Asystem that uses reflected radio waves to detect objects and to measure their distance and speed is called

Such system is called RADAR (RAdio Detection And Ranging).

The Radar emits radio waves, that are reflected back by the object. Since the speed of the radio waves is known (their speed is equal to the speed of light), by measuring the time the waves take to come back to the source it is possible to infer the distance they covered, and so the distance of the object.

Not what goes around on earth but the universe too.

Lexy is correct because angle r is between the incident wave,  n  = 0, and a diffracted wave.