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Antennas and Propagation, IEEE Transactions on

Issue 1 • Date January 1967

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

    Publication Year: 1967 , Page(s): 0
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    Freely Available from IEEE
  • Preface [to the Special Issue]

    Publication Year: 1967 , Page(s): 2 - 3
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    Freely Available from IEEE
  • Partial coherence: A nonstatistical approach, and some basic microwave experiments.

    Publication Year: 1967 , Page(s): 4 - 9
    Cited by:  Papers (1)
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    The basic concepts of second-order coherence theory are introduced, followed by a nonstatistical development of the coherence equations. The various possible generalizations of scalar second-order coherence are briefly described. Microwave experiments are reported in which incoherent as well as partially coherent radiating sources are simulated by suitable arrangements of noise tubes. Two effects in particular are examined: the factorization of the coherence function into space- and time-dependent factors under conditions of "spectral purity," and the spectral modulation of two superposed beams that have a large path delay between them (Alford and Gold effect). View full abstract»

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  • Coherence theory of radio-astronomical measurements

    Publication Year: 1967 , Page(s): 10 - 20
    Cited by:  Papers (12)
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    A unified theory of radio-astronomical measurements is presented within the framework of the theory of partial coherence. It is shown how different coherence functions are related to the spectrum, the brightness distribution, and the polarization of statistical electromagnetic fields, and to their measurement. These coherence functions can be derived from the space-time coherence tensor. Various radio-astronomical techniques for measuring the spectrum, the brightness distribution, and the polarization are discussed with special reference to correlation techniques. The connection between the theory of antennas and that of optical systems is discussed. In both cases the theory of partial coherence provides a unified theoretical foundation and an important framework for future research and development. View full abstract»

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  • Classification of wave phenomena and its relation to coherence theory

    Publication Year: 1967 , Page(s): 21 - 24
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    Various types of problems that arise within the framework of wave propagation through a medium are classified according to whether the medium or the source is random or nonrandom. When both medium and source are nonrandom, the applicable differential equation is of a deterministic nature; otherwise, it is stochastic. A representative case of a random medium and nonrandom source is the multiple scattering of a monochromatic wave by a randomly perturbed medium or by random scatterers. A case in which the medium is nonrandom and the source random is exemplified by the theory of partial coherence. Finally, when both medium and source are random we have the general case in which waves generated by random sources propagate through random media. The last case, which reduces under appropriate conditions to each one of the remaining types, is discussed in detail and its formal solution is obtained by the perturbation method. View full abstract»

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  • An analysis of the second moment of fluctuating electromagnetic fields part I: Theory

    Publication Year: 1967 , Page(s): 24 - 32
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    This paper presents a mathematical treatment of the second-order coherence properties of fluctuating vector electromagnetic fields of arbitrary spectral width. We consider only fields whose random fluctuations result exclusively from the chaotic nature of the source. The theory is expressed in terms of the second-order moment of the field vector and hence is a tensor theory. In order to apply it to fields of arbitrary spectral width, the theory is formulated in terms of a spectral representation. The principal field quantity, the dyadic field spectral density (DFS), is interpreted from both a statistical and a physical standpoint. The differential equations and boundary conditions governing the behavior of the DFS within and external to the source are presented. The differential equations are integrated with the aid of the dyadic Green's function and the resulting formulas are discussed. View full abstract»

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  • An analysis of the second moment of fluctuating electromagnetic fields part II: An application to measurement

    Publication Year: 1967 , Page(s): 32 - 36
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    The theory of the dyadic field spectrum (DFS) of a fluctuating electromagnetic field developed in Part I is applied to the analysis of a particular experiment. The experiment is simply the measurement of the DFS by means of a two-element interferometer. The analysis includes the effect of the polarization and receiving pattern of the interferometer on the measurement and applies to the DFS of a partially polarized, partially coherent radiation field of arbitrary spectral width radiated by an incoherent source. The approach used in this calculation is that described in Section III-C of Part I. It is based on the application of the dyadic Green's function of the electric type for the interferometer. The power at the receiving terminals of the interferometer is expressed in terms of the DFS of the source and the antenna pattern of the interferometer. A method for measuring the distribution of polarization over the source is described. View full abstract»

