Aperture synthesis is a type of interferometry that mixes signals from a collection instruments to produce measurements having the same angular resolution as an instrument the size of the entire collection. At each separation and orientation, the lobe_pattern of the interferometer produces an output which is a Fourier Transform of the spatial distribution of the brightness of the observed object.

This process is used in radio astronomy, where it was first developed by Martin Ryle and coworkers at the Mullard Radio Astronomy Observatory (part of the Cavendish Laboratory). During the late 60s and early 70s, as computers became available capable of handling the computationally-intensive Fourier Transform inversions required, they used aperture synthesis to synthesis first a 'One-Mile' and later a '5km' effective aperture. The technique was subsequently further developed in Very Long Baseline Interferometry. It is also used by a type of radar system known as synthetic aperture radar, and even in optical telescopes.