Scattering from narrow rectangular filled grooves

The solution of the integral equation for a small width rectangular groove is considered. It is shown that by retaining the dominant mode supported by the rectangular groove, the resulting quasi-static integral equations are comparable to those associated with the perfectly conducting narrow strip. They are, therefore, amenable to analytic solution yielding the exact field distribution or equivalent currents across the groove's aperture. The derived currents exhibit the same edge behavior as that associated with the currents of a perfectly conducting half-plane. The corresponding current behavior based on a (numerical) impedance simulation of the groove is quite different. However the resulting echowidths are comparable. Both transverse electric (TE) and transverse magnetic (TM) polarizations are treated     

Full-wave analysis of coupled perfectly conducting wires in amultilayered medium

A full-wave analysis of coupled perfectly conducting cylindrical wires in a multilayered dielectric medium is presented. The analysis is based on a Fourier series expansion of the unknown surface currents on each wire and on an integral equation for the longitudinal field on the wires. The calculations are not restricted to the propagation constants of the different modes, but explicit results are presented for the impedances associated with each wire and each eigenmode as a function of frequency. Propagation constants, longitudinal currents on the wires, and impedances lead to a complete equivalent circuit for the structures being considered     

Radio wave propagation along mixed paths through a four-layeredmodel of rain forest: an analytic approach

This paper presents a novel full-wave analysis of the radio waves that are excited from a dipole antenna located in the trunk layer and propagate inside a four-layered forest medium. The dyadic Green's functions for the four-layered geometry are applied first to derive the integral expression of the electric fields. The closed form of the electric fields is then obtained by using the quasi-static approximation, saddle-point technique, and branch-cut integrations in the complex plane and, hence, expressed in terms of direct waves, multiple reflected waves, and lateral waves. Two kinds of images, i.e., the quasi-dynamic and complex images, are considered in the integration in the complex plane. Among those waves excited by a dipole antenna in the four-layered medium, it is shown theoretically and numerically that the lateral wave along the upper-side air-canopy interface plays a role of dominant modes. The propagation mechanism of other lateral waves due to the air-canopy, canopy-trunk, and trunk-ground interfaces is also discussed and analyzed so as to gain an insight into the wave characteristics. Transmission losses of the lateral waves are calculated numerically     

A generalized MoM-SPICE iterative technique for field coupling to multiconductor transmission lines in presence of complex structures

A generalized method of moments (MoM)-SPICE iterative technique for field coupling analysis of multiconductor transmission lines (MTLs) in the vicinity of complex structures is presented. Telegrapher's coupling equations are modified with additional distributed voltage and current sources for more accurate analysis of the total current induced onto transmission line bundles in the presence of complex structures. These additional voltage and current sources are introduced to enforce the electric field boundary condition and continuity equation on MTLs beyond the quasi-static regime. The surrounding structure is modeled via the MoM and a SPICE-like simulator is used to simulate equivalent circuit model of the MTLs extracted via the partial element equivalent circuit method. The proposed technique is based on perturbation theory with the quasi-static current distributions on the transmission lines still assumed to be dominant. Validation examples for single and MTLs are given in the presence of complex structures.     

Circular-pad via model based on cavity field analysis

An equivalent circuit model of a circular-pad grounding via is proposed based on cavity modal analysis. The modes of the via are derived analytically. Each mode is represented by an equivalent circuit taking into account ohmic losses, as well as losses due to spatial and surface wave radiation. It is shown that the degradation of grounding via characteristics at high frequencies is caused by the multimode effects and radiation. The accuracy of the proposed semi-analytical via model is comparable with that of full-wave analysis up to 75 GHz. It is fast and is easily incorporated in high-frequency circuit simulators.     

A moment method analysis for coplanar waveguide discontinuityinductances

Based on the concept of duality, the quasi-static equivalent inductance of a coplanar waveguide discontinuity is determined from the equivalent capacitance of its complementary structure, i.e., a coplanar strip discontinuity in free space. For the capacitance calculation, an integral equation governing the excess charge distribution near the discontinuity is solved by the method of moments together with Galerkin's approach. Numerical results for the short end and symmetric step change are presented. The good agreement with the data available from the full-wave analyses reveals that this approach is simple, accurate, and very suitable in the CAD for MMICs     

A rigorous dispersive characterization of microstrip cross and Tjunctions

A full-wave spectral-domain analysis is applied to the characterization of multiport microstrip discontinuities. This method uses the moment method to find the currents in the microstrip circuits and subsequently the scattering parameters of the junctions. In this approach, all the physical effects are considered, including radiation and surface waves. The numerical results for a T- and a cross-junction are presented and agree well with the quasi-static values at low frequencies. The S-parameters of a T-junction are further compared with the measured results, with excellent agreement. The utilization of a shaped T-junction as a broadband equal-power divider is also discussed     

Frequency and bias-dependent modeling of correlated base and collector current RF noise in SiGe HBTs using quasi-static equivalent circuit

This paper presents modeling of correlated RF noise in the intrinsic base and collector currents of SiGe heterojunction bipolar transistors using quasi-static equivalent circuits. The noises are first extracted from measured noise parameters using standard noise circuit analysis. Using the extraction results, model equations are proposed to describe both the frequency and bias dependence of the correlated noise sources using a single set of model parameters. The model is demonstrated using noise data from both measurement and microscopic noise simulation. The model is shown to work at frequencies up to at least half of the peak f/sub T/ and at biasing currents below high injection f/sub T/ rolloff.     

