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Antennas and Propagation, IEEE Transactions on

Issue 1 • Date Jan. 1995

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Displaying Results 1 - 17 of 17
  • Comments on "Propagation of EM pulses excited by an electric dipole in a conducting medium" [with reply]

    Publication Year: 1995 , Page(s): 119 - 120
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    Comments that the authors of the original paper (see Song and Chen, ibid., vol.41, no.10, p.1414-1421, 1993) wish to determine the transient electromagnetic field generated in a conducting medium by an impulsive current in a short electric dipole. Their approach and their results, however, seem to be questionable. To start with, their choice of a delta-function excitation causes serious mathematical difficulties which have been overlooked. Because the spectrum of the delta-function pulse extends over all frequencies with equal Fourier amplitudes, the assumption that the conducting medium, specifically sea water, is characterized by frequency independent permittivity and conductivity is incorrect. The authors reply that they are aware that the conductivity and permittivity of sea water is frequency dependent. They made the approximation of constant conductivity and permittivity for two reasons. First, the exciting impulse current contains all the frequency components from zero to /spl infin/. The second reason for the assumption of constant conductivity and permittivity is that with this assumption we are able to obtain an exact solution for the EM field excited by an impulse current.<> View full abstract»

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  • Results from the Virginia Tech propagation experiment using the Olympus satellite 12, 20 and 30 GHz beacons

    Publication Year: 1995 , Page(s): 54 - 62
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (812 KB)  

    A comprehensive set of propagation experiments was performed using the Olympus satellite 12, 20, and 30 GHz beacons. This set of experiments is unique in North America because of simultaneous reception of signals spanning the Ku- and Ka-bands from the same orbital slot, which permits direct inference of the frequency behavior of signal variations. The elevation angle from the receiving site in Blacksburg, VA, to the satellite was 14 degrees. Beacon, radiometric, and weather data for one year were analyzed. The statistical results for rain rate, beacon attenuation, attenuation ratios, radiometrically derived attenuation, fade duration and fade slope are presented. They are important to the design of Ku- and Ka-band satellite communication systems. The beacon attenuation results include cumulative statistics for attenuation with respect to free space and with respect to clear air. Attenuation ratio data are presented using attenuation with respect to clear air to focus on rain effects. Instantaneous attenuation ratios computed from instantaneous beacon levels were found to be nearly identical to statistical attenuation ratios obtained from cumulative attenuation statistics at each frequency View full abstract»

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  • Electromagnetic scattering from dielectric-coated axisymmetric objects using the generalized point-matching technique (GPMT)

    Publication Year: 1995 , Page(s): 63 - 71
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (868 KB)  

    This paper describes the use of the generalized point-matching technique (GPMT) in analyzing plane electromagnetic (EM) scattering from 3-D bounded objects consisting of (or modeled by) an arbitrarily shaped axisymmetric perfect electrically conducting (PEC) or dielectric obstacle embedded in an arbitrarily shaped dielectric body of revolution and arbitrarily disposed with respect to the propagation direction of an arbitrarily polarized incident electric field vector. The treatment may be validly applied to scatterers whose boundary surfaces must have no sharp corners or edges which will introduce a discontinuity in the direction of the unit vector normal to the core and/or outer coat surfaces. It should be pointed out, however, that when applicable, the method is remarkably robust and capable of providing highly accurate numerical modelling predictions for the full-vector EM wave interactions with a large variety of arbitrarily shaped two-layered structures. Numerical results for a variety of scatterer configurations are provided and compared to exact or otherwise available results to demonstrate the potency and versatility of the suggested GPMT formulation View full abstract»

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  • Terrain-based propagation model for rural area-an integral equation approach

    Publication Year: 1995 , Page(s): 41 - 46
    Cited by:  Papers (46)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    A terrain-based propagation model for vertically polarized radio waves is described, based on the field integral equation for a smooth surface. The model is simplified from a 3D integral equation model to a one-dimensional integral equation by assuming that the surface is magnetically perfectly conducting (a soft surface) with no transverse variations. By assuming no back scattering, the integral equation is turned into a simple integral. The method is tested numerically with known solutions. The integral equation model is also applied to actual terrain profiles at four frequencies (144, 435, 970, 1900 MHz), and the results are compared with results from the Hata model and measurements. The standard deviation (STD) of the error is a growing function of frequency, from 3 to 9 dB View full abstract»

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  • Electromagnetic scattering for oblique incidence on impedance bodies of revolution

    Publication Year: 1995 , Page(s): 11 - 26
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1296 KB)  

