Receiver Lab Talks: 2020
Questions: Edward Tong
Time: Wednesday 1:00 PM EDT (5:00 PM UTC)
Where: Zoom
| Date | Speaker | Title | Summary |
|---|---|---|---|
| December 9 | Mark Reid CfA | Mapping the Milky Way with VLBI Parallaxes | We have been measuring trigonometric parallaxes to masers associated with massive young stars for more than a decade. These allow us to accurately trace the spiral structure of the Milky Way. The Bar and Spiral Structure Legacy (BeSSeL) survey used the VLBA and measured about 150 stars between Galactic longitudes of 0 and 240 degrees. In order to complete the mapping for longitudes 240 to 360 degrees, we need observations from the southern hemisphere. Owing to the need for large amounts of observing time (~1000 hours/year for 3 years), we have been working to upgrade the University of Tasmania's four radio telescopes, which have been mostly used for VLBI geodesy, and the Auckland Institute of Technology's 30-m for 6.7 GHz astrometry. |
| December 2 | Jim Moran CfA | You are never too old to learn something new about interferometry | I will talk about a few fundamental issues of interferometry from a basic level in the form of 4 questions. (1) If interferometers track the geometric delay, why do we need fringe rotators? (2) What ever happened to lag correlators? (3) Why is it so hard to beat the diffraction limit in image sharpness? (4) Why did physicists have such a problem with Hanbury-Brown's intensity interferometer? |
| November 18 | Derek Kubo ASIAA Hawaii Operations | SMA LO System | The SMA Local Oscillator system was designed in the late 1990s and has been in operation at Maunakea for nearly 20 years. I will provide a technical overview of this system along with performance numbers to show that it can continue to operate today without compromise to the array sensitivity. This will be followed by a short discussion on potential improvements to the system. |
| October 28 | James Cornelison Harvard University | Broad Spectrum Noise Sources for Calibration of the BICEP/Keck CMB polarimeters | The BICEP/Keck telescopes are a suite of CMB polarimeters located at the South Pole searching for evidence of inflationary gravitational waves. We invest much of our effort in acquiring high-fidelity calibrations of the optical performance to mitigate systematics in our results. To that end, we map far-field optical response using ground-based, non-thermal, finely-polarized Broad Spectrum Noise Sources (BSNS). We have so far constructed four BSNS's each operating at a different center frequency of 95GHz, 150GHz, 220GHz, and most recently 35GHz for use on the new BICEP Array receiver. In this presentation, I will discuss BSNS theory of operation, report on their performance, and discuss the various calibrations in which the BSNS's are used. |
| October 21 | Lingzhen Zeng CfA | wSMA Frontend Development | Waveguide LO injection and OMT polarization separation are two key features of the wSMA receiver system. Each of the wSMA frontend assembly consists of a few novel components, including a profiled corrugated feedhorn, a Bøifot type OMT, two silicon-chip-based LO couplers and a 90-degree waveguide twist. Because of the wide IF band specifications of the wSMA receivers, the frontend components are designed to operate over wide fractional bandwidths. In this talk, I will show the latest status and the future plans on the wSMA frontend developments. |
| October 14 | Paul Grimes CfA | Development of the wSMA Receiver Cryostat | As part of the wideband-Submillimeter Array (wSMA) upgrade project, we are developing new receiver cryostats for the SMA. We recently received the first prototype unit from the vendor contracted to design the cryostat, and have been testing this unit in the Receiver Lab. In this talk I will describe the wSMA Receiver Cryostat concept and design, give an update on the testing of the prototype unit in Cambridge, and the plans for the next steps in developing the wSMA Cryostat and receiver system. |
| October 7 | John Garrett CfA | Sideband Separating Receivers for the wSMA | In radio astronomy, sideband separating (2SB) receivers are used to divide the upper and lower sidebands of celestial signals into separate output channels. This has the advantage of significantly reducing the atmospheric noise from the unwanted sideband, thereby increasing the sensitivity of the receiver to narrowband emission. For the wSMA, a 2SB receiver would decrease the single sideband system noise temperature by ~30% and increase the mapping speed by approximately a factor of two. In this presentation, I will present an introduction to 2SB receivers, discuss the 2SB vs DSB sensitivity ratio, describe the construction of 2SB receivers, and present a short literature review. |
| September 30 | Kari Haworth EHT | The Next Generation Digital Back End Prototype | A “next-generation” DBE was envisioned by the DSP MRI nearly four years ago to replace the current ROACH2 used at the SMA and throughout the EHT array. Though the design concept has changed, the basic requirement remains the same – to quadruple the bandwidth processing capability from 2 GHz to 8 GHz. I’ll discuss the work that led to the current design, some results from the on-going prototype tests, and the path forward to deployment. |
