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Antennas and Propagation, IEEE Transactions on

Issue 1 • Date January 1965

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

    Publication Year: 1965 , Page(s): 0
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  • Comment on "The use of transforms to sum array factors"

    Publication Year: 1965 , Page(s): 174
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  • [Back cover]

    Publication Year: 1965 , Page(s): c4
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  • Theoretical investigations of scattering from plastic foams

    Publication Year: 1965 , Page(s): 88 - 94
    Cited by:  Papers (5)
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    The use of cellular or foamed plastics in various microwave applications, such as supports at radar ranges, makes it desirable to know the back scattering properties of such materials. Since the cell structure is of a random nature with some predictable average properties such as cell size and density, it is modeled by an aggregate of randomly distributed spherical shells. Assemblies of scatterers will in general have a coherent and an incoherent scatter. Coherent scattering comes primarily from sudden particle density changes such as that at the boundaries of a particle system. Since coherent scattering comes only from the boundaries of a constant density material, it can sometimes be reduced by appropriate shaping. Incoherent scattering is the result of the contribution of all the particles in the system, i.e, a volume or an interior effect. It represents the irreducible scattering contribution to the total back scatter. As such it can be looked upon as the minimum cross section that can be obtained from a foam structure provided all coherent scatter has been removed. The magnitude of the incoherent scattering is illustrated by calculating radar cross sections for a cylinder made of styrofoam. Since the compressive strength of styrofoam is known, the maximum load that a styrofoam structure can support and the minimum achievable cross section from it can be easily calculated. View full abstract»

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  • The propagation of transient electromagnetic fields into a cavity formed by two imperfectly conducting sheets

    Publication Year: 1965 , Page(s): 149 - 158
    Cited by:  Papers (10)
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    In this paper steady-state formulas are developed for the ratio of the resultant electromagnetic field in the screened space formed by dual, infinite, homogeneous metal plates to the incident field, and from these transfer functions the time history of the field in the cavity is computed for Gaussian-shaped input fields. View full abstract»

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  • Leaky waves supported by uniaxial plasma layers

    Publication Year: 1965 , Page(s): 94 - 105
    Cited by:  Papers (2)
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    Each discrete complex wave supported by a uniaxial layer corresponds to an isolated singularity in an appropriate Green's function. The location of a singularity depends on the geometry, plasma density, and the direction of the magnetic field, but not on the source. We have derived the discrete solutions for an infinite magnetic field that is parallel or perpendicular to the slab interfaces. For a parallel field, analytic expressions are obtained that yield the exact locations of the complex pole Ioci. Although similar expressions cannot be obtained if the field is perpendicular, the resonance relation which locates the poles can be solved by methods developed for an isotropic plasma. We find that improper modes and surface waves can be supported in the case of a parallel field, while a perpendicular field permits spectral complex modes as well. These results are applied to a Kirchhoff-Huygens integration of the leaky-wave distribution excited by a magnetic line source or an annular slot. A close correlation is shown between the radiation pattern derived by this procedure and the exact pattern calculated by the method of steepest descent. In particular, it is shown that the appearance of a peak in the pattern can be analytically correlated with the contributing pole, provided it corresponds to a dominant leaky wave. View full abstract»

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  • The circular loop antenna immersed in a dissipative medium

    Publication Year: 1965 , Page(s): 43 - 47
    Cited by:  Papers (3)  |  Patents (4)
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    Investigations were made of the radiating and circuit properties of circular loop antennas when immersed in conducting media with various loss tangents. The following quantities were experimentally examined and compared with the available theoretical results. 1) Driving point admittance Y_{\in} of circular loops as a function of the circumference per wavelength, 2\pi b/\lambda = \beta b . 2) Current amplitude and phase distributions. 3) Field patterns. In each case the loss tangent \sigma /\omega \epsilon_{r}\epsilon_{0} of the medium (conductivity \sigma , permittivity \epsilon_{r}\epsilon_{0} ) is taken as a parameter. The experimental results are in good agreement with the theory. A comparison between the behavior of the loop in a conducting medium and those of a linear dipole was made wherever possible. It was discovered that there is a cut off size beyond which the driving point admittance of a linear dipole is the same whether or not its ends are connected to form a loop. This particular loss tangent is 1.06, and the cut off size is \lambda /2 . A circular loop antenna with \beta b= 1.0 is excited predominantly in a dipole mode and its field pattern resembles that of a two element dipole array. A study was made to determine how this pattern becomes more like that of a monopole as the loss tangent of the solution is increased. View full abstract»

