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Antennas and Propagation, IEEE Transactions on

Issue 9 • Date September 1985

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Displaying Results 1 - 23 of 23
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • On the choice of expansion and weighting functions in the numerical solution of operator equations

    Page(s): 988 - 996
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    One of the objectives of this paper is to discuss the mathematical requirements that the expansion functions must satisfy in the method of moments (MM) solution of an operator equation. A simple differential equation is solved to demonstrate these requirements. The second objective is to study the numerical stability of point matching method, Galerkin's method, and the method of least squares. Pocklington's integral equation is considered and numerical results are presented to illustrate the effect of various choices of weighting functions on the rate of convergence. Finally, it is shown that certain choices of expansion and weighting functions yield numerically acceptable results even though they are not admissible from a strictly mathematical point of view. The reason for this paradox is outlined. View full abstract»

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  • Complex ray analysis of beam transmission through two-dimensional radomes

    Page(s): 963 - 975
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    Assessment of the radiation characteristics of certain types of radome covered antennas poses the problem of transmission of amplitude tapered large-aperture fields through a curved dielectric layer. Modeling the amplitude taper by a Gaussian, the incident illumination can be generated by a source at a complex coordinate location. The radome problem is then addressed by tracing complex ray fields from the complex source point through the complex extension of the radome configuration to the real location of the observer. No integrations over equivalent apertures are required here. The complex ray tracing has been performed for conventional complex geometric trajectories as well as more accurate trajectories with lateral shifts at the radome interfaces, and takes into account multiple reflections inside the radome. As previously for real rays, the multiple internally reflected complex rays can be combined into a "collective ray" that is weighted with a curvature and (or) taper corrected slab transmission coefficient. Numerical calculations for various two-dimensional circular cylindrical and wedge-tapered prototypes and various beam illuminations demonstrate the feasibility of the complex ray method, the efficiency of the collective ray concept, and the adequacy of the ray model without lateral shifts for the radome application. View full abstract»

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  • Diffraction by a wide double wedge with rounded edges

    Page(s): 1012 - 1015
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    The multiple diffraction by two conducting wedges with rounded edges is investigated, using an expression for the scattered field of a plane wave incident on a single wedge with rounded edge derived by Ross and Hamid, as well as the technique proposed by Karp and Keller for the diffraction by a slit in an infinite screen. Numerical results for the diffraction pattern, transmission coefficient and the effect of rounding are also presented. It is shown that small rounding of the two edges decreases the transmission coefficient for large separation distances between the wedges. View full abstract»

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  • Exact image method for impedance computation of antennas above the ground

    Page(s): 937 - 945
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    The principle of exact images recently developed by two of the present authors for the Sommerfeld problem is here applied for the classical impedance problem of antennas above the ground. In the present method, the effect of the ground is taken into account with an image source, which is located in complex space, leading to a modified Green function for the antenna current integral equation. The image of the antenna can be effectively determined through new expressions evaluated for the image current function. The stationary functional for the antenna impedance is extended to take into account the effect of the ground. As examples of the theory, impedance expressions for small dipoles and half-wave dipoles are formulated with numerical results calculated and compared with previous results. A simple method applicable for small microcomputers is suggested for calculating the impedance of wire antennas with finite thickness from that of infinitesimally thin antenna if the height of the antenna from the ground is not too small. Also, a practical method is suggested for the determination of ground parameters from horizontallambda/2dipole minimum resistance and height measurements. View full abstract»

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  • A technique for organizing large moment calculations for use with iterative solution methods

    Page(s): 1031 - 1033
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    Through a specific choice of evenly spaced basis and testing functions, one can construct a moment matrix formulation wherein significant redundancy is embodied in the matrix. A scheme that exploits this redundancy to effect substantial computer storage reduction in an iterative field solution, such as the conjugate-gradient method is described. The expense incurred is a modest increase in computation time. The redundancy results from translational similarity features of specific classes of geometries and leads to matrix equations that may be interpreted as discrete convolutions. For illustration, the analysis here is carried out on a planar scatterer, but the strategy can be applied to spherical or cylindrical scatterers. View full abstract»

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  • Correction of error in reduced sidelobe synthesis due to mutual coupling

    Page(s): 1025 - 1028
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    Standard Chebyshev and Taylor reduced sidelobe synthesis techniques ignore mutual coupling, and so can lead to pattern errors where the resulting array pattern departs significantly from the desired pattern. Two methods for correcting this error are described and examples of their application to eight-element dipole arrays are presented. One approach uses characteristic modes, while the other method employs a simpler array mode and point matching. The techniques can also be applied to synthesis of nonuniform arrays. View full abstract»

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  • Electromagnetic scattering from a dielectric-coated circular cylinder

    Page(s): 960 - 963
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    The normalized backscattering width of an infinitely long, dielectric coated circular cylinder is obtained via a high frequency ray solution. The ray solution provides a physical picture of the scattering process in terms of a geometrical optics ray and two surface waves. It is shown that the surface wave resonance phenomena in the backscattering fields of the coated cylinder can be predicted in terms of the Regge poles of the coated cylinder. The numerical results for the backscattering widths of the cylinder obtained via the high frequency ray solution show excellent agreement with the eigenfunction results. The trajectories of the Regge poles associated with the coated circular cylinder are also presented. View full abstract»

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  • Scattering from a periodic array of resistive strips

