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Antennas and Propagation, IEEE Transactions on

Issue 12 • Date Dec. 2001

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Displaying Results 1 - 25 of 42
  • Foreword to the special issue on millennium day of diffraction seminars

    Page(s): 1610 - 1611
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    Freely Available from IEEE
  • Author index

    Page(s): 1884 - 1891
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    Freely Available from IEEE
  • Subject index

    Page(s): 1891 - 1916
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    Freely Available from IEEE
  • Atmospheric transmission at microwaves (ATM): an improved model for millimeter/submillimeter applications

    Page(s): 1683 - 1694
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    We present a model of the longwave atmospheric spectrum that improves in many respects widely used older models such as the microwave propagation model (MPM), since it is based on broadband measurements and calculations. According to our data, the model is fully applicable from 0 to 2 THz while including lines up to 10 THz. Its primary goal is to simulate the millimeter/submillimeter region accessible from the ground (frequencies up to ~2 THz at most, with a few windows between 1 and 2 THz accessible only under exceptional conditions at very dry sites). Line-by-line calculations of the absorption are performed using a line database generated from the latest available spectroscopic constants for all relevant atmospheric species. The collisional line widths are obtained from published laboratory data. The excess of absorption in the longwave range that cannot be explained by the line spectrum is modeled by introducing two different continuum-like terms based on FTS measurements between 170 and 1100 GHz: collision-induced absorption of the dry atmosphere due to transient dipoles in symmetric molecules (N 2 and O2) and continuum-like water vapor opacity. All H2O lines up to 10 THz are included in order to correctly account for the entire H2O far-wing opacity below 2 THz for a given line-shape. Hence, this contribution does not need to be part of a pseudocontinuum term below that frequency cutoff (still necessary, as shown in this paper) in contrast to other models used to date. Phase delays near H2O and O2 resonances are also important for ground-based astronomy since they affect interferometric phase. The frequency-dependent dispersive phase delay function is formally related to the absorption line shape via the Kramers-Kronig dispersion theory, and this relation has been used for modeling those delays. Precise calculations of phase delays are essential for the future Atacama large millimeter array (ALMA) project. A software package called atmospheric transmission at microwaves (ATM) has been developed to provide the radioastronomy and aeronomy communities with an updated tool to compute the atmospheric spectrum in clear-sky conditions for various scientific applications. We use this model to provide detailed simulations of atmospheric transmission and phase dispersion for several sites suitable for submillimeter astronomy View full abstract»

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  • Attenuation and backscatter from a derived two-dimensional duststorm model

    Page(s): 1703 - 1711
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    Fundamentals of attenuation and radar backscatter through duststorms are reviewed. A duststorm is modeled as circularly symmetric having a visibility with a minimum at its center (e.g., maximum mass loading) and which exponentially increases radially to a fixed maximum visibility threshold level (minimum mass loading). This model enables the convenient calculation of the two dimensional (2-D) structure of radar backscatter and path attenuation. As an example, the parameters of the exponential function describing the visibility distribution for a particular duststorm was derived using measurements made in the Sudan by other investigators operating a 10.5 GHz, 25 km link. A comparison of the calculated and measured attenuation time-series showed relatively close agreement. Both attenuation levels and backscatter levels due to even intense duststorms are expected to be relatively small for frequencies up to 10 GHz. For example, the peak attenuation for the duststorm that contained visibilities smaller than 2 m was less than 6.5 dB. Modeled backscatter due to this duststorm gave levels smaller than that obtained by an equivalent rainrate of 0.6 mm/h. Although the calculations were obtained for X-band, they may be extended to higher frequencies. Frequency scaling at 37 GHz, for example, showed a peak equivalent path attenuation level of at least 26.6 and 48 dB under varying assumptions View full abstract»

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  • On the depolarization of bodies invariant under a rotation

    Page(s): 1868 - 1874
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    It is shown that a body of arbitrary material constitution, but invariant under a fixed rotation, must be periodic and will not monostatically depolarize under linear polarization axial incidence if reciprocal, unless the body is invariant under a rotation by 180°. For circular polarization, the result is more general, the body will not depolarize even if it is not reciprocal. Forward scattering and other considerations are also included. The theory is illustrated by application to a few selected scatterers View full abstract»

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  • Characteristics of vector propagation channels in dynamic mobile scenarios

