Simple and efficient finite-element analysis of microwave andoptical waveguides

A simple and efficient finite-element method for the analysis of microwave and optical waveguiding problems is formulated using three components of the electric or magnetic field. In order to eliminate spurious solutions, edge elements are introduced. In the edge element approach the nodal parameters are not limited to the magnetic field as in the conventional three-component formulation for the dielectric waveguiding problem. An eigenvalue equation that involves only the edge variables in the transversal plane and can provide a direct solution for the propagation constant is derived. To show the validity and usefulness of this approach, computed results are illustrated for microstrip transmission lines and dielectric waveguides     

New technique for analysing planar waveguides with finite metallisation thickness

A new technique for analysing planar waveguides with finite metallisation thickness, based on the spectral-domain immitance approach, is presented. Fast formulation to the eigen-problem is proposed, and numerical results obtained in this way agree well with other methods.     

Oversized waveguides and resonators for millimeter waves

If real monolithic systems^* turn out to be impractical at millimeter-wave frequencies, oversized waveguides and resonators are useful alternatives in component and system design. Low losses, high Q factors, and inexpensive manufacturing are their advantages. Starting with an explanation of the term “oversized”, the loss reductions, Q factors, inherently oversized guides, such as the H-guide and its modifications, excitation of higher-order modes, laterally oversized H-guides, and the effects of coupling are described. A brief consideration of applications concludes the presentation.     

An efficient implementation of the harmonic balance technique for solving nonlinear microwave problems

An efficient implementation of the harmonic balance method, using novel numerical algorithms, that are both robust and efficient, coupled with analytical expressions developed for the elements of the Jacobian matrix, is presented. The approach possesses excellent convergence property and speed. Simulated performances using the developed approach for a 10-GHz GaAs MESFET amplifier are found in good agreement with the measured results.     

An efficient analysis of planar microwave circuits using aDWT-based Haar MRTD scheme

A new wavelet-based technique to generate multiresolution time-domain schemes is presented in this paper. By using symbolic calculus, a rigorous and general formulation of subgridding at every level of multiresolution is obtained. As it is rigorously equivalent to a finer finite-difference time-domain (FDTD) scheme, it does not require any particular treatments for boundary conditions. This technique has been successfully applied to the study of microstrip structures. The near- and the far-field computation can be both improved in terms of CPU time and memory storage, while maintaining the same accuracy as the classical FDTD computation     

A spectral technique for the analysis of time and space-transientsin planar dielectric waveguides

A novel method is proposed for the analysis of transients in dielectric guide, e.g., when excited by a Gaussian beam pulsed in time and modulated by a cosine waveform. This approach, utilizing the full modal spectrum of the guide, results more reliable than existing numerical techniques, while, by virtue of its analytical nature, greatly reducing the computational complexity of the problem     

Fast frequency sweep technique for the efficient analysis of dielectric waveguides

This paper describes a new approach to spectral response computations of an arbitrary two-dimensional (2-D) waveguide. This technique is based on the tangential-vector finite-element method (TVFEM) in conjunction with the asymptotic waveform evaluation (AWE) technique. The former is used to obtain modes characteristics for a central frequency, whereas the latter employs an efficient algorithm to compute frequency moments for each mode. These moments are then matched via Pade approximation to a reduced-order rational polynomial, which can be used to interpolate each mode over a frequency band with a high degree of accuracy. Furthermore, the moments computations and subsequent interpolation for a given set of frequency points can be done much more rapidly than just simple simulations for each frequency point.     

An efficient perfectly matched layer based multilevel fast multipole algorithm for large planar microwave structures

An efficient multilevel fast multipole algorithm (MLFMA) formalism to model radiation and scattering by/from large planar microwave structures is presented. The technique relies on an electric field integral equation (EFIE) formulation and a series expansion for the Green dyadic, based on the use of perfectly matched layers (PML). In this way, a new PML-MLFMA is developed to efficiently evaluate matrix-vector multiplications arising in the iterative solution of the scattering problem. The computational complexity of the new algorithm scales down to O(N) for electrically large structures. The theory is validated by means of several illustrative, numerical examples.     

An enhanced quasi-monolithic integration technology for microwave and millimeter wave applications

A new technology for integration of high frequency active devices into low cost silicon substrate has been introduced. The novel fabrication process gives excellent advantages such as extremely low thermal resistance, and a much lower thermo-mechanical stress than the earlier quasimonolithic integration technology (QMIT) concept . This highly improves the packaging lifetime and electrical characteristics of the active devices. The fabrication process is simple and compatible with fabrication of high-Q passive elements. Successful integration of high-Q passive elements on low resistivity silicon substrate in this technology has been possible for the first time. In comparison to the earlier concept of QMIT, elimination of air-bridges in this technology not only reduces the parasitic elements but also enables the fabrication of the rest of the circuit after measuring the microwave characteristics of the embedded active devices. This makes very accurate microwave and millimeter-wave designs possible. Using the new fabrication process, microwave and millimeter-wave circuits (with both coplanar and microstrip lines) containing power devices have for the first time been possible. Furthermore, the enhanced QMIT can be considered as an organic deposited multi chip module (MCM-D), which is a potential candidate for integration an system on a package (SOP) at microwave and millimeterwave frequencies.     

