Showing papers in "Microwave and Optical Technology Letters in 1994"
TL;DR: A modified set of Maxwell's equations is presented that includes complex coordinate stretching along the three Cartesian coordinates that allow the specification of absorbing boundaries with zero reflection at all angles of incidence and all frequencies.
Abstract: A modified set of Maxwell's equations is presented that includes complex coordinate stretching along the three Cartesian coordinates. The added degrees of freedom in the modified Maxwell's equations allow the specification of absorbing boundaries with zero reflection at all angles of incidence and all frequencies. The modified equations are also related to the perfectly matched layer that was presented recently for 2D wave propagation. Absorbing-material boundary conditions are of particular interest for finite-difference time-domain (FDTD) computations on a single-instruction multiple-data (SIMD) massively parallel supercomputer. A 3D FDTD algorithm has been developed on a connection machine CM-5 based on the modified Maxwell's equations and simulation results are presented to validate the approach. © 1994 John Wiley & Sons, Inc.
1,660 citations
TL;DR: A multilevel algorithm is applied to the solution of an integral equation using the conjugate gradient method and shows that the complexity of a matrix-vector multiplication is proportional to N (log(N))2.
Abstract: In the solution of an integral equation using the conjugate gradient (CG) method, the most expensive part is the matrix-vector multiplication, requiring O(N2) floating-point operations. The fast multipole method (FMM) reduced the operation to O(N15). In this article we apply a multilevel algorithm to this problem and show that the complexity of a matrix-vector multiplication is proportional to N (log(N))2. © 1994 John Wiley & Sons, Inc.
303 citations
TL;DR: The fast multipole method is used to solve the electromagnetic scattering from three-dimensional conducting bodies of arbitrary shape by discretizing the electric field integral equation by the method of moments.
Abstract: The fast multipole method is used to solve the electromagnetic scattering from three-dimensional conducting bodies of arbitrary shape. The electric field integral equation is discretized by the method of moments. Instead of directly computing the matrix-vector multiplication, which needs N2 multiplications, this approach reduces the complexity to O(N1.5). © 1994 John Wiley & Sons, Inc.
128 citations
TL;DR: A nonnested, ray-propagation approach is used to compute a matrix-vector multiply in O(N4/3) operations, where N is the number of unknowns in the discretized integral equation.
Abstract: A new technique is presented for accelerating the fast multipole method, allowing rapid solution of surface integral equations for wave-scattering problems. A nonnested, ray-propagation approach is used to compute a matrix-vector multiply in O(N4/3) operations, where N is the number of unknowns in the discretized integral equation. © 1994 John Wiley & Sons, Inc.
100 citations
TL;DR: A multilevel algorithm is presented for evaluating fields generated by given distributions of electric current using the limited number of degrees of freedom that characterize a field observed over a domain that is well separated from a source domain.
Abstract: A multilevel algorithm is presented for evaluating fields generated by given distributions of electric current. The algorithm can be used to accelerate the solution of scattering problems using the method of moments and/or boundary element methods. The algorithm exploits the limited number of degrees of freedom that characterize a field observed over a domain that is well separated from a source domain. Both the memory requirements and the computational complexity of the algorithm are O(Ns log(Ns)), where Ns is the common number of sources and observation points. The multilevel algorithm can easily be incorporated into existing method-of-moments (MoM) programs. A simple physical interpretation of the algorithm is provided. © 1994 John Wiley & Sons, Inc.
95 citations
TL;DR: A microstrip array antenna for vertically polarized fan beam (approximately 2°×50°) for C-band SAR applications with a physical area of 1.7 m by 0.17 m comprises two rows of patch elements and employs a parallel feed to left and right-half sections of the rows as discussed by the authors.
Abstract: A microstrip array antenna for vertically polarized fan beam (approximately 2°×50°) for C-band SAR applications with a physical area of 1.7 m by 0.17 m comprises two rows of patch elements and employs a parallel feed to left- and right-half sections of the rows. Each section is divided into two segments that are fed in parallel with the elements in each segment fed in series through matched transmission lines for high efficiency. The inboard section has half the number of patch elements of the outboard section, and the outboard sections, which have tapered distribution with identical transmission line sections, terminated with half wavelength long open-circuit stubs so that the remaining energy is reflected and radiated in phase. The elements of the two inboard segments of the two left- and right-half sections are provided with tapered transmission lines from element to element for uniform power distribution over the central third of the entire array antenna. The two rows of array elements are excited at opposite patch feed locations with opposite (180° difference) phases for reduced cross-polarization.
