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Antennas and Propagation, IEEE Transactions on

Issue 7 • Date July 1991

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Displaying Results 1 - 25 of 29
  • Electromagnetic radiation and scattering from finite conducting and dielectric structures: surface/surface formulation

    Page(s): 1034 - 1037
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    An efficient and accurate numerical procedure for the analysis of the electromagnetic scattering and radiation from arbitrarily shaped, composite finite conducting and dielectric bodies is proposed. A set of coupled electric field integral equations involving surface equivalent electric and magnetic currents is used. The coupled integral equations are solved through planar triangular patch modeling and the method of moments. Two separate, mutually orthogonal vector functions for each edge connecting a pair of triangular patches have been developed. Numerical results for disk/cone and cylinder/cone structures are compared with other available data. Limited comparison with experimental data has also been made.<> View full abstract»

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  • Horizontal propagation through periodic vegetation canopies

    Page(s): 1014 - 1023
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    Experimental data suggest that a semideterministic technique is needed to model certain man-made vegetation canopies such as orchards, plantations, and row crops. A two-dimensional model has been developed to explain wave propagation through such canopies. The model is intended for media containing vertical cylinders, representing the stalks, and randomly oriented disks, representing the leaves. The formulation treats the canopy as a one-dimensional array of parallel rows, with each row comprising an array of parallel stalks and a random distribution of leaves. The quasi-static approximation used for computing scattering by the leaves is valid only when the dimensions of the leaves are smaller than the wavelength. The model is a field approach accounting for all coherent, multiple interactions occurring in the canopy. The experimental component of this study includes measurements of the attenuation and phase shift patterns for horizontally and vertically polarized waves transmitted through a fully grown canopy of corn plants observed at 1.5 GHz. The model has good agreement with the experimental results View full abstract»

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  • EM scattering from a vertical column of ionization in the Earth-ionosphere waveguide

    Page(s): 1051 - 1054
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    An idealized analysis is given for the mode conversion in the Earth-ionosphere waveguide produced by a tongue or stalactite of ionization below the normal reflecting layer. It is shown that the scattered signal may be significant even for perturbations located off the great circle path between source and observer View full abstract»

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  • Corner diffraction coefficients for the quarter plane

    Page(s): 976 - 984
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    The current near a right-angled corner on a perfectly conducting flat scatterer illuminated by a plane wave is expressed as a sum of three currents. The first is the physical optics current, which describes the surface effect. The second is the fringe wave current, which is found from the half-plane solution and accounts for the distortion of the current caused by the edges. The third is the corner current, which is found from the numerical solution to the electric-field integral equation applied to the square plate, and accounts for the distortion of the current caused by the corner. It is found that the corner current for the right-angled corner, illuminated from a forward direction, consists mainly of two edge waves propagating along the edges forming the corner. Analytical expressions for these edge wave currents are constructed from the numerical results. A corner diffracted field is calculated by evaluating the asymptotic corner contributions to the radiation integral over the sum of the three currents. It is found that the corner contribution from the edge wave currents in some cases is of the same size as the corner contributions from the physical optics current and the fringe wave current View full abstract»

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  • Radiation characteristics of wraparound microstrip antenna on spherical body

    Page(s): 1031 - 1034
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    The radiation characteristics of a wraparound microstrip antenna on a conducting sphere are investigated for different radii, frequencies, permittivities, and thickness of dielectric substrate. The near fields are determined from the magnetic ring currents at the edges of the strip by the use of spherical wave functions. Radiation patterns are obtained from a near-field-to-far-field transformation by the method of spherical wave expansion View full abstract»

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  • Mutual coupling between stacked square microstrip antennas fed on their diagonal

    Page(s): 1049 - 1051
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    Original results on mutual coupling between two identical stacked microstrip antennas are presented. The theoretical results, calculated by using the reciprocity theorem and the spectral domain method, are in good agreement with experiments. The mutual coupling between stacked structures is compared with that between unstacked patches View full abstract»

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  • Front-to-back ratio of paraboloidal reflectors

