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Antennas and Propagation, IEEE Transactions on

Issue 8 • Date Aug. 2001

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Displaying Results 1 - 20 of 20
  • Comments on "Validity of the measured equation of invariance" [with reply]

    Publication Year: 2001 , Page(s): 1242 - 1243
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (25 KB)  

    For original article by Yun-Sheng Xu et al. see ibid., vol.47, no.12, p.1814-19 (Dec. 1999). View full abstract»

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  • Author's reply

    Publication Year: 2001 , Page(s): 1242 - 1243
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (39 KB) |  | HTML iconHTML  

    First Page of the Article
    View full abstract»

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  • Call for papers

    Publication Year: 2001 , Page(s): 1243
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    Freely Available from IEEE
  • Multipath propagation study combining terrain diffraction and reflection

    Publication Year: 2001 , Page(s): 1204 - 1209
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB) |  | HTML iconHTML  

    A multiple knife-edge attenuation formula is derived by combining diffraction and ground reflection. As an example, the attenuation by double knife edges with ground reflection is derived in detail and the attenuation by a flat-topped obstacle with slanted sides is also calculated. The attenuated fields are proven to be the combination of eight field components, and the number of multipath reflection rays can be reduced based on the location of the main reflection point defined by path parameters. The formulas have clear physical meanings and can be used for field strength prediction in both mobile and fixed communications View full abstract»

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  • Effect of wet antenna attenuation on propagation data statistics

    Publication Year: 2001 , Page(s): 1183 - 1191
    Cited by:  Papers (11)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    Wet antenna attenuation during rain events is examined through carrying out simulated rain experiments. These were conducted on the receiving antenna of the Vancouver ACTS terminal under conditions similar to those prevalent when the propagation data on the Vancouver ACTS path were collected. The findings from these experiments are used to estimate path attenuation data for that path by adjusting the collected data for wet antenna attenuation via two different models. Primary and secondary statistics of the path attenuation data derived from the models at the two ACTS frequencies, nominally 20 and 27 GHz, are computed and compared with those for the unadjusted, measured data. This was done for the four-year period of December 1993 to November 1997 and includes average and worst month cumulative distribution functions and fade-duration and fade-slope statistics. While the two models yield similar statistics, these differ significantly from those derived from the unadjusted data. The comparison of the two sets of statistics suggests that the use of those of the unadjusted data to represent path attenuation would grossly exaggerate the requirements for system design View full abstract»

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  • Empirical characterization of wideband indoor radio channel at 5.3 GHz

    Publication Year: 2001 , Page(s): 1192 - 1203
    Cited by:  Papers (57)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB) |  | HTML iconHTML  

    Characteristics of wideband indoor radio channel at 5.3 GHz were defined based on an extensive measurement campaign using a wideband channel sounder with 19 ns delay resolution. Pathloss exponents were 1.3-1.5 in LOS and 2.9-4.8 in non-line of sight (NLOS). Large difference in NLOS exponents was due to different dominating propagation mechanisms in different types of building structures. The delay dispersion was characterized by cumulative distribution functions (CDF) of the RMS delay spreads, the values for CDF=0.9 varied from 20 to 180 ns in different setups in an office building and large hall environments. The correlation functions of the radio channel in spatial and frequency domains were extracted. Small scale models for five typical indoor scenarios were developed using tapped delay lines View full abstract»

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  • Quasi-static effective permittivity of periodic composites containing complex shaped dielectric particles

    Publication Year: 2001 , Page(s): 1174 - 1182
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB) |  | HTML iconHTML  

    A methodology is described for computing the quasi-static effective permittivity of a two-dimensional (2-D) or three-dimensional (3-D) lattice of dielectric particles. The particles in this composite material may have complicated shapes. This methodology uses a moment method based technique to determine the electric dipole moments of the particles immersed in a uniform electric field. The effective permittivity is then obtained using an appropriate macroscopic model. With this methodology, the mutual interaction between particles can be accounted for accurately. The computed effective permittivity for round cylinders and spheres suspended in a host are compared with our previous T-matrix method results as well as the Maxwell Garnett (MG) formula predictions. Three additional examples involving square (2-D), rounded square (2-D), and spherical (3-D) dielectric inclusions are also given, illustrating the shape effects on the computation of the quasi-static effective permittivity. While the square- and cubic-shaped particles can possess great mutual interaction, surprisingly their effective permittivity is well predicted for all volume fractions by the simple MG formula in both 2-D and 3-D problems View full abstract»

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  • The input impedance and the antenna gain of the spherical helical antenna

    Publication Year: 2001 , Page(s): 1235 - 1237
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (124 KB) |  | HTML iconHTML  

    The input impedance and the antenna gain of the spherical helical antenna are obtained theoretically and experimentally. Results indicate the better performance of the 3-turn antenna over the 7-turn one in terms of the impedance bandwidth and the stability of the antenna gain. The theoretical current distribution is also obtained and its salient characteristics are discussed View full abstract»

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  • Feed-reflector design for large adaptive reflector antenna (LAR)

