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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]

    Publication Year: 1983 , Page(s): 0
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  • Correction to "Radiation cones from feed-support struts of symmetric paraboloidal antennas"

    Publication Year: 1983 , Page(s): 1003
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  • Correction to "Tropospheric absorption and dispersion of millimeter and submillimeter waves"

    Publication Year: 1983 , Page(s): 1004
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  • [Back cover]

    Publication Year: 1983 , Page(s): c4
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  • A comparative study of microwave signal characteristics observed over two line-of-sight links

    Publication Year: 1983 , Page(s): 999 - 1002
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    A comparative study of microwave signal characteristics has been carried out over two line-of-sight (LOS) paths at 6.7 and 6.28 GHz situated in the eastern coastal region of India. The study reveals the effect of urban climate on microwave propagation resulting in wide variation of signal fluctuations at the same frequency, over two links in the same region. The signal amplitude fading is 4 to 5 dB for DumDum-Andul (6.7 GHz) line-of-sight path, while it is 1 to 2 dB over the Calcutta-Amdanga (6.28 GHz) line-of-sight path. View full abstract»

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  • On the usefulness of reciprocity in approximate scattering analyses

    Publication Year: 1983 , Page(s): 992 - 993
    Cited by:  Papers (3)
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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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  • Narrow multibeam satellite ground station antenna employing a linear array with a geosynchronous arc coverage of 60°, part II: Antenna design

    Publication Year: 1983 , Page(s): 966 - 972
    Cited by:  Patents (1)
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    A dually polarized narrow ( < 0.5\deg ) beam antenna which provides a geosynchronous arc coverage of 60\deg is 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 a 0.35\deg beamwidth Ku band earth station antenna show a 0.05\deg pointing 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 as 1\deg . View full abstract»

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  • Scattering from finite bodies of translation: Plates, curved surfaces, and noncircular cylinders

    Publication Year: 1983 , Page(s): 847 - 852
    Cited by:  Papers (13)
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    Electromagnetic scattering from finite, conducting bodies of translation (BOT) is examined using a formulation based on the electric field integral equation (EFIE) and solved by the method of moments (MM). The present approach provides a systematic, unified treatment for a wide class of finite, thin scatterers at all angles of illumination and polarization. Both concave and convex surfaces are considered. An entire-domain Galerkin expansion along one dimension of the body and a piecewise continuous one along the other are used to represent the unknown current variations. The scattering cross sections, obtained with this formulation, are compared with published results using more specialized methods and further confirmed by experimental measurements. View full abstract»

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

    Publication Year: 1983 , Page(s): 938 - 948
    Cited by:  Papers (6)
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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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  • Optimal polarizations of simple compound targets

    Publication Year: 1983 , Page(s): 996 - 999
    Cited by:  Papers (9)
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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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  • Yearly variations of rain-rate statistics at Wallops Island and their impact on modeled slant path attenuation distributions

    Publication Year: 1983 , Page(s): 918 - 921
    Cited by:  Papers (3)
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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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  • On the eigenfunction expansion of electromagnetic dyadic Green's functions

    Publication Year: 1983 , Page(s): 837 - 846
    Cited by:  Papers (44)
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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 functions \bar{\bar{G}}_{e} and \bar{\bar{G}}_{m} that are associated with \bar{E} and \bar{H} , respectively. This expansion of \bar{\bar{G}}_{e} and \bar{\bar{G}}_{m} contains only the solenoidal type eigenfunctions. In addition, the expansion of \bar{\bar{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 in \bar{\bar{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 of \bar{\bar{G}}_{e} and \bar{\bar{G}}_{m} reduce properly to those obtained previously for special geometries by Tai. View full abstract»

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

    Publication Year: 1983 , Page(s): 985 - 986
    Cited by:  Papers (10)
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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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  • Formulation for wire radiators on bodies of translation with and without end caps

    Publication Year: 1983 , Page(s): 853 - 862
    Cited by:  Papers (5)
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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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  • A new technique for reducing radar response to signals entering antenna sidelobes

    Publication Year: 1983 , Page(s): 993 - 996
    Cited by:  Papers (5)
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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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  • Polarization matching of wide angle conically scanned phased array beams

    Publication Year: 1983 , Page(s): 986 - 989
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    Multisatellite communication may require coverage of a segment of the geosynchronous arc as large as 60\deg . 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 a 60\deg segment 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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  • An offset dual-reflector antenna shaped from near-field measurements of the feed horn: Theoretical calculations and measurements

    Publication Year: 1983 , Page(s): 973 - 977
    Cited by:  Papers (20)
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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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  • Ray analysis of two-dimensional radomes

