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Antennas and Propagation, IEEE Transactions on

Issue 7 • Date July 2006

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Displaying Results 1 - 25 of 38
  • Table of contents

    Page(s): c1 - 1909
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  • IEEE Transactions on Antennas and Propagation publication information

    Page(s): c2
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  • Analysis of arbitrarily shaped dielectric radomes using adaptive integral method based on volume integral equation

    Page(s): 1910 - 1916
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    The adaptive integral method (AIM) is employed to solve the volume integral equation (VIE) for analyzing the radiation of the antenna with an arbitrarily shaped radome. Small dipoles are used as exciting sources. Modeling the radomes by tetrahedron cells, the induced volume current is determined by the AIM based on VIE. The application of AIM significantly reduces CPU time and computer memory requirement. Hence, the method presented in the paper can be applied to simulate electrically large sized radomes. Finally, the radiation patterns of small dipole arrays in the presence of spherical and conical radomes are calculated. View full abstract»

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  • The use of curl-conforming basis functions for the magnetic-field integral equation

    Page(s): 1917 - 1926
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    Divergence-conforming Rao-Wilton-Glisson (RWG) functions are commonly used in integral-equation formulations to model the surface current distributions on planar triangulations. In this paper, a novel implementation of the magnetic-field integral equation (MFIE) employing the curl-conforming n~×RWG basis and testing functions is introduced for improved current modelling. Implementation details are outlined in the contexts of the method of moments, the fast multipole method, and the multilevel fast multipole algorithm. Based on the examples of electromagnetic modelling of conducting scatterers, it is demonstrated that significant improvement in the accuracy of the MFIE can be obtained by using the curl-conforming n~×RWG functions. View full abstract»

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  • Thin dielectric sheet simulation by surface integral equation using modified RWG and pulse bases

    Page(s): 1927 - 1934
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    The conventional thin dielectric sheet surface integral equation, proposed by Harrington and Mautz, is reviewed. Due to its simplicity and inadequency for certain problems, a new surface integral equation is proposed to fill the gap. This new formulation takes both tangential and normal currents into account so that it can handle problems with high and low permittivity and grazing incident waves. Based on the D-field formulation, inhomogeneity and surface charge can be treated correctly. Modelling the geometry by triangles, this surface integral equation is discretized and is suitable for the method of moments to solve. Rao-Wilson-Glisson and pulse functions are employed simultaneously for basis and testing functions and so the moment solution has full descriptions of polarization current in the thin dielectric layer. Several examples are examined by both analytical and other published numerical methods. These results show excellent agreement and demonstrate the validity and effectiveness of this new integral equation. View full abstract»

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  • An isotropy-improved nonstandard finite-difference time-domain method

    Page(s): 1935 - 1942
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    By introducing extra degree of freedom into the space-domain stencils, an isotropy-improved nonstandard finite-difference (NSFD) (2,2) method is presented in this paper. The technique is also extended to the higher-order (2,4) stencils. Both analytical and numerical results are presented and compared to demonstrate the accuracy and the strengths of these methods. View full abstract»

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  • Nonuniform grid time domain (NGTD) algorithm for fast evaluation of transient wave fields

    Page(s): 1943 - 1951
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    A novel algorithm to efficiently compute transient wave fields produced by known three-dimensional source constellations is proposed. The algorithm uses domain decomposition concepts and comprises two steps to be repeated for each subdomain considered. In the first step, delay- and amplitude-compensated fields, produced by sources residing inside each subdomain are computed at a sparse set of points surrounding the observation domain. In the second step, total fields in the observer domain are evaluated by interpolation, delay and amplitude restoration, and aggregation of subdomain fields. The proposed scheme is well-suited to accelerate the solution of time domain integral equations by marching on in time, to carry out time domain physical optics calculations, and to realize near- to far-field transformations of transients. Moreover, the scheme automatically adapts to, and takes advantage of, special geometrical features of the source-observer constellation studied, a key benefit when analyzing quasi-planar configurations. In addition, it realizes a seamless transition from the dynamic to the quasi-static regime, thus facilitating a unified treatment of electrically large and small problems. Last but not least, the scheme is remarkably simple to implement. View full abstract»

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  • Numerical modeling of a spherical array of monopoles using FDTD method

