Since the ALMA North America Prototype Antenna was awarded to the Smithsonian Astrophysical Observatory (SAO), SAO and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) are working jointly to relocate the antenna to Greenland. This paper shows the status of the antenna retrofit and the work carried out after the recommissioning and subsequent disassembly of the antenna at the VLA has taken place. The next coming months will see the start of the antenna reassembly at Thule Air Base. These activities are expected to last until the fall of 2017 when commissioning should take place. In parallel, design, fabrication and testing of the last components are taking place in Taiwan.
This report presents a down-conversion method involving digital sideband separation for the Yuan-Tseh Lee Array (YTLA)
to double the processing bandwidth. The receiver consists of a MMIC HEMT LNA front end operating at a wavelength of
3 mm, and sub-harmonic mixers that output signals at intermediate frequencies (IFs) of 2–18 GHz. The sideband separation
scheme involves an analog 90° hybrid followed by two mixers that provide down-conversion of the IF signal to a pair of
in-phase (I) and quadrature (Q) signals in baseband. The I and Q baseband signals are digitized using 5 Giga sample per
second (Gsps) analog-to-digital converters (ADCs). A second hybrid is digitally implemented using field-programmable
gate arrays (FPGAs) to produce two sidebands, each with a bandwidth of 1.6 GHz. The 2 x 1.6 GHz band can be tuned to
cover any 3.6 GHz window within the aforementioned IF range of the array. Sideband rejection ratios (SRRs) above 20
dB can be obtained across the 3.6 GHz bandwidth by equalizing the power and delay between the I and Q baseband signals.
Furthermore, SRRs above 30 dB can be achieved when calibration is applied.
The Greenland Telescope project will deploy and operate a 12m sub-millimeter telescope at the highest point of the Greenland i e sheet. The Greenland Telescope project is a joint venture between the Smithsonian As- trophysical Observatory (SAO) and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA). In this paper we discuss the concepts, specifications, and science goals of the instruments being developed for single-dish observations with the Greenland Telescope, and the coupling optics required to couple both them and the mm-VLBI receivers to antenna. The project will outfit the ALMA North America prototype antenna for Arctic operations and deploy it to Summit Station,1 a NSF operated Arctic station at 3,100m above MSL on the Greenland I e Sheet. This site is exceptionally dry, and promises to be an excellent site for sub-millimeter astronomical observations. The main science goal of the Greenland Telescope is to carry out millimeter VLBI observations alongside other telescopes in Europe and the Americas, with the aim of resolving the event horizon of the super-massive black hole at the enter of M87. The Greenland Telescope will also be outfitted for single-dish observations from the millimeter-wave to Tera-hertz bands. In this paper we will discuss the proposed instruments that are currently in development for the Greenland Telescope - 350 GHz and 650 GHz heterodyne array receivers; 1.4 THz HEB array receivers and a W-band bolometric spectrometer. SAO is leading the development of two heterodyne array instruments for the Greenland Telescope, a 48- pixel, 325-375 GHz SIS array receiver, and a 4 pixel, 1.4 THz HEB array receiver. A key science goal for these instruments is the mapping of ortho and para H2D+ in old protostellar ores, as well as general mapping of CO and other transitions in molecular louds. An 8-pixel prototype module for the 350 GHz array is currently being built for laboratory and operational testing on the Greenland Telescope. Arizona State University are developing a 650 GHz 256 pixel SIS array receiver based on the KAPPa SIS mixer array technology and ASIAA are developing 1.4 THz HEB single pixel and array receivers. The University of Cambridge and SAO are collaborating on the development of the CAMbridge Emission Line Surveyor (CAMELS), a W-band `on- hip' spectrometer instrument with a spectral resolution of R ~ 3000. CAMELS will consist of two pairs of horn antennas, feeding super conducting niobium nitride filter banks read by tantalum based Kinetic Inductance Detectors.
