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Antennas and Propagation, IEEE Transactions on

Issue 6 • Date November 1983

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Displaying Results 1 - 25 of 32
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
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  • [Back cover]

    Page(s): c4
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    Freely Available from IEEE
  • Formulation for wire radiators on bodies of translation with and without end caps

    Page(s): 853 - 862
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    A formulation, based on the method of moments (MM), is presented for active and passive wire radiators attached to, or near, a broad class of bodies and surfaces, including open or closed cylinders of arbitrary cross section as well as finite flat or curved panels. The development expands the utility of the MM theory for various antenna problems. The analysis incorporates a special junction basis set for the antenna attachment points. Total domain and piecewise continuous expansion functions are used on the surfaces. The formulation is primarily intended for prediction of radiation patterns of wire antennas (such as monopoles and loops) on asymmetric bodies of translation, open or closed (capped). The present method has shown satisfactory agreement with published data in the prediction of antenna input impedances as well. View full abstract»

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  • On the eigenfunction expansion of electromagnetic dyadic Green's functions

    Page(s): 837 - 846
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    A relatively simple approach is described for developing the complete eigenfunction expansion of time-harmonic electric (bar{E}) and magnetic (bar{H}) fields within exterior or interior regions containing an arbitrarily oriented electric current point source. In particular, these results yield directly the complete eigenfunction expansion of the electric and magnetic dyadic Green's functionsbarbar{G}_{e}andbarbar{G}_{m}that are associated withbar{E}andbar{H}, respectively. This expansion ofbarbar{G}_{e}andbarbar{G}_{m}contains only the solenoidal type eigenfunctions. In addition, the expansion ofbarbar{G}_{e}also contains an explicit dyadic delta function term which is required for making that expansion complete at the source point. The explicit dyadic delta function term inbarbar{G}_{e}is found readily from a simple condition governing the behavior of the eigenfunction expansion at the source point, provided one views that condition in the light of distribution theory. These general expressions for the eigenfunction expansion ofbarbar{G}_{e}andbarbar{G}_{m}reduce properly to those obtained previously for special geometries by Tai. View full abstract»

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  • Rectangular microstrip patch antennas with infinite and finite ground plane dimensions

    Page(s): 978 - 984
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    The rectangular microstrip patch antenna has been extensively analyzed with regard to its input impedance and resonant frequency, both for infinite and finite ground plane dimensions. For infinite ground planes existing formulas have been compared and improved parameters presented. The influence from the side current radiation has been discussed as well. For finite ground plane dimensions the contribution from the ground plane edge diffraction has been accounted for in an equivalent radiation conductance and an equivalent diffraction susceptance. Formulas for these parameters have been developed on the basis of different theories. They are valid under the condition that only one of the ground plane dimensions are finite at the same time. Experimental investigations are carried out to test the accuracy of the developed formulas, showing good accuracy under the given conditions. View full abstract»

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  • A comparison of methods for randomizing phase quantization errors in phased arrays

    Page(s): 821 - 828
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    Beamsteering for phased arrays normally employs electronically switchable digital phase shifters. These can only approximate to the desired phase distribution across the array, and if a straightforward rounding off is used, a periodic phase error arises which causes a pointing deviation of the main beam and introduces a parasitic sidelobe. Various methods have been given in the literature for randomizing the phase errors to reduce these problems. Here a general formula is derived to evaluate the parasitic sidelobe level for different methods. The various methods are compared with reference to 1) the parasitic sidelobe level, 2) the variances of the field pattern and the pointing direction, 3) gain reduction, and 4) any extra array hardware requirements and beamsteering unit resources. View full abstract»

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  • An offset dual-reflector antenna shaped from near-field measurements of the feed horn: Theoretical calculations and measurements

    Page(s): 973 - 977
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    A synthesizing procedure for shaping dual-reflector offset antennas is described. The synthesis is based on geometrical optics and near-field measurements of amplitude and phase from the feed element. The procedure preserves good symmetry in mapping from feed to aperture which results in minimal distortions of the electrical characteristics of the antenna. A 1.8 m antenna has been manufactured and measured at 12 GHz. The radiation pattern is characterized by low sidelobes and cross polarization introduced by the offset geometry below -50 dB. View full abstract»

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  • Natural frequencies and modes of finite open circular cylinders

    Page(s): 910 - 917
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    The natural frequencies and natural modes of open circular cylinders of given aspect ratios are calculated by means of a Galerkin procedure involving entire domain bases. The results are validated by comparison with other calculations of natural frequencies and modes for cylinders and time response current for wires. The usefulness of a previously proposed method based on perturbation theory is examined in this context. View full abstract»

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  • Efficient computation of the far field of parabolic reflectors by pseudo-sampling algorithm

    Page(s): 931 - 937
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    The newly developed pseudo-sampling representation is applied for computing the far field of an offset parabolic reflector with a cluster feed illumination. A new comb-type fast Fourier transform (FFT) algorithm is used in a computer program. Both precision and computational time are analyzed, demonstrating the excellent performance of the method. View full abstract»