    Page(s): 1695 - 1702
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    In wireless communications, the performance of a smart antenna system depends heavily upon vector channels describing channel propagation between an antenna array and a mobile subscriber. The smart antennas perform quite well in stationary mobile environments in which channel propagation characteristics are stable. However, in dynamic wireless environments where the mobile user is in motion, knowledge of how vector channels are affected is necessary for the proper operation of smart antennas. Here, we experimentally investigate the variation of vector channel parameters such as spatial signatures, directions-of-arrival (DOAs), and complex path attenuations with small movement (2λ) of the mobile under typical line-of-sight (LOS), line-of-sight with local scatterer (LOSLS), and nonline-of-sight (NLOS) propagation scenarios. The experiments are conducted using a 1.8-GHz smart antenna testbed developed at The University of Texas at Austin and a mobile transmitter. The results show that with small displacements, DOAs remain approximately unchanged and spatial signatures change due primarily to complex attenuations. Spatial signatures are very susceptible to the movement in the NLOS scenario, reaching up to 90% relative angle change within 2λ displacement. However, in the LOS scenario, they exhibit small and periodic fluctuations with a period of 0.6λ View full abstract»

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  • Performance analysis of MVDR algorithm in the presence of amplitude and phase errors

    Page(s): 1875 - 1877
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    The sensitivity of spectrum estimation approach, the minimum variance distortionless response (MVDR) spectrum estimator, to random perturbations in the amplitude and phase of array sensors is studied. Analytical expressions for the mean and variance of the spatial spectrum are derived. The effects of the amplitude error on the spectrum is greater relatively than that of the phase error. Theoretical results are validated by the computer simulation. These expressions are then used to study the characteristics of the estimator View full abstract»

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  • Scattering from surface waves on finite FSS

    Page(s): 1782 - 1793
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    This paper discusses the presence of surface waves on periodic structures in general and on frequency selective surfaces (FSS) in particular. While certain types of surface waves can exist on infinite as well as finite periodic structures, this investigation centers around the types that can exist only on finite FSS. Radiation caused by these surface waves may lead to a significant scattering increase in the backscatter as well as the bistatic directions. Thus, this paper is of both theoretical and practical interest View full abstract»

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  • High-frequency scattering by objects buried in lossy media

    Page(s): 1649 - 1656
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    The uniform geometrical theory of diffraction (UTD) is extended so that it can be used to calculate the scattering from an object buried in a lossy medium. First, the accuracy of this high frequency method is examined by comparing numerical results for the scattering by a polygonal cylinder in a lossy medium of infinite extent with calculations based on a method of moments (MoM) solution. Next, the more difficult scattering problem of a polygonal cylinder in a lossy half space is treated. The UTD solution for the unbounded region is employed together with the fields of rays introduced by the interface between air and the lossy medium to obtain expressions for the scattered field in air and in the lossy medium View full abstract»

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  • Plane wave, pattern subtraction, range compensation

    Page(s): 1843 - 1851
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    Plane wave, pattern subtraction (PWPS) range compensation improves the performance of far field and compact, antenna pattern measurement systems by compensating errors introduced by antenna measurement facility (range) imperfections. The range-field model consists of a plane wave that represents an ideal range field plus a selectable number of plane waves representing range field imperfections. The error patterns introduced by the undesired range-field plane waves are estimated and subtracted from the measured pattern to produce a compensated pattern. This compensated pattern is used to obtain an improved estimate of the error patterns. This iterative procedure is continued until the compensation algorithm converges. The antenna measurement range field is measured on the surface of a sphere enclosing the test zone, and a plane-wave model of this range field is constructed View full abstract»

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  • Radiation characteristics of thin-wire V-antennas excited by arbitrary time-dependent currents

    Page(s): 1877 - 1880
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    This paper studies, from the point of view of the traveling-wave approach, the transient radiation by V-antennas including the dependence of the maximum directivity on the interior angle, on the length of the arms and on the characteristics of the exciting pulse. As particular examples, the cases when the antenna is excited by a harmonic signal and a Gaussian pulse are analyzed and the results obtained using the traveling-wave approach are compared with the ones obtained using numerical methods View full abstract»

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  • Admittance of transverse waveguide slots in cylindrical structures

    Page(s): 1733 - 1738
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    The self and mutual admittances of transverse slots in arbitrary conducting cylindrical structures are computed. The analysis is performed in the spectral domain, where all fields and currents have been Fourier transformed along the structure. There are, however, no transformations in the transverse directions. A system of integral equations for cylindrical structures are formulated and solved with the moment method. The induced currents on the structure can thus be determined and used to compute the spectral self and mutual admittance of the slots. The spectral admittance is inverse transformed and included in the overall slot antenna analysis. The analysis is rigorous with trigonometric basis function expansions at the inner and outer slot apertures. Computed results on scattering parameters in the waveguide show good agreement with measured data View full abstract»

