Showing papers in "IEEE Transactions on Antennas and Propagation in 1992"
TL;DR: In this article, the authors developed site-specific models based on the number of floors, partitions, and concrete walls between the transmitter and receiver, and provided simple prediction rules which relate signal strength to the log of distance.
Abstract: Qualitative models are presented that predict the effects of walls, office partitions, floors, and building layout on the path loss at 914 MHz. The site-specific models have been developed based on the number of floors, partitions, and concrete walls between the transmitter and receiver, and provide simple prediction rules which relate signal strength to the log of distance. The standard deviation between measured and predicted path loss is 5.8 dB for the entire data set, and can be as small as 4 dB for specific areas within a building. Average floor attenuation factors, which describe the additional path loss (in decibels) caused by floors between transmitter and receiver, are found for as many as four floors in a typical office building. Path loss contour plots for measured data are presented. In addition, contour plots for the path loss prediction error indicate that the prediction models presented are accurate to within 6 dB for a majority of locations in a building. >
977 citations
TL;DR: In this paper, the fast multipole method (FMM) is adapted to the second-kind integral equation formulation of electromagnetic scattering problems in two dimensions, where the number of sample points on the boundary of the scatterer is bounded by the condition number of the discrete system.
Abstract: The fast multipole method (FMM) developed by V. Rokhlin (1990) to efficiently solve acoustic scattering problems is modified and adapted to the second-kind-integral-equation formulation of electromagnetic scattering problems in two dimensions. The present implementation treats the exterior Dirichlet problem for two-dimensional, closed, conducting objects of arbitrary geometry. The FMM reduces the operation count for solving the second-kind integral equation from O(n/sup 3/) for Gaussian elimination to O(n/sup 4/3/) per conjugate-gradient iteration, where n is the number of sample points on the boundary of the scatterer. A sample technique for accelerating convergence of the iterative method, termed complexifying k, the wavenumber, is also presented. This has the effect of bounding the condition number of the discrete system; consequently, the operation count of the entire FMM (all iterations) becomes O(n/sup 4/3/). Computational results for moderate values of ka, where a is the characteristic size of the scatterer, are given. >
434 citations
TL;DR: In this paper, the mathematics of the FD/sup 2/TD method is developed using Z transform theory, which has the advantages of presenting a clearer formulation, and allowing researchers to draw on the literature of systems analysis and signal processing disciplines.
Abstract: The frequency-dependent finite-difference time-domain method (FD)/sup 2/TD method has been shown to be capable of correctly calculating electromagnetic propagation through media whose dielectric properties are frequency dependent. However, as researchers search for more elaborate applications, the formulation of the (FD)/sup 2/TD methods becomes more complex. In this work, the mathematics of the (FD)/sup 2/TD method is developed using Z transform theory. This has the advantages of presenting a clearer formulation, and allowing researchers to draw on the literature of systems analysis and signal processing disciplines. >
408 citations
TL;DR: In this paper, the recursive convolution approach is extended to media with dispersions described by multiple second-order poles, and the significant change from the first-order implementation is that the single backstore variable for each secondorder pole is complex.
Abstract: Previously, a method for applying the finite-difference time domain (FDTD) method to dispersive media with complex permittivity described by a function with a single first-order pole was presented. This method involved the recursive evaluation of a discrete convolution, and was therefore relatively efficient. In this work, the recursive convolution approach is extended to media with dispersions described by multiple second-order poles. The significant change from the first-order implementation is that the single backstore variable for each second-order pole is complex. The approach is demonstrated for a pulsed plane wave incident on a medium with a complex permittivity described by two second-order poles, and excellent agreement is obtained with the exact solution. >
389 citations
TL;DR: In this article, the authors generalized the FDTD method to include the accurate modeling of curved surfaces and proposed the contour path method, which accurately models the illumination of bodies with curved surfaces, yet retains the ability to model corners and edges.
