Full-wave Model Research Articles

CHARACTERIZATION OF LOSSY SIW RESONATORS BASED ON MULTILAYER PERCEPTRON NEURAL NETWORKS ON GRAPHICS PROCESSING UNIT

In recent years, Artiflcial Neural networks (ANNs) have been intensively employed to build smart model of microwave devices. In this paper a characterization of lossy SIW resonators by means of Multilayer Perceptron Neural Networks (MLPNNs) on Graphics Processing Unit (GPU), is presented. Once properly selected and trained, a MLPNN can evaluate the lossy SIW resonator's resonant frequency fr and the pertaining quality factor Q at a shorter time than the full-wave rigorous model. In this way, fast parametric models of SIW structures to employ for the design and optimization of microwave devices, exploiting the computational power of GPUs, can be obtained.

NEAR-FIELD OR FAR-FIELD FULL-WAVE GROUND PENETRATING RADAR MODELING AS A FUNCTION OF THE ANTENNA HEIGHT ABOVE A PLANAR LAYERED MEDIUM

The selection of a near-field or far-field ground-penetrating radar (GPR) model is an important question for an accurate but computationally effective characterization of medium electrical properties using full-wave inverse modeling. In this study, we determined an antenna height threshold for the near-field and far-field full-wave GPR models by analyzing the variation of the spatial derivatives of the Green's function over the antenna aperture. The obtained results show that the ratio of this threshold to the maximum dimension of the antenna aperture is approximately equal to 1.2. Subsequently, we validated the finding threshold through numerical and laboratory experiments using a homemade 1-3 GHz Vivaldi antenna with an aperture of 24 cm. For the numerical experiments, we compared the synthetic GPR data generated from several scenarios of layered medium using both near-field and far-field antenna models. The results showed that above the antenna height threshold, the near-field and far-field GPR data perfectly agree. For the laboratory experiments, we conducted GPR measurements at different antenna heights above a water layer. The near-field model performed better for antenna heights smaller than the threshold value (± 29 cm), while both models provided similar results for larger heights. The results obtained by this study provides valuable insights to specify the antenna height threshold above which the far-field model can be used for a given antenna.

Fast Simulation of Microwave Circuits With Nonlinear Terminations Using High-Order Stable Methods

This paper describes a new method for transient simulation, using high-order stable methods, of microwave structures modeled using a large number of lumped components. The target of the proposed technique is circuit-based simulation of the large linear circuits that arise from full-wave modeling of distributed structures, such as transmission lines and microstrip elements, along with the terminating nonlinear devices. In this case, the cost of the solution of the linear system typically dominates the computational effort. The proposed method takes advantage of the special structure of the block matrices in these applications to reduce the computational cost significantly. The core of the proposed algorithm is based on the idea of “node tearing” to separate the large linear sub-circuits from the nonlinear devices. This idea faciliates handling the linear sub-circuits using a better matrix factorization technique, resulting in faster simulations compared to classical techniques.

Models of ionospheric VLF absorption of powerful ground based transmitters

Ground based Very Low Frequency (VLF, 3–30 kHz) radio transmitters play a role in precipitation of energetic Van Allen electrons. Initial analyses of the contribution of VLF transmitters to radiation belt losses were based on early models of trans‐ionospheric propagation known as the Helliwell absorption curves, but some recent studies have found that the model overestimates (by 20–100 dB) the VLF energy reaching the magnetosphere. It was subsequently suggested that conversion of wave energy into electrostatic modes may be responsible for the error. We utilize a newly available extensive record of VLF transmitter energy reaching the magnetosphere, taken from the DEMETER satellite, and perform a direct comparison with a sophisticated full wave model of trans‐ionospheric propagation. Although the model does not include the effect of ionospheric irregularities, it correctly predicts the average total power injected into the magnetosphere within several dB. The results, particularly at nighttime, appear to be robust against the variability of the ionospheric electron density. We conclude that the global effect of irregularity scattering on whistler mode conversion to quasi‐electrostatic may be no larger than 6 dB.

