Showing papers in "Journal of Electromagnetic Waves and Applications in 1990"
TL;DR: In this article, the stability of a simple numerical scheme for solving the time dependent form of the Electric Field Integral Equation is investigated, in which the time step Δt times the speed of light c does not exceed the minimum spatial grid step Δ, and the surface current and charge distributions are found explicitly in terms of the distribution at earlier times.
Abstract: The stability of a simple numerical scheme for solving the time dependent form of the Electric Field Integral Equation is investigated in this paper. In this so-called "time marching" algorithm, the time step Δt times the speed of light c does not exceed the minimum spatial grid step Δ, and the surface current and charge distributions are found explicitly in terms of the distribution at earlier times. In order to obtain solutions which are stable in the long term, two points must be considered. (i) The product cΔt must not exceed Δ/√2. (Courant condition.) (ii) If the scatterer has internal resonances (i.e., is a closed body) or has a SEM pole close to the imaginary axis then, in addition to the Courant condition holding, an averaging procedure must be used. A four step averaging procedure is found to be necessary for closed bodies with internal resonances, such as the cube, whereas a three step procedure is found to be adequate for pair of parallel plates, which has no internal resonance, but does posses...
183 citations
TL;DR: In this article, a polarimetric radar calibration algorithm using three in-scene reflectors is developed based on the exact solution for general target choices, where the transmitting and receiving ports are modeled by two unknown polarization transfer matrices.
Abstract: A polarimetric radar calibration algorithm using three in-scene reflectors is developed based on the exact solution for general target choices. The transmitting and receiving ports of the polarimetric radar are modeled by two unknown polarization transfer matrices. These transfer matrices are solved in terms of measurements from three independent calibration targets with known scattering matrices. The solutions for several sets of calibration targets with simple scattering matrices are presented first. Then, when at least two of the target scattering matrices can be simultaneously diagonalized, polarimetric calibration is derived using the method of simultaneous diagonalization of two matrices. A transformation matrix is found to convert the general scattering matrices into the simple cases, and the problem is solved in the transformed domain. The solution to the original problem then can be expressed in terms of the solutions obtained for the simple scattering matrices. All possible combinations of calib...
61 citations
TL;DR: In this article, the exact averaging method for the Fourier-transformed field equations of the slab was used to calculate propagated and reflected fields for general excitation, and different approximations related to slabs thin either in wavenumbers in the normal or in transversal directions were considered.
Abstract: This paper discusses modelling of isotropic and chiral slabs by using vector circuits involving dyadic impedances and admittances and tangential field components. The analysis is based on the exact averaging method for the Fourier-transformed field equations of the slab. Then, by considering tangential electric and magnetic fields as voltages and currents, analogous vector circuits, such as equivalent two-port circuits, Thevenin and Norton circuits and T and II circuits, are given for isotropic and chiral isotropic and homogeneous and nonhomogeneous slabs. These vector circuits are most appropriate when calculating propagated and reflected fields for general excitation. In addition, different approximations related to slabs thin either in wavenumbers in the normal or in transversal directions or to slabs with different propagation constant ratios are considered. A case when a slab can be simulated by a sheet is also discussed. The results obtained can be useful in many practical situations, for example, f...
57 citations
TL;DR: In this paper, the authors presented basis and testing functions for which the resulting matrix is approximately sparse when N is large, provided that the scatterer contains "smooth" regions, that is, nearly all of the matrix elements are so small that they may be set equal to zero.
Abstract: Previous moment method calculations (based on integral equations) have generally required utilizing a full N x N matrix when there are N unknowns. In this paper, novel basis and testing functions are presented for which the resulting matrix is approximately sparse when N is large, provided that the scatterer contains "smooth" regions. That is, nearly all of the matrix elements are so small that they may be set equal to zero. The ways to develop such functions are considered in detail, as are their effect on the condition number of the resulting matrix. Numerical calculations elucidate the properties of the resulting matrix, while calculations of the Radar Cross Section (RCS) show good results when approximating these small elements by zero. The motivations for the choices of the functions considered are explained in detail, since even more effective choices of functions may remain to be discovered. This method reduces the storage requirements from Order N2 to Order N for an N unknown problem, and also cor...
