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Antennas and Propagation, IEEE Transactions on

Issue 9 • Date Sept. 1993

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Displaying Results 1 - 25 of 25
  • Comments on "Modeling of cylindrical objects by circular dielectric and conducting cylinders" [with reply]

    Page(s): 1342 - 1344
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (313 KB)  

    In the above-titled paper (see ibid, vol. 40, p.96-9, 1992) A. Z. Elsherbeni and A. A. Kishk introduced a general method and semianalytical solution for the modeling of composite two-dimensional scatterers. The commenters point out that unnecessarily large numbers of terms were used for thin conducting wires with TM excitation. The original authors point out that the expression for the number of terms they used is needed for the more general case. The commenters also suggest that the wire grid model for the scattering by a conducting cylinder yields, in general, a matrix equation of smaller order relative to the matrix equation generated by the circular cylinder model. The authors refute this suggestion and clarify a number of other points as well.<> View full abstract»

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  • Comments on a "A neural network approach to MVDR beamforming problem"

    Page(s): 1344 - 1346
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    Several corrections to the above-titled paper by P.R. Chang et al. (ibid, vol. 40, pp 313-322, 1992) are given by the commenter, who also discusses a number of Chang et al.'s results. The commenter also discusses the practical issues that arise when an array operates in a nonstationary environment.<> View full abstract»

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  • High-frequency RCS of complex radar targets in real-time

    Page(s): 1308 - 1319
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (980 KB)  

    This paper presents a new and original approach for computing the high-frequency radar cross section (RCS) of complex radar targets in real time with a 3-D graphics workstation. The aircraft is modeled with I-DEAS solid modeling software using a parametric surface approach. High-frequency RCS is obtained through physical optics (PO), method of equivalent currents (MEC), physical theory of diffraction (PTD), and impedance boundary condition (IBC). This method is based on a new and original implementation of high-frequency techniques which the authors have called graphical electromagnetic computing (GRECO). A graphical processing approach of an image of the target at the workstation screen is used to identify the surfaces of the target visible from the radar viewpoint and obtain the unit normal at each point. High-frequency approximations to RCS prediction are then easily computed from the knowledge of the unit normal at the illuminated surfaces of the target. The image of the target at the workstation screen (to be processed by GRECO) can be potentially obtained in real time from the I-DEAS geometric model using the 3-D graphics hardware accelerator of the workstation. Therefore, CPU time for RCS prediction is spent only on the electromagnetic part of the computation, while the more time-consuming geometric model manipulations are left to the graphics hardware. This hybrid graphic-electromagnetic computing (GRECO) results in real-time RCS prediction for complex radar targets View full abstract»

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  • Sensitivity of complex response zeros of linear power inversion arrays in the presence of random amplitude and phase errors

    Page(s): 1327 - 1331
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    This paper investigates the variation of the complex response zeros, commonly used for source location purposes, of a linear power inversion array with random amplitude and phase errors. In particular, after deriving the zero variances in terms of the optimal weights and the variances of the amplitude and phase errors, a simple guideline relating the zero variances to the number of elements and the amplitude and phase variances is obtained for situations when the sources are well separated and resolvable by the array. Some simulation results are then presented to verify the theoretical derivations View full abstract»

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  • Generalized method of interpolation factorization [EM diffraction]

    Page(s): 1320 - 1324
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    A novel effective method for rigorous analytical solution of two dimensional diffraction problems is presented. Simple analytical expressions and the original equivalent circuit are assumed for the wide class of these problems. For illustration the diffraction of a plane electromagnetic wave by a thick strip grating is considered View full abstract»

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  • Theoretical and numerical treatment of surface integrals involving the free-space Green's function

    Page(s): 1296 - 1301
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    This paper deals with the problem of the calculation of surface integrals for electromagnetic scattering in the case of the widely popular double-triangular basis functions first introduced by Rao, Wilton, and Glisson (1982). An entire set of formulas is obtained which overrides the difficulties inherent to the singularity of the integrands, and results showing the stability, accuracy, and efficiency of the methods developed are reported in an application of the method of moments to the case of perfectly conducting surfaces and computation of near field in domains including the surface itself. Furthermore, the authors provide insight as regards the capability of triangular basis functions to model near field patterns View full abstract»

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  • Analysis of scattering from cylinders with a periodically corrugated periphery using a current-model technique

    Page(s): 1265 - 1272
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (652 KB)  

