The Submillimeter Array

Receiver Lab Talks: 2021

Questions: Edward Tong
Time: Wednesday 1:00 PM EDT (5:00 PM UTC)
Where: Zoom

Date Speaker Title Summary
Dec 15Wei Yu and
Jonathan Weintroub
Prospects for Tensor Core GPU Correlation The advent of tensor core Graphics Processing Units (GPUs), and development work at ASTRON in the Netherlands, and SARAO in South Africa, has made software driven, real time wideband correlator-beamformers (CBF) feasible. Other key recent technologies include PCIe 4.0 peripheral bus for data transfer, DDR5 dynamic RAM, and SmartNIC technology running at 100 Gbps and faster. Two applications are in primary consideration at SAO: first, a strictly real-time correlator for the Submillimeter Array wSMA project, processing 8 GHz bandwidth per dual polarization block; second, acceleration of VLBI correlation for the higher data volumes of the next generation Event Horizon Telescope (ngEHT). Our talk covers the concept, and describes our first look at the challenges of our very wideband applications.
Dec 8Alex Raymond
EHT Team
Considerations for Future High-Frequency VLBI Observatories The EHT instrumentation has been developed specifically for high-frequency VLBI [EHTC (2019ii) ApJL, Doeleman et al. (2011) PASP, Vertatschitsch et al. (2015) PASP]. This talk will describe some of the considerations of ground-based observations at high frequency, which may be relevant to future experiments [Johnson et al. (2020) Sci. Adv., Haworth et al. (2019) arxiv 1909.01405, Pesce et al. (2019) arxiv 1909.01408].
Nov 17Michael Moebius
Draper Lab
MEMS Beamsteering for Solid State LiDAR and Metrology Draper has developed a novel solid-state beamsteering method for Light Detection And Ranging (LiDAR) systems, based on integrated photonics and Micro-Electro Mechanical Systems (MEMS). A focal plane array of MEMS-actuated grating switches, coupled to a camera lens, scans light across a scene. We have demonstrated a 10 x 10 piexel prototype time-of-flight LiDAR. Implementing this hardware with coherent LiDAR techniques can enable a powerful tool for metrology.
Nov 10Tony Stark
SPT-3G and SPT-4 plans SPT-3G is a detector system for the 10-m diameter South Pole Telescope at 90, 150 and 220 GHz that has been in operation for the past 3 years. It has a monolithic detector surface with ~10,000 bolometers fed by three alumina lenses that image and correct the Gregorian focus. SPT-4 is a planned successor instrument that will operate at higher frequencies, measurements that will enhance the interpretation of the SPT-3G survey data. The redesign of the optics for SPT-4 will allow the Event Horizon Telescope receivers for SPT to be co-located within the warm cabin environment, and permit a rapid, automated transition between receivers.
Nov 3Paul Grimes
Optics for wSMA and Beyond The wSMA upgrade will involve the complete replacement of the SMA receiver optics with new receiver selection and focusing optics contained in the wSMA cryostat and receiver cartridges. The new receiver system will have a somewhat different optical layout to the previous SMA receiver optics, eliminating several room temperature receiver optics elements, and the cooled receiver lenses. I will present the methods used to design, optimize and tolerance the new receiver optics for the wSMA, and discuss the optical alignment activities to confirm the alignment of the wSMA cryostat optics. I will also discuss the options for and constraints on guest receiver optics for single pixel and focal plane array receivers.
Oct 27Attila Kovacs
Kinetric Inductance Parametric Amplifiers for ultra-low-noise heterodyne applications Kinetic inductance Parametric Amplifiers (KIPAs) provide amplification via 3 or 4-wave mixing (3WM or 4WM) modes in the non-linear medium of a superconducting transmission line, whose local kinetic surface inductance (and impedance) is current dependent. KIPAs have been demonstrated to support broad bandwidths (up to ~30 GHz or more) with typical +30 dB amplification. Their noise, just above the quantum limit, is significantly below that of comparable HEMT amplifiers. Consequently, KIPAs are being explored for application with a wide range of cryogenic detectors. As IF amplifiers in heterodyne receivers, KIPAs could increase IF bandwidths and significantly enhance receiver sensitivities, compared to HEMTs. However, there are also challenges to using KIPAs in heterodyne systems, particularly with double-sideband heterodyne receivers. I will provide a brief overview of how KIPAs work, including the 3WM and 4WM operation. I will show where the technology stands today, and discuss the potential benefits and challenges of using KIPAs as IF amplifiers for heterodyne mixers in the (sub)millimeter and the SMA.
