Performance assessment of an adaptive beamformer for the submillimeter array

The Sub millimeter Array (SMA) was recently upgraded with a new wideband correlator that features a built-in beamforming system. This functionality enables the array to participate in a wider range of astronomical observations, such as Very Long Baseline Interferometry (VLBI) experiments, which require coherent combination of the signal-of-interest received by each element in the array. At millimeter and sub millimeter frequencies the propagation delay through the atmosphere varies significantly over time and across the array, and if not properly accounted for, it could severely degrade the signal-to-noise ratio (SNR) in the beam formed output. An adaptive beamformer is therefore needed to properly phase the array. Herein we describe such a beamforming system employed at the SMA and present results obtained through measurement and simulation to determine its efficacy.