54 citations
TL;DR: In this paper, the Galerkin formulation, time-discretization, and linearization of coupled electro-mechanical equations are presented, and the resulting global system is assembled and investigated.
Abstract: The transient analysis of a coupled electro-mechanical system is undertaken. The system consists partly of spatial regions, which may support magnetic fields, that are modelled by finite elements. The regions may be attached to external electrical sources and circuits, and may also be capable of rigid body motion with respect to one another. A method for coupling the electric circuit transient equations, transient magnetic field finite element equations, and the transient mechanical motion equations is described. Only the external source variation is assumed to be known; all other field, circuit, and mechanical motion quantities are treated as unknowns and calculated. Equations for transient analysis of a general, 2-dimensional, planar, non-linear, voltage-excited system are derived in detail. The Galerkin formulation, time-discretization, and linearization of these equations are presented. The resulting global system of coupled electro-mechanical equations is assembled and investigated. Included are exam...
52 citations
TL;DR: In this article, a quasi-static analysis similar to that leading to Rayleigh scattering expressions for dielectric and magnetic spheres is extended to small spheres of chiral material, where the internal field for linearly polarized plane wave is constant and elliptically polarized with nonorthogonal electric and magnetic field components.
Abstract: Quasi-static analysis similar to that leading to Rayleigh scattering expressions for dielectric and magnetic spheres is extended to small spheres of chiral material. It is seen that the problem unites electrostatics to magnetostatics, and the most natural way of considering the problem is in terms of wave fields, certain combinations of electric and magnetic fields, which is applied in the analysis. For exterior fields the chiral sphere can be replaced by an electric and a magnetic dipole, both having a cross-polarized component which vanishes for a nonchiral medium. The internal field for linearly polarized plane wave is constant and elliptically polarized with nonorthogonal electric and magnetic field components. The resulting expressions can be applied to scattering or measurement problems involving spheres of chiral material.
45 citations
TL;DR: In this paper, a novel geometric optics method for inhomogeneous chiral media is introduced applying normalized wave fields, which are certain complex combinations of the electric and magnetic fields, and two possible expressions for a chirality distribution capable of eliminating the inherent cross polarization, are derived.
Abstract: A novel geometric optics method for inhomogeneous chiral media is introduced applying normalized wave fields, which are certain complex combinations of the electric and magnetic fields. It is seen that for sufficiently small values of the chirality parameter, the geometrical optics rays can be calculated as for a chiral media and the main effect of the chirality is rotation of polarization along the ray. Thus, adding chirality to inhomogeneous lens antennas, their polarization properties can be improved. As an example, the Maxwell fish-eye lens is analyzed and two possible expressions for a chirality distribution capable of eliminating the inherent cross polarization, are derived.
43 citations
TL;DR: In this article, an accurate numerical solution of the plane wave diffraction by an infinite strip grating is presented, where the incident wave propagates in an arbitrary direction and is arbitrarily polarized.
Abstract: An accurate numerical solution of the plane wave diffraction by an infinite strip grating is presented, where the incident wave propagates in an arbitrary direction and is arbitrarily polarized We derive a set of singular integral equations and solve it by the moment method, where the Chebyshev polynomials are chosen for the basis and the testing functions The edge condition is incorporated in the expansion of the unknown functions in order to accelerate the convergence A decomposition of the kernel into a singular and a regular part enables us to avoid the relative convergence phenomenon Numerical results show the accuracy of the present method Some numerical examples are presented for the polarization discrimination characteristics and surface current distributions
40 citations
TL;DR: In this paper, a detailed moment method simulation of wave scattering from a computer generated-dielectric rough surface in two-dimensional space is given, and the validity of the numerical algorithm is verified by comparing simulation results with Kirchhoff and first order small perturbation theory at their valid regions.
