Scattering Parameter Measurements Research Articles

Accurate Characterization of Reverberation Chamber Resonant Modes From Scattering Parameters Measurement

This paper presents a novel approach to accurately extract the resonant modes of a mode-stirred reverberation chamber (RC) from measured transmission coefficient. This approach neither requires measurements with a fine stirrer rotation step nor assumes the pole continuity over a stirrer rotation. First, the number of modes to be extracted by the matrix pencil method needs to be overestimated in order to obtain most of the true (physical) modes with high accuracy. As this overestimation also implies the extraction of many spurious modes, the second step consists in automatically filtering these spurious modes based on a time-window increasing technique postprocess without a priori information. Performances of the introduced technique are first shown on a didactic example, especially in the presence of noise, and its limitations when increasing the modal overlap are investigated. Results obtained from measurement performed in a chaotic RC are then presented. The introduced approach allows extracting all the true cavity modes from measurement data while keeping the percentage of spurious modes below 3.5%.

Методика определения метрологических характеристик зондовой установки для измерения параметров рассеяния изделий СВЧ наноэлектроники на подложке

The method for determining the metrological characteristics of the probe system for the scattering parameter measurements of passive and active devices on a semiconductor substrate is presented. The main idea is to estimate the residual errors and determine the accuracy of the obtained estimates. The implementation of the idea is based on a special filtration technology by the processing of verification measurements and unscented transformation for the study of the quality of a verification set which consists of a single transmission line that can be made on a substrate with devices.

Measurement of surface conductivity of graphene at W‐band

AbstractGraphene has excellent mechanical and conducting properties. Scattering parameter measurements were made in W‐band (75‐110 GHz) on 25 mm × 25 mm monolayer graphene film printed on polyethylene terephthalate (PET) substrate. From near field measurements using WR10 horn antennas the surface conductivity was de‐embedded after calibrating the s11 data against the reflection of a copper plate of same cross‐sectional dimensions as the DUT and calibrating the s21 data against horn‐to‐horn measurements. A monolayer graphene strip (20 mm × 2 mm) printed on PET substrate (25 mm × 25 mm) showed higher reflection when it was aligned with the E field of the incident radiation (as compared to H field alignment). The surface conductivity of graphene was de‐embedded from s11 measurements using standard transmission line theory and from s21 measurements using cascade matrix theory. The measured real part of the surface conductivity of graphene ranges between 0.7 and 1.8 mS/sq.

Equivalent‐circuit–based modeling of the scattering and noise parameters for multi‐finger GaAs pHEMTs

AbstractThis study is focused on the experimental characterization of the high‐frequency linear behavior of interdigitated gallium arsenide (GaAs) pseudomorphic high‐electron‐mobility transistors (pHEMTs) in terms of scattering and noise parameters. A measurement‐based model is developed by using the equivalent‐circuit representation. The values of the extrinsic bias‐independent elements are obtained by means of the “cold” approach and then subtracted from the scattering parameter measurements at the bias point of interest, thereby enabling calculation of the intrinsic bias‐dependent elements. Next, the extracted small‐signal equivalent circuit is expanded by assigning an equivalent noise temperature to each resistor, thus obtaining the noise model. The validity of the extracted equivalent‐based model is fully confirmed by the good agreement between measurements and model simulations over a broad frequency range for devices having different number of gate fingers. In addition, the scaling of the achieved performance versus the total gate width is analyzed and discussed.

A study of reflection phase of reflectarray antennas with high loss organic substrates

<span>This paper presents an analysis of reflection phase of reflectarray antenna based on high loss organic substrate material. Paper substrate material derived from recycled materials was characterized for dielectric material properties. The material shows excellent dielectric material properties with permittivity of 1.63 and loss tangent of 0.048. Effect of substrate height variation over the reflection phase has been discussed. Full wave analysis of the simulated model depicts that the reduction in substrate height after a certain point results in reflection phase distortion of reflectarray element. Validation of the results has been done by simulation, fabrication and scattering parameters measurements of a rectangular patch element on proposed substrate material. The results show a broadband frequency response of 355 MHz and a phase range of 301º at a phase gradient of 0.14 º/MHz.</span>

