A robot-based antenna measurement system is proposed. The system configuration and initial operating procedure are briefly introduced. Using a laser tracker, three models of robots were tested to determine their positional accuracy. The vertical and horizontal accuracies of robots were within ± 0.15 mm in the working distance of 400 mm. We utilized the three-antenna method and present the preliminary antenna gain data of one KRISS W-band standard gain horn antenna to compare the measurement accuracy of KR-MANMS with that of a conventional fully anechoic chamber.

KRISS has introduced a 6-axis industrial robot into an antenna measurement system. This allows for various measurement applications and the continuous development of additional ones. Among these measurement applications, representative functions such as antenna gain measurement, material characteristics measurement, 3D field scanning, and RCS measurement are continuously being improved. The validity of the technology is discussed by comparing its results with measurements taken in a fully anechoic chamber.

We recently established an impedance standard for the D-band, one of the 6G candidate frequencies. However, primary standards are difficult to use for routine calibration because they require multiple impedance standards and a lot of time to calibrate the vector network analyzer (VNA). Therefore, a transfer standard is needed to efficiently apply the calibration value and to propagate the uncertainty of the primary standard to a device under test (DUT). In this paper, we describe a design method for a transfer standard with small uncertainty even when an arbitrary DUT is measured. This is achieved by propagating the uncertainty of the primary standard to the transfer standard and then propagating it again to the uncertainty of the DUT. We developed a calibration kit that has low uncertainty over a wide frequency band, from 110 GHz to 170 GHz, and consists of waveguide offset shorts for ease of production. We also propose a method to minimize DUT uncertainty and a method to minimize “phase distance” to find the optimal length of the offset short. When using three offset shorts, an uncertainty similar to that of the short-open-load-thru (SOLT) calibration kit was obtained, and when using four offset shorts, an uncertainty comparable to the primary standard was obtained. Lastly, this paper examines the repeatability of measurements and reproducibility during the production process.

Using the intermediate frequency (IF) substitution method, this study establishes a low-frequency attenuation measurement standard operating in the 9 kHz to 10 MHz frequency range. We designed and fabricated a low-frequency attenuation measuring instrument using a mixer that converts the input radio frequency signal into an output IF of 1 kHz. When varying the attenuation of a variable attenuator under test, an attenuation of up to 100 dB was measured. The IF output of the mixer was measured using a spectrum analyzer as the receiver. The receiver's performance was evaluated using an inductive voltage divider whose measurement capability is traceable to the electrical measurement standard. The measurement uncertainty, which accounts for uncertainty sources such as the performance of the receiver, mismatch, and mixer nonlinearity, was evaluated to be 0.005 dB to 0.058 dB (k = 2) in the attenuation range of 10 dB to 100 dB.

Vector network analyzer (VNA)-based material characterization kits (MCKs) are used to measure permittivity of materials in millimeter-wave and terahertz frequencies. Gated-reflect-line (GRL) calibration is basically used to remove errors associated with the MCK fixture. Thru-reflect-line (TRL) calibration with time-domain gating was introduced later. TRL as well as GRL calibrations include time-domain gating to eliminate spurious reflections of the MCK. In this paper, separation of TRL calibration and time-domain gating is proposed to allow for evaluating the uncertainty contribution due to each technique, assuming satisfactorily low reflections of the MCK. The permittivity of planar samples measured by a VNA-based WR-6.5 MCK and preliminary estimates of uncertainty due to effects of nonideal TRL calibration items are presented.

The design of a mannequin phantom replacing the human body for channel measurements on 5G and 6G communications is proposed. The phantom should mimic the human body in terms of a few wave propagation characteristics: penetration, reflection, diffraction, and surface propagation. We measured the characteristics of the human body at millimeter-wave frequencies with a precision robot-based measurement platform. We also present some of the preliminary data from the mannequin phantom measurements as the proof of concept.

This article describes an established ${D}$ -band waveguide impedance standard. The eight-term vector network analyzer (VNA) error model is used for our measurement system. A set of shims, a flush short, thru, and a reciprocal device are used as calibration standards to determine the error coefficients of the VNA error model. From the measured raw scattering parameters and dimensions of each shim, the error coefficients of the error model, the propagation constant of the shim, and the reflection coefficient of the flush short are found using nonlinear optimization. Then, we evaluate the uncertainty in the scattering parameter measurement by combining the fitting uncertainty, the dimension uncertainty of the shims, and the random effects of the VNA into the residual uncertainty model. Finally, we calculate the calibration and measurement capabilities (CMCs) of our measurement system.

