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Antennas and Propagation, IEEE Transactions on

Issue 7 • Date July 2004

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Displaying Results 1 - 25 of 42
  • Table of contents

    Publication Year: 2004 , Page(s): c1 - 1629
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  • IEEE Transactions on Antennas and Propagation publication information

    Publication Year: 2004 , Page(s): c2
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  • Rigorous analysis of the influence of the aspect ratio of Yee's unit cell on the numerical dispersion property of the 2-D and 3-D FDTD methods

    Publication Year: 2004 , Page(s): 1630 - 1637
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB) |  | HTML iconHTML  

    In this paper, the influence of the aspect ratio of Yee's unit cell on the numerical dispersion errors [in terms of the physical phase-velocity error (PVE) and the velocity-anisotropy error (VAE)] of two-dimensional (2-D) finite-difference time-domain (FDTD) and three-dimensional (3-D) FDTD methods is comprehensively investigated. Numerical results reveal that, for a fixed mesh resolution, the physical PVE and the VAE of both the 2-D and 3-D FDTD methods converge to certain limits for higher aspect ratio. Most importantly, it is found for the first time that for the 2-D and 3-D cases the converged dispersion errors (i.e., the limits) are, respectively, about 2.0 and 1.5 times of the corresponding square and cubic unit cells; and the validity of the above theoretical prediction is verified through numerical tests. The investigation carried out in this paper certainly confirms, from the numerical dispersion point of view, that very accurate numerical results can still be obtained even when the aspect ratio of the cells is higher. Consequently, it gives design engineers more freedom and confidence to use the FDTD methods, especially when the aspect ratio of the cells has to be greatly adjusted due to the special requirement of structures under study. View full abstract»

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  • A low-dispersion 3-D second-order in time fourth-order in space FDTD scheme (M3d24)

    Publication Year: 2004 , Page(s): 1638 - 1646
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB) |  | HTML iconHTML  

    A second-order in time fourth-order in space modified finite-difference time-domain (FDTD) scheme for three dimensional electromagnetic problems "M3d24" is presented. The algorithm enables the numerical phase error to be minimized, so that it leads to high accuracy with low resolution grids. The advantage of this method is demonstrated by considering the long distance propagation of the wave radiated from a time harmonic elementary dipole using a low resolution grid, and comparing the results with other FDTD schemes. View full abstract»

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  • A PML using a convolutional curl operator and a numerical reflection coefficient for general linear media

    Publication Year: 2004 , Page(s): 1647 - 1657
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (416 KB)  

    A general time domain representation of the Chew and Weedon [1994] stretched coordinate perfectly matched layer (PML) absorbing boundary condition is described. This new approach mathematically operates on the spatial field derivatives and allows the PML update equations to be trivially derived from any set of general linear medium update equations. A method for calculating the frequency dependent reflection coefficient for this form of the PML is derived for general linear media. Two and three dimensional numerical test results, which validate the calculation of the reflection coefficient, are presented. The range of numerical tests include the PML matching of free space, a magnetoplasma, and a free space waveguide. Improving the reflection coefficient is examined. View full abstract»

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  • Three-dimensional CAD-based mesh Generator for the Dey-Mittra conformal FDTD algorithm

    Publication Year: 2004 , Page(s): 1658 - 1664
    Cited by:  Papers (7)
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    It is well-known that the finite-difference time-domain (FDTD) method is subject to significant errors due to the staircasing of surfaces that are not precisely aligned with major grid planes. Dey and Mittra introduced a locally conformal method (D-FDTD) that has shown substantial gains in the accuracy of modeling arbitrary surfaces in the FDTD grid. A mesh generator for this purpose was reported by Yu and Mittra. In this paper, we present the formulation and validation of an alternative CAD-based mesh generator for D-FDTD that has improved capabilities for arbitrary three-dimensional (3-D) perfect electric conductor (PEC) geometries. This mesh generator is capable of importing AutoCad and ProE files of 3-D PEC scatterers and resonators. It can reduce the required FDTD grid resolution by up to 4:1 in each Cartesian direction in 3-D relative to conventional staircased FDTD models when modeling cavity resonances of complex PEC structures such as twisted waveguides. View full abstract»

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  • A method for introducing soft sources in the PSTD algorithm

    Publication Year: 2004 , Page(s): 1665 - 1671
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    This paper presents a method for introducing a soft source in the pseudospectral time-domain algorithm. In this method, a scalar weighting term ζ is introduced in the total field/scattered field approach in computational electromagnetics. Using our modified version of Maxwell's equations, soft sources can be introduced simply by adding incident terms in the 8-10-cell connecting region between the total field and the scattered field. One-dimensional (1-D) and two-dimensional (2-D) examples of soft source generation and a 2-D scattering study of a dielectric cylinder are given. View full abstract»