91 citations
TL;DR: In this paper, the resonant frequency of a coaxial-probe-fed rectangular microstrip antenna tuned by a number of passive metallic posts suitably placed within the antenna's boundary is obtained by using the frequency expression in the absence of the post.
Abstract: The resonant frequency of a coaxial-probe-fed rectangular microstrip antenna tuned by a number of passive metallic posts suitably placed within the antenna's boundary is obtained by using the resonant frequency expression in the absence of the post. The resonant frequency in the absence of the post is calculated from the fringing field extension and effective relative permittivity expressions. The theoretical resonant frequency results of tunable rectangular patch antenna obtained by using this method are in good agreement with experimental results available in the literature. © 1994 John Wiley & Sons, Inc.
45 citations
TL;DR: In this paper, an analytical antenna model for the polarizabilities of small bianisotropic wire-and-loop particles and a numerical simulation technique were used to calculate the electronic properties of artificial isotropic chiral composites.
Abstract: Electromagnetic properties of artificial isotropic chiral composites are calculated based on the analytical antenna model for the polarizabilities of small bianisotropic wire-and-loop particles and on a numerical simulation technique. Averaged media parameters are estimated using the Maxwell-Gamett model. Theoretical results are compared with the transmission coefficients for a composite slab measured at microwave frequencies. The analytical model is seen to provide an accurate description in the area of the first resonance of the structure and at lower frequencies, which corresponds to the approximations made in the theoretical modeling. © 1994 John Wiley & Sons, Inc.
31 citations
TL;DR: In this paper, high-speed, low-drivingvoltage operation of multiple-quantum-well (MQW) external modulators based on the quantum-confinement Stark effect (QCSE) operating at long wavelengths is reviewed.
Abstract: High-speed, low-driving-voltage operation of multiple-quantum-well (MQW) external modulators based on the quantum-confinement Stark effect (QCSE) operating at long wavelengths are reviewed We discuss the design and characteristics of ultrafast intensity and phase MQW modulators that have been developed by our group and we compare them with those of other material systems and structures based on a defined figure of merit for external modulators In addition, we discuss a new integrated light source that enables external modulation of an in-plane DFB laser to reduce wavelength chirping and coupling loss with a laser and a modulator Finally, we describe new applications for optical soliton pulse generation using the above intensity modulator © 1994 John Wiley & Sons, Inc
30 citations
TL;DR: The effect of noise in the data on the Cauchy method is discussed and the theoretical probability density function is verified by numerical simulation.
Abstract: In this article the effect of noise in the data on the Cauchy method is discussed. The noise is assumed to be zero mean and Gaussian. The resulting random variable is a ratio of two Gaussians. The theoretical probability density function is verified by numerical simulation. © 1994 John Wiley & Sons, Inc.
27 citations
TL;DR: Eigenmodal decomposition formulations for numerical solutions of the FDTD and the transmission-line-matrix (TLM) methods are given in this article, where the main advantage of this technique is that the eigenvalues and eigenvectors for a problem can be stored, and the numerical solutions then quickly processed with the stored data.
Abstract: Eigenmodal decomposition formulations are given for numerical solutions of the finite-difference time-domain (FDTD) and the transmission-line-matrix (TLM) methods. Instead of direct simulation with these time-recursive schemes, the analysis involves two steps: (1) solving an eigenvalue problem, and (2) analytically constructing the numerical solutions in terms of the eigenvalues and eigenvectors. The numerical solution at any time step can be obtained with only O(N) computation once the corresponding eigenvalue problem has been solved. The main advantage of this technique is that the eigenvalues and eigenvectors for a problem can be stored, the numerical solutions then quickly processed with the stored data. In addition, high-frequency numerical noise can be reduced simply by discarding the related high-frequency modes. © 1994 John Wiley & Sons, Inc.
TL;DR: A planar subarray composed of rectangular dielectric resonators fed by a microstrip-line / aperture combination has been devised and investigated in this paper, achieving a 10-dB impedance bandwidth and excellent radiation patterns.
