Although Maxwell's equations have been known for over 100 years, it was not until the last decade that they have seen regular use in applied high frequency design. The availability of sufficient computer processing capability is only part of the reason Maxwell's equations now enjoy regular application. Other developments requiring considerable effort are needed as well. These include increased attention to robustness, software testing, ease of use, portability, integration with other tools, and support. These developments are detailed in this paper.

In addition to their intended role in design and optimization of microwave circuits, subsystems and systems; network and field simulators serve a key role in design-oriented education and continuing education. This paper brings out how these simulators are currently used in university education, and how this educational role of simulators will be further emphasized in currently changing scenario for higher education. A generic model is proposed for learning tools that combine computer-based tutorials with microwave circuit and field simulators.

This paper presents the characterization and validation of a time-domain physical model for illuminated high-frequency active devices and shows the possibility of use of the electromagnetic analysis of FDTD not only for electromagnetic interaction and scattering but also for the device simulation as a good candidate for a microwave simulator. The model is based on Boltzmann's Transport Equation, which accurately accounts for carrier transport in microwave and millimeter wave devices with sub-micrometer gate lengths. Illumination effects are accommodated in the model to represent carrier density changes inside the illuminated device. The simulation results are compared to available experimental records for a typical MESFET for validation purposes. Simulation results show that the microscopic as well as the macroscopic characteristics of the active device are altered by the light energy. This fact makes the model an important tool for the active device design method under illumination control.

An efficient large-signal modeling method of FET using load-line analysis is proposed, and it is applied to non-linear characterization of FET. In this method, instantaneous drain-source voltage V_ds(t) and drain-source current I_ds(t) waveforms are determined by load-line analysis while non-linear parameters in a large-signal equivalent circuit of FET are defined as the average values over one period corresponding to instantaneous V_ds(t) and I_ds(t). Output power (P_out), power added efficiency (η_add), and phase deviation calculated by using such an equivalent circuit of FET agree well with the measured results at 933.5 MHz. Phase deviation mechanism is explained based on the large-signal equivalent circuit of FET, and it is shown how non-linear parameters, such as trans-conductance (g_m), drain-source resistance (R_ds), gate-source capacitance (C_gs), and gate leak resistance (R_ig) contribute to positive or negative phase deviations. The difference between small-signal and large-signal S-parameters (S₁₁, S₁₂, S₂₁, S₂₂) is also discussed. The proposed large-signal modeling method is considered to be useful for the design of high power, high efficiency, and low distortion amplifiers as well as the investigation of the behavior of FET in large-signal operating conditions.

This paper describes an improved nonlinear GaAs FET model and its parameter extraction procedure for almost all operating conditions such as the small-signal condition, the power saturated condition, and the controlled-resistance condition. The model is capable of modeling the gate voltage dependent drain current and its derivatives in the saturated region as well as the drain voltage dependent drain current and its derivatives in the linear region. The model can take into account the frequency dispersion effects of both transconductance and output conductance. The model describes forward conduction and reverse conduction currents. Deriving the capacitance part of the model from unique charge equations satisfies charge conservation. The model accurately predicts voltage-dependent S-parameters, spurious response in an active condition and inter-modulation response in the controlled-resistance condition of a GaAs FET.

A large-signal simulation program for multi-stage power amplifier modules by using a novel interpolation is presented. This simulation program has the function to make the Load-Pull and Source-Pull (LP/SP) data required for the simulation. By using the interpolation, a lot of LP/SP data can be made from a small number of measured LP/SP data. The interpolation is based on the calculation method using a two-dimensional function. By using the simulation program, we can calculate the large-signal characteristics depended on frequency and temperature of the multi-stage amplifier module. We apply the simulation program to the design of the amplifier. The calculated and measured results agree well. The accuracy of the presented interpolation is confirmed. It is considered that the presented program is useful to calculate large-signal characteristics of the amplifier module.

A simulation tool for analyzing circuit characteristics of microstrip-type MIC (Microwave Integrated Circuit) passive elements is presented. The major part of this tool is the electromagnetic wave analysis based on the FD-TD (Finite-Difference Time-Domain) method combined with the mode expansion theory. Although the element structures which can be treated in this tool are limited to only less than ten fundamental structures in the present stage, its extension to the more versatile tool applicable to other various element types is rather straightforward and simple in principle. When using this tool, we first choose the element configuration to be calculated and give, on a panel, necessary parameter values related to calculation range and mesh division scheme. Given these values, the first step calculation starts to obtain the characteristic impedance, cross sectional field distribution of the propagating mode, etc. of the basic microstrip line. Field distributions around the element configulation are calculated next with the mode field oscillation being given. Through this process the field distributions on a closed rectangular parallelepiped surface enclosing the element configuration are stored in files, from which S parameter and radiated fields are calculated by invoking the reaction integral with propagation modes and radiation modes, respectively. The results obtained in these three steps can be expressed, at our discretion, as line drawings or two-dimensional density plots.

