Question

The diagram shows a dish antenna which is used to receive television signals from a satellite. The antenna (signal detector) is fixed in front of the curved dish.

1. What is the purpose of the dish?
2. Should it be concave or convex?
3. Where should the antenna be positioned to receive the strongest possible signals?
4. Explain what change you would expect in the signals if a larger dish was used.

Answer 1

1. The dish is collecting a large amount of signal from the satellite, and converging it to the antenna.
2. The dish should be concave. A convex surface would scatter (diverge) the signals, while a concave surface would reflect parallel incoming waves inward so they meet.
3. The antenna should be positioned at the focus of the concave dish to receive the strongest possible signals.
4. If a larger dish were used, the aperture of the concave mirror would have been bigger; therefore, the signals received by the antenna would have been stronger.