    A novel solution is presented for the problem of two-dimensional electromagnetic scattering from a circular cylinder with periodically corrugated circumference. The application of the Floquet formalism is effected by representing the incident field as a sum of fields, each one obeying a Floquet periodicity condition involving a different phase factor. Respective sets of fictitious sources, comprising rotationally periodic and properly phase-modulated electric current distributions, are used to simulate the scattered field and the field in the cylinder region. Spectral and spatial formulations are presented. The solution procedure is simple to implement and is applicable to cylinders with corrugations of arbitrary profile. The accuracy of the method has been demonstrated. It has also been shown that in the limiting case of low corrugation the results of the numerical solution agree with results obtained by an approximate analytic solution View full abstract»

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  • Analysis of electromagnetic radiation from shaped-end radiators using the finite difference time domain method

    Page(s): 1324 - 1327
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The finite difference time domain (FDTD) technique is a popular method for analyzing electromagnetic scattering, radiation, and penetration problems. Several authors have recently applied the FDTD method to antenna radiation problems. To date, the antenna structures considered have been wire and conical monopole antennas, rectangular waveguides, pyramidal horn antennas, and microstrip antennas. Results from these analysis have been in the form of normalized field patterns and no results showing absolute gain have been presented. The article demonstrates the first staircased application of the FDTD method to the analysis of radiation from circular waveguides and other shaped-end radiators. Results of absolute gain versus angle are shown for a straight-cut circular waveguide and for two different shaped-end radiators. All FDTD analyses are full three-dimensional computations and are compared in each case with measured data View full abstract»

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  • Subsectional-polynomial E-pulse synthesis and application to radar target discrimination

    Page(s): 1204 - 1211
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    A new family of extinction-pulses (E-pulses), called subsectional-polynomial E-pulses, is presented. This new type of E-pulse is constructed by choosing polynomials of degree Q as subsectional basis-functions in the E-pulse expansion. The main feature of this family of E-pulses is that the waveforms are continuous and smooth. Several topics concerning the E-pulse technique are investigated, such as: insensitivity to the exact number of natural modes present in the target response; aspect-angle independence; and effects of additive white Gaussian noise. Numerical results, using the response of a thin cylinder and a sphere, show that the subsectional-polynomial E-pulses improve the results obtained using subsectional-rectangular E-pulses View full abstract»

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  • Complex signal received through an anisotropic panel intercepting a circularly polarized beam

    Page(s): 1339 - 1342
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    An inclined planar panel, which is generally anisotropic, intercepting a circularly polarized beam introduces loss and phase shift, and depolarizes the received signal. Orthogonal linearly polarized waves aligned to the symmetry planes are often used in the measurement of such panels. Using these data, convenient graphs are presented to illustrate the loss and phase shift of a circularly polarized beam, as well as the amount of depolarization into an orthogonal circularly polarized channel, without explicitly determining the intermediate axial ratio or polarization ellipse tilt angle of the emerging wave View full abstract»

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  • Scattering from conducting rough surfaces: a general perturbative solution

    Page(s): 1232 - 1241
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    The general term of the perturbation series is presented in closed form to treat scattering of horizontally polarized plane incident waves from a perfectly conducting rough surface. The use of the complete perturbation series obtained is illustrated through several examples of deterministic profiles, including the case of gently undulating surfaces (Kirchhoff limit) and the case of periodic gratings. Also, it is shown how specularity of the mean scattered field from statistically homogeneous surfaces can be proved in the present context View full abstract»

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  • Scan performance of infinite arrays of microstrip patch elements loaded with varactor diodes

    Page(s): 1273 - 1280
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    The analysis and scanning characteristics of an infinite array of rectangular microstrip patches each loaded with a varactor diode is presented. The analysis is based on full-wave moment method theory and uses attachment modes to accurately model the current through the feed and the diode. The effect of the biased varactor diode on the scan performance is presented, and it is shown that the impedance mismatch caused by a scan blindness can be eliminated. Other characteristics are also given such as: the active element gain, the efficiency of each loaded microstrip element, and the level of cross polarization generated by the loading of the patch. The effect of the diode biasing level as well as the position of the diode on each radiating element on these scan characteristics is also considered View full abstract»

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  • FDTD calculation of scattering from frequency-dependent materials

    Page(s): 1249 - 1257
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (688 KB)  

    An efficient method to include frequency-dependent materials in finite difference time domain calculations based on the recursive evaluation of the convolution of the electric field and the susceptibility function has previously been presented. The method has been applied to various materials, including those with the Debye, Drude, and Lorentz forms of complex permittivity, and to anisotropic magnetized plasmas. Previous demonstrations of this approach have been confined to total field calculations in one dimension. In this paper the recursive convolution method is extended to three-dimensional scattered field calculations. The accuracy of the method is demonstrated by calculating scattering from spheres of various sizes composed of three different types of frequency-dependent materials View full abstract»