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  • Radiation from electromagnetic sources in a plasma

    Publication Year: 1965 , Page(s): 79 - 88
    Cited by:  Papers (2)
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    The radiation from electromagnetic sources in an unbounded, isotropic plasma is treated. Using a two-fluid magnetohydrodynamic approach, the problem is formulated in terms of three orthogonal modes, namely, i) the electromagnetic mode, ii) the electron plasma mode and iii) the ion plasma mode. When formulated in this manner, the radiation from simple electromagnetic sources are obtained easily. Three specific sources are treated, namely, i) a point source of electric current, ii) a uniformly moving charge and iii) a short filament with prescribed current distribution. For the case of the electric dipole and the current filament, the total power radiated in each of the three modes are obtained. A point charge moving uniformly with the velocity of sound, for example, is found to excite only the ion plasma mode. The frequency and the angular spectrum of the emitted radiation are obtained. It is found that at frequencies less than a critical frequency which is approximately equal to \sqrt {2} times the ion plasma frequency, the radiation has the character of a simple sound wave. View full abstract»

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  • On the surface wave diffraction by a wedge

    Publication Year: 1965 , Page(s): 159 - 164
    Cited by:  Papers (1)
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    In two earlier papers [1], [2] the diffraction of a surface wave by a fight-angle wedge was treated; one face of this wedge is perfectly conducting and the other is reactive. It was pointed out that the Kirchhoff theory of diffraction provides a useful approximation here. A readily calculable result has not been obtained for wedge angles other than 90\deg and 180\deg , so the diffraction patterns for various wedge angles are calculated here by the Kirchhoff approximation and compared with some measured patterns of a wedge excited by a very narrow H-plane sectorial horn. Both the calculated and measured patterns show that in general the wedge angle has a relatively small effect on the diffraction pattern of a loosely bound surface wave, except when the wedge angle is close to 180\deg . View full abstract»

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  • The launching of surface waves on an axial-cylindrical reactive surface

    Publication Year: 1965 , Page(s): 126 - 134
    Cited by:  Papers (1)
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    The excitation of the dominant TM surface wave on an axial-cylindrical reactive surface is discussed. The surface wave launcher consists of a perfectly conducting, infinitely thin cylindrical surface of radius b coxial with a cylindrical reactive surface of a radius a where b > a . The reactive surface extends from -\infty < z< \infty , and the perfectly conducting surface extends from -\infty < z\leq0 . The incident field is the dominant TM mode in the coaxial portion of the structure propagating in the positive z -direction. Numerical results are obtained for the reflected field, the surface wave field, and the radiation field. These results are then compared with the results that use two approximate aperture distributions. This method of excitation was very efficient over a large range of frequencies and over wide variations in the surface reactance. View full abstract»

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  • Impedance matching a phased-array antenna over wide scan angles by connecting circuits

    Publication Year: 1965 , Page(s): 28 - 34
    Cited by:  Papers (20)
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    In a phased-array steerable-beam antenna, the active impedance of the radiating elements exhibits considerable change with scan angle. Because of this change, it is ordinarily possible to match the active impedance at only one angle. However, by the addition of lossless circuits which interconnect the element lines, good impedance match over a wide range of scan angles may be obtained. The effects of connecting circuits are easily analyzed in terms of simple equivalent circuits when the array is infinite. For this reason, and because no change is required in the radiating element, the connecting-circuit method is well suited for application to phased arrays containing a large number of regularly-spaced elements. As an example of the use of connecting circuits for wide-angle matching of an array, calculations are made for an infinite planar array of dipoles. Scanning the beam of this array within a 120\deg cone is assumed to cause a mismatch as great as 14-db SWR at some angles when no connecting circuits are used. With the addition of a set of connecting circuits in the E plane of the array and another set in the H plane, this limit is reduced to 4.5-db SWR. The improvement in this impedance match corresponds to a 2.3-db increase of gain realized by the antenna. View full abstract»

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  • Thinning and broadbanding antenna arrays by unequal spacings