    Combined field integral equations for the surface currents induced by an obliquely incident wave on a rotationally symmetric body are considered. The relative surface impedance is independent of the azimuthal angle but may vary along the profile of the scatterer in any plane containing the axis of symmetry; the currents are conveniently expressed in terms of Fourier series of uncoupled terms in the azimuthal angle. Simple integral expressions for the far field are given and a computer code is described and tested on a variety of scatterers. Geometry of scatterer, surface impedance and Fourier harmonics of induced currents are described by splines. The results are in agreement with physical interpretation View full abstract»

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  • Characteristics of aperture coupled microstrip antennas with various radiating patches and coupling apertures

    Publication Year: 1995 , Page(s): 72 - 78
    Cited by:  Papers (15)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    A full wave moment method is applied to the analysis of aperture coupled microstrip antennas, in which all components of the electric and equivalent magnetic surface currents are considered. The electric current distributions on the rectangular patch for different coupling aperture positions are presented with their radiation patterns. The effects of the coupling aperture shape and size on the input impedance and radiation performance are also discussed. As an example of new radiators, slotted patches are studied, and it is shown that they can be used to achieve dual-frequency operation View full abstract»

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  • Image theory for the soft and hard surface

    Publication Year: 1995 , Page(s): 117 - 119
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    Image theory is developed for sources above a planar anisotropic boundary surface, often labeled as soft and hard surface. Realizable with tuned corrugations so that the electric and magnetic field components along the corrugations become zero. The idea pursued is to decompose the original source in two components, giving rise to fields TE and TM to the direction of corrugation, respectively. This makes the problem split into two parts for which the image sources can be easily constructed. For an electric dipole, the image turns out to consist of a rotated dipole in the mirror image point plus a transmission-line current source parallel to the corrugations. The theory is readily applicable to various microwave problems involving a planar soft and hard surface View full abstract»

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  • Calculation of the characteristic impedance of TEM horn antennas using the conformal mapping approach

    Publication Year: 1995 , Page(s): 47 - 53
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    A new conformal mapping technique for determining the characteristic impedance of TEM horn antennas is presented. The original work by Carrel [1958], on noncoplanar fin antennas of this type, predicts incorrect impedance values which do not agree with experimental results. The present paper discusses fully the source of the error in Carrel and details the successive mappings involved in the new approach. Verification of the method is provided by experimental results and by comparison with an alternative numerical technique View full abstract»

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  • A generalized diffraction synthesis technique for high performance reflector antennas

    Publication Year: 1995 , Page(s): 27 - 40
    Cited by:  Papers (58)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1204 KB)  

    Stringent requirements on reflector antenna performances in modern applications such as direct broadcast satellite (DBS) communications, radar systems, and radio astronomy have demanded the development of sophisticated synthesis techniques. Presented in the paper is a generalized diffraction synthesis technique for single- and dual-reflector antennas fed by either a single feed or an array feed. High versatility and accuracy are achieved by combining optimization procedures and diffraction analysis such as physical optics (PO) and physical theory of diffraction (PTD). With this technique, one may simultaneously shape the reflector surfaces and adjust the positions, orientations, and excitations of an arbitrarily configured array feed to produce the specified radiation characteristics such as high directivity, contoured patterns, and low sidelobe levels, etc. The shaped reflectors are represented by a set of orthogonal global expansion functions (the Jacobi-Fourier expansion), and are characterized by smooth surfaces, well-defined (superquadric) circumferences, and continuous surface derivatives. The sample applications of contoured beam antenna designs and reflector surface distortion compensation are given to illustrate the effectiveness of this diffraction synthesis technique View full abstract»

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  • Optimal surface adjustment of Haystack antenna

    Publication Year: 1995 , Page(s): 79 - 86
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (836 KB)  

    The primary reflector panels of the 37-m (120-ft) diameter Haystack antenna are prestressed to form an integrated parabolic shell of revolution. The adjustment mechanisms of the reflector surface are highly interacting, and the region of influence of each adjustment mechanism is large and intersects in a major way the influence regions of other adjustment mechanisms. The influence surface for each adjustment is computed using a detailed finite-element model of the antenna and the reflector structures. The optimal adjustments, i.e. the adjustments that minimize surface RMS, are obtained using the computed influence surfaces by solving a quadratic programming problem. The resolution of holography introduces errors in the holography map, but the resulting error in the computed adjustments are eliminated by using, in lieu of the actual influence surfaces, the transformed influence surfaces obtained by the convolution of the actual influence surfaces with the holography resolution function. The procedure, which was used to reduce surface RMS of the Haystack from 639 micron (25.1 mil) to 194 micron (7.6 mil), is applicable to other antennas View full abstract»

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  • A Ka-band circularly polarized high-gain microstrip array antenna

