Challenges and progress on the wideband SMA (wSMA) upgrade for the submillimeter array

The Submillimeter array (SMA) is an array of 8 antennas operating at millimeter and sub-millimeter frequencies on Maunakea, Hawaii. At present, the frequency coverage of the SMA is from 180 to 420 GHz. Here we describe the challenges and progress of the SMA in implementing the wideband upgrade: the wSMA project, that we are undertaking. The existing or legacy instrument at the SMA consists of 4 single polarization Double-Side-Band (DSB) receivers. They are housed in a single cryostat with an aging He-4 GM/JT cryocooler. At the heart of the wSMA upgrade is a new receiver cryostat, cooled by a Cryomech PT410-RM pulse tube. The cryostat houses two dual-polarized receiver cartridges equipped with DSB SIS mixers. New Local Oscillator (LO) subsystems, based on a Voltage-Controlled Oscillator (VCO), as well as new mixer control electronics and IF processing upgrades are being introduced. Since there are differences between the existing SMA instrumentation and the new wSMA receiver system, in terms of sky frequency coverage and the available modes of operation, there are significant challenges of operating the legacy systems and the new wSMA instruments in parallel during the transition period. As it will take several years to replace the instrumentation in all 8 antennas, a detailed plan has been laid out to integrate the new instrument hardware and software packages into the array. We will present the transition plan to full wSMA operation, and we will also describe the antenna infrastructure changes, focusing on repurposing existing equipment and optics. In this presentation we will also discuss the comprehensive installation plan, in which the new wSMA cryostat, together with its associated compressor, chiller, electronics, LO's, cartridges, vacuum system are to be installed into the existing receiver cabin space. Another aspect of the project is to upgrade the internal computer networking that will be a key element of the upgrade, allowing the access and control of the distributed microcontrollers used in the entire instrumentation. The wSMA upgrade is expected to enhance the SMA's capabilities, further improve its sensitivity, as well as widening the Intermediate Frequency (IF) bandwidth. The transition plan that we have drawn up ensures that the wSMA upgrade will be easy to operate and will reduce the maintenance requirements by the SMA technical staff.