Abstract: The finite-difference-time-domain (FDTD) method is generalized to include the accurate modeling of curved surfaces. This generalization, the contour path CP), method, accurately models the illumination of bodies with curved surfaces, yet retains the ability to model corners and edges. CP modeling of two-dimensional electromagnetic wave scattering from objects of various shapes and compositions is presented. >
349 citations
TL;DR: In this article, the performance of the direct matrix inversion (DMI) method for antenna arrays of arbitrary geometry is analyzed by asymptotic statistical techniques and the effects of eigenspace disturbance caused by finite samples on the output interference and noise powers are examined under the unit gain constraint in the direction of the desired signal.
Abstract: The performance of the direct matrix inversion (DMI) method for antenna arrays of arbitrary geometry is analyzed by asymptotic statistical techniques. The effects of eigenspace disturbance caused by finite samples on the output interference and noise powers are examined under the unit gain constraint in the direction of the desired signal. The results show that the performance of the DMI method is degraded mostly by the disturbed noise subspace. That suggests the use of an eigenspace-based beamformer in which the weight vector is computed by using the signal-plus-interference subspace component of the sample correlation matrix. Convergence properties of the eigenspace-based beamformer are evaluated for the cases in which the source number is known and in which it is overestimated. Theoretical analyses validated by computer simulations indicate that the eigenspace-based beamformer has faster convergence rate than the DMI method. >
284 citations
TL;DR: In this article, an electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents, and the method of moments is used to transform the integral equation into a matrix one.
Abstract: An alternative method is presented for computing far-field antenna patterns from near-field measurements. The method utilizes the near-field data to determine equivalent magnetic current sources over a fictitious planar surface that encompasses the antenna, and these currents are used to ascertain the far fields. Under certain approximations, the currents should produce the correct far fields in all regions in front of the antenna regardless of the geometry over which the near-field measurements are made. An electric field integral equation (EFIE) is developed to relate the near fields to the equivalent magnetic currents. The method of moments is used to transform the integral equation into a matrix one. The matrix equation is solved with the conjugate gradient method, and in the case of a rectangular matrix, a least-squares solution for the currents is found without explicitly computing the normal form of the equation. Near-field to far-field transformation for planar scanning may be efficiently performed under certain conditions. Numerical results are presented for several antenna configurations. >
260 citations
TL;DR: In this paper, a technique called superabsorption is proposed for improving absorbing boundary conditions in finite-difference time-domain methods, which can be applied to every known absorbing boundary condition and greatly reduces the numerical error caused by the boundary reflection.
Abstract: The authors propose a technique, which they call superabsorption, for improving absorbing boundary conditions in finite-difference time-domain methods. This method can be applied to every known absorbing boundary condition and greatly reduces the numerical error caused by the boundary reflection. The principle and analysis of the superabsorption method are presented. Numerical tests indicating the improvements obtained on many absorbing boundary conditions are reported. >
211 citations
TL;DR: A parameterization of the Prony model specific to the radar target identification problem is chosen and several key components to the algorithm, including the use of singular value decomposition and the removal of spurious scattering centers, are presented.
Abstract: A method for characterizing radar signatures using a Prony model is developed based on the concept of scattering centers. A parameterization of the Prony model specific to the radar target identification problem is chosen and several key components to the algorithm, including the use of singular value decomposition and the removal of spurious scattering centers, are presented. The resulting algorithm is tested with data taken from a compact range. These tests include comparison of different targets, different aspect angles and frequency ranges, as well as robustness tests on the algorithm and evaluation of performance in noise. >
193 citations
TL;DR: In this article, the authors describe the radiation and scattering characteristics of microstrip antennas and arrays printed on ferrite substrates with a normal magnetic bias field, and show that the extra degree of freedom offered by the biased ferrite can be used to obtain a number of novel characteristics, including switchable and tunable circularly polarized radiation from a microstrip antenna having a single feed point.