Abstract: A new type of planar subarray composed of rectangular dielectric resonators fed by a microstrip-line / aperture combination has been devised and investigated Good performance has been achieved, including a 10-dB impedance bandwidth of 18% and excellent radiation patterns Results for impedance bandwidth, radiation patterns, and mutual coupling effects are presented © 1994 John Wiley & Sons, Inc
TL;DR: In this paper, a probe-fed superstrate-loaded rectangular microstrip antenna mounted on a cylindrical body is investigated by using a full-wave analysis and a moment-method calculation.
Abstract: A probe-fed superstrate-loaded rectangular microstrip antenna mounted on a cylindrical body is investigated by using a full-wave analysis and a moment-method calculation. Numerical results for the input impedance are calculated and the numerical convergence of the moment-method calculation is also shown. Variations of the input impedance with the superstrate thickness and curvature radius are presented and discussed. Both the HE01 and HE10 modes are studied. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, a probe-fed hemispherical dielectric resonator antenna with a polysilicon-coating was investigated rigorously by using a Green's function formulation.
Abstract: A probe-fed hemispherical dielectric resonator antenna with a dielectric coating is investigated rigorously by using a Green's function formulation. Numerical results for the input impedance at TE111 mode are calculated. It is found that, by coating the dielectric resonator antenna with a dielectric material having a relative permittivity about half that of the dielectric resonator antenna, the impedance bandwidth of the antenna can be significantly improved. This dielectric coating here serves as a transition region between the wave inside the dielectric resonator antenna and the free-space wave, and thus can increase the impedance bandwidth of the antenna. A broadband dielectric resonator antenna can thus be obtained. © 1994 John Wiley & Sons, Inc.
TL;DR: In this paper, a simple mathematical formula is used to simplify and improve the expression of the nonaxisymmetric distorted raindrop shapes, enabling the scattered field by rain to be derived analytically.
Abstract: The Pruppacher-and-Pitter (PP) raindrop model has been well accepted as a realistically distorted raindrop model. To employ this model for the investigation of radio wave attenuation by rain requires tedious numerical calculations. In this Letter a simple mathematical formula is used to simplify and improve the expression of the nonaxisymmetric distorted raindrop shapes, enabling the scattered field by rain to be derived analytically. The coefficients in the formula are determined for different raindrop sizes by translating the polar coordinates vertically and fitting the shapes of the Pruppacher-and-Pitter-form raindrops to the shapes discussed in this Letter. Using the least-squares method, a general expression for the coefficients in terms of the raindrop sizes is obtained. A comparison of the raindrop shapes obtained from the Pruppacher and Fitter expression and the expression in this Letter demonstrates the validity of the simplified formula for realistically distorted raindrops. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, the in-plane quantum energy control selective area metal-organic vapor-phase epitaxy of multiple-quantum-well (MQW) structures is applied to an electroabsorption modulator/distributed feedback laser integrated device.
Abstract: This article describes a novel fabrication technology for photonic integrated circuits (PICs) that easily produces a smooth and high-quality waveguide coupling between interconnected guided-wave elements. This technique is based on the in-plane quantum energy control selective area metal-organic vapor-phase epitaxy of multiple-quantum-well (MQW) structures. Good local quantum energy control over a very wide range is shown for simultaneously grown MQW crystals. Moreover, the crystal quality, well/barrier heterointerface, and flatness and uniformity of these selectively grown MQW crystals are bound to be as good as those of normally grown crystals. This technique is applied to an electroabsorption modulator/distributed feedback laser integrated device. Superior device performance, including a low threshold and high-efficiency lasing properties, as well as high-speed, low-drive-voltage, and low-chirp modulator characteristics are attained due to improved optical coupling, easy fabrication, and sufficient crystal quality of selectively grown MQW structures. 2.5 Gbit/s penalty-free data transmission is demonstrated over an 80-km normal single-mode fiber, which, combined with long-term device reliability, makes this integration technique more attractive for practical fabrication of semiconductor PICs. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, an approach to derive local boundary conditions that can be employed in conjunction with the finite-difference and finite-element methods (FD/FEM) to solve electromagnetic scattering and radiation problems is presented.