A robot-based multi-purpose measurement platform for sub-THz measurements is presented. This platform is composed of a pair of precision robot arms on a metric optical breadboard for precise alignment. The robot arm is capable of controlling its coordinates within a few tens of micrometers, with rotation angles of less than 0.1°. At sub-THz frequencies, the platform itself acts as a semi-anechoic chamber. In this paper, each robot arm was equipped with a sub-THz frequency extender with a horn antenna for scattering parameter measurements with a vector network analyzer. To demonstrate the capabilities of the platform, we present measurement results of the free-space loss, antenna pattern, and communication channel characteristics, specifically the power delay profile and angle of arrival, as examples.

Recently we established a D-band waveguide impedance standard. However, since it is very inefficient to use a primary standard for routine calibration service, here we design another offset shorts calibration kit. The optimal length of the offset shorts was set so that the uncertainty with respect to 1-port calibrations was the smallest when calibrating the DUT using the designed offset short. To meet this goal, we developed a novel design process to propagate the uncertainty of our primary standard to the uncertainty of the designed offset shorts, and then re-propagate to the uncertainty of the DUT to be calibrated. Then, to find the optimal length, the uncertainty of the DUT was made as small as possible by using a global optimization algorithm. We designed three offsets; in this case, the uncertainty was about 2 dB when the DUT had a reflection coefficient of -20 dB, and had an uncertainty of about 0.35 dB for the reflection coefficient of 0 dB. The proposed method can easily design a calibration kit composed of an arbitrary number of offset shorts and a calibration kit using reference standards with arbitrary reflection coefficients, such as load or mismatch.

Silicon (Si) is one of the most important materials used in many RF applications. On-wafer characterization of Si-based devices, components and circuits is widely adopted. Recent investigations have been devoted to the study of parasitic probe and neighborhood effects in commercial alumina-based calibration substrates. However, these parasitic effects have not been thoroughly investigated for commercial silicon-based calibration substrates. Therefore, this paper presents a detailed study of a commercial high-resistivity silicon (HRSi) calibration substrate. The neighborhood effect in conjunction with probe influences is investigated up to D-band frequencies.

We propose field-calibrated electrooptic probes that are designed for millimeter-wave (mm-wave) 5G phased array antenna and Ka-band rectangular waveguide. A method to enhance the probes’ sensitivity and the practical limit for realization are presented. The fabricated probes are specifically minute enough to fit inside a standard mm-wave waveguide section for calibration in a minimally invasive way. The proposed calibration method is validated by analyzing the field invasiveness and through a simulation. Using a calibrated probe associated with a heterodyning probe control system, electric field distributions with absolute V/m scale from an mm-wave antenna are presented.

A transmission line analysis based on a mode-matching technique (MMT) is proposed to compute the reflection behaviors of combinations of slotted and slotless coaxial connectors. The MMT enables us to rigorously obtain electric potential representations of the slotted coaxial line for the TEM mode and then we formulate a characteristic impedance of that line in a closed-form solution. Once the characteristic impedance is determined, various coaxial discontinuities including slotless coaxial connectors can be analyzed in terms of the transmission line theory. We compare our reflection results of slotted and slotless connections with a commercial electromagnetic software package and they give favorable agreement, thus confirming that our approach is efficient and useful for practical applications.

We propose a field-calibrated electro-optic probe designed for a millimeter-wave 5G phased array antenna at the Ka-band. The fabricated probe is calibrated through a WR-28 millimeter-wave waveguide in a minimally invasive manner. Using a calibrated probe associated with heterodyning probe control system, the electric field distribution of a 4×1 phased array patch antenna at 28 GHz is presented with absolute V/m.

In this article, we present a novel method for estimating the parameters of residual models, which are widely used to evaluate the measurement uncertainty of the scattering parameters measured by a vector network analyzer (VNA). Conventionally, the parameters of the residual model are obtained using the ripple method with an air line, where the insulator that distinguishes the inner and outer lines of the coaxial line is air. However, due to inaccuracies caused by losses from air lines, the usable range of frequencies is limited. In addition, methods using the invariance property of the cross ratio of complex numbers result in overestimation because the maximum error boundary is calculated. Above all, since both methods estimate only the magnitude uncertainty, the phase uncertainty estimation is not rigorous, and the correlation between the magnitude and the phase cannot be estimated. In contrast, the proposed method calculates the parameters of the residual model directly from the calibration standards uncertainty, including the phase as well as magnitude, achieving the same result as the VNA error model. The proposed parameter estimation for residual models can also easily propagate to the uncertainty of other measurements since it can obtain the correlation between magnitude and phase as well as the cross frequency. In this article, we compared the parameters of the residual model using the proposed method, the conventional ripple method, and the invariance property of the cross ratio of complex numbers. For validation, the uncertainty obtained using the residual model with the proposed parameter estimation was compared to the results from the VNA error model. The two uncertainties showed excellent agreement for highly reflective and matched devices. Finally, we discuss how to effectively manage the calibration and measurement capabilities of scattering parameters using the proposed uncertainty evaluation method.