Dispersive full-wave finite-difference time-domain analysis of the bipolar cylindrical cloak based on the effective medium approach

A dispersive full-wave finite-difference time-domain model is used to study the performance of bipolar cylindrical invisibility cloaking devices. We have considered two different cloaking structures generated by the mapping of the σ axis and the mapping of the τ axis of bipolar coordinates. The permittivity and permeability tensors for the cloaking devices are obtained from an effective medium approach in general relativity. The σ-axis mapped bipolar cylindrical cloak is found to be imperfect, and the cloaking performance is found to depend on the polarization of the incident waves, the direction of propagation of the waves, and the loss tangents of the metamaterial. Only the case of TM waves for the specific propagation direction shows good cloaking performance. On the other hand, the τ-mapped cloaking device shows good cloaking performance for all polarizations and directions of propagation. However, this structure has a singular boundary at the inner radius. Realistic cloaking materials with loss still show a cloak that is working, but attenuated backscattering waves exist.

Electrical Performance of the Recessed Probe Launch Technique for Measurement of Embedded Multilayer Structures

This paper explores the electrical performance of a recessed probe launch (RPL) technique for measurement of embedded (internal) printed circuit board (PCB) structures such as striplines and vias (plated through holes). The RPL uses high-frequency microprobes in combination with a milling technique that removes upper board layers and exposes internal probing points. A two-tier calibration technique is applied for the extraction of the S-parameters of the RPLs with the help of thru-reflect-line calibration standards designed on PCB. Full-wave models are used to corroborate and validate the obtained S-parameters. Good model-to-hardware correlation is obtained up to 40 GHz. Furthermore, the launch performance with respect to microprobe positioning and variations of the cavity size is investigated using the full-wave models. These simulations suggest techniques for launch optimization and probe modifications that improve the launch measurement bandwidth.

Electromagnetic Susceptibility Analysis Method of Electro-Explosive Devices

Electro-explosive device (EED) is easily influenced by electromagnetic interference (EMI) in war-field. To study the electromagnetic susceptibility of EED, the method based on full-wave physical modeling and resonance effect simulation is presented. The EMS of non-contact fuse is analyzed as an example. The test data validate the correction of the EMS analysis method, which is of great value for reference to Electromagnetic compatibility (EMC) design of EED.

Flat metasurfaces to focus electromagnetic waves in reflection geometry

We show that a flat metasurface with a parabolic reflection-phase distribution can focus an impinging plane wave to a point image in reflection geometry. Our system is much thinner than conventional geometric-optics devices and does not suffer the energy-loss issues encountered by many metamaterial devices working in transmission geometry. We designed realistic microwave samples and performed near-field scanning experiments to verify the focusing effect. Experimental results are in good agreement with full wave simulations, model calculations, and theoretical analyses.

Comparison of Surface Irrigation Simulation Models: Full Hydrodynamic, Zero Inertia, Kinematic Wave

Some phenomena such as surface irrigation are so complex that it is very difficult to implement them in nature. For this purpose, simulation models are used. In this study, ability of full hydrodynamic, zero inertia, and kinematic wave models has been investigated in surface irrigation simulation. Using SIRMOD software, their performance has been compared. The results showed that full hydrodynamic and zero inertia models were very powerful in simulation process. For increasing of filed slope until amount of 0.01 full hydrodynamic and zero inertia models had not any difference but for more increasing of S0 due to the increasing of velocity, accuracy of zero inertia model dropped. In full hydrodynamic and zero inertia models for increase in Manning’s roughness coefficient amount of error was increased until n=0.15. After this amount, error remained constant thus n=0.15 determined as critical discharge. Accuracy of kinematic wave model reduced in clay and heavy clay soils, high discharges, high Manning’s roughness coefficient, and basin irrigation. However, in many situations all three models had the same answers and were capable tools to simulating of surface irrigation processes.