    Publication Year: 2001 , Page(s): 1142 - 1154
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    A novel feed-reflector system for large Cassegrain antennas of radio astronomy and deep-space communication applications is investigated. This feed-reflector is used to illuminate a hyperboloid subreflector with a 5-10 m diameter located 500 m above the ground. Because the subreflector is located in the near field of the feed-reflector antenna, a theory based on the near field focusing properties of paraboloid reflectors is established. The focusing at near distance is formed by moving the feed horn away from the focal point of the feed-reflector. In this theory, the properties of axial defocused paraboloid reflectors at near distance are investigated in more detail. By using equivalence path law, the subreflector shape is obtained. It is found that the hyperbola can approximate the subreflector well. A detailed ray tracing is performed on the entire system which reveals that the feed system uses some part of the subreflector three times. The gain, side lobe level, cross polarization, and aperture distribution are calculated for different feed horn locations and taper at the edge of the feed-reflector and also for different sizes and eccentricities of the subreflector. Peak efficiency in excess of 74.8% and side lobe level around -20 dB are obtained for an unshaped system. The performance of the system over the operating band (1-22 GHz) is also studied and shown that the lower-frequency limit is dependent on subreflector and feed-reflector sizes View full abstract»

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  • Generalized Sierpinski fractal multiband antenna

    Publication Year: 2001 , Page(s): 1237 - 1239
    Cited by:  Papers (35)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB) |  | HTML iconHTML  

    A new set of fractal multiband antennas called mod-p Sierpinski gaskets is presented. Mod-p Sierpinski fractal antennas derive from the Pascal triangle and present a log-periodic behavior, which is a consequence of their self-similarity properties. Mod-p Sierpinski fractal antennas constitute a generalization of the classical Sierpinski antenna View full abstract»

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  • Dyadic analysis of partially coherent submillimeter-wave antenna systems

    Publication Year: 2001 , Page(s): 1226 - 1234
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    We describe a procedure for simulating the behavior of partially coherent submillimeter-wave antenna systems. The procedure is based on the principle that the second-order statistical properties of any partially coherent vector field can be decomposed into a sum of fully coherent, but completely uncorrelated, natural modes. Any of the standard electromagnetic analysis techniques-physical optics, geometrical theory of diffraction, etc.-can be used to propagate and scatter the modes individually, and the statistical properties of the total transformed field reconstructed at the output surface by means of superposition. In the case of modal optics-plane waves, Gaussian optics, waveguide mode matching, etc.-the properties of the field can be traced directly by means of scattering matrices. The overall procedure is of considerable value for calculating the behavior of astronomical instruments comprising planar and waveguide multimode bolometers, submillimeter-wave optical components, and large reflecting antennas View full abstract»

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  • Enhanced detection of a target in a sea clutter environment using a stepped, ultra-wideband signal and E-pulse cancellation

    Publication Year: 2001 , Page(s): 1166 - 1173
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (152 KB) |  | HTML iconHTML  

    A new ultra-wideband technique to detect a sea-skimming missile in a sea-surface clutter background is presented. This technique, based on the E-pulse concept, is shown to be effective in maximizing the target to clutter ratio. Results using both measured and theoretical data from simulated sea surfaces demonstrate the usefulness of this method View full abstract»

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  • Prompt aperture efficiencies of impulse radiating antennas with arrays as an application

    Publication Year: 2001 , Page(s): 1155 - 1165
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB) |  | HTML iconHTML  

    A concept of prompt aperture efficiency is introduced for the purpose of comparing and optimizing the performance of impulse radiating antennas (IRAs). The aperture efficiencies of popular lens and reflector IRAs are computed as the ratios of peak radiated power densities on boresight compared with that produced by an ideal IRA with an aperture of equal area and equal total input power. Loss of aperture efficiency occurs through two distinct mechanisms: from power that falls outside the aperture and is lost and from nonuniform power and polarization distributions within the aperture. Both loss mechanisms are addressed, and means for increasing efficiencies are identified. The optimum aperture for a given feed structure is derived. Prompt aperture efficiencies approaching 100% are feasible in TEM-horn arrays and similar structures View full abstract»

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  • Unbounded and scattered field representations of the Dyadic Green's functions for planar stratified bianisotropic media

    Publication Year: 2001 , Page(s): 1218 - 1225
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    This paper presents a rigorous formulation of the spectral-domain dyadic Green's functions for planar stratified bianisotropic media. The media may consist of any number of layers bounded by optional impedance/admittance walls. Both electric and magnetic dyadic Green's functions for arbitrary field and source locations are derived simultaneously. Based on the principle of scattering superposition, these dyadics are decomposed into unbounded and scattered parts. The scattered dyadic Green's functions are determined without cumbersome operations using the concepts of effective reflection and transmission of outward-bounded and inward-bounded waves. The scattering coefficient matrices are expressed in compact and convenient forms involving global reflection and transmission matrices. Corresponding to the impedance/admittance boundary walls, the global reflection matrices are related directly to the wall impedance/admittance dyadics. For illustration, the general expressions of dyadic Green's functions are applied to the configuration of a grounded bianisotropic slab embedded in isotropic halfspace View full abstract»