| September 23 | Edward Tong CfA | An optically-controlled silicon chip based waveguide attenuators for wSMA local oscillator | We have developed an optically-controlled variable attenuator of submillimeter waves by illuminating a high resistivity silicon chip with near-IR radiation. The principle of operation of such an attenuator, as well as the design of the waveguide circuitry will be presented. This attenuator will be used in wSMA Local Oscillator modules to control the amount of LO power incident on the SIS mixers. |
| September 16 | Sridharan (TK) Tirupati CfA | Holographic Antenna Validation Measurement Techniques | Radio holography is the preferred method for the assessment of the surface accuracy and alignment of high gain microwave and millimeter/sub-millimeter-wave antennas and relay optics chains used in radio astronomy. High signal-to-noise-ratio measurements using transmitters in the near-field are used to assess and correct small scale deviations. Elevation dependent large scale deformations are studied using measurements on celestial sources. The principles and practice of these measurement techniques will be discussed using our experience with the sub-millimeter wavelength antennas of the Submillimeter Array (SMA), the Atacama Pathfinder experiment (APEX) and the Greenland Telescope (GLT) as illustrative examples. |
| September 9 | Lingzhen Zeng CfA | A wideband cryogenic isolator for the wSMA | I will show a brief history on magnetism and ferrite materials, and talk about the interaction between electromagnetic waves and ferrite materials, followed by a quick review on popular isolator designs. After that, I will focus on the wSMA wideband cryogenic isolator design, fabrication and test. Finally, will discuss the applications in other fields and future development. |
| August 5 | Derek Kubo ASIAA Hawaii Operations | Local oscillator and intermediate frequency design for the Greenland Telescope | The Greenland Telescope (GLT) has been participating in global very-long- baseline-interferometry (VLBI) observations from Thule Air Base since the spring of 2018. Located in northwestern Greenland, the telescope has provided an important northern location for global VLBI campaigns for studying supermassive black holes. The telescope has been completely rebuilt and commissioned, with many new components, from the ALMA North America Prototype antenna and equipped with a new set of sub-millimeter receivers operating at 86, 230, and 345 GHz, as well as a complete set of instruments and VLBI backends. This talk will discuss the design and progress of the local oscillator (LO) and intermediate frequency (IF) portion of the electronics from the past two years (2018 - 2020). |
| July 22 | Pual Grimes CfA | Optical Simulations of Small Aperture CMB Telescopes | The CMB-S4 project is a US-wide collaboration to build the next generation of CMB polarization telescopes targeting detection of primoridal gravitational waves from the Big Bang. The project follows on from the BICEP/Keck, SPT-3g and Simons Observatory projects. It is currently in the project development stage, with development funding from DoE and NSF. CMB-S4 will build 18 Small Aperture Telescopes (SATs, ~0.5m aperture), as well as 3 Large Aperture Telescopes (LATs, ~6m aperture), equipped with bolometric detector arrays operating between 30 and 300 GHz. The design of the SATs' cold refracting optics and ground shielding is of critical importance for achieving the performance necessary to reach the 10 nK sensitivity to B-mode polarization required to constrain the tensor-scalar ratio r of primordial fluctuations from gravitational waves in the early universe to < 0.001. In this talk, I will give an overview of the CMB-S4 project, and describe the work being done in collaboration between the Receiver Lab and John Kovac's CMB group to validate the design simulated performance of the SATs, using GRASP physical optics simulations, and laboratory measurements, and field measurements of the BICEP3 and BICEPArray instruments. |
| July 8 | Edward Tong CfA | The Schottky Detector Diode -- an unsung hero of radio-astronomy | Reviewing the basics of the operation of the Schottky detector diode, which is widely used in radio-astronomical instrumentation. We will look at the linearity and noise level of these detector diodes as well as some common applications. |
| July 1 | Marion Dierickx Post-doctoral Fellow, CfA | Constraining the primordial gravitational wave signal with BICEP/Keck observations of CMB polarization from the South Pole | Currently the most promising pathway for constraining inflationary gravitational waves is to search for their imprint on the cosmic microwave background (CMB) as a B-mode polarization pattern. The BICEP/Keck experiments target this extremely faint primordial signature by observing the polarized microwave sky at degree-scale resolution from the South Pole. I will present the latest constraints from BICEP/Keck data and report on the recent deployment of the “Stage-3” BICEP Array experiment, which will expand in frequency range and steadily improve our sensitivity by an order of magnitude over the next few years. |
