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A Waveguide-coupled Thermally-isolated Radiometric Source
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Author and Affiliation:
Rostem, Karwan(Johns Hopkins Univ., Baltimore, MD, United States);
Chuss, David T.(NASA Goddard Space Flight Center, Greenbelt, MD, United States);
Lourie, Nathan P.(NASA Goddard Space Flight Center, Greenbelt, MD, United States);
Voellmer, George M.(NASA Goddard Space Flight Center, Greenbelt, MD, United States);
Wollack, Edward(NASA Goddard Space Flight Center, Greenbelt, MD, United States)
Abstract: The design and validation of a dual polarization source for waveguide-coupled millimeter and sub-millimeter wave cryogenic sensors is presented. The thermal source is a waveguide mounted absorbing conical dielectric taper. The absorber is thermally isolated with a kinematic suspension that allows the guide to be heat sunk to the lowest bath temperature of the cryogenic system. This approach enables the thermal emission from the metallic waveguide walls to be subdominant to that from the source. The use of low thermal conductivity Kevlar threads for the kinematic mount effectively decouples the absorber from the sensor cold stage. Hence, the absorber can be heated to significantly higher temperatures than the sensor with negligible conductive loading. The kinematic suspension provides high mechanical repeatability and reliability with thermal cycling. A 33-50 GHz blackbody source demonstrates an emissivity of 0.999 over the full waveguide band where the dominant deviation from unity arises from the waveguide ohmic loss. The observed thermal time constant of the source is 40 s when the absorber temperature is 15 K. The specific heat of the lossy dielectric MF-117 is well approximated by Cv(T) = 0.12 T(exp 2.06) mJ/g/K between 3.5 K and 15 K.
Publication Date: Apr 12, 2013
Document ID:
20130014424
(Acquired Aug 19, 2013)
Subject Category: ASTROPHYSICS
Report/Patent Number: GSFC-E-DAA-TN8635
Document Type: Journal Article
Contract/Grant/Task Num: NNX09AC98A
Financial Sponsor: NASA Goddard Space Flight Center; Greenbelt, MD, United States
Organization Source: Johns Hopkins Univ.; Baltimore, MD, United States
Description: 11p; In English; Original contains color and black and white illustrations
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright; Distribution as joint owner in the copyright
NASA Terms: SUBMILLIMETER WAVES; THERMAL CONDUCTIVITY; POLARIZATION (WAVES); KINEMATICS; CRYOGENICS; LOW CONDUCTIVITY; THERMAL EMISSION; RADIOMETERS; SPECIFIC HEAT; TIME CONSTANT
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