths, but only three are useful for communication satellite • Three paths that a satellite can follow as it rotates around the Earth : inclined, equatorial or polar

Polar Orbit

13

Equatorial Orbit

14

Inclined Orbit

15

Antenna Tracking and Adjustment

16

Azimuth Angle

17

Elevation Angle

18

Earth Station

19

Types of Satellites

Geostationary satellites - located 22,236

miles or 35,786 km from earth at the

geosynchronous orbit

Low Orbital Satellites (LEO) located 300 to

1500 km above earth

Medium Orbital Satellites (MEO) located

8000 to 20000 km from earth

20

Application of Geostationary Satellites

21