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Antennas and Propagation, IEEE Transactions on

Issue 1 • Date Jan. 2003

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Displaying Results 1 - 20 of 20
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  • A sheet impedance approximation for electrically thick multilayered shields

    Page(s): 67 - 73
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (518 KB) |  | HTML iconHTML  

    This paper describes an extension of the sheet impedance concept to treat inhomogeneous or multilayered shields that may be thick in terms of material shield wavelengths. For shields with magnetic materials, a simple relation between the equivalent electric and magnetic currents representing the shield is obtained. This allows the magnetic current to be treated as a dependent unknown and the electric current to be found as the solution of a single surface integral equation shown to be a perturbation of that for a perfect electric conducting (PEC) surface. By using the proper interior equivalent problem, it is shown that the method produces accurate and stable results for shielding by a rectangular box. View full abstract»

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  • Derivation of parameters of Y-Z power-law relation from raindrop size distribution measurements and its application in the calculation of rain attenuation from radar reflectivity factor measurements

    Page(s): 12 - 22
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (771 KB) |  | HTML iconHTML  

    The work reported herein empirically derived the coefficients of the power-law relation between the specific attenuation Y and each of two other quantities: the radar reflectivity factor Z and the rainfall rate R. The derivation was accomplished using raindrop size distributions (DSDs) measured in Montreal and Toronto using the precipitation occurrence sensor system (POSS) and a Joss-Waldvogel disdrometer (JWD). The specific attenuation was calculated for both spherical and oblate spheroidal raindrops. Prior to doing so, the effects of inaccuracies in small drop detection by the two systems on the resulting Y-Z and Y-R relations were examined. In computing the relations, the influence of grouping the DSDs according to the corresponding values of Z was assessed. The results from the two sites were then combined in a regression analysis to determine the coefficients of the power-law expressions. The final expressions were used to calculate the probability distribution of rain attenuation over several path lengths at 30 GHz. Conclusions that can be drawn from this work include that (i) the uncertainties in the measurements of small drops do not appear to be critical to the derived relations for some frequencies considered in this work, (ii) in computing rain attenuation estimates from radar reflectivity factors, different criteria for grouping the reflectivity factor measurements can be adopted without changing the statistics of the corresponding attenuation estimates, (iii) differences, which are the smallest for frequencies around 20-30 GHz, are observed in the coefficients derived from the measured DSDs compared with those recommended by the ITU-R, and (iv) the attenuation statistics at 30 GHz computed by applying the Y-Z power-law expression are resistant to spatial averaging. View full abstract»

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  • Worldwide techniques for predicting the multipath fading distribution on terrestrial LOS links: comparison with regional techniques

    Page(s): 23 - 30
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (711 KB) |  | HTML iconHTML  

    A revised worldwide method has been recommended by the Radiocommunications Sector of the International Telecommunication Union (ITU-R) in Recommendation ITU-R 530-8 for predicting the deep-fading distribution due to multipath propagation in the average worst month on VHF-EHF terrestrial line-of-sight links. This paper presents detailed testing results for the revised method on a 239-link database from 22 countries around the world in comparison with results for the leading regional methods still frequently used by some link designers for worldwide applications (viz., the Barnett-Vigants (1972, 1970) method of the United States and the Morita (1970) method of Japan). An evaluation of the form of the prediction equation is given for the revised and previous ITU-R methods and several regional methods. The revised ITU-R method is shown to perform significantly better than the other methods for both overland and coastal/overwater links. View full abstract»

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  • Finite element analysis of electromagnetic scattering from a cavity

    Page(s): 130 - 137
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (499 KB) |  | HTML iconHTML  

    A finite element method (FEM) is implemented to compute the radar cross section of a two-dimensional (2D) cavity embedded in an infinite ground plane. The method is based on the variational formulation which uses the Fourier transform to couple the fields outside the cavity and those inside the cavity; hence, the scattering problem can be reduced to a bounded domain. The convergence of the discrete finite element problem is analyzed. Numerical results are presented and compared with those obtained by the standard finite element-Green function method and by the 2D integral equation method. View full abstract»

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  • Measurement and modeling of propagation losses in brick and concrete walls for the 900-MHz band

    Page(s): 31 - 39
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB) |  | HTML iconHTML  

    The prediction of wall losses is a fundamental aspect in the planning of cellular systems. The broad variety of building materials and construction codes makes accurate attenuation prediction very difficult without the support of specific construction data or measurements. In this paper, the attenuation and equivalent electric parameters ε and σ of brick and doubly reinforced concrete walls are estimated for the 900-MHz band by fitting simple ray tracing models to empirical transmission data. The measurement setup is described, and extensive experimental results justifying the quasioptical modeling are presented. View full abstract»

