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Antennas and Propagation, IEEE Transactions on

Issue 4 • Date Apr 1992

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Displaying Results 1 - 19 of 19
  • A least mean square error synthesis with pattern constraints at multiple frequencies

    Page(s): 463 - 465
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    The pattern synthesis techinque described allows the power pattern to be optimized in a very useful sense over the desired operating band of the antenna array. This is an improvement over previous techniques involving constraints on such artificial parameters as source norm and superdirectivity ratio, which do not, in fact, ensure a useful pattern bandwidth. The procedure described provides minimum mean square error over an arbitrary number of discrete frequencies View full abstract»

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  • On the performance of the generalized sidelobe canceller in coherent situations

    Page(s): 465 - 468
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    The convergence rate for the adaptive weights to reach the optimum value in an adaptive array system depends on the eigenvalue spread ratio of the autocovariance matrix. How the eigenvalue spread ratio in a generalized sidelobe canceller (GSC) is affected by the various parameters is studied. Expressions for the output power of the GSC in coherent situations are derived, and numerical results are included View full abstract»

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  • Finite-difference time-domain modeling of curved surfaces [EM scattering]

    Page(s): 357 - 366
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    The finite-difference-time-domain (FDTD) method is generalized to include the accurate modeling of curved surfaces. This generalization, the contour path CP), method, accurately models the illumination of bodies with curved surfaces, yet retains the ability to model corners and edges. CP modeling of two-dimensional electromagnetic wave scattering from objects of various shapes and compositions is presented View full abstract»

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  • Optimal control of the feed voltage of a dipole antenna

    Page(s): 414 - 421
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    An iterative algorithm is described for the construction of the input voltage of a dipole antenna for a specified electric field response at a given far-zone point. A functional is optimized subject to the state equation, which is an ordinary differential equation. The state equation used is Pocklington's equation where the control is the input voltage waveform and the state is the current distribution on the antenna. The Lagrange multiplier function, which is introduced by augmenting the functional, satisfies the adjoint Pocklington's equation. In the descent algorithm these two equations are solved at each step. All calculations are carried out in the time domain, so there is no need for additional specification related to frequency domain. However, the procedure implicitly determines the frequency bandwidth of the signals used View full abstract»

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  • Low frequency electromagnetic scattering from an island

    Page(s): 439 - 442
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    Adopting a simple model, a formulation is presented for the scattering from a circular island surrounded by an otherwise smooth sea. Both the surface impedance and the height profile of the island are functions of the radial distance. Employing the electromagnetic compensation theorem, an expression for the mutual impedance between two small ground-based vertical antennas is derived. To simplify the analysis these antennas are assumed to be located at distances that are large compared with the radius of the island. It is shown that the relative importance of the surface impedance and the height profile will depend on the scattering angle subtended, at the island center, by the direction to the source and receiving antennas. The results are relevant to the propagation of electromagnetic waves in the earth-ionosphere waveguide at very low frequencies (VLF) View full abstract»

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  • Electromagnetic waves in Faraday chiral media

    Page(s): 367 - 374
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    Plane wave propagation in two kinds of Faraday chiral media, where Faraday rotation is combined with optical activity, is studied to examine methods of controlling chirality. The two types of media studied are magnetically biased chiroplasmas and chiroferrites. For propagation along the biasing magnetic field, four wavenumbers and two wave impedances are found which are dependent on the strength of the biasing field. Dispersion diagrams for the chiroplasma case are plotted. Propagation at the plasma frequency of the chiroplasma is also investigated View full abstract»

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  • Scanning properties of large dual-shaped offset and symmetric reflector antennas