    Publication Year: 1983 , Page(s): 870 - 884
    Cited by:  Papers (18)  |  Patents (1)
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    The fields transmitted from a line source through a two-dimensional curved dielectric layer of variable thickness are constructed by geometric-optical ray tracing that accounts for multiple reflections on the concave side, where the source is located, as well as for reflections between the layer boundaries. Moreover, internally trapped rays, excited by evanescent tunneling, are included when source and observer are near the layer boundaries but laterally displaced along it. By applying Poisson summation to the ray series, the multiple reflected contributions, for weakly tapered configurations, can be summed to yield trapped and leaky local modes guided along the layer, as well as a "collective" ray field that incorporates a plane layer transmission coefficient, with curvature and slope corrections, instead of the conventional coefficients for individual boundaries. Detailed calculations are performed for the special cases of a circularly curved layer of constant thickness and a tapered layer with nonparallel plane boundaries. For the former, the various ray-optically derived solutions agree completely with those obtained from a rigorous analysis. For the latter nonseparable configuration, no rigorous solution is available. With direct summation of conventional ray fields taken as a reference, extensive numerical results demonstrate the economies effected by the collective ray formulation and the importance of including the curvature or slope corrections in the equivalent slab transmission coefficients. View full abstract»

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

    Publication Year: 1983 , Page(s): 949 - 955
    Cited by:  Papers (119)  |  Patents (6)
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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 a 50 \Omega coaxial 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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  • A comparison of methods for randomizing phase quantization errors in phased arrays

    Publication Year: 1983 , Page(s): 821 - 828
    Cited by:  Papers (21)  |  Patents (1)
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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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  • Data analysis for dual-polarized communication link experiments

    Publication Year: 1983 , Page(s): 989 - 992
    Cited by:  Papers (1)
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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 versus A relationship. Three ways of displaying XPD versus A data 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 versus A data sets using mean and median can be safely compared, but equiprobable results must be treated with caution. View full abstract»

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  • Reply to "Comments on `Unified theory of near-field analysis and measurement́"

    Publication Year: 1983 , Page(s): 1002 - 1003
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    Wacker comments on Berger's question, (see ibid., vol. AP-30, no. 6, p. 1268, 1982), concerning the usefulness of the special conformal transformations of the conformal group for near-field electromagnetic scanning problems. Wacker believes the special transformations may be useful in nonhomogeneous media and/or nonlinear systems View full abstract»

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  • Reflection from a periodically perforated plane using a subsectional current approximation

    Publication Year: 1983 , Page(s): 829 - 836
    Cited by:  Papers (34)
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    The scattering from a zero thickness plane having finite sheet resistance and perforated periodically with apertures is calculated for arbitrary plane wave illumination. The surface current density within the unit cell is approximated by a finite number of current elements having rooftop spatial dependence. The transverse electric field is expressed in terms of the current, and the electric field boundary condition is satisfied in an integral sense over the conductor, generating a finite dimension matrix equation whose solution is the current density. Since the conductor shape is defined through the locations of subsectional current elements, arbitrary shaped apertures can be handled. The reflection coefficient and current distribution are calculated for square apertures in both perfectly conducting and resistive sheets, and for cross-shaped apertures. Finite resistivity is shown to cause the magnitude of the transverse magnetic (TM) reflection coefficient to decrease more rapidly and its phase to decrease less rapidly, as the angle of incidence approaches glancing. Through detailed plots of the current density, the current crowding around the apertures is made clearly evident. View full abstract»

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

    Publication Year: 1983 , Page(s): 922 - 930
    Cited by:  Papers (5)
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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 when Q , the reciprocal of the fractional bandwidth, is less than the array size L/\lambda (measured in units of wavelength), the peak sidelobe power level is approximately N^{-1}\ln Q , where N is the number of array elements. For larger values of Q , the level asymptotes approximately to N^{-1}\ln(L/\lambda ) . View full abstract»

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  • Electromagnetic scattering from perfectly conducting rough surfaces in the resonance region

    Publication Year: 1983 , Page(s): 885 - 895
    Cited by:  Papers (5)
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    A rigorous integral formalism for the problem of scattering of electromagnetic radiation from a cylindrical, perfectly conducting rough surface of arbitrary shape is introduced. The computer code obtained from this theory enables us to show that the range over which the incident field affects the surface current density is of the order of the radiation wavelength. This phenomenon is explained using a new approximate theory, able to express the scattered field in the form of an integral whose integrand is known in closed form. Using the rigorous computer code, we show that the new approximate theory is better than the Kirchhoff approximation in the resonance region. Finally, it is shown that the phenomenon of short interaction range of the incident field permits the rigorous computation of the field scattered from a rough surface of arbitrary width. 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