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  • Time-domain radiation from large two-dimensional apertures via narrow-waisted Gaussian beams

    Page(s): 78 - 88
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1461 KB) |  | HTML iconHTML  

    This paper deals with the short-pulse radiation of three-dimensional (3-D) vector electromagnetic fields from arbitrarily polarized large two-dimensional (2-D) truncated aperture distributions, which are parameterized in terms of narrow-waisted ray-like pulsed Gaussian basis beams centered on a discretized Gabor lattice in a four-dimensional (4-D) configuration-spectrum phase space. The study extends our previous Gabor-based investigation of time-domain (TD) short-pulse radiation of 2-D fields from 1-D large truncated apertures with nonphased, linearly phased (delayed) and nonlinearly phased focusing aperture field profiles . We begin with, and summarize, a Gabor-based frequency domain (FD) formulation of the 2-D aperture problem which has been presented and tested elsewhere, but we include additional numerical examples for validation and quality assessment. As done by Galdi, Felsen and Castanon (see ibid., vol 49, p. 1322-32, Sept. 2001) we access the time domain by Fourier inversion from the FD, starting from the initial 3-D space-time Kirchhoff formulation (whose numerical integration furnishes reference solutions), and then passing on to Gabor-parameterized field representations in terms of pulsed beam (PB) wavepackets which are launched by linearly and nonlinearly phase-delayed focusing aperture distributions. Example calculations and comparisons with numerically generated reference data serve to calibrate the Gabor-PB algorithms and assess their domains of validity. View full abstract»

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  • Dual-band, single CPW port, planar-slot antenna

    Page(s): 137 - 139
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB) |  | HTML iconHTML  

    A dual-band planar-slot antenna that operates through a single coplanar waveguide (CPW) port in two 10% wide-frequency bands, one octave apart is presented. An input T-match circuit is used to match the antenna in both bands, without increasing its size and keeping the CPW feed advantages. A case antenna covering the two Global System for Mobile communications bands (0.88-0.96 GHz and 1.71-1.88 GHz) and the Digital Enhanced Cordless Telecommunications band (1.88-1.9 GHz) has been designed, built, and measured, to demonstrate the technique. A proprietary program, based on the method of moments, has been used to analyze and optimize the antenna. View full abstract»

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  • A microwave beacon and guiding signals for airports and their approaches

    Page(s): 110 - 114
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (367 KB) |  | HTML iconHTML  

    A novel circular array of 90 equally spaced vertical dipoles is described. It is driven by just one element. When the spacing, length, and radius of the identical elements are properly chosen, the entire array is resonant with large currents in each element. These alternate 180° in phase and set up a far field that consists of 90 sharp spikes separated by 90 s. When dimensioned for a microwave frequency of 3 GHz, the array generates a field pattern that can be applied to provide a microwave beacon and guiding signals for aircraft approaching an airport. These would supplement the normal central high-intensity light and the approach lights, and provide a potentially useful guidance system for coastal airports embedded in dense fog that obscures the lights. View full abstract»

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  • A uniform asymptotic evaluation of the field radiated from collinear array antennas

    Page(s): 89 - 102
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1617 KB) |  | HTML iconHTML  

    A uniform asymptotic representation of the electromagnetic field radiated from arbitrary collinear array antennas is presented. The asymptotic field is obtained applying the saddle-point technique to the radiation integrals after expressing the current excited along the array axis by means of a Fourier spectral representation. The resulting electromagnetic field is expressed in terms of propagating and evanescent truncated Floquet waves (FWs). The leading asymptotic term of the FWs exhibits an optical behavior and is responsible for the slow decay of the array near-field, which can be described as cylindrical in character. The transition toward the spherical wave propagation regime is due to the interference of the cylindrical field with the relevant scattered field from the array truncations, while the reactive energy storage is due to the evanescent FWs, as well as to the progressive inductive and progressive electrostatic FWs excited close the antenna axis. Using the asymptotic field representation, prediction formulas for the spatial locations where the array near-field exhibits peak deviation from the cylindrical decay, and where the transition from cylindrical to spherical wave propagation regime takes place, have been derived. The proposed analytical technique can be adopted to analyze the spatial field distributions and the radiation mechanisms of periodic and nonperiodic linear arrays. View full abstract»

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  • Hybrid-coupled broadband triangular microstrip antennas

