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Antennas and Propagation, IEEE Transactions on

Issue 3 • Date May 1967

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Displaying Results 1 - 25 of 39
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Flush mounted rectangular cavity slot antennas--Theory and design

    Page(s): 342 - 351
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    The loaded rectangular cavity slot antenna is analyzed using variational methods in conjunction with simplified equivalent circuit techniques to derive accurate design guides for efficiency, bandwidth, and resonant frequency. The aperture admittance is computed and the effects of a compound aperture plane iris and of material loading are analyzed. The aperture admittance of all such loaded cavity antennas is proportional tomu_{r},sqrt{mu_{r}/epsilon_{r}}, or1/epsilon_{r}, which characteristic lends to a common method of optimization of|T|^{2}(transmission cofficient). Experimental results include: 1) measurements of aperture field; 2) a comparison of theoretical and experimental value of bandwidth, efficiency, resonant frequency, and beam pattern for several experimental models; and 3) the measurement of the effect of applied dc magnetic field. View full abstract»

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  • A class of notched omnidirectional antennas

    Page(s): 352 - 356
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    A class of antennas featuring a steerable notch in an otherwise omnidirectional pattern is described. This type of antenna presents an alternative to a narrow beam antenna for certain applications; it is attractive when a small antenna capable of360degpattern rotation is desirable. The notch characteristic is obtained by combining in a single antenna three basic modes of radiation. One mode is omnidirectional, the other two are figure-8 patterns that are crossed in space. By controlling the amplitude and phase of these radiation modes, a family of patterns exhibiting different notch characteristics may be realized. The notch can be steered a full360degin azimuth by a single phase-shifter. An experimental model of a notch-omnidirectional antenna has been fabricated and tested at X-band. Notch pattern synthesis and rotation techniques have been demonstrated. View full abstract»

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  • Gain optimization for arbitrary antenna arrays subject to random fluctuations

    Page(s): 356 - 366
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    A general procedure is formulated for the maximization of the expected directive gain for arbitrary antenna arrays whose excitation amplitudes and phases as well as element positions are subject to random errors. Correlations are allowed to exist between the random fluctuations, and the general formulation imposes no restrictions on either the magnitude or the probability distribution of the fluctuations. Numerical examples are given which illustrate the dependence of the expected gain, the main-beam radiation efficiency, the radiation pattern, and the optimum element excitations on the standard deviation and correlation distance of the parameter errors. It is shown that, in typical cases, the properly optimized array yields not only a higher directive gain and a higher mainbeam radiation efficiency but also a better radiation pattern than an array which is "optimized" under the assumption of no random errors. View full abstract»

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  • An analytical approach to the coverage of a hemisphere by n planar phased arrays

    Page(s): 367 - 371
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    The coverage of a hemisphere byNplanar phased arrays arranged in pyramids or pyramidal frustra is discussed. Transformations between the spherical coordinates of individual arrays and of the hemisphere of coverage are derived. These results are then used to determine the minimum value of the maximum scan angle required of each array and the positioning of the arrays. Numerical results are given. These transformations are also used to minimize the number of elements needed in a given array aperture. This is shown for an example with both equilateral triangular and rectangular element spacing. It is further demonstrated how the use of an isosceles triangular element spacing affords additional reduction of the number of elements needed. View full abstract»

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  • Resistive receiving and scattering antenna

    Page(s): 371 - 376
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    This work is a sequel to two earlier papers devoted to detailed theoretical and numerical analyses of the imperfectly conducting cylindrical transmitting antenna [1], [2]. A knowledge of the driving-point impedance of the transmitting antenna, as previously reported, and the short-circuit current, as derived in this paper, completely determine the receiving properties of the resistive antenna. It is assumed that an internal impedance per unit length may be defined for the resistive cylinder. This study was prompted primarily by the desire to determine the current distribution along an ionized column of gases when the dielectric constant and conductivity are known, and also along imperfectly conducting missiles in free flight following burnout. The radar cross section of a gas column is readily obtained from the induced current distribution. Current distributions along several representative resistive cylinders as well as scattering cross sections are computed considering broadside illumination by a plane-wave field. The analysis yields accurate results whenk_{0}a ll 1, h gg a, andk_{0} h leq 5pi /4. Herek_{0}is the free-space wave number;handaare the antenna half length and radius, respectively. View full abstract»

