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Antennas and Propagation, IEEE Transactions on

Issue 4 • Date July 1977

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Displaying Results 1 - 25 of 33
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Comments on "Study by conformal mapping of TE and TM waves in open dielectric waveguides

    Page(s): 593 - 595
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    Significant conceptual errors appear in a recent analysis of various open dielectric waveguides by conformal mapping of theH- guide configuration. Probable reasons for the failure are suggested and a corrected development of the technique is outlined. View full abstract»

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  • Mathematical models for the reflection coefficients of lossy dielectric half-spaces with application to transient responses of chirped pulses

    Page(s): 490 - 495
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    Reflection coefficients are found at normal incidence for a large class of homogeneous lossy half-spaces with a one-dimensionally inhomogeneous or stratified lossy layer on top. Solutions are in terms of Hankel functions of complex argument to decrease cancellation error at high frequencies. One special case is that of layers on a homogeneous half-space where the dielectric constant in each layer may vary in a quite general manner. A Wronskian is used to insure the critical computations are correct. The reflection of chirped pulses is considered. Solutions are obtained by applying the fast Fourier transform. It is found that for a typical relatively long normalized "long" pulse the power reflected as a function of time is essentially the power reflection coefficient for the frequencies swept out, whereas for a relatively short "long" pulse, with the same relative change in frequency and the same number of oscillations there is only the uniform attenuation by the power reflection coefficient of the center frequency. By a "long" pulse we mean a pulse whose spatial length is long compared to the thickness of the reflecting layer. View full abstract»

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  • Satellite site diversity: Results of a radiometer experiment at 13 and 18 GHz

    Page(s): 483 - 489
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    Joint attenuation statistics for a model site-diversity satellite system which would operate at 18 and 30 GHz were gathered in a radiometer experiment conducted at sites near Atlanta, GA, and Denver, CO. The receiver is of the classic Dicke radiometer type, monitoring sky-noise power at 13.6 and 17.8 GHz. Scaling provides the means to derive 30 GHz performance. The experiment, which commenced in May 1973, provides an expedient means of acquiring essential rain attenuation statistics without the use of active signal sources, such as a satellite beacon. This article describes the experiment and presents the results, including representative data samples from the 1½A year measurement period. Based on these measurements, a model satellite system operating during, the measuring period in Atlanta, at 18 and 30 GHz with 8 and 18 dB fade margins, respectively, would require 14-mi site diversity to insure no more than 0.005 percent propagation outage. During the same time period, site diversity was found unnecessary to satisfy this objective with operation in Denver. View full abstract»

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  • Receiving antenna design for miniature receivers

    Page(s): 528 - 530
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    A design procedure is described which determines the minimum required volume and the optimum dimensions for a ferrite loaded loop receiving antenna. The frequency of operation, bandwidth, transmitted signal strength, desired signal-to-noise ratio, receiver sensitivity, and the relative permeability of the ferrite are required to determine the design. Useful approximations for flux averaging, demagnetization factor, atmospheric noise, and chassis loadedQare given. View full abstract»

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  • The receive voltage transmission function of a phased array antenna element

    Page(s): 542 - 547
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    A general method has been developed for determining the voltage response of a phased array element to an incoming electric field. The incident field may arrive from any scan angle, and mutual coupling effects are accounted for in terms of the array element active reflection coefficient. The method defines a receive voltage transmission functionbar{T}(theta, phi, f)as a term whose product with the incident electric fieldE_{i}(theta, phi, f) results in the array element voltage response. The derivation ofbar{T}(theta, phi, f)is obtained by treating each phased array antenna element as a receiving aperture, having an active impedance related to the mutual coupling in the array. The element effective length is formulated using an array element receive equivalent circuit, and the transmission functionbar{T}(theta, phi, f)is obtained using this effective length formulation. The usefulness of the transmission function for studying the response of a phased array element to particular radar signal waveforms is suggested, and an experimental evaluation ofbar{T}(theta phi, f)is described using mutual coupling measurements on a 37-element crossed dipole test array. View full abstract»