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  • Electromagnetic properties of nonreciprocal composite chiral-ferrite media

    Page(s): 1289 - 1295
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The theoretical properties of a composite chiral-ferrite medium are developed, The composite is constructed from a general chiral medium and a nonreciprocal ferrite medium. Application of the reaction theorem allows proof of nonreciprocity based on the constitutive relationships. Vector Helmholtz E- and H-field equations are derived, and from these equations reciprocal space Green's function dyadics are found. The direct space dyadics are then determined. Characteristic dispersion equations are found from the sourceless vector phasor Helmholtz equations. E-field polarization is obtained by projecting the E-field vector onto the polarization plane selected. Diagonalization of the elliptic equation through coordinate rotation allows major and minor axis determination View full abstract»

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  • Analysis of radiating slots in a rectangular waveguide inhomogeneously loaded with a dielectric slab

    Page(s): 1212 - 1221
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    Longitudinal and transverse radiating slots in the broad wall of a rectangular waveguide inhomogeneously loaded with a dielectric slab are analyzed. The formulation used involves the moment method solution of a pair of coupled integral equations containing the dyadic Green's function of the inhomogeneously loaded waveguide. Both an edge-condition for the electric field in the slot aperture and the correct form of the ψ=constant waveguide mode are included in the analysis. Computed and measured results are compared to verify the theoretical analysis View full abstract»

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  • Optimization of two-dimensional radome boresight error performance using simulated annealing technique

    Page(s): 1195 - 1203
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    A systematic approach to radome design is presented. The problem is formulated as a global optimization procedure such that the radome performance is optimized by properly adjusting the thickness of the radome layer over the entire radome surface. In this approach the thickness profile is parameterized via B-splines representation. Simulated annealing technique is applied to finding the best thickness profile so that the maximum boresight error is reduced to as small as possible over the entire range of the antenna look angle. A two-dimensional design example is given. The best possible thickness profile is found and the boresight error is reduced considerably compared to that due to a uniform layer. The method is general and can be applied without difficulty to other realistic three-dimensional radomes of arbitrary shapes View full abstract»

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  • Uniform PO and PTD solution for calculating plane wave backscattering from a finite cylindrical shell of arbitrary cross section

    Page(s): 1336 - 1339
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    The plane wave backscattering from a perfectly conducting three-dimensional shell of arbitrary cross section has peen studied. A uniform physical optics (PO) solution, valid across the reflection limits, is derived. The solution, derived from an asymptotic evaluation of the PO integral, includes end-point contributions that account for the diffracted field on edges. It can be improved by the fringe fields derived from an analytical integration of the equivalent edge currents of the physical theory of diffraction (PTD). It is computationally efficient for electrically large shells and compares very well with the finite-element method View full abstract»

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  • An analysis of antenna coupling between arrays on a polyhedron structure

    Page(s): 1242 - 1248
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    Antenna coupling between arrays on a polyhedron structure is investigated. First of all, a high-frequency asymptotic closed-form formula is derived for the mutual admittance between two linearly polarized circular microstrip antennas located on the different faces of a perfectly conducting wedge. The microstrip antennas are modeled by the cavity model, and the mutual coupling caused by the wedge-diffracted field is analyzed by the EMF method using Keller's GTD diffraction coefficients for the diffracted field. Next, the antenna coupling between arrays is calculated and compared with an experimental result. Good agreement between them supports the theory. Finally, the properties of the antenna coupling are described by some numerical simulations View full abstract»

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  • The scattering and absorption characteristics of material-coated periodic gratings under oblique incidence

    Page(s): 1281 - 1288
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    A boundary integral formulation is presented for calculating the scattering from material-coated periodic gratings under oblique incidence. Periodic boundary conditions and expansion of the fields in terms of Floquet harmonics allow the boundary integral formulation to treat just a single period of the infinite grating. Numerical results for an etched conducting grating designed for use at infrared wavelengths are presented and shown to be in good agreement with a series of measurements. Results for a number of dielectric gratings for both normal and oblique incidence also agree well with other published data. The conductor-backed coated grating is studied, and it is shown that the groove profile can be used to significantly alter the absorbing characteristics for lossy material coatings View full abstract»

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  • New frequency-dependent edge mode current density approximations for TM scattering from a conducting strip grating