    Page(s): 877 - 882
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    An analysis is presented which uses the uniform geometrical theory of diffraction for determining the near fields diffracted by a paraboloid either with or without a conical flange attached to its circular rim when an axially propagated plane wave is incident on the concave or convex portion of the paraboloidal reflector. The field correlation theorem is used to determine the power coupled by a prime focus feed associated with the paraboloid which is being illuminated by a uniform plane wave. Based on this analysis, the front-to-back ratio of unflanged and flanged paraboloids is computed. Computed results show satisfactory agreement with the available measured as well as computed results based on alternative procedures. The variation in the on-axis gain on a prime-focus reflector when the feed is displaced from the focus is studied. Typical computed results are presented and compared with the available measured data. Computed results on the front-to-back ratio of paraboloids (flanged or unflanged) illuminated by a PFF whose radiated field exhibits phase variation over a constant radius are also presented View full abstract»

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  • A new approach to the analysis of rough surface scattering

    Page(s): 943 - 948
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    A novel approach to the problem of scattering by a randomly rough surface is developed based on combining normalization and the method of smoothing. Previous uses of smoothing have been forced to assume small surface heights in order to guarantee the dominance of the scattered field by its average or specular part. The term that causes the average scattered field to be so sensitive to the height is identified, and is normalized out of the basic integral equation. Smoothing is then applied to the normalized integral equation with a subsequent reintroduction of the normalizing factor after smoothing. The results are shown to extend beyond existing approximations, and they contain none of the divergent integral behavior that has recently been observed with a pure second order iterative approximation. An examination of the conditions under which the technique provides very accurate results shows that it is essentially an extension of the so-called composite surface scattering model View full abstract»

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  • Characteristics of circular patch on thick substrate and superstrate

    Page(s): 1038 - 1041
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    Accurate formulation for the wall admittance of a circular patch on a thick substrate/superstrate is presented. The principle of equivalence is invoked at the physical aperture of the patch, which yields equivalent electric and magnetic surface currents for the outside fields. The unknown electric current, in terms of the aperture electric field, is obtained from the field continuity condition on the aperture surface. Numerical results reveal that for a small substrate thickness, the equivalent electric current may be ignored. It should, however, be included in the analysis for larger substrate thicknesses. Numerical results for the wall conductance, wall susceptance, and radiation efficiency of a patch with various substrates and superstrates are presented View full abstract»

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  • Transient analysis of radiated field from electric dipoles and microstrip lines

    Page(s): 910 - 918
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    The transient response of the field radiated from electric dipole sources and microstrip lines with arbitrary time waveforms is analyzed. By using the three-dimensional Fourier transform of the spectral dyadic Green's function, relative to the integrated structure, an analytical closed-form solution is obtained and equivalent circuits for the analysis of the transient phenomena in the far-field region are derived. Numerical examples are provided to obtain noticeable insights to the behavior of planar circuits working under Gaussian pulsed excitation View full abstract»

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  • Scattering theorems with anisotropic surface boundary conditions for bodies of revolution

    Page(s): 1041 - 1043
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    Two theorems relating the scattered fields when a special anisotropic boundary condition is imposed on the scattering surface are proven. The results of the theorems should serve as useful checks in numerical electromagnetic calculations. The authors have also verified the theorems numerically, based on the computations of a numerical method of moment code View full abstract»

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  • A slot design for uniform aperture field distribution in single-layered radial line slot antennas

    Page(s): 954 - 959
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    A single-layered radial line slot antenna (RLSA) is proposed for a direct broadcast from a satellite (DBS) subscriber antenna. It utilizes a radially outward-traveling wave and the aperture field is intolerably tapered if the uniform slots are used. Two novel techniques are applied. First, the slot design for uniform aperture field distribution is introduced. Second, the radial line is terminated by a matching spiral, in place of a dummy load. It suppresses reflection and radiates all the residual power in circular polarization. For a model antenna of 600-mm diameter, the efficiency of 65% is observed View full abstract»

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  • Offset dual-shaped reflectors for dual chamber compact ranges

    Page(s): 1007 - 1013
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    The application of the theory of the synthesis of offset dual-shaped reflectors to the design of compact ranges is examined. The object of the compact range is to provide a uniform plane wave with minimum amplitude and phase ripple over as large a volume as possible for a given size reflector. Ripple can be lowered by reducing the edge diffraction from the reflector producing the plane wave. This has been done either by serrating or rolling the edge. An alternative approach is to use dual offset-shaped reflector synthesis techniques to produce a reflector aperture distribution that is uniform over most of the aperture, but with a Gaussian taper near the edge. This approach can be used together with rolling and/or serration if desirable. The amount of phase and amplitude ripple obtained with two different dual-shaped reflector designs is studied as a function of position in the plane wave zone and reflector size in wavelengths. The amount of both transverse and longitudinal (z-component) cross polarization is studied View full abstract»