Making up a microwave simulator is tried, which has an analysis method based on the finite-element method as a solver and commercial tools as a pre- and post-processor of a graphical user interface. The platform of this simulator is Windows, but, since the codes and configuration files to be created are common on Windows, Unix, and Linux, the simulator running on any platform may be made up at the same time, except a document on which all the commands of the simulator are embedded and executable. Using the simulator, the transmission properties of a 2- and 3-D waveguide discontinuity in a microwave circuit and eigenmodes of a 2- and 3-D waveguide are analyzed, and the computed results are presented in graphs of S parameters and plots of the electric field distribution.

As a solver in a simulator, advantages of use of a wavelet function were investigated for analysis of a dipole antenna using the Moment Method. Realization of a sparse matrix due to orthogonality and due to inherent nature of the wavelet is confirmed by observing an impedance matrix using each Daubechies' wavelet. Calculated results of the input impedance, the impedance matrix, and the current distribution are compared in variation of the wavelet in two integral equations for a dipole antenna. Use of the Daubechies' wavelet of the high number with a small matrix and a threshold in the Hallen's Integral Equation is suitable for the reduction of the matrix size and of the calculation cost.

For on-chip matching Si-MMIC fabricated on a conventional low resistivity Si substrate, the loss of on-chip inductors is quite high due to the dielectric loss of the substrate. In order to reduce the loss of on-chip matching circuit, the use of high resistivity Si substrate is quite effective. By using electro-magnetic simulation, the relationship between coplanar waveguide (CPW) transmission line characteristics and the resistivity of Si substrate is discussed. Based on the simulated results, the resistivity of Si substrate is designed to achieve lower dielectric loss than conductor loss. The effectiveness of high resistivity Si substrate is evaluated by the extraction of equivalent circuit model parameters of the fabricated on-chip spiral inductors and the measurement of the fabricated on-chip matching Si-MMIC LNA's.

In this paper, we propose a full-wave finite-difference time-domain formulation for ferrite magnetized in arbitrary direction solving the equation of motion of the magnetization vector including magnetic loss with Maxwell's equation consistently. The FDTD formulation and algorithm for ferrite are derived from Gilbert's equation without making any restrictions on the direction of the magnetization. In order to confirm the validity and generality of the the axial independence of the formulation, full-wave analyses for a ferrite filled waveguide resonator are demonstrated and compared with theoretical results given from the conventional Polder's permeability tensor. The FDTD results of the quality factor and the resonant frequency of the resonators magnetized in off-axial direction agree very well with the theoretical results, and validity and generality of the formulation are confirmed.

As the capacity of a personal computer and workstation increases rapidly, many electromagnetic simulators solving antenna problems are widely used. In this paper, the IE3D electromagnetic simulator, which is a commercial software product, is applied to the analysis of handset antennas in the vicinity of the human body. Firstly, basic characteristics of popular handset antennas such as whip and planar inverted-F antennas are obtained by the IE3D electromagnetic simulator and calculated results are compared with measured results quoted from the referenced paper. Secondly, on the basis of newly considered design concept for a handset antenna, a loop antenna system for the handset, which we have proposed in order to reduce the influence of human body, is taken as an example of a balance-fed antenna and is analyzed theoretically and experimentally including the influence of the human body. In a result, calculated results by the IE3D electromagnetic simulator are in good agreement with measured results and it is confirmed that the simulator is very effective in analyzing the handset antenna in the vicinity of the human body.

The microwave coagulation therapy has been used mainly for the treatment of hepatocellular carcinoma (small size tumor in the liver). In the treatment, a thin microwave antenna is inserted into the tumor, and the microwave energy heats up the tumor to produce the coagulated region including the cancer cells. At present, a problem occurs: the size of the coagulated region is insufficient, especially in the perpendicular direction of the antenna axis. In order to overcome this problem without increasing the physical load of the patient, the authors introduced a new type of array applicator composed of two coaxial-slot antennas. However, we cannot estimate heating characteristics of this array applicator precisely by using the FDTD calculation, because the use of staircasing approximation, which employs rectangular parallelepiped cells, is unsuitable for the analysis. Therefore, in this paper, we introduce the finite element method (FEM), which employs tetrahedral cells, to estimate the heating characteristics of the array applicator.

