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.

The dielectric properties of materials are critical parameters considered in the design phase of circuits and subsystems operating at millimetre (mm)-wave and terahertz (THz) frequencies. In this work, material properties of four commonly used laminates were measured in four waveguide bands across frequencies from 50 GHz to 750 GHz using the material characterisation kit (MCK) based method. The results are presented, along with an analysis of uncertainty contributions associated with two key factors. It is expected that this study will be of interest to designers of low-cost circuits and sub-systems operating up to THz frequencies.

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 En 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.

Development of large-scale quantum computing systems will require radio frequency (RF) and microwave technologies operating reliably at cryogenic temperatures down to tens of milli-Kelvin (mK). The quantum bits in the most promising quantum computing technologies such as the superconducting quantum computing are designed using principles of microwave engineering and operated using microwave signals. The control, readout, and coupling of qubits are implemented using a network of microwave components operating at various temperature stages. To ensure reliable operation of quantum computing systems, it is critical to ensure optimal performance of these microwave components and qubits at their respective operating temperatures, which can be as low as mK temperatures. It is, therefore, critical to understand the microwave characteristics of waveforms, components, circuits, networks, and systems at cryogenic temperatures. The UK's National Physical Laboratory (NPL) is focussed on developing new microwave measurement capabilities through the UK's National Quantum Technologies Programme to address various microwave test and measurement challenges in quantum computing. This includes the development of various measurement capabilities to characterize the microwave performance of quantum and microwave devices and substrate materials at cryogenic temperatures. This paper summarizes the roadmap of activities at NPL to address these microwave metrology challenges in quantum computing.

As part of a joint program three National Measurement Institutes around Europe—the National Physical Laboratory in the UK, the Physikalisch-Technische Bundesanstalt in Germany and the Laboratoire National de métrologie et d’essais in France—have each established new capabilities for the traceable measurement of S-parameters up to 90 GHz in the new 1.35 mm (E band) coaxial connector. Each institution has established their own measurement systems to access the full frequency band for the connector, utilising a variety of commercially available equipment and measurement setups. Each have also developed their own calibration techniques and verification methods using different vector network analyser calibration routines. These include optimised multi-line Through Reflect Line, multiple Offset Shorts Through and Short Open Load Reciprocal (SOLR) schemes. Uncertainties for each of these setups and calibration schemes were determined utilising theoretical models of the systems and calibration standards, or through verification methods, with different effects being derived from the dimensional characteristics for each of the different standards or verification artifacts. The different dimensional systems used to make these measurements were also developed and established previously as part of the same program. The last part of this exercise was a three-way intercomparison between the laboratories. The comparison involved the measurement of a set of four traveling standards, including both 1-port and 2-port as well as plug (male) and jack (female) devices, each with different reflection and transmission characteristics to better test and demonstrate the equivalence of the capabilities.

Main text This report summarizes the results of the measurements performed as a CIPM Key Comparison (CCEM.RF-K27.W) on high frequency power in waveguide among eight National Metrology Institutes (NMIs) of Germany (PTB), UK (NPL), France (LNE), China (NIM), Russia (VINIIFTRI), USA (NIST), Korea (KRISS), Japan (NMIJ). The Pilot Laboratory (PL) is NIM. The comparison was performed between May 2019 and December 2021. In this comparison, the effective efficiency and calibration factor of two WR15 (R620) waveguide thermistor mounts (travelling standards) were measured in the frequency range 50 GHz to 75 GHz. In the final report the list of participants, measurement quantities, methods of measurement, and measured results are given. The repeatability of the travelling standards, the key comparison reference values (KCRVs) and the degree of equivalence (DoE) of participating institutions are discussed. The appendix also provides the measurement method, measurement results and uncertainty budget of each participant. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA). To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCEM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

A bolometric thin-film-based transfer standard with a novel structure for absolute power detection in D-band (110–170 GHz) is reported. It uses a resonance-type matching technique with thin-film resistive lines. The same line functions as the sensing element. The change in the resistivity of the line under the incident wave is calibrated to measure the absolute RF power in the D-band. This article presents the analysis using equivalent circuit models, the full-wave electromagnetic design, the fabrication, and the comprehensive characterization of the device. The comparison between a single and a folded-line matching structure is performed, showing the wideband capability of the latter. The transfer standard consists of two sensors in one waveguide housing for RF power measurement, as well as for monitoring and calibrating out the ambient temperature variation. It has shown a very good short-term time response with only $\sim $ 0.19% deviation in a given time interval, which is very close to a commercial PM5 sensor with $\sim $ 0.27% deviation. The long-term time response is also impressive, with a deviation of less than 0.6%, similar to a commercial PM5 sensor. The fast response time, good thermal isolation, and ambient compensation ability make it suitable for transfer/working standards, which can be used in ambient temperature environments.

Traceability for power measurements at high millimeter-wave and terahertz frequencies presents significant challenges since traditional waveguide micro-calorimetry systems are only readily available at frequencies up to 110 GHz. There are, however, different types of commercially available power meters which operate at frequencies above 110 GHz, where a lack of traceability means the accuracy and associated uncertainty of measurements using these power meters is not well understood. This paper describes the characterisation and traceable calibration of a commercially available waveguide power meter (VDI Erickson PM5) which is designed to operate from 75 GHz to 3 THz, using appropriate waveguide tapers. This includes an assessment of the overall system performance along with an evaluation of the uncertainty in measurements made using the system. The assessment is carried out at W-band (75 to 110 GHz) by comparison with micro-calorimeter systems which are used as primary standard power measurement systems at these frequencies.

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 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.

