Mr. Robert D. Christensen Profile

Robert D. Christensen

SMA Engineering Manager at Smithsonian Astrophysical Observatory

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Publications (11)

Proceedings Article | 24 August 2024 Poster

Challenges and progress on the wideband SMA (wSMA) upgrade for the submillimeter array

Robert Christensen, Edward Tong, Paul Grimes, Lingzhen Leng, Steve Leiker, John Test, Nigel Atkins

Proceedings Volume 13099, 130991K (2024) https://doi.org/10.1117/12.3020602

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The Submillimeter array (SMA) is an array of 8 antennas operating at millimeter and sub-millimeter frequencies on Maunakea, Hawaii. At present, the frequency coverage of the SMA is from 180 to 420 GHz. Here we describe the challenges and progress of the SMA in implementing the wideband upgrade: the wSMA project, that we are undertaking. The existing or legacy instrument at the SMA consists of 4 single polarization Double-Side-Band (DSB) receivers. They are housed in a single cryostat with an aging He-4 GM/JT cryocooler. At the heart of the wSMA upgrade is a new receiver cryostat, cooled by a Cryomech PT410-RM pulse tube. The cryostat houses two dual-polarized receiver cartridges equipped with DSB SIS mixers. New Local Oscillator (LO) subsystems, based on a Voltage-Controlled Oscillator (VCO), as well as new mixer control electronics and IF processing upgrades are being introduced. Since there are differences between the existing SMA instrumentation and the new wSMA receiver system, in terms of sky frequency coverage and the available modes of operation, there are significant challenges of operating the legacy systems and the new wSMA instruments in parallel during the transition period. As it will take several years to replace the instrumentation in all 8 antennas, a detailed plan has been laid out to integrate the new instrument hardware and software packages into the array. We will present the transition plan to full wSMA operation, and we will also describe the antenna infrastructure changes, focusing on repurposing existing equipment and optics. In this presentation we will also discuss the comprehensive installation plan, in which the new wSMA cryostat, together with its associated compressor, chiller, electronics, LO's, cartridges, vacuum system are to be installed into the existing receiver cabin space. Another aspect of the project is to upgrade the internal computer networking that will be a key element of the upgrade, allowing the access and control of the distributed microcontrollers used in the entire instrumentation. The wSMA upgrade is expected to enhance the SMA's capabilities, further improve its sensitivity, as well as widening the Intermediate Frequency (IF) bandwidth. The transition plan that we have drawn up ensures that the wSMA upgrade will be easy to operate and will reduce the maintenance requirements by the SMA technical staff.

Proceedings Article | 18 July 2024 Poster + Paper

Upgrading the submillimeter array: wSMA and beyond

Paul Grimes, Garrett Keating, Raymond Blundell, Robert Christensen, Mark Gurwell, Attila Kovacs, Timothy Norton, Scott Paine, Ramprasad Rao, Edward C.-Y. Tong, Jonathan Weintroub, David Wilner, Robert Wilson, Lingzhen Zeng, Qizhou Zhang

Proceedings Volume 13096, 1309639 (2024) https://doi.org/10.1117/12.3020046

KEYWORDS: Receivers, Shape memory alloys, Cryostats, Antennas, Calibration, Prototyping, Polarization, Cryogenics, Beam splitters, Astrophysics

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Proceedings Article | 13 December 2020 Poster + Paper

A distributed Raspberry-Pi control system for wSMA frontend

C.-Y. Edward Tong, P. S. Leiker, Robert Wilson, Ram Rao, Brian Force, Paul Grimes, Nimesh Patel, Robert Christensen

Proceedings Volume 11453, 114533V (2020) https://doi.org/10.1117/12.2561887

KEYWORDS: Control systems, Spectroscopy, Receivers, Oscillators, Polarization, Switches, Waveguides, Attenuators, Temperature metrology, Bandpass filters

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Proceedings Article | 6 July 2018 Paper

The WIYN one degree imager in 2018: an extended 30-detector focal plane

Daniel Harbeck, Mike Lesser, Wilson Liu, Bob Stupak, Ron George, Ron Harris, Gary Poczulp, Jayadev Rajagopal, Ralf Kotulla, David Ouellete, Eric Hooper, Michael Smith, Dustin Mason, Peter Onaka, Greg Chin, Emily Hunting, Robert Christensen