Abstract: In this article we present a novel approach to deriving local boundary conditions that can be employed in conjunction with the finite-difference and finite-element methods (FD/FEM) to solve electromagnetic scattering and radiation problems. The key step in this approach is to derive linear relationships that link the values of the field at the boundary grid points to those at the neighboring points. These linear relationships are satisfied, to within a certain tolerance, by all of the outgoing wave components. They can thus be used in lieu of the FD/FEM equations employing the usual absorbing boundary conditions for the boundary points. The present approach not only provides a simple way to derive an accurate boundary condition for mesh truncation, but also preserves the banded structure of the FD/FEM matrices. © 1994 John Wiley & Sons, Inc.
TL;DR: In this paper, a simple method was used to design a microstrip flat reflect-array antenna for X-band, 12-element array of rectangular microstrip patches for the first time to reflect the main beam 20 degrees off broadside.
Abstract: A simple method was used to design a microstrip flat reflect-array antenna. An X-band, 12-element array of rectangular microstrip patches was demonstrated for the first time to reflect the main beam 20 degrees off broadside. A redirection efficiency of 65.8% was observed. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, a new way of feeding an SSFIP antenna to obtain two orthogonal linear or two circular (RHCP/LHCP) polarizations is presented, and the advantages of the method are its simplicity, a perfect symmetry of the structure and of the pattern, and an excellent decoupling between input ports.
Abstract: A new way of feeding an SSFIP antenna to obtain two orthogonal linear or two circular (RHCP/LHCP) polarizations is presented. The advantages of the method are its simplicity, a perfect symmetry of the structure and of the pattern, and an excellent decoupling between input ports. The enhanced element retains the desirable properties of conventional SSFIP elements: wide bandwidth, low cost, robustness, and low thickness and weight. © 1994 John Wiley & Sons, Inc.
TL;DR: In this paper, the authors introduced a new method to analyze saturated ferrite structures by a FDTD algorithm where the convolution between the permeability tensor [μ(t)] = F−1 ([μ(ω)]) and the magnetic field H(t) = F −1 (H(ω)) are calculated.
Abstract: When subjected to a constant magnetic field, ferrites exhibit anisotropic constitutive parameters. This anisotropy can be described in the frequency domain by using a permeability tensor [μ(ω)] instead of the usual scalar permeability. This article introduces a new method to analyze saturated ferrite structures by a FDTD algorithm where the convolution between the permeability tensor [μ(t)] = F−1 ([μ(ω)]) and the magnetic field H(t) = F−1 (H(ω)) are to be calculated. Results are obtained for a two-dimensional problem and are compared with those given by direct differential FDTD algorithm [1] and a mode-matching method [2]. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, a new three-dimensional time-domain method is proposed, where the computational domain consists of a union of tetrahedrons with electric fields assigned on the edges, and fields are updated from the integral form of Maxwell's equations in conjunction with the use of Whitney two-form elements.
Abstract: A new three-dimensional time-domain method is proposed. The computational domain consists of a union of tetrahedrons with electric fields assigned on the edges. Fields are updated from the integral form of Maxwell's equations in conjunction with the use of Whitney two-form elements. A rectangular waveguide is modeled as an example. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, an iterative inversion in angular spectral domain based on the quasi Newton's procedure is presented, which is shown to be more insensitive to the noise in the scattered field than configuration domain reconstruction.
Abstract: An iterative inversion in angular spectral domain based on the quasi Newton's procedure is presented. Angular spectral-domain reconstruction is shown to be more insensitive to the noise in the scattered field than configuration domain reconstruction. It is also shown by closed-form solution of a homogeneous circular cylinder that the local minima hindering this inversion process exist in the cost function. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, the radiation pattern of a pseudochiral point-source antenna is analyzed in the presence of an isotropic half-space, and the expression of the electric field radiated by a grounded slab is given in a form such as to simplify the extraction of noticeable information to be used during the project.
Abstract: We present certain novel characteristics of the radiation pattern of a pseudochiral point-source antenna, which consists of an elemental antenna embedded in a grounded pseudochiral substrate in the presence of an isotropic half-space. The pseudochiral Ω medium is a new synthetic bianisotropic material, recently introduced by Engheta and Saadoun [1]. The expression of the electric field radiated by a pseudochiral grounded slab is given in a form such as to simplify the extraction of noticeable information to be used during the project, about the influence of frequency, constitutive parameters, thickness of the slab, and position of the electric source. © 1994 John Wiley & Sons, Inc.
