How does a parabolic dish focus radio waves in a radio telescope?

A radio telescope uses a parabolic antenna to collect and focus incoming radio waves. Because cosmic radio sources are extremely weak, the large surface area of the dish acts as a collector, reflecting incoming radiation toward a specific point known as the focal point.1

The geometry of the paraboloid surface is essential to this process: it is shaped such that all incoming parallel rays from a distant source are reflected to converge at the focus. At this focal point, a small antenna called the feed—typically a waveguide horn—captures the concentrated signal and transfers it to a sensitive radiometer for amplification and analysis.21

In many modern designs, secondary reflectors are placed in the path of the radiation to redirect the signal to a more accessible location, such as the vertex of the main dish, which allows for easier maintenance and the use of multiple receivers.1