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Antennas and Propagation, IEEE Transactions on

Issue 1 • Date January 1984

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Displaying Results 1 - 19 of 19
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Editorial

    Page(s): 2 - 5
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    Freely Available from IEEE
  • [Back cover]

    Page(s): c4
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    Freely Available from IEEE
  • A class of broad-band patch microstrip traveling wave antennas

    Page(s): 98 - 100
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    Measured voltage standing-wave ratio (VSWR) and radiation characteristics are presented for a class of antennas consisting of nonuniform arrays of rectangular patches having variable dimensions, and excited by traveling waves on microstrip lines. The results indicate that when properly designed these linearly polarized antennas are capable of providing large bandwidths with regard to input VSWR and radiation properties. View full abstract»

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  • The radar cross section of dielectric disks

    Page(s): 6 - 12
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    A solution is presented for the backscatter (monostatic) radar cross section of dielectric disks of arbitrary shape, thickness, and dielectric constant. The result is obtained by employing a Kirchhoff-type approximation to obtain the fields inside the disk. The internal fields induce polarization and conduction currents from which the scattered fields and the radar cross section can be computed. The solution for the radar cross section obtained in this manner will be shown to agree with known results in the special cases of normal incidence, thin disks, and perfect conductivity. It will also be shown that the solution can be written as a product of the reflection coefficient of an identically oriented slab times the physical optics solution for the backscatter cross section of a perfectly conducting disk of the same shape. This result follows directly from the Kirchhoff-type approximation without additional assumptions. View full abstract»

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  • Synthesis of offset dual shaped subreflector antennas for control of Cassegrain aperture distributions

    Page(s): 86 - 92
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    Many existing large ground reflector antennas have been designed as Cassegrain systems-i.e., paraboloid/hyperboloid combinations. Other large ground antennas are simply paraboloid designs. Upgrading the gain of these systems to a gain comparable to that obtainable with a dual shaped reflector antenna system has been an important and costly objective of many such ground stations. A potentially economic method for such an antenna upgrade is presented herein. It involves a redesign of only the subreflector portion of a Cassegrain antenna or the introduction of a subreflector feed system for a parabaloid. A pair of offset subreflectors are synthesized which will give a controllable high gain amplitude distribution in the aperture of the large paraboloid. The synthesis method that is used is based on an approximate formulation for an offset dual shaped high gain antenna that was first presented by Galindo-Israel and Mittra in 1977. In that approximate formulation, the geometrical optics (GO) energy was scattered from a subreflector and then from a second large reflector which reflected a uniform phase distribution. In the present offset dual shaped subreflector (DSS) antenna, the second reflection is from a smaller (sub) reflector and it scatters a spherical wave that feeds a hyperboloid or feeds a large paraboloid directly. Excellent results are shown for the approximate synthesis of the DSS. View full abstract»

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  • A new method of analysis of the near and far fields of paraboloidal reflectors

    Page(s): 13 - 19
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    An analytical technique for predicting accurately the near (electric and magnetic) fields as well as the far fields of a reflector antenna with a pencil beam is presented. The technique proposed involves the near-field geometrical theory of diffraction (GTD) analysis of reflector antennas developed earlier and spherical vector mode functions. The proposed technique does not place any restriction on the range of polar angles or radial distances of the observation point. It is demonstrated that the technique proposed can predict the fields radiated by the reflector with greater accuracy by comparing the calculated results with the available measured results. A few important applications of the analysis proposed are also highlighted. View full abstract»

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  • A tetrahedral modeling method for electromagnetic scattering by arbitrarily shaped inhomogeneous dielectric bodies

    Page(s): 77 - 85
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    A method for calculating the electromagnetic scattering from and internal field distribution of arbitrarily shaped, inhomogeneous, dielectric bodies is presented. A volume integral equation is formulated and solved by using the method of moments. Tetrahedral volume elements are used to model a scattering body in which the electrical parameters are assumed constant in each tetrahedron. Special basis functions are defined within the tetrahedral volume elements to insure that the normal electric field satisfies the correct jump condition at interfaces between different dielectric media. An approximate Galerkin testing procedure is used, with special care taken to correctly treat the derivatives in the scalar potential term. Calculated internal field distributions and scattering cross sections of dielectric spheres and rods are compared to and found in agreement with other calculations. The accuracy of the fields calculated by using the tetrahedral cell method is found to be comparable to that of cubical cell methods presently used for modeling arbitrarily shaped bodies, while the modeling flexibility is considerably greater. View full abstract»