NPL, PTB, and LNE designed and produced three different microcalorimeters for the WG29/WR7 band. The microcalorimeters used different correction methods to characterize effective efficiency. Finally, the three laboratories measured thermoelectric power sensors from 110 GHz to 170 GHz to demonstrate equivalence and results show good agreement.

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 paper describes the design, fabrication and testing of 3-D printed primary standards for use with the calibration of microwave vector network analysers. The standards are a short-circuit and a quarter wavelength section of line that are designed for use with the Thru-Reflect-Line calibration technique. The standards are realised in metal-pipe rectangular waveguide, covering the frequency range from 12 GHz to 18 GHz (i.e., Ku-band). The standards are polymer-based 3-D printed, which is subsequently metal plated to provide the required electrical conductivity. The performance of the standards is compared with conventionally machined standards that are used as part of the UK's primary national measurement system for microwave scattering parameters. The authors believe that this is the first time that 3-D printing techniques have been used to produce such calibration standards, and, that this could lead to a new approach to providing metrological traceability for these types of measurement. Crown Copyright (C) 2020 Published by Elsevier Ltd. All rights reserved.

The UK’s National Physical Laboratory (NPL) is responsible for developing and maintaining the UK’s most accurate standards of measurement. For high frequency power measurement, NPL provides the UK’s contribution to the Calibration and Measurement Capabilities (CMCs) listed in the International Bureau of Weights and Measures (BIPM) key comparison database (KCDB) [1]. This demonstrates the international equivalence of these measurements via the International Committee of Weights and Measures (CIPM) Mutual Recognition Arrangement (MRA) [2]. At present, the KCDB only shows power measurements up to 110 GHz. No traceability in the UK exists for power measurements above this frequency. However, a European project, entitled “TEMMT” [3], is establishing a programme of work to extend this traceability to higher millimeter-wave frequencies, and above. This programme of work is based around using a commercially available power meter [4], as shown in Fig 1. However, in order to demonstrate the suitability of this power meter as a standard at frequencies above 110 GHz, a comparison is first needed with the existing primary power measurement standards that are used at frequencies below 110 GHz. The UK’s primary standards for power measurement at millimetre-wave frequencies [5] are used for this purpose – specifically, a microcalorimeter operating at W-band (75 GHz to 110 GHz), as shown in Fig 2. This calorimeter is used to provide traceability to the international system of units (SI) for power measurements in rectangular waveguide. This calorimeter has previously been verified using free space measurement techniques [6]. This paper describes the comparison, between the commercial power meter and the NPL microcalorimeter using a direct comparison transfer method and presents some initial results obtained using these measurement systems. Fig. 3 shows results for the expected indicated power for a fixed incident power, for this commercial power meter and a conventional thermistor. This is expected to be different for each based on their respective reflection coefficients and efficiencies. In use a correction would then be applied to correct for these. The degree of equivalence between the two sets of measurements can then be investigated and used as a means of demonstrating the overall performance of the commercial power measurement system (with respect to the UK primary national standard microcalorimeter system). Once the commercial power measurement system has been verified at W-band, its performance will be further evaluated in other waveguide bands used for higher millimetre-wave frequencies, and above, where currently no other reference standards for power measurements exist. This will then provide the first reference for power measurement traceability in the UK, at these millimetreand submillimetrewave frequencies. Fig. 1. Photograph showing the commercial power meter used for power measurement at millimetre-wave frequencies and above.

This paper introduces the first fully 3-D printed tunable microwave subsystem, consisting of 26 circuit elements. Here, a polymer-based 3-D printed Ku-band 4-element steerable phased-array antenna with fully integrated beam-forming network is demonstrated. Polyjet was adopted for fabricating the main body of the subsystem, as it is capable of producing a geometrically complex structure with high resolution over a large volume. Low-cost fused deposition modeling was chosen to manufacture the dielectric inserts and brackets for the phase shifters. The measured radiation pattern revealed that the phased-array antenna subsystem has total beam steering angles of 54° and 52° at 15 GHz and 17 GHz, respectively. Excellent input return loss behavior was observed across the optimum operational frequency range of 15 to 17 GHz, with a worst-case measured return loss of 12.9 dB. This work clearly shows the potential of using 3-D printing technologies for manufacturing fully integrated subsystems with complex geometric features.

This paper introduces the first fully 3-D printed tunable microwave subsystem, consisting of 26 circuit elements. Here, a polymer-based 3-D printed Ku-band 4-element steerable phased-array antenna with fully integrated beam forming network is demonstrated. The measured radiation pattern revealed that the phased-array antenna subsystem has a total beam steering angle of 54°. This work clearly shows the potential of using 3-D printing technologies for manufacturing fully integrated subsystems with complex geometric features.

We describe a method for direct intercomparison of terahertz permittivities at 200 GHz obtained by a Vector Network Analyzer and a Time-Domain Spectrometer, whereby both instruments operate in their customary configurations, i.e., the VNA in waveguide and TDS in free-space. The method employs material that can be inserted into a waveguide for VNA measurements or contained in a cell for TDS measurements. The intercomparison experiments were performed using two materials: petroleum jelly and a mixture of petroleum jelly with carbon powder. The obtained values of complex permittivities were similar within the measurement uncertainty. An intercomparison between VNA and TDS measurements is of importance because the two modalities are customarily employed separately and require different approaches. Since material permittivities can and have been measured using either platform, it is necessary to ascertain that the obtained data is similar in both cases.

A method is described for direct comparison of dielectric measurements obtained by a vector network analyzer and a time domain spectrometer. The method employs a material that can be inserted into a waveguide for VNA measurements or contained in a cell for TDS measurements.