Showing papers in "Journal of Electromagnetic Waves and Applications in 1993"
TL;DR: In this paper, a finite-difference time-domain (FDTD) method is used to obtain numerical solutions without resorting to frequency-domain analysis and Fourier transformation.
Abstract: Scattering of electromagnetic waves from periodic surfaces is considered in time-domain for an oblique angle of incidence. The finite-difference time-domain (FDTD) method is used to obtain numerical solutions without resorting to frequency-domain analysis and Fourier transformation. For the application of FDTD method to the oblique incidence case, Maxwell's equations are transformed such that the computational domain can be truncated by using periodic boundary conditions. The FDTD method is then used to solve the transformed equations. In solving the transformed equations by the FDTD method, the absorbing boundary conditions are modified and the eigenvalues of the system are determined for the stability analysis. The final results are obtained by using the inverse transformation. Since the transformation is very simple, the computational time is primarily determined by the FDTD solution of the transformed equations. The theoretical results are illustrated by calculating the scattered fields in the computa...
129 citations
TL;DR: In this article, an iterative scattering technique is developed to evaluate both the near and far fields due to any arbitrary number of interactions between the cylinders, where cylinders are made of homogeneous, isotropic dielectric material, perfectly conducting material, or a combination thereof.
Abstract: The scattering of a Gaussian beam by an array of parallel circular cylinders is investigated using an iterative scattering procedure. The cylinders are made of homogeneous, isotropic dielectric material, perfectly conducting material, or a combination thereof. The iterative scattering technique is developed to evaluate both the near and far fields due to any arbitrary number of interactions between the cylinders. The technique starts with the exact series representation of the initial scattered fields from each cylinder due to the incident Gaussian beam. Then, the sum of the initial scattered fields from all cylinders is considered to be the field of an incident wave on each individual cylinder. The additional scattered field contribution is then obtained and successive scattering takes place until the boundary conditions on the surface of every cylinder are satisfied. An error criterion is developed to predict the number of iterations required to satisfy certain predetermined percentage error in the near...
79 citations
TL;DR: In this article, a banded matrix iterative approach is applied to study scattering of a TE incident wave from a perfectly conducting one-dimensional random rough surface, which is much faster than the full matrix inversion approach or the conjugate gradient method.
Abstract: A banded matrix iterative approach is applied to study scattering of a TE incident wave from a perfectly conducting one-dimensional random rough surface. It is much faster than the full matrix inversion approach or the conjugate gradient method. When compared to the Kirchhoff iterative approach, it is of comparable CPU time, and works for cases when the Kirchhoff iteration is erroneous. The method is illustrated for a variety of parameters with particular application to large scale rough surface problems. The largest surface length used is 400 wavelengths with 3200 unknowns, and all the coherent wave interactions are included within the entire surface length. The accuracy of the banded iterative approach is demonstrated by showing that the results overlie those of the exact matrix inversion and the conjugate gradient method. The numerical method is also easy to implement. With this approach, we are able to compute the new response characteristics of composite rough surfaces with much larger scales. The ca...
67 citations
TL;DR: In this paper, two efficient ways of calculating the vector addition theorem are presented, one of which is derived by relating the coefficients of vector addition to that of the scalar addition theorem for which an efficient recurrence relation exists.
Abstract: Two efficient ways of calculating the vector addition theorem are presented. One is obtained by relating the coefficients of the vector addition theorem to that of the scalar addition theorem for which an efficient recurrence relation exists. The second way is to derive recurrence relations directly for the coefficients of the vector addition theorem. These new ways of calculating the coefficients are of reduced computational complexity. Hence, when the number of coefficients required is large, the present methods are many times faster than the traditional method using Gaunt coefficients and Wigner 3j symbols.
54 citations
TL;DR: In this paper, the authors developed a fully polarimetric minimum mean square error (MMSE) filter under the multiplicative speckle noise model assumption for one-look images.
