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Antennas and Propagation, IEEE Transactions on

Issue 9 • Date September 1986

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Displaying Results 1 - 14 of 14
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Radiation by a probe through a substrate

    Page(s): 1080 - 1091
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    Radiation by a probe through a grounded substrate layer is considered. The reaction concept is adopted and the coaxial line aperture effects are taken into account. Image theory is invoked to simplify the evaluation of the involved Sommerfeld type integrals. These integrals are computed through a real axis integration which combines numerical and analytical techniques. An interpolation method is introduced which eliminates repetitive calculation of reaction quantities. The properties of the probe such as input, mutual impedance, radiation pattern and radiation efficiency are examined as functions of substrate parameters such as thickness and dielectric constant. The probe length may be chosen to be smaller than, equal to or greater than the substrate thickness. The effect of substrate transverse magnetic (TM) surface wave modes is analyzed and it is found that at each mode cutoff omnidirectional radiation is obtained in thebar{H}-plane with maximum radiation along the horizon. The effect of small substrate loss on the probe parameters is also considered. View full abstract»

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  • The physical optics fields of an aperture on a perfectly conducting screen in terms of line integrals

    Page(s): 1155 - 1159
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    The physical optics fields due to an aperture on a perfectly conducting screen are expressed in terms of line integrals over the boundary of the aperture. These line-integral representations have the same properties as the ones in terms of surface integrals over the aperture; in particular, they admit arbitrary, source distributions, and are continuous everywhere in the source-free half-space, including the geometric optics shadow boundary. View full abstract»

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  • Reflection and transmission characteristics of a slab with periodically varying surfaces

    Page(s): 1159 - 1163
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    Using a plane wave spectral decomposition of the relevant electromagnetic (EM) fields and the T-matrix solution philosophy, a T-matrix is formulated which completely characterizes the EM response of an infinite material plate bounded by two homogeneous half-spaces, the two interfaces being periodically rough. Individual T-matrices for either of the two periodic bimaterial interfaces are used in this derivation. Using the computed results, the anomalies in the scattering response of the rough slab are explained in terms of reflectionless and transmissionless modes, the Brewster angle, and the conditions for propagation or evanescence of a given plane wave mode. View full abstract»

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  • On the fields in a conical horn having an arbitrary wall impedance

    Page(s): 1092 - 1098
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    The electromagnetic fields propagating up a cone having an arbitrary wall impedance are found using an asymptotic solution. Three special cases are then considered: the smooth-metal wall, the corrugated wall, and the metal wall with a lossy-dielectric lining. The last case, in the form of an absorber-lining is then shown to behave like a corrugated horn since it too provides a highly taperedE-plane andH-plane aperture distribution. Furthermore, it does this over a much larger bandwidth, over 3:1, with negligible gain drop. View full abstract»

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  • A vector space approach to direction finding in a coherent multipath environment

    Page(s): 1069 - 1079
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    The superresolution methods of spatial spectrum estimation heretofore reported are known to break down when arriving signals from different directions are coherent. It is shown here that this deficiency can be overcome by replacing the direction-of-arrival (DOA) search vector ordinarily used with a linear combination of such vectors. Particular attention is here given to extending the multiple signal classification (MUSIC) method to cover such cases. A procedure for determining the proper linear combination is presented so that determination of the separate coherent signal arrival angles involves a multidimensional search in angle only. Such a search is demonstrated for coherent two-ray and three-ray multipath environments. View full abstract»

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  • The design of slot arrays including internal mutual coupling

    Page(s): 1149 - 1154
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    Improved array performance (lower sidelobe levels, a better input match) requires elimination of approximations in earlier design procedures. One important change is to include internal higher order mode coupling. That is done here and is found to cause a simple but significant change in existing design formulas. View full abstract»

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  • Axial mode helical antennas

    Page(s): 1143 - 1148
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    The radiation characteristics of helical antennas operating in the axial mode are evaluated on the basis of the theoretical current distributions and are verified by experimental work. A comparison between monofilar helix and bifilar helix antennas is made, and a helical antenna with a parasitic helix (HAP) is proposed in order to enhance the power gain. It is found that the gain of the HAP in which the parasitic helix is wound from a point diametrically opposite to that of one and one-half turns of the driven helix is about 1 dB higher than that of the monofilar helix. The ratio of the frequency band in which the HAP radiates a circularly polarized wave within an axial ratio of 3 dB is calculated to be 1:1.8. View full abstract»

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  • Effective earth radius for refraction of radio waves at altitudes above 1 km

