A parallel FFT accelerated transient field-circuit simulator

A novel fast electromagnetic field-circuit simulator that permits the full-wave modeling of transients in nonlinear microwave circuits is proposed. This time-domain simulator is composed of two components: 1) a full-wave solver that models interactions of electromagnetic fields with conducting surfaces and finite dielectric volumes by solving time-domain surface and volume electric field integral equations, respectively, and 2) a circuit solver that models field interactions with lumped circuits, which are potentially active and nonlinear, by solving Kirchoff's equations through modified nodal analysis. These field and circuit analysis components are consistently interfaced and the resulting coupled set of nonlinear equations is evolved in time by a multidimensional Newton-Raphson scheme. The solution procedure is accelerated by allocating field- and circuit-related computations across the processors of a distributed-memory cluster, which communicate using the message-passing interface standard. Furthermore, the electromagnetic field solver, whose demand for computational resources far outpaces that of the circuit solver, is accelerated by a fast Fourier transform (FFT)-based algorithm, viz. the time-domain adaptive integral method. The resulting parallel FFT accelerated transient field-circuit simulator is applied to the analysis of various active and nonlinear microwave circuits, including power-combining arrays.     

Vectorial FDTD Technique for the Analysis of Optical Second-Harmonic Generation

A vectorial time-domain simulator of integrated optical structures containing second-order nonlinearities has been formulated and tested. The technique is based on the direct time-domain representation of the coupled nonlinear Maxwell's equations of the propagating fields. The proposed algorithm accounts for the full optical coefficient tensor, input depletion, and device-wave interactions, where the inaccuracies associated with the scalar and paraxial approximations are avoided. Error analysis associated with the proposed scheme is also given. The proposed model should find application in a wide range of device structures and also in the analysis of short-pulse propagation in second-order nonlinear devices.      

The Response of a Transmission Line Illuminated by Lightning-Induced Electromagnetic Fields

This paper presents the theory and procedures used to estimate the voltages and currents induced on long transmission lines by cloud-to-cloud lightning. A model for cloud-to-cloud lightning phenomena is presented, and the theory necessary to calculate the electromagnetic fields created by the lightning stroke is derived. The time-domain transmission-line equations in the presence of external electromagnetic fields are presented. A time-domain formulation is more convenient if, in the future, nonlinear effects are to be included. The results of sample calculations, using finite-difference techniques for the solution of the transmission-line equations, are presented.     

A TDIE-based asynchronous electromagnetic-circuit simulator

A time-domain integral-equation based hybrid electromagnetic (EM)-circuit (CKT) simulator that allows the signals (fields/voltages/currents) in each EM or CKT subsystem to be sampled and tracked using a local, subsystem-specific, time-step size is proposed. The proposed asynchronous time-stepping/coupling approach generalizes the standard synchronous time-stepping/coupling approach, where all the signals in the entire system are tracked using one system-global time-step size. The nonlinear analysis of a bipolar junction transistor driven chip-to-package interconnect demonstrates that the asynchronous simulator exhibits improved accuracy, efficiency, and convergence.     

A time-domain algorithm for the analysis of second-harmonicgeneration in nonlinear optical structures

A time-domain simulator of integrated optical structures containing second-order nonlinearities is presented. The simulation algorithm is based on nonlinear wave equations representing the propagating fields and is solved using the finite-difference time-domain method. The simulation results for a continuous-wave operation are compared with beam propagation method simulations showing excellent agreement for the particular examples considered. Because the proposed algorithm does not suffer from the inaccuracies associated with the paraxial approximation, it should find application in a wide range of device structures and in the analysis of short-pulse propagation in second-order nonlinear devices     

A new global time-domain electromagnetic simulator of microwavecircuits including lumped elements based on finite-element method

This paper proposes an extension of the finite-element time-domain method for the global electromagnetic analysis of complex inhomogeneous microwave distributed circuits, containing linear or nonlinear lumped elements. This technique combines Maxwell's equations and circuit equations, directly using SPICE software for the lumped part. Its validation is performed through the study of a strongly coupled two-element active antenna     

An efficient electromagnetic-physics-based numerical technique for modeling and optimization of high-frequency multifinger transistors