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  • Collision frequencies of raindrops

    Page(s): 583 - 585
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    Using an exponential model spectrum for raindrop sizes, calculations are made of how often raindrops collide with one another. The collision of a large drop with another occurs after an interval of a few seconds. Large drops are likely to be markedly aspherical, and to oscillate, rather than to follow collectively a mean canting angle. Such variabilities should be considered in calculating depolarization and differential attenuation of microwaves in rain. View full abstract»

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  • Fourier transforms in propagation and scattering problems

    Page(s): 585 - 586
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    Three-dimensional Fourier transforms are applied to electromagnetic wave propagation problems. After obtaining functions in transform space, inversion and contour integration yield a plane wave integral representation. View full abstract»

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  • Experimental investigations of a loop antenna as electron plasma wave radiator and detector

    Page(s): 524 - 528
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    The radiation and reception characteristics of a circular loop antenna for an electron plasma wave are investigated experimentally. As a result, it is shown that the measured directional radiation and reception patterns agree well with the theoretically predicted ones, and that the quantitatively measured amplitude of the radiated wave potentials are also found to agree fairly well with the theoretically predicted values. View full abstract»

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  • Synthetic radar imagery

    Page(s): 477 - 483
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    A method for producing three-dimensional isometric images of a conducting radar target from measured ramp response waveforms is tested for the case of nonmutually orthogonal viewing angles. It is found that, in general, image quality is somewhat degraded and several new parameters are introduced, but useful images can still be obtained. Methods for obtaining the new parameters are included as well as other modifications which were developed to enhance image quality. Images of three aerospace-type targets obtained from low frequency scattering data are presented. View full abstract»

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  • The dipole moments of a dielectric cube

    Page(s): 590 - 592
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    As a part of a general study of the low frequency scattering properties of atmospheric particles of various shapes, the dipole moments of homogeneous dielectric rectangular parallelepipeds have been examined and data obtained for the special case of a cube. The results are presented and differ substantially from those previously reported in the literature. View full abstract»

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  • Scattering by a dielectric wedge: A numerical solution

    Page(s): 570 - 571
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    A numerical method is presented for the scattering by a general penetrable wedge. A set of coupled integral equations may be forumlated from Maxwell's equations, Green's theorem, and boundary conditions. The numerical solutions to the unknown surface fields on the boundary are first obtained by flat-pulse expansion for the fields near the tip and physical optics fields away from the tip and then point matching. Results are presented for a right-angled lossless dielectric wedge illuminated by a TE incident plane wave. The analysis should prove useful for extending the ability of GTD methods to handle dielectric wedge tips. View full abstract»

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  • Electromagnetic fields of dipoles in stratified media

    Page(s): 547 - 552
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    A general theory for the electromagnetic fields of dipoles in stratified isotropic media is outlined. The stratified model consists of a stack of layers sandwiched between two semi-infinite media. Either an electric or a magnetic dipole can be placed at any position in the stack, or in the upper or lower half-space. Dipoles can be electric or magnetic and can be oriented horizontally or vertically. The fields in the layer containing the source are given in terms of reflection coefficients, impedance and admittance terms, and wavenumber ratios. Recursion relations are developed to propagate the Hankel-domain field coefficients to other layers or to the half spaces. This allows the observation point to be placed anywhere except at the source. Numerical checks show that the derived algebra is at least self-consistent. View full abstract»

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  • Analysis of weather radar return

    Page(s): 457 - 470
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    A mathematical model of detected clutter from an airborne weather radar of conventional design is developed. The model is the joint probability density of samples of radar return from hydrometeors at the same nominal range and scan angle. It is developed from analysis of the effect on the received signal of the following parameters: inhomogeneous hydrometeor motion, radar frequency stability, pulsewidth, antenna beamwidth, scan angle, scan rate, and aircraft speed. In addition, the influence of finite pulse volume on radar sensitivity to hydrometeor motion is examined. View full abstract»