    Page(s): 422 - 432
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    The scanning properties of shaped reflectors, both offset and circularly symmetric, are examined and compared to conic section scanning characteristics. Scanning of the pencil beam is obtained by lateral and axial translation of a single point source feed. The feed is kept pointed toward the center of the subreflector. The effects of power spillover and aperture phase error as a function beam scanning are examined for several different types of large reflector design including dual-offset, circularly symmetric large f/D, and smaller f/D dual reflector antenna system. It is shown that the Abbe-sine condition for improved scanning of an optical system cannot, inherently, be satisfied in a dual-shaped reflector system that is shaped for high gain and low feed spillover. The gain loss, with scanning, of a high-gain shaped reflector pair is demonstrated to be due to both aperture phase error loss and power spillover loss View full abstract»

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  • A fast algorithm for plotting and contour filling radiation patterns in three dimensions

    Page(s): 453 - 456
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    An algorithm is presented for plotting antenna and scattering patterns in three dimensions. The algorithm exploits the property of single-valued surfaces to allow the implicit removal of hidden lines with virtually no extra computation. This reduces the processing time significantly over that required by more general plotting methods. The algorithm is based on finding a systematic sequence to draw the plot from back to front as a collection of quadrilaterals. Each quadrilateral can be broken into two triangles, which allows a simple contour filling scheme to be incorporated into the algorithm View full abstract»

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  • Microstrip antenna on a conical surface

    Page(s): 460 - 463
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    A theoretical analysis of microstrip antennas on conical conducting surfaces is presented. The resonant frequency, input impedance, radiation pattern, quality factor, and efficiency are obtained for a general geometry. Numerical results for a patch antenna with a cone angle θ0=33.88° operating in the fundamental TM01 mode are shown View full abstract»

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  • A reflection cancelling slot set in a linearly polarized radial line slot antenna

    Page(s): 433 - 438
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    A radial line slot antenna (RLSA) is a high-gain and high-efficiency planar antenna. A linearly polarized RLSA (LP-RLSA) is attractive for applications of various subscriber radio systems. However, the slot arrangement for linear polarization gives rise to serious reflection from slots, which disturbs the normal antenna operation. A new LP-RLSA slot design is presented where reflection canceling slots are added to the conventional ones; four slots form one slot set as a unit radiator of linear polarization. The experiments confirm the design: the antenna return-loss is improved from -2 to -10 dB. Antenna efficiencies of 48 and 54% are measured for 400 and 600-mmφ antennas, respectively. This is the first report of the normal operation of LP-RLSAs View full abstract»

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  • Field feedback computation of scattering by 2-D penetrable objects

    Page(s): 445 - 450
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The field feedback formulation is applied to the solution of time-harmonic plane wave scattering by 2-D penetrable objects of arbitrary shape and composition. A conformal mesh, finite element algorithm is employed in the forward operator construction while a near-field Green's function integration is used in forming the feedback operator. Scattering validations for midresonance sized objects include a circular cylinder, a two-region bisected cylinder, a half-circular cylinder, a semiconductor shell and a thin lossy planar strip View full abstract»

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  • Modeling and simulation of mobile satellite propagation

    Page(s): 375 - 382
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    Mobile satellite systems are subject to severe fading due to blockage of the line-of-sight (LOS) path by roadside vegetation. A thorough understanding of the fading effects is necessary for the design of a reliable land-mobile satellite system. Analytical and empirical models are presented for predicting fade statistics for vegetative shadowing of mobile satellite terminals. A software simulator for generating simulated fade data is also presented. A physical model relating physical path parameters to propagation model parameters is presented, and results using the model are shown View full abstract»

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  • Grid decoupling in finite element solutions for Maxwell's equations

    Page(s): 443 - 445
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    Certain finite-element discretization methods used in time-domain electromagnetic modeling reduce to a type of finite-difference method when applied on a regular mesh. The form of this underlying finite-difference method is unusual; it consists of two decoupled grids, rotated 45° from the original finite element mesh View full abstract»

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  • Characterization of strip-fed cavity-backed slots

    Page(s): 405 - 413
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (868 KB)  

