Wideband 67−116 GHz receiver development for ALMA Band 2

Abstract

Context. The Atacama Large Millimeter/submillimeter Array (ALMA) has been in operation since 2011, but it has not yet been populated with the full suite of its planned frequency bands. In particular, ALMA Band 2 (67-90 GHz) is the final band in the original ALMA band definition to be approved for production. Aims. We aim to produce a wideband, tuneable, sideband-separating receiver with 28 GHz of instantaneous bandwidth per polarisation operating in the sky frequency range of 67-116 GHz. Our design anticipates new ALMA requirements following the recommendations of the 2030 ALMA Development Roadmap. Methods. The cryogenic cartridge is designed to be compatible with the ALMA Band 2 cartridge slot, where the coldest components -the feedhorns, orthomode transducers, and cryogenic low noise amplifiers -operate at a temperature of 15 K. We use multiple simulation methods and tools to optimise our designs for both the passive optics and the active components. The cryogenic cartridge is interfaced with a room-temperature (warm) cartridge hosting the local oscillator and the downconverter module. This warm cartridge is largely based on GaAs semiconductor technology and is optimised to match the cryogenic receiver bandwidth with the required instantaneous local oscillator frequency tuning range. Results. Our collaboration has resulted in the design, fabrication, and testing of multiple technical solutions for each of the receiver components, producing a state-of-the-art receiver covering the full ALMA Band 2 and 3 atmospheric window. The receiver is suitable for deployment on ALMA in the coming years and it is capable of dual-polarisation, sideband-separating observations in intermediate frequency bands spanning 4-18 GHz for a total of 28 GHz on-sky bandwidth per polarisation channel. Conclusions. We conclude that the 67-116 GHz wideband implementation for ALMA Band 2 is now feasible and that this receiver provides a compelling instrumental upgrade for ALMA that will enhance observational capabilities and scientific reach. 1 https://www.almaobservatory.org of construction. Recent technological developments in cryogenic monolithic microwave integrated circuits (MMICs) and optical components, such as wide bandwidth feedhorns, orthomode transducers (OMT), and lens designs -have opened up the opportunity to extend the originally-planned radio-frequency (RF) bandwidth of this receiver, to cover the 67-116 GHz frequency range on-sky with a single receiver. This holds the potential for combining ALMA Band 2 (67-90 GHz) with ALMA Band 3 (84-116 GHz), serving as an upgrade that paves the way for wider bandwidth ALMA operations. As discussed in Mroczkowski et al. 2019a, this approach offers several opera-Article number, page 1 of 23

Feasibility Study of a W-Band Multibeam Heterodyne Receiver for the Gregorian Focus of the Sardinia Radio Telescope

“…The RF requirements of the OMT across the 70-116 GHz frequency band are the following: input return loss >15 dB, insertion loss <0.7 dB (measured at room temperature), cross-polarization and isolation between outputs >25 dB. Our team has demonstrated experience in the design and characterization of mm-wave OMTs [52]- [56] and INAF in particular successfully developed prototypes of W-band OMTs and feed-horns, specifically for the ALMA (Atacama Large Millimeter Array) Band 2+3, 67-116 GHz, receiver cartridge [57]- [58]. Such passive components are based on platelet design.…”

Superconducting Receiver Technologies Supporting ALMA and Future Prospects

“…The first Band 1 receiver has been installed in the ALMA telescope, and a subsequent first light will occur soon. Regarding the Band 2 receivers, preproduction of the first six receivers has been launched by another consortium led by the European Southern Observatory in Germany, in collaboration with numerous other institutes, including NAOJ (Yagoubov et al., 2020). It should be noted that the expected RF coverage is 67–116 GHz.…”

Measuring Magnetic Field With Atacama Large Millimeter/Submillimeter Array

“…Currently, ALMA antennas are equipped with eight receivers, covering the range of wavelengths from 0.3 mm (Band 10, 950 GHz) to 3.6 mm (Band 3, 84 GHz). Two receivers for longer wavelengths are planned to be added, with one receiver up to 8.6 mm (Band 1, 35 GHz, Huang et al, 2016Huang et al, , 2018 being in construction, and the second one, for the wavelengths up to 4.6 mm (Band 2, 67-116 GHz, Yagoubov et al, 2020), being under development. The array is reconfigurable in multiple patterns (configurations) ranging in size from 150 m (compact) up to 16 km (extended), depending on the required sensitivity and spatial resolution.…”