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  • Geometric analysis of partially polarized electromagnetic waves

    Publication Year: 1967 , Page(s): 37 - 40
    Cited by:  Papers (9)
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    Some invariant properties of partially polarized electromagnetic waves are studied geometrically. Transformations of the complex degree of correlation and the degree of polarization are studied in the Poincaré and Cayley-Klein models of three-dimensional non-Euclidean hyperbolic space by means of simple geometric constructions which lucidly show the relationships between these quantities. View full abstract»

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  • Hologram coherence effects

    Publication Year: 1967 , Page(s): 41 - 48
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    Holograms formed from opaque particles in a clear aperture illuminated with quasi-monochromatic, partially coherent light are considered. The method used to formulate the general boundary-value problem for the pair of wave equations propagating the mutual-coherence function is described. The effect of a reduction in spatial coherence on the resolution limit of a Fraunhofer (far-field) hologram is discussed. Bandwidth considerations of the same hologram define a usable far-field region from which resolvable reconstructions can be expected. The effects of spatial coherence upon Fresnel (near-field) holograms are shown, and experimental results that confirm these calculations are presented. View full abstract»

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  • Coincident arrays for the direct measurement of the principal solution in radio astronomy

    Publication Year: 1967 , Page(s): 49 - 59
    Cited by:  Papers (9)
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    Multiplication techniques are used on a single array to synthesize a product pattern (effectively the product of the voltage patterns of two coincident arrays), which yields the principal solution when it scans a source distribution. A formula for the array-element weighting coefficients is obtained. The behavior of these coefficients for various array sizes is investigated. It is also shown that by using the same weighting coefficients with two separated arrays (forming the "elements" of an interferometer) one can synthesize a large aperture which also yields the principal solution. The output signal-to-noise performance of the coincident system is compared to that of the compound interferometer having almost the same power pattern. The improvement factor IF defined as the quotient of the output signal-to-noise ratios of the coincident system and the compound inteferometer, is shown to be always greater than unity and increases for increasing noise levels and array sizes. View full abstract»

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  • Propagation of a spherically symmetric mutual coherence function through a random medium

    Publication Year: 1967 , Page(s): 66 - 69
    Cited by:  Papers (1)
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    In this paper, an approximate solution obtained by iteration is given for the development of a spherically symmetric mutual coherence function, representing radiation propagating through a statistically homogeneous and isotropic random medium. Only small angle scattering about the radial propagation direction is considered. The results are compared to the problem where propagation is principally in a single direction. View full abstract»

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  • Guided waves in bounded media with random gross inhomogeneities

    Publication Year: 1967 , Page(s): 70 - 75
    Cited by:  Papers (1)
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    A formalism to deal with propagation in waveguides containing media with statistically inhomogeneous, random, gross inhomogeneities over a finite axial range is proposed. Statistics of the propagating fields are obtained in terms of those of the medium through an iterative perturbation technique which does not use expansion in a small parameter. A modal expansion, with a nonlinear phase progression term in the exponent of the axial dependence of the incident mode, is utilized and permits the direct calculation of all desired field statistics from the formal perturbation expressions for the modal amplitudes and phase progression. Examples are presented to show that many quantities of interest, involving mode coupling and transmission and reflection parameter., may straightforwardly be determined through this procedure. Some prevalent notions concerning the significance of the mean wave are discussed. View full abstract»

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  • Application of coherence theory to propagation of a quasi-monochromatic field in a random medium

    Publication Year: 1967 , Page(s): 76 - 80
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    Starting from the partial differential equation for scalar wave propagation in a random medium, an integral equation is derived for the propagation of the second-order correlation function. In order to obtain the exact integral equation without resorting to perturbation theory, it is necessary to assume statistical independence of the wave function and the refractive index fluctuations. The physical basis for this assumption is reviewed, and a criterion for its applicability is proposed. The integral equation for the second-order correlation is then transformed into a wavenumber-spectral representation, resulting in appreciable simplification and permitting some direct interpretation. View full abstract»