Abstract: The usual polarimetric speckle filters optimally combine the polarization channels into a single image [10] or only restore the radiometric information [8], i.e., only the four Ihh, Iυυ,Ιhυ and Iυh backscattered intensities (or the three Ihh, Iυυ, Ihυ intensities in the reciprocal case). The phase differences for one-look images are not restored. This implies a loss of information compared to the initial data, which contain five independent real parameters plus one absolute phase for the one-look scattering matrix format in the reciprocal case. In this paper we develop a fully polarimetric minimum mean square error (MMSE) filter under the multiplicative speckle noise model assumption for one-look images. This model assumes the data to be the product of the non-stationary "unspeckled" signal by statistically independent speckle noise, characterized by the covariance matrix of a stationary complex multivariate Gaussian random process, representing the sensor effects. For each pixel, one obtains on output of...
47 citations
TL;DR: It is shown that the ISAR image can be reconstructed by Fourier inversion of the bistatic scattered field data under the physical optics approximation.
Abstract: The feasibility of utilizing bistatic scattered field data to obtain the microwave ISAR image of a target is investigated. The principle and results of the bistatic imaging algorithm are presented. It is shown that the ISAR image can be reconstructed by Fourier inversion of the bistatic scattered field data under the physical optics approximation. Bistatic scattered field data is faster to simulate using the shooting and bouncing ray technique than monostatic scattered field data hence the bistatic scheme results in time savings. Monostatic and bistatic ISAR images are presented for different targets. The tradeoff between time savings and image fidelity for the two schemes is discussed.
40 citations
TL;DR: In this paper, the authors considered the transient scattering of an electrically polarized, two-dimensional, pulsed wave by a two-dimensionally inhomogeneous, lossy dielectric cylinder embedded in free space.
Abstract: We consider the transient scattering of an electrically polarized, two-dimensional, pulsed wave by a two-dimensionally inhomogeneous, lossy dielectric cylinder embedded in free space. The problem is formulated in terms of a contrast-source domain integral equation over the interior of the cylinder. This integral equation is solved numerically, with the aid of the "marching-on-in-frequency" method recently proposed in [1]. To this end, a new discretization procedure is introduced, which is more accurate than the usual piecewise-constant moment-method approach. This discretization preserves the convolution-type structure of the continuous equation, which enables the repeated application of the "conjugate-gradient FFT" method. The initial estimates required in this method are generated by marching on in frequency, using a special extrapolation scheme. Numerical results are presented and compared with the results obtained by applying alternative techniques.
38 citations
TL;DR: In this paper, a method of retrieving a temperature-depth profile in biological object from a set of multi-frequency microwave radiometric data has been developed, which is a combination of model-fitting and Monte Carlo techniques and is capable of estimating a profile and its confidence interval as a function of the depth.
Abstract: A method of retrieving a temperature-depth profile in biological object from a set of multi-frequency microwave radiometric data has been developed. The method is a combination of model-fitting and Monte Carlo techniques and is capable of estimating a profile and its confidence interval as a function of the depth. We use 2σ -intervals as a measure of the precision of tissue temperature measurements. The method was tested and supported by an experiment in which temperature distributions in a muscle equivalent agar phantom were measured using a 5-band, 1-3.8 GHz radiometer with the brightness temperature resolution of 0.05-0.07 K. A typical result of the experiment showed that 2σ -intervals were 1 K or less for 0 < z < 3 cm, 1.4 K at z = 4 cm, and 3 K at z = 5 cm. A numerical simulation study was made using this technique to assess effects of the selection of measurement frequencies, number of frequency bands, brightness temperature resolution of radiometer and thickness of fat layer on the precision. Resul...
35 citations
TL;DR: In this paper, a formulation for the dyadic Green's function of cylindrical multilayered chiral media is presented at first using the methods of eigenfunction expansion and scattering superposition.