Time-domain skin-effect model for transient analysis of lossy transmission lines

A skin-effect equivalent circuit consisting of resistors and inductors is derived from the skin-effect differential equations for simulating the loss of a transmission line. A numerical method is used to analyze the transmission-line differential equations and the skin-effect equivalent circuit, yielding a model which relates the new values of node voltages and line currents to their values at the previous time step. Based on this model, a very simple program was written on a desk-top computer for the transient analysis of lossy trammission lines. Two examples are presented. The first example is an analysis of the step and pulse responses of a 600-m RG-8/U coaxial cable. The computed results show excellent agreement with measured data. The second example studies the current at the end of a 12-in 7-Ω strip line under different loading conditions. Very good agreement has been obtained between the calculated steady-state solution and that obtained by the frequency-domain method.     

Speeding Up PEEC Partial Inductance Computations Using a QR-Based Algorithm

The partial element equivalent circuit (PEEC) approach has been used in different forms for the computation of equivalent circuit elements for quasi-static and full-wave electromagnetic models. In this paper, we focus on the topic of large scale inductance computations. For many problems as part of PEEC modeling, partial inductances need to be computed to model interactions between a large numbers of objects. These computations can be very time and memory consuming. To date, several techniques have been devised to reduce the memory and time required to compute the partial inductance entities, as well as the time required to use them in a circuit analysis compute step. Some of the existing methods use hierarchical compression while some others are based on issues like properties of the inverse of the partial inductance matrix. However, because of inherent limitations, most of these methods are less suitable for PEEC applications. In this paper, we present an approach which is based on the compression of the partial inductance matrix utilizing the QR decomposition of the far coefficients submatrices. The QR-decomposed form is represented as a compressed SPICE-compatible circuit. This yields an efficient and mathematically consistent approach for reducing the storage and time requirements     

Scalarization of dyadic spectral Green's functions and networkformalism for three-dimensional full-wave analysis of planar lines andantennas

A novel and systematic method is presented for the complete determination of dyadic spectral Green's functions directly from Maxwell's equations. With the use of generalized scalarizations developed in this paper, four general and concise expressions for the spectral Green's functions for one-dimensionally inhomogeneous multilayer structures, excited by three-dimensional electric and magnetic current sources, are given in terms of modal amplitudes together with appropriate explicit singular terms at the source region. It is shown that Maxwell's equations in spectral-domain can be reduced, by using dyadic spectral eigenfunctions, to two sets of z-dependent inhomogeneous transmission-line equations for the modal amplitudes. One set of the transmission-line equations are due to the transverse current sources and the other set due to the vertical current sources. Utilizing these equations, network schematizations of the excitation, transmission and reflection processes of three-dimensional electromagnetic waves in one-dimensionally inhomogeneous multilayer structures are achieved in a full-wave manner. The determination of the spectral Green's functions becomes so simple that it is accomplished by the investigation of voltages and currents on the derived equivalent circuits. Examples of singleand multilayer structures are used to validate the general expressions and the equivalent circuits     

More investigations of leakage and nonleakage conductor-backedcoplanar waveguide

Through rigorous full-wave analysis, the effective dielectric constant, normalized attenuation constant, characteristic impedance, and radiation pattern of two types of conductor-backed coplanar waveguides are obtained. The analytic results show that the leakage effect is not only controlled by the thickness and dielectric constant of the substrate but also by the slot width. The leakage power transforms to a radiation space wave and a surface wave, the transverse electric field diagrams in the substrate and the far-zone radiation pattern verify the leakage phenomenon. The first structure has the maximum radiation intensity in the endfire direction, while the second one which has more leaky waves radiates into the air, is better served as a radiating device. For both structures under the nonleakage condition, the characteristic impedance is sensitive to the change of the strip width but not the slot width. Using these properties, the nonleaky and leaky circuits can exist on the same circuit board by choosing appropriate circuit dimensions     

Computer-aided modeling of quasi-resonant converters in thepresence of parasitic losses by using the MISSCO concept

