Development of RF and microwave metrology capabilities at cryogenic temperatures is critical for the development of high-performance microwave devices to facilitate commercialization of cryogenic quantum technologies. This article presents a broadband microwave S-parameter calibration scheme suitable for cryogenic environments operating at temperatures down to tens of milli-kelvin (mK). The technique is based on a weighted multi-line thru-reflect-line (TRL) calibration approach and is demonstrated using coaxial air line calibration standards. One-and two-port microwave devices commonly used in cryogenic quantum computing applications, a cryogenic 50 $~\Omega$ matched load and a cryogenic 6 dB attenuator, were measured. The measured results at mK temperatures indicate that when combined with calibration standards of appropriate electrical length, the weighted multi-line TRL calibration scheme allows broadband frequency coverage compared to conventional TRL calibration schemes utilizing a single line standard. The mechanical and electrical properties of the line standards at mK temperatures were investigated and discussed. These findings establish the feasibility of utilizing multiple off-the-shelf coaxial air lines to enhance the frequency range of calibrations at mK temperatures.

The millimeter-wave (mm-wave) and terahertz (THz) regions of the electromagnetic spectrum are seeing increasing prominence, with a range of established and emerging applications—wireless backhaul for mobile networks for 5G and 6G infrastructure, automotive radar sensors, space-deployed radiometers for Earth observation, climate monitoring, weather forecasting, and more—exploiting these frequencies. Measurement techniques informed by the latest metrological research into the measurement of electrical quantities underpin the development of components and circuits for such applications by enabling the accurate and consistent measurement results to be obtained.

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.

This article reports on an extensive interlaboratory comparison of measurements of material properties between 2 GHz and 1 THz using both vector network analyzer (VNA)-based and optical-based methods. For the former, techniques including open resonators, conventional free-space quasioptical systems, and a relatively new guided free-space approach through use of material characterization kits (MCKs) were utilized. The optical-based methods included both time-domain spectroscopy (TDS) and frequency-domain spectroscopy (FDS). Measurement setups for these five techniques located at five well-established laboratories have been employed in the measurements of seven types of commonly used dielectric materials. The results of the measurements by the participating laboratories using each of these techniques were compared to assess levels of agreement between the utilized techniques and thereby establish confidence in the characterizations of each material. Measurement results of these seven materials are presented, together with detailed discussion. This is the first time that an interlaboratory measurement comparison of material properties has been conducted over nearly three decades of frequency and involving such a range of techniques. This work should prove beneficial to applications where material properties need to be known accurately in the microwave to terahertz region.

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.

Multi-port microwave devices operating at cryogenic temperatures are used in quantum computing to enable complex quantum operations. These components need to be precisely characterized at their operating temperature to ensure adequate overall system performance. In this work, an S-parameter measurement system to characterize the performance of coaxial connectorized microwave devices having up to four ports at temperatures of 3 K and above is presented. A four-port calibration setup is implemented at the 3 K temperature stage inside a dilution refrigerator. Measurement results for devices under test at 3 K are presented and the performance of the measurement system is evaluated.