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Antennas and Propagation, IEEE Transactions on

Issue 6 • Date November 1968

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Displaying Results 1 - 25 of 40
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Contributors and back cover

    Page(s): c4
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    Freely Available from IEEE
  • A log-periodic antenna with vertically polarized omnidirectional radiation

    Page(s): 752 - 753
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    This communication reports the results of an experimental investigation of a new log-periodic (LP) antenna. The antenna consists of an LP array of radial waveguides excited by a two-wire transmission line. The antenna exhibits a vertically polarized omnidirectional radiation pattern which is essentially constant over the designed bandwidth. View full abstract»

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  • Radio propagation over a cylindrical hill including the effect of a surmounted obstacle

    Page(s): 700 - 705
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    An analysis is presented for wave propagation over a smooth cylindrical surface of constant curvature when the boundary impedance is specified. High-frequency approximations are introduced which permit a universal plot of the diffraction loss as a function of a hill-height parameter. The results are extended to allow for the presence of a knife-edge obstacle located on the crest of the rounded hill. For the conditions considered, the latter produces a substantial gain which, to some extent, overcomes the diffraction loss associated with the hill. The results have direct application to HF and VHF radio propagation over heavily vegetated and forested terrain. View full abstract»

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  • Log-periodic antennas with modulated impedance feeders

    Page(s): 633 - 642
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    The proper phasing of the active region of a log-periodic array can be obtained by means of a feeder without the conventional transposition of the wires. This is of practical importance for arrays of monopoles and slots where the transposition is not possible. However, the input impedance of such structures, when fed from a line with constant impedance, varies greatly with frequency. The impedance variation has been traced to reflections from a stop region between the antenna feedpoint and the active region. By introducing a step modulation of the characteristic impedance of the feedline, the reflections can be reduced and a stable impedance obtained. View full abstract»

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  • The pointing calibration of the Haystack antenna

    Page(s): 746 - 751
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    We have applied techniques of optical astronomy to calibrate the pointing of a high-resolution pencil-beam antenna by using radiometric measurements of cosmic radio sources. The Haystack antenna, a 120-ft paraboloidal reflector on an azimuth-elevation mount, was calibrated at a frequency of 15.25 GHz. The beamwidth at this frequency is 36 millidegrees; the rms residual pointing error after calibration was 2.90 millidegrees in azimuth and 3.45 millidegrees in elevation. A total of 172 measurements of pointing error were made on eight sources, and these data were fitted by the method of least squares to determine seven instrumental parameters that take into account axis-alignment errors and gravitational effects on the antenna structure. These techniques are not restricted to antennas used as radio telescopes, and they may be useful in the pointing calibration of other antennas. View full abstract»

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  • A note on the radiation characteristics and forced surface wave phenomena in triangular-grid circular waveguide phased arrays

    Page(s): 760 - 762
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    Forced surface wave resonances are shown to occur in dielectric-free 45-degree triangular-grid circular waveguide phased arrays. Similar surface wave phenomena were observed in an identical grid array of rectangular waveguides in theH-plane of scan. In the circular waveguide array, however, the resonance is observed in theE-plane and is shown to be an isolated point. This isolation is further illustrated by observing certain vector symmetries in the radiation patterns. View full abstract»

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  • The field pattern of a long antenna with multiple excitations

    Page(s): 643 - 646
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    The field pattern of an asymmetrically driven long antenna is obtained by the Wiener-Hopf procedure. The formula is algebraic in form and involves no numerical integration. Comparison with experiment is made and the agreement is found to be satisfactory. Application of the result to field pattern synthesis is discussed and two examples are given. View full abstract»

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  • A log-periodic cavity-backed slot array

    Page(s): 756 - 758
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    This communication describes the element investigation, design, and testing of a backfire log-periodic cavity-backed slot array operating from 2.8 to 5.9 GHz in a frequency-independent fashion. The gain of the antenna is approximately 10 dB, and the VSWR is below 2.5 to 1. TheH-plane power patterns are given with nearfield plots along file array. The advantages of the antenna are a simple stripline feeding system and the fact that the structure protrudes a little because shallow cavities are used. View full abstract»

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  • Spectral resolution and solution of field problems in an anisotropic and compressible medium

    Page(s): 741 - 745
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    It is shown that when source currents are present in a compressible and anisotropic plasma, the longitudinal components of the electric and magnetic fields and the pressure variation satisfy a coupled inhomogeneous equation. Based on the spectral resolution of a square matrix, a general method for the solution of such an equation is presented. The solution of the coupled-wave equation is thus reduced to the evaluation of some simple integrals. Formulas for the determination of the transverse components are given. To demonstrate the simplicity of the method, fields due to a magnetic line source are worked out in detail. Some numerical results are also included. View full abstract»

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  • Phase stabilization of widely separated oscillators

    Page(s): 683 - 688
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    Techniques for reducing propagation-induced phase fluctuations in frequency distribution systems are discussed and compared. Examples of both microwave and optical methods are presented. Stabilization to a few parts in10^{8}over a 15-km path seems to be feasible. View full abstract»

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  • Studies of the focal region of a spherical reflector: Stationary phase evaluation

    Page(s): 646 - 656
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    The geometric optics and polarization properties of a spherical reflector are used to develop an integral representation of its focal region fields. These integrals are evaluated by the extended method of stationary phase for field points off the caustics, on the axial caustic, on the caustic surface, and at the paraxial focus. The contributions to the field at a field point are shown to arise respectively from three ordinary stationary points: a stationary ring and a stationary point at the vertex; an ordinary stationary point and a caustic type stationary point; and a fourth-order stationary point. The resulting formulas are used to compute the value of the focal region fields. The computed results are then compared to measured data. View full abstract»