First-Order Modeling of Errors Due to Coaxial Connector Interface

We present an approach for first-order modeling of errors in vector-network-analyzer (VNA) measurements caused by the coaxial-connector interface. These errors result primarily from the presence of a gap in the inner conductor. Our approach relies on an approximate model of the connector interface that comprises an analytical equivalent-circuit for the inner conductor gap section and a behavioral scattering-parameter model for the socket-contact section. We verify this model using full-wave electromagnetic simulations for the 1.85, 2.4, 3.5 mm, and Type-N coaxial-connector interface for different inner conductor-gap widths. We further apply this model to asses first-order errors in VNA calibration introduced by the tolerance on the inner conductor-gap width. We show that the inner conductor-gap effect can be accounted for with a series inductance inserted at the inner conductor mating-plane while the effect of the socket contact can be lumped into the VNA calibration coefficients. We verify this error model experimentally by measuring a Type-N offset load with an adjustable inner conductor gap. We also demonstrate that including our error model in coaxial offset-short definitions leads to improved consistency of a one-port VNA calibration with 3.5-mm coaxial offset-short standards. Our results can be used in the uncertainty analysis and accuracy enhancement of VNA scattering-parameter measurements.

Millimeter Wave Beam Steering Reflectarray Antenna Based on Mechanical Rotation of Array

This work provides design and analysis of a beam steering reflectarray antenna, designed at 26 GHz, based on the mechanical rotation of the array. Unit cells based on circular ring elements are designed, and scattering parameter measurements have been carried out for obtaining progressive phase distribution. The unit cell measurements demonstrated a maximum reflection loss of 4 dB with a total phase range of almost 360°. Symmetricity of the array and the resonant elements has been exposed to steer the main beam by tilting the reflectarray at different angles. A beam steering range of more than ±60° has been demonstrated by varying the tilt angle from +30°to -30°. The designed 20 × 20 element array provided a maximum gain of 26.47 dB at 0° which reduced to 19.8 dB at 61.9° in the elevation plane. On the other hand, the reflectarray antenna demonstrated a maximum bandwidth of 13.1% with a minimum side lobe level of -25.9 dB.

Measurement and Modeling of Heterogeneous Chip-Scale Interconnections

We present precision scattering-parameter measurements of chip-to-chip connections in heterogeneous integrated circuits: indium phosphide or gallium nitride “chiplets” mounted on Silicon Complementary Metal-Oxide-Semiconductor carrier chips. We demonstrate methodology, experimental results, and modeling results of these chip-scale interconnections from dc to 110 GHz. We used thru-reflect-line on-wafer calibration to establish reference planes inside heterogeneous integrated circuits, and then, we translated those reference planes to the proximity of the chip-to-chip transitions to isolate their contribution to the scattering parameters.

Measurement and Modeling of Heterogeneous Chip-Scale Interconnections

We present precision scattering-parameter measurements of chip-to-chip connections in heterogeneous integrated circuits: indium phosphide or gallium nitride “chiplets” mounted on Silicon Complementary Metal-Oxide-Semiconductor carrier chips. We demonstrate methodology, experimental results, and modeling results of these chip-scale interconnections from dc to 110 GHz. We used thru-reflect-line on-wafer calibration to establish reference planes inside heterogeneous integrated circuits, and then, we translated those reference planes to the proximity of the chip-to-chip transitions to isolate their contribution to the scattering parameters.

Thickness invariant parameter retrieval techniques for permittivity and permeability measurement

The study investigates the use of scattering parameters measurement to retrieve the permittivity, permeability, refractive index and intrinsic impedance of materials over the wide range of frequencies. The approach is demonstrated for thin as well as thick materials to clarify the complex branching problems of the logarithm and sign ambiguities. The special requirement of simulation and measurement setup and their alternative solution are also suggested in this work. The paper aims to simplify and streamline the approach of parameter retrieval for any thickness of material. The approach is verified using CST Microwave studio simulation and results obtained are validated using rectangular waveguide measurement method.

