How does very long baseline interferometry improve radio telescope resolution?

Very long baseline interferometry (VLBI) improves the resolution of radio telescopes by allowing for the creation of interferometer systems with essentially unlimited element separation.1

In standard radio interferometry, antennas must be physically connected via cables or links to combine signals in real time. Because these physical connections become impractical over long distances, VLBI overcomes this limitation by recording signals at each individual antenna site onto high-density computer disks. These recordings are synchronized with extreme precision—within a few billionths of a second—using hydrogen maser frequency standards. The disks are then transported to a central location, where the signals are replayed and correlated to form interference fringes.12

By enabling antennas to be spread across vast distances—such as across continents or even into space—VLBI synthesizes a massive effective aperture. Since the angular resolution of a telescope depends on the ratio of the observation wavelength to the size of the instrument, this technique allows radio telescopes to achieve extraordinary resolution, far surpassing that of single-dish antennas or smaller arrays.123