    Page(s): 1952 - 1963
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    In this paper, the spherical-coordinate finite-difference time-domain method is applied to numerical analysis of phased array of monopoles distributed over a sphere. Outer boundary of the given problem is modeled by accurate spherical-coordinate anisotropic perfectly matched layer. The problem of increased cell aspect ratio near the sphere poles causing degradation of results is solved by dispersion optimization through artificial anisotropy. The accuracy of the approach is verified by comparing a model case with an exact solution. Finally, radiation patterns obtained by frequency-domain near-to-far-field transform and s-parameters of the array elements are presented and validated by comparing with measurement data. View full abstract»

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  • Be´zier representations for the multiobjective optimization of conformal array amplitude weights

    Page(s): 1964 - 1970
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    For conformal phased arrays, generally the excitation amplitude of the array elements must be adjusted in order to maintain low sidelobes as the array is scanned. While the desired phase weights for maximum gain are deterministically set by the array geometry and scan angle, the representation of optimum low sidelobe amplitude weights remains an open problem. Following up on prior work using the efficiency-constrained optimization of a modified Bernstein polynomial for low sidelobe conformal array synthesis, a Be´zier surface is shown to provide a good representation of the optimized amplitude weights with a reduced number of parameters, while demonstrating ε-constraint multi-objective optimization of conformal aperture efficiency versus sidelobe level. These results are extended to include a Be´zier volume representation for the multiobjective optimization of conformal aperture efficiency versus both sidelobe level and scan angle. View full abstract»

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  • Wave propagation and coupling in linear arrays with application to the analysis of large arrays

    Page(s): 1971 - 1978
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    Waves inside linear arrays are analyzed for the case of single-port excitation. A frequency-domain method is proposed for the extraction of the amplitude decay and phase velocity of the waves, based on simulation results obtained for terminal excitation at one end and near the middle of the array. The waves reflected by the array ends are also extracted, under a single-reflection assumption. This model is then exploited for estimating the port currents when other elements of the array are excited, as well as for larger arrays. Simulation results are shown for port currents and element patterns in arrays of broad-plate dipoles. View full abstract»

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  • Array thinning by using antennas in a Fabry-Perot cavity for gain enhancement

    Page(s): 1979 - 1990
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    A Fabry-Perot cavity (FPC) between a ground plane and a partially reflective surface (PRS) is used here to design array antennas with large distance between the radiating elements. This configuration provides some advantages: i) a reduction of the number of array elements to achieve high directivity; ii) large space between contiguous elements that may host a bulky feeding network as required for dual polarization or active antennas; iii) small coupling and easy feeding network designs because of the smaller number of elements with larger inter-element distance. We show that when designing the FPC antenna a frequency shift of the gain maximum may occur, especially in this sparse array configuration. We also show the existence of preferred distances between elements that controls both the directivity and the side lobe level, and how the presence of the FPC and the relaxed requirement of the interelement distance result in a lower interelement coupling. The presented dual polarized antenna comprises two interleaved 2 × 2 arrays placed in a 2-layer FPC, and exhibits a 19 dBi gain and 30 dB of isolation between the two ports over an operating bandwidth of approximately 5.7%, i.e., typical for patch antennas. View full abstract»

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  • Performance of adaptive array antenna with arbitrary geometry in the presence of mutual coupling

    Page(s): 1991 - 1996
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    The effect of the mutual coupling between the array elements on the performance of the adaptive array antennas (AAA) is investigated when the actual received voltages which include the mutual coupling are directly used to estimate the weight vector based on the adaptive algorithm. The output signal-to-interference-noise ratio (SINR), the convergence of the adaptive algorithm and the synthesized pattern are evaluated to study the effect due to the existence of the mutual coupling. It is found that the mutual coupling affects the antenna adaptive gain, but does not affect the adaptive processing. It is also found that the mutual coupling does not always degrade the iterative convergence of the adaptive algorithm. It is proved that any invertible matrix for compensating the mutual coupling cannot improve the output SINR. It is also indicated that the radiation pattern can be correctly synthesized in the presence of the mutual coupling by introducing the universal steering vector (USV) whose element corresponds to the array element pattern. View full abstract»

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  • A novel amplitude-phase weighting for analog microwave beamforming

    Page(s): 1997 - 2008
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    A simple receiver and transmitter structure for smart antennas and phased array antennas is proposed. A new technique for amplitude and phase weighting in microwave domain is presented. Signals of different antenna elements are sampled using pulses with adjusted time delay and duty cycles. The first replica of the sampled signal is reconstructed to provide the proper phase shift and amplitude weighting. A new switch circuit is designed to improve the power efficiency of the proposed structure and to lower the effects of switching on the impedance matching. The effect of nonideal switching on the performance of the system is analyzed. Procedures are proposed to integrate the proposed structure with adaptive signal processing tasks. Signal to noise ratio of the structure is studied under different scenarios. View full abstract»