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  • Resolution limitations of a finite aperture

    Page(s): 376 - 381
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    Methods of increasing antenna resolution by data processing are of interest in radio astronomy and radiometric mapping applications. This paper deals with the fundamental limitations of such operations. Communication theory techniques using prolate spheroidal wave functions have already been applied to antenna pattern synthesis. These techniques are applied to the problem of reconstituting an observed temperature distribution. The manner in which noise limits this reconstitution process is clearly shown. A least expected mean square error reconstitution process is also detailed. An interesting analogy between data processing and supergaining is noted. Finally, the limitation set by noise on the resolution of a data processed finite aperture is concluded. View full abstract»

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  • Digital recording and short-term prediction of oblique ionospheric propagation

    Page(s): 382 - 389
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    Synchronized oblique step-frequency ionosphere sounding are electrically recorded on punched paper tape without the intervening medium of photographic film. The resulting data are then automatically analyzed to yield statistics on the MOF, LOF, and MPF (a frequency below which multipath exceeds a pre-set limit). The MOF time autocorrelation decays smoothly to 0.87 in 9 minutes and to 0.5 in 65 minutes with minor maxima during the day-night transition periods. The MOF standard deviation between data observed on different days is higher daring the day than at night, and is approximately equal to 0.17 times the corresponding MOF mean value. The electrically analyzed innograms are processed in a manner simulating real time prediction of the above quantities, and their variances. The observed reduction of MOF variance is 0.54 at a prediction lead of 10 minutes, rising to 0.89 at 60 minutes, and is within 5 percent of the limiting values determined by the autocorrelation of the data. A technique for applying the basic propagation predictions to real time frequency management is simulated on a large computer, and reduced to practice on a small sounder accessory computer, with encouraging results. View full abstract»

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  • Short-term forecasting for a high-frequency long-distance point-to-point communication path

    Page(s): 390 - 394
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    Three techniques are presented which can allow the communicator to make maximum usable frequency forecasts. First, one-half hour, one hour, and two hour forecasts are made using running five-day median MOF curves obtained from data acquired by a synchronized step frequency sounder system. Fifty percent of the half-hour forecasts had an error no greater than 0.4 MHz. Second, short-term forecasts are also made using predicted information. Third, an independent forecasting method using selected frequency sampling of the failure time and recovery time of assigned frequencies is presented. As an example, forecasts for a 7800 km midlatitude HF propagation path are presented. View full abstract»

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  • Measurements of rainfall attenuation at 8 and 15 GHz

    Page(s): 394 - 403
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    Measurements of attenuation at frequencies of 8 and 15 GHz, and their correlation with rainfall rate, along a 15.78 km path near Ottawa, are described. Empirical expressions which relate the observed attenuation to the measured rainfall rate are derived and compared with similar expressions obtained on the basis of earlier theoretical studies of the problem. It is concluded that while the theoretical predictions of attenuation in rain are reasonably satisfactory, at least for rains observed at Ottawa, there is a definite tendency for observed attenuations at low rainfall rates to be somewhat higher than the expected values. The cumulative distribution of rainfall attenuation over a six-month period is compared with the attenuation predicted on the basis of average rainfall data obtained during the last five years. Although the agreement between observation and prediction, using the theoretical relation between rainfall rate and attenuation, is good for path attenuations greater than 2 dB, it can be greatly improved if the empirical expression relating rainfall rate to attenuation is used. View full abstract»

