D.C. DeGroot

Free University of Brussels, Bruxelles, Brussels Capital Region, Belgium

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Publications (44)20.13 Total impact

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    ABSTRACT: Extracting quantities, such as the propagation factor or the characteristic impedance of a transmission line based on measured S -parameters, can be more involved than expected. Experience teaches that even if the S -parameter measurements look smooth and are of good quality, the derived quantities can contain large spikes that tend to grow when connection imperfections are present. In this paper, the presence of the peaks is shown in practical measurements, a possible explanation for their presence is provided, and a sensitive indicator (the image parameters) for the imperfections is proposed.
    IEEE Transactions on Instrumentation and Measurement 11/2007; · 1.36 Impact Factor
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    ABSTRACT: We develop an empirical model for the warm-up drift in a harmonic phase standard used to calibrate the phase distortion of a nonlinear vector network analyzer. The model enables us to estimate the time at which the standard reaches stability
    IEEE Transactions on Instrumentation and Measurement 07/2007; · 1.36 Impact Factor
  • IEEE T. Instrumentation and Measurement. 01/2007; 56:1967-1972.
  • IEEE T. Instrumentation and Measurement. 01/2007; 56:931-937.
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    ABSTRACT: Measured S-parameters are a key factor in many measurement and/or modeling applications. Experience teaches that quantities that are derived from the measurements can contain spikes, and that they tend to grow with connection imperfections. In this paper, a possible theory is provided and the presence of the peaks is shown in practical measurements. The measured propagation constant (γ((ω)) and characteristic impedance (Z<sub>0</sub>(ω)) of a transmission line are used as an illustrative example.
    ARFTG Conference Digest, 2005. Spring 2005. 65th; 07/2005 · 1.36 Impact Factor
  • G. Loglio, J. Jargon, D.C. DeGroot
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    ABSTRACT: We describe a method for preserving time-invariant phase determination of nonharmonically related signals. In particular, signals produced by intermodulation are considered. We provide simple examples to illustrate our technique, and show how this method is suitable for intermodulation measurements of nonlinear devices and circuits operating at microwave frequencies.
    ARFTG Conference Digest, 2005. Spring 2005. 65th; 07/2005
  • G. LoogIio, J. Jargon, D.C. DeGroot, Z. Popovic
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    ABSTRACT: Not Available
    ARFTG Conference Digest, 2005. Spring 2005. 65th; 07/2005
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    ABSTRACT: We present new frequency-dependent measurements of both the magnitude and phase of the nonlinear response in superconducting thin films at microwave frequencies obtained using a large-signal network analyzer. Our measurements show that the nonlinear inductance dominates the nonlinear response in thin YBCO films at 76 K, and our analysis yields two current-density scales corresponding to the real and imaginary components of the nonlinear response. The current-density scale associated with the dominant inductive response likely results from intrinsic pair-breaking, while the current-density scale associated with the nonlinear resistive term is smaller than the expected value due to pair-breaking, and could originate from vortex motion or other extrinsic effects.
    IEEE Transactions on Applied Superconductivity 07/2005; · 1.20 Impact Factor
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    ABSTRACT: A new 16-term statistical calibration has been developed for the correction of the vector network analyzer (VNA) data. The method uses multiple measurements of generic transmission line and reflection standards. Using a functional model of the system and transmission line standards, we apply a nonlinear least-squares estimator to simultaneously optimize the correction terms in the measurement model and the propagation constant. The method provide estimates of the uncertainty on each of the parameters using the final Jacobian. This paper shows for the first time an application of the new calibration to a commercial nonlinear VNA, plus quantitative statements regarding the quality of the parameters.
    Microwave Symposium Digest, 2004 IEEE MTT-S International; 07/2004
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    ABSTRACT: We develop an empirical model for the warm-up drift in harmonic phase standards used to calibrate the phase distortion of nonlinear vector network analyzers. This model will enable us to estimate the time at which the standards reach stability
    Precision Electromagnetic Measurements Digest, 2004 Conference on; 07/2004
  • J.A. Jargon, K.C. Gupta, D.C. DeGroot
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    ABSTRACT: First Page of the Article
    ARFTG Conference Digest Spring, 2004. 63rd; 02/2004
  • Y. Rolain, W. Van Moer, D. DeGroot
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    ABSTRACT: First Page of the Article
    ARFTG Conference Digest Spring, 2004. 63rd; 02/2004
  • J.A. Jargon, D.C. DeGroot, D.F. Vecchia
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    ABSTRACT: In this paper, we present the first published repeatability study of commercial harmonic phase standards (HPS) measured by a nonlinear vector network analyzer. Specifically, we measure two harmonic phase standards, one of which is specified to 20 GHz and the other to 50 GHz. By performing 5 calibrations and making 100 measurements from 600 MHz to 19.8 GHz at each calibration, we determine the repeatability bounds for the complex wave-variable vectors and associated phases and magnitudes of each harmonic component. We also compare the mean phase values to those supplied by the manufacturer. While we achieve standard uncertainties of no greater than 0.73°, we find significant variations in the mean values with changing HPS conditions and show evidence of a substantial thermal contribution.