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  • A new technique for reducing radar response to signals entering antenna sidelobes

    Page(s): 993 - 996
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    A new technique for reducing a radar's response to undesired signals entering a radar's sidelobes is described and analyzed theoretically. This technique involves moving a phased array antenna's phase center to Doppler shift sidelobe signals out of the radar receiver's passband. View full abstract»

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  • Narrow multibeam satellite ground station antenna employing a linear array with a geosynchronous arc coverage of 60°, part II: Antenna design

    Page(s): 966 - 972
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    A dually polarized narrow (< 0.5deg) beam antenna which provides a geosynchronous arc coverage of60degis proposed and analyzed. To track the geosynchronous arc accurately, the properly oriented antenna produces a conically scanned beam by means of a linear array of feed horns with bias cut apertures illuminating a pair of parabolic cylinder reflectors in an imaging arrangement. This design, with reduced size array and singly carved reflectors, is relatively simple to construct. Calculations for a0.35degbeamwidthKuband earth station antenna show a0.05degpointing accuracy with scan loss due to aberrations less than 1 dB and little pattern degradation throughout the scan region. For multiple beam capability, a Rotman lens is proposed and analyzed as a means of exciting the feed array. It allows communication with multiple satellites spaced as close as1deg. View full abstract»

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  • The effects of subreflector diffraction on the aperture efficiency of a conventional Cassegrain antenna--An analytical approach

    Page(s): 903 - 909
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    An asymptotic theory is presented with which the reduction in aperture efficiency caused by diffraction from a subreflector edge can be calculated for any dual-reflector system. The theory is applied to conventional Cassegrain antennas, for which approximate analytical effieiency formulas are derived. These formulas show that subreflector diffraction may represent a significant efficiency loss even for subreflector diameters as large as 20 wavelengths. The formulas are used to obtain an optimum subreflector size which represents the best trade-off between losses due to subreflector diffraction and geometrical shadowing. View full abstract»

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  • Data analysis for dual-polarized communication link experiments

    Page(s): 989 - 992
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    Performance of dual-polarized radio links operating in the microwave and millimeter wave regions is affected by the propagation medium. The attenuation (A) and cross-polarization discrimination (XPD) are used to quantify the medium effects. Of particular importance is the XPD versusArelationship. Three ways of displaying XPD versusAdata are examined: mean, median, and equiprobable. It is shown that mean and medium are essentially identical measures, whereas equiprobable is sensitive to several error sources and is especially sensitive to ice depolarization. It is concluded that XPD versusAdata sets using mean and median can be safely compared, but equiprobable results must be treated with caution. View full abstract»

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  • On the usefulness of reciprocity in approximate scattering analyses

    Page(s): 992 - 993
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    The use of reciprocity in estimating the accuracy of approximate scattering analyses is discussed. The physical optics and image induction approximations, valid for large smooth body scattering, are combined to demonstrate that approximate solutions satisfying reciprocity may not be any more accurate than nonreciprocal ones. The purpose of this communication is to point out that while it is certainly better, in general, to deal with approximate solutions which are reciprocal, it is not always possible to relate reciprocity and accuracy. View full abstract»

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  • Rigorous asymptotic analysis of transmission through a curved dielectric slab

    Page(s): 863 - 870
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    A circular cylindrical dielectric layer is an idealized but rigorously analyzable model for radome covers. With a line source located on the concave side, an exact integral formulation is derived for the field transmitted to the convex side. Alternative representations are developed therefrom in terms of discrete guided modes and continuous spectra, and of ray integrals which, asymptotically at high frequencies, yield geometric optical fields that experience multiple internal reflections between the layer boundaries and also multiple reflections on the concave side. It is then shown that the higher order multiple reflected contributions can be expressed collectively as a ray field with a weighted transmission coefficient that is equivalent to the plane wave transmission coefficient for a plane parallel layer but includes a simple curvature correction. When source and observer are close to the inner and outer layer boundaries, respectively, and are also separated by a large angular interval, guided mode effects may have to be included as well. The result is a general and novel representation of the transmitted field in terms of a certain number of ordinary multiple reflected geometric optical ray fields, a single "collective" ray field, which includes in a composite manner all of the remaining internal reflections, and, possibly, the guided modes along the layer. View full abstract»

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  • Yearly variations of rain-rate statistics at Wallops Island and their impact on modeled slant path attenuation distributions

    Page(s): 918 - 921
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    Rain gauge measurements at Wallops Island, VA over a five-year period have been reduced and cumulative rain-date distributions have been determined for yearly, successively combined years, and overall average cases. Yearly variations of the predicted slant path attenuation statistics for two International Radio Consultative Committee (CCIR) models (referred to as modified method I and method II) and the global model at 28.56 GHz were calculated using the yearly measured rain rates at Wallops Island. This frequency was selected as it coincided with the beacon frequency of the COMSTAR geostationary satellite which was also simultaneously monitored at Wallops Island for a period of three years enabling a comparison with the measured rain-fade statistics. The year to year variations of the predicted fades as well as the percent deviations relative to the five-year average case were examined. View full abstract»

