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Antennas and Propagation, IEEE Transactions on

Issue 1 • Date January 1964

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Displaying Results 1 - 25 of 31
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • [Back cover]

    Page(s): c4
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    Freely Available from IEEE
  • Propagation of ELF waves below an inhomogeneous anisotropic ionosphere

    Page(s): 74 - 83
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    The ionospheric anisotropy is considered with horizontal magnetic field either for transverse (East-West or West-East) or for longitudinal (South-North) propagation. For transverse propagation in a vertically stratified medium the differential equations of the various field components are uncoupled and a closed form solution is given for identical exponential height variation of the components of tensor conductivity. For arbitrary height variation of the tensor conductivity numerical solutions are obtained after expressing the surface impedance below the ionosphere in terms of a Riccati-type differential equation. The West-East direction of propagation exhibits a lower attenuation constant than the East-West direction forf < 1000cps. This is contrary to the expectations based on a model of a homogeneous anisotropic ionosphere. For longitudinal propagation the differential equations of the various field components are coupled, with the coupling being particularly strong above theDregion. The differential equations are simplified by assuming no coupling in the lower ionosphere and strong coupling above a pre-selected altitudey_{1}. For exponential height variation of the tensor conductivity components the closed form solution differs negligibly from the isotropic case. For arbitrary height varition of the tensor conductivity numerical solutions are obtained similarly as for the transverse propagation. Over most of the frequency range the attenuation figures for South-North propagation are intermediate between the corresponding figures for West-East and East-West propagation. View full abstract»

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  • Electromagnetic scattering from a spherical nonuniform medium-part II: The radar cross section of a flare

    Page(s): 91 - 96
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    The radar cross section for scattering of electromagnetic waves by a plasma having an electron concentration proportional tor^{-2}is calculated. The exact solution is compared with the scalar approximation. It is found that the exact solution can be orders of magnitude smaller than any of the usual approximations. View full abstract»

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  • Evaluation of antenna Q

    Page(s): 23 - 27
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    A method is presented for evaluating theQof an antenna, where theQis defined as in conventional network theory. The method consists of subtracting the energy density associated with the power flow from the total energy density, thus enabling the magnetic and electric reactive energy to be computed. Specific application of the method is made to the evaluation of theQof spherical and cylindrical modes. It is verified that theQbecomes very large when the order of the mode exceedsk_{0}awhereais the radius of the sphere or cylinder on which the sources are located. View full abstract»

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  • On the scattering of electromagnetic waves by a moving tropospheric layer having sinusoidal boundaries

    Page(s): 51 - 64
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    The trans-horizon signal is assumed to be adequately described by a simple Waterman scatter model and to be ascribable to a partial reflection from a "rippled atmospheric layer." Here it is assumed that the boundary of this layer is space sinusoidal in a plane normal to the line determined by the transmitter and receiver points. The thickness of the layer is approximately uniform and the permittivity is assumed to vary in a Gaussian manner. Theoretical and experimental descriptions of the vertical-transverse permittivity spectrum are obtained and compared. A corresponding comparison is made between the theoretical and Waterman experimental received power vs azimuth angle patterns. In both cases, there is qualitative agreement provided the ratio of ripple amplitude to ripple wavelength is large. In addition, an estimate of the trans-horizon signal power spectrum is compared with experimental observations. Experimentally, the power spectrum is found to broaden with increasing scattering angle and beamwidth, while the present scatter model yields a power spectrum whose width is an inverse function of scattering angle and beamwidth. View full abstract»

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  • The echo area of small rectangular plates with linear slots

    Page(s): 101 - 104
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    The echo area of rectangular plates on the order of1lambda times 1lambdain size and smaller with linear slots is discussed. Approximations are given which allow one to explain qualitatively the experimental results given. Afrac{1}{2} lambda times 1lambdaplate is considered both analytically and experimentally and by choosing the proper length slot or a slot with the proper reactive loading the echo area has been reduced by more than 8 db from the solid plate return. View full abstract»

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  • A parasitic slot array

    Page(s): 10 - 16
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    The analysis of an endfire array of tunable parasitic slots is described. Self and mutual admittances between thin half-wavelength slots are found by an application of Babinet's Principle. To solve the circuit equations of the array, the condition is imposed that the phase velocity remain constant along the array. Then, by matrix inversion, the excitation amplitude and self-reactance of the parasitic elements are determined. The phase of the reflector is chosen to maximize the coupling between the driven element and the directors. Finally, experimental patterns are compared with computed results. View full abstract»

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  • Input impedance of arc antennas and short helical radiators

    Page(s): 2 - 9
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    The problem of the input impedance of curved wire antennas is generally formulated in terms of an integral equation. A stationary formula is used in evaluating the input impedances of arc antennas and short helical radiators of which the cylindrical antenna is a special case. The computational results are presented in graphical form. The impedance characteristics of these curved antennas are discussed. View full abstract»

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  • Radiation from an aperture in an infinite conducting wedge

    Page(s): 96 - 101
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    In this paper the problem of the far field radiation of an infinite aperture occupying one side of an infinite conducting wedge is solved. For uniform illuminations as well as for illuminations tapered to zero at the edges, it is shown that the radiated field can be effectively represented by line sources situated along the edge of the wedge. Also, for the special case of illuminations which taper to zero at the edges within a few wavelengths, it is shown that the shadow region radiation is proportional to the rate of taper. View full abstract»