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  • Singular higher order complete vector bases for finite methods

    Publication Year: 2004 , Page(s): 1672 - 1685
    Cited by:  Papers (47)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    This paper presents new singular curl- and divergence-conforming vector bases that incorporate the edge conditions. Singular bases complete to arbitrarily high order are described in a unified and consistent manner for curved triangular and quadrilateral elements. The higher order basis functions are obtained as the product of lowest order functions and Silvester-Lagrange interpolatory polynomials with specially arranged arrays of interpolation points. The completeness properties are discussed and these bases are proved to be fully compatible with the standard, high-order regular vector bases used in adjacent elements. The curl (divergence) conforming singular bases guarantee tangential (normal) continuity along the edges of the elements allowing for the discontinuity of normal (tangential) components, adequate modeling of the curl (divergence), and removal of spurious modes (solutions). These singular high-order bases should provide more accurate and efficient numerical solutions of both surface integral and differential problems. Sample numerical results confirm the faster convergence of these bases on wedge problems. View full abstract»

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  • Multilevel fast multipole method solution of volume integral equations using parametric geometry modeling

    Publication Year: 2004 , Page(s): 1686 - 1692
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    We present a multilevel fast multipole method (MLFMM) solution for volume integral equations dealing with scattering from arbitrarily shaped inhomogeneous dielectrics. The solution accuracy, convergence, computer time and memory savings of the method are demonstrated. Previous works have employed the MLFMM for impenetrable targets. In this paper, we integrate the MLFMM with the volume integral equation method for scattering by inhomogeneous targets. Of particular importance is the use of curvilinear elements for better volume representation and the use of simple basis functions for ease of parallelization. View full abstract»

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  • Fast dual-MGS block-factorization algorithm for dense MoM matrices

    Publication Year: 2004 , Page(s): 1693 - 1699
    Cited by:  Papers (23)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    A robust method is introduced for efficiently compressing dense method of moments (MoM) matrices using a dual modified Gram-Schmidt block-QR-factorization algorithm based on low-rank singular value decomposition. The compression is achieved without generating the full matrix or even full subblocks of the matrix. The compressed matrix may then be used in the iterative solution of the MoM problem. The method is very robust because it uses a reduced set of the original matrix entries to perform the compression. Furthermore, it does not depend on the analytic form of the Green's function, so it may be applied to arbitrarily complex media. View full abstract»

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  • A fast algorithm for calculating the radiation pattern in the longitudinal plane of antennas with cylindrical structure by applying asymptotic waveform evaluation in a spectrum of two-dimensional solutions

    Publication Year: 2004 , Page(s): 1700 - 1706
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    When dealing with electromagnetic problems of small three-dimensional (3-D) elements, such as dipole, microstrip patches and slots, in the vicinity of two-dimensional (2-D) structures, it is very efficient to find the radiation characteristics of the 3-D elements by using a spectrum of 2-D solutions (S2DS). Only one 2-D solution in the spectral domain is needed to obtain the radiation pattern in the transverse plane defined by θ=90°. For the radiation in a longitudinal plane defined by a fixed azimuth angle φ, one 2-D problem has to be solved for each value of the polar angle θ. This paper presents a fast algorithm by which the radiation pattern in the longitudinal plane can be computed more efficiently. The algorithm applies the method of asymptotic waveform evaluation (AWE) in the 2-D spectral domain. For the cases shown in the paper, the algorithm needs only three 2-D solutions to determine the complete radiation pattern in the longitudinal plane. View full abstract»

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  • An efficient multiregion model for electromagnetic scattering and radiation by PEC targets

    Publication Year: 2004 , Page(s): 1707 - 1716
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB) |  | HTML iconHTML  

    An efficient multiregion model has been proposed for the fast implementation of the electromagnetic scattering by perfectly electrical conducting (PEC) targets and the radiation of point sources or wire antennas near PEC targets. In the multiregion model, the PEC target under consideration is divided by multiple regions depending on the position of point source/antenna or the incident direction of plane waves. Then the method of moments (MoM) is used on the first region, which is close to the source or is the illuminated region, to obtain the accurate electric current. The mutual coupling between different regions are considered approximately based on the magnetic-field integral equation, from which closed-form approximations for electric currents on other regions are derived. Because MoM is only performed on the first region, the number of unknowns in the new model is much fewer than that in the full MoM analysis, making the new model much more efficient. Compared with the published hybrid methods, the multiregion model gives a more reasonable physical explanation, and provides a better accuracy in both currents and scattered fields. Numerical simulations for two-dimensional (2-D) problems (transverse-magnetic/transverse-electric) and 3-D problems are given to test the validity and efficiency of the proposed modeling. View full abstract»

