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 a way of coupling the electronic circuit to the medium of communication called free space.
The antenna dish 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 maximum signal strength.
The same reason why a concave mirror is used in a reflecting telescope; it gathers all the photons and focuses them to one single point.
The satellite is situated in an orbit of 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.