M4L11: High Throughput Communication Satellites

Satellite communications make it possible for so much of today's technology to function. From GPS and HDTV, to the safety and protection our armed forces provide, there are many uses for satellites. However, different uses require different techniques for transmitting the data back to earth in the most effective way.

If you look closely at the bands, you would see that L and S band have the lowest frequencies. This is because, these frequencies do not interfere with the atmosphere. In contrast, the higher frequency bands are more susceptible to signal degradation due to ‘rain fade’ (the absorption of radio signals by atmospheric rain, snow or ice).

Majority of the satellites in India use L-band (1–2 GHz) and S-band (2–4 GHz). Which means, they cannot provide adequate speed for broadband. If India wants to make the Digital India program successful, it needs to ramp up the speed of the Internet at affordable rates. For this purpose, satellite-based broadband can provide the best solution as fiber optic-based broadband is expensive.

Now high frequency waves carry more energy. This makes them more capable to provide higher data carrying capacities. The highest among them comes in Ka band. However, one thing, that misses attention is the fact, that with higher frequencies, wavelength also reduces proportionally.

However, it should be noted that waves with less wavelength also have less range. They cannot travel long. This means that if the satellite uses Ka band to offer high data carrying speeds, it will have to compromise somewhere in the amount of area, that comes under its coverage. Such satellites are called spot beam satellites or High Throughput communication (HTC) Satellite. In this case, the receiver antenna needs to be pointed towards the satellite.

GSAT 11 is a HTC satellite.

In case of DTH service (Direct to Home) TV signals have to carry huge amounts of data. For that purpose, they use Ku or Ka Band. So, have you seen the satellite dish antennas pointing to the Geo Stationary Satellites from which it receives signals? Why because, in that case, the satellite would be using Ka band to beam the data.

Now think the other way. In the case of L and S band, the frequency is low. This means that the amount of data, it carries will be obviously less. And the range will be quite more. Thus, while L band and S band provide less data carrying speeds, the satellite using it will have larger coverage. Such satellites are called as wide beam satellites and the receiver does not need a directional antenna to receive of the signals. So now, may I ask if mobile phones use L band / S band or something else?