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Antennas and Propagation, IEEE Transactions on

Issue 3 • Date May 1977

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Displaying Results 1 - 25 of 42
  • [Front cover and table of contents]

    Publication Year: 1977 , Page(s): 0
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    Freely Available from IEEE
  • In memoriam: Samuel Silver

    Publication Year: 1977 , Page(s): 289
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    Freely Available from IEEE
  • Comments on "A uniform geometrical theory of diffraction for an edge in a perfectly conducting surface"

    Publication Year: 1977 , Page(s): 447 - 451
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    The edge diffraction coefficients of Kouyoumjian and Pathak, when applied to edges in curved screens produce discontinuities in the diffracted fields which do not coincide with those of the specular field on the concave side of the screen. In regions where coincidence occurs the discontinuities add, rather than cancel. The field calculated from the diffraction coefficient violates the principle of reciprocity. View full abstract»

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  • A nonlinear minimax optimization program not requiring derivatives

    Publication Year: 1977 , Page(s): 454 - 456
    Cited by:  Papers (5)
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  • Coupled azimuthal potentials for electromagnetic field problems in inhomogeneous axially symmetric media

    Publication Year: 1977 , Page(s): 413 - 417
    Cited by:  Papers (24)
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    Classical electromagnetic potential formulations are, with the exceptions of a few special cases of one-dimensional stratification, restricted to use in uniform media. A recently developed potential formulation that provides a flexible basis for numerical computation of time-harmonic field problems involving continuously and discretely inhomogeneous axially symmetric media is the topic of this paper. The formulation manifests itself in both a differential equation system and, alternately, a variational criterion. Typical numerical applications include solutions of scattering by arbitrarily shaped material bodies of revolution and radiation from inhomogeneously loaded rotationally symmetric antenna structures. Current numerical investigations by the authors, using Mei's unimoment method in conjunction with both finite-difference and finite-element techniques, have shown the formulation to be highly feasible for computation of field problems having dimensions as large as several wavelengths. View full abstract»

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  • Holographic measurement of k-factor on line-of-sight microwave routes containing knife-edge obstacles

    Publication Year: 1977 , Page(s): 445 - 446
    Cited by:  Papers (1)
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    It is pointed out that the effective earth radius factor k can be estimated directly from a holographic interpretation of standard height-gain plots for line-of-sight microwave routes containing dominant knife-edge obstacles. View full abstract»

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  • Frequency scaling of rain attenuation

    Publication Year: 1977 , Page(s): 446 - 447
    Cited by:  Papers (13)
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    A simple method of frequency scaling for rain attenuation is presented. This method includes a correction factor for rain inhomogeneity and takes into account the high correlation between peak rainfall rate and attenuation. The results are compared with Drufuca's empirical method. The discrepancies between theoretical scaling and empirical scaling are found to be reduced by about a factor of two when the corrections presented herein are incorporated. View full abstract»

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  • Isotropic transmission-line antenna and its toroid-pattern modification

    Publication Year: 1977 , Page(s): 386 - 392
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    The far-field strength of the \lambda /4 transmission-line antenna is derived as a complex vector containing amplitude, phase, and direction of the E vector. The product of this phasor-vector and its conjugate is constant and proves that the transmission-line antenna is an isotropic radiator with respect to the powerflow density of coherent electromagnetic waves. Folding of the line conductor parallel to the symmetry plane reduces the pattern to toroid shape analogous to radiation of a short dipole. While the unbalanced straight transmission-line antenna is used on rockets and vehicles, the unbalanced folded type is suitable as efficient transmit antenna at VLF, LF, or MF. View full abstract»

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  • An electrically small cassegrain antenna with optically shaped reflectors

    Publication Year: 1977 , Page(s): 346 - 351
    Cited by:  Papers (3)
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    The efficiency of an electrically small (diameter less than 30 \lambda ) Cassegrain antenna was increased by specially shaping the reflectors using ray optics. Diffraction effects were reduced by modification of the reflector designs in the central region and at the edges. Special attention was given to the reduction of gain loss caused by blockage. Although the antenna was very small, the technique resulted in an overall efficiency varying from 60-65 percent over a 1.16:1 frequency band. An "unshaped" Cassegrain antenna was also built and tested for comparison. Measured data shows an increase in gain of 0.5 dB over the conventional Cassegrain. About 0.35 dB of this difference is attributed to reflector shaping, and the remainder is the result of replacing the subreflector quadripod legs with a dielectric cone. The conclusion is that the efficiency of electrically small Cassegrain antennas can be significantly increased by specially shaping the reflectors according to ray optics with allowances for diffraction effects. View full abstract»

