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Antennas and Propagation, IEEE Transactions on

Issue 9 • Date September 1987

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Displaying Results 1 - 16 of 16
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Jacobi-Bessel analysis of reflector antennas with elliptical apertures

    Page(s): 1070 - 1074
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    Although many reflector antennas possess circular projected apertures, there are recent satellite and ground antenna applications for which it is desirable to employ reflectors with elliptical apertures. Here a modification of the Jacobi-Bessel expansion is presented for the diffraction analysis of reflectors with elliptical apertures. A comparative study is also performed between this modified Jacobi-Bessel algorithm and the one which uses the Jacobi-Bessel expansion over a circumscribing circular region. Numerical results are presented for offset reflectors with elliptical and circular apertures and the improved convergence properties of the modified algorithm are highlighted. View full abstract»

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  • Two-dimensional beam diffraction by a half-plane and wide slit

    Page(s): 1077 - 1083
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    The far field of a two-dimensional beam resulting from an electric line source at a complex position is described, its half-power beamwidth determined, and its validity as an antenna beam indicated. Farfield diffraction by a half-plane is then determined from an exact uniform solution for an isotropic line source by making the source position complex. The same basic solution and technique are used for beam diffraction by a wide slit, with first-order interaction between the slit edges included. Numerical results for normal incidence illustrate the evolution of the diffraction patterns from those for an omnidirectional source to those for a highly directive beam. Results for plane wave incidence by a slit also come out of this solution. The remarkable simplicity and convenience of this method relative to alternative asymptotic procedures is discussed. View full abstract»

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  • Analysis of the tapered slot antenna

    Page(s): 1058 - 1065
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    A method for calculating the radiation pattern of end-fire tapered slot antennas with or without dielectric substrate is presented. The method involves a two-step procedure: 1) determine the field distribution of a traveling wave along the tapered slot, and 2) compute the radiation from this slot field by using the half-plane Green's function to account for termination effects. Acceptable estimates of the slot field usually can be obtained from a stepped approximation to the tapered geometry. The method has been verified by comparisons to measured patterns for various dielectric substrates and antenna dimensions. However, the effect of lateral truncation has not yet been successfully modeled. Experimental patterns showing this effect are presented. View full abstract»

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  • A note on the relationship between the conjugate gradient method and polynomials orthogonal over the spectrum of a linear operator

    Page(s): 1089 - 1091
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    The relationship between the conjugate gradient method and polynomials orthogonal over the spectrum of a linear operator is discussed. It is shown that as a byproduct of the conjugate gradient construction, two sets of polynomials are generated which are orthogonal with respect to a positive real measure over the spectrum of a self-adjoint operator. The roots of these polynomials can, under certain circumstances, be used to track the eigenvalues or singular values of the relevant operator. View full abstract»

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  • Wire grid modeling of surfaces

    Page(s): 1045 - 1048
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    When a surface is numerically modeled with a wire grid, results are sensitive to the wire diameter. It is shown that the best accuracy is obtained when the wire satisfies the "same surface area" rule of thumb, for the canonical problem of scattering (or radiation) from an infinite circular cylinder. It is important to note that wires that are too thick are just as bad as wires that are too thin. It is also shown that the boundary value match between wires is not a reliable check on the validity of farfield results. Finally, data are given on the effect of wire spacing. Results are obtained from exact solutions of both the true problem and the wire grid model, thus isolating the effects of wire grid modeling per se. View full abstract»

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  • Complex rays for radiation from discretized aperture distributions

    Page(s): 1031 - 1044
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    Many electromagnetic propagation problems require tracking of fields radiated by large actual or induced aperture distributions through complicated environments before reaching the observer. For a systematic approach to this problem area, it is desirable to represent the aperture field in terms of basis functions which are physically informative and well adapted to traversing the propagation path. At high frequencies, Ganssian beam-type basis functions meet these requirements. After referring to a rigorous aperture discretization scheme, various quasi-Gaussian basis field profiles are examined, with a special view toward expressing their radiation properties in terms of complex rays; complex ray tracing is promising for field tracking in complicated surroundings. By comparing reference solutions from numerical integration of radiation integrals with complex ray asymptotics, it is concluded that the true Gaussian has the most favorable attributes for matching aperture discretization, propagation requirements, and complex ray tracing. Thus, the analysis here may point the way toward systematic treatment of the above-noted class of propagation problems. View full abstract»

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  • Steerable ELF/VLF radiation produced by an array of ionospheric dipoles generated from HF heating

    Page(s): 1022 - 1030
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    A very low frequency (VLF) or extremely low frequency (ELF) dipole source has been created within the lower ionosphere by modulating the atmospheric dynamo currents with a ground-based high power HF source from the Arecibo Observatory. The authors and their colleagues have demonstrated that ELF or VLF generated in this way and injected into the earth-ionosphere waveguide could be received a few thousand kilometers away. The injection properties due to an array of ionospheric dipoles as a function of array geometry and element currents that will allow steerable ELF/VLF radiation within the earth-ionosphere waveguide are investigated theoretically. The ionospheric array factors for a linear and a planar array of Hertzian dipole sources are developed and their properties examined. The principle of pattern multiplication is then applied to include the effect of the ionospheric array element. This provides a means for predicting the field strengths at a remote receiving site due to a steerable linear or planar array of ionospheric sources generated by high power HF periodic plasma heating. View full abstract»