Charge carrier velocity in graphene field-effect transistors

To extend the frequency range of transistors into the terahertz domain, new transistor technologies, materials, and device concepts must be continuously developed. The quality of the interface between the involved materials is a highly critical factor. The presence of impurities can degrade device performance and reliability. In this paper, we present a method that allows the study of the charge carrier velocity in a field-effect transistor vs impurity levels. The charge carrier velocity is found using high-frequency scattering parameter measurements followed by delay time analysis. The limiting factors of the saturation velocity and the effect of impurities are then analysed by applying analytical models of the field-dependent and phonon-limited carrier velocity. As an example, this method is applied to a top-gated graphene field-effect transistor (GFET). We find that the extracted saturation velocity is ca. 1.4×107 cm/s and is mainly limited by silicon oxide substrate phonons. Within the considered range of residual charge carrier concentrations, charged impurities do not limit the saturation velocity directly by the phonon mechanism. Instead, the impurities act as traps that emit charge carriers at high fields, preventing the current from saturation and thus limiting power gain of the GFETs. The method described in this work helps to better understand the influence of impurities and clarifies methods of further transistor development. High quality interfaces are required to achieve current saturation via velocity saturation in GFETs.

Exposure Setup and Dosimetry for a Study on Effects of Mobile Communication Signals on Human Hematopoietic Stem Cells in vitro

Abstract. In this paper we describe the design of an exposure setup used to study possible non-thermal effects due to the exposure of human hematopoietic stem cells to GSM, UMTS and LTE mobile communication signals. The experiments are performed under fully blinded conditions in a TEM waveguide located inside an incubator to achieve defined environmental conditions as required for the living cells. Chamber slides containing the cells in culture medium are placed on the septum of the waveguide. The environmental and exposure parameters such as signal power, temperatures, relative humidity and CO2 content of the surrounding atmosphere are monitored permanently during the exposure experiment. The power of the exposure signals required to achieve specific absorption rates of 0.5, 1, 2 and 4 W kg−1 are determined by numerical calculation of the field distribution inside the cell culture medium at 900 MHz (GSM), 1950 MHz (UMTS) and 2535 MHz (LTE). The dosimetry is verified both with scattering parameter measurements on the waveguide with and without containers filled with cell culture medium and with temperature measurements with non-metallic probes in separate heating experiments.

Fast and precise data acquisition for broadband microwave tomography systems

Microwave imaging (MWI) is a noninvasive diagnosis method, which has been investigated for a wide range of applications. MWI techniques include radar-based approaches as well as microwave tomography (MWT). One major challenge designing broadband MWI systems is the development of a data acquisition unit that allows for fast broadband scattering parameter measurements with a high measurement precision and a high dynamic range (DR), at reasonable cost. The cost-performance criteria cannot readily be achieved using commercial, continuous wave (CW) vector network analyzers (VNA) or pulse-based systems. Therefore, in this paper we propose a data acquisition unit, based on the well-known method of frequency modulated continuous wave (FMCW) network analysis. It offers fast scattering parameter measurements without compromising the measurement precision and the DR, and is particularly advantageous for MWI systems requiring a high number of frequency samples. A 2-port metadyne prototype electronics with low hardware complexity was developed, which allows very fast, precise, and accurate reflection and transmission measurements in the frequency range from 0.5 GHz to 5.5 GHz. To the best of the authors’ knowledge, a system with combined performance in terms of bandwidth, sweep time (1 ms), DR (80 dB) and maximum signal-to-noise-and-spurious ratio (65 dB) has not previously been reported. The design, the calibration, and the characterization of the prototype electronics are described in detail, and the measurement results are compared to those obtained with commercial high-end CW VNA. The advantages and limitations of the metadyne FMCW technique compared to the heterodyne CW technique are discussed. The applicability of the prototype electronics and the described calibration technique for microwave imaging has been demonstrated based on measurements using an 8-port MWT sensor and a switching matrix.

Phase-ambiguity-free and accurate permittivity determination from waveguide measurements.

A microwave method has been proposed for accurate and unique extraction of relative complex permittivity (εr) of dielectric materials from 2π phase-ambiguity-free amplitude-only two-port and one-port scattering parameter measurements. Improved accuracy has been shown by the applied uncertainty analysis. For the validation of our method, εr of low-loss and lossy samples was extracted.

Noniterative complex permittivity retrieval using calibration-independent waveguide measurements

Calibration-independent nonresonant measurements can be employed to eliminate the need for calibration before microwave measurements. These methods generally assume that the location of the sample in its measurement cell is known after the sample is positioned or shifted within the cell and that the length of the measurement cell is known. In addition, in general these methods necessitate some sort of numerical analysis to retrieve the complex permittivity of the sample. In this research paper, we propose a calibration-independent nonresonant waveguide method to first eliminate measurement errors arising from inaccurate knowledge of the location of the sample within its cell (after shifting) and arising from improper knowledge of the length of the measurement cell and second to determine the complex permittivity explicitly. In addition, our proposed method needs scattering parameter measurements from three different measurement configurations – another improvement with respect to a similar calibration-independent method requiring measurements from four different configurations. Furthermore, it does not necessitate that the sample be flushed to the measurement cell. We analyzed repeatability of cell connection and investigated uncertainty in the measurement of complex permittivity for a change in length of the sample and the cell and when air gap present between sample surfaces and guide walls. We validated the proposed method by measuring the complex permittivity of polyethylene sample and distilled water at X-band (8.2–12.4GHz).