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  • Compact light weight UHF arrays using long slot apertures

    Page(s): 2009 - 2015
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    A wideband low profile phased array using long slot aperture was recently developed for radar and EW applications. A prototype UHF array with 4 × 8 (32) elements (1.12 m×2.24 m×23 cm) was built and tested for 150-600 MHz operation. Array patterns, gain, and cross-pol level were measured. Excellent performance was observed. The array is 23 cm thick, and it weighs 7 kg (2.8 kg/m2). Lossy loading material may be used to make it thinner, but this is believed to be the lightest and thinnest UHF array reported for wideband applications without gain penalty. View full abstract»

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  • On the analysis of slotted waveguide arrays

    Page(s): 2016 - 2021
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    A strategy for the full-wave analysis of slotted waveguide planar arrays is presented and demonstrated. The core of the method is a suitable segmentation of the antenna into two fundamental regions: an "internal" one, formed by the waveguide circuit, and the "external" one, consisting of the half space above the plate where the radiating slots are located. The internal region is further segmented into several blocks, connected to each other via their generalized admittance matrices (GAMs). The latter are calculated by means of either a commercial or a home made tool. The front plate is considered as a whole and analyzed by the moment method, in terms of modes of the slots. The latter are considered as short sections of waveguide whose length is just the conductor thickness, connecting the internal and external regions. The approach has been applied with success to a number of large planar arrays, both in rectangular and ridge waveguide. View full abstract»

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  • On two types of convergence in the method of auxiliary sources

    Page(s): 2022 - 2033
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    The method of auxiliary sources (MAS) is often applied to problems involving an externally illuminated, smooth, perfect electric conductor (PEC). One seeks to approximately satisfy the boundary condition on the PEC surface using N auxiliary sources located inside the PEC surface. Usually, the underlying auxiliary surface is also smooth and closed. The currents on the auxiliary sources ("MAS currents") are the initial unknowns; once they have been found, one can easily determine the field due to them ("MAS field") at all points external to the auxiliary surface and, in particular, at all points external to the PEC scatterer. We show that, in the limit N→∞, it is possible to have a convergent MAS field together with divergent MAS currents, and that this phenomenon is accompanied by an abrupt behavior of the limiting value of the MAS field. We show this possibility through an analytical study of a two-dimensional scattering problem involving a circular cylinder, in which MAS fields and currents can be determined explicitly. The analytical study proceeds from first principles; it involves fundamental electromagnetics and relatively simple mathematical manipulations. Numerical results supplement the analytical study and demonstrate the nature of the aforementioned divergence. Our study sheds light on other aspects of MAS; in particular, it establishes interesting similarities and differences between MAS and its "continuous version," and reveals many similarities between MAS currents and numerical solutions of Halle´n's integral equation with the approximate kernel. View full abstract»

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  • Linear source in a circular tunnel

    Page(s): 2034 - 2047
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    We study models for propagation in circular tunnels. The excitation is a fundamental electric current source. We produce expressions for the fields in terms of a Fourier transform over the axial variable. We perform an asymptotic analysis of the complex wavenumbers for use as initial estimates in a complex root finder. We then produce the modes in the lossy structure by contour integration techniques. We include numerical results for the field intensity as a function of axial distance for several frequencies and constitutive parameters of interest. We comment in particular concerning the modal content and the specific form of the field both near to and far from the antenna source. View full abstract»

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  • Modified theory of physical optics solution of impedance half plane problem

    Page(s): 2048 - 2053
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    The scattering of electric polarized plane waves from an impedance half plane problem is examined by the method of modified theory of physical optics (MTPO). Two integrals, consisting of incident and reflected scattered fields, are obtained. These integrals are evaluated asymptotically by the methods of stationary phase and edge point. The obtained scattered fields are compared with the exact solution numerically. View full abstract»

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  • Electromagnetic scattering from vibrating penetrable objects using a general class of time-varying sheet boundary conditions

    Page(s): 2054 - 2061
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    Calculation of electromagnetic (EM) scattering from vibrating penetrable cylinders of arbitrary cross-section is presented using a general class of time-varying sheet boundary conditions (SBCs) in conjunction with the method of moments (MoM). Sheet impedance and admittance expressions are first derived from the exact scattering solution for a penetrable circular cylinder with perturbed radius. Then, using the SBCs, integral equations are derived and solved numerically so that vibrating cylinders with arbitrary cross-section can be treated. Cylinder vibrations are assumed to be non-relativistic, allowing a simplified calculation of the scattered Doppler spectrum. A critical factor in the calculation of the potentially small Doppler components is that the time-varying nature of the cylinder boundary, contained within the sheet impedance and admittance expressions, can be isolated from the unperturbed terms in the scattered field. Comparison with exact and analytical perturbation solutions are presented to demonstrate the accuracy of the numerical solution. View full abstract»

