We present the results of a digital calibration technique applied to an Atacama Large Millimeter/submillimeter Array sideband separating wideband astronomical receiver of 275 to 500 GHz radio frequency (RF) and 3 to 22 GHz intermediate frequency bandwidth. The calibration technique consists of computing the magnitude ratio and the phase difference of the receiver output, and then applying correction constants to the digitized signals. Two analog-digital converters are used to digitize the signals and an field-programmable gate array for the processing. No modification in the analog receiver is required to apply the calibration, as it works directly on upper sideband/lower sideband signals. The technique improved the receiver temperature compared with the double sideband case by increasing the sideband rejection ratio by around 30 dB on average. It is shown that even more rejection can be obtained with more careful control of the RF calibration input power.
Currently, we are performing a large-scale survey of molecular clouds toward the Galactic Plane in 12CO, 13CO, and C18O(J = 2–1) with the 1.85-m mm-submm telescope from Nobeyama Radio Observatory. In addition, we are proceeding with the preparation of a new project to observe several additional molecular lines including higher transitions of CO isotopes, such as 12CO, 13CO, and C18O(J = 2–1, 3–2) simultaneously with a wideband receiver (210–375 GHz). The optics has a Cassegrain reflector antenna with Nasmyth beam-waveguide feed and is composed of Main-reflector, Sub-reflector, ellipsoidal mirrors, and plane mirrors. New wideband optics will be required to achieve this goal. In order to accomplish the optics, we have designed a corrugated horn with a fractional bandwidth of ∼56 %, and frequency independent optics to couple the beam from the telescope onto the horn. The corrugated horn has a conical profile and the variable corrugation depth. It has been optimized by using CHAMP, our targeting return loss of better than −20 dB, cross-polarization loss of better than −25 dB, and far-field good radiation pattern. The simulation of the corrugated horn results in low return loss, low crosspolarization, and symmetric beam pattern in that frequency band. The simulated aperture efficiency of the designed receiver optics on the 1.85-m telescope is above 0.76 at all frequencies by using GRASP. Recently, we have succeeded in simultaneous observation of 12CO, 13CO, and C18O(J = 2–1 and 3–2) toward Orion KL with the optics for the first time.
The 1.85-m mm-submm telescope has been operated at Nobeyama Radio Observatory to observe molecular clouds in the nearby Galactic Plane based on the molecular lines of 12CO, 13CO, C18O(J = 2–1). We are planning to relocate the telescope to a site (∼2,500 m) at the Atacama Desert in Chile and to newly install a dual-band receiver for simultaneous observations of lines of CO isotopes with the transitions of J = 2–1 and J = 3–2. In order to achieve this goal, we have developed a wideband diplexer to separate radio frequency (RF) 211–275 GHz (ALMA Band 6) and 275–373 GHz (ALMA Band 7). We adopted a waveguide type FrequencySeparation Filters (FSF) as the basic concept of the wideband diplexer in 210–375 GHz. The wideband diplexer (α) has already been fabricated and measured as the prototype, and we thus obtained reasonable performance in the CO lines band. On the other hand, the measurement result indicates the return loss is relatively worse in 280–300 GHz, although it doesn’t affect the simultaneous observations of 230 GHz and 345 GHz band. We carried out 3D shape measurement with an optical microscope, and then, found that there are machining errors in the parts of the resonator in High Pass Filter. The analysis based on electromagnetic simulation reveals that the errors significantly affect return loss around cut-off frequency. In this paper, we describes the design of the waveguide diplexer, S-parameter measurement, and detailed analysis to verify the discrepancy between simulation and measurement.
A compact 780–950 GHz sideband separating (2SB) superconductor-insulator-superconductor (SIS) mixer measuring 22 mm × 27 mm × 11 mm is designed in this study. In this mixer block, all components such as a radio frequency (RF) 90° hybrid coupler, a local oscillator (LO) power splitter, two LO couplers, two identical SIS chips, and an intermediate frequency (IF) 90° hybrid coupler are integrated. To minimize the waveguide length for the RF signal path, we separate the placement of the waveguide components into two layers in parallel. One layer contains the RF hybrid and LO couplers, and another layer contains the LO power splitter located above the RF hybrid coupler. They are connected by waveguides fabricated via wire electric discharge machining. We performed three-dimensional electromagnetic simulations and confirmed the results. Furthermore, a 4-12-GHz IF 90° hybrid coupler to combine the IF signals from each SIS chip is designed with an alumina substrate having a relatively high dielectric constant to be integrated in the mixer block. The preliminary test result of single sideband noise temperatures of the fabricated 2SB SIS mixer partly complied with the current Atacama Large Millimeter/submillimeter Array (ALMA) specifications without any loss correction in front of the receiver. Because the RF and LO interfaces of the mixer block are the same as that of the current ALMA band 10 mixer block, band 10 cartridges are expected to be upgraded to 2SB configurations without significant changes in optics.
NAOJ have studied wideband receiver technologies at submillimeter wavelengths toward implementation as future upgrades into the Atacama Large Millimeter/submillimeter Array telescope. We have developed critical components and devices such as waveguide components and superconductor-insulator-superconductor (SIS) mixers targeting radio frequencies (RF) in the 275-500 GHz range and an intermediate frequency (IF) bandwidth of 3-22 GHz. Based on the developed components, quantum-limited low-noise performance has been demonstrated by using a double-sideband receiver frontend in combination with a high-speed digitizer. In addition, a preliminary demonstration of a wideband RF/IF sideband-separating SIS mixer was performed. This paper describes the status of our efforts to develop technology toward wideband receivers for ALMA.
