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Antennas and Propagation, IEEE Transactions on

Issue 7 • Date July 1986

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Displaying Results 1 - 17 of 17
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
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  • The use of vector transforms in solving some electromagnetic scattering problems

    Page(s): 871 - 879
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    It is shown that there exists a class of vector transforms and vector series expansions that are independent of their scalar counterparts. They can be used to simplify the solutions of a class of vector electromagnetic scattering problems. The applications are shown of vector Fourier, Hankel, and Mathieu transforms and series expansions to the formal solutions of scattering by rectangular, circular and elliptical disks and open-ended waveguides. The problems solved are canonical problems, however, more complex problems for applications in microwaves, microstrip integrated circuits, geophysical probing, etc. can be solved in a similar fashion. View full abstract»

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  • High-gain backup antenna design for Pioneer Venus Orbiter spacecraft

    Page(s): 891 - 895
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    The development and performance is described of a high-gain antenna designed to serve on the Pioneer Venus Orbiter spacecraft as a backup to the principal high-gain antenna unit in the unlikely event the mechanically despun antenna mechanism malfunctioned. The final design, a center-fed standing wave array of six sleeve dipoles enclosed in a fiber glass radome, performed successfully, as did all the antennas, on the Pioneer Orbiter spacecraft which was launched on May 20, 1978, as part of the Pioneer Venus mission. Photographs of experimental models giving details of design and construction are included, as well as graphs showing measured pattern and impedance matching characteristics of the subject antenna. View full abstract»

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  • Input impedance of a probe-fed circular microstrip antenna with thick substrate

    Page(s): 905 - 911
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    A method of computing the input impedance for the probe fed circular microstrip antenna with thick dielectric substrate is presented. Utilizing the framework of the cavity model, the fields under the microstrip patch are expanded in a set of modes satisfying the boundary conditions on the eccentrically located probe, as well as on the cavity magnetic wall. A mode-matching technique is used to solve for the electric field at the junction between the cavity and the coaxial feed cable. The reflection coefficient of the transverse electromagnetic (TEM) mode incident in the coaxial cable is determined, from which the input impedance of the antenna is computed. Measured data are presented to verify the theoretical calculations. Results of the computation of various losses for the circular printed antenna as a function of substrate thickness are also included. View full abstract»

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  • A mixed-field solution for scattering from composite bodies

    Page(s): 955 - 958
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    The mixed-field solution combines different integral equations on different parts of a scatterer. It can be used for a variety of problems involving composite bodies. It is particularly useful on bodies having both "thin" and "thick" parts, It also appears capable of providing a good approximation to scattering from discontinuous surface-impedance distributions. View full abstract»

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  • A comparison of spherical wave boundary value matching versus integral equation scattering solution for a perfectly conducting body

    Page(s): 857 - 865
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    A spherical-wave expansion (SPEX) technique for calculating the scattering from a smooth perfectly conducting body is presented. Sample case results are compared with the well-known Lawrence Livermore National Laboratory Numerical Electromagnetics code (NEC), which is based on the integral equation formulation. The internal fields are computed for both results using a third surface current integration program, which is totally independent of both SPEX and NEC. The internal fields, which would be zero for a perfect solution, are much more sensitive to the currents than the scattered fields. The SPEX solution, which uses fewer unknowns and less computer time than NEC, also produces a lower internal field. The SPEX technique also allows a direct check on satisfaction of the boundary condition at any set of points on the surface, independent of the points used to obtain the solution. This provides a valuable built-in test feature for quickly validating results, which is one of the most attractive features of the technique. View full abstract»

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  • Dielectric spectroscopy using monopole antennas of general electrical length

    Page(s): 919 - 929
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    A procedure is developed for measuring the complex dielectric permittivity of a material over a broad range of frequencies using a monopole antenna. No restrictions are placed on the electrical size of the antenna. The antenna is calibrated one time by measuring the input admittance in a standard medium with known permittivity, such as air. Next, the admittance is measured with the antenna immersed in a material with unknown permittivity. These two sets of admittances are then used to determine the permittivity of the material. As an application of the procedure, the complex permittivity of the alcohol 1-butanol and saline solutions were measured using a cylindrical monopole antenna. The measured permittivities are in good agreement with those determined by previous investigators. View full abstract»

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  • Radar target discrimination by convolution of radar return with extinction-pulses and single-mode extraction signals

    Page(s): 896 - 904
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    A new method of radar target discrimination and identification is presented. This new method is based on the natural frequencies of the target. It consists of synthesizing aspect-independent discriminant signals, called extinction-pulses (E-pulses) and single-mode extraction signals which, when convolved numerically with the late-time transient response of an expected target, lead to zero or single-mode responses. When the synthesized, discriminant signals for an expected target are convolved with the radar return from a different target, the resulting signal will be significantly different from the expected zero or single-mode responses, thus, the differing targets can be discriminated. Theoretical synthesis of discriminant signals from known target natural frequencies and experimental synthesis of them for a complex target from its measured pulse response are presented. The scheme has been tested with measured responses of various targets in the laboratory. View full abstract»

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  • Elimination of infinities in equivalent edge currents, part I: Fringe current components