We present a fast wavelet-based time-domain modeling technique to study the effect of electromagnetic (EM)-wave propagation on the performance of high-power and high-frequency multifinger transistors. The proposed approach solves the active device model that combines the transport physics, and Maxwell's equations on nonuniform self-adaptive grids, obtained by applying wavelet transforms followed by hard thresholding. This allows forming fine and coarse grids in the locations where variable solutions change rapidly and slowly, respectively. A CPU time reduction of 75% is achieved compared to a uniform-grid case, while maintaining the same degree of accuracy. After validation, the potential of the developed technique is demonstrated by EM-physical modeling of multifinger transistors. Different numerical examples are presented, showing that accurate modeling of high-frequency devices should incorporate the effect of EM-wave propagation and electron-wave interactions within and around the device. Moreover, high-frequency advantages of multifinger transistors over single-finger transistors are underlined through numerical examples. To our knowledge, this is the first time in the literature a fully numerical EM-physics-based simulator for accurate modeling of high-frequency multifinger transistors is introduced and implemented.     

Nonlinear analysis of microwave superconductor devices usingfull-wave electromagnetic model

This paper presents a full electromagnetic wave analysis for modeling the nonlinearity in high temperature superconductor (HTS) microwave and millimeter-wave devices. The HTS nonlinear model is based on the Ginzburg-Landau theory. The electromagnetic fields associated with the currents on the superconducting structure are obtained using a three-dimensional full wave solution of Maxwell's equations. A three-dimensional finite-difference time-domain algorithm simultaneously solves the resulting equations. The entire solution is performed in time domain, which is a must for this type of nonlinearity analysis. The macroscopic parameters of the HTS, the super fluid penetration depth and the normal fluid conductivity, are calculated as functions of the applied magnetic field. The nonlinear propagation characteristics for HTS transmission line, including the effective dielectric constant and the attenuation constant, are calculated, As the power on the transmission line increases, the phase velocity decreases and the line losses increase. The nonlinearity effects on the current distributions inside the HTS, the electromagnetic field distributions, and the frequency spectrum are also analyzed     

Performance of MODFET and MESFET, a comparative study includingequivalent circuits using combined electromagnetic and solid-statesimulator

A combined electromagnetic and solid-state (CESS) simulation model for the analysis of submicrometer semiconductor devices including the electromagnetic-wave propagation effects is presented. The performance comparison of two important high-frequency devices-modulation doped field-effect transistor (MODFET) and metal-semiconductor field-effect transistor (MESFET)-are illustrated using this model. The CESS simulator couples a semiconductor model to the three-dimensional (3-D) time-domain solution of Maxwell's equations. The semiconductor model is based on the moments of the Boltzmann's transport equation. The simulation uses the electromagnetic-wave concept to emphasize the better performance of MODFET over MESFET. The electromagnetic-wave propagation effects on the two devices are thoroughly analyzed. The use of the electromagnetic model over the conventional quasi-static model provides the actual device response along the gatewidth at high frequencies. The exchange of energy between the electrons and the electromagnetic wave is observed. The CESS model also facilitates the optimum choice of the device width in terms of the output voltage. This model is capable of predicting the large-signal behaviour of the submicrometer devices as well. The equivalent-circuit parameters are extracted at high frequencies for MODFET and MESFET, using a time-domain approach as well as a quasi-static approach     

Modal analysis for a bounded-wave EMP Simulator - part I: effect of test object

We have analyzed the electromagnetic-mode structure inside a bounded-wave electromagnetic pulse (EMP) simulator. This has been done by the application of the singular value decomposition method to time-domain data generated by self-consistent, three-dimensional finite-difference time-domain simulations. This combination of two powerful techniques yields a wealth of information about the internal mode structure which cannot be otherwise obtained. To our knowledge, this is the first time such a comprehensive study has been done. In the absence of a test object, the transverse electromagnetic (TEM) mode is dominant throughout the simulator length. TM/sub 1/ dominates over other transverse electromagnetic (TM) modes over most of the length. Close to the termination, the TEM mode weakens marginally, while higher order TM modes become stronger. The enhancement of TM/sub 2/, and the weakening of TEM near the termination, have been explained in physical terms. Placement of a perfectly conducting test object in the parallel-plate section increases the strength of higher order TM modes, at the cost of TEM. Hence, the object is subjected to electromagnetic fields that deviate significantly from the desired TEM form. A physical interpretation has been provided for this phenomenon. The enhancement of electromagnetic fields near the top and bottom faces of the object are explained in terms of the Poynting flux distribution.     

