ALMA, located in the Atacama desert in northern Chile at an altitude of 5,000m above sea level, is comprised of 66 antennas working as an interferometer. This allows it to achieve extremely high resolutions, revealing detailed structures in the millimeter and submillimeter wave bands, and produce images up to ten times sharper than the Hubble Space Telescope. Each ALMA antenna is currently equipped with 8 different receivers, covering wave bands from 84 GHz to 950 GHz. The Band-1 receiver is one of two remaining missing receiver bands, eventually completing the planned 10 wave bands.
The Band-1 receiver is a most impressive technological achievement. With its extremely low noise across a very wide bandwidth of 35 GHz to 50 GHz (6 to 8.5 mm in wavelength) it is among the most sensitive receivers of its generation. Its development and complex technical realization were only possible with an international team under the leadership of ASIAA. In Taiwan, in particular the collaboration between ASIAA and the Aeronautical Systems Research Division in National Chung-Shan Institute of Science and Technology (ASRD, NCSIST) has been central to the success of this international project. “The realization of Band-1 is a testimony of Taiwan’s outstanding engineering capabilities which allow us to be at the forefront of radio instrumentation in astronomy and contribute to key components in the most advanced observing facilities,” says Patrick Koch at ASIAA, the principal investigator of the Band-1 project. “ASRD has been cooperating with ASIAA for decades and participated in a number of international research projects, such as the SMA (Submillimeter Array), the YTLA (Yuan Tseh Lee Array), the GLT (Greenland Telescope), and the ALMA East-Asia Front End Integration Center in Taiwan. With this we have gained international recognition. Our institute is deeply proud and honored to be a member of the project team,” says Eric Chi, the NCSIST ASRD Director. “After obtaining the R&D authorization for the Band-1 receiver, ASIAA once again selected the ASRD to perform the mechanical design and analysis, verification and acceptance of microwave components, receiver assembly and testing, and quality assurance report. The first successful fringes with the Band-1 receivers delivered to the OSF (Operations Support Facility) in Chile are an encouragement to the Band-1 receiver development team and represent a phased approach to success. We are proud of being a member of the team.”
For any new receiver, the successful ‘first light’ marks a major breakthrough as it is the first time that an astronomical signal (light) goes through the entire telescope, from the antenna that is collecting the light, through the receiver with all the backend electronics, to a computer screen at the end displaying the result. It is the ultimate test that design, fabrication, and assembly are all perfect. After more than 10 years of hard and meticulous work, the Band-1 receiver successfully achieved first light observing the edge of the moon on 14 August 2021, from the ALMA site in Chile. “This is the proudest moment for all of us to see the first results from ALMA Band-1 using a set of antennas. This achievement allows the ALMA Band-1 to bridge the gap between millimeter/submillimeter and centimeter-wave radio astronomy. This is an important milestone for the entire project that demonstrates a big accomplishment in the state-of-the-art radio astronomy instrumentation,” says the Band-1 project manager Ted Huang at ASIAA. “This is really exciting news,” adds the Band-1 systems engineer Chau-Ching Chiong at ASIAA. “The Band-1 receiver project could not have been fulfilled without the help of the local microwave communities in Taiwan, providing their support in design, manufacturing, assembling, and testing, from component to system level. This achievement fully demonstrates our potential for leading future international projects in radio astronomy.” The first light was immediately followed by a ‘first fringe’ detection on 17 August, where the signals of two Band-1 receivers installed in two different antennas were correlated. On 27 August, phase closure with three antennas was successfully demonstrated, and the first radio spectrum towards an evolved star was detected. This was all achieved at the ALMA site in Chile in collaboration with the local staff of ALMA Partners and the Joint ALMA Observatory (JAO). “One of the most challenging issues has been the remote coordination of the activities of all the people involved,” says Giorgio Siringo, the ALMA Senior Engineer, “that had to be carried out from different continents during the pandemic emergency.”
The Band-1 receiver, once installed on all 66 ALMA antennas, will break new ground in various science areas. Being the lowest-frequency receiver on ALMA, it is sensitive to wave ranges close to 1 cm. This will allow it to peer out at the distant red-shifted Universe further than any other receiver on ALMA, making it possible to detect the most distant objects in the submillimeter Universe. Band-1 is also much anticipated to make the next breakthrough discoveries in the study of planet formation. “It will enable the detection of centimer-sized dust grains and small pebbles in regions where planets can form. With this we can study the growth of dust grains and eventually understand how planets form out of interstellar dust,” says Hsi-Wei Yen, the Band-1 project scientist at ASIAA. The delivery of all 66 and 7 spare Band-1 receivers from Taiwan to ALMA in Chile is expected to be completed by the end of 2022, with the installation of all receivers concluding shortly afterwards.
"The Band-1 project is really a long-term effort and commitment for us, starting from scratch to reaching this important milestone of first light,” comments the Band-1 project engineer Yuh-Jing Hwang at ASIAA. The beginning of research into a possible Band-1 project at ASIAA goes back to 2005, when the receiver laboratory started investigating circuit designs of key components. “It would be impossible for us to reach this milestone without the continuous funding support from Academia Sinica and the Ministry of Science and Technology of Taiwan, and the seamless cooperation with all the partners around the world. The fruitful knowledge and experience accumulated from the ALMA Band-1 receiver project will be the basis and starting point for us when facing the challenges of developing the next-generation radio instrument for astronomy.”
"The first light of the ALMA Band-1 receiver is a major milestone in this project and the East Asia ALMA Development Program, and brings us one step closer to offering this new and highly anticipated frequency band to the astronomical community,” says Álvaro González, the East Asian ALMA Program Manager at NAOJ. “It represents another major achievement of the long-term collaboration between NAOJ and ASIAA for ALMA." As part of the East-Asian ALMA Development program, the Band-1 receiver project is led by the Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA) in Taiwan, in collaboration with the National Astronomical Observatory of Japan (NAOJ), the NRC Herzberg Astronomy and Astrophysics Research Centre in Canada, the National Radio Astronomy Observatory (NRAO) in the US, and the Departamento de Astronomía, Facultad de Ciencias Físicas y Matemáticas Universidad de Chile (UCh). Locally, ASIAA also collaborates with National Taiwan University (NTU), National Central University (NCU), National Chung-Cheng University (CCU) and National Taipei University (NTPU) in the joint development of key millimeter-wave electronic components and with the Aeronautical Systems Research Division in National Chung-Shan Institute of Science and Technology (ASRD, NCSIST) for integration, verification, and assembly. The Band-1 research project was supported in Taiwan by Academia Sinica and grants from the Ministry of Science and Technology of Taiwan.