Measurement Uncertainty Model for Vector Network Analyzers With Frequency Extension Modules at Terahertz Frequencies

In this paper, we propose a new measurement uncertainty analysis method for scattering parameter measurements in waveguide devices operating in the frequency range from 750 GHz to 1.1 THz. The measurement uncertainty of vector network analyzers (VNAs) has been analyzed from the uncertainty of primary standards and repeatability. However, uncertainties in waveguide VNA measurements above 110 GHz were underestimated in the case of comparing two measurement systems at terahertz frequencies. Other uncertainty contributions, such as deviations in the connection torque and the effects of IF cables between the VNA and the frequency extension modules, have been incorporated in the new model. Using the new uncertainty model, results from two different systems, have been shown to agree within the uncertainty [1] .

Accurate and Efficient Self-Calibration Algorithm of Broadband On-Wafer Scattering-Parameter Measurements for Production Test Applications Up to 110 GHz

This paper presents an accurate and efficient on-wafer calibration algorithm of broadband scattering-parameter measurements for radio-frequency integrated circuit production test applications. Three on-chip calibration standards with the same probe positions as those of the devices under test (DUTs) were designed to take advantage of fixed probe heads in the x–y directions during calibration and measurements. In addition, three on-chip standards—a series resistor and a shunt resistor (both of which have an offset line segment) as well as a transmission line (TL)—do not have to be characterized in advance, and the measurement reference impedance can be acquired further though self-calibration without an impedance-standard substrate (ISS). Simulation studies and experimental confirmation were conducted on GaAs substrates, from 2 to 110 GHz, in addition to comparisons of the multiline thru-reflect-line (TRL) calibration results.

Permanent magnetic ferrite based power-tunable metamaterials

Power-tunable metamaterials based on barium permanent magnetic ferrite have been proposed and fabricated in this research. Scattering parameter measurements confirm a shift in resonant frequency in correlation to changes in incident electromagnetic power within microwave frequency band. The tunable phenomenon represented by a blue-shift in transmission spectra in the metamaterials array can be attributed to a decrease in saturation magnetization resulting from FMR-induced temperature elevation upon resonant conditions. This power-dependent behavior offers a simple and practical route towards dynamically fine-tunable ferrite metamaterials.

Thickness-Invariant Complex Permittivity Retrieval from Calibration-Independent Measurements

A calibration-independent method is proposed for accurate complex permittivity ( $\varepsilon _{r}$ ) determination of dielectric samples from raw scattering parameter measurements without resorting to any information of thickness ( $L$ ), especially for thinner samples. X-band waveguide measurements of two polyethylene samples were carried out for validation of our method. From our analysis, we note that while our method extracts similar $\varepsilon _{r}$ for both samples (thickness-invariant), accuracy of tested methods greatly degrades by an inaccurate knowledge of $L$ .

A new method for the precise multiband microwave dielectric measurement using stepped impedance stub

This article presents a new method of wideband dielectric measurement at microwave frequencies. This method can be used to determine the complex dielectric properties of solid and semisolid materials from 0.9 GHz to 4.5 GHz, including the ISM bands of 915 MHz and 2450 MHz. The new method is based on the scattering parameter measurement of a stepped impedance open circuited micro-strip stub, partly loaded with dielectric test material. Current microwave wideband spectroscopy techniques generally measure dielectric materials over a wide range of frequencies but their accuracy is limited. In contrast, narrowband techniques generally measure dielectric properties to a high accuracy but only at a single frequency. This new technique is capable of measuring dielectric properties over a wide range of frequencies to a high accuracy. The technique has been verified by the empirical characterisation of the dielectric properties of Teflon and Duroid 5880 materials. Empirical results were in good agreement with values in the manufacturer’s Data Sheets. The complex permittivity data will be useful for further microwave processing of the materials.