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  • Integrated millimeter-wave corner-cube antennas

    Page(s): 1000 - 1006
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    An integrated corner-reflector antenna has been designed, fabricated and measured at millimeter-wave frequencies. The structure consists of a traveling-wave antenna integrated on a 1.2-μm dielectric membrane, and suspended in a longitudinal cavity etched in a silicon wafer. A novel traveling wave antenna design, the modified-bend antenna, with an antenna length of 1.2 λ and spacing 0.96 λ from the apex, results in a wideband input impedance centered at 140 Ω and low cross-polarization levels. Measurements at 180-270 GHz show a well-defined pattern with low sidelobe levels, and a main-beam efficiency of 93% and 83% at 180 and 222 GHz, respectively. The monolithic approach allows the integration of a matching network and a Schottky-diode or SIS detector at the base of the antenna to yield a low-noise monolithic millimeter-wave receiver View full abstract»

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  • Microstrip Yagi array antenna for mobile satellite vehicle application

    Page(s): 1024 - 1030
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    A novel antenna structure formed by combining the Yagi-Uda array concept and the microstrip radiator technique is discussed. This antenna, called the microstrip Yagi array, has been developed for the mobile satellite (MSAT) system as a low-profile, low-cost, and mechanically steered medium-gain land-vehicle antenna. With the antenna's active patches (driven elements) and parasitic patches (reflector and director elements) located on the same horizontal plane, the main beam of the array can be tilted, by the effect of mutual coupling, in the elevation direction providing optimal coverage for users in the continental United States. Because the parasitic patches are not connected to any of the lossy RF power distributing circuit the antenna is an efficient radiating system. With the complete monopulse beamforming and power distributing circuits etched on a single thin stripline board underneath the microstrip Yagi array, the overall L -band antenna system has achieved a very low profile for vehicle rooftop mounting, as well as a low manufacturing cost. Experimental results demonstrate the performance of this antenna View full abstract»

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  • Effects of measurement errors on microwave antenna holography

    Page(s): 933 - 942
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    The effects of measurement errors appearing during the implementation of the microwave holographic technique are investigated in detail, and many representative results are presented based on computer simulations. The numerical results are tailored for cases applicable to the utilization of the holographic technique for the NASA's Deep Space Network antennas, although the methodology of analysis is applicable to any antenna. Many system measurement topics are presented and summarized View full abstract»

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  • Observation and explanation of an unusual feature of random arrays with a nearest-neighbor constraint

    Page(s): 1047 - 1049
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    When a nearest-neighbor constraint (which prevents elements from lying closer than some specified distance from each other) is imposed on a large random planar array of isotropic radiators, the corresponding radiation pattern contains a region around the main beam where random sidelobes are suppressed. This effect is mostly clearly manifested if the array is densely packed, i.e. if the array contains nearly the maximum number of elements consistent with the chosen constraint. A theory to account for this effect is developed View full abstract»

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  • A direct profile inversion for weakly conducting layered medium

    Page(s): 907 - 909
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    By using the Werner-Kramer-Brillouin method to solve for the field inside the medium in half-space, a simple scheme of a profile inversion from the reflection data is obtained for a weakly pure conducting medium. Some examples show the applicability of this scheme View full abstract»

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  • The near field of a wire grid model

    Page(s): 994 - 999
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    The extreme near-field behavior of the wire grid model of a conducting surface is examined. Using a wire grid model of an infinite transverse magnetic circular cylinder, it is verified that the best accuracy for the E-field is obtained when the wire satisfies the `same surface area' rule of thumb. Two excitations are considered: a uniform surface current and plane wave incidence. In the first case, although the boundary value match between the wires is poor the extreme near field is still quite accurate. In the second case, the near field is also accurate, however, the largest errors occur not between the wires, but in the interior of the scatterer. In both cases, the boundary match between the wires as a check on the accuracy of the solution is misleading View full abstract»