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  • Radio gain

    Page(s): 404 - 410
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    The radio gain or power transfer between two short electric dipole antennas in free space is derived. When the antennas are above and parallel to a perfectly conducting plane, the radio gain approaches a constant as the antennas approach the ground. As the antennas are raised the radio gain is approximately proportional to the square of the product of the antenna heights. At greater heights the interference between the direct and reflected wave causes the radio gain to oscillate. At low antenna heights on vertical polarization the radio gain is the same as in free space. As the antennas are raised it increases and oscillates about four times its free space value. At greater heights the oscillation of the radio gain has greater amplitude. The maxima on vertical polarization occur at the same height as the minima on horizontal polarization and vice versa. For antennas above an imperfectly conducting plane, the radio gain decreases indefinitely as the antennas are lowered and depends upon the polarization and whether the antennas are electric or magnetic dipoles. Numerical values are given forsigmalambda = 1. Vertical loop antennas give greater radio gain for ground wave propagation. View full abstract»

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  • Path diversity in propagation of millimeter waves through rain

    Page(s): 410 - 415
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    Cumulative distributions of attenuation due to rain are computed for the frequencies 11,18.5, and 30 GHz. The results are derived from a four-year sample of rainfall data obtained on a highly resolving areal rain gauge network in Bedfordshire, England. Lack of correlation of attenuation on both orthogonal and parallel paths is discussed and the effect of path diversity is demonstrated for the frequency 30 GHz. Examples of computer-generated maps of intense rain showers at the earth's surface are given. View full abstract»

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  • Polarization and angle-of-arrival fluctuations for a plane wave propagated through a turbulent medium

    Page(s): 416 - 421
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    The correlation function of the fluctuations of the depolarized component of a plane wave as a function of the distance between two parallel line-of-sight paths is derived in terms of the index of refraction variations. A first-order solution to the wave equation is found using spectral analysis techniques. The mean square polarization fluctuation is predicted to have alambda^{2}dependence, in contrast to the work of another author which showed no wavelength dependence. Some numerical values are calculated and the restrictions on the solutions are discussed. At optical wavelengths the depolarized component is extremely small. From the point of view of minimizing the noise introduced by a turbulent atmosphere, polarization modulation seems attractive compared to amplitude or angle modulation. The problem of determining the angle-of-arrival fluctuations when using a wave optics formulation is discussed. If one accepts the statement that the angle-of-arrival is the normal to the wave front at any point, then the correlation function of the angle-of-arrival is simply related to the correlation function of the phase fluctuations and agrees with the ray optics results. View full abstract»

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  • Perturbation analysis of axially nonuniform electromagnetic structures using nonlinear phase progression.

    Page(s): 422 - 430
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    A perturbation technique is developed to deal with axial, as well as transverse, perturbations of an electromagnetic propagating structure which is otherwise axially uniform. The method, an adaptation and extension of time-dependent perturbation theory of quantum mechanics, uses a nonlinear phase progression term in the axial propagating factor of the fields to accommodate and readily calculate, without secular terms, corrections to the progressive phase delay along the perturbed structure. The technique admits inhomogeneities and anisotropy and does not depend upon quasi-static or quasi-optic assumptions. It is particularly useful for axially dependent perturbations which give rise to a phase shift, or to radiation, or to any other effect of interest which is strongly dependent on the phase progression of the wave. The method is first illustrated by an analysis of simple axial loading of a waveguide, and then by a calculation of the radiation from a surface wave structure with a ridged dielectric binding medium. Finally, the casting of Maxwell's equations for general situations into a form appropriate for the application of this perturbation analysis is discussed. View full abstract»

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  • Electromagnetic propagating structures with nonuniform gross perturbations

    Page(s): 431 - 437
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    The perturbation technique presented in a companion paper is here extended to permit even gross perturbations. A generalization and modification of the Brillouin-Wigner method, the present iterative procedure circumvents expansions in powers of a perturbation parameter, but retains a normal mode expansion. Much improvement in convergence is obtained over the previous technique, an adaptation of the usual Rayleigh-Schroedinger perturbation expansion, which converges only for small perturbations. Following a demonstration of improved convergence, through an example whose exact solution is known, the generalized method is applied to problems involving time-harmonic electromagnetic radiation from axial arrays of parasitic elements perturbing an open traveling-wave structure. Both the element pattern and the space factor, corrected to include the change in phase progression of the exciting traveling wave in the presence of the parasites, are automatically included in the expressions for the radiated power. Mutual coupling, or multiple scattering, and polarization effects due to the vector character of the electromagnetic fields are also included in the formalism. View full abstract»

