SWARM: A 32 GHz Correlator and VLBI Beamformer for the Submillimeter Array

TL;DR

SWARM is a high-bandwidth, flexible correlator and beamformer designed for the SMA, enabling advanced VLBI observations and participation in the EHT with 32 GHz bandwidth and real-time data processing.

Contribution

This paper introduces SWARM, a novel 32 GHz correlator and VLBI beamformer for SMA, integrating open-source hardware and high-speed data recording for enhanced astronomical observations.

Findings

Successfully deployed at SMA with verified performance.

Supports 32 GHz bandwidth for VLBI and interferometry.

Enables participation in EHT observations.

Abstract

A 32 GHz bandwidth VLBI capable correlator and phased array has been designed and deployed at the Smithsonian Astrophysical Observatory's Submillimeter Array (SMA). The SMA Wideband Astronomical ROACH2 Machine (SWARM) integrates two instruments: a correlator with 140 kHz spectral resolution across its full 32 GHz band, used for connected interferometric observations, and a phased array summer used when the SMA participates as a station in the Event Horizon Telescope (EHT) Very Long Baseline Interferometry (VLBI) array. For each SWARM quadrant, Reconfigurable Open Architecture Computing Hardware (ROACH2) units shared under open source from the Collaboration for Astronomy Signal Processing and Electronics Research (CASPER) are equipped with a pair of ultra-fast Analog-to- Digital Converters (ADCs), a Field Programmable Gate Array (FPGA) processor, and eight 10 Gigabit Ethernet ports. A VLBI data recorder interface designated the SWARM Digital Back End, or SDBE, is implemented with a ninth ROACH2 per quadrant, feeding four Mark6 VLBI recorders with an aggregate recording rate of 64 Gbps. This paper describes the design and implementation of SWARM, as well as its deployment at SMA with reference to verification and science data.