Satellite Dishes, Receivers and LNBs
Satellite dishes are a kind of parabolic antennas designed in such a way that they receive signals through microwave from circulating communication
satellites. The communication satellites send out signals or broadcasts (satellite television) as well as data transmissions.
Due to their parabolic shape, the satellite dishes can reflect these signals to the center of the dishes. Typically the satellite dish is support on brackets
at its center and the center or the focal point of the dish is called â€˜feedhorn.' The feedhorn is instrumental in gathering and conducting the signals to
a low-noise â€˜block down converter' also known as Low Noise Block or LNB.
Low Noise Block or LNBs
What the LNB does is it converts the various signals emitted from radio or electromagnetic waves to a more readable electrical signal. It also has the
capability to shift the signals received from various downlinked banks such as C and Ku to the L band. Most satellite dishes that are used for direct
broadcasting have an LNBF that combines the capabilities of both the LNB with those of feedhorn.
Recently a new omni-directional satellite aerial that doesn't require a parabolic dish is being used for moving platforms like a vehicle etc.
Physics of Satellite Dishes
As the frequency increases so does the directive gain. However, the factual gain is really dependent on many other factors that include the surface
finish of the dish, the amount of accuracy employed to create the shape, and the feedhorn matching. The most commonly used commercial type
satellite dishes having 60 cm diameter have a gain value of 37.50dB at 11.75 GHz.
Lower frequencies like C-band offer satellite dish designers' flexibility with materials. Larger sized dishes are now being designed using metal mesh
within a metal framework. The lower the frequency, the more versatility in materials and the better the performance. However, as the frequencies
increase, metal meshes can't be used.
Size of Satellite Dishes