Electromagnetic Design and Performance of a Conical Microwave Blackbody Target for Radiometer Calibration

Houtz, Derek; Emery, William J.; Gu, Dazhen; Jacob, Karl; Murk, Axel; Walker, D. A.; Wylde, Richard

doi:10.1109/tgrs.2017.2694319

Cited by 21 publications

(9 citation statements)

References 23 publications

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“…These easily customizable absorbers can achieve adequate performance for stray light termination at low cost and as a thermal plastic-not a foam-they can be used cryogenically. The fabricated absorbers are not intended to serve as extremely low reflectivity calibration targets, such as pyramidal array 10 and cone-shaped 11 targets that have been detailed in the literature. Furthermore, due to the intended use case, only a low power regime has been evaluated.…”

Section: Introductionmentioning

confidence: 99%

A 3D-printed broadband millimeter wave absorber

Petroff

Appel

Rostem

et al. 2019

Review of Scientific Instruments

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We present the design, manufacturing technique, and characterization of a 3D-printed broadband graded index millimeter wave absorber. The absorber is additively manufactured using a fused filament fabrication (FFF) 3D printer out of a carbon-loaded high impact polystyrene (HIPS) filament and is designed using a space-filling curve to optimize manufacturability using said process. The absorber's reflectivity is measured from 63 GHz to 115 GHz and from 140 GHz to 215 GHz and is compared to electromagnetic simulations. The intended application is for terminating stray light in Cosmic Microwave Background (CMB) telescopes, and the absorber has been shown to survive cryogenic thermal cycling.

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Section: Introductionmentioning

confidence: 99%

A 3D-printed broadband millimeter wave absorber

Petroff

Appel

Rostem

et al. 2019

Review of Scientific Instruments

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“…Pre-launch calibration of target emissivity and temperature sensors, although an essential part of an instrument calibration plan, is not within the scope of this paper. However, a recent development in that area at the U.S. National Institute of Standards and Technology is described in [9].…”

Section: Introductionmentioning

confidence: 99%

Climate-Quality Calibration for Low Earth-Orbit Microwave Radiometry

2020

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Improvements in radiometric calibration are needed to achieve the desired accuracy and stability of satellite-based microwave-radiometer observations intended for the production of climate data records. Linearity, stability and traceability of measurements to an SI-unit standard should be emphasized. We suggest radiometer design approaches to achieve these objectives in a microwave calibration-reference instrument. Multi-year stability would be verified by comparison to radio-occultation measurements. Data from such an instrument could be used for climate studies and also to transfer its calibration to weather-satellite instruments. With the suitable selection of an orbit, a climatology of the diurnal variation in the measured parameters could be compiled, which would reduce uncertainties in climate trends inferred from earlier microwave radiometers over past decades.

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“…I N MICROWAVE radiometry, the absolute radiometric calibration of a remote-sensing instrument relies on the availability of accurate calibration sources. The application of blackbody calibration targets is a frequently used method to provide a brightness temperature reference [1]- [6] and the performance of these calibration targets directly influences the accuracy of radiometric measurements [7]- [9]. Hence, a blackbody target should exhibit a microwave emissivity close to unity as well as a homogeneous and well known temperature distribution to provide a distinct brightness temperature reference [8], [9].…”

Section: Introductionmentioning

confidence: 99%

“…However, these absorber materials are not well suited to be applied as calibration targets because their very low thermal conductivity can lead to significant temperature gradients. Therefore, most state-of-the-art calibration targets make use of a thin absorber layer based on iron loaded epoxy resins, which is coated onto a metal structure to ensure a homogeneous temperature distribution [1], [4], [6], [14]. On the one hand this coating needs to be sufficiently thick to absorb the entire radiation, but on the other hand it should be thin enough to be well coupled to the metal backing and keep the temperature gradients in the material small.…”

Section: Introductionmentioning

confidence: 99%

“…On the one hand this coating needs to be sufficiently thick to absorb the entire radiation, but on the other hand it should be thin enough to be well coupled to the metal backing and keep the temperature gradients in the material small. But even with this design it is not trivial to ensure low thermal gradients in the absorber coatings, especially if brightness temperatures shall be obtained, which deviate from the thermal environment [2], [6], [9], [14]. In addition, temperature fluctuations in the thermal environment like a diurnal temperature variation or the influence of an air-conditioning system in the laboratory lead to an inhomogeneous temperature distribution, which cannot be measured by using only few temperature sensors attached to the metal backing.…”

Section: Introductionmentioning

confidence: 99%

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Radiometric Characterization of a Water-Based Conical Blackbody Calibration Target for Millimeter-Wave Remote Sensing

Jacob

Schröder

Murk³

et al. 2019

IEEE J. Sel. Top. Appl. Earth Observations Remote Sensing

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In this paper, we present the design and radiometric characterization of a water-based conical blackbody calibration target to be applied as a precise reference source in laboratories and for the accurate calibration of ground-based microwave instruments. The concept of aqueous blackbody targets circumvents the conflict between the electromagnetic and thermal properties of traditional calibration target designs. The temperature controllable target consists of a conical low loss plastic shell, which has been manufactured using a stereolithography three-dimensional printer to define the water-air interface. An advanced exponential profile of the shell is used to compensate the comparatively high refractive index of water and to obtain a high emissivity. Simulations and active measurements of the coherent backscattering S 11 have been performed verifying its excellent electromagnetic properties. Furthermore, radiometric measurements at 110 GHz demonstrate the outstanding thermal performance at various target temperatures between 10 and 60°C. The differences between the brightness temperature and the water temperature are measured to be less than 40 mK and therefore significantly smaller in comparison to traditional calibration targets. In addition, the measured baseline ripples in the spectra caused by the water-based calibration target are small compared to established blackbody concepts.

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Electromagnetic Design and Performance of a Conical Microwave Blackbody Target for Radiometer Calibration

Cited by 21 publications

References 23 publications

A 3D-printed broadband millimeter wave absorber

A 3D-printed broadband millimeter wave absorber

Climate-Quality Calibration for Low Earth-Orbit Microwave Radiometry

Radiometric Characterization of a Water-Based Conical Blackbody Calibration Target for Millimeter-Wave Remote Sensing

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