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.
We report on the design of a 240 GHz double-side-band receiver for the Submillimeter Array (SMA). The heart of this
receiver is a 3-junction series connected SIS mixer, which allows it to provide intermediate frequency (IF) output up to
more than 12 GHz. We have custom built a low noise Amplifier-Multiplier Chain for use as the receiver’s Local
Oscillator module, which is tunable from 210 to 270 GHz. The receiver has demonstrated low noise performance in
laboratory. 7 out of the 8 SMA antennas are now equipped with this receiver. The receiver has already participated in
Event Horizon Telescope observations in April 2016, working with the SMA-200 receiver to provide dual polarization
coverage for the EHT Hawaii Station. This receiver has enabled the SMA to provide 32 Gbit per second data stream to
the EHT observations. We are currently trying to improve the on-sky beam co-alignment of this receiver with respect to
other SMA receivers.
The Submillimeter Array (SMA) is an 8-element mm/sub-mm interferometer on the summit of Maunakea, Hawaii that is
operated jointly by the Smithsonian Astrophysical Observatory (SAO) and the Academia Sinica Institute of Astronomy
and Astrophysics (ASIAA). After nearly 13 years of operation, we are undertaking a major upgrade of the array's
cryogenics, receivers and other systems that will enhance the science capabilities of the array and replace components
reaching end-of-life. Here we describe the new receivers, containing dual-polarization, ultra-wideband SIS mixers
operating at 230 and 345 GHz, the new ultra-wideband IF signal transport and correlator system, and the enhanced
observing capabilities that will be enabled by this upgrade.
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
In the spring of 2010, the Academia Sinica Institute of Astronomy and Astrophysics, and the Smithsonian Astrophysical
Observatory, acquired the ALMA North America prototype antenna – a state-of-the-art 12-m diameter dish designed for
submillimeter astronomy. Together with the MIT-Haystack Observatory and the National Radio Astronomy
Observatory, the plan is to retrofit this antenna for cold-weather operation and equip it with a suite of instruments
designed for a variety of scientific experiments and observations. The primary scientific goal is to image the shadow of
the Super-Massive Black Hole in M87 in order to test Einstein’s theory of relativity under extreme gravity. This requires
the highest angular resolution, which can only be achieved by linking this antenna with others already in place to form a
telescope almost the size of the Earth. We are therefore developing plans to install this antenna at the peak of the
Greenland ice-sheet. This location will produce an equivalent North-South separation of almost 9,000 km when linked
to the ALMA telescope in Northern Chile, and an East-West separation of about 6,000 km when linked to SAO and
ASIAA’s Submillimeter Array on Mauna Kea, Hawaii, and will provide an angular resolution almost 1000 times higher
than that of the most powerful optical telescopes. Given the quality of the atmosphere at the proposed telescope location,
we also plan to make observations in the atmospheric windows at 1.3 and 1.5 THz. We will present plans to retrofit the
telescope for cold-weather operation, and discuss potential instrumentation and projected time-line.
The Cold-Electron Bolometer (CEB) is a sensitive millimetre-wave detector which is easy to integrate with superconducting
planar circuits. CEB detectors have other important features such as high saturation power and very fast response. We
have fabricated and tested CEB detectors integrated across the slot of a unilateral finline on a silicon substrate. Bolometers
were fabricated using two fabrication methods: e-beam direct-write trilayer technology and an advanced shadow mask
evaporation technique. The CEB performance was tested in a He3 sorption cryostat at a bath temperature of 280mK. DC
I-V curves and temperature responses were measured in a current bias mode, and preliminary measurements of the optical
response were made using an IMPATT diode operating at 110GHz. These tests were conducted by coupling power directly
into the finline chip, without the use of waveguide or feedhorns. For the devices fabricated in standard direct-write technology,
the bolometer dark electrical noise equivalent power is estimated to be about 5×10-16W/√Hz, while the dark
NEP value for the shadow mask evaporation technique devices is estimated to be as low as 3×10-17W/√Hz.
We present the design of a broadband superconductor-insulator-superconductor (SIS) mixer operating near
700 GHz. A key feature of our design is the utilisation of a new type of waveguide to planar circuit transition
comprising a unilateral finline taper. This transition is markedly easier to design, simulate and fabricate than the
antipodal finline we employed previously. The finline taper and the superconducting circuitry are deposited on
a 15 μm thick silicon substrate. The employment of the very thin substrate, achieved using Silicon-On-Insulator
(SOI) technology, makes it easy to match the incoming signal to the loaded waveguide. The lightweight mixer chip
is held in the E-plane of the waveguide using gold beam leads, avoiding the need for deep grooves in the waveguide
wall. This new design yields a significantly shorter chip, free of serrations and a wider RF bandwidth. Since
tuning and all other circuits are integrated on the mixer chip, the mixer block is extremely simple, comprising
a feed horn and a waveguide section without any complicated mechanical features. We employ a new type
of smooth-walled horn which exhibits excellent beam circularity and low cross polarisation, comparable to the
conventional corrugated horn, and yet is easier to fabricate. The horn is machined by standard milling with
a drill tool shaped into the horn profile. In this paper, we describe the detailed design of the mixer chip
including electromagnetic simulations, and the mixer performance obtained with SuperMix simulations. We also
present the preliminary measurements of the smooth-walled horn radiation patterns near the mixer operating
Finlines are planar structures which allow broadband and low loss transition from waveguide to planar circuits.