A numerical technique for the determination of the propagationcharacteristics of nonlinear planar optical waveguides

A numerical method is proposed and implemented into computer code for the analysis of propagation characteristics of nonlinear optical waveguides. This technique follows the concept of the shooting method, and the fourth-order Runge-Kutta method is adapted to integrate the differential wave equation from one side to the other. An error function is defined to estimate the discrepancy between the computed and expected boundary values. A secant method is then used to evaluate the sign and magnitude of the correction term for the initial guesses of effective index. This procedure is performed in an iterative manner until the error reduces to a specified range. Experiments show that very accurate results can be obtained through this method, and only six to seven iterations are needed for solutions to converge. With this method we analyze nonlinear waveguides with varying guide parameters for realization of their behavior. All the findings and results can be used in further investigations of optical devices composed of waveguide structures     

An efficient scalar finite element formulation for nonlinearoptical channel waveguides

A self-consistent numerical approach based on the scalar finite element method is described for the analysis of both TE-like and TM-like nonlinear guided waves in optical channel waveguides. In order to improve the convergence and accuracy of solutions, isoparametric elements and numerical integration formulae derived by Hammer et al. are introduced. Numerical results are presented for nonlinear elliptical core optical fibers, and it is confirmed that in this approach, highly accurate solutions can be obtained with small scale computation. Furthermore, graded-index nonlinear optical channel waveguides are also analyzed, and the influence of refractive-index profiles on propagation characteristics of the nonlinear guided waves is investigated     

A nonuniform FDTD technique for efficient analysis of propagationcharacteristics of optical-fiber waveguides

In this paper, we present a highly efficient one-dimensional cylindrical nonuniform finite-difference time-domain (1-D CNUFDTD) method, which utilizes the unsplit anisotropic perfectly matched layer (APML) for mesh truncation along the radial direction to analyze axisymmetric optical-fiber waveguides. As a first step, we validate the proposed FDTD algorithm by analyzing a uniform dielectric waveguide of circular cross section and show that the results are in excellent agreement with the conventional mode theory solutions. Next, we apply the algorithm to analyze propagation characteristics of a number of commonly used optical-fiber waveguides, i.e., step-index multimode, graded-index multimode, and single-mode step-index configurations     

Advanced ceramic packaging for microwave and millimeter waveapplications

Advances in integrated circuit technologies have produced devices with higher speeds, frequencies, powers, and functional complexity. In addition, these attributes have been realized with smaller and smaller semiconductor devices. Such improvements are primarily due to the effective control and management of wafer-scale interconnect technology. It has become apparent, however, that the next level of interconnect technology to be addressed is in the packaging of these high performance semiconductors. As frequency or speed increases, packaging can quickly become the chief inhibitor to electrical response by degrading signal propagation or by contributing to structural configurations that foster cavity resonances or waveguide modes. The paper attempts to lay out the electrical, structural, material, and cost considerations that need to be simultaneously addressed by the microwave engineer to design the best interconnection method possible between the die and the subsystem. Several packaging concepts are reviewed-from single transition design to multilayer, multichip modules for phased-array applications     

Practical microwave circuits for groove waveguides

Groove guides have been known for many years. No practical microwave circuits have yet been described although these types of transmission lines could be used in many cases. This paper discusses the physical realizability of some wide band designs such as matched load, directional coupler, hybrid coupler, bend and phase shifter. Both closed and open groove guides have been investigated. Optical type components seem to be inappropriate for groove guide transmission. The best way to design components for these guides is to adapt those of standard rectangular guides, which perturb only the Rf fields in the vicinity of the narrow walls and to optimize the dimensions of the groove structure as a function of the losses and the symmetry of the induced spurious modes.     

Stepped leaky-wave antennas for microwave and millimeter wave applications

This work presents the complete general features of a recently proposed class of leaky-wave antennas, derived from stepped rectangular-section waveguides with radiating slits. Based on very favorable topological features, straightforward but extremely effective design procedures are shown to be possible for achieving sophisticated radiation properties. Furthermore, new possibilities are considered as concerns in both the use of linear arrays to scan in two dimensions, and in the introduction of dielectric parts to improve the angular pointing range and to also protect the radiating elements. The analysis of all these properties illustrates very attractive characteristics and perspectives for this type of antenna which can profitably find applications both at microwaves and at millimeter waves.     

An iterative method for optical reconstruction of graded indexprofiles in planar dielectric waveguides

A nondestructive technique for the reconstruction of refractive index profiles in planar waveguides is presented and analyzed. The approach is based on the integral scattering equations, which permit one to relate the refractive index of an inhomogeneous layer to the reflected field intensity at different incidence angles. From this formulation, an iterative algorithm is developed, such as at each iteration step the problem is formulated as the minimization of a functional representing the error between the measurements and the model data. The recovered profile is then used to improve the validity of the approximation in performing the next step. In this approach, the unknown index profile is represented as the sum of a finite series of basis functions avoiding to select a priori the particular functional form (e.g., Gaussian function, complementary error function, etc). The practical effectiveness of this approach is demonstrated by numerically simulating the measurements for different planar waveguides. The influence of measurement uncertainty and noise on the stability of the technique is also evaluated     

An Integral-equation technique for solving thick irises in rectangular waveguides

This paper presents an efficient integral-equation (IE) technique for analysis of thick irises inside multilayered rectangular waveguides. The IEs remain the same as in the case of zero-thickness iris and the thickness is accounted for only as a correction term in the IE kernel. This technique halves the number of unknowns on the iris, thus leading to computational effort and simulation times comparable to the zero-thickness case. In this paper, two efficient ways for computing the correction term are introduced and the accuracy of the approach is discussed on several waveguide structures and filters.     

An efficient technique for eigenspace-based adaptive interferencecancellation

This paper presents a technique for the computation of the interference subspace for eigenspace-based interference cancellation. Using a subarray partitioning scheme, we construct the interference subspace from the subarray interference subspaces. In the case of uniform linear arrays, the proposed technique has the advantages of reclaiming the lost degrees of freedom due to signal blocking and reduced computational burden over existing techniques. The proposed technique also possesses the capabilities to cope with the case of using nonuniform linear arrays in the environment of partially correlated signals. A computer simulation example is provided for illustration and comparison