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Antennas and Propagation, IEEE Transactions on

Issue 5 • Date May 1987

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Displaying Results 1 - 18 of 18
  • [Front cover and table of contents]

    Publication Year: 1987 , Page(s): 0
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    Freely Available from IEEE
  • Comments on "Application of FFT and the conjugate gradient method for the solution of electromagnetic radiation from electrically large and small conducting bodies"

    Publication Year: 1987 , Page(s): 607 - 609
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    In the original paper, (ibid., vol.AP-34, no.5, p.635-40, 1986) T.K. Sarkar et al. describe how the fast Fourier transform (FFT) and the conjugate gradient method (CGM) can be used to efficiently make use of the convolutional form of the electric field integral equation for straight wire antennas. The commentators agree that the CGM converges more rapidly than the previously used method of steepest descent and the spectral iteration technique. They also point out that experience with the dyadic Green's function encountered in the two-dimensional transverse electric (TE) and three-dimensional equations for dielectric bodies is not so encouraging. It is found that for these cases the CGM convergence can be quite slow, degrading the efficiency of the algorithm. In addition, the solution obtained using the pulse-basis point-matching method to discretize the integral equation are very inaccurate for the two-dimensional TE and three-dimensional cases. A reply to these comments from the authors of the original paper is included View full abstract»

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  • Correction to "Radiation from a Dipole in the Proximity of a General Anisotropic Grounded Layer"

    Publication Year: 1987 , Page(s): 607
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    First Page of the Article
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  • [Back cover]

    Publication Year: 1987 , Page(s): c4
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    Freely Available from IEEE
  • Roadside tree attenuation measurements at UHF for land mobile satellite systems

    Publication Year: 1987 , Page(s): 589 - 596
    Cited by:  Papers (32)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    Tree attenuation results at 870 MHz are described for experiments conducted in October 1985 and March 1986 in Central Maryland. These experiments employed a helicopter as a source platform and a van with receiver and data acquisition instrumentation. Tree attenuation results were obtained for the cases in which the van was stationary and in motion. The experiments were performed for the purpose of providing the designers of planned land mobile satellite systems with important elements in the determination of link parameter requirements; namely, the expected fading statistics due to roadside trees for both mobile and stationary vehicles. Single tree attenuation results gave worst case median fades as high as 15 dB although roadside tree values were noted to produce fades in excess of 20 dB for small percentages of time. The cumulative fade distributions and their relative contributions as a function of path elevation angle, right side versus left side driving, and different road types are derived from the field measurements. Upon comparing the attenuations from bare deciduous trees (March 1986) with those due to trees in full foliage (October 1985), the increase in dB attenuations were, in general, less than 25 percent for the dynamic cases, and less than 40 percent for the worst case static configuration. This result demonstrates thai the dominant fading is caused by the wooded tree branches as opposed to the leaves on these branches. The tail end of the observed fade distributions was observed to follow lognormal distributions with respect to dB attenuation. View full abstract»

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  • On the use of metallized cavities in printed slot arrays with dielectric substrates

    Publication Year: 1987 , Page(s): 477 - 487
    Cited by:  Papers (26)
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    A detailed analysis of infinite slot arrays excited by delta-function current sources is presented. The existence of severe array blindness is proved for most of the cases of slots without metallic cavity separators. View full abstract»

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  • Weakly dispersive spectral theory of transients, part II: Evaluation of the spectral integral

    Publication Year: 1987 , Page(s): 574 - 580
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    In the spectral theory of transients formulated in Part I of this paper, the transient response for weakly dispersive wave processes has been expressed in terms of canonical integrals in the complex spatial wavenumber domain. The real and complex singularities in the integrands, which dominate the behavior of the spectral integrals, have been categorized and associated with generic physical wave processes. The integrals are now evaluated by Contour deformation around the singularities. This yields general expressions for the transient Green's function that are applicable to a broad class of propagation and diffraction problems. The generic results, which can be grouped into contributions from real or complex singularities; express the transient field in terms of compact (and therefore physically incisive) wave spectra, in contrast to alternative procedures that always constrain the spectra to be real. These aspects, together with simplifying explicit wavefront approximations, are explored in the present paper, with the application to specific problems relegated to Part III. View full abstract»

