Full-wave Model Research Articles

Full-Wave Model of Frequency-Dispersive Media With Debye Dispersion Relation by Circuit-Oriented FEM

Dispersive materials play an important role in a wide variety of applications (e.g., waveguides, antenna structures, integrated circuits, bioelectromagnetic applications). In this paper, a full-wave finite-element method (FEM-SPICE) technique for modeling dispersive materials is proposed. A finite-element formulation employing Whitney elements capable of analyzing electromagnetic geometries with dispersive media is described, and a Norton equivalent network is developed for each element. The overall network can be analyzed using a circuit simulator based on SPICE, and is suitable for both frequency- and time-domain analysis. This approach exploits the flexibility of finite-element mesh generation and computational efficiency of modern circuit simulators. Simple test configurations are analyzed to validate the proposed formulation.

Altering infrared metamaterial performance through metal resonance damping

Infrared metamaterial design is a rapidly developing field and there are increasing demands for effective optimization and tuning techniques. One approach to tuning is to alter the material properties of the metals making up the resonant metamaterial to purposefully introduce resonance frequency and bandwidth damping. Damping in the infrared portion of the spectrum is unique for metamaterials because the frequency is on the order of the inverse of the relaxation time for most noble metals. Metals with small relaxation times exhibit less resonance frequency damping over a greater portion of the infrared than metals with a longer relaxation time and, subsequently, larger dc conductivity. This leads to the unexpected condition where it is possible to select a metal that simultaneously increases a metamaterial’s bandwidth and resonance frequency without altering the geometry of the structure. Starting with the classical microwave equation for thin-film resistors, a practical equivalent-circuit model is developed predicting the sensitivity of infrared metamaterials to complex film impedance. Several full-wave electromagnetic models are developed to validate the resonant-circuit model, and excellent agreement is demonstrated between modeled and measured results.

Study of High Tc Superconducting Microstrip Antenna

Resonant characteristics of microstrip antennas with superconducting fllms is pre- sented. The analysis is based on a full electromagnetic wave model with London's equations and the two-∞uid model. It is shown that the full-wave analysis presented here gives numerical results which are in excellent agreement with the measured data available in the literature. Re- sults showing the efiect of the temperature on the resonant frequency and half-power bandwidth of superconducting microstrip antenna are given. Variations of the resonant frequency with the high Tc superconducting fllm thickness are also presented. Superconducting passive microwave devices such as antennas, fllters, transmission lines, and phase shifters have shown signiflcant superiority over corresponding devices fabricated with normal con- ductors such as gold, silver, or copper due to the advantages of superconductors (1). Advantages of using high Tc superconducting materials at high frequencies include (2): 1) very small losses, which means reduction of attenuation and noise level; 2) very small dispersion up to frequencies of several tens of GHz; 3) smaller devises due to the lower losses, which leads to larger integration density; and 4) the propagation time can be greatly reduced because of the smaller size and the shorter interconnects. In the literature, the studies concerning the resonance characteristics of microstrip antennas using perfectly conducting patches are abundant. However, few works have been done for the case of microstrip antennas using superconducting patches. The determination of the resonant frequencies of superconducting microstrip patch antennas was initially carried out by means of the magnetic wall cavity model (3). Later on, these resonant frequencies were obtained by using the rigorous full-wave analysis (4). To validate the theoretical analysis, the authors in (4) have compared their numerical results with the experimental data of Richard etal. (3). This comparison has not been done in a convenient way for two reasons: the variation of the permittivity of the lanthanum aluminate substrate with the variation of the temperature, as indicated by the experiment of Richard etal. (3), has not been take into account by Silva etal. (4) and the efiect of varying the temperature on the resonant frequency is insigniflcant. In this paper, we present a theoretical and numerical analysis of the resonant frequencies of high Tc superconducting rectangular microstrip antennas which yields excellent agreement with the mea- sured data of Richard etal. (3). To include the efiect of the superconductivity of the microstrip patch in the full-wave analysis, a surface complex impedance is considered. This impedance is de- termined by using London's equation and the two-∞uid model of Gorter and Casimir (2). Numerical results for the efiect of the temperature on the resonant frequency and half-power bandwidth of superconducting microstrip antenna are given. Finally, the in∞uence of the thickness of the high Tc superconducting fllm on the resonant frequency is also presented. 2. THEORY

THE CONTRAST SOURCE-EXTENDED BORN MODEL FOR 2D SUBSURFACE SCATTERING PROBLEMS

In this paper, we describe a new full-wave integral equation model to tackle electromagnetic scattering problems arising from objects buried in layered media. Such a model is a rewriting of the usually adopted Contrast Source integral equation and is named Contrast Source-Extended Born (CS-EB) owing to this circumstance and to the relationship existing among its linearization and the Extended Born approximation. By means of this alternative formulation, it is possible to modify the relationship among the scatterer permittivity and the fleld it scatters, thus possibly reducing the degree of non-linearity of this latter relationship. Accordingly, in these cases, the adoption of the CS-EB model may be convenient with respect to traditional ones in both forward and inverse scattering problems.

