Communications using Satellites in Geosynchronous/Geostationary Orbit

Communications using Satellites in Geosynchronous/Geostationary Orbit

  • Satellites in geosynchronous or geostationary orbits revolve around the Earth at the same rate as the Earth’s rotation. This means they are always over the same point on the Earth’s surface, approximately 35,786 km above the equator.

  • These satellites are predominantly used for communication purposes as they can receive signals from a ground station and then transmit those signals across wide areas on Earth.

  • Communication from ground to satellite (uplink) and from satellite to ground (downlink) is achieved through the use of electromagnetic waves in the form of radio waves or microwaves. These waves are part of the electromagnetic spectrum and can travel through space.

  • The uplink and downlink frequencies are different to avoid interference between the signals sent and the signals received by the satellite.

  • The time it takes for the signal to travel from the ground, to the satellite and then back to the ground is approximately a quarter of a second. This delay is known as the ‘latency’ and can often cause a slight delay in satellite communications.

  • As the signals in the form of radio waves or microwaves travel in straight lines, the Earth’s curvature may affect the transmission. In order to avoid this, multiple geostationary satellites are used providing a coverage network.

  • The transmission and reception of signals are possible due to the use of large parabolic dishes that concentrate the weak signals from the satellite at the antenna. The larger the dish, the greater is its ability to concentrate weak signals.

  • Satellites’ longevity in geostationary orbits is reliant on their solar panels and on-board energy sources being able to power the on-board systems. These include transponders which receive, amplify and retransmit signals back to Earth.

  • Signal quality can be affected by weather conditions on Earth, particularly heavy rain which can absorb microwaves. This is known as ‘rain fade’.

  • It is important to recognise that while geostationary satellites are helpful in providing global coverage, they have limitations. For instance, they are less effective in higher latitudes due to Earth’s curvature.

  • Finally, remember that electromagnetic waves, including radio and microwaves, are a form of energy and they obey the wave equation: wave speed = frequency x wavelength. In the context of satellite communication, increasing the frequency of the wave can allow for more information to be sent over a period of time, but it can also make the wave more susceptible to being absorbed or scattered by the atmosphere.