The ALMA North America Prototype Antenna was awarded to the Smithsonian Astrophysical Observatory (SAO) in 2011. SAO and the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), SAO’s main partner for this project, are working jointly to relocate the antenna to Greenland to carry out millimeter and submillimeter VLBI observations. This paper presents the work carried out on upgrading the antenna to enable operation in the Arctic climate by the GLT Team to make this challenging project possible, with an emphasis on the unexpected telescope components that had to be either redesigned or changed. Five-years of inactivity, with the antenna laying idle in the desert of New Mexico, coupled with the extreme weather conditions of the selected site in Greenland have it necessary to significantly refurbish the antenna. We found that many components did need to be replaced, such as the antenna support cone, the azimuth bearing, the carbon fiber quadrupod, the hexapod, the HVAC, the tiltmeters, the antenna electronic enclosures housing servo and other drive components, and the cables. We selected Vertex, the original antenna manufacturer, for the main design work, which is in progress. The next coming months will see the major antenna components and subsystems shipped to a site of the US East Coast for test-fitting the major antenna components, which have been retrofitted. The following step will be to ship the components to Greenland to carry out VLBI
The Array for Microwave Background Anisotropy (AMiBA) is a radio interferometer for research in cosmology,
currently operating 7 0.6m diameter antennas co-mounted on a 6m diameter platform driven by a hexapod
mount. AMiBA is currently the largest hexapod telescope. We briefly summarize the hexapod operation with
the current pointing error model. We then focus on the upcoming
13-element expansion with its potential
difficulties and solutions. Photogrammetry measurements of the platform reveal deformations at a level which
can affect the optical pointing and the receiver radio phase. In order to prepare for the 13-element upgrade, two
optical telescopes are installed on the platform to correlate optical pointing tests. Being mounted on different
locations, the residuals of the two sets of pointing errors show a characteristic phase and amplitude difference
as a function of the platform deformation pattern. These results depend on the telescope's azimuth, elevation
and polarization position. An analytical model for the deformation is derived in order to separate the local
deformation induced error from the real hexapod pointing error. Similarly, we demonstrate that the deformation
induced radio phase error can be reliably modeled and calibrated, which allows us to recover the ideal synthesized
beam in amplitude and shape of up to 90% or more. The resulting array efficiency and its limits are discussed
based on the derived errors.
The Submillmeter Array (SMA) consists of 8 6-meter telescopes on the summit of Mauna Kea. The array has been
designed to operate from the summit of Mauna Kea and from 3 remote facilities: Hilo, Hawaii, Cambridge,
Massachusetts and Taipei, Taiwan. The SMA provides high-resolution scientific observations in most of the major
atmospheric windows from 180 to 700 GHz. Each telescope can house up to 8 receivers in a single cryostat and can
operate with one or two receiver bands simultaneously. The array being a fully operational observatory, the demand for
science time is extremely high. As a result specific time frames have been set-aside during both the day and night for
engineering activities. This ensures that the proper amount of time can be spent on maintaining existing equipment or
upgrading the system to provide high quality scientific output during nighttime observations. This paper describes the
methods employed at the SMA to optimize engineering development of the telescopes and systems such that the time
available for scientific observations is not compromised. It will also examine some of the tools used to monitor the SMA
during engineering and science observations both at the site and remote facilities.
Using the array of seven 0.6m antennas in Hawaii, we have conducted short observations on several galaxy clusters through
the Sunyaev-Zeldovich effect at 3mm wavelength in 2007. The observations were done with a resolution of 6', and we
have chosen the low redshift (z=0.09-0.32) massive clusters to optimize detection. Major contamination to the data comes
from instrumental offset and ground pickup. We will demonstrate the results based on a simple on source - off source
switching observing scheme. In addition, the performance of a wideband analog 4-lag correlator was also investigated.
Atmospheric water vapor causes significant undesired phase fluctuations for the SMA interferometer, particularly in its highest frequency observing band of 690 GHz. One proposed solution to this atmospheric effect is to observe simultaneously at two separate frequency bands of 230 and 690 GHz. Although the phase fluctuations have a smaller magnitude at the lower frequency, they can be measured more accurately and on shorter timescales due to the greater sensitivity of the array to celestial point source calibrators at this frequency. In theory, we can measure the atmospheric phase fluctuations in the 230 GHz band, scale them appropriately with frequency, and apply them to the data in 690 band during the post-observation calibration process. The ultimate limit to this atmospheric phase calibration scheme will be set by the instrumental phase stability of the IF and LO systems. We describe the methodology and initial results of the phase stability characterization of the IF and LO systems.
A wideband correlator system with a bandwidth of 16 GHz or more is required for Array for Microwave Background Anisotropy (AMiBA) to achieve the sensitivity of 10μK in one hour of observation. Double-balanced diode mixers were used as multipliers in 4-lag correlator modules. Several wideband modules were developed for IF signal distribution between receivers and correlators. Correlator outputs were amplified, and digitized by voltage-to-frequency converters. Data acquisition circuits were designed using field programmable gate arrays (FPGA). Subsequent data transfer and control software were based on the configuration for Australia Telescope Compact Array. Transform matrix method will be adopted during calibration to take into account the phase and amplitude variations of analog devices across the passband.