Compact Broadside Coupled Directional Coupler Based on Coplanar CRLH Waveguides

A compact broadside coupled (BSC) backward directional coupler based on composite right/left-handed (CRLH) coplanar waveguide (CPW) is proposed. The design is symmetric on both sides of the substrate and comprises of series gap capacitor, broadside-coupled capacitor, and shunt meandering short-circuited stub inductor. Compared to existing directional couplers, the proposed coupler has much smaller size, broader bandwidth, phase balance and easy fabrication. An equivalent circuit model including series inductance, capacitance, shunt inductance and capacitance tank has also been established. Good agreement between the full-wave simulation and equivalent circuit model verifies the effectiveness of the proposed circuit model. Measured bandwidth from 9.9 ∼ 14.7 GHz centered at 12 GHz (40%) is observed with the device size of 1.8 × 1.3 cm2.

Investigation of the poloidal spectral resolution of O-mode reflectometry with two-dimensional full-wave modeling

Both the plasma poloidal curvature and the curvature of the probing wave-front play an important role for the spectral resolution of microwave reflectometry. The propagation of electromagnetic waves in a cylindrical plasma with a refractive index monotonically decreasing towards its center leads to elongation of the wave-front (i.e. an increase of the radius of curvature near the axis of radiation). Such a phase-front alteration can result in a major modification of the reflectometry response regarding on high k θ fluctuations. At the same time, the curvature of the cutoff surface in cylindrical plasma is always less than the curvature of the cutoff density for an O-mode wave. For specific geometry of the TEXTOR tokamak we perform numerical two-dimensional full-wave reflectometry synthesizing. The response from poloidaly rotating coherent density perturbation was analyzed on the variety of the plasma cutoff curvature and density scale length, which affects the incident wave-front curvature. The simulations are shown that the increase of the incident wave front curvature extends the spectral resolution of conventional reflectometer with gain antennas. On the other hand, the effect from the cutoff curvature is found to be much weaker as compare to the wave-front effect.

Flip-Chip Interconnect for Coplanar Strip Lines

A flip-chip interconnect configuration with coplanar strip (CPS) lines on printed circuit boards (PCBs) is reported for millimeter-wave applications. For CPS lines, the signal and ground electrodes both lie on the top surface of a chip or substrate. The flip-chip configuration was designed and implemented using a test chip on a dielectric board. Geometrical parameter analysis was carried out using full-wave simulation and equivalent circuit model for wideband performance. The chip was connected to the board using solder bumps. For a typical flip-chip assembly, the measured insertion loss is less than 3dB for frequencies of up to 35GHz and the return loss is higher than 15dB for frequencies of up to 29GHz using CPS flip-chip configuration.

A Unified Finite-Element Solution From Zero Frequency to Microwave Frequencies for Full-Wave Modeling of Large-Scale Three-Dimensional On-Chip Interconnect Structures

It has been observed that a full-wave finite-element-based solution breaks down at low frequencies. This hinders its application to on-chip problems in which broadband modeling from direct current to microwave frequencies is required. Although a static formulation and a full-wave formulation can be stitched together to solve this problem, it is cumbersome to implement both static and full-wave solvers and make transitions between these two when necessary. In this work, a unified finite-element solution from zero frequency to microwave frequencies is developed for full-wave modeling of large-scale three-dimensional on-chip interconnect structures. In this solution, a single full-wave formulation is used. No switching to a static formulation is needed at low frequencies. This is achieved by first identifying the reason why a full-wave eigenvalue-based solution breaks down at low frequencies, and then developing an approach to eliminate the reason. The low frequency breakdown problem was found to be attributed to the discrepant frequency dependence of the real part and the imaginary part of the eigenvalues, which leads to an ill-conditioned eigenvalue system at low frequencies. The discrepant frequency dependence of the real part and the imaginary part is further attributed to the different scaling of the transverse and longitudinal fields with respect to frequency in a transmission-line type structure. By extracting transverse and longitudinal fields separately in the framework of a full-wave formulation, we avoid the numerical difficulty of solving an ill-conditioned eigen-system at low frequencies. The validity of the proposed approach is demonstrated by numerical and experimental results.