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  • Propagation in random media--Cumulative effect of weak inhomogeneities

    Publication Year: 1967 , Page(s): 81 - 89
    Cited by:  Papers (10)
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    The effect of weak, random inhomogeneities on wave propagation is studied. Of particular concern is the case of long distance propagation where the nature of the wave is significanfly affected by the inhomogeneities. Conventional perturbation techniques such as geometrical optics and the Born and Rytov approximations cannot be applied in this realm. The approximation technique employed is basically a selective summation technique of the type utilized in other areas of physics such as quantum electrodynamics and the theory of many-body interactions. Results are obtained for the average value and two-point correlation function of an arbitrary, initial wave. A physical interpretation of the results in terms of coherent and incoherent scattering and the classical theory of dielectrics is given. Wave statistics and the application of the results to the problem of determining the effect of the atmosphere on coherent optical communication are discussed. View full abstract»

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  • Image degradation with random wavefront tilt compensation

    Publication Year: 1967 , Page(s): 90 - 98
    Cited by:  Papers (4)
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    The perturbations on electromagnetic wavefronts resulting from the propagation of plane waves through a random medium are resolved into two components: a random tilt and a random residual phase perturbation. This analysis permits the determination of the mean square angle of arrival from knowledge of the aperture plane phase correlation. It also suggests the use of the statistics of the residual phase perturbation in calculations of resolution and of antenna power patterns. The mean square angle of arrival is calculated for linear and circular apertures with various exponential weightings using the description of phase statistics derived by Tatarski from the Obukhov-Kolmogorov theory of locally homogeneous turbulence. Integrals for tilt-compensated average power patterns are derived. It is demonstrated that a significant reduction in the image degradation results when the aperture tracks the random tilt of the wavefront. View full abstract»

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  • Scattering by random distribution of spheres vs. concentration

    Publication Year: 1967 , Page(s): 99 - 118
    Cited by:  Papers (7)
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    We give data and theory for scattering of 5-mm waves by Styrofoam spheres moving randomly within a slab region Styrofoam container. The results summarize two systematic programs of measurements for the forward scattered coherent phase, the average intensities (coherent, incoherent, and total), and for the variances and covariance of phase-quadrature components of the instantaneous field. These were obtained separately and simultaneously vs. the number ( N ) of spheres in the container for concentrations corresponding to sparse gases through dense gases, on to the limiting case of an amorphous solid. Two relatively distinct "compression processes" for which the coherent phase increased linearly with increasing N were studied: the amplitude of the covariance was either as large or as small as we could obtain. The data records for the small case are in relatively good accord with computations; those for the large show departures in the direction indicated by qualitative considerations of the effects of clumping. View full abstract»

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  • Comparison of distribution functions from scattering data on different sets of spheres

    Publication Year: 1967 , Page(s): 118 - 135
    Cited by:  Papers (2)
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    We compare certain reduced data records for scattering of 5-mm electromagnetic waves by two sets of Styrofoam spheres of different diameter, moving randomly within a slab-region Styrofoam container. For the small spheres we summarize raw measurements for the forward scattered coherent phase, for the average intensities, and for the variances and covariance of phase-quadrature components of the instantaneous field; analogous results for the large spheres were given previously [1]. The emphasis is on the relative behavior of the two sets of reduced data records obtained by using scattering theory to eliminate sphere size, etc., from the original data. In particular, we compare appropriate, reduced data with statistical mechanics approximations for the "hard sphere gas" in order to delineate differences, and to indicate that the analytical procedures developed for the "dynamical gas model" may be applied to isolate the analogous functions for naturally occurring distributions. View full abstract»

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  • Measurements of spatial coherence in 3.2-mm horizontal transmission