TL;DR: This communication suggests that three parameters derived from correlation functions can prove useful in assessing validation comparisons in numerical modeling tools.
Abstract: Numerical modeling has an important role to play in optical, microwave, and EMC design. An objective assessment of the accuracy of such numerical modeling tools using experimental data is often hampered by the general complexity of the data to be compared. It is therefore difficult to quantify the resulting comparisons. This communication suggests that three parameters derived from correlation functions can prove useful in assessing validation comparisons. © 1994 John Wiley & Sons, Inc.
TL;DR: In this paper, curve-fitting formulas based on moment-method results are presented for the resonant frequency of the TM11 mode of a coaxially fed circular patch antenna with or without superstrate.
Abstract: Curve-fitting formulas based on moment-method results are presented for the resonant frequency of the TM11 mode of a coaxially fed circular patch antenna with or without superstrate. The formulas can be used for a wide range of substrate and superstrate thicknesses and permittivities. Results predicted by these computer-aided design formulas agree well with moment-method results and with measurement. © 1994 John Wiley & Sons, Inc.
TL;DR: In this paper, a very simple radiation quality factor expression was presented for a rectangular microstrip antenna, and the theoretical resonant resistance results obtained by using this new radiation QF expression were in very good agreement with the experimental results available in the literature.
Abstract: A new very simple radiation quality factor expression is presented for a rectangular microstrip antenna. The theoretical resonant resistance results obtained by using this new radiation quality factor expression are in very good agreement with the experimental results available in the literature. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, an analysis using a generalized transmission line model (GTLM) for a probe-fed cylindrical-rectangular microstrip antenna is presented, where the equivalent circuit elements for the microstrip antennas modeled as a transmission line loaded with wall admittances are derived, and the expression for the input impedance is given.
Abstract: An analysis using a generalized transmission-line model (GTLM)for a probe-fed cylindrical-rectangular microstrip antenna is presented. The equivalent circuit elements for the microstrip antenna modeled as a transmission line loaded with wall admittances are derived, and the expression for the input impedance is given. Numerical results of the input impedance are calculated and presented as a function of the cylinder radius and the substrate thickness. Excellent agreement of the GTLM solutions with the experimental results is observed. © 1994 John Wiley & Sons, Inc.
TL;DR: In this paper, the radiation characteristics of an aperture-coupled hemispherical dielectric resonator (DR) antenna excited at the broadside TE111mode were investigated both theoretically and experimentally.
Abstract: The radiation characteristics of an aperture-coupled hemispherical dielectric resonator (DR) antenna excited at the broadside TE111mode is investigated both theoretically and experimentally. The Green's functions of the DR antenna are presented for the evaluation of fields in the upper-half plane, and the stationary phase technique is used for the back-lobe radiation. The effect of the slot length on the radiation is studied, and the cross-polarized fields of the antenna are discussed. © 1994 John Wiley & Sons, Inc.
TL;DR: In this article, a wavelet transform is applied to the moment-of-moments solution for TM (transverse magnetic) scattering from a cylinder of elliptic cross section.
Abstract: The recent application of wavelet transforms in method-of-moments solutions for scattering problems is extended to cases involving metallic cylinders whose periphery contain a variety of length scale features ranging from smoothly varying large-scale features to rapidly varying small-scale ones. The basic idea is to first consider a periodic extension of the equivalent current in the arc-length variable with a period identical to the scatterer circumference, and then to expand this representation, using a set of periodic wavelets derived from a conventional basis of wavelets by a periodic extension. Using a Galerkin method and subsequently applying a threshold procedure, a substantial reduction in the number of elements of the moment-method matrix is attained without virtually affecting the solution accuracy. The proposed extension is illustrated by a numerical study of TM (transverse magnetic) scattering from a cylinder of elliptic cross section. © 1994 John Wiley & Sons, Inc.
TL;DR: In this paper, the interplay of spatial and temporal periodicities in a cholesteric liquid crystal is responsible for the three zones into which axial propagation may be classified, each of which is marked by specific attenuation and handedness characteristics.
Abstract: The interplay of spatial and temporal periodicities in a cholesteric liquid crystal is responsible for the three zones into which axialpropagation may be classified. Each of the three zones is marked by specific attenuation and handedness characteristics. 0 1994 John Wiley & Sons, Znc.