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  • An advanced field prediction model including diffuse scattering

    Publication Year: 2004 , Page(s): 1717 - 1728
    Cited by:  Papers (55)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB) |  | HTML iconHTML  

    Ray tracing (RT) models are now widely adopted for field prediction in urban environment. Nevertheless, conventional RT tools still suffer for excessive central processing unit (CPU) time and inaccuracy in wide-band prediction. By increasing the maximum number of successive interactions (reflections, diffractions) little improvement in wide-band results can be usually achieved while CPU time increases exponentially. In the present paper, it is shown that by integrating reflection/diffraction with diffuse scattering, good narrow-band and wide-band results can be obtained with a low number of interactions. The adopted scattering model is a simple ray-based model, which has been embedded in a three-dimensional (3-D) RT program. The impact of diffuse scattering on narrowband and wide-band parameters is analyzed in the paper and the complete model is compared with measurements in a variety of cases, showing the validity of the approach. View full abstract»

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  • Analysis of the time-reversal operator for a small spherical scatterer in an electromagnetic field

    Publication Year: 2004 , Page(s): 1729 - 1738
    Cited by:  Papers (31)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB) |  | HTML iconHTML  

    The time-reversal operator (TRO) for a planar array of crossed dipole elements illuminating a small conducting and/or dielectric sphere is investigated in order to determine the general properties of an electromagnetic time-reversing array system. The behavior of such a system for a given frequency is analyzed by studying the eigenvalues and eigenvectors of the TRO. Each eigenvector specifies a set of complex driving currents for the array elements that produce received voltages that are proportional to the conjugates of the drive currents. The proportionality constant is equal to the square root of the associated eigenvalue and is the same for all elements. The eigenvalues and eigenvectors can be determined by performing a singular value decomposition (SVD) on the multistatic data matrix of the array. The eigenvalues of the TRO are the squares of the singular values, and the eigenvectors are identical to the singular vectors. We have shown that the maximum number of singular vectors associated with the sphere is equal to the number of orthogonal orientations of the dipole moments induced in the sphere when irradiated by the array, so there is a maximum of six for a conducting sphere but only three are significant when the conductivity is small and the sphere may be considered being just a dielectric. Numerical results are presented for linear and circular arrays to show the general behavior of the system. View full abstract»

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  • Considerations for source pulses and antennas in UWB radio systems

    Publication Year: 2004 , Page(s): 1739 - 1748
    Cited by:  Papers (146)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB) |  | HTML iconHTML  

    This paper addresses two vital design considerations in ultrawide-band radio systems. One is that radiated power density spectrum shaping must comply with certain emission limit mask for coexistence with other electronic systems. Another is that the design of source pulses and transmitting/receiving antennas should be optimal for the performance of overall systems. The design of source pulses and transmitting/receiving antennas under the two considerations is discussed. First, the characteristics of transmitting/receiving antenna systems are described by a system transfer function. Then, the design of source pulses and transmitting antennas are studied based on the considerations for emission limits. Finally, the design of transmitting and receiving antennas are investigated in terms of pulse fidelity and system transmission efficiency. In the studies, thin wire dipoles with narrow bandwidths and planar dipoles with broad bandwidths are exemplified. View full abstract»

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  • Full-wave analysis and wide-band design of probe-fed multilayered cylindrical-rectangular microstrip antennas

    Publication Year: 2004 , Page(s): 1749 - 1757
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB) |  | HTML iconHTML  

    The input impedance and radiation pattern of the probe-fed multilayered cylindrical-rectangular microstrip antennas (PMCMSA) are analyzed by using a novel approach which combines the conformal finite-difference time-domain (FDTD) and Gedney's unsplit version of the perfectly matched layer absorbing boundary condition method and the Green's functions in cylindrically stratified media. The near fields of such antennas and the current distributions on the patches are obtained by the conformal FDTD method numerically and then the modified spectral-domain Green's functions in arbitrary cylindrically stratified media are used to determine the radiation pattern. The effect of the small radius of the probe on the performance of antennas is investigated through the thin-wire algorithm in cylindrical coordinates. A simple design scheme of the probe-fed cylindrically stacked antennas is also proposed for increasing the impedance bandwidth. View full abstract»