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  • Dynamic programming applied to unequally spaced arrays

    Page(s): 35 - 43
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    The application of the optimization technique known as dynamic programming to the design of "thinned" arrays with unequally-spaced elements is described. Dynamic programming is a systematic procedure for efficiently utilizing the capabilities of modern high-speed digital computing machines to find solutions to problems not computationally feasible by conventional means. In this paper it is applied to the design of linear arrays of 25 elements spaced within a 50 wavelength aperture. The results obtained compare favorably with similar results found by other design techniques. The effect on the sidelobes of varying the angular region of optimization and the spacing-quantization is also explored. View full abstract»

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  • An experimental study of the variation of the tropospheric scattering cross section and air velocity with the position in space

    Page(s): 65 - 73
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    An experimental study of the spatial homogeneity of the tropospheric permittivity and air velocity fields is presented. Knowledge regarding the homogeneity is imperative in order to measure the 4-dimensional spectrum of the permittivity fluctuations to be discussed in a later report. It is found that in most cases the scattering ability of the troposphere is enhanced with height. The variation of scattered power with position of the scattering volume along a horizontal direction varies very little. Similarly, it is shown that the wind velocity varies very little with height in the height region under consideration, while the velocity varies somewhat in a horizontal direction. Velocity and scattered power do not seem to correlate. View full abstract»

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  • On the applicability of the image theory

    Page(s): 127 - 128
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    First Page of the Article
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  • A backward angle-fire array antenna

    Page(s): 48 - 50
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    A new type of array is described which consists of a grid or mesh structure situated parallel and close to a flat conducting sheet. It operates as a linearly polarized traveling-wave antenna with the main lobe of radiation in a backward angle-fire direction. The direction of the beam is a function of the frequency. Operation of the antenna is analyzed by simple array theory and comparisons are made between calculated and measured performance. An application of the array as a radio telescope antenna is mentioned. View full abstract»

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  • A Gregorian corrector for spherical reflectors

    Page(s): 44 - 47
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    The inherent spherical aberration of a spherical reflector antenna is corrected by using an auxiliary Gregorian reflector feed system that rotates about the center of curvature of the reflector. Tests at bothX- andK-band frequencies demonstrate feasibility of the design for wide-angle scanning. View full abstract»

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  • Electromagnetic scattering from a spherical nonuniform medium-part I: General theory

    Page(s): 86 - 90
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    The scattering of electromagnetic waves by a spherically symmetric continuous dielectric is examined. Two distinct methods for calculating the scattering amplitude are derived. It is shown that the scalar approximation is, in general, extremely poor. The radar cross section is discussed in some detail. View full abstract»

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  • On the mapping by a cross-correlation antenna system of partially coherent radio sources

    Page(s): 118 - 124
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    In this paper it is shown that by means of a crosscorrelation antenna system it is possible to measure the mutual power distribution,T(u, v), of partially coherent radio sources. The two linear antennas of the system are scanned independently to give a two-dimensional output which can be written asbar{R}(u, v) = T(u, v) ast A(-u)B^{ast}(-v)whereA(u)andB(v)are the patterns of the two antennas. A two-dimensional Fourier analysis of the output shows it to be a smoothed version of the true mutual power distribution. One can define a principal solution,T_{0}(u, v), which is a generalization to two dimensions of the well-known principal solution,T_{0}(u), which occurs when the sources are incoherent. The limiting cases of complete coherence and complete incoherence are considered. It is shown that for coherent sources the principal solution is factorable,T_{0}(u, v)=varepsilon_{0}(u)varepsilon_{0}^{ast}(v). For incoherent sources it is shown that the spatial frequency spectrum ofT_{0}(u, v)is a function of only the difference,x-y, of the spatial co-ordinates,t_{0}(x, y) = t_{0}(x- y). View full abstract»

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  • An experimental investigation on the behavior of the dipole antenna near the interface between the conducting medium and free space

    Page(s): 27 - 35
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    An experimental study was made of the driving-point admittance and the relative amplitude and phase distributions of the current for a dipole antenna near and parallel to the interface between the conducting medium and free space. (The antenna was always located in the conducting medium, unless otherwise specified.) The depthdof the antenna from the interface was varied fromd/lambda=4.4to 0. The loss tangentsigma/omegaepsilon_{r}epsilon_{0}of the conducting medium was varied from 0.036 to 8.8, a range which includes a variety of media such as poor insulators, the ionosphere, plasmas, dry earth, wet earth, lake water, and sea water. The antenna heightbeta hin radians was varied frombeta h=0.1through2pi. Comparisons were made, wherever possible, between the characteristics of the dipole antenna in the half space and in a space completely filled with the dissipative medium. The driving-point admittances in the limiting casedrightarrow inftyare in good agreement with the available theories by King and Harrison [1], and Wu [2], which have already been verified experimentally by Iizuka and King [3]. Since all measured results are given in terms of dimensionless parameters such asbeta h,d/lambda_{u},sigma/omegaepsilon_{r}epsilon_{0}, and1/sqrt{epsilon_{r}}, they may be applied to any combination of conductivity, frequency, dielectric constant, and distance of the antenna from the interface [4]. 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