This article presents the design, fabrication, and characterization of a D-band (110–170 GHz) bolometric power sensor, used for millimeter-wave metrology. This sensor type is new thin-film-based sensor, which consists of a multilayer chip embedded in a silicon substrate as a microwave absorber. The sensor demonstrates reasonable performance with a return loss of better than 15 dB across the entire D-band and the rise and fall times better than 1.8 ms. The sensor achieves high power linearity between −10 and +8 dBm. Frequency response of the sensor was measured, and its flatness changes no more than 20% across the frequency band. Furthermore, this power sensor has been characterized in the microcalorimeter, and an effective efficiency of over 90% could be achieved. For the first time, the design, fabrication, and characterization of a novel power sensor prototype with excellent performance at D-band are presented.

The aim of this study is to examine the characterization of a thermal isolation section (TIS) for a waveguide microcalorimeter, used to characterize the effective efficiency of a thermistor power sensor (TPS). The power loss in the TIS has been analyzed for both the dielectric and conductor losses. Its effect on the thermopile output has been assessed using a foil short method through analysis of the heating ratio. This method involves a one-off measurement of the microcalorimeter system with the foil short before the unknown power sensor measurement and does not require additional S-parameters measurements of the isolation section. The estimated value of the heating ratio effect has been obtained between 1 for a fully reflected signal from the input of the unknown power sensor and 2 for a perfectly matched power sensor. The full analytical model and an estimated model for the heating ratios have been calculated for the National Physical Laboratory (NPL)'s WG25 (WR15) microcalorimeter and a commercial TPS. The analytical model has been applied to an effective efficiency measurement, and good agreement has been obtained when compared with the existing methodology used at NPL. This model can be applied to any metallic waveguide-type TIS in other bands. A rigorous uncertainty analysis of the analytical model for the heating ratio is also presented and shows an expanded uncertainty between 0.008 and 0.023 ( k = 2) for this microcalorimeter.

This article proposes a new calorimetry-based measurement method to measure absolute microwave power obtained through dc substituted power from 110 to 170 GHz (WG 29, WR 6/7, or D-band) using a custom-designed thin-film microwave power sensor. This method complements traditional microcalorimetry techniques used to provide traceability for microwave power in this band while diversifying the potential applications and accessibility to such traceability. The thermopile of the measurement system was characterized using a known dc power with the microwave sensor and the thermopile coefficient obtained. Absolute microwave power on the microwave sensor was calculated using the thermopile coefficient and was used to remove the effect of a thermal isolation section (TIS) and calorimeter unbalance effect. To transfer the power traceability from the calorimeter to microwave power measurement applications, the effective efficiency of a device under test (DUT), consisting of a power sensor/meter combination, was defined using the calorimeter’s absolute microwave power and the $S$ -parameters of the measurement system and the DUT. The effective efficiency (EE) of the DUT was obtained between 0.9386 and 0.9815 for the whole frequency band.

The aim of this paper is to compare the power measurement capabilities in millimetre- and sub-millimetre-wave frequency bands of several national metrology institutes and one research institute. The first comparison, in WR-6.5 waveguide (110 GHz to 170 GHz), involved NPL, TUBITAK UME and PTB. The second comparison, in WR-1.5 waveguide (500 GHz to 750 GHz), involved NPL, METAS, TUBITAK UME, LNE, WAT, GUM and VDI. Two types of travelling standards were used for these comparisons: a thermoelectric power sensor in the WR-6.5 band and a calorimetric power sensor in the WR-6.5 and WR-1.5 bands. The thermoelectric power sensor was characterised by the participants against their own standards and a generalised effective efficiency was calculated. The calorimetric power sensor operating in the WR-6.5 band was measured to observe its behaviour during the comparison and was also measured in the WR-1.5 band after being fitted with a suitable waveguide taper and used in conjunction with a frequency multiplier. The participants measured the output of the calorimetric power sensor and their own power sensor standard. A normalised power ratio method was used as a comparison parameter for the WR-1.5 band measurements. In addition, a pyroelectric power standard was used by METAS to measure absolute power, and a frequency of 650 GHz was used as a link between the absolute power and the power ratios. Finally, all but two of the measurement points compared between the participants achieved agreement in terms of $\left|E_n\right|$ scores less than 1. For the first time, an interlaboratory comparison of power measurements at sub-millimetre frequencies has been performed and, overall, good agreement was achieved between the different laboratories.

Recent developments in microwave-based quantum computing technologies have motivated the need for the development of new and improved cryogenic microwave devices packaged in coaxial connectorized technology, and for their performance to be accurately characterized through S-parameter measurements made at cryogenic operating temperatures. To facilitate such accurate characterization, S-parameter measurement systems utilizing in-situ calibration techniques at cryogenic temperatures have been developed. This required use of cryogenic RF switches inside cryostats to select between calibration standards and devices to perform calibration and measurement in a single cooling cycle. However, this caused significant measurement errors due to non-identical signal paths due to differences in switch paths limiting the measurement accuracy of such measurement systems. In this work, a new technique is proposed to significantly improve the accuracy of cryogenic S-parameter measurements of coaxial connectorized devices by accounting for non-ideal effects in such switch-based cryogenic calibration units. The technique is demonstrated at room temperature (296 K) and cryogenic temperature (1.5 K) through S-parameter measurements of coaxial devices with up to two ports.