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  • Plane-wave scattering-matrix formulation for two interfaces plus a scatterer (uniplanar case)

    Page(s): 1852 - 1861
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    Kern's plane-wave scattering-matrix formulation is extended to treat the case of two interfaces plus a scatterer imbedded in the second region. This formulation can treat different shapes for the scatterer and only requires two different evaluations depending upon the location of the observer: 1) in the near field, a two-dimensional (2-D) fast Fourier transform (FFT) (one-dimensional (1-D) FFT is treated by an analytical integration), and 2) in the far-field an asymptotic evaluation of the integral. These two regimes are in contrast to the Sommerfeld integral approximations where different approximations are required for various parameter ranges (quasistatic, saddle-point evaluation for the radiation field, saddle point evaluation for the surface field when the saddle point is near a pole, and the lateral wave field evaluated using a uniform asymptotic evaluation for the integrals) View full abstract»

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  • A reciprocity approach for calculating the far-field radiation patterns of a center-fed helical microstrip antenna mounted on a dielectric-coated circular cylinder

    Page(s): 1754 - 1762
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    This paper presents an efficient approach based on reciprocity for calculating the far-field radiation pattern of a center-fed helical microstrip antenna mounted on a circular cylinder. The reciprocity theorem is used to find a completely analytical solution to the problem assuming that the helical microstrip is sufficiently thin with a sinusoidal current distribution. Two degenerate cases of the helical microstrip antenna, i.e., an axially and an azimuthally fed half-wave cylindrical-rectangular patch, are examined and compared to known results in order to provide validation for the general analytical solution. Further comparisons are made between the analytical results and the results obtained using a numerically rigorous method of moments (MoM) computer code View full abstract»

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  • Hybrid PO-MoM analysis of large axi-symmetric radomes

    Page(s): 1657 - 1666
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    Over the last three decades, intensive work has been done to develop techniques aimed at accurate and efficient analysis of antenna radome systems. Some applications involve radar operating in the millimeter wave range and for those cases the radome size can be on the order of one hundred wavelengths or so in length. For practical simulations of such large radomes, a hybrid physical optics-method of moments (PO-MoM) technique is presented for accurate and efficient analysis of electrically large radomes. The procedure combines the method of moments (MoM) for modeling the tip region of the dielectric radome and ray optics in conjunction with physical optics (PO) for treating the flatter smooth section of the radome. Calculated far-field patterns using the new technique agree well with measured data for a reflector antenna radiating in the presence of a large radome. The computational time for simulating the performance of a 46λ reflector in the presence of an 88λ long radome was a mere 4 h on a 233 MHz PC View full abstract»

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  • A crack identification microwave procedure based on a genetic algorithm for nondestructive testing

    Page(s): 1812 - 1820
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    This paper is aimed at exploring the possibility of using a microwave approach based on a genetic algorithm to detect a defect inside a known host object. Starting from the knowledge of the scattered field, the problem solution is recast as a two-step procedure. After defining a cost function depending on the geometric parameters of the crack, a minimization procedure based on a hybrid-coded genetic algorithm is applied. The influence of the noise as well as of the geometry of the defect on the crack detection and reconstruction is investigated. Moreover, the numerical effectiveness of the iterative approach is examined View full abstract»

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  • Analysis of the zonal and rectangular slots on a conducting spherical cavity

    Page(s): 1739 - 1745
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    The zonal slot cut on a conducting spherical cavity is analyzed rigorously. The slot is excited asymmetrically, which excites higher order azimuthal modes. The Green's function approach is used to formulate an integral equation for the magnetic current in the slot, which is solved using the moment method (MoM). New recurrence formulas are derived so that within their stable region the admittance integrals can be evaluated without the need for any numerical integration. In this case, the solution is very easy to implement with extremely short computation time. The effects of the latitude angle on the peak resistance and percentage bandwidth are investigated. Furthermore, the cavity resonance modes and their degeneracy are examined by plotting the expansion coefficients of the magnetic current. In addition, the problem of a rectangular slot in the nonequatorial plane is also studied. Measurements are carried out and good agreement between theory and experiment is obtained View full abstract»

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  • High-frequency Green's function for a semi-infinite array of electric dipoles on a grounded slab .I. formulation

    Page(s): 1667 - 1677
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    A uniform, high-frequency solution is presented for the electromagnetic field radiated at finite distance by a semi-infinite array of elementary electric dipoles placed on an infinite grounded dielectric slab. This solution is useful for the efficient analysis of printed arrays. The field is represented in terms of a series encompassing propagating and evanescent truncated Floquet waves together with their corresponding diffracted rays, which arise from the edge of the array. The high-frequency formulation also includes surface and leaky wave contributions excited at the array edge. The diffracted waves contain discontinuities which compensate the disappearance of surface, leaky and truncated Floquet waves at their pertinent shadow boundaries View full abstract»