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  • On the role of measurement configuration in contactless GPR data processing by means of linear inverse scattering

    Page(s): 2062 - 2071
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    This paper deals with a linear two-dimensional inverse scattering problem within a half space geometry with data gathered far away from the interface, which is relevant in ground penetrating radar contactless data processing. In particular, the role of the measurement configuration is discussed with regard to the information retrievable from multifrequency data. View full abstract»

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  • Bistatic scattering from rough dielectric soil surface with a conducting object partially buried by using the GFBM/SAA method

    Page(s): 2072 - 2080
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    A hybrid approach of the generalized forward-backward method (GFBM) with spectral accelerate algorithm (SAA) and Monte Carlo method is developed in this paper. It is applied to numerical simulation of bistatic scattering from one-dimensional arbitrary dielectric constant soil surface with a conducting object partially buried under the horizontal and vertical tapered wave incident at low grazing angle. The energy conservation is used to valuate accuracy of the GFBM/SAA. Numerical simulations of bistatic scattering at low grazing angle are discussed in this paper. View full abstract»

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  • Algebraic multigrid preconditioner for homogeneous scatterers in electromagnetics

    Page(s): 2081 - 2087
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    Electromagnetic wave scattering from large and complex bodies is currently the most challenging problem in computational electromagnetics. There is an increasing need for more efficient algorithms with reduced computational complexity and memory requirements. In this work we solve the problem of electromagnetic wave scattering involving three-dimensional, homogeneous, arbitrarily shaped dielectric objects. The fast multipole method (FMM) is used along with the algebraic multigrid (AMG) method, that is employed as a preconditioner, in order to accelerate the convergence rate of the Krylov iterations. Our experimental results suggest much faster convergence compared to the non preconditioned FMM, and hence significant reduction to the overall computation time. View full abstract»

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  • Plane wave scattering and absorption by flat gratings of impedance strips

    Page(s): 2088 - 2095
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    The problem of the plane wave scattering by a flat impedance-strip grating located in free space is considered. The formulation involves a set of generalized boundary conditions relating limiting values of the fields to effective electric and magnetic currents. We develop an accurate numerical solution to this problem using the dual series equations and the method of analytical regularization (MAR) based on the main part inversion. This guarantees a fast convergence and controlled accuracy of computations. Reflected, transmitted, and absorbed power fractions as a function of the frequency and the grating parameters are analyzed. Sharp resonances are revealed in the H-polarized scattering near to the grazing of the higher-order modes; these resonances are absent for the perfect electrically conducting strip grating. Low-frequency asymptotics for the reflectance and transmittance in the single-mode regime are presented and compared with numerical solutions. View full abstract»

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  • Eigenmodes and scattering by an axial array of tape rings

    Page(s): 2096 - 2104
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    Source-free and forced solutions for the electromagnetic fields in and around a periodic array of finite-length conducting cylinders are assembled from a Galerkin procedure using a Chebyshev polynomial basis with built-in edge-condition behavior. A localized source excites slow surface-waves under certain conditions on the electrical circumference and spacing of the tubular structure. These eigenmodes are the solutions to the homogeneous boundary value problem. A numerical search for the axial propagation constant that minimizes the smallest singular value of the governing Galerkin matrix provides the required dispersion relation. View full abstract»

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  • Experimental verification of the reduction of coupling between dipole antennas by using a woodpile substrate

    Page(s): 2105 - 2112
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    In this paper, the mutual coupling between dipole antennas placed on top of a woodpile structure is experimentally investigated. The coupling between dipoles backed by a woodpile substrate is compared with that obtained when the dipole antennas are placed on a dielectric substrate and when they radiate into free space. On average, between 2 and 7 dB reduction of the mutual coupling is achieved with respect to the dielectric substrate case when the woodpile substrate is used. The free space coupling is also reduced in the H-plane configuration case. However, the E-plane coupling slightly increases due to modification of the radiation pattern. Imaging array applications could potentially benefit from the use of EBG substrates due to the improved isolation between pixels. View full abstract»

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IEEE Transactions on Antennas and Propagation includes theoretical and experimental advances in antennas.

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Editor-in-Chief                                                 Kwok W. Leung