An antenna has an active element that picks up or sends out radio waves. This active element is the one connected to the electronic circuitry. An antenna is essentially a transducer. It converts electrical energy into electromagnetic energy as as way of coupling the electronic circuit to the medium of communication called free space.
Dish antenna is curved so that all the radiation that strikes it is reflected to converge at one single point – its focus – where the amplifier or the receiver is placed. It is a parabolic reflector – a curved surface with the cross-sectional shape of a parabola that directs the incoming waves to the focal point. This enables the maximum signal strength.
The same reason why a concave mirror is used in a reflecting telescope; it gathers all the photons and focusses it to one single point.
The satellite is situated in an orbit about 22,000 miles, or 36,000 km for those who like to count in tens, up. At this point the orbit of the satellite matches that of the Earth, and so for all practical intents and purposes it occupies the same place in the sky constantly when viewed from the ground.
It sends out radio waves. Typically satellites will operate either in the C band (3.7 to 4.2 GHz) or the Ku band (12 to 18 GHz).
The reason we have two is because of the characteristics of each. The C band is highly susceptible to ground fade but not rain. The Ku band is highly susceptible to rain fade but not ground. Consequently where there are densely populated areas where it doesn’t rain much, Ku is better. In remoter areas where you may get a monsoon, C band is a better choice.
Parabolic antenna is used as high-gain antennas for point-to-point communications, in applications such as microwave relay links that carry telephone and television signals between nearby cities, wireless WAN/LAN links for data communications, satellite communications and spacecraft communication antennas. They are also used in radio telescopes.