Abstract: In this paper, a formulation for the dyadic Green's function of cylindrical multilayered chiral media is presented at first using the methods of eigenfunction expansion and scattering superposition. The specific expressions of the dyadic Green's function are also found in terms of normalized cylindrical vector wave functions, when the electric current sources are placed both inside and outside of a chiral circular cylinder and a cylindrical chirodome. The radiation characteristics of a point dipole antenna on the axis of chiral circular cylinder and cylindrical chirodome are analysed. For both cases, the results show that by changing the size of chiral circular cylinder, the thickness of cylindrical chirodome and the parameters of chiral media, purely circular and linear polarization can be obtained in the far field. Also, the expressions of dyadic Green's function given in this paper can be directly used to analyse the radiation characteristics of cylindrical chirostrip antennas.
32 citations
TL;DR: In this article, the angular dependence of the back scattered signal power from anisotropic turbulent inhomogeneities is described in Born approximation with the help of the power spectrum model with constant anisotropy.
Abstract: A study is done for the angular dependence of the back scattered signal power from anisotropic turbulent inhomogeneities which is described in Born approximation with the help of the power spectrum model with constant anisotropy. The aspect sensitivity obtained theoretically are compared with published data and estimations are made of the anisotropy coefficient in the low and middle atmosphere.
30 citations
TL;DR: In this paper, the theoretical behavior of TE-plane wave scattering from a dielectric-loaded semicircular trough in a conducting half-space is investigated, and the difference between the TE and TM-scattering angular patterns is also observed.
Abstract: The theoretical behavior of TE-plane wave scattering from a dielectric-loaded semicircular trough in a conducting half-space is investigated. The dielectric loading is made of a circular cylinder which is partially buried in a semi-circular trough in a perfectly conducting plane. The scattered field is numerically evaluated to investigate the angular scattering pattern under the various dielectric loading conditions. The presence of the dielectric loading in the trough can substantially affect the angular scattering behavior. The difference between the TE and TM-scattering angular patterns is also observed. The field magnitude inside the trough is found to be much greater than the outside, thus indicating that the trough focuses the incident beam inside the trough.
TL;DR: In this article, a four-frequency microwave radiometer system has been tested on a two-dimensional thermal phantom consisting of a hotter tube embedded eccentrically in a colder circular container simulating a cylindrical body region with an inhomogeneous temperature distribution.
Abstract: Due to the interest in the non-invasive measurement of subcutaneous temperature, a four-frequency microwave radiometer system has been tested on a two-dimensional thermal phantom consisting of a hotter tube embedded eccentrically in a colder circular container simulating a cylindrical body region with an inhomogeneous temperature distribution. It is shown that measured radiometric data agree with a theoretical model of the electromagnetic radiation from thermal structures. An equation for retrieving temperature distributions in homogeneous circular cylinders has been obtained by taking regularity properties of temperature functions into account. Results of temperature reconstructions from both measured and synthetic data are reported showing the capability of the method.
TL;DR: In this paper, a mixed boundary value problem is formulated for the surface currents induced by a time-harmonic plane wave incident upon an open-ended conducting tube of finite length.
Abstract: A mixed boundary value problem is formulated for the surface currents that are induced by a time-harmonic plane wave incident upon an open-ended conducting tube of finite length. Scattered fields are represented by spatial Fourier transforms in the axial dimension for each of the uncoupled azimuthal Fourier modes of this body of revolution. Numerically efficient mathematical expressions having explicit physical significance are derived to solve the set of linear equations from a Galerkin expansion of the currents in terms of Chebyshev polynomials with edge-condition weighting. Resultant surface currents and axial fields are calculated for several combinations of scatterer geometry and frequency, and interpreted partially in terms of travelling waves external and internal to the conducting cylinder.
TL;DR: In this article, a vector transmission-line theory is introduced for problems involving plane wave propagation, reflection and transmission in multilayered general bi-isotropic (BI) structures, where the structure is replaced by a transmission line with vector voltage and current quantities and dyadic line parameters.