    Page(s): 1099 - 1105
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    Atmospheric refractivity gradients are responsible for the bending of radio and microwave propagation paths such that the electromagnetic line-of-sight deviates from the geometrical line-of-sight. Such refraction effects must be accounted for when the performance of airborne surveillance radar systems is modeled. For propagation paths within 1 km of the earth's surface, the effective earth radius model is normally valid and commonly used. In the present work, a ray trace method for determination of propagation paths in a semi-empirical, stratified atmosphere is described. Results obtained from the ray trace model are employed to show that the effective earth radius method (EERM) can be used for approximate determinations of grazing angle, ground range and slant range for higher altitude paths. Effective earth radius scale factors are given as functions of transmitter altitude for selected values of surface refractivity. View full abstract»

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  • The electromagnetic edge wave due to a point source of current radiating in the presence of a conducting wedge

    Page(s): 1125 - 1132
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    Cylindrical wave expansions for the dyadic Green's functions for electric and magnetic fields of a point source of electric current radiating in the presence of a perfectly conducting wedge are derived using a scalarization procedure developed by Levine and Schwinger. The forms derived from this procedure involve a sum over angular wavenumbers and a continuous spectral integral which may be expressed either as an integration over a longitudinal or a radial spectral variable. Some relationships between these two representations are discussed. The longitudinal spectrum integral has a pair of branch points as its only singularities and may be evaluated asymptotically along a steepest descent path away from one of the branch points. The resulting asymptotic representation is found to agree with an earlier result obtained by Kouyoumjian and Buyukdura. The edge-guided wave interpretation of the asymptotic field is discussed, both in light of the longitudinal spectral representation and of the physical content of the asymptotic representation. View full abstract»

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  • Ionospheric radio propagation models and predictions--A mini-review

    Page(s): 1163 - 1170
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    The ionosphere affects radio waves that are propagated within and through it. The magnitude of the effects depends upon the structure of the ionosphere and the frequency of the radio wave. Ionospheric models have been developed over the years to aid in predicting the impact of the ionosphere on ionospheric-dependent telecommunication systems. The status of ionospheric modeling and prediction efforts that are geared toward radio wave propagation system assessment is reviewed. View full abstract»

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  • High-frequency multiple diffraction by a flat strip: Higher order asymptotics

    Page(s): 1106 - 1112
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    By including correction terms in inverse powers of the wavenumberk, one may hope to extend the range of applicability of multiple edge diffracted geometrical theory of diffraction (GTD) to lower frequencies, and also to extend thereby the range of validity of the corresponding time domain solutions. The correction can be applied to each of the surface rays in the hierarchy that has been proposed by us recently as a model for multiple interaction between parallel edges separated by a plane surface segment on a two-dimensional perfectly conducting scatterer. The surface rays, which were found to explain the structure of the complex resonances in transient scattering, are excited for each interaction by equivalent line sources, dipole line sources, and their derivatives, with strengths determined from the asymptotic expansion of the edge diffracted field. This procedure is applied in detail toE- andH- polarized plane wave scattering by a perfectly conducting flat strip, up to quadruple diffraction, including consistentO(k^{-2})corrections with respect to the dominant term. The procedure is applied also to generate corrected multiple diffracted individual surface ray fields, which lead to an improved equation for the complex resonances in the "layer" synthesized in the complex frequency plane by a surface ray of a particular order. Inclusion of the low frequency corrections reduces further the already small discrepancy between the ray optically calculated low frequency resonances and those computed numerically by the moment method. View full abstract»

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  • A technique for an array to generate circular polarization with linearly polarized elements

    Page(s): 1113 - 1124
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    A method is presented for generating circularly polarized radiation from an array composed of linearly polarized elements having unique angular and phase arrangements. With this technique the complexity, weight, and RF loss of the array feed can be significantly reduced, especially in a large array. This uniquely formed array has the capability of generating excellent circular polarization (CP) over a relatively wide frequency bandwidth. In addition, the array is capable of scanning its main beam in the principal planes to relatively wide angles from its broadside direction without serious degradation to its CP quality. Another feature of this uniquely arranged array is a reduction in the occurrence of mutual coupling. The discussion in this paper places special emphasis on the microstrip type of radiator, although the technique presented can be adapted to most types of linearly polarized antenna elements. View full abstract»

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  • Optimum optical limited scan antenna

    Page(s): 1133 - 1142
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    An optical limited scan antenna system is considered for applications such as spot coverage of a small portion of the earth from a satellite. The optimum criterion relating aperture efficiency, number of control elements, and angular coverage is revisited briefly. The optical scheme advocated utilizes a bootlace aperture lens, a generalized Luneberg lens focused to the near field, and a small array of active elements. The operation of the system is described first in terms of geometrical optics and elementary diffraction principles. The subarray viewpoint is then developed using simplified diffraction concepts. These results form the basis of a design procedure for the synthesis of high performance limited scan systems. An accurate solution necessary for the analysis of small antennas is developed using a modal decomposition and the wave equation. Numerical computations for a case of practical interest verify the expectation of near optimum performance. 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