Why does a satellite receiving radio signals, has an aerial with a concave parabolic reflector?

A parabola has the unusual property that anything incident upon the interior of a parabola while traveling parallel to its axis will reflect directly towards the focus of the parabola. Even though radio signals radiate evenly in all directions from a source, they behave as if they are parallel if you are far enough from the source. So if a parabola is pointed directly at a distant source, the entire portion of the signal that hits the dish will bounce directly into the focus of the parabola, which is where the receiver is located. This enables the antenna to receive a much greater portion of the signal.