    Page(s): 1302 - 1307
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    Two new frequency-dependent strip-grating current densities are derived for TM mode incidence on a conducting strip grating. The current densities are assumed to be the product of a spatial function and a frequency function. One spatial function is the traditional frequency-independent edge mode current density. The other is found by the use of conformal mapping. The frequency function is derived by use of the radiation integral and the periodic Green's function. The new resultant current densities are both exact for small strip widths. The conformally mapped solution is also valid for wide strips and is exact in the limit as the strip width equals the grating period. Although the solutions are not as accurate as the moment method at all frequencies, they produce computationally faster solutions and offer further insight into strip-grating behavior View full abstract»

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  • Experimental assessment of rain anisotropy and canting angle in a horizontal path at 30 GHz

    Page(s): 1331 - 1335
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB)  

    Rain anisotropy and canting angle data, obtained during a two-year measurement campaign on a short terrestrial radio link at 30 GHz are presented. The purpose of the campaign was to obtain the full-matrix description of a dual-polarization transfer channel at 30 GHz in the presence of rain and to model it by means of two physical parameters, anisotropy and canting angle, proposed in the literature some years ago and widely accepted in the scientific community both for terrestrial and slant paths. Event-based and statistical results are presented and studied in the light of current models of rain microphysics View full abstract»

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  • A contoured beam synthesis technique for planar antenna arrays with quadrantal and centro-symmetry

    Page(s): 1222 - 1231
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (888 KB)  

    A method is described for the synthesis of planar array antennas with prescribed contoured beams. The technique utilizes a transformation which divides the problem into two decoupled subproblems. One subproblem involves the determination of certain coefficients of the contour transformation in order to achieve the required footprint contours. The number of coefficients which need to be used depends on the complexity of the desired contour, but is very small in comparison to the number of planar array elements. The other subproblem consists of a linear array shaped beam synthesis, for which there already exist powerful methods for determining appropriate element excitations. The size required for this prototype linear array depends on the number of contour transformation coefficients used and the size of the final planar array. Simple formulas then determine the final planar array excitations from the information forthcoming from the above two subproblem solutions View full abstract»

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  • Interference suppression via orthogonal projections: a performance analysis

    Page(s): 1187 - 1194
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    Several recent studies indicate the promise of subspace separation principles when applied to adaptive jammer suppression in phased array antennas. This paper theoretically analyzes the performance of a subspace separation technique based on orthogonal projections (OP) for adaptively suppressing interference in phased arrays; the theoretical performance predictions are validated using computer simulations. This analysis holds for the case when it is possible to differentiate between the vector spaces spanned by jammers and additive noise. The performance parameters used are (a) the average residual interference (jammer plus noise) power at the output of the adapted array as a function of the number of jammer snapshots used for calculating the weight vector, and (b) the similarity of the adapted array pattern to the design pattern away from the jammer locations. The performance of the OP-based subspace separation technique is compared with the sample matrix inversion (SMI) algorithm. It is shown that the weight vector calculated using OP converges more quickly to the optimal solution (infinite number of interference snapshots) than the SMI weight vector. Further, in contrast to the SMI adapted pattern, which exhibits large sidelobe levels away from the jammer locations, the OP adapted pattern closely follows the design pattern both in the mainbeam and in the sidelobe region away from the jammer locations View full abstract»

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  • Electromagnetic scattering from a plane conductor containing two slots terminated by a microwave network, TE case

    Page(s): 1258 - 1264
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    The problem of electromagnetic scattering from a plane conductor containing multiple apertures is studied. Two slots are terminated or interconnected by a microwave network internal to the plane through two waveguides. The problem is formulated as an operator equation. A matrix method of solution is outlined using the method of moments and is interpreted using generalized network parameters. Several examples are discussed and their magnetic field strength patterns are presented View full abstract»

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  • Radiation characteristics of uniform and nonuniform dielectric leaky-wave antennas

    Page(s): 1177 - 1186
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (684 KB)  

    An approach based on a waveguide model for analyzing the uniform and nonuniform dielectric leaky-wave structures is proposed for which the Galerkin solution method is applied. In the first part of the paper the far-field radiation of the uniform antenna is determined theoretically and experimentally in the Ku band and also the dependence of beamwidth and sidelobe level as function of strip width and frequency is demonstrated. In addition, an analysis of the antenna with a tapered-strip distribution-is presented. The second part describes a novel tapering procedure, performed by changing the width of the uniform antenna, for obtaining the radiation pattern with lower sidelobe levels. Sinusoidally and exponentially shaped dielectric leaky-wave structures are analyzed as nonuniform antennas. Finally, the radiation and scanning characteristics of these antennas are theoretically presented 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