| June 24 | Ranjani Srinivasan ASIAA Hawaii Operations | Yuan-Tseh Lee Array: Instrumentation, commissioning and preliminary science verification results | The Yuan-Tseh Lee Array (YTLA; formerly AMiBA) is a coplanar 13 element interferometer, which is located on Mauna Loa, Hawaii at an altitude of 3400 m on a 6 meter hexapod platform. The AMiBA Sunyaev-Zeldovich (SZ) experiment was concluded in 2014, and subsequently, plans were initiated to repurpose the telescope to study the Epoch of Reionization (EoR) using Carbon Monoxide (CO) at high redshifts (z ~ 6) with Intensity Mapping (IM) techniques. Using IM, one can study aggregate emission from several galaxies (~100 - 1000) spread over large angular scales on the sky. I will be presenting the instrumentation details of the YTLA in its current re-incarnation and the commissioning effort. Some of the outstanding problems and issues encountered will be illustrated. These include measurements of antenna System Equivalent Flux Density (SEFD), sideband separation in terms of the Sideband Rejection Ratio (SRR), and some preliminary science verification data. |
| June 9 | Prof. Tobias Marriage Johns Hopkins University | The Cosmology Large Angular Scale Surveyor | The Cosmology Large Angular Scale Surveyor (CLASS) is a project to probe reionization and inflation by measuring the largest scales in the Cosmic Microwave Background (CMB) polarization. These scales are made accessible due to specialized front-end modulation technology and a survey strategy that covers 75% of the sky from Chile's Atacama Desert. Operating since 2016, CLASS observes at frequencies from 40 to 220 GHz to distinguish between CMB and Galactic emission. We are currently publishing results from the first two years of 40 GHz observations, which demonstrate recovery of large angular scale polarization. In this talk, I will give an overview and an update on CLASS as well as a discussion of the two-year results. |
| June 2 | Prof. Joseph Bardin UMass Amherst | An update in SiGe cryogenic LNA research at UMass | During the past 15 years, SiGe LNAs have emerged as a new option for use in applications in the sub-10 GHz frequency range; however, the performance of commercially available SiGe LNAs still lags that of InP HEMT amplifiers. In this talk, we will review recent progress in reducing the noise and power consumption of cryogenic LNAs. We will describe experimental results, including an amplifier with noise optimized SiGe HBTs. The talk will conclude with a discussion of ongoing research, such as amplifiers with digitally programmable response. |
| May 19 | Jonathan Weintroub CfA | Wideband Digital Technology for SMA & wSMA and the EHT and ngEHT | As radio astronomy receiver bandwidth increases, it is necessary to increase the speed of analog-to-digital conversion (ADC) as well as the digital signal processing (DSP) in the telescope's back end. This introductory talk gives an overview of various projects active at SAO in ADC, DSP, fast digital communications, and software based big data processing. These projects service the Submillimeter Array, which is a component of the Event Horizon Telescope (EHT), and also the instrument needs of the EHT more broadly. |
| May 12 | Nimesh Patel CfA | The Greenland Telescope: Current Status, Operations and Future Plans | The Greenland Telescope is a 12 m diameter ALMA (North America) Prototype Antenna that is refurbished and deployed at the Thule Air Force Base in northern Greenland. I will present a report on the status of the project and current operations for VLBI observations at 86, 230 and 345 GHz, and briefly describe plans for future developments. |
| May 5 | Edward Tong CfA | SIS Mixer -- some basic concepts and history | This is an introductory talk which touches on some basic concepts of the Superconductor-Insulator-Superconductor (SIS) mixer that is at the heart of the SMA. We will also look at some history of superconductivity and of the SIS mixer. The talk is suitable for those who has used the mixer and wants to know more about some of its basics. |
| April 28 | Martina Wiedner Observatoire de Paris, France | The Origins Space Telescope and its Heterodyne Receiver Study | The Origins Space Telescope is one of four large satellite studies that has been submitted to the Astro2020 Decadal Review. In this talk I will briefly lay out the science that defined the design of Origins. The satellite and its 5 instruments will be introduced. The HEterodyne Receiver for Origins (HERO) is one of the 5 instruments designed for Origins. I will give an overview of the HERO design and its defining features. HERO is the first heterodyne array receiver designed for a satellite and some of its components still require development. We therefore defined a receiver roadmap, which I will touch upon at the end of the talk. |
| April 21 | Jake Connors NIST, Boulder CO | Towards Photon Counting Kinetic Inductance Detectors for Far-IR Spectroscopy | Microwave kinetic inductance detectors (MKIDs) are a developing bolometric detector technology, whose natural frequency multiplexing allows for simple readout of large highly sensitive arrays. A candidate for use in future far-infrared space based spectrometers, MKIDs are currently about a factor of ~10 behind superconducting transition edge sensors (TES) in terms of raw noise performance. I will describe our work towards developing more sensitive MKIDs, eventually aimed at achieving single-photon counting sensitivities, which could greatly benefit instruments on-board future missions such as the Origins Space Telescope (OST). In addition to novel fabrication processes and device design, I will describe our ultra-low background measurement facility and it's integrated cryogenic blackbody calibrator, which we plan to use in the characterization of our highly sensitive devices. |