    The use of strip-fed cavity-backed slots is an attractive approach for compact conformal antenna arrays. This configuration also offers greater potential than traditional designs for additional antenna functions demanded by high-performance system requirements. As with previous approaches, it is desirable to avoid costly, time-consuming empirical design techniques, which in turn requires highly accurate analytic/numerical models. A full-wave integral equation analysis is presented, which by using the dyadic Green's functions for multilayered substrates, models this array element with a high degree of accuracy. Using a previously presented Green's function for a grounded slab, the analysis also accounts for dielectric-covered slots. Comparisons are made with measurements to validate the results View full abstract»

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  • High frequency inverse scattering and the Luneberg-Kline asymptotic expansion

    Page(s): 450 - 453
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    The problem of estimating the relative distance to individual scatterers within a complicated multiscatter target from radar backscattered signals is addressed. The scattered signal amplitudes produced by these scatterers are estimated. Such information can be useful for detection and identification of targets. An extension is described of the linear prediction algorithm for estimating these quantities applied to a signal model given by the Luneberg-Kline asymptotic expansion for electromagnetic scattering. This model includes the geometrical optics signal model as a special case View full abstract»

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  • On the synthesis of exact free space absorbing boundary conditions for the finite-difference time-domain method

    Page(s): 456 - 460
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (484 KB)  

    An exact and nonlocal analytical absorbing boundary condition (ABC) for use in the finite-difference-time-domain (FDTD) method is proposed. The ABC requires no assumptions regarding a minimum spacing between scatterers and the artificial termination planes, and is not a function of the angle of an incident wave component with respect to the ABC truncation plane. Hence the size of the volumetric computational domain may be kept to a minimum. The derivation of the ABC makes use of the surface equivalent theorem and the vector potentials after an analytical frequency to time domain transformation. The new ABC contains derivatives with respect to both time and space, and may be approximated in the FDTD method via appropriate finite difference approximations View full abstract»

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  • Analytical and numerical solution to the two-potential Zakharov-Shabat inverse scattering problem

    Page(s): 399 - 404
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    An analytical and a numerical method are presented in order to solve the inverse scattering problem associated with the two-potential Zakharov-Shabat coupled mode equations. The numerical solution, which uses leapfrogging in space and time, represents a direct numerical solution to the coupled Gel'fand-Levitan-Marchenko (GLM) integral equations as an extension of the authors' previous work on GLM equations of simpler form. The analytical method, which is applied for one-pole reflection coefficients, consists in constructing appropriate differential operators which transform the coupled GLM equations to ordinary linear differential equations. An application of these methods for nonuniform transmission line synthesis is presented View full abstract»

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  • Accuracy of a Gaussian beam

    Page(s): 391 - 398
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    The accuracy of a multimode Gaussian beam is discussed. Novel modifications are given to the conventional Gaussian beam formulation derived using the paraxial approximation. With the modifications, the field can be calculated accurately with the Gaussian beam. Modified multimode Gaussian beam techniques are used for calculation of the beam of a corrugated horn antenna. Phase and amplitude patterns given by this method are compared with measurements and other theoretical methods, namely Huygen's principle and the modal matching technique. The meaning of the phase and phase center is also discussed View full abstract»

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  • Electromagnetic scattering by a two-dimensional wedge composed of conductor and lossless dielectric

    Page(s): 383 - 390
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    Electromagnetic scattering by two-dimensional wedges composed of perfectly conducting and lossless dielectric material is considered. Heuristic geometrical theory of diffraction type diffraction coefficients are presented and a hybrid moment-method/physical-optics technique is developed to verify the accuracy of the proposed diffraction coefficients. The purpose is to show that the heuristic approach can yield acceptably accurate results for a number of composite wedge geometries, rather than to present rigorous diffraction coefficients for the composite wedge per se. Calculated results are presented in which the results obtained by means of the two methods are compared. Very good agreement is achieved for a variety of wedge geometries 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