1. Satellite Communications and Graduation Project:
My graduation project was in one of the main applications of satellite communications. The
project title was" Direct Broadcasting Satellite System for TV Reception". I worked in this
project during the fifth year of my Engineering study.
Satellite communication uses are rapidly increasing, specially with the technological
advancement. Applications of Satellite Communications include Meteorology, weather
forecasting, astronomy, TV broadcasting, Remote sensing, Military Applications, Global
Positioning System (GPS) and many others.
In Satellite communications, different bands of frequency are used such as C, & K Bands.
The higher the frequency band, the bandwidth becomes wider. However, for geostationary
satellites, there are certain high frequencies that cannot be used due to the ionosphere
attenuation and the rain-fade.
The uplink frequency is usually different from downlink's, for the purposes of band separation
and avoidance of interference.
In my project, I gained good knowledge in the following topics:
- Satellite Orbits and Orbital Parameters:
I studied the laws governing the movement of a satellite orbiting the earth, namely "Kepler
Laws". I learned about the different satellite orbits, such as inclined orbit, polar, and
geostationary orbit.
I also studied the satellite mounting tools, and how to draw the mounting arc for any place on
earth. The arc which allows a satellite receiving antenna to move along with the geostationary
orbit to receive from different geostationary satellites.
- Satellite Link and link budget equation for geostationary satellites:
I understood the factors affecting satellite transmission, such as attenuation due to distance
(35,871 Km). I learned how to calculate the Free Space Losses, and how to make the link
budget calculations. The transmitted signals to satellites has usually high power (Mega
Watts), while the received signals from satellites are fractions of mille-watts, yet the signals
can be recovered and information can still be received accurately. I also learned about the
satellite's space segment and earth segment. The telecom part in satellites is called
"Transponder" which is shown in figure 3.3. The figure shows a typical block diagram for a
DBS (Direct Broadcasting Satellite) system.
Figure 3.3: Block Diagram of a Transponder
From above figure 3.3, It's clear that the transponder can receive and re-transmit many
channels (n), mainly due to the wide Band width resulted from the use of high frequency. The
De-Multiplexing & Multiplexing functions are responsible for separating each individual
channel in preparation for amplification, and then re-multiplexing them for downlink
transmission.