Abstract: The detailed moment method simulation of wave scattering from a computer generated-dielectric rough surface in two-dimensional space is given. The validity of the numerical algorithm is verified by comparing simulation results with Kirchhoff and first order small perturbation theory at their valid regions. The efficiency and versatility of the numerical simulation algorithm as a practical tool to study rough surface scattering is demonstrated. It is found that the Kirchhoff series solution always gives an estimate that is between the VV and HH polarizations for both Gaussian and composite surface if the correct correlation function is used. It is also found that for a single scale surface, the effect of increasing frequency on the backscattering coefficient is to gradually diminish the VV and HH polarization separation from that of Perturbation to Kirchhoff. For surfaces with distinctively different roughness scales, the frequency behavior of the backscattering coefficient depends on the dominance of indi...
37 citations
TL;DR: In this paper, strong permittivity fluctuation theory is used to solve the problem of scattering from a medium composed of completely randomly oriented scatterers under a low frequency limit.
Abstract: Strong permittivity fluctuation theory is used to solve the problem of scattering from a medium composed of completely randomly oriented scatterers under a low frequency limit. Gaussian statistics are not assumed for the renormalized scattering sources. Numerical results on effective permittivity are illustrated for oblate and prolate spheroidal scatterers and compared with the results for spherical scatterers. The results are consistent with discrete scatterer theory. The effective permittivity of a random medium embedded with nonspherical scatterers shows a higher imaginary part than the spherical scatterer case with equal correlation volume. Under the distorted Born approximation, the polarimetric covariance matrix for the backscattered electric field is calculated for half-space randomly oriented scatterers. The nonspherical geometry of the scatterers shows significant effects on the cross-polarized backscattering returns, and the correlation coefficient between HH and VV returns. The polarimetric backscattering coefficients can provide useful information in distinguishing the geometry of scatterers.
35 citations
TL;DR: In this article, the Ewald sphere representation for the Fourier space data in the monostatic and bistatic frequency diversity imaging is described, and it is shown that the reconstruction method is equivalent to the backprojection method.
Abstract: The Ewald sphere representation for the Fourier space data in the monostatic and bistatic frequency diversity imaging is described. From that representation we prove that the Fourier transform reconstruction method is equivalent to the backprojection method. Prediction of an image obtained by the Fourier transform method can be simplified in two steps: first obtaining the range profile at each aspect, and then graphically back-projecting the range profile of each aspect to the image plane along the directions normal to the bisection line. Accordingly, any object image given specified imaging scheme and spectral and angular windows can be predicted. The monostatic image and the bistatic image can look similar if the angular windows utilized in the two imaging schemes are suitably chosen. However, the monostatic image has better resolution. Numerical results verify our interpretation.
TL;DR: In this article, second order boundary conditions are derived for a three-layer dielectric coating on perfectly conducting cylindrical structures and integral equations are presented based on the derived conditions.
Abstract: Higher order boundary conditions involve derivatives of the fields beyond the first and were recently shown to be more effective than the traditional first order conditions in modeling dielectric coatings and layers In this paper we derive second order boundary conditions simulating a three-layer coating on perfectly conducting cylindrical structures Both E and H polarizations are considered and integral equations are presented based on the derived conditions A moment method implementation of the resulting integral equation(s) is given and results are presented for various coatings illustrating the accuracy of the higher order conditions
TL;DR: In this paper, the diffusion de feuilles d'impedances et resistances planaires, avec des variations uni-dimensionnelles, is studied, and a solution approximative, en utilisant une technique de perturbation dans la transformee de Fourier, is presented.
Abstract: On etudie la diffusion de feuilles d'impedances et resistances planaires, avec des variations uni-dimensionnelles. On obtient une solution approximative, en utilisant une technique de perturbation dans la transformee de Fourier. On donne sous une forme recursive, la solution pour le courant induit sur la feuille en fonction de la fonction de resistivite
TL;DR: Focusing properties of dipole arrays placed near a three-layer lossy sphere are investigated analytically in this paper, where an exact solution is obtained employing the spherical wave functions and the multilayer sphere is used to model the human head.
Abstract: Focusing properties of dipole arrays placed near a three-layer lossy sphere are investigated analytically An exact solution is obtained employing the spherical wave functions The multilayer sphere is used to model the human head to investigate the feasibility of employing external dipole arrays in hyperthermia applications Several array geometries and current excitations are considered operating at 432 and 915 MHz
TL;DR: In this article, an absorbing boundary condition for an arbitrary outer boundary is introduced for the purpose of truncating the unbounded region surrounding the transmission line in an efficient manner, and the application of the boundary condition is illustrated for three different microstrip line configurations, viz., a single line, two coupled lines, and a six-conductor line.