As the capacity of the personal computer and workstation increase rapidly, many electromagnetic simulators are widely used. In this paper, Ansoft's High Frequency Structure Simulator (HFSS), which is a commercial software product, is applied to design a mode converter operating at 35 GHz is fabricated based on the simulation results. The numerical results are in good agreement with the measured data.

The genetic algorithm is used to reconstruct the shapes of multiple perfectly conducting cylinders. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations is derived and the imaging problem is reformulated into an optimization problem. The genetic algorithm is then employed to find out the global extreme solution of the object function. Numerical examples are given to demonstrate the capability of the inverse algorithm. Good reconstruction is obtained even when the multiple scattering between two conductors is serious. In addition, the effect of Gaussian noise on the reconstruction results is investigated.

We propose the architecture of efficiently and flexibly extensible solver system for electromagnetic wave simulations, that can load multi kinds of schemes such as Finite-Difference Time-Domain (FDTD) scheme, Finite Element Method (FEM), and a circuit simulator, with various boundary conditions in the system. Object-oriented approach is a promising method for efficient development of the flexible simulator. The primary object in the architecture is found through our object-oriented analysis as decomposed "region" from whole the simulation space. The decomposed region is considered to be the stage on which the electromagnetic fields play under the local rules. Developers who will extend the functionality of the system can add new classes inherited from the abstract classes in our design depending on the grid structure, the scheme, or the boundary processing method.

The finite-difference time-domain (FDTD) method incorporating Berenger's PML absorbing boundary condition is developed to model three-dimensional dielectric resonators. The fast Fourier transform (FFT) coupled with the Pade interpolation technique is employed to obtain frequency domain results with satisfactory resolution and accuracy, and to reduce the computation time significantly compared with that needed when the conventional FFT algorithm is used. Computed resonant frequencies of two types of cylindrical dielectric resonators are compared with theoretical and measured results. A good agreement is observed.

A method for estimating complex permittivity of a material using a rectangular waveguide with a flange is presented by the finite difference time domain (FDTD) method. An advantage of the present method is that it is not necessary to vary the material structure in order to insert it into the waveguide. Therefore estimation errors related to the dimensions of the material are almost negligible. In this case, fluoridated rubber is chosen as the low-loss material. The comparison of the complex permittivity of the material determined by the present method with FDTD and the conventional waveguide method at 10 GHz is performed. It was confirmed that the present method is effective for estimating the complex permittivity under the condition that the length of the flange is about 50 mm (1.7λ) square.

This paper presents a novel concept of a Two-Dimensional (2-D) Finite-Difference Time-Domain (FDTD) formulation for the numerical analysis of electromagnetic fields. FDTD method proposed by Yee is widely used for such analysis, although it has an inherent problem that there exist half-cell-length and half-time-step distances between electric and magnetic field components. To dissolve such distances, we begin with the finite-difference approximation of the wave equation, not Maxwell's equations. Employing several approximation techniques, we develop a novel algorithm which can condense all field components to equidistant discrete nodes. The proposed algorithm is evaluated in comparison with several conventional algorithms by computer simulations.

The diffraction of a plane electromagnetic wave by an impedance wedge whose boundary is described in terms of the skew coordinate systems is treated by using the Wiener-Hopf technique. The problem is formulated in terms of the simultaneous Wiener-Hopf equations, which are then solved by using a factorization and decomposition procedure and introducing appropriate functions to satisfy the edge condition. The exact solution is expressed through the Maliuzhinets functions. By deforming the integration path of the Fourier inverse transform, which expresses the scattered field, the expressions of the reflected field, diffracted field and the surface wave are obtained. The numerical examples for these fields are given and the characteristics of the surface wave are discussed.

We examined the creep properties and hazard rates of plastic ferrules to ensure the long-term reliablity of optical fiber connections. The endface deformation ΔL had to be smaller than 3 µm to keep the insertion-loss and return-loss fluctuation to acceptable levels in the worst case of random concatenation of similarly deformed plastic ferrules. From the fluctuation data, we estimated the time-to-failure t_f at which the ΔL value became 3 µm. We estimated the acceleration parameters, median lifetimes ξ, and hazard rates λ by using t_f values based on Weibull statistics. The ξ values decreased rapidly with increasing temperature and relative humidity. We found we could expect small λ values of < 0.1 FIT (FIT=10^-9/hour) and of 1 FIT for 20 years in a normal atmosphere (25C/50%RH) and in a more severe case of 25C/90%RH, respectively.