A Fast Frequency-Domain Eigenvalue-Based Approach to Full-Wave Modeling of Large-Scale Three-Dimensional On-Chip Interconnect Structures

As on-chip circuits have scaled into the deep submicron regime, electromagnetics-based analysis has increasingly become essential for high-performance integrated circuit (IC) design. Not only fast, but also high-capacity electromagnetic solutions are demanded to overcome the large problem size facing on-chip design community. In this paper, we present a novel, high-capacity, and fast approach to the full-wave modeling of 3-D on-chip interconnect structures. In this approach, the interconnect structure is decomposed into a number of seeds. In each seed, the original wave propagation problem is represented as a generalized eigenvalue problem. The resulting eigenvalue representation can comprehend both conductor and dielectric losses, arbitrary dielectric and conductor configuration in the transverse cross section, and arbitrary material. A new mode-matching technique applicable to on-chip interconnects is developed to solve large-scale 3-D problems by using 2-D-like CPU time and memory. A junction matrix acceleration technique is proposed to speed up the mode matching process. A fast frequency sweep technique is employed to obtain the response over the entire frequency band by solving at one or a few frequency points only. An extraction technique is developed to obtain S-parameters from the solution of the eigenvalue system. The entire procedure is numerically rigorous without making any theoretical approximation. Experimental and numerical results demonstrate its accuracy and efficiency.

Full-wave electromagnetic modelling of fabrics and composites

In this paper different types of fabrics and composites with conducting yarns are considered. The topology of the fabrics or composites is described using the type of format used in software tools originally developed to model their mechanical properties. The topology is simplified using a special conversion technique in order to allow fast electromagnetic analysis. Different possible approximations of conducting yarns used in the electromagnetic analysis are discussed. The analysis itself consists of the solution of the integral equations for the electric currents flowing on the conducting yarns, using the method of moments (MoM). For plane wave excitation the shielding effectiveness is calculated. The agreement between theory and experiments confirms the validity of the approach.

Path Loss From a Transmitter Inside an Aircraft Cabin to an Exterior Fuselage-Mounted Antenna

The increasing use of mobile electronic devices by passengers and equipment on large aircraft may increase the likelihood of with the aircraft's electronic systems. Thus, the interference path loss from a transmitting device inside the cabin of such aircraft to the antenna terminals of a victim system of the aircraft is of interest. Full-wave modeling and other deterministic techniques are impractical or undesirable for this purpose due to the potentially large electrical dimensions of the aircraft, as well as the variability of the cabin configuration. An alternative hybrid analysis technique applicable to frequencies above very high frequency is proposed in which one first estimates the power that escapes the cabin using a simple method based on microwave cavity theory. Next, the radiating windows are modeled as magnetic currents on a cylinder modeling the fuselage, and the resulting electric field at the location of the victim antenna is determined using the uniform geometrical theory of diffraction. Finally, the power delivered to the victim antenna is estimated as the coherent sum of fields incident from the windows. This technique yields results consistent with measured results and yields additional physical insight that would be difficult to obtain through measurements or full-wave methods.

Electromagnetic analysis of cylindrical cloaks of an arbitrary cross section

We extend the design of radially symmetric invisibility cloaks through transformation optics as proposed by Pendry et al. [Science 312, 1780 (2006)] to coated cylinders of an arbitrary cross section. The validity of our Fourier-based approach is confirmed by both analytical and numerical results for a cloak displaying a non-convex cross section of varying thickness. In the former case, we evaluate the Green's function of a line source in the transformed coordinates. In the latter case, we implement a full-wave finite-element model for a cylindrical antenna radiating a p-polarized electric field in the presence of a F-shaped lossy object surrounded by the cloak.

Compact 90$^{\circ}$ Twist Formed by a Double-Corner-Cut Square Waveguide Section

Simple and compact rectangular waveguide 90deg twist is proposed. The twist transformer region is a square waveguide section with two square corner cuts. The twist full-wave model is based on the mode-matching and generalized <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> -matrix techniques. It is found that the optimized twists can provide the bandwidths of no less than 30% at the 30-dB return-loss level or 16% at the 40-dB level over a lower, middle, or higher part of the rectangular waveguide operating band. The twist lengths are five times less than the rectangular waveguide wavelength at the central frequency of the chosen operating band. Role of evanescent modes in the interaction of two small-distanced twist transitions is discussed. The design results are confirmed by the results of real device measurements.

A Transmission-Line Model for Full-Wave Analysis of Mixed-Mode Propagation

The paper presents a generalized transmission line model able to describe the high-frequency mixed-mode propagation along electrical interconnects. The model is derived from a full-wave formulation and extends the validity of the standard transmission line (TL) model to frequency ranges where the propagation is no longer of transmission electron microscopy (TEM)-type. This generalized TL model describes the high-frequency differential and common mode propagation and the mode conversion. Within its validity limits, the proposed model provides solutions in good agreement with those obtained through full-wave models. Case studies are carried out to evaluate the high-frequency mode conversion in asymmetric interconnects.