Abstract: Open microwave transmission line structures are analyzed in this paper in the quasi-TEM regime using the finite element method. An absorbing boundary condition (ABC) for an arbitrary outer boundary is introduced for the purpose of truncating the unbounded region surrounding the transmission line in an efficient manner. The application of the boundary condition is illustrated for three different microstrip line configurations, viz., a single line, two coupled lines, and a six-conductor line. Numerical results are compared with those published elsewhere and good agreement is found.
TL;DR: In this paper, a modified pseudo-differential operator approach is employed to derive absorbing boundary conditions for both circular and elliptical outer boundaries, which leads to a condition equivalent to that of Bayliss and Turkel's second-order condition.
Abstract: Finite difference methods are becoming increasingly popular in the computational electromagnetics community. A major issue in applying these methods to electromagnetic wave scattering is to limit the computational domain to a finite size, which is accomplished by selecting an outer boundary and imposing absorbing boundary conditions to simulate free space. In this paper, the pseudo-differential operator approach is employed to derive absorbing boundary conditions for both circular and elliptical outer boundaries. The pseudo-differential operator approach employed by Engquist and Majda is modified to derive improved absorbing boundary conditions. In the case of the circular outer boundary, the modified pseudo-differential operator approach leads to a condition equivalent to that of Bayliss and Turkel's second-order condition. The modified pseudo-differential operator is then used to derive the second-order absorbing boundary condition for the elliptical outer boundary. The effectiveness of the second-order...
TL;DR: In this article, the reflection coefficient for the TEM mode of the coaxial line sensor is calculated using an integral formula for the tangential magnetic field at the aperture, and the concept of the surface impedance is used to decouple the internal and external field problems.
Abstract: The analysis of the open-ended coaxial line sensor is presented. The reflection coefficient for the fundamental TEM mode of the coaxial line is calculated using an integral formula for the tangential magnetic field at the aperture. Properties of the Fourier-Bessel expansion are used to determine field distributions of the aperture. The concept of the surface impedance is used to decouple the internal and external field problems. The results of the analysis are compared with the experimental data obtained for sensors immersed in distilled water.
TL;DR: In this paper, a pole shifting technique on the Poincare sphere is used to develop a theory of the polarization diversity system for any polarization basis, and formulas for backscatter coefficients and null locations are found to be universal.
Abstract: A pole shifting technique on the Poincare sphere is used to develop a theory of the polarization diversity system for any polarization basis. Referred to the appropriate frame of reference, formulas for backscatter coefficients and null locations are found to be universal. The procedure leads to an independent derivation of the conditions for maximum and minimum power return and for the polarization "fork" for reciprocal targets. Also included is a brief discussion of the theory of non-reciprocal backscatter measurements.
TL;DR: In this paper, a first approach is presented for estimating the improvement in rain outage performance caused by triple-site diversity protection, based on the lognormal assumption for the point rainfall rate distribution at the location under consideration.
Abstract: In heavy rain climatic regions (e.g., climatic zones F, H, K, L, M, N, P given by C.C.I.R.) attenuation caused by rain presents a great problem for satellite communications, at frequencies above 10 GHz. Double-site diversity is an available method to reduce the rain outage time for these systems. In some severe cases, double-site protection can be proved to be inadequate and consequently triple-site diversity becomes indispensable. In this paper, a first approach is presented for estimating the improvement in rain outage performance caused by triple-site diversity protection. The method is based on the lognormal assumption for the point rainfall rate distribution at the location under consideration. Experimental results taken from some parts of the United States such as New Jersey, Florida and Atlanta, Georgia are compared with the theoretical values and the agreement was found to be encouraging.
TL;DR: In this paper, the phase perturbation technique is numerically examined in the case of scalar waves scattered by one-dimensional normally distributed random rough surfaces, on which Dirichlet boundary conditions hold.