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  • Adaptive beamforming with conjugate symmetric weights

    Page(s): 926 - 932
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    The Hermitian persymmetric maximum likelihood estimator (MLE) is better than the conventional MLE in estimating the covariance matrix of a symmetrically distributed antenna array. Though using the Hermitian persymmetric MLE improves the performance of adaptive beamforming, it increases the computational load due to the forward-backward averaging of array input sample data. By observing that the weight vector obtained from the Hermitian persymmetric MLE is conjugate symmetric if the phase origin is chosen at the array geometry center, methods are developed to reduce the computational load of the direct-form beamformer and the generalized sidelobe canceler (GSC). The weights of both beamformers can be adapted with real computations, with significant savings in computation time View full abstract»

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  • Electromagnetic field excited by a line source placed at the edge of an impedance wedge

    Page(s): 1043 - 1046
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    An exact integral representation for the field radiated by a line source located at the edge of an impedance wedge has been obtained. To this end, the plane wave spectrum of the source is used in connection with the plane wave response of the wedge. Uniform high-frequency expressions for the total field are derived from that solution. They include the description of surface wave excitation mechanisms, and provide field patterns that are smooth and continuous across the surface wave shadow boundaries. Numerical examples are presented to investigate these evanescent wave contributions View full abstract»

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  • Scattering of electromagnetic waves by a material half-space with a time-varying conductivity

    Page(s): 898 - 906
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    The electromagnetic wave penetration and scattering interactions for a material half-space with sinusoidally time-varying conductivity are analyzed. Two limiting cases are considered. The first assumes that the material conductivity is almost a constant with a small temporal perturbation. The problem is accordingly attacked with first-order perturbation methods. The second exploits a large dimensionless parameter and yields an asymptotic expansion of the field inside a highly conducting material undergoing sinusoidal time variation. Illustrative examples are given which agree well with numerically obtained finite-difference time-domain (FDTD) results View full abstract»

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  • Near-field multiple source localization by passive sensor array

    Page(s): 968 - 975
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    The localization of multiple near-field sources in a spatially white Gaussian noise environment is studied. A modified two-dimensional (2-D) version of the multiple signal classification (MUSIC) algorithm is used to localize the signal sources; range and bearing. A global-optimum maximum likelihood searching approach to localize these sources is discussed. It is shown that in the single source situation, the covariances of both the 2-D MUSIC estimator and the maximum likelihood estimator (MLE) approach the Cramer-Rao lower bound as the number of snapshots increases to infinity. In the multiple source situation, it is observed that for a high signal-to-noise ratio (SNR) and a large number of snapshots, the root mean square errors (RMSEs) of both localization techniques are relatively small. However, for low SNR and/or small number of snapshots, the performance of the MLE is much superior that of the modified 2-D MUSIC View full abstract»

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  • A new surface impedance function for the aperture surface of a conducting body with a dielectric-filled cavity

    Page(s): 960 - 967
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    A surface impedance function (SIF) appropriate for use on the aperture surface of a conducting body with a dielectric-filled cavity, is presented. Unlike the usual SIFs that might be used on an aperture, this SIF takes into account not only the wave transmitted through the aperture but also the wave reflected from the inside of the cavity the shape of the aperture and cavity, and the polarization and direction of the incident wave. The SIF is derived heuristically from the series-reflection solution for a plane wave normally incident on an infinite flat conducting plate with a flat dielectric coating. The SIF was developed and used in a combined method of moments solution for the scattered fields due to an incident plane wave. This combined technique greatly reduces the number of current expansion coefficients to be determined using the method of moments and hence also reduces the number of impedance elements required for calculation in the method of moments. Application of the SIF in a combined method is illustrated for a two-dimensional object View full abstract»

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  • Reconfigurable arrays by phase-only control

    Page(s): 919 - 925
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    Due to space or cost reasons, a single array antenna can be required to radiate more than one pattern, each pattern being selected by an electronic control, in which only the phase can be modified. A synthesis method for such a problem that is able to determine both the common amplitude and the various phases in an integrated way is presented. Moreover, the approach is flexible enough to take into account additional constraints and allows an efficient implementation. Some test cases showing the effectiveness of the method are 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