Using TEM Cell Measurements to Estimate the Maximum Radiation From PCBs With Cables Due to Magnetic Field Coupling

Common-mode currents can be induced on cables attached to printed circuit boards (PCBs) due to electric and magnetic field coupling. This paper describes a technique for using transverse electromagnetic (TEM) cell measurements to obtain an effective common-mode voltage (or magnetic moment) that quantifies the ability of traces and integrated circuits on PCBs to drive common-mode currents onto cables due to magnetic field coupling. This equivalent common-mode voltage can be used to reduce the complexity of full-wave models that calculate the radiated emissions from a system containing the board. It can also be used without full-wave modeling to provide a relative indication of the likelihood that a particular board design will have unintentional radiated emissions problems due to magnetic field coupling.

Efficient Full-Wave Characterization of Discrete High-Density Multiterminal Decoupling Capacitors for High-Speed Digital Systems

This paper presents an efficient surface-based finite-element method for the full-wave characterization of high-density and multiterminal decoupling capacitors (2, 8, 14, and any arbitrary number of terminals). In contrast to traditional finite-element methods that involve 3-D volumetric unknowns, this method reduces the unknowns one needs to solve to those on 2-D surfaces only. In addition, the reduction from the 3-D volume-based matrix to a 2-D surface-based one is achieved efficiently by exploiting the geometrical specialty of the decap structure. The entire numerical procedure is numerically rigorous without making any approximation. Its efficiency and accuracy have been demonstrated by both measurements and numerical experiments. Based on its fast and accurate solution, different design configurations of capacitors were studied to identify the optimal configuration that can maximize the performance of a decoupling capacitor. Furthermore, the full-wave model obtained from the proposed method was employed to assess the accuracy of conventional series lumped RLC capacitor models. In addition, the full-wave model was incorporated into a high-performance microprocessor's power delivery network to investigate system performance.

Full-wave modeling and optimization of Bøifot junction ortho-mode transducers

The full-wave design of broadband ortho-mode transducers based on the Bøifot junction has two main aspects: an efficient analysis method and a design process divided into tasks with relatively low computational effort. In the analysis part, a rigorous mode-matching technique has been developed to obtain the generalized admittance matrix of the Bøifot junction. The other elements of the device are also analyzed by mode-matching. With respect to the design, the proposed procedure starts with the optimization of the individual building blocks of the device. Their interaction is also taken into account in a systematic process. The analysis and design methods have been validated with other numerical methods and an experimental prototype. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.

Reconfigurable Fresnel-Zone-Plate-Shutter Antenna with Beam-Steering Capability

A reconfigurable Fresnel-zone-plate (FZP) antenna, capable of dynamic beam scanning, is introduced. The FZP consists of a series of thin metal shutters, which discretize the antenna aperture into a number of reconfigurable transparent and opaque zones. The shutters are individually controlled to focus the beam at a desired location. Beam scanning of at least +40deg from broadside with a small degradation in gain is possible in one plane using this design. This paper examines the effects of zone discretization on the ideal radiation patterns using full-wave numerical modeling. These effects are then verified by the measurements of a prototype antenna designed at 23 GHz.

Simulation and evaluation of phase noise for optical amplification using semiconductor optical amplifiers in DPSK applications

A thorough simulation and evaluation of phase noise for optical amplification using semiconductor optical amplifier (SOA) is very important for predicting its performance in differential phase-shift keyed (DPSK) applications. In this paper, standard deviation and probability distribution of differential phase noise at the SOA output are obtained from the statistics of simulated differential phase noise. By using a full-wave model of SOA, the noise performance in the entire operation range can be investigated. It is shown that nonlinear phase noise substantially contributes to the total phase noise in case of a noisy signal amplified by a saturated SOA and the nonlinear contribution is larger with shorter SOA carrier lifetime. It is also shown that Gaussian distribution can be useful as a good approximation of the total differential phase noise statistics in the whole operation range. Power penalty due to differential phase noise is evaluated using a semi-analytical probability density function (PDF) of receiver noise. Obvious increase of power penalty at high signal input powers can be found for low input OSNR, which is due to both the large nonlinear differential phase noise and the dependence of BER vs. receiving power curvature on differential phase noise standard deviation.

Modal and numerical analysis of the transverse magnetic-passing property of laminated cladding

An accurate investigation of an integrated optical polariser has been presented. The transverse magnetic (TM)-passing property for an asymmetrical slab with anisotropic cladding that behaves as negative or positive uniaxial crystal has been evaluated. After a modal analysis, the polarisation of the electromagnetic (EM) field is evaluated by means of transmission line matrix-integral equation (TLMIE) method which performs a 3D full-wave modelling of the structure (i) including dielectric losses and (ii) for different slant angle of the laminated cladding. The TLMIE method permits to maximise the TM-passing property for a single-mode channel with anisotropic cladding.