    Publication Year: 1967 , Page(s): 136 - 141
    Cited by:  Papers (7)
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    An experiment designed to measure wavefront statistics in 3.2-mm wavelength horizontal transmission over an 18.95-km path is described. A frequency-stabilized signal is transmitted over the path and is received in two spaced antennas having variable separation. The receivers are instrumented to measure phase difference and amplitude fluctuations. A simultaneous beam-swinging experiment using a precision-controlled 4.57-m antenna colocated with the phase difference receivers provides data on wavefront tilt fluctuations. Preliminary results indicate that the random wavefront tilt is the predominant atmosphere-induced wavefront phase disturbance. They further suggest that spatial coherence of wavefronts is of sufficient extent that apertures in excess of 7 m in diameter are feasible at the 3.2-mm wavelength. View full abstract»

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  • Experimental comparison of scattering of coherent and incoherent light

    Publication Year: 1967 , Page(s): 141 - 147
    Cited by:  Papers (2)
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    Light scattering experiments have been performed using as sources a continuous-wave He-Ne gas laser radiating at 6328 Å and a high-pressure xenon arc lamp, which was limited to a 100-Å bandwidth centered at 6328 Å. Both sources were used to determine, us a function of scattering angle, the intensity of light scattered by latex spheres ranging in diameters from 0.088 to 3.49 \mu . It was found that for the four particle sizes studied, the results agree to within the possible experimental error of 20 percent and \pm 1\deg . View full abstract»

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  • An analysis of plasma emission by correlation radiometry

    Publication Year: 1967 , Page(s): 147 - 151
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    Correlation radiometry is proposed as a method of distinguishing between collective and individual particle processes in plasma radiation. Several schemes of correlation radiometry are investigated and the appropriate one is selected to examine correlation between radiation emitted at axially separated points in a beam-plasma discharge column at the harmonics of the electron cyclotron frequency. The correlation measurements establish the usefulness of correlation radiometry and add to the understanding of the collective nature of the cyclotron harmonic emission process. View full abstract»

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  • Laser interferometry and photon scattering in plasma diagnostics

    Publication Year: 1967 , Page(s): 152 - 162
    Cited by:  Papers (1)
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    Various methods for determining the characteristics of high-temperature plasmas using lasers are reviewed. Ordinary interferometric techniques are discussed with the extension of these ideas to active and passive laser cavity probing. It is seen that these methods well complement existing techniques for the determination of electron densities within the range 10^{10} \le n_{e}\le 10^{17} electrons/cm3. Plasma probing using photon scattering is examined and it is shown that the electron density, electron temperature, and ion temperature may be found. In addition a considerable amount of information can be obtained which pertains to the kinetic theory of plasmas. Experimental detail pertaining to these methods is given along with their practical limitations. View full abstract»

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  • Space-time correlation theory for information-carrying signals

    Publication Year: 1967 , Page(s): 163 - 171
    Cited by:  Papers (1)
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    A theory is presented for the analysis and optimization of systems which process electromagnetic fields carrying information. The theory is thus intended for use primarily by communications and radar engineers. The definitions are motivated by a fundamental requirement that the input-output space-time mutual information transfer be a maximum. The theory can be applied to problems involving nonstationary and nonergodic processes in space and time. The technique proposed is particularly useful in the analysis and optimization of controlled systems carrying man-made information, such as radar and communications. System optimization is carried out by maximization of the trans-correlation function with respect to the variable parameters of the system. The transcorrelation function is a space- and time-averaged correlation function between the desired and the actual system outputs. The optimization technique is applied to the problem of an antenna embedded in a nonstationary medium, such as a hot plasma. The amplitude and phase shading of the array are the variable parameters chosen for optimization of the system, and medium effects, background (object) noise, receiver noise, etc., are considered. View full abstract»

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  • Spatial spectral density functions

    Publication Year: 1967 , Page(s): 184 - 185
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  • On the multidimensional aspects of the coherence tensor excited by a distributed source

    Publication Year: 1967 , Page(s): 185 - 186
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  • Some quantum aspects of interference experiments

    Publication Year: 1967 , Page(s): 186 - 187
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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