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  • Scattering by a groove in a conducting plane-a PO-MoM hybrid formulation and wavelet analysis

    Page(s): 1807 - 1811
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    A novel method is presented to solve the two-dimensional (2-D) problem of scattering of an electromagnetic plane wave by a groove in a perfectly conducting infinite plane. In this method, the unknown induced current is expressed in terms of the known physical optics solution of the unperturbed problem of scattering by an infinite conducting plane plus a yet to be determined localized correction current placed in the vicinity of the groove. It is then shown that a good approximation of the induced current can be obtained using only a few dominant functions in the wavelet expansion of the correction current. Moreover, the same set of dominant wavelet functions serves the purpose of approximating the induced current at different angles of incidence. A numerical example demonstrates these various features of the proposed method of solution View full abstract»

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  • Performance analysis of a GLRT automated target discrimination scheme

    Page(s): 1827 - 1835
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    The use of a generalized likelihood ratio test (GLRT) based on the late-time scattered return for target discrimination was recently presented by J.E. Mooney et al. (see ibid., vol.46, p.1817-23, Dec. 1998). The performance of the GLRT was demonstrated by direct simulation with scattering data from a target library consisting of several thin-wire targets. In this paper, a numerical procedure for analytically evaluating the performance of the GLRT is presented. At the heart of this procedure is the computation of the probability density of the GLRT decision statistic. Unlike previous works that rely solely on some simulation examples to demonstrate performance, our accurate analytical results provide strong evidence of the effectiveness of the GLRT method. The resulting analysis yields a measure of the discrimination capability of the GLRT. This measure, which is referred to as the probability of correct identification, is computed as a function of signal-to-noise ratio (SNR) using the theoretical scattering data from several thin-wire targets. These results are compared to the direct simulation results presented by Mooney et al. to demonstrate the accuracy of the analysis View full abstract»

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  • A feeding circuit with CPW for CA-RLSA

    Page(s): 1862 - 1867
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    For a concentric array radial line slot antenna (CA-RLSA) with a boresite beam, a rotating mode should be excited. A planar feeding circuit exciting a rotating mode in a parallel-plate waveguide is proposed in this paper. The structure consists of a coplanar waveguide (CPW), ring slot, and cavity, which is planar and suitable for integrating and minimizing even in a millimeter-wave band. The experimental results agree well with the simulation View full abstract»

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  • High-frequency scattering by an isorefractive wedge with the parabolic equation method

    Page(s): 1628 - 1632
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    The parabolic equation (PE) method is applied to the problem of the high-frequency scattering from a diaphanous wedge, that is, a wedge made of a material which is isorefractive with respect to the surrounding medium, illuminated by a plane wave or by a line current parallel to the edge. The proposed approach is able to handle any wedge aperture and incidence angle and presents some novelties that allows overcoming the problems arising in the numerical solution of the parabolic equation applied to penetrable wedges View full abstract»

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  • Wave emission from an open-ended cylindrical channel in a cold magnetoplasma

    Page(s): 1645 - 1648
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    We study wave emission from a transmitting system consisting of a magnetic-field-aligned cylindrical plasma channel of enhanced density and a loop antenna immersed in it. An ambient medium is assumed to be a cold uniform magnetoplasma. It is found that when the plasma density in the near-antenna zone increases, the total power radiated from the antenna increases considerably due to the efficient excitation of guided modes on the channel. We consider the emission of these modes from the channel end, assuming that the plasma density in the channel decreases gradually with distance from the loop. It is shown that under ionospheric conditions this transmitting system can be useful for improving the antenna coupling to VLF waves of the ambient plasma View full abstract»

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  • Millimeter-wave proximity-coupled microstrip antenna on an extended hemispherical dielectric lens

    Page(s): 1769 - 1772
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    A low-cost, high-gain, millimeter-wave antenna is presented. The antenna is composed of a proximity-coupled microstrip patch mounted on the back surface of a substrate lens. The antenna utilizes low dielectric constant, low-cost materials and is therefore suitable to many commercial millimeter-wave systems. A full-wave analysis was developed to analyze the performance of the printed antenna and a prototype was developed for operation at 38 GHz. The impedance bandwidth of the prototype was 8% and the gain was approximately 30 dBi across this frequency span with a front-to-back ratio greater than 60 dB 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