We propose a new residual model to analyze the uncertainty of scattering parameters (S-parameters) calibrated by an electronic calibration unit (ECU). Residual errors are usually estimated from the observed ripple after connecting a load or a short at the end of an airline. Therefore, this ripple method can only be used in a frequency range where the airline loss was not large. We, however, obtained the residual error from the uncertainty of the calibration kit using a simple numerical approach. As a result, we can determine the correlations between real/imaginary and magnitude/phase uncertainties. The proposed residual model showed the same results as a VNA error model. We also added a new error term to account for the effect of temperature-dependent drift of the ECU. In addition, we analytically derived the sensitivity coefficients for a 2-port DUT based on the proposed residual model. The proposed residual model will be helpful for the uncertainty analysis of S-parameters calibrated using the ECU.

In this paper, a novel method is proposed by which to correct the pin gaps of coaxial calibration standards for Thru-Reflect-Line (TRL) or Line-Reflect-Line (LRL) calibration. This method is a post-process in which the pin-gap correction is applied to the measured S-parameters of the device under test (DUT) after TRL or LRL calibration. It is based on the perturbation equations derived from the sensitivity-coefficient approach. These equations enable us to obtain the correction quantity of the DUT-S-parameter due to the pin gaps. We verify the proposed method by simulation for a 2.4 mm coaxial line, and the result shows that the pin-gap correction works successfully. Because the method is based on the perturbation equations, the smaller the pin gap, the better the correction results. Nevertheless, we can achieve sufficient correction results within the range of the pin-gap to at least 10 times the nominal value. In addition, the proposed pin-gap correction can play the role of impedance renormalization, even though the two LRL calibration lines have different characteristic impedance. Finally, we demonstrate the correction method for a 2.4 mm coaxial LRL calibration kit through measurement.

To establish the RF power traceability up to 50 GHz in Mexico by means of a primary standard for microwave power and millimeter-wave power, a new coaxial microcalorimeter system in 2.4-mm line size along with thermoelectric-type transfer standards (TSs) were developed and their metrological characterization was performed. Coaxial microcalorimeters allow both broadband operation and power substitution through its feeding line; however, characterization and fabrication of millimeter-wave coaxial lines are technologically difficult. Thus, the design of the microcalorimeter is described, as well as the RF performance of its adiabatic lines. To overcome the lack of coaxial TSs up to 50 GHz, commercially available 2.4-mm thermoelectric power sensors are investigated to use them as low-frequency (LF) power substitution detectors. The effective efficiency is measured in the microcalorimeter by means of calorimetric measurements and the substitution of LF power; the developed measurement procedure is presented as well as the measurement results and the uncertainty analysis. The theoretical basis for the procedure employed to determine the microcalorimeter correction factor, based on the use of specially constructed open and short standards, is described with the measurement results and uncertainties are shown as well. To avoid the drift of the millimeter-wave power during the calorimetric measurements, a novel software leveling loop method for thermoelectric power sensors was devised. This method allows to keep the RF power level variations less than 100 ppm and being a straightforward solution to recent complex hardware realizations.

This paper presents the current characteristics inside a cutoff cavity slot probe applied to crack detection using the forced resonance microwave method (FRMM). Crack detection using FRMM has two stages: preparation and detection. In the preparation stage, the current characteristics inside the probe with a shorting plate are important for determining the crack signal and detection sensitivity. The cutoff cavity probe produces a forced resonance by adjusting a control element. There are two kinds of forced resonance: series resonance (SR) and parallel resonance (PR). Four types of current characteristics are applied to crack detection using FRMM: SR, the region around SR, the region around PR, and non-resonance. These current characteristics are discussed from the point of view of current change for crack detection. The experimental results are compared with the theoretical results to check the current state inside the cutoff cavity probe.

In this paper, we introduce a newly fabricated water bath-type type-N coaxial microcalorimeter at Korea Research Institute of Standards and Science. Preliminary data of the system was compared with our previous dry-type one. Novel design of adiabatic lines and their performance were briefly introduced. Improved aspects of system, such as, evaluation standard and torque wrench support tool are introduced.