Abstract: Vector transmission-line theory is introduced for problems involving plane wave propagation, reflection and transmission in multilayered general bi-isotropic (BI) structures. The structure is replaced by a transmission line with vector voltage and current quantities and dyadic line parameters. The characteristic admittance and propagation factor are both dyadic quantities, which have different expressions for waves propagating in opposite directions along the transmission line. Vector circuit theory, developed earlier for plane-wave propagation and reflection problems in layered chiral and general BI structures, is formulated in terms of vector transmission line parameters. The theory is verified by checking special cases. It is claimed that, with the present formalism, analysis can be done more systematically, with less effort and particular results can be memorized more easily than when operating with scalar component quantities. Numerical examples show new and interesting results indicating possible ap...
TL;DR: The method of exact eigenfunctions has proven to be effective for the scalar grating problem as mentioned in this paper, which makes it worthwhile to apply the method to vectorial grating problems.
Abstract: The method of exact eigenfunctions has proven to be effective for the scalar grating problem. This makes it worthwhile to apply the method to the vectorial grating problem, also referred to as the ...
TL;DR: In this paper, a modal method is used for the determination of the near field weighting functions related to the power transmitted from a rectangular waveguide aperture towards a lossy material and, by reciprocit...
Abstract: A modal method is used for the determination of the near field weighting functions related to the power transmitted from a rectangular waveguide aperture towards a lossy material and, by reciprocit...
TL;DR: In this paper, the reflection and transmission of waves on a nonuniform LCRG transmission line of finite length with frequency-dependent parameters are considered and a Green function technique combined with wave splitting is used both in the frequency domain and the time domain.
Abstract: The reflection and transmission of waves on a nonuniform LCRG transmission line of finite length with frequency-dependent parameters are considered. A Green function technique combined with wave splitting is used both in the frequency domain and the time domain. In the frequency domain ordinary differential equations (ODEs) for the time-harmonic Green functions are obtained. In the time domain the transmission line model is established through a set of dispersion kernels. Partial differential equations (PDEs) for the time-domain Green functions are derived. Numerical results for transient reflected, transmitted and internal currents are presented. Furthermore, it is noted that a special case of the present formalism can be used to determine the reflected, transmitted and internal fields for normal plane wave incidence on a stratified dispersive and dissipative slab.
TL;DR: In this paper, a layer model is developed and applied to interpret radar backscattering coefficients at 5.3 GHz for a soybean canopy, where the canopy is modeled as a random medium containing spheroidal scatterers for the leaves.
Abstract: A layer model is developed and applied to interpret radar backscattering coefficients at 5.3 GHz for a soybean canopy. The canopy is modeled as a random medium containing spheroidal scatterers for the leaves. The data were taken over an extended time period from early to late stage of the vegetation. The theoretical results and the experimental data are in good agreement. The lateral correlation length is observed to be highly correlated with the canopy fractional volume. With consideration of the interrelations among biophysical parameters, the model is then used to simulate backscattering coefficients under various conditions. The results provide sensitivity domains of radar responses to soil moisture and vegetation biomass for inversion assessment. Furthermore, the polarization signatures of the vegetation canopy are synthesized to illustrate structural information conveyed by polarimetric data.
TL;DR: In this paper, the far field (incl. RCS) of a thin square conducting plate is calculated, and the choice of basis functions is crucial for the numerical efficiency, provided the basis functions efficiently approximate the unknown function.
Abstract: The method of moments is used to solve electromagenetic boundary value problems numerically. It is known that the choice of basis functions is crucial for the numerical efficiency. Fast convergence is achieved provided the basis functions efficiently approximate the unknown function. In this paper the far field (incl. RCS) of a thin square conducting plate is calculated. Basis functions with correct edge and corner singularities are shown to greatly enhance the convergence compared to ordinary "rooftop" functions. The calculations of the matrix elements as well as the right side of the matrix equation and the scattered field are simplified by the use of a multipole technique.