Transient analysis of electromagnetic systems with multiple lumped nonlinear loads

A novel method for transient analysis of electromagnetic systems with multiple lumped nonlinear loads is presented. The uniqueness of this approach is that we develop time-domain Green's functions for the multiport linear part of the electromagnetic system by suitably terminating the ports. This ensures a short duration of Green's functions. Hence the amount of frequency-domain data necessary to obtain the time-domain Green's functions is modest. The application of this technique to an arbitrary excitation is just a straightforward convolution. With this technique one can analyze responses of systems with arbitrary nonlinear loads (even with memory) as we have at any time instant Thevenin's equivalent of the linear portion of the electromagnetic system. Examples are presented to illustrate the application of this technique to multiport nonlinearly loaded antennas.     

The time-domain characteristics of a traveling-wave linear antenna with linear and nonlinear parallel loads

The time-domain characteristics of a traveling-wave linear antenna with linear and nonlinear parallel loads are discussed. The fast Fourier transform (FFT) is used to analyze the antenna with a linear parallel load. A numerical time-stepping finite-difference equation method is used to analyze the antenna with a nonlinear parallel load. The nonlinear effect is treated by the Newton-Raphson iteration technique. The effects of various linear and nonlinear parallel loads are examined. Physical insight into the nonlinear parallel loading of the antenna is also given in terms of detected time-domain sinusoidal electromagnetic (EM) waves.     

Channel model for wireless communication around human body

A channel model for a wireless body area network at 400 MHz, 900 MHz and 2.4 GHz is derived. The electromagnetic wave propagation around the body is simulated with a finite-difference time-domain simulator. Creeping waves were identified as the propagation path around the body. Its impact on the delay spread in an indoor environment is discussed.     

An extension of the lumped-network FDTD method to linear two-port lumped circuits

The lumped-network finite-difference time-domain (LN-FDTD) technique is an extension of the conventional finite-difference time-domain (FDTD) method that allows the systematic incorporation of linear one-port lumped networks (LNs) into a single FDTD cell. This paper presents an extension of the LN-FDTD technique, which allows linear two-port (TP)-LNs to be incorporated into the FDTD framework. The method basically consists of describing a TP-LN by means of its admittance matrix in the Laplace domain. By applying the Mobius transformation technique, we then obtain the admittance matrix of the TP-LN in the Z-transform domain. Finally, appropriate digital signal-processing methodologies are used to derive a set of difference equations that models the TP-LN behavior in the discrete-time domain. These equations are solved in combination with the Maxwell-Ampere's equation. To show the validity of the TP-LN-FDTD technique introduced here, we have considered the equivalent circuit of a chip capacitor and a linear circuit model of a generic metal-semiconductor field-effect transistor. These LNs have been placed on a microstrip gap and the scattering parameters of the resulting hybrid circuit have been computed. The results are compared with those obtained by using the electromagnetic simulator Agilent HFSS in combination with the circuital simulator ADS, and with those calculated by ADS alone. For the chip capacitor, experimental measurements have also been carried out. The agreement among all the simulated results is good. Generally speaking, the measured results agree with the simulated ones. The differences observed are mainly due to the influence of the subminiature A connectors and some mismatching at the ports.     

Artificial composite materials consisting of nonlinearly loadedelectrically small antennas: operational-amplifier-based circuits withapplications to smart skins

Several new artificial nonlinear composite materials are introduced in this paper. They consist of electric molecules constructed with nonlinearly loaded electrically small dipole antennas. Their behaviors are studied with an augmented finite-difference time-domain (FDTD) simulator. The loads are based upon the use of multiple diodes and ideal operational amplifiers. The resulting composite materials are shown to have nonlinear electromagnetic properties including the ability to create any desired set of harmonics and subharmonics from an input wave having a single fixed frequency. Curve shaping circuits are introduced, simulated, and used to design materials that produce output signals of specified forms. Because the operating points of these curve shapers are adjustable, they could be modified in real time. The resulting smart materials could be designed in the microwave region to produce any specified response to a recognized input signal     