    Page(s): 139 - 141
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    Two broadband configurations consisting of three hybrid-coupled equilateral and isosceles triangular microstrip antennas have been proposed. Both configurations yield more than four times the bandwidth as compared with the corresponding single triangular microstrip antenna. The radiation pattern of a hybrid-coupled isosceles triangular microstrip antenna is in the broadside direction with very small variation over the entire bandwidth. In addition, this antenna has wide half power beamwidth, making it suitable as an element for the large scan broadband antenna array. View full abstract»

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  • Quadrifilar loop antenna

    Page(s): 115 - 120
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB) |  | HTML iconHTML  

    A new quadrifilar antenna has been developed for generating circularly polarized backfire radiation. The antenna consists of two orthogonal rectangular conducting loops, each incorporating capacitive coupling and fed using either a single or two coaxial cables. Though the geometry is much simpler than a conventional quadrifilar helix antenna, the radiation pattern performance is very similar. Measured and simulated patterns are compared for two antennas with different feed arrangements. It is shown that the resonant structure can produce a cardioid pattern with a directivity of 4.5 dB (120° 3 dB beamwidth) and a front-to-back ratio of more than 20 dB at the center operating frequency. A 10% impedance bandwidth (VSWR<2) over which the axial ratio is less than 3 dB is demonstrated. View full abstract»

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  • A low-profile planar monopole antenna for multiband operation of mobile handsets

    Page(s): 121 - 125
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (703 KB) |  | HTML iconHTML  

    A novel planar monopole antenna is proposed. It has a very low profile (antenna height less than 0.04 times the operating wavelength in free space) and is capable of multiband operation. The proposed antenna has a planar rectangular radiating patch in which a folded slit is inserted at the patch's bottom edge. The folded slit separates the rectangular patch into two subpatches, one smaller inner subpatch encircled by the larger outer one. The proposed antenna is then operated with the inner subpatch resonating as a quarter-wavelength structure and the outer one resonating as both a quarter-wavelength and a half-wavelength structure. The proposed antenna, 12 mm high and 30 mm wide, has been constructed, and the obtained bandwidths cover the global system for mobile communication (890-960 MHz), digital communication system (1710-1880 MHz), personal communication system (1850-1990 MHz), and universal mobile telecommunication system (1920-2170 MHz) bands. Details of the proposed design and obtained experimental results are presented and discussed. View full abstract»

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  • Three-dimensional orthogonal vector basis functions for time-domain finite element solution of vector wave equations

    Page(s): 59 - 66
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (471 KB) |  | HTML iconHTML  

    Three-dimensional (3-D) orthogonal vector basis functions are developed for the time-domain finite element solution of vector wave equations. These basis functions enforce both the tangential continuity of the electric field and the normal continuity of the electric flux. The stability of the resulting time-domain finite element schemes is investigated and demonstrated to be guaranteed. The use of the proposed basis functions completely eliminates the matrix solution at each time step required by the time-domain finite element solution of vector wave equations. The computational cost thereby scales as O(NtN) with Nt and N denoting the number of time steps and the number of unknowns, respectively. Defined over tetrahedral elements, the proposed basis functions increase the solution efficiency without compromising the geometry modeling flexibility. Both numerical results and comparison with traditional vector basis functions demonstrate the accuracy as well as the efficiency of the proposed three-dimensional orthogonal vector bases. View full abstract»

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  • UHF and L band propagation measurements to obtain log-normal shadowing parameters for mobile satellite link design

    Page(s): 126 - 130
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (466 KB)  

    Tree shadowing is significant for mobile satellite radio propagation investigation and must be known for successful link design. Therefore, there are limited data on the relevant problem. For this purpose, propagation measurements at L and UHF band were performed in Trabzon, Turkey, in 1993 and 1996, respectively. These experiments were executed with a transmitter on the top of a high building, and the receiver system was located in a van outfitted with the antenna on its roof and receiver equipment in its interior. Measurements were carried out for 14 different tree types, and the results of both bands are presented in tabular and graphical forms. Experiments were repeated for the same trees during the months April to September. The variations of the tree attenuation were examined during these months with and without foliage. Average values of the tree attenuations were found to be 8.60 and 11.00 dB for UHF and L band, respectively. The scaling factor between L and UHF band attenuations in decibels was determined to be approximately 1.32. Using these measured parameters, fade depth statistics were calculated using a lognormal shadowing model. To establish validity of obtained results for the design of mobile satellite links, the results were compared with previous investigations. View full abstract»

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  • Properties and applications of the large circular resonant dipole array

    Page(s): 103 - 109
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (517 KB) |  | HTML iconHTML  