Abstract: The phase perturbation technique is numerically examined in the case of scalar waves scattered by one-dimensional normally distributed random rough surfaces, on which Dirichlet boundary conditions hold. Particular attention is devoted to surfaces for which the Rayleigh parameter has intermediate or large values. It is shown that the considered method is not limited to either small roughness or gentle undulations. It is demonstrated that the phase perturbation technique smoothly interpolates between the two classical approximations, namely the perturbation approach and the Kirchhoff method. The cases in which the phase perturbation theory converges to physical optics are characterized by large values of the Lynch parameter. A conclusion is drawn that the phase perturbation technique is amenable to surfaces whose roughness spectra are wide. Asymptotic expansions, simplifying the evaluation of the phase perturbation backscattering cross-section in the high roughness limit are derived.
TL;DR: In this paper, an alternative representation of the Green's functions is presented for broad wall slot analysis, which is based on a Fourier transform in the direction along the guide and Fourier series in one of the transverse directions.
Abstract: The representation of the Green's functions normally used in rectangular waveguide analysis is based on Fourier series analyses in the two transverse directions. This paper presents an alternative form particularly suited for broad wall slot analysis. It is based on a Fourier transform in the direction along the guide and a Fourier series in one of the transverse directions. It is superior to the conventional form because it simplifies the z-dependence of the Green's functions, thus simplifying the convolution of these functions with method of moments basis and testing functions. This paper also shows how to use the alternative representation to find the conventional series representation of the convolutions. For many slot geometries this approach is actually easier than the conventional method. The alternative form also has educational benefit because the boundary conditions, relating magnetic current and the tangential electric field in any plane parallel to the broad wall, are more readily seen.
TL;DR: In this article, an approximate solution for the spatial Fourier transform (in the axial direction) of the Sommerfeld type integrals for axial and vertical electric fields from a current on a thin wire of infinite length above lossy earth is derived.
Abstract: Approximate solutions for the spatial Fourier transform (in the axial direction) of the Sommerfeld type integrals for the axial and vertical electric fields from a current on a thin wire of infinite length above lossy earth are derived These solutions are valid over a wide band of frequencies (1 Hz - 1 GHz) and for distances from field points to the wire which are essentially unrestricted, as well as for a wide range of values of the Fourier transform variable, γ Calculations based on these solutions are shown to be consistent with numerical integrations of the exact integrals The method used in this paper can be easily used to find solutions for other field components
TL;DR: In this paper, the authors considered the scattering of electromagnetic wave from fractally fluted dielectric and conducting cylinders and found closed-form perturbation solutions using procedures similar to the Debye method.
Abstract: We consider the scattering of electromagnetic wave from fractally fluted dielectric and conducting cylinders. The azimuthal variation of the cylinder surface is described by a bandlimited fractal function. We find closed-form perturbation solutions using procedures similar to the Debye method. Connections between the scattering distribution of the fields and fractal descriptors of the fluted cylinders are discussed.
TL;DR: In this paper, various experimental methods have been used to measure the real (permittivity e') and imaginary (dielectric loss e″) components of the complex permittivity of high loss liquids at microwave frequencies.
Abstract: This paper reviews the various experimental methods that have been used to measure the real (permittivity e') and imaginary (dielectric loss e″) components of the complex permittivity of high loss liquids at microwave frequencies. These methods can be classified as being in either the frequency- or the time-domain. The sample cells used are either reflection or transmission and of either fixed- or variable- length. The achievable accuracy at 9 GHz has been 1% until recently when a new instrumentation system has been described which makes it possible to attain a 1 σ precision of ∼0.01%. This system uses either a variable-length transmission or reflection sample cell and consists of a dual channel, double superheterodyne signal processing system which coherently transfers the phase and amplitude information from 9 GHz to 60 MHz and then to 1 kHz. The amplitude and phase can be measured to 2% at 9 GHz but to about 0.001 dB and 0.01 ° at 1 kHz. The details of this system and the factors that limit the precisi...
TL;DR: A technical concept for an X-band phased array synthetic aperture radar mounted on a polar orbiting satellite and the interdependency of various parameters, such as geometric resolution, swath width and off-nadir angle, is shown.