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  • Accurate numerical modeling of the TARA reflector system

    Publication Year: 2004 , Page(s): 1758 - 1766
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB) |  | HTML iconHTML  

    The radiation pattern of the large parabolic reflectors of the Transportable Atmospheric RAdar system (TARA), developed at Delft University of Technology, has been accurately simulated. The electric field integral equation (EFIE) formulation has been applied to a model of the reflectors including the feed housing and supporting struts, discretised using the method of moments. Because the problem is electrically large (the reflector has a diameter of 33λ) and nonsymmetrical, this lead to a badly conditioned linear system of approximately half a million unknowns. In order to solve this system, an iterative solver (generalized minimum residual method) was used, in combination with the multilevel fast multipole method. Because of the bad conditioning, the system could only be solved by using a huge preconditioner. A new block-incomplete LU preconditioner (ILU) algorithm has been employed to allow for efficient out-of-computer core memory preconditioning. View full abstract»

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  • Effect of aperture feed and reflector configuration on the time- and frequency domain radiation patterns of reflector impulse radiating antennas

    Publication Year: 2004 , Page(s): 1767 - 1776
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB) |  | HTML iconHTML  

    The prompt off-boresight radiation from an arbitrary reflector impulse radiating antenna (IRA) is considered in both the time and frequency domains using a time-domain physical optics formalism. The theory is used to compare the performance between reflector IRAs with common transverse electromagnetic feed configurations that have been designed to maximize the boresight fields. It is found that moving the feed arms of reflector IRAs toward the vertical helps to reduce sidelobe levels, as reflector IRAs with their feed arms oriented at 60° from the horizontal have sidelobes that are 4-5 dB lower in the H plane and 1-2 dB lower in the E plane than more traditional reflector IRAs with feed arms oriented at 45°. The lower sidelobes are accompanied by a higher peak gain, albeit with a wider beamwidth. There are corresponding significant differences in the time domain waveforms that result. The theory is verified by comparison with experimental data from a half IRA with feed arms at 45°. The peak fields, pulse widths, and overall waveform shapes agree well between theory and experiment, though there are temporal asymmetries in the measured data that are not predicted by the theory. View full abstract»

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  • Characteristics of the large deployable antenna on HALCA Satellite in orbit

    Publication Year: 2004 , Page(s): 1777 - 1782
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    This paper describes measurements of the characteristics of a large deployable antenna using the tensioned cable truss scheme in orbit. From observations of celestial radio sources, the antenna gain degradation after launch was shown to be acceptable at L- and C-bands. At Ka-band, however, serious degradation of 24 dB was measured. From observations of the earth and moon, the degradation at Ka-band was shown to be attributed to the transmission line loss. The systematic and random errors of the main reflector surface are separated on the basis of these measurement results and theoretical analysis. Accordingly, the reflector status in orbit is estimated. View full abstract»

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  • Single-conductor strip leaky-wave antenna

    Publication Year: 2004 , Page(s): 1783 - 1789
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    This paper presents a leaky-wave antenna with only a single-conductor strip on a substrate without a practical ground plane. The full-wave integral equation method is used to investigate the EH01 leaky mode of this single-conductor strip structure. When this single-conductor strip is on a thin substrate with a low dielectric constant, a broad-band radiation regime can exist for the EH01 leaky mode. The balanced microstrip lines and the inverted balanced microstrip lines are used to excite this EH01 leaky mode. This work presents both the numerically simulated and measured data. The measured bandwidth of a voltage standing-wave ratio ≤2 is from 6.55- 13.75 GHz (2.34:1). In this case, the normalized phase constant is very close to 1 and this results in a fixed main-beam radiation pattern in the end-fire direction. This leaky-wave antenna with only a single rectangle stripline of length 110 mm can achieve the same broad-band performance as a tapered microstrip leaky wave antenna with a length 310 mm, as previously reported by the authors. View full abstract»

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  • Multiband folded planar monopole antenna for mobile handset

    Publication Year: 2004 , Page(s): 1790 - 1794
    Cited by:  Papers (49)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    This paper introduces a folded planar monopole antenna, which has a very low profile of about one twentieth of the wavelength of the lowest operating frequency. The effect is achieved by using a bended rectangular radiating patch and an inverted L-shape ground plane. The proposed antenna can be used in multiband operation, with omnidirectional radiation patterns for all operating bands. Its impedance bandwidth, determined by 10 dB return loss, covers almost all present wireless communication systems: Global System for Mobile Communication (GSM), Digital Communication System (DCS), Personal Communication System (PCS), Universal Mobile Communication System (UMTS), and Industrial Science Medical (ISM) band. This paper presents the design and experimental results of the proposed antenna. Moreover, the study also investigates the tuning effects of the geometry parameters on impedance matching. View full abstract»