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  • Preliminary study on offset scan-corrected reflector antenna system

    Page(s): 30 - 35
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    Preliminary study on offset shaped dual reflector antenna systems has been carried out to assess the feasibility for multibeam satellite applications. The two-dimensional offset shaped reflector antenna geometry is generated by first creating the nodal points according to a bifocal condition and then connecting the nodal points by smooth curves to form the profiles of the main and subreflectors. The three-dimensional geometry is created by body revolution. The offset geometry is obtained by properly tailoring the three-dimensional geometry. This offset shaped reflector antenna system has an inherent astigmatism which can be either fully or partially compensated. For applications requiring a scan range in azimuth more than \pm 5 beamwidths, the offset shaped dual reflector antenna systems offer better scan performance (in terms of peak gains) than offset Cassegrain geometries at the expense of the performance of the on-axis beams. In elevation with a 16 beamwidth scan range, the shaped design provides 0.3 dB less scan loss than the Cassegrain design. View full abstract»

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  • Finite conductivity uniform GTD versus knife edge diffraction in prediction of propagation path loss

    Page(s): 70 - 76
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    Diffraction propagation over hills and ridges at VHF and UHF is commonly estimated using Fresnel knife edge diffraction. This approach has the advantage of simplicity, and for many geometries yields accurate results. However, since it neglects the shape and composition of the diffracting surface, it can in some cases yield results which are in serious disagreement with measurements. To remedy this, attempts have been made to approximate the diffracting hill or ridge by other shapes, most notably cylinders. These approaches have not been widely adopted, due in large part to their greater numerical complexity. In this paper it is proposed to apply wedge diffraction in the format of the geometrical theory of diffraction (GTD), modified to include finite conductivity and local surface roughness effects. It is shown that, for geometries with grazing incidence and/or diffraction angles, significant improvement in accuracy is obtained. Further, the GTD wedge diffraction form used is based on the Fresnel integral, so that it is only slightly more complex numerically than knife edge diffraction. Finally, the GTD includes reflections from the sides of the ridge (wedge faces), and can be extended to multiple ridge diffraction and three-dimensional terrain variations. View full abstract»

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  • Element pattern approach to design of dielectric windows for conformal phased arrays

    Page(s): 44 - 53
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    Modal analysis is presented for the realized element gain E - and H -plane patterns for a two-dimensional circular cylindrical arrays with concentric dielectric sleeve. Numerical results indicate presence of significant surface wave effects. A design method of dielectric windows to reduce the guided wave effects is proposed. The method, validated by direct evaluation of the element pattern for the optimized window geometries, shows significant reduction of surface wave effects. View full abstract»

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  • Short-wavelength target modeling

    Page(s): 105 - 111
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    A simplified model has been employed to review the scattering characteristics of targets in the short wavelength limit. It is demonstrated that the reflected signal can be modeled as a diffuse plus a finite number of coherent returns (also called glints). It is then demonstrated that for accurate target location and direction it is usually necessary to decorrelate these glint returns. The conditions required for this are derived. View full abstract»

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  • Scattering by right angle dielectric wedge

    Page(s): 61 - 69
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    An asymptotic solution of electromagnetic waves scattered by a right-angled dielectric wedge for plane wave incidence is obtained. Scattered far fields are constructed by waves reflected and refracted from dielectric interfaces (geometric-optical fields) and a cylindrical wave diffracted from the edge. The asymptotic edge diffracted field is obtained by adding a correction to the edge diffraction of physical optics approximation, where the correction field in the far-field zone is calculated by solving a dual series equation amenable to simple numerical calculation. The validity of this result is assured by two limits of relative dielectric constant \varepsilon of the wedge. The total asymptotic field calculated agrees with Rawlins' Neumann series solution for small \varepsilon , and the edge diffraction pattern is shown to approach that of a perfectly conducting wedge for large \varepsilon . Calculated far-field patterns are presented and the accuracy of physical optics approximation is discussed. View full abstract»