Abstract: Radiation and scattering characteristics of microstrip antennas and arrays printed on ferrite substrates with a normal magnetic bias field are described. The extra degree of freedom offered by the biased ferrite can be used to obtain a number of novel characteristics, including switchable and tunable circularly polarized radiation from a microstrip antenna having a single feed point, dynamic wide-angle impedance matching for phased arrays of microstrip antennas, and a switchable radar cross section reduction technique for microstrip antennas. Results are obtained from full-wave moment method solutions for single microstrip antennas and infinite arrays of microstrip antennas. A cavity model solution for a circular patch antenna on a biased ferrite substrate is also presented, to aid in understanding the operation of these antennas. >
189 citations
TL;DR: In this paper, two implementations of the surface impedance boundary condition are presented: a constant surface-imperceptible boundary condition and a dispersive boundary condition that is applicable over a very large frequency bandwidth and over a large range of conductivities.
Abstract: Surface impedance boundary conditions can be utilized to avoid using small cells, made necessary by shorter wavelengths in conducting media throughout the solution volume. The standard approach is to approximate the surface impedance over a very small bandwidth by its value at the center frequency, and then use that result in the boundary condition. In this paper, two implementations of the surface impedance boundary condition are presented. One implementation is a constant surface impedance boundary condition and the other is a dispersive surface impedance boundary condition that is applicable over a very large frequency bandwidth and over a large range of conductivities. Frequency domain results are presented in one dimension for two conductivity values and are compared with exact results. Scattering width results from an infinite square cylinder are presented as a two dimensional demonstration. >
TL;DR: In this paper, a solution procedure to obtain the transient scattering by arbitrarily shaped conducting objects directly in the time-domain using the marching-on-in-time method is presented, and the late-time oscillations are eliminated by a simple stabilization procedure which involves a negligible amount of extra computation.
Abstract: A solution procedure to obtain the transient scattering by arbitrarily shaped conducting objects directly in the time-domain using the marching-on-in-time method is presented. The late-time oscillations are eliminated by a simple stabilization procedure which involves a negligible amount of extra computation. Numerical results for surface current density and far-scattered fields are given for various structures and compared with other methods. >
TL;DR: In this paper, a subcell model for thin material sheets in the finite-difference time-domain method is presented, which leads to greatly reduced storage requirements and a corresponding reduction in the number of time steps needed.
Abstract: A subcell model is presented for including thin material sheets in the finite-difference time-domain method. The subcell model removes the normal restriction which sets the spatial grid increment at least as small as the smallest physical feature in the solution space. Removing this restriction leads to greatly reduced storage requirements and a corresponding reduction in the number of time steps needed. The subcell model is verified by comparison with the exact results for the loss and phase shift for a parallel plate waveguide loaded with a thin material sheet. Specifically, thin conducting as well as thin dielectric sheets are investigated for both TEM and TM/sub 1/ time-harmonic excitations of the waveguide. The FDTD results are in very good agreement with the exact results. Finally, the subcell model is used in the analysis of a practical problem-a resistively loaded monopole antenna formed from a thin-walled conducting tube. The FDTD results are compared with accurate measurements for this antenna, and, again, the two are in very good agreement. >
TL;DR: In this article, surface impedance boundary conditions (SIBC) are introduced into the FDTD method to reduce the solution space and produce significant computational savings, and an efficient implementation of this FDTD-SIBC based on the recursive properties of convolution with exponentials is presented.
Abstract: Surface impedance concepts are introduced into the finite-difference time-domain (FDTD) method. Lossy conductors are replaced by surface impedance boundary conditions (SIBC), reducing the solution space and producing significant computational savings. Specifically, a SIBC is developed to replace a lossy dielectric half-space. An efficient implementation of this FDTD-SIBC based on the recursive properties of convolution with exponentials is presented. Finally, three problems are studied to illustrate the accuracy of the FDTD-SIBC formulation: a plane wave incident on a lossy dielectric half-space, a line current over a lossy dielectric half-space, and wave propagation in a parallel-plate waveguide with lossy walls. >
TL;DR: In this paper, the plane wave propagation in two kinds of Faraday chiral media, where Faraday rotation is combined with optical activity, is studied to examine methods of controlling chirality.