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  • Truncation of infinite sheath spiral antennas

    Publication Year: 1977 , Page(s): 359 - 365
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    The effect of truncation of the infinite sheath spiral antenna is analyzed by superimposing two known solutions of the structure. The two solutions, one for excitation at the center (CE) and one for excitation with a ring source (RE) at a radius \rho_{0} , are superimposed to achieve a cancellation of the current distribution for \rho > \rho_{0} It is shown numerically that by choosing the relative amplitudes of the two sources such that the surface wave part of the two Solutions would cancel, the reminder of the current for \rho > \rho_{0} is about 20 dB below that for \rho < \rho_{0} . Other features of the RE solution and the superimposed solution are explored. In particular the RE solution, which was not explored completely before, is analyzed in full, and certain ambiguities are removed. View full abstract»

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  • Limitations on oceanographic use of beam-limited target-referenced radars

    Publication Year: 1977 , Page(s): 312 - 318
    Cited by:  Papers (4)
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    A general development is undertaken to determine the limitations on the use of beam-limited target-referenced radars in the measurement of ocean wave height. This class of radars is concerned only with the range extent of the target, not the range to the target. The nonzero range extent of a flat waveless sea and the compounding effect of pointing errors due to radar platform instability cause difficulty in measuring low wave heights and impose a maximum operating altitude on such systems. It is seen that it is impractical to obtain accurate measurements for wave heights of interest at altitudes above those used by commercial aircraft (10 000 m). Additionally, the typical ratio of dominant wavelength to significant wave height (SWH) of 30 for wind-driven gravity waves imposes an upper limit on the (SWH) measurable for a given altitude and beamwidth. View full abstract»

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  • Asymptotic approximations for surface scattering integrals

    Publication Year: 1977 , Page(s): 443 - 445
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    Asymptotic approximations of integrals with the saddle point method depend on the power series and their inversions utilized. This dependence is evident in the second and subsequent terms in the asymptotic series. Modifications for double integrals and poles are also indicated. View full abstract»

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  • Complex radiation patterns of dual mode pyramidal horns

    Publication Year: 1977 , Page(s): 436 - 438
    Cited by:  Papers (2)
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    The radiation patterns of the dual mode horn and its related performance are influenced by the phase difference between component modes at the horn aperture and the phase distribution associated with the horn flare angle. Both effects are shown to deteriorate beam symmetry and increase sidelobe levels. Radiation pattern functions and fractional power distributions associated with the dual mode pyramidal horn are illustrated for a range of mode and distribution phase errors. View full abstract»

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  • Aperture cooling through long, parallel slots

    Publication Year: 1977 , Page(s): 453
    Cited by:  Papers (1)
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    First Page of the Article
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  • Effects of a human body on a dipole antenna at 450 and 900 MHz

    Publication Year: 1977 , Page(s): 376 - 379
    Cited by:  Papers (12)
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    The VSWR and pattern characteristics of a dipole held close to or touching a human body have been experimentally determined and the results are reported. Two choke-sleeve dipoles, tuned for the two test frequencies of 450 and 900 MHz, were used for this study. The measurements were made with the antenna held at a person's waist, chest, and shoulder levels and also held above the head. The radiation characteristics of the combined body and antenna were compared with the dipole characteristics in free space. Propagation shadowing by the body and the effects of the body on the VSWR characteristics are illustrated. View full abstract»

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  • A new approach to the thin scatterer problem using the hybrid equations

    Publication Year: 1977 , Page(s): 402 - 406
    Cited by:  Papers (7)
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    A new set of integral equations for electromagnetic scattering problems, the "hybrid" equations, is presented. The advantages of these equations for thin perfect conductors are discussed in comparison to the magnetic and electric field integral equations. Specific comparisons are made with the solution of the electric field integral equation for a finite hollow cylinder. It is demonstrated that the primary advantage of these equations is obtained by minimizing the coupling between component equations for the two surface currents. View full abstract»

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  • Caustics and caustic corrections to the field diffracted by a curved edge