The ALMA telescope has been producing ground-breaking science since 2011, but it is mostly based on technology from the 2000s. In order to keep ALMA competitive in the coming decade, timely updates are necessary in order to further improve the science output of the telescope in the coming decades. In this contribution, we will present the status of the different projects and studies which constitute the contribution of East Asia to the ALMA Development Program, such as the production of band 1 receivers, the development of band 2 receivers optics, and of the ACA spectrometer. We will also update on the different hardware and software studies towards the implementation of the ALMA Development Roadmap and additional opportunities.
We are investigating a possible microwave amplifier with low noise and low power consumption at cryogenic temperature for large scale multi-pixel heterodyne superconductor-insulator-superconductor (SIS) receivers at millimeter and submillimeter wavelengths. We propose the use of SIS junctions as amplifier elements based on quasi-particle mixing. By connecting an SIS up-converter and an SIS down-converter in series with gain in both converters, a lownoise and low-power-consumption high-frequency amplifier can be obtained in principle. A proof-of-concept study has been made by configuring an amplifier with two Nb/Al-AlOx/Nb mixers in the 150-GHz band in a standard noise and gain measurement setup at 4 K with a microwave noise source as an input signal. We observed a maximum gain of more than 10 dB and a minimum noise temperature of less than 10 K, which suggests that our proposed SIS amplifier is capable for multi-pixel SIS receivers. On the other hand, we also observed a periodical behavior in frequency dependence of the measured noise temperature and gain due to a standing-wave effect between the two SIS mixers, which is a problem to be solved.
In recent years, NAOJ has contributed designs and production of waveguide and optics components for ALMA bands 1 (35-50 GHz) and 2 (67-116 GHz) receivers. This includes several novel ideas in the design of corrugated horns and OMTs and the application of 3D printing for the fabrication of key components of radio receivers. These frequency bands coincide approximately with bands 5 and 6 of ngVLA, the most promising project in the 2020s to exploit synergies with ALMA with the goal of increasing the scientific output of both facilities. This paper reports on the recent ALMA development results and discusses their future application to ngVLA.
The ALMA telescope has been producing ground-breaking science since 2011, but it is mostly based on front-end and back-end technology from the 2000s. In order to keep ALMA competitive in the coming decade, timely updates are necessary in order to further improve the science output of the telescope. In NAOJ, we have been doing research leading to technological developments which aim to increase the field-of-view of the telescope, and the RF and instantaneous bandwidth for more efficient and accurate spectral surveys. In this contribution, we will describe the most important technical achievements by our group in recent years.
We present in this paper a study of a low-power consumption cryogenic amplifier with GaAs-based HEMT. A two-stage MMIC low noise amplifier for 2.5-4.5 GHz frequency range has been designed, fabricated and measured at a low-power condition with the temperature range from 300 K to 4 K. To design such a cryogenic MMIC amplifier, firstly we extracted the model of the bare-die transistor at cryogenic temperatures fabricated together with the MMIC. The temperature-dependent DC and RF characteristics of the HEMT have been measured. From the approximate noise model based on the DC characteristics, we verified that the HEMTs offer sufficient gain and reasonably noise at a relative lowpower operation condition. Subsequently, we designed a low-power dissipation cryogenic MMIC amplifier utilizing the cryogenic s2p model of the HEMTs biased at the optimal low-power condition. At cryogenic temperature, the GaAsbased amplifier achieves a gain larger than 20dB and a noise temperature as low as 10 K with a total power consumption of 1.2 mW. The low-power amplifiers can be used as first-stage IF amplifiers in a superconductor-insulatorsuperconductor (SIS) receiver, and are especially useful in focal plane arrays with large pixel count because of the merit of the total power consumption.
ALMA has already produced many impressive and scientifically compelling results. However, continuous technical upgrades and development are key for ALMA to continue to lead astronomical research through the 2020-2030 decade and beyond. The East Asia ALMA development program consists of the execution of short term projects, and the planning and initial studies for longer term developments that are essential for future upgrades. We present an overview of all these ongoing East Asia ALMA development projects and upgrade studies, which aim to maintain and even increase the outstanding scientific impact of ALMA in the near future and over the coming decades.
ALMA has been demonstrating its exceptional capabilities with unprecedented scientific results achieved over the past six years of operation. To keep ALMA as a leading-edge telescope, it is essential to continue technical upgrades and development of new potential. While our future development programs have already achieved remarkable technological breakthroughs at the level of front-end receivers, we are discussing the upgrades of the analog and digital backend and the correlator. We report the required concept design of the interferometric system focused on these sub-systems to realize new science use cases.
This paper summarizes the performance of all the 73 ALMA band 10 cartridges in terms of noise performance and/or optical efficiencies compared to the required ALMA specifications. In particular, the measured optical performance is compared with the results of novel statistical Monte Carlo analyses carried out before receiver production. Some of the technical difficulties encountered during production are briefly described. Finally, some of the first light results of the first receivers used in Chile are presented.
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