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  • Plane-wave diffraction by a wedge--A spectral domain approach

    Page(s): 20 - 29
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    The canonical problem of plane wave diffraction by a wedge in the context of the spectral domain approach which exploits the relationship between the induced current on a scatterer and its far field is investigated. It is shown how the exact solution to the wedge diffraction problem can be manipulated in a form which enables one to interpret the far scattered field as the Fourier transform of the physical optics (PO) current on the two faces of the wedge augmented by the fringe current near the tip of the wedge. A uniform asymptotic expansion for the total field which slightly modifies the Ansatz in the uniform asymptotic theory of electromagnetic edge diffraction is constructed. View full abstract»

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  • Multipath interference for in-flight antenna measurements

    Page(s): 100 - 104
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    Formulations are presented to predict the pattern of interference (multipath) between direct rays and those reflected from the surface of the earth. These formulations can be used to assess the performance of ground-to-air, air-to-ground, ground-to-ground, and air-to-air communication and antenna measuring systems. Methods are also introduced to determine accurately the point of reflection and the path phase difference between the direct and reflected waves. Various divergence factors, used to account for energy spreading from a curved surface, are presented and compared. The formulations introduced can account for any polarization state (linear, circular, elliptical), sense of rotation (right hand, left hand), and tilt angle of the transmitting and receiving elements, and for polarization changes due to reflection. View full abstract»

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  • Slant path rain attenuation and path diversity statistics obtained through radar modeling of rain structure

    Page(s): 54 - 60
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    Single and joint terminal slant path attenuation statistics at frequencies of 28.56 and 19.04 GHz have been derived employing a radar data base obtained over a three-year period at Wallops Island, VA. Statistics were independently obtained for path elevation angles of 20\deg , 45\deg , and 90\deg for purposes of examining how elevation angles influences both single terminal and joint probability distributions. Both diversity gains and autocorrelation function dependence on site spacing and elevation angles were determined employing the radar modeling results. Comparisons with other investigators are presented. An independent path elevation angle prediction technique was developed and demonstrated to fit well with the radar derived single and joint terminal radar derived cumulative fade distributions at various elevation angles. View full abstract»

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  • Determination of the current distribution on an infinite periodic structure of thin-metallic wires

    Page(s): 93 - 95
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    The singular integral equation of the diffraction by thin metallic wires is used to determine the current distribution on an infinite periodic structure in one dimension. The periodic pattern can be constituted by thin wires, joined or not between the cells. This method is specifically applied to a meander line. The induced current-distribution on this structure illuminated by a plane wave of any incidence, polarized either vertically or horizontally, is obtained by means of a matrix inversion algorithm deduced from a particular method of moments. This method does not need an estimation of the initial solution as in the iterative methods and finds its application in the domain of middle frequency waves and especially in the low frequency range. View full abstract»

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  • End-fire hybrid array antennas

    Page(s): 36 - 43
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    A heuristic approach useful in the design of end-fire array antennas is described. When an array is scanned "beyond end fire," the last elements of the array, in the direction of the end-fire beam, generally receive net power transmitted by other elements of the array. This received power might conceivably be recirculated and reradiated at the price of substantial complexity in the feed network. It is relatively simple to absorb this power in appropriate resistive loads at the price of reduced gain. The resulting end-fire antenna is a hybrid-array consisting of two classes of elements: elements excited directly and elements excited parasitically. A compromise termination of these parasitic elements in reactive loads especially determined to preserve desired pattern characteristics is examined. View full abstract»

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  • Scattering by a rotating conducting sphere

    Page(s): 95 - 98
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    The scattering of a plane wave by a rotating sphere with finite conductivity is investigated. The problem is solved by means of the "instantaneous rest-frame" hypothesis. It is shown that a surface current must be taken into account to calculate the jump in the tangential magnetic field at the surface of the sphere, even in the case of finite conductivity. The analytical solution shows that the influence of the rotation becomes negligible in the limit of a perfectly conducting sphere. View full abstract»

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Aims & Scope

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

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Editor-in-Chief                                                 Kwok W. Leung