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A Waveguide-coupled Thermally-isolated Radiometric SourceThe 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.
Document ID
20130014424
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
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)
Date Acquired
August 27, 2013
Publication Date
April 12, 2013
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN8635
Funding Number(s)
CONTRACT_GRANT: NNX09AC98A
Distribution Limits
Public
Copyright
Public Use Permitted.
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