Wideband 67-116 GHz cryogenic receiver development for ALMA Band 2

The Atacama Large Millimeter/sub-millimeter Array (ALMA) is already revolutionising our understanding of the Universe. However, ALMA is not yet equipped with all of its originally planned receiver bands, which will allow it to observe over the full range of frequencies from 35-950 GHz accessible through the Earth's atmosphere. In particular Band 2 (67-90 GHz) has not yet been approved for construction. Recent technological developments in cryogenic monolithic microwave integrated circuit (MMIC) high electron mobility transistor (HEMT) amplifier and orthomode transducer (OMT) design provide an opportunity to extend the originally planned on-sky bandwidth, combining ALMA Bands 2 and 3 into one receiver cartridge covering 67-116 GHz. The IF band definition for the ALMA project took place two decades ago, when 8 GHz of on-sky bandwidth per polarisation channel was an ambitious goal. The new receiver design we present here allows the opportunity to expand ALMA's wideband capabilities, anticipating future upgrades across the entire observatory. Expanding ALMA's instantaneous bandwidth is a high priority, and provides a number of observational advantages, including lower noise in continuum observations, the ability to probe larger portions of an astronomical spectrum for, e.g., widely spaced molecular transitions, and the ability to scan efficiently in frequency space to perform surveys where the redshift or chemical complexity of the object is not known a priori. Wider IF bandwidth also reduces uncertainties in calibration and continuum subtraction that might otherwise compromise science objectives. Here we provide an overview of the component development and overall design for this wideband 67-116 GHz cryogenic receiver cartridge, designed to operate from the Band 2 receiver cartridge slot in the current ALMA front end receiver cryostat.Comment: 8 pages, proceedings from the 8th ESA Workshop on Millimetre-Wave Technology and Applications (https://atpi.eventsair.com/QuickEventWebsitePortal/millimetre-wave/mm-wave

RF waveform method for the determination of the safe operating area of GaN HFET's for amplifiers subjected to high output VSWR

Solid state power amplifiers are ordinarily fitted with an isolator at the output port to protect the transistors from large variations in the load impedance. Using GaN transistor technology should allow safe transistor operation to higher field levels and also to higher channel temperatures, which may remove the necessity for the isolator component - reducing circuit losses, and reducing circuit cost and weight. The resulting required transistor mismatch withstand capability is conventionally verified by selecting a specified fundamental frequency VSWR level and sweeping the load phase. The resulting load-line trajectories, mapping the RF voltage and current excursions, are not normally accessible. In the technique described in this paper the RF IV waveforms are directly observed for a variety of load-line characteristics appropriate for mismatch conditions. Load-lines for conventional VSWR's of 10:1 are compared to worst case loads corresponding to total reflection at the fundamental. The role of harmonic terminating impedance is also discussed - and it is demonstrated that the manipulation of the 2nd and 3 rd harmonic impedances can 'shape' the load-lines. Measurements are performed on 2×50μm GaN HFET transistor

RF Waveform Investigation of VSWR Sweeps on GaN HFETs

Solid state amplifiers are often fitted with an isolator component on the output to protect them from impedance mismatch. GaN based HFET’s could offer the potential to remove the isolator due to their high breakdown voltages and high channel temperature operation. However the absence of an isolator would mean that the transistor would have to be able to withstand any load impedance that could be presented to it. The usual method to test for impedance mismatch is to select a fixed VSWR ratio and then sweep the load phase through 360°. In this paper a range of VSWR sweeps are investigated. The measurements are performed in a system that provides the RF voltage and current waveforms, as a consequence novel impedance contour plots can be generated. These plots can then aid in identifying potential failure mechanisms and load conditions to avoid

Development of a RF Waveform Stress Test Procedure for GaN HFETs Subjected to Infinite VSWR Sweeps

An RF waveform stress test has been developed in order to assess device degradation caused by the infinite VSWR conditions that could result from the removal of a protection isolator. The proposed stress test involves both DC and RF characterization of a device, before and after an RF stressing mechanism is applied. The procedure was first applied with the device being stressed whilst driving into its optimum impedance and secondly with the device being stressed by one of the three potential failure regions that result from an infinite VSWR sweep

Wideband 67−116 GHz receiver development for ALMA Band 2

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

Wideband 67-116 GHz receiver development for ALMA Band 2

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.\u3cbr/\u3e\u3cbr/\u3eAims. 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.\u3cbr/\u3e\u3cbr/\u3eMethods. 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.\u3cbr/\u3e\u3cbr/\u3eResults. 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.\u3cbr/\u3e\u3cbr/\u3eConclusions. 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.\u3cbr/\u3e\u3cbr/\u3eKey words: instrumentation: interferometer

Wideband 67−116 GHz receiver development for ALMA Band 2

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.\u3cbr/\u3e\u3cbr/\u3eAims. 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.\u3cbr/\u3e\u3cbr/\u3eMethods. 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.\u3cbr/\u3e\u3cbr/\u3eResults. 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.\u3cbr/\u3e\u3cbr/\u3eConclusions. 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.\u3cbr/\u3e\u3cbr/\u3eKey words: instrumentation: interferometer