    Publication Year: 1977 , Page(s): 297 - 303
    Cited by:  Papers (10)
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    The caustics for the singly diffracted rays from a circular disk are investigated when the rays emanate from a source which is placed off the axis of the disk. Either two or four singly diffracted rays appear dependent on the far-field direction. The caustics separate the region of space with two singly diffracted rays from the regions with four singly diffracted rays. Corrections are derived which allow the ray description to be continued across the caustics. These corrections depend on the local properties of the edge at the point of diffraction and may be used for edges with arbitrary curvature. Numerical examples are included to demonstrate how the caustic corrections improve calculations based on the geometrical theory of diffraction (GTD). View full abstract»

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  • Efficiency of electrically small antennas combined with matching networks

    Publication Year: 1977 , Page(s): 369 - 373
    Cited by:  Papers (15)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    The efficiency of an antenna combined with a matching network constructed from elements with finite Q is determined by applying the principle of conservation of energy. The conditions which must be satisfied to obtain maximum efficiency are examined. An analysis shows that for many electrically small antennas the conditions for maximum efficiency can be met using a simple L section as the matching network. Examples are presented to show the importance of including the matching network in efficiency calculations for electrically small antennas. View full abstract»

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  • Receiving characteristics of a flanged parallel-plate waveguide

    Publication Year: 1977 , Page(s): 424 - 425
    Cited by:  Papers (4)
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  • Synthesis of equally excited linear arrays

    Publication Year: 1977 , Page(s): 425 - 428
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    Synthesis of linear arrays employing a perturbation technique to achieve sidelobe reduction by varying element positions alone or phases of antenna currents alone, keeping magnitudes of antenna currents equal, is discussed. Both the mean squared and mini-max error criteria are employed. The technique may also be used to yield patterns with all sidelobes equal. View full abstract»

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  • A graphical aid for extracting circular-polarized components from spinning-linear patterns

    Publication Year: 1977 , Page(s): 451 - 452
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    Gain measurements of circularly polarized antennas are often made with spinning linearly polarized gain standards rather than circularly polarized (CP) gain standards. This communication describes a graphical aid for quickly extracting the CP components. View full abstract»

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  • Metallic flanges on sectoral horns as corner reflectors

    Publication Year: 1977 , Page(s): 431 - 435
    Cited by:  Papers (3)
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    Metallic flanges attached to sectoral horn antennas show striking resemblances to corner reflectors. This suggest the possibility of interpreting some of the earlier results on E -plane sectoral horns which could not be explained on the basis of the usual geometrical theory of diffraction (GTD). View full abstract»

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  • On the maximum off-axis gain of symmetrical pencil-beam antennas

    Publication Year: 1977 , Page(s): 435 - 436
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    For a general class of symmetrical pencil-beam antennas, the gain at a given off-axis angle can be maximized by choosing the proper antenna size. The maximum gain at the given angle relative to the on-axis gain is independent of the given angle and dependent only on the main-beam pattern. It is computed here for four commonly used gain functions. Its value, in all cases, is close to 4 dB. This result is important in the definition of service areas for communication and broadcast satellites. View full abstract»

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  • The range limitation on radar-acoustic sounding systems (RASS) due to atmospheric refractive turbulence

    Publication Year: 1977 , Page(s): 319 - 326
    Cited by:  Papers (3)
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    The effects of acoustic refractivity fluctuations on the operation of a radar-acoustic sounding system (RASS) have been calculated. Using the Born approximation, the electromagnetic field scattered from a spherical acoustic pulse whose sphericity is perturbed by transmission through the turbulent medium between the source and scattering volume was determined. The resultant system gain reduction factor changes the dependence on range R of the total received power from an R^{-2} dependence for a homogeneous atmosphere to R^{-18/5} in strong turbulence. This new range dependence can occur at distances of the order of a few hundred meters for sufficiently strong turbulence. View full abstract»

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  • Variability of EHF air refractivity with respect to temperature, pressure, and frequency

    Publication Year: 1977 , Page(s): 336 - 345
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    EHF transfer properties of air are expressed by a complex refractivity N , yielding phase dispersion and attenuation due to the microwave spectrum of oxygen. Based upon an experimetally verified theory (Rosenkranz band shape), the variability of N with respect to temperature, pressure, and frequency variations is analyzed across the 40 to 140 GHz band for atmospheric conditions up to 40 kilometers in altitude ( 300-200\deg K, 760-5 torr). The discussion centers on the usefulness of such information when treating problems of possible propagation limitations imposed by turbulent air and of remote sensing atmospheric states. 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