    Page(s): 1009 - 1011
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    The problem of scattering from a resistive strip grating is formulated in the spectral domain. Results of numerical calculations of the reflection coefficient are presented for perfectly conducting strips and strips with resistivities up to750Omega/square. View full abstract»

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  • A theoretical formula for the prediction of cross-polarized signal phase

    Page(s): 997 - 1002
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    An approximate theoretical formula for the prediction of cross-polarized signal phase relative to co-polar signal is presented. In the formula, the phase of cross-polarized signal induced by rain is related to rainfall rate or rain-induced attenuation. The relation is derived by calculating the forward scattering amplitudes of the Pruppacher-Pitter type raindrops at 33 frequencies ranging from 3 to 40 GHz. The dependence of the relation on raindrop-size distribution is also discussed. View full abstract»

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  • Analysis of elliptical and circular microstrip antennas using moment method

    Page(s): 954 - 959
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    A method of calculating the input impedance of either a circular or a slightly ellipitcal microstrip antenna excited by a coaxial probe is presented. Using the reaction integral equation and the exact dyadic Green's function, the finite substrate thickness is taken into account in the formulation. Good agreement with experimental results for an elliptical patch is obtained and a design procedure for a circularly polarized antenna is presented. View full abstract»

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  • Radar target discrimination using the extinction-pulse technique

    Page(s): 929 - 937
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    An aspect independent radar target discrimination scheme based on the natural frequencies of the target is considered. An extinction-pulse waveform upon excitation of a particular conducting target results in the elimination of specified natural modal content of the scattered field. Excitation of a dissimilar target produces a noticeably different late-time response. Construction of appropriate extinction-pulse waveforms is discussed, as well as the effects of random noise on their application to thin cylinder targets. Also presented is experimental verification of this discrimination concept using simplified aircraft models. View full abstract»

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  • Design formulas for an asymmetric coplanar strip folded dipole

    Page(s): 1028 - 1031
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    The planar folded dipole is an appealing choice as a radiating element due to the properties that it can be constructed using printed circuit technology and its input impedance can be adjusted over a wide range of values. The input impedance of this type of antenna depends on three quantities: the impedance of the transmission line mode, the impedance of the dipole mode, and the impedance step-up ratio. The solution to three problems associated with these three quantities is developed and design formulas for a planar folded dipole are presented. View full abstract»

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  • On uniform asymptotic Green's functions for the perfectly conducting cylinder tipped wedge

    Page(s): 1020 - 1025
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    Uniform asymptotic expressions are derived for the Green's functions describing scattering of electric or magnetic type plane waves by a perfectly conducting cylinder tipped wedge (CTW). These expressions are found to agree analytically with heuristic expressions available using the geometrical theory of diffraction (GTD). Numerical comparison of these expressions with results obtained from eigenfunction expansions show good agreement for cylinder diameters >1.5 lambda. View full abstract»

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  • Optimum low sidelobe high crossover multiple beam antennas

    Page(s): 946 - 954
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    Simultaneous multiple beam antennas (MBA's) with low sidelobe high crossover beams are considered. A simplified proof is presented which shows dissipative loss of typically -3 dB must be accepted. The optimum efficiency for the constrained fed MBA is shown to be achieved by placing attenuation in the aperture of a Butler matrix (BM) in accordance with the desired tapered aperture distribution. A combination of aperture attenuation and feed design, including the use of overlapping orthogonal feed distributions, is considered for lens type MBA's. The optimum efficiency is shown to be achieved with relatively simple feeds for a broad class of desired beam shapes. View full abstract»

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  • Gain enhancement methods for printed circuit antennas

    Page(s): 976 - 987
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    Resonance conditions for a substrate-superstrate printed antenna geometry which allow for large antenna gain are presented. Asymptotic formulas for gain, beamwidth, and bandwidth are given, and the bandwidth limitation of the method is discussed. The method is extended to produce narrow patterns about the horizon, and directive patterns at two different angles. View full abstract»

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  • The effect of a finite distance source on an Applebaum array

    Page(s): 1003 - 1008
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    The effect of the finite distance of the signal source on the performance of a far-field steering Applebaum type adaptive array is examined. The output signal-to-noise ratio (SNR) is expressed in terms of 1) the distance between the signal and the array center, 2) the input SNR, 3) the element number and locations, and 4) the signal direction. From that expression a rule of thumb is drawn to determine the distance between the signal source and the array center at which the degradation of the output SNR is 1 dB. That distance is in general much larger than the far-field range of a conventional beam forming array. View full abstract»

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  • Cubic splines as expansion functions for the current distribution of microstrip stub antennas

    Page(s): 1033 - 1036
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    The current distribution on microstrip stub antennas is calculated with the appropriate Green's functions via an integral equation, which is solved with the moment method. As expansion functions for the current cubic spline functions are used. The calculated data are used for the design of a microstrip array with Chebyshev characteristics. View full abstract»

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  • Analysis of transient responses between coupled dipole antennas by using a simple equivalent circuit

    Page(s): 1015 - 1020
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    Transient responses between two dipole antennas were analyzed by using a simple equivalent circuit of a dipole antenna. This equivalent circuit is composed of a lossless transmission line and two shunt resistances representing electrical discontinuities at a feed point and tips of the dipole antenna. A closed-form formula for the induced load voltage in the time domain was derived. Since the damping factor due to radiation from antennas is included in this expression, this formulation gives better results than those given by the conventional transmission-line approximation. Measured time histories support the validity of theoretical results. 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