Abstract: Plane wave propagation in two kinds of Faraday chiral media, where Faraday rotation is combined with optical activity, is studied to examine methods of controlling chirality. The two types of media studied are magnetically biased chiroplasmas and chiroferrites. For propagation along the biasing magnetic field, four wavenumbers and two wave impedances are found which are dependent on the strength of the biasing field. Dispersion diagrams for the chiroplasma case are plotted. Propagation at the plasma frequency of the chiroplasma is also investigated. >
TL;DR: In this article, the scattering of an incident plane wave from an array of parallel circular dielectric and/or conducting cylinders is derived rigorously using a boundary value approach using both transverse electric (TE) and transverse magnetic (TM) polarized incident plane waves.
Abstract: The scattering of an incident plane wave from an array of parallel circular dielectric and/or conducting cylinders is derived rigorously using a boundary value approach. Both transverse electric (TE) and transverse magnetic (TM) polarized incident plane waves are considered. The validity and accuracy of the method are verified by comparing the numerical results with those based on other available methods. The advantage of the proposed analysis is the simplicity and efficiency in computation. The modeling of two-dimensional objects of arbitrary cross section and composite material is outlined and sample numerical results are presented to illustrate the versatility of the method. >
TL;DR: In this paper, a finite-difference time-domain formulation which incorporates both anisotropy and frequency dispersion, enabling the wideband transient analysis of magnetoactive plasma, is described.
Abstract: When subjected to a constant magnetic field, both plasmas and ferrites exhibit anisotropic constitutive parameters. For electronic plasmas this anisotropy must be described by using a permittivity tensor in place of the usual scalar permittivity. Each member of this tensor is also very frequency dependent. A finite-difference time-domain formulation which incorporates both anisotropy and frequency dispersion, enabling the wideband transient analysis of magnetoactive plasma, is described. Results are shown for the reflection and transmission through a magnetized plasma layer, with the direction of propagation parallel to the direction of the biasing field. A comparison to frequency-domain analytic results is included. >
TL;DR: In this article, a parabolic equation model has been developed for use in tropospheric radiowave propagation and a simple technique to model range-dependent environments has been implemented.
Abstract: A parabolic equation model has been developed for use in tropospheric radiowave propagation. A simple technique to model range-dependent environments has been implemented. Results from the model are compared with experimental data at 170, 520, 3240, 3300, and 9875 MHz in measured range-dependent environments. The experimental data are taken from two separate experiments performed during 1947 and 1948. Measurements were made on overwater paths from Guadalupe Island to San Diego, CA, in one experiment, and the other was located in the South Island of New Zealand, also known as the Canterbury Project. The results are presented as one-way propagation factor in decibels versus height. The technique used to model range-dependent environments is shown to give a reasonably good estimate of the environment between measurements, leading to excellent agreement between the predicted fields and observed radio data. >
TL;DR: In this article, a multidimensional Fresnel integral is proposed for the case of near-grazing incidence, where the angle of incidence with respect to the plane containing the edges is small and each edge is in the transition region of the previous edge.
Abstract: Multiple forward diffraction past an array of many absorbing half-screens whose separation is large compared to wavelength is examined. Starting with the physical optics approximation for half-planes that are equally spaced and of equal height, the field incident on successive edges is represented by a multidimensional Fresnel integral, which is then expanded into a series of functions studied by Boersma (1978). When the angle of incidence with respect to the plane containing the edges is small, each edge is in the transition region of the previous edge, which precludes the use of the geometrical theory of diffraction and related asymptotic theories. The solution obtained applies for incidence either from above or below the plane containing the edges, and is especially suited to the case of near-grazing incidence. This method of solution allows for numerical evaluation of a large number of half-screens and shows how the multiple diffracted fields are influenced by the physical parameters. Both incident plane waves and incident cylindrical waves can be treated. >
TL;DR: In this paper, the transient excitation of a straight thin-wire segment is analyzed with the aid of a one-dimensional integral equation for the current along the wire, in which only the radial current on the end faces is approximated.