Oct 20Lingzhen Zeng
Updates on the wSMA Receiver Cartridge Development The wSMA receiver cartridges are highly-integrated receiver systems that are challenging to design and build. In this talk, I will give an overview of the wSMA receiver cartridge design features, followed by the difficulties we encountered and the solutions we provided during the cartridge development. Finally, I will be presenting the latest measurement results on the two science cartridges that have been fully populated.
Oct 13Tyler St. Germaine
Harvard University
Beam and FTS Systematics in the BOCEP/Keck Array CMB ExperimentsInflation, an extension to the standard cosmological (LCDM) model which posits a brief, accelerated expansion early in the Universe, naturally solves the horizon and flatness problems and provides a source of the initial perturbations that seed large-scale structure. Inflation predicts a background of gravitational waves which would imprint a unique B-mode pattern in the polarization of the Cosmic Microwave Background (CMB), with an amplitude parametrized by the tensor-to-scalar ratio r. The BICEP/Keck Array series of CMB experiments has been observing the polarized CMB from the South Pole since 2006, using small-aperture, on-axis refractors, and has produced world-leading constraints on r from B-mode measurements. As a pair-differencing experiment, an important systematic that must be controlled is the differential beam response between the co-located, orthogonally polarized detectors. In this talk I present high-fidelity measurements of the beam response, and use specialized simulations to predict the bias on r from temperature-to-polarization leakage. I consider other utility of these beam measurements, including optical model comparison and the development of simple metrics used to facilitate model comparisons. I also present measurements of the detector spectral response with a field-deployable Fourier Transform Spectrometer, and discuss how bandpass uncertainties affect the constraint on r.
Oct 6Edward Tong
A Singularity-free Method of extracting Noise Parameters using Noise Power MeasurementsThe noise performance of a microwave amplifier can be described by its noise parameters, which determine the amplifier noise as a function of its source impedance. These parameters are essential for low noise receiver systems, for example SIS mixers tightly integrated with a low noise amplifier, and MHz amplifiers attached to a wideband dipole antenna. In this talk, I will describe the traditional method of noise parameter extraction and a new singularity-free approach using noise power measurements.
May 12Ram Rao
Polarimetry at the SMA: Current Status and EvolutionI will be presenting a primer on polarization observations with an interferometer array especially focussing on the SMA. Polarimetric observations were first started in 2003 and were aimed at measuring the polarization of the galactic center. They have been extensively used to study polarization phenomena from different types of astrophysical objects including solar system objects, star forming regions, and also AGNs. This talk will cover the basics of the technical aspects of conducting polarization observations and also discuss the future system when the wSMA is online.
May 5Derek Kubo
Sampler clock for digitization within the antenna receiver cabinOne future development option for the SMA is to digitize the receiver IF output within the antenna receiver cabin similar to what ALMA is presently doing. In order to understand what such a project involves, we are looking into the requirements for the sampler clock. In this talk, I will propose some implementation options based on the existing infrastructure of the SMA.
April 21Alex Raymond
Resampling of SWARM Phased Array Output for VLBI CorrelationThe SWARM Phased Array produces four-bit real, four-bit imaginary channelized samples across a 2288 MHz Nyquist band. For correlation with other EHT stations, those data must be down-converted to 2048 MHz, two-bit time-domain samples. This talk will explain how this conversion is done using tools developed by Katherine Rosenfeld, André Young, Mark Peryer, and Jonathan Weintroub, and how we hope to do conversion in the future
April 7TK Sridharan
Coherence, Interferometry & Phase Noise - SMAStarting with a quick conceptual introduction to coherence and interferometry we will discuss the impact of phase fluctuations on interferometric observations. The electronic component of the phase fluctuations arising from the local oscillator (LO) and its quantification will be outlined. Measurements of the phase noise performance of the voltage controlled oscillator (VCO) based wSMA LO will be presented and its adequacy discussed.