Their planar structure and large substrate makes them ideal for integration with other planar circuits and
components, allowing the development of an on chip polarimeter. We have developed a method of extending the
employment of finlines to thick substrates with high dielectric constants by drilling or etching small holes into
the substrate, lowering the effective dielectric constant. We present the results of scale model measurements at
15GHz and cryogenic measurements at 90GHz which illustrate the excellent performance of finline transitions
with porous substrates and the suitability of this technique for extending the bandwidth of finline transitions.
We have fabricated TES bolometers with finline transitions for the CℓOVER project. We have measured the
optical response of CℓOVER's first prototype 97-GHz detectors and find that they have a detection efficiency
close to 100%. We have also investigated the effects of misalignment of the finline in the waveguide and of
thinning the substrate. The prototype detectors have dark NEPs as low as 1.5 x 10-17W/√Hz and satisfy
the requirement of photon-noise limited operation on CℓOVER. We describe the optical tests of CℓOVER's
prototype 97-GHz detectors and discuss their implications for the design of the science-grade detectors.
CℓOVER is a multi-frequency experiment optimised to measure
the Cosmic Microwave Background (CMB) polarization, in
particular the B-mode component. CℓOVER comprises two
instruments observing respectively at 97 GHz and 150/225 GHz.
The focal plane of both instruments consists of an array of
corrugated feed-horns coupled to TES detectors cooled at 100
mK. The primary science goal of CℓOVER is to be sensitive to
gravitational waves down to r ~ 0.03 (at 3σ)in two years of operations.
Several technologies are now being considered for modulating the polarization in various B-mode instruments, including rotating quasioptical half-wave plates in front of the focal plane array, rotating waveguide half-wave plates and Faraday rotators. It is not at all clear that any of these techniques is feasible without heavy penalty in cost or performance. A potentially much more efficient method is to use a pseudo-correlation polarimeter in conjunction with a planar circuit phase switch.
We investigate three different devices for use as mm-wave switches, SIS tunnel junctions, capacitively coupled superconducting nanostrips and RF MEMS. The SIS tunnel junction switches operate by switching between two different bias voltages, while the nanostrip switch operates by changing the impedance of a resonant circuit by driving the nanostrip from the superconducting to normal state. In each case the RF signal sees two substantially different complex impedance states, hence could be switched from one transmission line branch to another. In MEMS this is achieved by mechanical movement of one plate of a parallel plate capacitor system. Although RF MEMS have been reported at high microwave and low mm-wave frequencies, in this work we have investigated cryogenic MEMS for operation at high mm-wave frequencies (225 GHz) using superconducting transmission lines.
We present and compare designs and simulations of the performance of phase switches based on all three switching technologies, as well as preliminary experimental results for each of the switches. Finally we also present designs of phase shift circuits that translates the on/off switching into phase modulation.
CℓOVER is an experiment which aims to detect the signature of gravitational waves from inflation by measuring
the B-mode polarization of the cosmic microwave background. CℓOVER consists of three telescopes operating
at 97, 150, and 220 GHz. The 97-GHz telescope has 160 horns in its focal plane while the 150 and 220-GHz
telescopes have 256 horns each. The horns are arranged in a hexagonal array and feed a polarimeter which
uses finline-coupled TES bolometers as detectors. To detect the two polarizations the 97-GHz telescope has 320 detectors while the 150 and 220-GHz telescopes have 512 detectors each. To achieve the required NEPs the
detectors are cooled to 100 mK for the 97 and 150-GHz polarimeters and 230 mK for the 220-GHz polarimeter.
Each detector is fabricated as a single chip to guarantee fully functioning focal planes. The detectors are
contained in linear modules made of copper which form split-block waveguides. The detector modules contain
16 or 20 detectors each for compatibility with the hexagonal arrays of horns in the telescopes' focal planes. Each
detector module contains a time-division SQUID multiplexer to read out the detectors. Further amplification of
the multiplexed signals is provided by SQUID series arrays. The first prototype detectors for CℓOVER operate
with a bath temperature of 230 mK and are used to validate the detector design as well as the polarimeter
technology. We describe the design of the CℓOVER detectors, detector blocks, and readout, and give an update
on the detector development.
The Quantum Theory of Mixing developed by Tucker provides a solid framework for understanding the behaviour of SIS mixers, and subsequent developments allow the simulation of complete mixer circuits. These methods operate, however, under the assumption of small signal levels, and so neglect the non-linear behaviour of the signal path. The non-linearity of the mixer's response to applied signals is of vital importance to the calibration of SIS receiver systems. We have previously reported a procedure for calculating the full quantum behaviour of tunnel junction circuits under multiple high-level signals, allowing the accurate prediction of the saturation characteristics of SIS mixers. In this paper, we apply our procedure to both an idealized SIS mixer and one of our previously tested 700 GHz finline mixers. We find that the small signal behaviour predicted by our procedure agrees well with other simulation methods, and that the saturation properties of both of these mixers differ from that predicted by previous estimates of saturation behaviour.
We report the successful operation of a 700 GHz SIS finline mixer employing a Nb tunnel junction and Nb transmission lines. In particular, we discuss the properties of a new mixer feed and the influence of tuning on the mixer performance. Experimental and simulation work shows that the performance of the mixer below the superconducting gap is strongly dependent on the electrical properties of the tuning stub, while at frequencies above the gap the mixer performance is dominated by both tuning and transmission line losses.