Abstract: The transient excitation of a straight thin-wire segment is analyzed with the aid of a one-dimensional integral equation for the current along the wire. An almost exact derivation of that equation, in which only the radial current on the end faces is approximated, is given. The integral equation obtained turns out to be identical to the reduced version of Pocklington's equation. On the basis of this derivation, existing and new numerical solution techniques are critically reviewed. Pocklington's equation and Hallen's equivalent form are solved directly by marching on in time as well as indirectly via a transformation to the frequency domain. For Pocklington's equation, a conventional moment-method discretization leads to a Toeplitz matrix that is inverted with Levinson's algorithm. For Hallen's equation, the Toeplitz structure is disturbed, and the frequency-domain constituents are determined with the aid of the conjugate-gradient-FFT method. Illustrative numerical results are presented and discussed. >
TL;DR: In this paper, a microstrip antenna composed of parallel dipole resonators of different lengths fed by a rectangular slot cut in the ground plane of the microstrip line is analyzed using an integral equation technique solved in the spectral domain using the Galerkin method of moments.
Abstract: A microstrip antenna composed of parallel dipole resonators of different lengths fed by a rectangular slot cut in the ground plane of a microstrip line is analyzed using an integral equation technique solved in the spectral domain using the Galerkin method of moments. Multifrequency operation of this antenna is demonstrated using two different configurations. Experimental data are shown to be in good agreement with predicted results. The fundamental parameters influencing the realization of multifrequency operation, as well as impedance matching of the different resonances, are studied. Lastly, the radiation patterns of the antenna at different frequencies and the relative contribution of the dipoles to the radiation are investigated. >
TL;DR: In this article, the ability of the finite-difference-time-domain (FDTD) method to calculate radiation patterns, input impedance, and gain for a monopole antenna on a conducting box is demonstrated.
Abstract: The ability of the finite-difference-time-domain (FDTD) method to calculate radiation patterns, input impedance, and gain for a monopole antenna on a conducting box is demonstrated. Results are given for the bare box and with the box coated with a dielectric layer. Radiation patterns are compared with measurements and with the method of moments for the bare box. Radiation patterns for the dielectric-covered box and all impedance and gain results are compared with measurements only. Good agreement is obtained in all cases. The FDTD approach includes a dielectric covering quite easily, while this would be quite difficult for a method of moments approach. The FDTD method requires similar computer time as the method of moments for a single-frequency result, but produces wide-bandwidth impedance and gain results with much less computer time. >
TL;DR: In this article, it is shown how to use many overlapping conformal grids in the neighborhood of the scatterer while using a rectangular grid away from it for solving Maxwell's equations.
Abstract: It is shown how to use many overlapping conformal grids in the neighborhood of the scatterer while using a rectangular grid away from the scatterer for solving Maxwell's equations. The locally conformal grids allow better approximation of the boundary condition on the scattering object while the rectangular grid preserves the simplicity and accuracy of the regular finite-difference time-domain (FDTD) algorithm. These grids overlap typically about three zones. It is shown how to connect together the calculations done in different overlapping grids. >
TL;DR: It is shown how the ESPRIT (estimation of signal parameters via rotational invariance techniques) algorithm may be used with a square array of crossed dipoles to estimate both the two-dimensional arrival angles and the polarization of incoming narrowband signals.
Abstract: It is shown how the ESPRIT (estimation of signal parameters via rotational invariance techniques) algorithm may be used with a square array of crossed dipoles to estimate both the two-dimensional arrival angles and the polarization of incoming narrowband signals. The ESPRIT algorithm exploits the invariance properties of such an array so that both angle and polarization estimates may be computed. Some typical examples showing the use of this approach are presented. >
TL;DR: In this article, the authors used the finite difference time-domain (FDTD) method to model and predict the radiation patterns of wire and aperture antennas of three basic configurations, including a pyramidal horn antenna.
Abstract: The finite-difference time-domain (FDTD) method is used to model and predict the radiation patterns of wire and aperture antennas of three basic configurations. A critical step in each is the modeling of the feed. Alternate suggestions are made and some are implemented. The first antenna is a quarter-wavelength monopole and the second is a waveguide aperture antenna. In both bases the antenna is mounted on ground planes, either perfectly conducting or of composite material. The results obtained using the FDTD technique are compared with results obtained using the geometrical theory of diffraction (GTD) and measurements. The third configuration of interest is a pyramidal horn antenna. To model the flared parts of the horn, a staircase approximation was applied to the antenna surface. The computed radiation patterns compared well with measurements. >
TL;DR: In this article, a polarimetric wave propagation model for field strength forecasting and coverage prediction in the VHF/UHF frequency range is presented, which uses a digital terrain data bank and considers multipath propagation.
