In 1946 he built the first multi-element astronomical radio interferometer.
From the en.wikipedia.org
On October 4, 1957, the very evening of the launch of Sputnik, students and faculty met at the Observatory and constructed an improvised radio interferometer.
From the en.wikipedia.org
Interferometer arrays produced the first extremely high-resolution images using aperture synthesis at radio, infrared and optical wavelengths.
From the en.wikipedia.org
Radio interferometers have also been used to obtain detailed images of the anisotropies and the polarization of the Cosmic Microwave Background, like the CBI interferometer in 2004.