The DC and small-signal models of quasi-resonant converters, operating in both half-wave and full-wave modes, are developed in a suitable form for computer simulation. The starting step is the extraction of a minimum separable switching configuration (MISSCO) containing all power switches but a minimum number of other components (resonant ones). By using the step-response analysis and average technique, and by perturbing and separating the DC and AC components in the resulting equations, the equivalent models of MISSCO are derived. They are introduced in the converter structure to replace the circuit initially extracted. Models of different quasi-resonant converters can be obtained by this general approach. The analysis takes into account the conduction losses of the switching devices and reactive elements, which improves considerably the model accuracy. Model-based computer simulation agrees with the experimental results     

Generalized Partial-Element Equivalent-Circuit Analysis for Planar Circuits With Slotted Ground

A generalized partial-element equivalent-circuit (PEEC) method is proposed for modeling a planar circuit with a thin narrow slot on the ground. The approach is based on the coupled mixed potential integral equations for a problem with mixed electric and magnetic currents. The coupled integral equations are converted into a lumped-element circuit network using Kirchhoff's voltage law and Kirchhoff's current law of the circuit theory. The full-wave Green's functions for a grounded dielectric substrate problem are used. The interactions between electric current on a microstrip line and magnetic current on a slot are taken into account by introducing two kinds of controlled sources. This generalized PEEC model will be very useful in signal-integrity analysis for multilayered circuits. To validate the generalized model, three numerical examples consisting of microstrip lines and slots on the ground are presented. The results obtained by the proposed generalized PEEC model are compared with those obtained by commercial electromagnetic simulation software and published experimental results. Good agreement is obtained.      

On the backscattering from two arbitrarily located identical parallel wires

A study of the backscattering from two identical perfectly conducting, thin wires illuminated by a plane wave at an arbitrary angle of incidence is presented. The theory is based on an integral equation method. By decomposing the induced currents into symmetric and antisymmetric modes, the simultaneous integral equations for the induced currents are converted into independent integral equations similar to the one for a single wire for which the solution has already been carried out. The induced currents on and the backscattering cross sections of the wires are determined. Numerical examples include nonstaggered, staggered, and collinear cases of both half-wave and full-wave wires. Comparisons are made between the calculated and measured values of the echo area. The experimental results are in good agreement with theory.     

Complex media microstrip ridge structures: formulation and basiccharacteristics of ferrite structures

Microstrip transmission lines residing on bianisotropic material ridges embedded in a multilayered environment are studied using a coupled set of integral equations (IE's). The full-wave IE formulation accounts for general linear media in the ridge region using equivalent polarization currents residing in a multilayered bianisotropic background. Numerical results showing basic propagation characteristics are presented for a variety of single and coupled ferrite ridge structures. It is shown that the use of finite width ferrite ridges as either substrates or superstrates can produce nonreciprocity while confining the ferrite material to a small area in the vicinity of the transmission line     

Broadside coupled strip inset dielectric guide and its directionalcoupler application

A theoretical and numerical method is presented for the analysis of broadside-coupled strip inset dielectric guide. The method of analysis is based on an integral equation formulation and Galerkin's procedure. Besides propagation constants for two fundamental and higher order modes, the characteristic impedances for the two fundamental modes are calculated using the total propagating power and the longitudinal strip currents. The propagation characteristics of the two fundamental modes are then used to compute 4-port circuit parameters that are essential for accurate analysis and design of coupled line circuits. The effects of various structural parameters on the S-parameters are investigated and it is found that this broadside coupled strip IDG structure is useful for the realization of the directional couplers. Examples of strong and weak directional couplers are given. Furthermore, the propagation constants and S-parameters of coaxially excited coupled strips are measured, and are in good agreement with the theoretical analysis     

A small-signal analysis of the electron cyclotron backward-wave oscillator

In an earlier report on the construction and performance of the electron cyclotron backward-wave oscillator, it was shown, through physical arguments, that in an unloaded waveguide supporting the dominant mode, an electron having transverse rotation at its cyclotron frequency will interact with RF fields of approximately equal frequency. This transverse motion will deliver energy to the RF E fields and interact with the RF H fields, thus producing longitudinal bunching. A small-signal analysis is presented in this paper. With the use of the normal mode expansion analysis, the circuit equation is obtained by considering the normal mode in approximate synchronism with the beam. The RF current is computed by considering electron motion under the dc and circuit fields, but neglecting RF space-charge fields. Combining these equations leads to a sixth-order equation of propagation constants. Two waves are far from synchronism and are therefore neglected; the remaining four are two waves which originate from the "fast cyclotron waves" and two waves which originate from the forward and reflected circuit waves. The "fast cyclotron wave" so obtained has a different meaning from the usual definition and is discussed in detail. Theoretical start-oscillation current is found to depend critically on the reflection coefficient at the electron gun end. Proper adjustment of this parameter leads to excellent agreement between the theoretical and experimental start-oscillation currents.