    ARFTG Microwave Measurements Conference, 2003. Fall 2003. 62nd; 01/2004
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    ABSTRACT: We describe the design, fabrication, and testing of a superconducting passive nonlinear reference device that has a calculable phase relationship between the fundamental RF drive signal and resulting higher order harmonic components. We show this passive device to be a useful standard for verifying the phase calibration of nonlinear vector network analyzers, as the magnitude and phase of the third-order product are found directly from independent measurements of the field-dependent surface impedance. Microwave power-dependent measurements of coplanar waveguide (CPW) resonators fabricated from thin film high-T<sub>c</sub> superconductor materials yield the transmission line resistance and inductance per unit length as a function of rf current. With these values and the line geometry we computed both the nonlinear surface impedance of the material and the phase and magnitude of the third-order product of a traveling wave in a quasi-linear transmission line. To demonstrate our CPW reference device, we measured both the magnitude and the phase of third-harmonic components generated in a number of 133 mm long meander transmission lines using a commercial nonlinear vector network analyzer. We demonstrate agreement to within 10 degrees between the measured and the predicted phase for third-harmonic signals relative to the fundamental.
    ARFTG Microwave Measurements Conference, 2003. Fall 2003. 62nd; 01/2004
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    ABSTRACT: We expand the definitions of power gain, transducer gain, and available gain by taking harmonic content into account. Furthermore, we show that under special conditions, these expanded definitions of gain can be expressed in terms of nonlinear large-signal scattering parameters. Finally, we provide an example showing how these expanded forms of gain and nonlinear large-signal scattering parameters can provide us with valuable information regarding the behavior of nonlinear models. Published 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13, 357–369, 2003.
    International Journal of RF and Microwave Computer-Aided Engineering 08/2003; 13(5):357 - 369. · 0.75 Impact Factor
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    ABSTRACT: We introduce a new technique which allows us to measure the admittance conversion matrix of a two port device, using a large-signal vector network analyzer. This method is applied to extract the conversion matrix of a 0.25 um PHEMT, driven by a 4.8 GHz signal, at different power levels, using an intermediate frequency of 600 MHz. A discussion of the up- and down-conversion is provided.
    Microwave Symposium Digest, 2003 IEEE MTT-S International; 07/2003
  • J.C. Booth, S.A. Schima, D.C. DeGroot
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    ABSTRACT: The origin of the detrimental nonlinear response in high T<sub>c</sub> superconductor (HTS) microwave devices is currently not well understood. In order to help elucidate the origin of these nonlinear effects, we have developed a description of the nonlinear response in superconductors in terms of a current-dependent complex conductivity. We demonstrate that such a treatment can consistently describe the results of power-dependent surface impedance measurements in resonator geometries as well as harmonic generation and intermodulation distortion effects in transmission line geometries. This approach yields a device-independent quantity that describes the nonlinear response of the superconducting material itself, which is suitable for comparisons of different materials and for material optimization. A further benefit of this description of nonlinear effects is that the relative importance of the nonlinear resistive and inductive components of a superconductor can be examined. We use this approach to predict the phase of the nonlinear response in HTS planar transmission lines, and compare our predictions with new phase-sensitive measurements made using a nonlinear vector network analyzer.
    IEEE Transactions on Applied Superconductivity 07/2003; · 1.20 Impact Factor
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    ABSTRACT: We analyze the input networks of the samplers used in the nose-to-nose calibration method. Our model demonstrates that the required input network conditions are satisfied in this method and shows the interconnection errors are limited to measurement uncertainties of input reflection coefficients and adapter S-parameters utilized during the calibration procedure. Further, the input network model fully includes the effects of mismatch reflections, and we use the model to reconcile nose-to-nose waveform correction methods with traditional signal power measurement techniques.
    05/2003;
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    ABSTRACT: We describe a method for preserving time-invariant phase relationships when ratios are taken between any two harmonically related, complex signals. We provide a simple example to illustrate our technique, and show how this method is implemented when defining time-invariant nonlinear large-signal scattering parameters.
    ARFTG Conference Digest, Fall 2002. 60th; 01/2003
  • Conference Paper: Multiline TRL revealed
    D.C. DeGroot, J.A. Jargon, R.B. Marks
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    ABSTRACT: We reveal the techniques underlying actual implementation of the NIST MultiCal software, an evolved, automated implementation of the Multiline TRL (Thru-Reflect-Line) calibration method for vector network analyzers (VNAs). We describe the sequence of events in MultiCal for the Multiline TRL calibration and show how the program operates more like a state-machine than a solver of simultaneous equations. Our report details the steps used in estimating the transmission-line propagation-constant and the VNA correction coefficients.
    ARFTG Conference Digest, Fall 2002. 60th; 01/2003