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  • A system for on line imaging of scattering centers on rotating radar targets

    Page(s): 592 - 593
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    A simple measurement and data processing system is presented which, at the output, on a television screen, continuously and on line yields a one-dimensional radar image of rotating targets together with the corresponding two-dimensional optical image. The system makes use of the well-known fact that the fine structure in the instantaneous Doppler spectrum of the radar echo from a rotating target yields high cross range resolution of the scattering centers. It is very useful for the analysis of the scattering center distribution on complicated targets, for on line evaluation of the effect of comouflaging and for related areas as glint analysis and RCS prediction, for example. View full abstract»

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  • Electromagnetic pulse propagation in a weakly nonlinear plasma

    Page(s): 587 - 589
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    An investigation of the propagation of electromagnetic pulses in a weakly nonlinear, cold, collisionless plasma is described. It is found that a transverse electromagnetic pulse generates, through nonlinear effects, a small amplitude, longitudinal electric pulse field. The transient behavior of this longitudinal electric field is studied. One particular case is considered in detail: the nonlinear generation of a longitudinal electric field by a transverse electromagnetic pulse which is excited by a suddenly turned-on cosinusoidal electric field of frequencyomega_{0}. Computer plots of numerical calculations of the second-order transient longitudinal field are presented. View full abstract»

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  • Scattering by arbitrarily cross-sectioned layered, lossy dielectric cylinders

    Page(s): 518 - 524
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    The scattering properties of TM or TE illuminated lossy dielectric cylinders of arbitrary cross section are analyzed by the surface integral equation techniques. The surface integral equations are formulated via Maxwell's equations, Green's theorem, and the boundary conditions. The unknown surface fields on the boundaries are then calculated by flat-pulse expansion and point matching. Once the surface fields are found, scattered field in the far-zone and radar cross section (RCS) are readily determined. RCS thus obtained for circular homogeneous dielectric cylinders and dielectric coated conducting cylinders are found to have excellent agreements with the exact eigenfunction expansion results. Extension to arbitrary cross-sectioned cylinders are also obtained for homogeneous lossy elliptical cylinders and wedge-semicircle cross-sectioned cylinders, with and without a conducting cylinder in its center. RCS dependences on frequency and conductivity as well as the matrix stability problem of this surface integral equation method are also examined. View full abstract»

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  • Influence of the wall geometry on reflection and transmission in an E -plane sectoral horn

    Page(s): 556 - 560
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    For a gradual waveguide-sectoral horn junction excited in the TEM mode, the influence of the wall geometry on reflection and transmission is investigated. The wall profile of the junction has the shape of a circular arc. When increasing the circle radius from zero, an abrupt junction changes to a smooth one. The magnitude of the reflection coefficient is reduced in a broadband manner whereas the phase variation increases. Clearly, the transmission increases too, but the ratio of dominant horn mode to the next higher mode will be diminished considerably. The analysis is rigorous and combines the "generalized telegraphist's equations" with a mode matching technique. This method is particularly suited for the calculation of waveguide-horn junctions. View full abstract»

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  • Field behavior near anisotropic and multidielectric edges

    Page(s): 571 - 575
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    Field behavior near edges involving an anisotropic medium and edges involving three isotropic dielectrics is analyzed. Equations are presented which relate this behavior to the geometry and the electrical properties of the media surrounding the edge. It is found that for the three-dielectric configuration, geometric singularities do not necessarily imply field singularities. View full abstract»

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  • Scattering from axisymmetric dielectrics or perfect conductors imbedded in an axisymmetric dielectric