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  • Polarization diversity measurements and analysis for antenna configurations at 1800 MHz

    Publication Year: 2004 , Page(s): 1795 - 1810
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (704 KB) |  | HTML iconHTML  

    In wireless communication systems, multipath interference has a significant impact on system design and performance. Fast fading variations are caused by the coherent summation of multiple echoes from many reflection points reaching the receive antenna. Antenna diversity is one technique that can be used to overcome multipath fading. A test system used to measure the diversity performance of an antenna pair was used to experimentally determine the complex correlation coefficient between the two antenna branches. A local mean estimation algorithm based on the channel mean square error equalization was implemented. Thus, the two parameters that determine the expected diversity gain, i.e., the complex correlation coefficient and the mean level signal difference, were estimated. The test system was used to evaluate the polarization diversity performance of different antenna pairs in Rayleigh and Rician environments, both in the absence and in the presence of a human head phantom. View full abstract»

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  • Optimum design of Yagi-Uda antennas using computational intelligence

    Publication Year: 2004 , Page(s): 1811 - 1818
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB) |  | HTML iconHTML  

    Optimization of Yagi-Uda antennas is a challenging design problem, since the antenna characteristics such as gain, input impedance, maximum sidelobe level etc., are known to be extremely sensitive to the design variables viz., element lengths and their spacings. This corresponds to a highly nonlinear and multimodal function space with functional and slope discontinuities that limit the use of conventional gradient based optimization approaches. Although, stochastic, zeroth-order methods like genetic algorithm and evolutionary algorithm are attractive choices for such classes of problems, their successful application requires scaling and aggregating parameters to handle constraints and objectives that may not be easy to provide. In this paper, we introduce a stochastic, zeroth-order optimization algorithm that handles constraints and objectives separately via Pareto ranking that eliminates the problem of scaling and aggregation. The algorithm is based on principles of learning and is embedded with three key learning strategies that control whom to learn from (i.e., leader identification and leader selection) and what to learn (i.e., information acquisition) in order to better guide the search. The leader identification mechanism partitions the individuals into a set of leaders and a set of followers. The followers interact with the leader and move toward the better performing leaders in search for better solutions. As the algorithm does not require parameters for scaling or aggregation, it provides the designer the true flexibility that is necessary to handle various forms of the design problem effectively and at a computational cost that is comparable to existing stochastic optimization methods. Results of three single objective antenna design examples (a four-element, a 15-element and a fixed boom length 22-element design) are presented and compared with published results to illustrate the behavior of the proposed algorithm and highlight its benefits in solving a wide variety of antenna design problems. A new set of results are presented for a multiobjective formulation of the design problem. View full abstract»

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  • Fast beamforming of electronically steerable parasitic array radiator antennas: theory and experiment

    Publication Year: 2004 , Page(s): 1819 - 1832
    Cited by:  Papers (88)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB) |  | HTML iconHTML  

    A low-power consumption, small-size smart antenna, named electronically steerable parasitic array radiator (ESPAR), has been designed. Beamforming is achieved by tuning the load reactances at parasitic elements surrounding the active central element. A fast beamforming algorithm based on simultaneous perturbation stochastic approximation with a maximum cross correlation coefficient criterion is proposed. The simulation and experimental results validate the algorithm. In an environment where the signal-to-interference-ratio is 0 dB, the algorithm converges within 50 iterations and achieves an output signal-to-interference-plus-noise-ratio of 10 dB. With the fast beamforming ability and its low-power consumption attribute, the ESPAR antenna makes the mass deployment of smart antenna technologies practical. View full abstract»

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  • Beam steering of nonlinear oscillator arrays through manipulation of coupling phases

    Publication Year: 2004 , Page(s): 1833 - 1842
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    This paper describes three phase-shifterless beam steering techniques which exploit the synchronization properties of coupled nonlinear oscillator arrays. In each, the control parameters are the coupling phases of the local interactions between elements. The one-dimensional oscillator arrays under consideration are described by Phase Model-type equations, implying the assumption that the amplitude dynamics have achieved a steady state. Linear stability analyzes for each technique are provided which reveal significant differences in attainable scan angles. 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