Simulation of flexural waves in drill pipes including the effects of the gravitational field

We design a full-wave modeling method to simulate flexural (bending) waves in pipes of variable cross-section and material properties, subject to the effects of the gravitational field. The study finds application in propagation through drill strings and stability of hydrocarbon wells while drilling. The algorithm is based on a direct (grid) method, where the spatial derivatives are computed with the Fourier pseudospectral method. The modeling is successfully tested against the analytical solution for flexural waves propagating in a uniform pipe. Moreover, we obtain reciprocity relations for the lateral deflection, particle velocity and bending moment due to sources applied in the force-balance and constitutive equations. The relations are then verified by the simulations and at the same time provide a test of the consistency of the numerical algorithm in inhomogeneous media, where there is no closed-form analytical solution.We analyze the effects of the gravitational field and show that for negative axial loads (compressive stresses) there is an instability below a critical wavenumber, while the system is stable for positive (tensile) loads. Such a situation appears below the neutral point of a drill string when the gravitational force is taken into account. A plane-wave analysis yields the phase and group velocities when the load is uniform along the pipe and in the case of a suspended pipe subject to a gravitational force with a neutral point downhole. In the latter case, the signal propagates with attenuation. Propagation along a realistic drill string, simulating the drill bit as a stress-free end, is illustrated. Moreover, propagation subject to an axial gravitational load shows that the signal is slower for a tensile prestress.

Numerical modeling of MOS transistor with interconnections using lumped element-FDTD method

A detailed three-dimensional (3-D) full-wave time-domain simulation model is presented for the analysis of an active semiconductor device. Microwave analysis of the nMOS transistor using monolithic microwave integrated circuit (MMIC) is simulated. A three-dimensional finite-difference time-domain (3D-FDTD) scheme is adopted to describe the circuit passive part, whereas numerical device simulation techniques are employed for the active semiconductor devices. The proposed algorithm provides the time and space distribution of the unknown functions electrostatic potential, carriers' concentration, and current density for the MOS transistor. Fast Fourier transform (FFT) analysis is performed on the obtained time response to calculate the scattering matrix of the S-parameters and phase frequency dependencies. Finally, the obtained results are presented and show a good agreement with those based on a hydrodynamic model.

Antenna-Generalized Scattering Matrix in Terms of Equivalent Infinitesimal Dipoles: Application to Finite Array Problems

A full-wave antenna modeling method by means of elementary sources described in terms of colocalized infinitesimal dipoles is presented in this paper. The procedure provides a generalized scattering matrix (GSM) in terms of equivalent infinitesimal dipoles from the GSM of the antenna by using rotation and translation of spherical modes. The number of equivalent infinitesimal dipoles and their positions are optimized by using a genetic algorithm. The application to the full-wave analysis of arrays is also presented, providing very accurate results even when the minimum spheres of the antennas in the array environment overlap considerably, which cannot be solved by the direct coupling of generalized scattering matrices in terms of spherical waves. Some examples of antenna modeling and their application to the analysis of arrays of antennas on a metallic plane will be shown.

Polarizers on a segment of square waveguide with diagonal ridges and adjustment iris

Configuration of a polarizer that converts the dominant wave of input rectangular waveguide into the wave with elliptical polarization of output square waveguide. The phase-shifting section is implemented on a segment of a square waveguide with two diagonal square ridges and output iris with finite thickness. The full-wave model of the polarizer is created using partial regions and generalized scattering matrices methods. Based on results of numerical optimization of polarizers with input rectangular waveguide dimensions 19×9.5 mm2 it is revealed that they can provide bandwidth of at least 13% for ellipticity coefficient r < 1 dB and return loss not worse than 25 dB in lower, middle and upper parts of rectangular waveguide’s operating band.

Research on the EM Modeling of Optimization of PCB Grounded Via

Grounded vias modeling is used to analyze the impact on the high speed PCB EMC and SI issues in three aspects, including theoretical analysis, simulator modeling and practical PCB test. In this paper, we discuss the full-wave complex scattering parameter model and full-wave model. Then the full-wave analysis model of the through holes for model validation and comparison are established, by using numerical simulation software HFSS and CST Microwave Studio. The initial test results on the practical PCB show that the analyzed method is reasonable and accurate. And optimized design parameters can ensure the continuity of the impedance of vias, and introduce lesser return loss and insertion loss. It is shown that the signal transmission performance is greatly improved with the grounded via added, which is helpful in specifying the manufacturing tolerance of via designs.

