In this paper, a novel approach is described to design an interdigital capacitor (IDC) using artificial neural networks (ANNs) and genetic algorithm (GA). The scattering parameters of the training samples are computed by the finite-difference time-domain (FDTD) and ANN is applied to describe the models of IDC. According to the engineering requirement, the dimensions of IDC can be designed with GA using the trained ANN models. This design procedure is proved to be time saving and of high accuracy.

This paper presents a class of new easy-to-fabricate ferrite-sphere-based waveguide Y-junction circulators for potentially low-cost millimeter-wave applications. A new threedimensional modeling strategy using a self-inconsistent mixedcoordinates-based modal field-matching procedure is developed to characterize electrical performance of the proposed circulator. It is found that the circulating mechanism of the ferrite-sphere post is different from its full-height ferrite counterpart in that the new structure operates in a turnstile fashion with resonant characteristics, while the conventional device operates on a transmission cavity model. Extensive comparable studies between he new and conventional circulators are made to show that the electrical behaviors of the new structure are also distinct and radial power-density profiles are not stationary, as in the case of the full-height ferrite post circulator for different geometrical parameters. Results obtained by the analysis techniqueare compared with the available results for a full/partial-height ferrite circulator, showing an excellent agreement. Our calculated and measured results are also presented for W-band circulators with the proposed ferrite-sphere technique, indicating some interesting characteristics such as the frequency offset behavior of the isolation and reflection curves. In addition, radial power-density profiles are plotted inside and outside the ferrite sphere to illustrate its intrinsic circulating mechanism, as well as its difference, as compared to its full-height ferrite structure.

The anisotropic media and active properties of the perfectly matched layer (PML) absorbers significantly deteriorate the finite element method (FEM) system condition and as a result, convergence of the iterative solver is substantially slowed down. To address this issue, the symmetric successive over-relaxation (SSOR) preconditioning scheme is applied to the generalized minimal residual (GMRES) for solving a large sparse and non-symmetric system of linear equations resulting from the analysis of ferrite waveguide device by use of edge-based FEM. Consequently, this preconditioned GMRES (PGMRES) approach can reach convergence ten times faster than GMRES for the typical structures. Copyright # 2004 John Wiley & Sons, Ltd.

In this paper, the electromagnetic wave scattering is analysed by the efficient Krylov subspace iterative fast Fourier transform (FFT) technique in terms of the electric field integral equation (EFIE) for a dielectric body of general shape, inhomogeneity, and anisotropy. However, when the permittivity of the scatter becomes large, the convergence rate of Krylov subspace iterative methods slow down. Therefore, the innerouter flexible generalized minimum residual method (FGMRES) is used to accelerate the iteration. As a result, nearly 10 times convergence improvement is achieved for high permittivity cases. Copyright

A novel numerical de-embedding scheme called the short-open calibration (SOC) technique, in conjunction with the vector finite element method (FEM), has been developed to characterize two-port network of arbitrarily shaped, three-dimensional discontinuities in microwave circuits. This SOC technique is effectively implemented into the FEM for boundary truncation of the unbounded circuit structures. In such a manner, fast convergence of iterative solver for large-sparse linear matrix equations from FEM is achieved. The SOC technique is used to remove parasitic effects brought by the approximation of the impressed voltage source and also the problem of resulting consistency between the two-and threedimensional simulations. Scattering parameters of discontinuous sections are constructed from the definition of port voltages and currents. Numerical solutions are well compared with those published in the available literatures. It is demonstrated that the features of the SOC technique are advantageous when combined with FEM for electromagnetic problems.

This paper presents an approximate, but efficient field treatment of the new easy-to-fabricate ferrite-sphere-based-plane waveguide circulator for potentially low-cost millimeter-wave communication systems. A new three-dimensional modeling strategy using a self-inconsistent mixed-coordinates-based mode-matching technique is developed, i.e., the solutions of the Helmholtz wave equations in the ferrite sphere and in the surrounding areas are deduced in the form of infinite summation of spherical, cylindrical, and general Cartesian modes, respectively. The point-matching method is then used on the interface between the ferrite sphere and air within the cylindrical junction, as well as the interface between the junction and waveguides to numerically obtain the coefficients of different orders of basis functions of the field. Therefore, the field distributions, as well as the characteristics of the circulator, are numerically calculated and good agreement is observed between the numerical results and measured data.

A gradient optimization technique along with a definition of cost function is applied to the CAD of the circulator with a magnetized ferrite sphere for millimeter wave communications. A three. dimensional Finite. Difference Time-Domain (FDTD) approach for the analysis of this ferrite sphere based microstrip circulator is presented. The topology of the structure is enforced at each sted Of optimization and its physical dimensions are used as optimization variables. The cost function is defined using location of zeros and poles of the circulator's transmission, isolation. and reflection functions. Numerical tests show that theoptimization process converges from an arbitrarily selected starting point with the new definition of the cost fimction.

Currently extended finite-difference time domain (FDTD) formulations require the permittivity and conductivity to be independent of frequency. However, for many real materials of interest, these parameters vary significantly with frequency. The extended frequency-dependent finite-difference time domain (FD)2TD method makes it possible to analyze hybrid integrated circuits with lumped element within dispersive medium by combining lumped parameters (R, C, or L) and frequencydependent dielectric substrate in the algorithm. This method allows the full-wave analysis of virtually hybrid integrated circuits and gets parameters with a wide frequency range with one simulation.

this paper, electromagnetic wave scattering is formulated in terms of the electric-field integral equation (EFIE) for a dielectric body of general shape, inhomogeneity, and anisotropy. Applying the pulse-function expansion and the point-matching technique, the integral equation can be solved by the efficient Krylov subspace iterative fast Fourier transform (FFT) technique. Several typical Krylov subspace iterative FFT methods are used to solve the problems and their convergence behaviors are compared.

The symmetric successive overrelaxation (SSOR) preconditioning scheme is applied to the conjugate-gradient (CG) method for solving a large system of linear equations resulting from the use of edge-based finite-element method (FEM). For this scheme, there is no additional computing time required to construct the preconditioning matrix and it contains more global information of the coefficient matrix when compared with those of the banded-matrix preconditioning scheme. The efficient implementation of this preconditioned CG (PCG) algorithm is described in details for complex coefficient matrix. With SSOR as the preconditioner and its efficient implementation in the CG algorithm, this PCG approach can reach convergence in five times CPU time shorter than CG for several typical structures. By comparison with other preconditioned techniques, these results demonstrate that SSOR preconditioning strategy is especially effective for CG iterative method when an edge FEM is applied to solve large-scale time-harmonic electromagnetic-field problems.