| April 14 | Scott Paine CfA | Atmospheric radiation in the submillimeter and far-infrared | Water vapor plays a dominant role in atmospheric radiative transfer -- a fact keenly felt by ground-based submillimeter and infrared astronomers who struggle to see through it. This talk will review two field campaigns that aimed to improve spectroscopic data for water vapor in the thermal infrared. Along the way we'll touch on the basics of the submillimeter spectrum of the atmosphere, the greenhouse effect, and the use of modern meteorological reanalyses as a tool for interpreting and characterizing the radiative properties of the atmosphere. |
| April 7 | Alexander Raymond EHT Team | EHT Sites | The Event Horizon Telescope is a VLBI array comprised of independent radio observatories like the Submillimeter Array. There is an active effort to design a next-generation EHT that augments the existing stations with dedicated antennas at new sites around the globe (Blackburn et al., 2019). We will briefly describe our approach to evaluating candidate sites using the atmospheric modeling and radiative transfer code developed by Scott Paine and other tools. |
| March 31 | Beverly Brown Harvard University | A tunable waveguide filter -- for low noise local oscillator module for wSMA receivers | This talk summarizes an undergraduate senior thesis project which explores the use of a tunable waveguide filter to reduce the receiver noise at intermediate frequencies below 4GHz created by the power amplifiers in the local oscillator chains in receivers for the Submillimeter Array antennas. Multiple tuning options are explored using ANSYS High-Frequency Structure Simulator (HFSS) simulations and prototypes. A 23.5GHz - 30GHz tunable waveguide filter was produced, using a split-block design and a non-contacting backshort, and is shown to significantly reduce receiver noise when a noisy signal source was used as the base oscillator in an Amplifier - Multiplier - Chain based local oscillator. |
| March 10 | Edward Tong CfA | An empirical probe to the operation of SIS receivers: the technique of intersecting lines | The technique of intersecting lines is a well established tool for the evaluation of the input noise temperature of SIS receivers. In this presentation, we examine the theoretical basis of this technique. This method is applied to determine the insertion loss of optical components used in SIS receivers. |
| March 3 | Keara Carter CfA | Characterization of Dielectric Material at 300 GHz for Vacuum Window Applications | As receiver technology continues to develop, the need for wide aperture, low-loss, broadband, and reliable vacuum windows is increasing. This presentation will describe the requirements present for the new wideband Submillimeter Array (wSMA) vacuum window, the current efforts being made by the Receiver Lab to characterize the electrical and mechanical properties of plastic candidate materials, and will conclude with future planned work. |
| February 18 | TK Sridharan CfA | An ISRO-CfA Himalayan Sub-mm Observatory Initiative | The Submillimeter Receiver Laboratory of the CfA is engaged in discussions with the Space Applications Centre of the Indian Space Research Organization (SAC-ISRO) towards a prospective collaboration on the sub-mm wave observatory SAC is developing in the high altitude deserts of the Himalayas. The science motivations for this engagement, site characteristics, current infrastructure and plans for the new observatory and its instruments will be presented. The current status of the development and future prospects will be briefly discussed. |
| February 10 | Lingzhen Zeng CfA | wSMA Frontend Waveguide Components | The frontend of each wSMA receiver consists of a number of waveguide components, including a corrugated feedhorn, a BΦifot type orthomode transducer (OMT), two silicon chip based LO couplers and a stepped waveguide twist. Because of the wideband specifications of the wSMA receivers, all waveguide components are designed to operate over a 1.4:1 bandwidth. This presentation describes the latest status and the future plans on the wSMA frontend waveguide component developments. |
| February 3 | John Garrett CfA | A Multibeam Receiver for the SMA | Once the wSMA upgrade is complete, there will be enough room to host guest cryostats within the SMA receiver cabins. This will allow us to test new receiver designs on the SMA, including new multibeam receivers, which provide significantly faster mapping speeds than single-beam systems. In this presentation, I present a brief literature review of focal plane arrays, I discuss the challenges of multibeam systems, and I present a preliminary concept for a multibeam receiver. |
Previous presentations available here: CfA managed Google Drive
