G-band Reflectivity Results of Conical Blackbody for Radiometer Calibration
Derek A. Houtz, Dazhen Gu
Two hollow conical cavities have been developed and built for the National Institute of Standards and Technology (NIST) for use as radiometric brightness temperature sources, or blackbodies. According to Kirchoff's reciprocity relation, a good absorber is a good emitter, and a blackbody aims to maximize emissivity. Thus, we desire low reflectivity to approximate an ideal blackbody. We present new results of the reflectivity of the smaller conical blackbody in G-band between 130 GHz and 230 GHz. We found monostatic reflectivity, or return loss, no larger than -45 dB at critical remote sensing bands near 165 GHz, 183 GHz, and 229 GHz. We found that use of a thin closed-cell polyethylene insulation layer has a significant impact on reflectivity performance. We compare the reflectivity of the conical blackbody with the reflectivity of a pyramidal absorber array of the type typically used as on-board radiometer calibration sources. The insulated conical blackbody showed an average of 15 dB lower reflectivity than the pyramidal array over the measured band.
Proceedings of Microwave Measurement Conference (ARFTG) by IEEE, 2017 90th ARFTG
and Gu, D.
G-band Reflectivity Results of Conical Blackbody for Radiometer Calibration, Proceedings of Microwave Measurement Conference (ARFTG) by IEEE, 2017 90th ARFTG, Boulder, CO, US, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=924586
(Accessed October 4, 2023)