TL;DR: In this article, a systematic development of three distinct mixedpotential integral equations for the analysis of printed circuits, microstrip resonators, and antennas embedded in multi-layered, planar, uniaxial media of infinite lateral extent, with emphasis on microstrip structures comprising non-planar conductors of irregular or arbitrary shapes.
Abstract: A systematic development is presented of three distinct mixed-potential integral equations for the analysis of printed circuits, microstrip resonators, and antennas embedded in multi-layered, planar, uniaxial media of infinite lateral extent, with emphasis on microstrip structures comprising non-planar conductors of irregular or arbitrary shapes.
TL;DR: In this article, two approaches based on the Born approximation are presented: a differential reconstruction method which allows to visualize dielectric alterations and a matched synthesis method intended to minimize the distortion suffered by the illuminating field within the body.
Abstract: In this work the active tomographic imaging of biological bodies which exhibits a high dielectric contrast is studied. Two approaches based on the Born approximation are presented: a differential reconstruction method which allows to visualize dielectric alterations and a matched synthesis method intended to minimize the distortion suffered by the illuminating field within the body. The presented techniques have been investigated by numerical simulations and experimentally in a cylindrical tomographic microwave system recently developed, considering the possible applications like Hyperthermia treatment monitoring in cancer.
TL;DR: In this article, the emissivity of snowpack has been calculated by a quasi-static method and by applying the equation of radiative transfer, taking into account the physical-mechanical properties of the real snowpack obtained by direct glaciological methods.
Abstract: Microwave radiometers, operating at 3.95, 19.5, 37.5 and 150 GHz and placed in a tower, were used for snow measurements during the winters of 1985-1989. The effects of snow structure, wetness, and grain size were examined in detail. The emissivity of snowpack has been calculated by a quasi-static method and by applying the equation of radiative transfer. The latter takes into account the physical-mechanical properties of the real snowpack obtained by direct glaciological methods. The experimental data are compared against theoretical results. The quasistatic model is shown to be adequate for f < 20 GHz whereas the radiative transfer model agrees for f < 150 GHz, especially when the size distribution of ice particles in snow is included.
TL;DR: In this article, a new formulation of the Stratton-Chu scattering problem was proposed, in which the six boundary unknowns are the electric field and its normal derivative, and three of the four 3 x 3 block matrices are diagonal.
Abstract: In all exact versions of scattering from a rough dielectric interface, six boundary unknowns must be found. In the Stratton-Chu equations, for example, the unknowns are the electric field (tangential and normal to the interface) and the boundary electric currents. Once determined, they are used to evaluate the three components of the scattered field and the three components of the transmitted field. The 6 x 6 operator matrix to be inverted consists of four 3 x 3 block matrices, two of which are diagonal. The other non-diagonal matrices describe the coupling. We describe a new formulation of this scattering problem in which the six boundary unknowns are the electric field and its normal derivative. In this formalism, three of the four 3 x 3 block matrices are diagonal. All the coupling resides in the fourth block.
TL;DR: In this paper, the problem of reconstructing a strongly scattering object, consisting of a small unknown perturbation to a known background object, from scattered field data using the Distorted-Wave Born approximation is considered.
Abstract: We consider the problem of reconstructing a strongly scattering object, consisting of a small unknown perturbation to a known background object, from scattered field data using the Distorted-Wave Born approximation. Assuming that the background object comprises an homogeneous cylinder we develop a filtering operation on the data allowing a Fourier transform relation to be established between the filtered data and unknown object similar to that between the scattering object and data within the Born approximation. This allows the unknown perturbation to be reconstructed using approaches already developed for the Born approximation. The behaviour of the algorithm is illustrated by numerical examples.
TL;DR: This paper uses range profiles as the feature vectors for data representation, and uses the matching score method and the neural network approach to automatically identify aerospace objects and proposes a centroid-aligned method to overcome the range shift problem.