    Publication Year: 1965 , Page(s): 34 - 42
    Cited by:  Papers (40)  |  Patents (2)
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    This paper presents a theory for, and a method of designing a thinned or broad-band antenna array by means of unequal spacings. Using the theory of unequally spaced arrays developed by one of the authors, an antenna array can be designed to produce a desired beamwidth and sidelobe level with the average spacing many wavelengths apart. The patterns are expressed in a series of the Anger functions and its sidelobe level is shown to decrease approximately as N^{-0.5}\sim N^{-0.4} where N is the total number of elements, and the gain is approximately equal to N . It is also shown that the sidelobe level can be improved by varying the amplitude distribution. Numerical examples are given to illustrate the method. View full abstract»

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  • International symposia of the antenna and propagation group

    Publication Year: 1965 , Page(s): 2
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  • Radiation resitance of an elementary loop antenna in a magnetoionic medium

    Publication Year: 1965 , Page(s): 21 - 27
    Cited by:  Papers (5)
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    Radiation resistance for an elementary loop antenna immersed in a magnetoionic plasma is investigated. Based on an integral expression given by Kogelnik and Motz, extensive numerical results are obtained and their validity and utility are discussed. In addition a simple analytic expression is derived for the case of small magnetic fields. View full abstract»

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  • Radiation propagating transverse to the external magnetic field from an electromagnetic source in an unbounded plasma

    Publication Year: 1965 , Page(s): 106 - 115
    Cited by:  Papers (1)
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    The radiation characteristics of a line source of magnetic current embedded in an unbounded plasma are investigated for the case in which a uniform magnetic field is impressed externally throughout the medium in the direction of the source. The plasma is assumed to be a homogeneous and macroscopically neutral mixture of compressible gas of electrons and ions. A two-fluid continuum theory of plasma dynamics is employed. It is shown that it is possible to define three suitable wave functions which satisfy separately simple wave equations whose solutions are written down by inspection. These wave functions specify the three possible modes which are identified, respectively, to be the modified forms of the electromagnetic, the electron plasma and the ion plasma modes. The limiting behavior of these modes are discussed for the following two cases: 1) infinite source frequency and 2) vanishing external magnetic field. The dispersion relations for the three modes are examined in detail for the general case using a perturbation procedure. It is shown that the modified ion plasma (MIP) mode propagates for all frequencies whereas both the modified electron plasma (MEP) mode and the modified electromagnetic (MEM) mode have a low-frequency cutoff. Explicit expressions for the cutoff frequencies are obtained. The power radiated in each of the three modes is also evaluated. It is found that the power radiated in the MEM mode is always lower than that due to the line source in free space, whereas the power radiated in the two plasma modes is higher than that value for certain ranges of frequency. View full abstract»

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  • Point-to-point wave propagation through an intermediate layer of random anisotropic irregularities: Phase and amplitude correlation functions

    Publication Year: 1965 , Page(s): 48 - 52
    Cited by:  Papers (1)
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    The problem of wave propagation from a point source to a point of observation through an intermediate slab containing random weak dielectric irregularities is considered. Under the assumption that the spatial correlation of the permittivity is a Gaussian one with correlation distances much larger than the wavelength, the phase and amplitude auto- and cross-correlations are computed for any distance of source and receiver to the slab. Comparison is made to the analyses by Karavainikov and Yeh which are shown to be limiting cases of the present work. View full abstract»

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  • An approximate method of designing nonuniformly spaced arrays

    Publication Year: 1965 , Page(s): 177 - 179
    Cited by:  Papers (2)
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  • A numerical technique for the determination of scattering cross sections of infinite cylinders of arbitrary geometrical cross section

    Publication Year: 1965 , Page(s): 141 - 149
    Cited by:  Papers (26)
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    A method has been developed for calculating the scattering from an infinitely long cylinder of arbitrary (but smooth) cross section. The equations have been programmed for a computer and monostatic and bistatic cross sections calculated for circular and elliptic cylinders. A number of checks and limiting cases are applied to the results in order to establish the limits within which the assumed expansion gives acceptable numerical results. For the case of monostatic scattering from circular cylinders a numerical check is possible and the result was in agreement with Mie series calculations to six significant figures. View full abstract»

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  • Radiation from a uniformly moving distribution of electric charge in an anisotropic, compressible plasma

