Closed Form Formulas for Distributed Circuit Model of Discontinuities in HTS Microstrip Transmission Lines (original) (raw)
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Strategies are explored to reduce the electromagnetic simulation time of electrically large superconducting transmission line structures while retaining model accuracy. The complex surface reactance of an infinite thin-film superconducting sheet is evaluated with the BCS (Bardeen-Cooper-Schrieffer) theory and used as an input to model the phase velocity and characteristic impedance of finite width transmission line structures. Commercially available electromagnetic simulation software are employed for the calculations and the results are compared with limiting analytic forms from the literature. The influences of line width, metallization thickness, and substrate height on microstrip transmission line propagation are considered in detail and a scaling approach is presented to compensate for the leading order effect in numerical simulations. These findings are particularly important near the energy gap of the superconductor due to the influence of the kinetic inductance on the transmission line dispersion.
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CiteSeerX - Document Details (Isaac Councill, Lee Giles): OF THE MASTER'S THESIS Author: Luis de Jussilainen Costa Name of the thesis: Implementation of a superconducting microstrip line model Date: August 14, 1995 Number of pages: 83 Faculty: Electrical Engineering ...
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We present a full wave analysis to compute the propagation constant of electromagnetic waves traveling in a normal and superconducting microstrip transmission line. The transverse wavenumber in the dielectric substrate is obtained as the root of a set of transcendental equation, derived by matching the tangential fields at the dielectric-conductor and dielectric-air interfaces. The propagation constant can then be obtained by substituting the transverse wavenumber into the dispersion relation. For normal microstrip lines, we found good agreement between our results and those obtained using the quasi-static methods. As compared to some of the available techniques used to calculate loss in superconducting microstrip lines, such as Maticks and Yassin-Withingtons method, our method gives higher loss especially in the regime of millimeter and submillimeter wavelengths. Since our method takes into account the superposition of TE and TM modes, we attribute the differences as due to the fringing fields effect and the existence of the longitudinal field components in our formulation.
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Microwave and Optical Technology Letters, 2004
We present a spectral-domain analysis of thin superconducting microstrip structures in which the effects of superconducting materials, finite conductivity, and finite thickness are taken into account, using the concept of complex surface impedance. Numerical simulations showing variation of the propagation and attenuation characteristics of transmission lines and the quality factor of resonators with regard to temperature and frequency are presented. Some of the theoretical results are compared with the available data to document the validity of the approach. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 55–59, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20045
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The surface impedance of high-Tc superconducting microstrip lines and its temperature dependence is studied using the full-wave Finite Difference Time Domain (FDTD) technique. Maxwell's equations are modified to incorporate the two-fluid London model that describes superconductivity. The supercurrent density and the average current along the microstrip line are calculated as function of temperature and the width of the microstrip line. In addition, the surface resistance and reactance as function of temperature have been calculated and compared to published results.
IEEE Transaction on Applied Superconductivity
Superconducting materials are known to exhibit nonlinear effects and to produce harmonic generation and intermodulation distortion in superconductive circuits. In planar structures, these nonlinearities depend on the current distribution on the strip which is mainly determined by the structure of the device. This paper investigates the current distribution at the step-in-width discontinuity in superconducting microstrip transmission lines, which is computed by a numerical approach based on a 3-D finite-element method. This current distribution is used to obtain the parameters of the nonlinear circuit model for the superconducting microstrip step-in-width discontinuity. The proposed equivalent nonlinear circuit can be solved using the harmonic balance method. Examples of two superconducting structures which contain the steps in width are given and validated by comparison with electromagnetic full-wave results. The proposed model can be used for effective optimization of the superconducting microwave filter resonators in order to minimize their nonlinear distortions.
In this study, an equivalent linear and non-linear circuit model of superconducting microstrip T-junction (SMT) structures is proposed. Two types of SMT structures are analysed using suggested model and their scattering behaviour is compared using both the method of moment and the finite-element method (FEM). The fundamental and third-order harmonic outputs are obtained using harmonic balance method to observe the non-linear behaviour in SMT structures. A linear and non-linear model for enhanced SMT structures is also suggested and verified by S-parameters comparison between the model and FEM method. The non-linearity in enhanced structures is modelled similarly and compared with results of normal structures.
Microstrip Line Discontinuities Simulation at Microwave Frequencies
Advances in Physics Theories and Applications, 2013
Microwave and Millimeter wave integrated circuits (MICs) have experienced a tremendous growth over the last 50 years. Microstrip line is one of the popular lines in these MICs. Due to the layout necessities, an electromagnetic wave that propagates down a microstrip line may encounter discontinuities such as T-junctions, Bends and vias. A simulation model is presented here for analysing these discontinuities in microstrips through Sonnet Software. The parameters of microstrip lines are determined from the empirical formulae which are based on full wave analysis. The simulation work has been performed on Alumina substrate. The discontinuities are simulated and compensated which gives important results for designing high frequency microwave circuits.
Characteristics of microstrip transmission lines with high-dielectric-constant substrates
IEEE Transactions on Microwave Theory and Techniques, 1991
An efficient numerical code is developed from a full-wave analysis in the Fourier transform domain to determine the characteristics of a single-strip or multistrip coplanar transmission line. Modes of both even and odd symmetries are included. The impedance of the transmission line is calculated using the power-current equivalent model. Coupling constants between the even and the odd modes are also calculated. Results are provided for a shielded two-strip coupled microstrip transmission line on high-dielectric-constant substrate such as lanthanum aluminate with applications to superconducting transmission lines.
Current Distribution and Nonlinearity of Open-ends and Gaps in Superconducting Microstrip Structures
Journal of Superconductivity and Novel Magnetism
Superconducting devices are known to produce nonlinear effects. In planar structures, these nonlinearities depend on the current distribution on the strip, which definitely depends on the structure of device. This paper used a numerical method based on 3D-FEM to obtain the current distribution in the open-ends and gaps in the superconducting microstrip structures. This is used to present the nonlinear distributed circuit modeling of these discontinuities and its impact on the nonlinear phenomenon. This nonlinear circuit model is used in the Harmonic Balance (HB) method to analyze nonlinearity in the superconducting microwave devices. Therefore, this simple accurate enough nonlinear circuit model is warmly welcomed to retire the seemingly inevitable use of time- and memory-consuming numerical techniques for nonlinear analysis of discontinuities in superconducting microwave structures. As an example, we analyze a microstrip superconducting end-coupled band pass filter (BPF). These results are very useful for optimizing the resonators of the superconducting microwave filters in order to minimize its nonlinear distortions.