2D full wave modeling for a synthetic Doppler backscattering diagnostic

Doppler backscattering (DBS) is a plasma diagnostic used in tokamaks and other magnetic confinement devices to measure the fluctuation level of intermediate wavenumber (k(θ)ρ(s) ~ 1) density fluctuations and the lab frame propagation velocity of turbulence. Here, a synthetic DBS diagnostic is described, which has been used for comparisons between measurements in the DIII-D tokamak and predictions from nonlinear gyrokinetic simulations. To estimate the wavenumber range to which a Gaussian beam would be sensitive, a ray tracing code and a 2D finite difference, time domain full wave code are used. Experimental density profiles and magnetic geometry are used along with the experimental antenna and beam characteristics. An example of the effect of the synthetic diagnostic on the output of a nonlinear gyrokinetic simulation is presented.

Electrical characterization of a RF power transistor ceramic package including multiple wirebonds

This article presents an approach for modeling of RF power transistor packages including bondwires. The approach is based on measurements of a real package in which the transistor chip was replaced with a 2-port of known parameters and connected to the package leads with multiple parallel wirebonds. Using the measurement results, an equivalent circuit of the package is constructed. The response of the circuit is then compared to measurements and results obtained through full-wave electromagnetic modeling to reveal good agreement. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013. © 2013 Wiley Periodicals, Inc.

Electromagnetic Inverse Scattering Algorithm and Experiment Using Absolute Source Characterization

We present the results of a free-space microwave inverse scattering algorithm and experiment. The inversion algorithm is based on the Born iterative method but with a new integral equation operator that directly links the material contrasts we wish to image to S-parameter measurements of a vector network analyzer. This is done with a full-wave antenna model based on the source-scattering matrix formulation. This model allows us to absolutely calibrate an inverse scattering setup without the need for calibration targets. We describe the new operator and how it modifies the inversion algorithm, and explain how to make the algorithm and experiment consistent. We then give the results of imaging several dielectric objects and show the limits of the algorithm in experiment.

Reconstruction of the turbulence radial profile from reflectometry phase root mean square measurements

Simple expressions allowing estimation of the turbulent density perturbation from reflectometry phase root mean square (rms) measurements and accounting for the turbulence correlation length are given. A numerical procedure for precise turbulence radial profile reconstruction for different turbulence wave number spectra and both O-mode and X-mode reflectometry is proposed. It is validated using a full-wave 1D modeling of ordinary (O) mode reflectometry in the case of arbitrary density fluctuation profiles.

Prototype Design of a Modular Ultrawideband Wavelength-Scaled Array of Flared Notches

A prototype modular ultrawideband wavelength- scaled array of flared notches has been designed, built, measured and validated with full-wave modeling tools. Wavelength-scaled arrays operate over ultrawide bandwidths with significantly-reduced element counts, maintaining a relatively-constant beam size by utilizing phased-array radiators of different size. The prototype phased array presented here is designed to operate over an 8:1 bandwidth (1-8 GHz), demonstrating a 12-degree beam capacity at 2 GHz, 4 GHz, and 8 GHz. The architecture achieves a reduction in element count by a factor of 6.4-only 160 elements per polarization as compared to a conventional 1024-element phased array of the same aperture size-at the cost of reduced beamwidth capacity in the higher frequency range. Performance metrics (active VSWR and radiation characteristics) of the wavelength-scaled array are measured and validated against full-wave simulations. The technology is presented as a viable alternative to more expensive conventional ultrawideband arrays with dense uniform element layouts.

Full-wave modeling of superconducting microstrip lines including the nonlinearity behavior

This paper describes a new theoretical model to characterize the superconducting microstrip line and carefully studies the effects of the nonlinearity of superconductors, the strip thickness and losses on circuit performances. The microstrip line has been considered as a multilayered structure. The integral equation for the electrical field has been formulated, in the spectral domain, using the exact dyadic Green’s function of bianisotropic planar media. The Galerkin’s technique has been used for solving this integral equation. Obtained results concern the effective permittivity constant and the attenuation constant versus frequency and temperature rate.