    Large closed-curve antenna arrays have been a subject of research for many years and have been shown to have many interesting properties. The paper investigates some of the properties of such a dipole array when the closed curve is a circle. Recently, because of its unique horizontal field pattern, a 90-element circular array of this type has been proposed as a microwave beacon for the coastal navigation of ships and airplanes. In the design of these arrays, it is suggested that the array be rotated mechanically. The question arises: can the mechanical rotation be replaced by an electronic rotation? We show that electronic rotation is not possible for the 90-element circular array originally described, but is possible for a modified array. The subtle difference between these two arrays is clarified and a simple criterion is given for the general case. Also presented is the derivation of an asymptotic formula for the radiation pattern of a resonant circular array of N equal elements with only one element driven. Since the theory for such an array is complicated and involves numerous numerical difficulties, a simple asymptotic formula for the field pattern has advantages over other methods. The simple formula is shown to produce a vertical field pattern that is indistinguishable from its numerically calculated counterpart. Generalization to noncircular arrays is discussed briefly. View full abstract»

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  • Selecting sampling interval of transient response for the improved Prony method

    Page(s): 74 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (338 KB) |  | HTML iconHTML  

    A sampling interval selection scheme for use with the improved Prony method is proposed. Since natural frequency extraction is a numerically ill-conditioned problem, a small change in the sampling interval results in a large change in the extracted natural frequencies. From the perturbation of the eigenvectors of the matrix, the accuracy criterion of the extracted natural frequencies is derived. The proposed scheme is validated using natural frequency extraction from the synthetic response, the method of moments (MM) response, and the measured response. View full abstract»

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  • DOA estimation in the asynchronous DS-CDMA system

    Page(s): 40 - 47
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (559 KB) |  | HTML iconHTML  

    It was previously shown that the number of array elements must exceed the number of sources for subspace-based directional-of-arrival (DOA) estimation. This is clearly not practical for a direct-sequence code-division multiple access (DS-CDMA) wireless system since the number of mobile users is very large. To overcome the restriction, a DOA's estimator employing the code-matched filters and parallel MUSIC algorithms is proposed. In the asynchronous DS-CDMA system, we show that the multiple access interference (MAI) throughout the code-matched filter tends toward the real Gaussian distribution with zero mean. In addition, based on the singular value decomposition (SVD) of a finite amount of data, we achieve a theoretical expression for the mean-squared error (MSE) of the DOA's estimation. With the advantage of code-matched filter inherent in the DS-CDMA system, we prove that the proposed technique can obtain an unbiased DOA estimation with low MSE, even in the environment where the number of mobile users far exceeds the number of array elements. Simulation results verify the theoretical derivation. View full abstract»

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  • Sparse matrix/canonical grid method applied to 3-D dense medium simulations

    Page(s): 48 - 58
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1087 KB) |  | HTML iconHTML  

    The sparse matrix/canonical grid (SMCG) method, which has been shown to be an efficient method for calculating the scattering from one-dimensional and two-dimensional random rough surfaces, is extended to three-dimensional (3-D) dense media scattering. In particular, we study the scattering properties of media containing randomly positioned and oriented dielectric spheroids. Mutual interactions between scatterers are formulated using a method of moments solution of the volume integral equation. Iterative solvers for the resulting system matrix normally require O(N2) operations for each matrix-vector multiply. The SMCG method reduces this complexity to O(NlogN) by defining a neighborhood distance, rd, by which particle interactions are decomposed into "strong" and "weak." Strong interaction terms are calculated directly requiring O(N) operations for each iteration. Weak interaction terms are approximated by a multivariate Taylor series expansion of the 3-D background dyadic Green's function between any given pair of particles. Greater accuracy may be achieved by increasing rd, using a higher order Taylor expansion, and/or increasing mesh density at the cost of more interaction terms, more fast Fourier transforms (FFTs), and longer FFTs, respectively. Scattering results, computation times, and accuracy for large-scale problems with rd up to 2 gridpoints, 14×14×14 canonical grid size, fifth-order Taylor expansion, and 15 000 discrete scatterers are presented and compared against full solutions. View full abstract»

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  • Plane-wave reflection from double arrays of small magnetoelectric scatterers

    Page(s): 2 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    An analytical model of reflection and transmission of plane waves in double regular arrays of bianisotropic particles is developed. A method to correct approximate values of the particle polarizabilities so that the energy conservation requirements are exactly satisfied is proposed. Double arrays of planar omega particles are studied in detail, and it is shown that very sharp Bragg resonances exist in such arrays. The theory is verified by comparison with numerical simulations based on the method of moments. 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