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  • Magneto optical technique for beam steering by ferrite based patch arrays

    Publication Year: 2001 , Page(s): 1239 - 1241
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (92 KB) |  | HTML iconHTML  

    An improved technique is presented to scan a beam of a phased antenna array on a ferrite substrate through use of time delays instead of phase shifts provided by nonlinear transmission lines coupled to elements of the array. A coplanar transmission line loaded with a varactor diode when subjected to varied optical illumination offers bias dependent time delays to the elements of the arrays over a wide range of tunable operating frequencies at lower UHF without scan blindness effect. This method results in a broadband ferrite based phased antenna array with reduced weight, loss and complexity of the integrated system. This technique has proved to have a special application potential in case of beam steering by ferrite based microstrip antenna arrays at lower UHF (800 MHz-2 GHz) View full abstract»

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  • Pseudo-3-D moment method for rapid calculation of electric field distribution in a low-loss inhomogeneous dielectric

    Publication Year: 2001 , Page(s): 1117 - 1122
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (104 KB) |  | HTML iconHTML  

    Numerous applications of dielectric modeling require computation of the distribution of the total electric field in an inhomogeneous dielectric, in response to an applied electric field. An integral equation method would normally use an electric field volume integral technique using the moment method and hence compute the field in three-dimensional (3-D) space. For those instances where the third dimension of the region is assumed to be invariant, such as when determining the spatial sensitivity of a time-domain reflectometry sensor, the heavy resource use of calculating the additional dimension is an unnecessary burden. The new method reported in this paper sums the field contributions from the invariant third dimension at each stage of a two-dimensional (2-D) calculation, reducing the order of the model matrix by 2n2 where n is the number of cells in each dimension. Thus, by accepting a small loss in accuracy of less than 3%, this procedure reduces the required memory resource by more than 2n2,and execution time is dramatically improved. Assuming an essentially lossless permittivity, we use the calculated electric field distribution from a parallel transmission line to calculate the line's propagation velocity and demonstrate favorable comparison with measured values. Moisture content measurement is used as an example View full abstract»

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  • Fringe integral equation method for a truncated grounded dielectric slab

    Publication Year: 2001 , Page(s): 1210 - 1217
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    The problem of scattering by a semi-infinite grounded dielectric slab illuminated by an arbitrary incident TMz polarized electric field is studied by solving a new set of “fringe” integral equations (F-IEs), whose functional unknowns are physically associated to the wave diffraction processes occurring at the truncation. The F-IEs are obtained by subtracting from the surface/surface integral equations pertinent to the truncated slab, an auxiliary set of equations obtained for the canonical problem of an infinite grounded slab illuminated by the same source. The F-IEs are solved by the method of moments by using a set of subdomain basis functions close to the truncation and semi-infinite domain basis functions far from it. These latter functions are properly shaped to reproduce the asymptotic behavior of the diffracted waves, which is obtained by physical inspection. The present solution is applied to the case of an electric line source located at the air-dielectric interface of the slab. Numerical results are compared with those calculated by a physical optics approach and by an alternative solution, in which the integral equation is constructed from the field continuity through an aperture orthogonal to the slab. The applications of the solution to an array of line currents are also presented and discussed View full abstract»

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  • Fields of the contrawound toroidal helix antenna

    Publication Year: 2001 , Page(s): 1138 - 1141
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (92 KB) |  | HTML iconHTML  

    Exact vector potential integrals are written in spherical coordinates for the CWTHA. From these the far fields are expressed, both for the CWTHA (dipole field) and for a single winding (loop field). The vector potentials are numerically integrated; the results give the dipole field for a given current and ratio of dipole field to loop field View full abstract»

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  • A study of the CTHA based on analytical models

    Publication Year: 2001 , Page(s): 1130 - 1137
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB) |  | HTML iconHTML  

    The first electromagnetic analysis of the contra-wound toroidal helix antenna (CTHA) is presented. This very-low-profile antenna is seen to have characteristics derivable from a transmission line with a standing current wave and an array of small loops. Formulas for the far-field radiation and efficiency are given. These are used, in conjunction with a numerical model, to develop some trends relating performance and design parameters View full abstract»

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  • On the use of spatio-temporal multiresolution analysis in method of moments solutions of transient electromagnetic scattering

    Publication Year: 2001 , Page(s): 1123 - 1129
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB) |  | HTML iconHTML  

    A novel method of moments approach to the solution of time-domain integral-equation formulation of electromagnetic scattering problems is presented. The method is based on a spatio-temporal multiresolution analysis. This analysis facilitates a basis from which a small number of expansion functions is selected via an iterative procedure and utilized to model the unknown current distribution. In contrast to marching-on-in-time sequential procedures, the proposed method models the unknown current simultaneously at all the time steps within the time frame of interest. This new method is applied to a one-dimensional (1-D) problem of electromagnetic plane wave interaction with a dielectric slab. A comparison of the computed results with results based on the analytic solution demonstrates that the method is capable of attaining accurate results while achieving substantial reduction in computation time and resources 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