One-port Vector Network Analyzer Research Articles

A substitution method for nanoscale capacitance calibration using scanning microwave microscopy

This paper presents a calibration method and an uncertainty budget for capacitance measurements performed on micrometric size capacitors at microwave frequencies and nanometric resolution using a scanning microwave microscopy (SMM). The method applies the classical one-port vector network analyzer calibration for SMM using three known capacitance standards. These standards are established from a commercial calibration kit placed close to the microcapacitors in order to be calibrated. The calibration kit is composed of a large number of Metal-Oxide-Semiconductor (MOS) microcapacitors with capacitance values C ranging from 0.1 fF to 8.6 fF. Diligent selection criteria were established for the choice of the three capacitors. Their capacitance values were calculated from the AFM measured values of the area of the top electrodes and the dielectric thickness and considering the contribution of fringing fields. The combined type uncertainty on these calculated values amounts between 5% and 14% in relative value (uncertainty given at one standard deviation). The comparison between the capacitance values measured on calibration kit capacitors using the calibrated SMM and the calculated values show a good agreement for capacitances higher than 0.8 fF within uncertainties varying between 6% and 9%. For smaller capacitances, most of the observed deviations are not significant at two standard deviations. The uncertainties are mostly dominated by dimensional measurements and less importantly by unwanted capacitance effects. Based on these results, capacitances of two sets of microcapacitors were calibrated. The combined uncertainties vary from 14% to 7% for capacitances ranging from 0.1 fF to 3.1 fF respectively. The permittivity values of the dielectric layer of the two samples have been determined. They are found equal to 4.0 and 4.1 with a standard uncertainty of 0.6 and correlate with the expected value of 3.9.

A Position-Independent Reflection-Only Method for Complex Permittivity and Permeability Determination with One Sample

AbstractThis paper presents a position-independent reflection-only method for determining complex permittivity and permeability of a sample. In this method, both the short and match calibration kits are used to measure the reflection coefficients. Only one sample positioned arbitrarily is measured using a one-port vector network analyzer (VNA), while the complex permittivity and permeability of the sample are determined simultaneously. Experimental results in X-band for the Acrylonitrile Butadiene Styrene plastic (ABS) are included to exhibit the validity of the proposed method. The results show that the complex permittivity and permeability determined by the proposed method have a good agreement with the parameters determined by the well-known Nicolson–Ross–Weir (NRW) method. In addition, a magnetic material is simulated to further validate the proposed method.

One-Port Vector Network Analyzer Characterization of Soil Dielectric Spectrum

Accurate determination of soil complex-dielectric-permittivity spectrum is important for various applications, especially for the development of soil moisture sensors that can be used, e.g., in agriculture and for environmental monitoring. Wideband measurement of soil dielectric spectrum requires the use of large-diameter coaxial transmission-line cells connected to a vector network analyzer (VNA). We present a new method for soil dielectric-spectrum characterization in the frequency range of 0.05–3 GHz. Our methodology is based on a wideband one-port VNA measurement of a soil sample inserted into a large-diameter coaxial cell. The key part of our approach is the use of a variable load terminating the coaxial cell to extract the scattering parameters of the sample, which are then fed into a dielectric permittivity extraction algorithm. The system provides quick and repeatable measurements without the use of flexible microwave cables. Also, application of a portable one-port VNA significantly lowers the cost of the system in comparison to two-port setups. We verify our methodology based on measurements of reference materials—polytetrafluoroethylene, isopropanol, and ethanol—and then apply it to characterize the soil samples with different moisture content and salinity. Experimental results confirm the validity of our approach.

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.

Scanning microwave microscopy applied to semiconducting GaAs structures.

A calibration algorithm based on one-port vector network analyzer (VNA) calibration for scanning microwave microscopes (SMMs) is presented and used to extract quantitative carrier densities from a semiconducting n-doped GaAs multilayer sample. This robust and versatile algorithm is instrument and frequency independent, as we demonstrate by analyzing experimental data from two different, cantilever- and tuning fork-based, microscope setups operating in a wide frequency range up to 27.5 GHz. To benchmark the SMM results, comparison with secondary ion mass spectrometry is undertaken. Furthermore, we show SMM data on a GaAs p-n junction distinguishing p- and n-doped layers.

Time-Domain Optoelectronic Vector Network Analysis on Coplanar Waveguides

The development of a one-port laser-based vector network analyzer (VNA) is described. Measurements are carried out in the time domain using a femtosecond laser for the generation and detection of ultrashort voltage pulses on a coplanar waveguide (CPW). The accurate separation of voltage signals propagating in forward and backward directions, being one of the key tasks of vector network analysis, is achieved by measuring voltage pulses at different positions on the CPW. This separation technique even works in the case of temporally overlapping forward and backward propagating signals. With this laser-based VNA, a frequency spacing of 500 MHz, a measurement bandwidth of approximately 500 GHz, and a dynamic range of more than 40 dB are obtained. As an application example, the laser-based VNA is used to realize an ultra-broadband voltage pulse standard.

Determination of the Complex Residual Error Parameters of a Calibrated One-Port Vector Network Analyzer

A novel approach for the determination of the complex residual error parameters of a calibrated one-port vector network analyzer (VNA) is proposed. The method is based on a single-reflection measurement employing a high-precision airline terminated by a short. The complex-valued residual directivity and source match are extracted over the entire measured frequency range by applying a sophisticated data analysis scheme utilizing low-pass filtering and linear prediction. By including an additional reflection measurement of the utilized short, the method allows the residual reflection tracking to be evaluated. Based on numerical simulations, advisable settings of method parameters are determined. In addition to the verification of the VNA calibration, the complex residual error parameters can be used for a second-order correction of the measured data. The significant enhancement of accuracy, which can be achieved this way, is demonstrated for standard calibrations by comparing the second-order corrected reflection data with results obtained from the well-established cross-ratio (quarter-wave) method.

PERMITTIVITY MEASUREMENT OF THIN DIELECTRIC MATERIALS FROM REFLECTION-ONLY MEASUREMENTS USING ONE-PORT VECTOR NETWORK ANALYZERS

We have proposed a simple waveguide method for complex permittivity determination of dielectric materials which are not completely fllling the entire sample holder. The method reconstructs the permittivity from measured re∞ection-only scattering parameters by a one-port vector network analyzer of two conflgurations of the sample holder. It not only eliminates the necessity of any knowledge of the location of the shifted sample inside its holder but also decreases measurement errors occurring with the presence of undesired air gaps, which seriously afiect the measurement accuracy of transmission- only measurements, present between the sample and holder walls. Furthermore, the reconstruction of permittivity can be realized by any one-port vector network analyzer, which is less expensive than their two-port counterparts. Therefore, the proposed method is cost-efiective. We have analyzed the accuracy of the proposed method and noted a good compromise between the reference data and measured values of permittivities of low-loss polyvinyl-chloride and polytetra∞uoro.ethylene samples (less than 8 percent for dielectric constant and less than 15 percent for loss tangent values).