The NOEMA phasing system

Aims. With its large collecting area, the NOrthern Extended Millimeter Array (NOEMA) is a prime candidate for a highly sensitive very long baseline interferometry (VLBI) station in the millimeter range. In this work, we describe the phasing system used for coherently adding the 12 antennas of the array. Methods. We developed and installed VLBI dedicated hardware and a new correlator firmware mode to achieve this goal. We also developed an active phasing software to compensate in real time for tropospheric phase variations across the array. Results. This phasing system enabled the NOEMA array to achieve a level of sensitivity equivalent to a ∼50 m single dish antenna. Since 2021, phased NOEMA has been participating regularly in VLBI observations as part of the existing millimeter VLBI networks: the Global Millimeter VLBI Array (GMVA) and the Event Horizon Telescope (EHT).