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  • Coupling in reflector arrays

    Page(s): 759 - 760
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    In order to reduce the space occupied by a reflector array, it is desirable to arrange the array antennas as close to each other as possible; however, in this case coupling between the array antennas will reduce the reflecting properties of the reflector array. The purpose of the present communication is to demonstrate that this is true for a Van Atta reflector consisting of four half-wave dipoles arranged on a line. Theoretical results obtained by using the methods described in references are compared with experimental results. In contrast to previous experimental results which have been presented as normalized, the results described are absolute View full abstract»

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  • Synthesis of oblique ionograms for a quasi-linear isonospheric model and spherical earth-ionosphere geometry

    Page(s): 771
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    A method is described by means of which exact and direct synthesis of oblique incidence ionograms can be performed for a quasi-linear ionospheric model with spherical earth-ionosphere geometry but neglecting earth's magnetic field. A sample ionogram synthesized in accordance with this method is presented. View full abstract»

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  • Displacement of rays in a turbulent medium

    Page(s): 678 - 683
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    The Fokker-Planck equation associated with the fluctuation (ray) equation is derived. The resulting equation for an isotropic turbulence is in the form of a diffusion equation. It has been found that the diffusion coefficient is more naturally defined in terms of the logarithmic refractive index. In the limit of weak turbulence, the present definition reduces to the conventional one. For a general and arbitrary "initial" condition, certain moments of the diffusion equation have been obtained. These moments give 1) the probability of finding a ray with a given ray direction and given path length, and 2) the mean and mean-square position of the ray in a given direction and given path length. View full abstract»

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  • A multipole-field study for the multiarm log-spiral antennas

    Page(s): 656 - 664
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    The electromagnetic field radiated by an arbitrary source is represented as the multipule expansion of the left-hand circularly polarized and of the right-hand circularly polarized modal fields. In particular, the multiarm log-spiral antennas have been investigated using such an approach. With approximated current distributions, the multipole coefficients and the circularly polarized field patterns for a few typical log spirals are computed and compared with the measured results. Generally, only a few dominant modes are sufficient to describe the major radiating characteristics of the log spirals; therefore, a better insight as to the polarization and the angular dependence can be gained through the modal-field point of view. View full abstract»

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  • Scattering of a beam wave by a spherical object

    Page(s): 724 - 727
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    The theoretical analysis of the scattering of a beam wave by a small spherical object, which exists at the neighborhood of the beam waist on the propagation axis, is treated. In this analysis, the property of a spherical object is generalized so as to have anr-dependent dielectric constant. Through numerical calculations for the case of the conducting sphere, the difference between the scattering of a beam wave and that of a plane wave are discussed. View full abstract»

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  • Pattern synthesis of circular arrays with many directive elements

    Page(s): 758 - 759
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    A method for synthesizing the radiation pattern of a circular array with directive elements is presented. The required excitations are determined from an explicit formula which requires no reduction or inversion of matrices. It is particularly useful for designing large circular arrays with many elements. View full abstract»

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  • Theoretical and experimental studies on the long dipole antenna

    Page(s): 664 - 673
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    The long transmitting dipole antenna is studied theoretically and experimentally. The Wiener-Hopf technique is used to obtain explicit expressions for the current and charge distributions along the antenna. These quantities are also measured. The theoretical and experimental results are in good agreement. View full abstract»

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  • ELF and VLF fields of a horizontal electric dipole

    Page(s): 689 - 700
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    The waves in the spherical guide between the earth and ionosphere are excited by a horizontal electric dipole. The guide boundaries are characterized by surface impedances and the resulting waves are expressed as a superposition of TM and TE modes. The wavenumbers, excitation factors, height-gain functions, and height-dependent impedances are examined for both types of modes. A thin-shell approximation of the radial wave functions is shown to be adequate for phase velocity estimates; but other propagation parameters are of restricted validity in the VLF range where Airy integral approximations provide more reliable data. A horizontal electric dipole is shown to provide a nearly omnidirectional coverage of horizontal field components in the frequency range of the lower Schumann resonances. For an elevated source the horizontal fields are essentially omnidirectional also in the VLF range. Near fields are expressed as a summation of waveguide modes. The vertical field components vanish at the antipode, but the horizontal components remain of finite magnitude. View full abstract»

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  • Conjugate echoes in Alouette-2 topside-sounder data

    Page(s): 771 - 774
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    Three types of ionograms containing symmetric conjugate echo traces which appear frequently in the Alouette-2 satellite topside-sounder data are presented and explained in terms of multiple reflections between conjugate points of the field line passing through the satellite. Such symmetric traces have not been previously reported in the literature. The high intensity of these traces gives credence to the existence of magnetospheric waveguides along which signals can propagate with very little attenuation. View full abstract»

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  • Analysis of mode conversion in waveguide transition sections with surface impedance boundaries applied to VLF radio propagation

    Page(s): 673 - 678
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    First- and second-order correction terms are derived for the reflection and transmission scattering coefficients for a step-type transition between two uniform waveguides with surface impedance boundaries. This analysis yields rigorous expressions for the differential transmission and reflection coefficients defined for an infinitesimal step transition. These coefficients are essential in the derivation of the coupled differential equations for the wave amplitudes in a transition section of gradually varying height. View full abstract»

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  • The arbitrarily driven long cylindrical antenna

    Page(s): 769 - 770
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    An approximate solution is described for the current distribution on a long, thin cylindrical antenna driven at an arbitrary point along its length. This solution is reasonably accurate, and the form is simple enough to be useful in the analysis and synthesis of antennas with lumped active or passive elements located along their length. 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