March 31 Edward Tong &
John Test
Sideband Separation using Analog Circuits from I and Q Outputs of 2SB Receivers at Low IFLast week, Karto has proposed a digital approach to separate the 2 sidebands detected by 2SB SIS receivers of an interferometer -- an approach particularly appealing to IF near DC. As a follow-up of his talk, we are examining the various schemes by which the sideband separation at low IF can be implemented using analog circuits, which would be useful for single dish radio-telescopes as well as for lab and initial interferometric tests. Assuming a pair of 0.2-4 GHz in-phase(I) and out-of-phase(Q) outputs from the cryostat, the proposed schemes will generate the 2 sidebands from these baseband signals
March 24 Garrett Keating
A Potential Astronomical Calibration Technique for a 2SB InterferometerAs discussion surrounding a potential 2SB system on SMA has increased, a question has arisen about the optimal technique for separating the two sidebands, particularly at the near-DC IF frequencies that the SMA is slated to expand down to. In this talk, I will discuss a potential technique utilizing astronomical sources to digitally reconstruct the separated sidebands in offline processing, in similar fashion to how astronomical calibrators are used for bandpass calibration. If validated, it could provide a natural, efficient path for upgrading the SMA from a DSB to 2SB receiver set at some future date.
March 10Todd Hunter
ALMA Front-End and Digitizer Technical Requirements to Enable the ALMA 2030 Development RoadmapThe ALMA Development Roadmap defines a new long-term development strategy for the upgrade of hardware, software, and analysis tools to enhance the science capabilities of ALMA for the next decade. I will present highlights of the draft report from the working group on the ALMA Front End and Digitizer Requirements Upgrade, beginning with a summary of the original specification and current performance of these components of the ALMA system. I will then show the proposed new specifications, which are still under review.
March 3Edward Tong &
John Garrett
Implementation of 2SB ReceiversIn this talk, we will examine how digital signal processing techniques have helped to advance the state-of-the-art of side-band-separating receivers (2SB receivers). These techniques open the possibility for 2SB receivers for wSMA, which will feature a dual IF system, extending from close to DC to 16+ GHz. The goal of the talk is to initiate further discussions to develop a road map for the development and deployment of 2SB receivers for wSMA.
February 24Lingzhen Zeng
Development of orthomode transducers for the wSMAOrthomode transducers (OMTs) are important passive components widely used in millimeter wave and Terahertz band for remote sensing and astronomical observations. By separating the received signal into two orthogonal linearly polarized components, the OMT proves to be an essential for receiver systems designed to observe the two orthogonal polarization simultaneously. In this presentation, I will first summarize the popular OMT designs in millimeter/submillimeter wavebands. Then I will focus on the wSMA OMT design, fabrication, measurement and integration.
February 10Edward Tong
Tuning circuits for SIS mixersThis is a follow-up of the introductory talk I gave in May 2020: "The Superconductor-Insulator-Superconductor mixer -- some basic concepts and history". I will review the different tuning circuits used in SIS mixer design. These circuits tune out the geometrical capacitance of the SIS junction and allow the SIS mixer to deliver quantum-limited sensitivities.
February 3John Garrett
Waveguide Attenuation: Conductor and Dielectric LossIn this talk, we present a new technique to measure waveguide attenuation. We have used this technique to measure the conductor loss of different WR-2.8 waveguides (copper, gold and aluminum) at both room and cryogenic temperatures. We have also measured the loss tangent of different dielectric materials loaded inside a WR-28 waveguide (HDPE, PTFE and nylon).
January 27Kuan-Yu Liu
Replacement SIS mixers for HARP at JCMTReplacement superconductor-insulator-superconductor (SIS) mixer chips have been developed and fabricated for the 16-element Heterodyne Array Receiver Program (HARP) instrument, which operates between 330 and 375 GHz on the James Clerk Maxwell Telescope (JCMT). The availability of these new mixer chips is very important for the repair and upgrade of HARP. Three of the sixteen mixers have been replaced and the results indicate that the performance of these new mixers is as good as the best original mixers.

Previous presentations available here: CfA managed Google Drive