    Publication Year: 1995 , Page(s): 113 - 116
    Cited by:  Papers (30)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    In this article, the development of a circularly polarized microstrip array with 28 dBic of gain at 32 GHz is presented. Two primary objectives of this development are minimizing the microstrip array's insertion loss and maintaining a reasonable frequency bandwidth (3%). The parallel/series feed technique for the array's power distribution circuit and the sequential rotation method for the element arrangement are employed to meet these objectives View full abstract»

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  • Comparison of local radiation boundary conditions for the scalar Helmholtz equation with general boundary shapes

    Publication Year: 1995 , Page(s): 6 - 10
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    The relative accuracy of several local radiation boundary conditions based on the second-order Bayliss-Turkel (1980) condition are evaluated. These boundary conditions permit the approximate solution of the scalar Helmholtz equation in an infinite domain using traditional finite element and finite difference techniques. Unlike the standard Bayliss-Turkel condition, the generalizations considered here are applicable to noncircular solution domains. The accuracy of these conditions are investigated for elliptical and linear/circular boundaries View full abstract»

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  • An incremental theory of diffraction: electromagnetic formulation

    Publication Year: 1995 , Page(s): 87 - 96
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (844 KB)  

    A scalar formulation of the incremental theory of diffraction (ITD) has been introduced by Tiberio and Maci (see ibid., vol.42, no.5, 1994), which provides a self-consistent, high-frequency description of a wide class of scattering phenomena, within a unified framework. In this paper, this method is extended to electromagnetic problems. The total field is represented as the sum of a generalized geometrical optics field plus incremental diffracted field contributions. Explicit dyadic expressions of incremental diffraction coefficients are derived for wedge-shaped configurations. The formulation of the field is uniformly valid at any incidence and observation aspects, including caustics and shadow boundaries of the corresponding ray field description. Numerical results are presented and compared with those obtained from different techniques View full abstract»

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  • Constructing the phase converters consisting of arbitrary number of translucent surfaces

    Publication Year: 1995 , Page(s): 109 - 113
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    An effective analytical method of synthesis of an artificial anisotropic structure has been developed. At a design frequency, it ensures perfect match and a phase shift given. The structure may be formed by arbitrary number of inductive and capacitive grids. The method has been applied to constructing circular polarizers and twist polarizers. The geometrical parameters of the polarizers were found in the explicit form. Analytical criteria for an estimate of the bandwidth of the devices have been derived. Performance of the polarizers over a frequency band was studied. A circular polarizer has been proposed which consists of both a cascade of two inductive grids and a cascade of two capacitive grids. The polarizer can be used when very high axial ratio is needed. It ensures more than 10% bandwidth for 0.99 axial ratio. Measurements have been presented that prove adequacy of the mathematical model for real inductive and capacitive screens View full abstract»

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  • Computation of attenuation, phase rotation, and cross-polarization of radio waves due to rainfall in tropical regions

    Publication Year: 1995 , Page(s): 1 - 5
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    Computation of attenuation, phase rotation, and cross-polarization of radio waves due to rain in tropical regions using finite element method is the subject of this work. Computations are made of the forward-scattering amplitudes of oblate spheroidal raindrops at 20 and 30 GHz, assuming plane waves at normal incidence to the raindrop axis. The forward-scattering amplitudes are employed to obtain the required attenuation, phase rotation, and cross-polarization using the rainfall rate data for Nigeria, a tropical African country. The results obtained in this work compare with those existing in the open literature View full abstract»

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  • Spectral theory of EM wave scattering by periodic strips

    Publication Year: 1995 , Page(s): 97 - 104
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    A new method is proposed for analyzing electromagnetic (EM) wave scattering and waveguiding by a planar periodic system of thin and perfectly conducting strips. The method exploits some known properties of Fourier series with coefficients expressed by Legendre polynomials. The method can be used to solve problems associated with EM wave propagation and polarization having an arbitrary angle with respect to strips in arbitrary anisotropic media, multiperiodic systems of strips, and layered systems of skewed periodic strips. In the paper the method is presented by an example, namely the scattering of EM waves from a grating consisting of perfectly conducting strips in vacuum. Numerical calculations show that the method converges much faster than do alternative methods View full abstract»

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  • Italsat-Olympus 20-GHz orbital diversity experiment at Spino d'Adda

    Publication Year: 1995 , Page(s): 105 - 108
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    This paper reports results of the 20 GHz orbital diversity experiment between the geostationary satellites Olympus (19°W) and Italsat (13°E), as viewed from Spino d'Adda, Po Valley, northern Italy. The results show that: (a) the statistical gain is significant; and (b) for a small angular separation in the geostationary orbit between the satellites (32° in our experiment) the gain, normalized to single link attenuation and expressed in percent, is, as a rule of thumb, of the order of magnitude of this angle expressed in degrees, 30% in our experiment 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