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  • High-frequency surface currents induced on a perfectly conducting cylindrical sheet by an obliquely incident plane wave

    Publication Year: 1987 , Page(s): 545 - 552
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Explicit expressions for the surface currents of different kinds induced on a perfectly conducting cylindrical sheet by an obliquely incident high-frequency plane wave are derived. The results are in such forms that they can both be used directly in numerical applications and permit us to understand the structure of the induced surface current. It is shown that the components due to the surface and edge diffractions propagate along certain geodesic lines on which the transfer coefficients as well as the attenuation constants are dependent only on the curvature radius. View full abstract»

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  • Improved boundary element techniques for two-dimensional scattering problems with circular boundaries

    Publication Year: 1987 , Page(s): 539 - 544
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    The application of the boundary element method (BEM) in two-dimensional scattering problems with circular boundaries is considered. Uniform discretization of the boundaries results in circulant or block-circulant matrices which provide a great economy in memory storage requirements, and through the use of fast Fourier transform (FFT) techniques, reduction in computation time. Some of the described methods can be applied in problems with regular polygonal boundaries. View full abstract»

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  • A physical optics correction for backscattering from curved surfaces

    Publication Year: 1987 , Page(s): 553 - 561
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    The conventional physical optics (PO) approximation used to calculate the scattered fields from a conducting body leads to incorrect scattered fields even in the specular reflection region. This is true even when all other subdominant terms are assumed to be absent. The inaccuracy stems from the fact that the surface currents used in the PO approximation suddenly truncate at the shadow boundary of curved surfaces resulting in an erroneous contribution. Expressions for these shadow boundary (end point) contributions are presented in this paper. It is shown that if these end point contributions are subtracted from the conventional PO results, one obtains a better representation of the true scattered field. For illustration, backscattered fields from various conducting bodies are computed using the corrected PO solution and are compared with the exact scattered fields. View full abstract»

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  • A generalized self-survey technique for self-cohering of large arrays

    Publication Year: 1987 , Page(s): 496 - 503
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (872 KB)  

    A technique is proposed for locating the elements of a flexible phased array sufficiently accurately to form high-quality beams. The technique requires beacon signal phase measurements and baseline measurements, but does not require the accurate beacon-location knowledge which is characteristic of radio navigation schemes. The effects of phase measurement errors and baseline measurement errors on array beam gain and pointing error are predicted and verified by experiments. View full abstract»

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  • Scattering of TM excitation by coupled and partially buried cylinders at the interface between two media

    Publication Year: 1987 , Page(s): 529 - 538
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (784 KB)  

    An analysis of scattering from coupled conducting cylinders near the planar interface between two semi-infinite, homogeneous halfspaces of different electromagnetic properties and from partially buried conducting cylinders is presented. The perfectly conducting cylinders of general cross sections are of infinite extent and the excitation is transverse magnetic to the cylinder axes. Coupled integral equations for the unknown current induced on the cylinders are derived and a numerical method for solving them is described. In addition, a simple technique is employed to determine the far-zone scattered field from knowledge of the cylinder current. Data displaying the distribution of the induced current and the scattered field patterns for cylinders of interest are presented and discussed. View full abstract»

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  • Rays versus modes: pictorial display of energy flow in an open-ended waveguide

    Publication Year: 1987 , Page(s): 605 - 607
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB)  

    The problem of a plane wave impinging on a semi-infinite parallel-plate waveguide is investigated. It is demonstrated that, for waveguide separation large compared to the wavelength, the fields inside the waveguide obey a simple ray optics description. The beam behavior persists for more than 1000 \lambda into a 50 \lambda waveguide. For a small 3 \lambda waveguide, the beam picture begins to blur approximately 5 \lambda into the guide. View full abstract»