Abstract: In this paper we use range profiles as the feature vectors for data representation, and use the matching score method and the neural network approach to automatically identify aerospace objects. The backpropagation model is employed in the neural network approach to train a neural network. Recognition performances with different training methods are compared and discussed. Experimental results show that the neural network approach has a little greater capability in identifying similar feature vectors and has stronger immunity to Gaussian noises than the matching score method does in certain cases. However, the latter method is range-shift invariant while the former method may fail to recognize a shifted feature vector. We propose a centroid-aligned method to overcome the range shift problem. Simulated results show that this method is simple and effective.
TL;DR: In this paper, the inversion of resistivity data was used to solve the resolution of a thin sandwiched layer employing DC resistivity or electromagnetic (EM) sounding methods, which is a tricky problem and often eludes adequate detectability.
Abstract: Resolution of a thin sandwiched layer employing DC resistivity or electromagnetic (EM) sounding methods is a tricky problem and often eludes adequate detectability. The inversion of resistivity dat...
TL;DR: In this article, different methods for controlling the coupling between a two-conductor microstrip transmission line are investigated based on the equivalence principle, a free space Green's function, and the method of moments.
Abstract: Different methods for controlling the coupling between a two-conductor microstrip transmission line are investigated in this paper. The transmission line consists of two thin perfectly conducting strips with a rectangular notch between the strips, two layers of dielectric substrate, and a dielectric overlay. The formulation and solution technique are based on the equivalence principle, a free space Green's function, and the method of moments. It has been found that the coupling between the conducting lines can be reduced significantly if dielectric material between the lines is removed. Further reduction in coupling is observed when the relative permittivity of the upper substrate layer is made smaller than that of the lower substrate. Coupling can be maximized if the notch is filled with dielectric material having large relative permittivity compared to that of the substrates. If the strips are covered with a dielectric overlay (or superstrate), the coupling will be substantially increased. Moreover, wit...
TL;DR: In this article, the high frequency electromagnetic diffraction by a finite length resistive strip attached to a wedge with equal impedance faces is considered, where the problem considered is two dimensional where the in...
Abstract: The high frequency electromagnetic diffraction by a finite length resistive strip attached to a wedge with equal impedance faces is presented. The problem considered is two dimensional where the in...
TL;DR: In this paper, the experimental results on the subsurface radars are described and several new techniques including noise and clutter rejection techniques are introduced in order to develop a sub-surface radar which has high target resolution, extended range and clear image.
Abstract: Subsurface or underground radars to detect buried object such as gas and water pipes, and to map the underground structure for archeology and mining purposes have been developed since early 1960. This paper describes the experimental results on the subsurface radars. Several new techniques including noise and clutter rejection techniques are introduced in order to develop a subsurface radar which has high target resolution, extended range and clear image. Experimental results are presented to demonstrate improved capabilities.
TL;DR: In this paper, the effects of lossy chiral material on guided electromagnetic waves in parallel-plate waveguides have been discussed theoretically and their guiding properties for lossless chiral materials have been recently studied and reported.
Abstract: In this paper, we discuss theoretically the effects of lossy chiral material on guided electromagnetic waves in parallel-plate waveguides. The guided-wave structures filled with chiral materials have been named chirowaveguides, and their guiding properties for lossless chiral materials have been recently studied and reported in the literature. Here, we extend the analysis of chirowaveguides to the case of lossy chiral materials, and we theoretically investigate the effect of material loss on guided modes in parallel-plate chirowaveguides. Dispersion diagrams for the real and imaginary parts of wave numbers of guided modes along with their electric and magnetic field components are given and the similarities and differences of these quantities with those of the lossless chirowaveguides are addressed. These guided-wave structures can have potential applications in the design of novel devices and components, and in electromagnetic shielding. The associated theoretical analyses for lossy chirowaveguides are s...