Proceedings Volume 10702, 1070229 (2018) https://doi.org/10.1117/12.2311528

KEYWORDS: Sensors, Camera shutters, Telescopes, Stray light, Calibration, Charge-coupled devices, Image processing, Data processing, Mirrors, Imaging systems

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Proceedings Article | 23 July 2014 Paper

Vector near-field beam scanner for the SMA

Robert Christensen, Ramprasad Rao, T. Sridharan, Edward Tong

Proceedings Volume 9153, 915330 (2014) https://doi.org/10.1117/12.2057124

KEYWORDS: Receivers, Mirrors, Scanners, Antennas, Shape memory alloys, Transmitters, Polarization, Near field, Astronomy, Near field optics

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Proceedings Article | 22 July 2014 Paper

The Greenland Telescope (GLT): antenna status and future plans

Philippe Raffin, Juan Carlos Algaba-Marcosa, Keiichi Asada, Raymond Blundell, Roberto Burgos, Chih-Cheng Chang, Ming-Tang Chen, Robert Christensen, Paul Grimes, C. Han, Paul T. Ho, Yau-De Huang, Makoto Inoue, Patrick Koch, Derek Kubo, Steve Leiker, Ching-Tang Liu, Pierre Martin-Cocher, Satoki Matsushita, Masanori Nakamura, Hiroaki Nishioka, George Nystrom, Scott Paine, Nimesh Patel, Nicolas Pradel, Hung-Yi Pu, H.-Y. Shen, William Snow, Tirupati Sridharan, Ranjani Srinivasan, Edward Tong, Jackie Wang

Proceedings Volume 9145, 91450G (2014) https://doi.org/10.1117/12.2056836

KEYWORDS: Antennas, Telescopes, Inspection, Prototyping, Servomechanisms, Computer programming, Manufacturing, Carbon, Reflectors, Astrophysics

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Proceedings Article | 12 July 2008 Paper

Overview of engineering activities at the SMA

R. Christensen, D. Kubo, Ramprasad Rao

Proceedings Volume 7016, 701608 (2008) https://doi.org/10.1117/12.787673

KEYWORDS: Receivers, Antennas, Shape memory alloys, Optical correlators, Cameras, Ozone, Telescopes, Observatories, Polarization, Astronomy

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Proceedings Article | 10 July 2008 Paper

The eSMA: description and first results

Sandrine Bottinelli, Ken Young, Richard Chamberlin, Remo P. Tilanus, Mark Gurwell, Dave Wilner, Hiroko Shinnaga, Hiroshige Yoshida, Per Friberg, Huib Jan van Langevelde, Ewine van Dishoeck, Michiel Hogerheijde, A. Meredith Hughes, Robert Christensen, Richard Hills, John Richer, Emily Curtis

Proceedings Volume 7012, 70120D (2008) https://doi.org/10.1117/12.788949

KEYWORDS: Shape memory alloys, Antennas, Galactic astronomy, Spatial resolution, Stars, Calibration, Absorption, Polarization, Observatories, Receivers

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Proceedings Article | 27 June 2006 Paper

Characterization of instrumental phase stability

D. Kubo, T. Hunter, R. Christensen, P. Yamaguchi

Proceedings Volume 6275, 62751Y (2006) https://doi.org/10.1117/12.672927

KEYWORDS: Antennas, Receivers, Analog electronics, Oscillators, Astronomy, Calibration, Phase measurement, Shape memory alloys, Control systems, Optical correlators

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Proceedings Article | 29 September 2004 Paper

Holographic surface setting of the Sub-millimeter Array antennas

Tirupati Sridharan, Masao Saito, Nimesh Patel, Robert Christensen

Proceedings Volume 5495, (2004) https://doi.org/10.1117/12.550939

KEYWORDS: Antennas, Holography, Shape memory alloys, Near field, Astronomy, Spatial resolution, Telescopes, Receivers, Efficient operations, Optical testing

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Proceedings Article | 13 December 2002 Paper

Receiver control for the submillimeter array

Todd Hunter, Robert Wilson, Robert Kimberk, P. Leiker, Robert Christensen

Proceedings Volume 4848, (2002) https://doi.org/10.1117/12.461362

KEYWORDS: Receivers, Microcontrollers, Calibration, Oscillators, Antennas, Computer programming, Shape memory alloys, Actuators, Servomechanisms, Attenuators

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Showing 5 of 11 publications

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