    Page(s): 912 - 918
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    New expressions are derived for the fringe current components of the equivalent edge currents. They are obtained by asymptotic endpoint evaluation of the fringe current radiation integral over the "ray coordinate" measured along the diffracted ray grazing the surface of the local wedge. The resulting expressions, unlike the previous ones, are finite for all aspects of illumination and observation, except for the special case where the direction of observation is the continuation of a glancing incident ray propagating "inwards" with respect to the wedge surface (the Ufimtsev singularity). View full abstract»

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  • A review of the early developments of circular-aperture hybrid-mode corrugated horns

    Page(s): 930 - 935
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    The simultaneous but independent development in the United States and Australia of circular-aperture corrugated horns in the early 1960's is reviewed. The features of this development include the wide flare-angle corrugated "scalar" horn and the characteristics of focal-region fields of reflector antennas and the single- and multimode cylindrical corrugated horns necessary to feed them. View full abstract»

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  • Current induced by TE excitation on a conducting cylinder located near the planar interface between two semi-infinite half-spaces

    Page(s): 880 - 890
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    An analysis is presented for determining the current induced by a known transverse electric excitation on a perfectly conducting cylinder located near the planar interface separating two semi-infinite, homogeneous half-spaces of different electromagnetic properties. The conducting cylinder of general cross section is of infinite extent and the excitation is transverse electric to the cylinder axis. Two types of integral equations, the magnetic field integral equation and the electric field integral equation, are formulated, and the Green's functions for the integral equations are derived in an appendix. Numerical solution methods for solving the integral and integrodifferential equations are presented. For a strip parallel or perpendicular to the interface, a circular cylinder, and a rectangular cylinder, data are presented and discussed for selected parameters, including the case of a cylinder resting on the interface. View full abstract»

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  • Comparison of measured and calculated mutual coupling in the near field between microwave antennas

    Page(s): 952 - 955
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    Measurements of near-field mutual coupling between two moderate sized microwave antennas were performed and compared to coupling calculated using recently developed computer programs. Required input data for the programs are the complex far-field radiation patterns of the antennas and various geometrical factors describing the relative positions and orientations of the two antennas. Measured and calculated coupling as a function of both transverse and radial displacement showed good agreement. View full abstract»

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  • A regression model for forecasting microwave radio fading at Palmetto, GA

    Page(s): 936 - 942
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    Refractive fading degrades telecommunications transmissions on microwave radio systems. Since fading occurrence is highly variable from one night to the next, forecasts of the probability of fading occurring at a given location on the upcoming night would be useful for reducing the adverse impact of fading on transmission performance. In this work logistic regression analysis was used to develop an empirical formula for forecasting refractive fading probability from meteorological parameters forecast by the National Weather Service's numerical forecast models. The formula was developed using 40 months of daily meteorological and fading measurements collected near Palmetto, GA. The performance of the method was evaluated using eight and one-half months of meteorological forecast data. For days when fading was forecast to be relatively unlikely (0-40 percent probability), 90 percent of those days experienced less than 3 s of fading below -20 dB. For days when fading was forecast to be relatively likely (80-100 percent probability), 75 percent of those days experienced more than 3 s of fading below - 20 dB. These results demonstrate the feasibility of forecasting microwave refractive fading a day in advance. View full abstract»

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  • Field singularities at the tip of a metallic cone of arbitrary cross section

    Page(s): 865 - 870
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    The "spherical-harmonics" problem is investigated for a cone of arbitrary cross section. The analysis shows that two basic singularities must be considered: 1) the electric singularity, in whichbar{e}becomes infinite likeR^{nu-1}near the tip of the cone, 2) the magnetic singularity, in whichbar{h}becomes infinite likeR^{tau-1}. Numerical results, in particular concerningnuandtau, are given for: 1) the elliptic cone and its limiting case the sector, 2) the pyramidal corner. View full abstract»

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  • Polynomial approximation of Maliuzhinets' function

    Page(s): 942 - 947
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    Approximate formulas for the Maliuzhinets functions which give the solutions for the wedge diffraction with face impedance, are derived using the Chebyshev polynomials for various wedge angles. The coefficients of the polynomials are listed in a table. Although the formulas are derived for real variables, it is found that they can be used for the restricted range of complex variables. Since the validity of the formulas depends on both real and imaginary part when applied to complex variables, the equi-error contour of the formulas is given for the special case where the exact solution is available. An alternative but empirical formula for Maliuzhinets' functions is also obtained, which can be applied to arbitrary wedge angles. View full abstract»

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  • Diffraction by a wide double wedge with cylindrically capped edges

    Page(s): 947 - 951
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    The diffraction by two conducting sharp wedges with cylindrically capped edges is investigated using a recent asymptotic solution proposed by the authors for the diffraction by a wide double wedge. AnE-polarized plane wave incident at any angle is considered and the cap is assumed to be either a conducting or dielectric cylinder whose axis coincides with the wedge edge and its radius is much less than the separation between the two virtual sharp edges. The effects of the cap radius, permittivity, and wedge angle on the diffraction pattern, transmission coefficient, and edge-edge interaction term are presented. The transmission coefficient of the aperture is increased over the uncapped wedge case for dielectric caps and decreased for conducting caps. Other effects of the caps on the diffraction pattern such as beamwidth, level, and position of the first sidelobe are also investigated. 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