A path integral time-domain method for electromagnetic scattering

A new full wave time-domain formulation for the electromagnetic field is obtained by means of a path integral. The path integral propagator is derived via a state variable approach starting with Maxwell's differential equations in tensor form. A numerical method for evaluating the path integral is presented and numerical dispersion and stability conditions are derived and numerical error is discussed. An absorbing boundary condition is demonstrated for the one-dimensional (1-D) case. It is shown that this time domain method is characterized by the unconditional stability of the path integral equations and by its ability to propagate an electromagnetic wave at the Nyquist limit, two numerical points per wavelength. As a consequence the calculated fields are not subject to numerical dispersion. Other advantages in comparison to presently popular time-domain techniques are that it avoids time interval interleaving and it does not require the methods of linear algebra such as basis function selection or matrix methods     

Electromagnetic wave effects on microwave transistors using afull-wave time-domain model

A detailed full-wave time-domain simulation model for the analysis of electromagnetic effects on the behavior of the submicrometer-gate field-effect transistor (FET's) is presented. The full wave simulation model couples a three-dimensional (3-D) time-domain solution of Maxwell's equations to the active device model. The active device model is based on the moments of the Boltzmann's transport equation obtained by integration over the momentum space. The coupling between the two models is established by using fields obtained from the solution of Maxwell's equations in the active device model to calculate the current densities inside the device. These current densities are used to update the electric and magnetic fields. Numerical results are generated using the coupled model to investigate the effects of electron-wave interaction on the behavior of microwave FET's. The results show that the voltage gain increases along the device width. While the amplitude of the input-voltage wave decays along the device width, due to the electromagnetic energy loss to the conducting electrons, the amplitude of the output-voltage wave increases as more and more energy is transferred from the electrons to the propagating wave along the device width. The simulation confirms that there is an optimum device width for highest voltage gain for a given device structure. Fourier analysis is performed on the device output characteristics to obtain the gain-frequency and phase-frequency dependencies. The analysis shows a nonlinear energy build-up and wave dispersion at higher frequencies     

A planar triangular monopole antenna for UWB communication

A planar triangular monopole antenna (PTMA) is presented for high-frequency structure simulator ultra-wideband (UWB) communication. The high-frequency structure simulator three-dimensional electromagnetic solver is employed for design simulation. A printed PTMA has been realized by using the FR-4 printed circuit board substrate. The measured voltage standing wave ratio is less than 3 from 4 to 10 GHz. In the UWB communication frequency range, the measured phase distribution of the input impedance is quite linear and the H-plane patterns are almost omni-directional. The Kirchhoff's surface integral representation was adopted in the developed finite-difference time-domain code to compute the far field distributions from the near filed ones in time-domain. This is to investigate the radiated power density spectrum (PDS) shaping to comply with FCC emission limit mask. The effect of various source pulses (first-order Rayleigh pulses with /spl sigma/ of 20, 30, and 50 ps) on the radiated PDS shaping is also studied.     

A two-dimensional transmission line matrix microwave fieldsimulator using new concepts and procedures

A two-dimensional field simulator for microwave circuit modeling is described. It incorporates a number of recently developed concepts and advanced transmission line matrix (TLM) procedures. In particular, a discrete Green's function concept based on P.B. John's and K. Akhlarzad's time-domain diakoptics is realized, providing a high level of processing power through modularization of large structures at the field level, simulation of wideband matched loads or absorbing walls, modeling of frequency-dispersive boundaries in the time domain, and large-scale numerical preprocessing of passive structures. Nonlinear field modeling concepts are also implemented in the TLM field simulator. It can analyze two-dimensional circuits of arbitrary geometry containing both linear and nonlinear media. The circuit topology is input graphically. Both time-domain and frequency-domain responses can be computed and displayed. The capabilities and limitations of the simulator are discussed, and several microstrip and waveguide components are modeled to demonstrate its important features     

A New Carrier-Free Nonlinear FDTD Algorithm Suitable for the Moving Computational Window Technique

The model equations of the vectorial time-domain simulator of second-harmonic generation in integrated optical structures have been reformulated by extracting the signal carrier. The moving computational window technique is then used to ease the computational burden in the finite-difference time-domain solution. Results show that the technique provides considerable savings in computation power especially for long propagation distances.