    Page(s): 575 - 580
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    Waterman'sT-matrix formulation of classical electromagnetic scattering from a single, homogeneous scatterer has been extended by Peterson and Ström to include scattering from multilayered scatterers. TheT-matrix refers to expansions in spherical wave solutions of the vector Helmholtz equation. This theory and the computational method for calculating backscattering cross sections for axisymmetric scatterers are developed. This approach, using the equivalence principle, yields a more concise and systematic development to theT-matrix formulation than that of Peterson and Ström which relies upon the conceptually similar Poincare-Huygens principle. The method is realistically applicable to scatterers of sizes up toka sim 2piand for a wide range of dielectric constants. Sample computations are compared with extended Mie theory calculations of scattering by concentric shells of varying size and with measured backscattering cross section obtained from a displaced spherical perfect conductor imbedded in a lossy, spherical dielectric. View full abstract»

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  • A note on the asymptotic physical optic solution to the scattered fields from a paraboloidal reflector

    Page(s): 531 - 534
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    The asymptotic physical optic (APO) formulation for the scattered fields from a paraboloid has been found to give results which agree with experiment except in the rear region. The disagreement here is due to the inexact nature of the assumed geometric optic (GO) edge currents as used in APO. A means of correcting for the error in these currents is given here by appealing to the equivalent half plane problem of Sommerfeld. This correction method is called CAPO ("corrected" APO). The resulting corrected diffraction coefficients are shown to be numerically indistinguishable from those of GTD. Comparisons of predictedE- andH-plane field patterns, based on these corrected results, with measurements in the rear region are given and shown to be quite acceptable; the corrections having negligible effect elsewhere. The "static" nature (in the sense of implicitly ignoring slope diffraction) of APO, GTD, and CAPO is discussed. View full abstract»

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  • An antenna beam modeling algorithm

    Page(s): 534 - 539
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    A parametric model is presented in this paper which characterizes the beam response behavior of a given antenna for circular, linear vertical, and linear horizontal polarizations. The model parameters are defined by a nonlinear Kalman filtering algorithm which effectively estimates these parameters from measured antenna pattern data. Results of the modeling process are shown and compared against the actual (measured) beam pattern data. View full abstract»

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  • The electrically small magnetically loaded multiturn loop antenna

    Page(s): 496 - 505
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    An analytical model of a class of electrically small multiturn loop antennas has been formulated and compared with experimental measurements over a frequency range of 3 to 86 MHz. Both air core and magnetically loaded eases were examined. Transmitted signal enhancement as high as 10 dB was predicted and observed by magnetic loading. Several interesting properties of the transmitting antenna were investigated experimentally and by analysis based upon the model. It is concluded that transmitted signals can be enhanced in the 2-30 MHz range, at reasonable power levels, as much as 10 dB with state-of-art ferrite materials. Secondly, the analytical model described in this paper should prove an effective design aid for a volumetrically constrained antenna of the class. View full abstract»

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  • Near-field distribution of a paraboloidal reflector

    Page(s): 589 - 590
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    A major problem in communication antenna design is to obtain maximum gain and efficiency from large reflector antennas; few paraboloidal or dish antennas have efficiencies greater than 70 percent. The basic problem is the spreading of power by the source feed located at or near the focus of the reflector, which causes a concentration of power near the center of the aperture. In order to determine what kind of field distribution is required in the feed region to produce a uniform distribution over the reflector the authors have studied the inverse problem of a plane wave incident normally upon a paraboloidal reflector View full abstract»

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  • Radio wave propagation along mixed paths in forest environments

    Page(s): 471 - 477
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    The propagation of radio waves is examined for communication paths that may be partly within a forest and partly in regions outside the vegetation. Analytic results are found for simple canonic geometries in which the fields can be described in terms of ray-trajectories. By viewing a realistic forest environment as a combination of such canonic cases, it is possible to evaluate radio losses in complex situations by using a ray-tracking approach. The pertinent fields can then be expressed in terms of relatively simple analytical expressions, which hold well for frequencies between 2 and 200 MHz. 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