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  • Transient response of an infinite cylindrical antenna in a dissipative medium

    Publication Year: 1987 , Page(s): 562 - 573
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (800 KB)  

    The transient solution of an infinite cylindrical antenna in a dissipative medium caused by an impulse excitation at a delta gap is obtained via an exact solution in the form of definite integrals and a simple asymptotic formula. This formula is used to obtain an integral for calculating the antenna current caused by a double exponential input voltage at the gap; furthermore, the resulting integral reduces to Sunde's classic result under the diffusion limit. These results are applied to the transient response of a buried wire subject to an electromagnetic pulse (EMP) or nearby lightning incident wave. View full abstract»

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  • Scattering from cavity-backed apertures: The generalized dual series solution of the concentrically loaded E -pol slit cylinder problem

    Publication Year: 1987 , Page(s): 504 - 528
    Cited by:  Papers (41)
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    The generalized dual series solution to the scattering of an E -polarized ( E -pol) plane wave from an infinite circular cylinder having an infinite axial slot and enclosing an infinite concentric impedance cylinder is presented. This solution explicitly exhibits the correct edge behavior, and it can handle cylinders that are either electrically small or large without special considerations. The angle of incidence is arbitrary. A variety of current, field, and cross-section results are presented. These are compared with the corresponding H -pol problem results to establish the polarization dependencies of the aperture coupling. It is also shown that effects corresponding to the presence of the interior cavity dominate all of the scattering data. In particular, the bistatic cross sections in either case and the current induced along an interior wire in the E -pol case exhibit new resonance features that are due to the cavity-backed nature of the aperture. View full abstract»

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  • Spatial and temporal filtering of scintillation in remote sensing

    Publication Year: 1987 , Page(s): 597 - 604
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (856 KB)  

    The concept of spatial filtering as applied to remote sensing of the transverse flow velocity and refractive-index spectrum along a line-of-sight propagation path was first outlined in 1974. The technique was applied to optical propagation through the turbulent atmosphere. Random fluctuations in the field were produced by irregularities advected across the optical path by a mean flow. We extend and modify this earlier work to include source and receiver motion, temporal filtering, and dispersion of the refractive index structure. The technique described in this study can be applied to the remote probing of random atmospheric, ionospheric, and oceanic flows using either electromagnetic or acoustic sources. It can also be used for the remote sensing of rough surfaces such as the sea surface. The analysis indicates that this technique is a new, powerful tool with a unique capability for probing the spatial and temporal structure, and evolution of geophysical flows. View full abstract»

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  • A new iterative algorithm for extrapolation of data available in multiple restricted regions with application to radar imaging

    Publication Year: 1987 , Page(s): 581 - 588
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (856 KB)  

    A new iterative method for extrapolation of incomplete segmented data available in multiple separated bands is proposed and tested. The method uses the Burg algorithm to find the linear prediction parameters and an iterative procedure to improve the estimation of the linear prediction parameters and the extrapolation of the data. This method is especially effective when the spectra (Fourier transform of the observed data) are in discrete forms, in the context of radar imaging represented here, this means the objects consist of distinctly spaced scattering centers. The advantages of this algorithm are demonstrated using both numerically generated and realistic experimental data pertaining to high resolution radar imaging. View full abstract»

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  • Monopole element at the center of a circular ground plane whose radius is small or comparable to a wavelength

    Publication Year: 1987 , Page(s): 488 - 495
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB)  

    The input impedance and directive gain of a monopole element at the center of a circular ground plane in free space are summarized for arbitrary element length and element radius with ground plane radii of zero to more than two wavelengths. Numerical results are obtained by utilizing various models and are compared with measurements. The models include a ground plane of zero extent, the integral equation method, method of moments, oblate spheroidal wave functions, and the method of moments combined with the geometric theory of diffraction (GTD). 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