Abstract: A polarimetric wave propagation model for field strength forecasting and coverage prediction in the VHF/UHF frequency range is presented. The model uses a digital terrain data bank and considers multipath propagation. Based on the uniform geometrical theory of diffraction (UTD) and physical optics an approach is described for calculating the propagation effects in natural 3-D terrain, given by topological and morphographical data. The method for field strength forecasting is described and methods for the analysis of the predicted multipath signal are discussed. It is shown how the complex probability density function (PDF) for the receiver field strength and the field strength delay spectrum can be derived. Methods for further evaluation of the transmitting channel characteristics are discussed. >
TL;DR: In this paper, an efficient method of analysis of large infinite arrays based on a convolution technique that allows one to obtain the finite array characteristics from the infinite array results is presented.
Abstract: An efficient method of analysis of large infinite arrays based on a convolution technique that allows one to obtain the finite array characteristics from the infinite array results is presented. The edge effects are taken into account by convoluting the infinite array results with the proper current amplitude window on the array. The method is based on the use of Poisson's sum formula in the case of finite arrays applied here to microstrip antennas. It is an approximate technique that can be assimilated into a perturbation method. >
TL;DR: In this paper, the well-known procedure for determining the electric field in a structure consisting of an arbitrary number of planar dielectric layers is modified in order to obtain a form specially suited for the analysis of multiprobe multipath configurations.
Abstract: The well-known procedure for determining the electric field in a structure consisting of an arbitrary number of planar dielectric layers is modified in order to obtain a form specially suited for the analysis of multiprobe multipath configurations. In general, the field is generated by arbitrary currents in the layers and arbitrary sheet currents in the transitions between the layers. The currents may be electric as well as magnetic, and the dielectric layers are isotropic, homogeneous, and lossy. The procedure results in Green's functions especially suited for the analysis of multiprobe multipatch configurations. They can be used in an efficient mixed-potential integral expression formulation. The theoretical procedure is applied in the case of a probe current source situated in one of the dielectric layers of the structure. For this probe current a highly efficient attachment current distribution is derived. Comparison of measured and calculated results for example structures proves the accuracy of both the approach and the attachment mode. >
TL;DR: In this article, the authors derived analytical bounds on the characteristics of beams generated by an arbitrary pulse-driven array and supported them with numerical calculations, and showed that for certain measures of performance involving these beam characteristics, a localized wave pulse driven array can outperform similar continuous-wave-driven arrays.
Abstract: Analytical bounds on the characteristics of beams generated by an arbitrary pulse-driven array are derived and supported with numerical calculations. These bounds extend the meaning of near-field distances or diffraction lengths to the situation where the array driving functions can be broad-bandwidth signals. Particular attention is given to transmitting and receiving array systems which consist of elements that are not large in comparison to the shortest wavelength of significance contained in the signals driving them. Their output signals constitute higher-order beams whose coherence properties are degraded more slowly by diffraction than lower-order beams. It is shown that for certain measures of performance involving these beam characteristics, a localized wave pulse-driven array can outperform similar continuous-wave-driven arrays. An array with independent addressable elements is required to realize these localized wave effects. The enhanced localization effects are intimately coupled to the proper spatial distribution of broad-bandwidth signals driving the array. >
TL;DR: In this article, a low-profile array antenna composed of two-turn 4 degrees pitch angle helices is designed for a frequency band of 11.7 GHz to 12.0 GHz.
Abstract: A low-profile array antenna composed of two-turn 4 degrees pitch angle helices is designed for a frequency band of 11.7 GHz to 12.0 GHz. The feed wire of each helix is inserted into a radial waveguide through a small hole and excited by a traveling wave flowing in the transverse electromagnetic mode between the two parallel plates of the waveguide. The measured aperture efficiency shows a maximum value of 77% for a beam radiated in the normal direction and 69% for a 30 degrees beam tilt. >