Abstract: This paper presents a technical concept for an X-band phased array synthetic aperture radar mounted on a polar orbiting satellite The interdependency of various parameters, such as geometric resolution, swath width and off-nadir angle, is shown as well as their influence on the sensitivity of the system A description is given of the layout of the phased array system with a new dual polarized slotted waveguide array and attached GaAs transmit/receive modules The antenna pattern is investigated for specified scanning ranges in elevation and azimuth direction Descriptions are given of a possible high resolution mode (azimuth look steering mode) and a survey mode (scan SAR) Future SAR systems require a high stability in their system parameters or, at least, the possibility of calibrating their performance in an operational mode External and internal radiometric calibration procedures are discussed A method which monitors 64 sub-arrays and can be relatively easily implemented is suggested for internal c
TL;DR: In this paper, an integro-differential equation for backscattering from a vegetative layer consisting of a mixture of randomly orientated discrete scatterers is modelled using the radiative transfer theory.
Abstract: Electromagnetic backscattering from a vegetative layer consisting of a mixture of randomly orientated discrete scatterers is modelled using the radiative transfer theory. For simplicity, the layer is assumed to be bounded at the bottom by a planar half-space. Circular disks are used to model the leaves while prolate ellipsoids are used to model the stems and small branches. The integro-differential equations are then solved using an iteration method. A first order solution is explicitly given. The results are compared with measurements from fields of soybean, corn, wheat and milo. To show the interactions between scatterers, a second order solution for a half-space of mixed scatterers is also given. It is found that interactions between scatterers appear in the form of extinction coefficients and cross products of phase matrices of the components of the mixture.
TL;DR: An accurate analysis of planar aperture sectoral horns is presented, based on a simple adaptation of the mode matching technique, which allows for the inclusion of the aperture effect in the analysis without resorting to the conventional integral equations formulation.
Abstract: An accurate analysis of planar aperture sectoral horns is presented. It is based on a simple adaptation of the mode matching technique, which allows for the inclusion of the aperture effect in the analysis without resorting to the conventional integral equations formulation. This technique provides accurate results, which are confronted with experiments and then used in a parametric study of the sectoral horns, aimed at achieving a constant beamwidth over an octave bandwidth or more. It is concluded that for the narrow E- plane aperture horn this objective is hard to attain, hence a different, convex aperture antenna is used. Experimental design of this configuration leads to the desired performance of a nearly constant beamwidth over more than an octave.
TL;DR: In this paper, a nonlinear renormalization technique is implemented for the one-dimensional inverse scattering in the time-domain, which is tested with both band-limited and noisy data.
Abstract: A nonlinear renormalization technique is implemented for the one-dimensional inverse scattering in the time-domain. This algorithm, which is approximate but highly accurate, is tested with both bandlimited and noisy data. The merits of this algorithm are its ease of implementation, increased understanding of the scattering process, and its robustness to noise corruption and bandwidth limitations. Several examples are shown to demonstrate the effectiveness of the algorithm.
TL;DR: In this article, a waveguide mechanism for the whistler wave propagation along the earth's magnetic field in the low-latitude ionosphere near the F-layer maximum is proposed.
Abstract: A waveguide mechanism for the whistler wave propagation along the earth's magnetic field in the low-latitude ionosphere near the F-layer maximum is proposed. The particular properties of the ionospheric waveguide characterized by very high values (600 ∼ 800) of the refractive index, are studied. It is shown that waves in the frequency range 1 ∼ 3 kHz can be used for direct communication between two satellites. New possibilities for global diagnostics of the effective thickness of the F-layer are discussed. Contrary to the traditional local sounding techniques, the method proposed in this paper can be used for global diagnostics of the F-layer parameters averaged in the meridional direction over distances smaller than 2 x 103 km during times of the order of 3∼5 seconds.
TL;DR: In this article, the authors deduced the currents induced in parallel wires in an interface for an incident plane wave with the electric vector parallel to the wires, expressed in terms of the modified Bessel function K1 of generally complex argument.
Abstract: The currents induced in parallel wires in an interface are deduced for an incident plane wave with the electric vector parallel to the wires. The results are expressed in terms of the modified Bessel function K1 of generally complex argument.