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Published July 2018 | public
Journal Article

A Programmable Cryogenic Waveguide Calibration Load With Exceptional Temporal Response and Linearity


We have developed a programmable, fast switching, accurate, and miniaturized calibration load for use in millimeter and submillimeter low-noise amplifier characterization, and Earth/planetary science radiometers. The proposed solution uses a thermally conductive waveguide vane attenuator with low thermal mass, integrated heater, and silicon thermometer. In the present design, we utilize a 125-μm-thick z-cut crystal quartz vane due to its low dielectric constant (relative to silicon), high cryogenic thermal conductivity, chemical robustness, and small thermal contraction. To provide adequate attenuation, the bottom side of the quartz fabrication wafer has an nm thick resistive Ti metal layer deposited. On the top of the quartz wafer, a pattern of Au is deposited to allow adhesion of the heater resistor, thermometer, and internal heat strap. The z-cut quartz vane is mounted on three low thermally conductive Torlon posts, centered on the maximum E-field, and positioned across the waveguide. With this approach the quartz vane, protruding all the way into the waveguide, approximates a blackbody with a physical temperature T. The design uniqueness lies in the choice of cryogenically suitable materials coupled with detailed thermal analyses and proper miniaturization. When operated in a proportional−integral−derivative loop, these properties combine to facilitate a programmable calibration load with a switching speed of ≲10 s. It will be shown that the W-band design operates overmoded to ∼230 GHz and that the concept is in principle scalable to terahertz frequencies.

Additional Information

© 2018 IEEE. Manuscript received December 3, 2017; accepted April 4, 2018. Date of publication May 17, 2018; date of current version July 2, 2018. This work was supported in part by the Gordon and Betty Moore Foundation, in part by the Kenneth and Eileen Norris Foundation, in part by the Associates of the California Institute of Technology, in part by the NSF under Grant AST-9977420, Grant AST-0116558, and Grant AST-1040504 in the development of the cryogenic calibration loads at the California Institue of Technology's Cahill Radio Astronomy Laboratory, and in part by the National Aeronautical and Space Administration at the Jet Propulsion Laboratory, California Institute of Technology, under a contract, which allowed further characterization of the calibration loads.

Additional details

August 19, 2023
October 18, 2023