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  • Characterization of multipath parameters for line-of-sight microwave propagation

    Page(s): 938 - 948
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    Ray equations are derived for microwave multipath propagation in a two-layer atmosphere, and the connection between the different solutions is demonstrated by numerical examples. Analytical expressions are developed to characterize the condition for multiple rays, the variation in angle-of-arrival (AOA), and the delay spread. The results suggest that more than three rays will be rare in practice and that the three-ray model (obtained from the zero-order rays defined in the paper) may provide a good representation of selective fading on microwave links. View full abstract»

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  • The wave antenna for transmission and reception

    Page(s): 956 - 965
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    The traveling-wave horizontal-wire antenna over the earth is analyzed in its original form with vertical ground connections (the Beverage antenna) and with these replaced by horizontal terminations. For transmission, the electromagnetic field of an antenna with optimum length is determined, both along the surface of the earth in air and in the earth, in an accurate but simple form that takes full account of the proximity of the earth (lake, sea) on the distribution of current. For reception, the induced currents in the antenna and in the load are determined for a field incident along the surface of the earth. The two types of termination are compared and their contributions shown to be small when the horizontal wire has a length near the optimum. View full abstract»

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  • The bilocal approximation for the electric field in strong fluctuation theory

    Page(s): 985 - 986
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    Equations are derived for the electric field in a medium with strong random fluctuations in its dielectric constant. Both the mean electric field and the field fluctuations from its mean level are treated. View full abstract»

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  • Optimal polarizations of simple compound targets

    Page(s): 996 - 999
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    The optimal polarization properties of simple extended targets are investigated for the purpose of assessing the usefulness of polarization concepts to target classification. It is found that for large targets with unresolved scattering centers, the polarization null and maximum loci as functions of aspect are usually very complex. Except for certain special cases, this phenomenon indicates that narrow-band polarimetry is not generally useful for target classification. View full abstract»

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  • Analysis and optimized design of single feed circularly polarized microstrip antennas

    Page(s): 949 - 955
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    Analysis and optimized designs are presented of three types of single feed circularly polarized microstrip antennas, namely, a diagonal fed nearly square, a truncated-corners square and a square with a diagonal slot. The Green's function approach and the desegmentation methods are used. The resonant frequencies are calculated for two orthogonal modes which together yield circular polarization. Optimum feed locations are determined for the best impedance match to a50 Omegacoaxial feed line. Axial-ratio bandwidths, voltage standing-wave ratio (VSWR) bandwidths and radiation patterns are evaluated and verified experimentally. View full abstract»

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  • Sidelobe reduction of random arrays by element position and frequency diversity

    Page(s): 922 - 930
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    The high sidelobes of random, thinned arrays can be reduced through the use of diversity techniques. Element position diversity and frequency diversity are considered in this paper. Image artifacts due to the high sidelobes change their locations from image to image when the element positions are altered or the operating frequency is changed. Superimposing or averaging images tends to build up stable, correct portions of an image while reducing, by smoothing, the image artifacts. In principle, all the sidelobe crests can be reduced to the average background level and all the troughs in the side radiation pattern will rise to this level. The theory, supported by simulation experiments, indicates that dual position diversity reduces the sidelobe level by 2 to 2 1/2 dB, depending upon array size. Higher order position diversity reduces the sidelobe level several dB further. Under frequency diversity it is found that whenQ, the reciprocal of the fractional bandwidth, is less than the array sizeL/lambda(measured in units of wavelength), the peak sidelobe power level is approximatelyN^{-1}lnQ, whereNis the number of array elements. For larger values ofQ, the level asymptotes approximately toN^{-1}ln(L/lambda). View full abstract»

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  • Polarization matching of wide angle conically scanned phased array beams

    Page(s): 986 - 989
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    Multisatellite communication may require coverage of a segment of the geosynchronous arc as large as60deg. A properly oriented ground station antenna can cover the above segment by means of a beam whose axis traces a conical surface (i.e., conically scanned beam). The antenna consists of two linear arrays feeding an imaging reflector arrangement through a polarization diplexer. This diplexer separates the incoming wave into two orthogonal polarizations without loss. In general, the polarization of the wave reflected by the diplexer does not remain the same as that corresponding to the feed array as the beam is scanned (polarization mismatch). This mismatch can cause an appreciable degradation of the antenna gain when the feed array is scanned in certain directions. For example, a ground station located at Seattle, WA could experience 3.6 dB reduction in gain due to polarization mismatch when the antenna beam is scanned along a60degsegment of the geosynchronous satellite arc. The above polarization mismatch loss can be substantially reduced by the use of two properly inclined polarization rotators. These devices are sufficiently broadband to cover the entire 12/14 GHz satellite communication band. Design formulas for the inclination angle between the polarization rotators are presented. Applying these formulas we have reduced the above-mentioned polarization mismatch loss to less than 0.01 dB. 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