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  • An improved thinning method for density tapering of planar array antennas

    Page(s): 1066 - 1070
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    A thinning method is presented to realize the desired aperture distribution in a planar array antenna with elements fixed on an array lattice. In this method elements to be excited are determined by quantizing cumulative weights which are calculated from the desired aperture distribution. At first, this method is applied to density tapering on orthogonal axes of a planar array. Radiation patterns of the planar array determined by this method are compared with those by the desired amplitude distribution, and the results show good coincidence. Next, this method is extended to density tapering on four axes, that is, orthogonal and diagonal axes of a planar array. Moreover, this method is applied to density tapering with multi-amplitude level elements in order to enhance directive gain of thinned array. Lastly, a rectangular planar array was fabricated, and its radiation patterns were measured. Measured results were in good coincidence with calculated ones, and the usefulness of this method was verified. View full abstract»

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  • The strip-loaded hybrid-mode feed horn

    Page(s): 1086 - 1089
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    A novel typed of hybrid-mode feed horn is presented. It comprises a hollow conical dielectric waveguide whose outer surface is metallized, and whose inner surface is coated with circumferentially oriented conducting strips. It may be designed to have mimimal cross polarization at two arbitrarily separated frequencies, as for a dual depth corrugated horn. Compared to the corrugated horn, it has the potential of lower weight and lower price. Small horns will have some cross polarization due to undesired radiation from the fields transmitted within the dielectric. View full abstract»

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  • The hat feed: A dual-mode rear-radiating waveguide antenna having low cross polarization

    Page(s): 1010 - 1016
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    The hat antenna is a new self-supported rear-radiating waveguide feed, related to existing feeds known as splashplate and waveguide cup antennas. An analytical model for the radiation pattern of the hat antenna, a model which includes the axial waveguide itself is presented. This model shows that by exciting the feed with two modes it is possible to use the waveguide constructively as one of the dominant radiating parts of the feed instead of having to live with it as an undesirable blockage effect. Thereby aperture efficiencies up to 81 percent and cross-polar sidelobes down to -30 dB are available. The results are confirmed by measurements on a practical model, but the bandwidth is narrow. View full abstract»

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  • Sidelobe suppression of planar array antennas by the multistage decision method

    Page(s): 1017 - 1021
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    The sidelobe level of a planar array antenna with equal amplitude excitation can be suppressed by element thinning. The method of element thinning employed here is a kind of multistage decision procedure or steepest descent approach. Although this method gives the local optimum results, the reduced sidelobe level is assured to be within the obtained level over the whole radiation region. The sidelobe level, for example, can be suppressed -29.7 dB where the array contains 3120 elements arranged within a circular aperture capable of 5815 elements if fully filled. The computation time is also discussed, and it is shown that the computation time decreases drastically by the use of the design method. View full abstract»

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  • Analytic expressions for a function occurring in diffraction theory

    Page(s): 1083 - 1086
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    Simple expressions are derived for the Maliuzhinets (integral) function which arises in connection with diffraction by an impedance wedge. The given expressions allow the computation of the function with remarkable accuracy throughout the entire complex plane for any exterior wedge angle. View full abstract»

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  • Optimal design of multiply fed dipole antennas

    Page(s): 1001 - 1009
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    The gain of a mulitply fed dipole antenna of lengthL, small radiusaand arbitrary locations of feed voltages along the antenna is computed using the well-known moment method. An optimization routine is then employed to study the possibility of maximizing the gain in a specified angular direction and minimizing it at other directions for any given number of excitations and antenna length in order to determine the optimum complex values and location of each source. The results are presented in tables and graphs for a wide range of antenna length and number of feeds. It is shown that both the gain and beamwidth are improved by this technique at the expense of appearance of new sidelobes and requirement to design a more complicated feed network. The Fourier series expansion method is extended in order to determine the gain of a multiply fed wire antenna, and the results for the radiation pattern show good agreement with those based on the moment method. View full abstract»

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  • The backscattered field of a thin wire loop for H-polarization

    Page(s): 1049 - 1057
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    For a thin wire loop illuminated by a plane electromagnetic wave, the backscattered field is determined when the incident magnetic vector is parallel to the plane of the loop. The complete second-order geometrical theory of diffraction (GTD) solution is obtained and found to be in excellent agreement with numerical data at angles close to normal incidence on the loop. At wide angles, however, the data exhibit a significant lobe that is not predicted by GTD. Analysis of the data shows that the lobe is due to currents circulating around the loop and the properties of these currents are deduced. Using a simple model for the current, the corresponding contribution to the backscattered field is determined. When this is added to the GTD solution, the resulting expression for the backscattered field is in good agreement with the numerical data for all angles of incidence and all loop diameters greater than a wavelength. View full abstract»

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  • Resonant electromagnetic field coupled into a lossy cavity through a slot aperture

    Page(s): 1074 - 1077
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    A new approach is proposed for determining the electromagnetic fields coupled from an incident plane wave into a lossy conducting cavity through a slot aperture under resonant conditions. Use is made of the duality between a slot and a conducting strip and of the equivalence between a strip and a wire. Simplified formulas are derived that are explicit and flexible. Determination of resonant fields inside a cavity is reduced to simple calculations. Numerical examples are given. 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