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  • Scattering from low-density dielectric bodies

    Page(s): 437 - 441
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    It is shown that the coherent scattering integral provides a convenient and mathematically tractable method of solving scattering problems of large, low-density, dielectric bodies. In this method the solid dielectric body is replaced by an assembly of particles whose boundary coincides with the outside surface of the dielectric body. Considering the coherent scattering integral, and realizing that coherent scattering comes primarily from sudden particle density changes such as the boundaries of a particle system, it is shown that for low-density dielectric bodies of arbitrary shape the coherent scattering integral yields the physical optics cross section of the dielectric body. Backscattering echo areas for a cylinder, sphere, lens, and various truncated cones are derived and discussed. View full abstract»

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  • Scattering by an infinite cylinder coated with an inhomogeneous and anisotropic plasma sheath

    Page(s): 452 - 457
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    The problem of the interaction of an incidentHwave with an infinite conducting cylinder coated with an inhomogeneous and anisotropic plasma sheath is treated analytically. Numerical results for the farfield pattern of the scattered field as well as the backscattering cross sections are presented for various interesting ranges of the parameters involved. Detailed discussion of the effects of the impressed static magnetic field, the sheath thickness, and the density and profile of the plasma sheath on the scattered wave is also presented. A parabolic electron density profile is assumed. View full abstract»

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  • Mutual coupling between sectoral horns side by side

    Page(s): 475 - 477
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    The mutual coupling between two sectoral horns side by side is formulated in terms of the rays, modes, and mode caustics excited in each horn. The coupling term is attributed to the multiple interaction between the aperture edges of both horns and is calculated using Keller's geometrical theory of diffraction. It is shown that this asymptotic method leads to an excellent agreement with experiment and is a considerable improvement over more complicated solutions based on the Huygens' principle. View full abstract»

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  • Resonances of loops

    Page(s): 477 - 478
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    First Page of the Article
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  • A consideration of the phase center of aperture antennas

    Page(s): 478 - 480
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    The previous formula of Nagelberg for determining the location of the phase center of aperture antennas is examined by calculating the phase patterns of a radiation field. The results show that the phase center should not be located at the aperture, but at the point determined by the expression derived here. View full abstract»

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  • Fresnel diffraction and focusing properties of apertures under partially coherent illumination

    Page(s): 480 - 481
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    Fresnel diffraction from an aperture is investigated in order to determine how the focusing property of the aperture depends on the length of coherence of the illuminating field. The computations show how the focusing property becomes poorer as the coherence length decreases and the focus displaces itself toward the aperture. View full abstract»

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  • Radio-optical dispersion observed over a 25-km tropospheric path

    Page(s): 487 - 488
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    Data from a 25-km path show a 0.99 correlation coefficient between microwave range variation and microwave-optical dispersion. View full abstract»

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  • Characteristics of a tapered anechoic chamber

    Page(s): 488 - 490
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    The characteristic features of a tapered anechoic chamber are described. The smooth illumination amplitude in the chamber makes it usable as an indoor range for antenna pattern measurements, even at low frequencies. Variations in the transmission attenuation in the chamber as compared to free space require careful interpretation of absolute gain and cross section data. View full abstract»

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  • Near field of a conducting wedge

    Page(s): 490 - 492
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    The diffraction coefficients used in Keller's geometrical theory of diffraction are extended to the near field and shadow boundary regions of the edge. Two correction factors are introduced for the amplitude and phase terms of these coefficients and are calculated by comparison with the exact solution. The attractive features of these correction factors are briefly discussed, and their importance in solving near-field transmission problems between horns and double wedges is mentioned. 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