    Publication Year: 1965 , Page(s): 71 - 78
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    The radiation characteristics of a linear distribution of electric charge moving with a uniform velocity in a homogeneous electron plasma of infinite extent are investigated for the case in which a uniform static magnetic field is impressed externally throughout the medium. The linear distribution of charge and its direction of motion are assumed to be parallel and perpendicular, respectively, to the direction of the external magnetic field. Of the two possible modes of waves of small amplitude, namely, the modified electromagnetic mode and the modified electron plasma mode, the uniformly moving charge distribution excites the modified electron plasma mode. The emitted radiation has no frequencies less than the plasma frequency. For a particular value of the ratio of the gyrotropic to the plasma frequency of the electrons, the frequency and the angular spectrum of the emitted radiation are determined for two values of the velocity of the charge. View full abstract»

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  • Admittance of a waveguide radiating into stratified plasma

    Publication Year: 1965 , Page(s): 64 - 70
    Cited by:  Papers (26)
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    A slot covered by a stratified plasma is assumed to radiate into a wide waveguide instead of free space. The slot admittance approximates the free space admittance of the slot for waveguide diameters exceeding 6 to 10\lambda . For thick plasma layers the computed slot admittance checks with earlier admittance calculations for a laterally unbounded plasma. When approximating a plasma profile of a typical hypersonic re-entry, a multilayer plasma model in a wide waveguide appears to provide a more accurate slot admittance than a single-layer approximation in a laterally unbounded geometry. View full abstract»

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  • Scattering of radio waves by dense turbulent plasmas

    Publication Year: 1965 , Page(s): 122 - 126
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    An analysis is made of the scattering of radio waves by plasmas in which turbulent variations of free-electron number density occur. Second-order terms for the scattered field are included. An additional term (as compared to the first-order Born approximation) is found in the expression for the scattering cross section, This term is proportional to gama(\omega _{p}/\omega )^{2} where gama is a numerical factor determined by the scale of the turbulence. View full abstract»

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  • Diagonal representation of the radar scattering matrix for an axially symmetric body

    Publication Year: 1965 , Page(s): 176 - 177
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  • The circular loop antenna multiloaded with positive and negative resistors

    Publication Year: 1965 , Page(s): 7 - 20
    Cited by:  Papers (10)
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    Studies are made of both the driving-point impedance and the amplitude and phase distributions of the current in a circular loop which is driven by an arbitrary number of delta-function generators and loaded with an arbitrary number of lumped impedances. The only restriction imposed in the present treatment is that the elements (either generator or load) are spaced at equal intervals of 2\pi b/m along the circumference where m is the total number of elements and b is the radius of the loop. The numerical calculations include loads with negative resistances in order to take account of loops loaded with an element like an Esaki tunnel diode, with proper precautions against both self-oscillation and switching effects. A study of such precautions is to be considered separately. The experimental results agree quite well with theory except for the larger values of \beta b . The radiation patterns of the loop antennas with \beta b=1 loaded with various resistors were also measured. View full abstract»

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  • Observations of the effect of magnetic fields on the radiation from plasma-covered antennas

    Publication Year: 1965 , Page(s): 169 - 173
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    Measurements of the broadside radiation from an anisotropic plasma-covered slot are compared with theoretical predictions which neglect input impedance changes and coupling to electroacoustic or Tonks-Dattner resonances. For a magnetic field normal to the plasma layer, the results demonstrate transmission enhancement and underscore the necessity of a strong field ( \omega _{c} > \omega ). They also highlight some of the limitations of existing theoretical treatments. In particular, it is concluded that collisional damping, impedance variations, and electroacoustic resonances must be included for an accurate prediction of magnetic field effects. The experimental system consists of a narrow aperture in a large ground screen covered by a bank of long discharge tubes which are collectively equivalent to a plane layer. All measurements are performed at a fixed frequency of 565 Mc during the afterglow of the pulsed discharge. View full abstract»

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  • A wave polarization converter for circular polarization

    Publication Year: 1965 , Page(s): 3 - 7
    Cited by:  Papers (18)  |  Patents (1)
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    A linearly polarized wave may be converted to a circularly polarized wave by means of a panel which provides 90\deg difference in transmission phase between two crossed linear components. This phase difference is obtained over a wide frequency band by means of thin sheets containing both inductive and capacitive shunt susceptance. Low reflection and near unity axial ratio may be obtained by means of three sheets which are spaced for least reflection. An experimental polarizer has been constructed using three photo-etched sheets and a dielectric honeycomb core. Over a 20 per cent band the axial ratio of the circular polarization is within 1.7 db and the insertion loss is within 0.5 db. Over a 46 per cent band the axial ratio is less than 2.0 db and the insertion loss is less than 1.0 db. 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