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Antennas and Wireless Propagation Letters, IEEE

Issue 1 • Date 2003

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Displaying Results 1 - 25 of 104
  • Bandwidth, cross-polarization, and feed-point characteristics of matched Hilbert antennas

    Page(s): 2 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (538 KB) |  | HTML iconHTML  

    We have applied a moment-method-based simulation code to perform a detailed parametric study of the bandwidth, cross-polarization level, and the feed location characteristics of the matched Hilbert antenna. It is shown that a properly chosen off-center near-the-end feed point may provide an approximate 50 /spl Omega/ real input impedance at the fundamental resonant frequency. The role of different iteration orders for Hilbert antennas, approximately matched to the 50 /spl Omega/ line, on the bandwidth and cross-polarization level of such antennas is investigated numerically. As was shown by K.J. Vinoy et al., the radiation patterns resemble those of a linear dipole and, for a fixed-area-matched Hilbert antenna, the resonant frequency can be lowered by increasing the iteration order n. However, for such matched antennas, the bandwidth for VSWR<2 is decreased and the cross-polarization level may be different for the higher iteration-order antennas. View full abstract»

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  • A shorted elliptical patch antenna for GPS applications

    Page(s): 6 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB) |  | HTML iconHTML  

    An L1 Global Positioning System (GPS) antenna with improved multipath-rejection capability is presented. The antenna is realized with a shorted annular elliptical patch (SAEP). Some of the characteristics of SAEP are presented briefly and a detailed account of the design is given. Measured results are presented and discussed. View full abstract»

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  • Electromagnetic analysis of effective and apparent diversity gain of two parallel dipoles

    Page(s): 9 - 13
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (311 KB) |  | HTML iconHTML  

    Two parallel dipoles are often used as a reference case for measuring diversity gain. The present paper shows how to calculate the radiation efficiency, effective diversity gain, and apparent diversity gain of two parallel dipoles and how they depend on dipole spacing. We treat several cases for different terminations of the neighboring dipole; open-circuited, short-circuited, and 50 /spl Omega/ termination. The results for 50 /spl Omega/ termination are verified by measurements of effective diversity gain in a reverberation chamber. View full abstract»

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  • Use of modified Gaussian beams to optimize shaped reflectors

    Page(s): 14 - 17
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1030 KB) |  | HTML iconHTML  

    An efficient electromagnetic method for the optimization of shaped reflectors is presented. The repeated computation of scattering from a reflector surface at each iteration, using the conventional numerical techniques of either physical optics (PO) or aperture integration (AI), usually makes the iterative procedures very inefficient for the synthesis of large reflectors. An asymptotic Gaussian beam (GB) technique has been developed and applied successfully to the fast analysis of reflector antennas of various shapes (Cabbage, H.-T. et al., Proc. IEEE Ant. and Propag. Society URSI Symp., vol. 4, p.2336-9, 1999). This GB technique completely avoids numerical integration and thus makes the analysis very efficient. Our method uses the GB technique, coupled with a local description of the primary source and the reflector. The primary source radiation is expanded using a modified Gaussian beams basis. An antenna pattern calculation is demonstrated on a reflector that is described by local parameters in a novel way. By virtue of these local properties and the use of a steep step descent algorithm, a basic display of antenna pattern optimization is presented to illustrate the effectiveness of our method. View full abstract»

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  • Two-dimensional scattering by a periodic array of gyrotropic cylinders embedded in a dielectric slab

    Page(s): 18 - 21
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (370 KB)  

    Two-dimensional scattering of a periodic array of circular homogeneous and gyrotropic-type cylinders embedded in an isotropic dielectric slab is studied using the T-matrix of an isolated circular cylinder and the lattice sums. The T-matrix of a single circular gyrotropic cylinder is given numerically and then the generalized reflection and transmission matrices for the embedded array are obtained using the T-matrix and lattice sums. The harmonic fields in each of the four regions are given analytically. Numerical results of the power reflection and transmission coefficients based on the fundamental mode and the near-scattered field distribution are shown and discussed. View full abstract»

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  • Efficiency of a resistively loaded microstrip patch antenna

    Page(s): 22 - 25
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB) |  | HTML iconHTML  

    Resistive loading has been proposed as a method for improving the bandwidth of planar antennas. The paper assesses the impact of resistive loading on the performance of a microstrip patch antenna. While resistively loaded antennas offer the benefit of large improvements in antenna bandwidth, it is illustrated through the use of theoretical developments, numerical simulations, and experiment, that the efficiency of some of the antennas reported in the literature is unacceptably low. View full abstract»

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  • Compensating for the mutual coupling effect in direction finding based on a new calculation method for mutual impedance

    Page(s): 26 - 29
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (245 KB)  

    A new method for the calculation of mutual impedance is introduced for the compensation of the mutual coupling effect in a dipole antenna array employed for direction finding. This method uses an estimated current distribution and a different method for the calculation of the open-circuit voltage. It is shown that the new method can significantly improve the performance of the array in terms of the sharpness and accuracy of the spatial spectrum response of the MUSIC algorithm. View full abstract»

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  • Miniature built-in quad-band antennas for mobile handsets

    Page(s): 30 - 32
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (285 KB) |  | HTML iconHTML  

    A new built-in quad-band handset antenna for covering GSM900, DCS1800, PCS1900, and UMTS2000 bands is presented. Details of the antenna are discussed along with measured and simulated results. The simulation is based on the finite-difference time-domain (FDTD) method. View full abstract»

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  • Design of an unequally spaced reflectarray

    Page(s): 33 - 35
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (286 KB) |  | HTML iconHTML  

    We present the design and experimental results of an X-band unequally spaced reflectarray of microstrip patch elements. For a given number of elements, it is shown that reduced sidelobe levels can be attained for unequally spaced reflectarrays compared to that of equally spaced reflectarrays with no significant change in directivity and array size. The synthesis tool used for deriving the element positions is a variant of the genetic algorithm, namely the differential evolution algorithm. View full abstract»

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  • Dual-frequency broad-band stacked microstrip patch antenna

    Page(s): 36 - 39
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (479 KB) |  | HTML iconHTML  

    A microstrip antenna formed by two stacked patches is proposed for dual-frequency and broad-band performance. Different E-plane and H-plane arrangements are studied to achieve an isolation between bands better than 30 dB. A prototype operating at the 1.8 GHz and 3.5 GHz bands has been simulated and tested. View full abstract»

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  • On localization aspects of frequency-domain scattering from low-contrast objects

    Page(s): 40 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (233 KB) |  | HTML iconHTML  

    The (phase-space) local spectrum of the field scattered by a low-contrast object due to Gaussian beam incidence is evaluated in the high-frequency regime. The scattering problem is linearized using the Born approximation for which the incident field and local transform domain Green's function can be evaluated asymptotically. The scattering phenomenology is described in terms of local samplings of the object function which are localized in the object domain according to the incidence and processing parameters. Application in the field of inverse scattering are expected to yield fast and efficient algorithms due to the availability of analytic solutions for both the incident wave and the local domain Green's function. View full abstract»

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  • On the use of numerical phantoms in the study of the human-antenna interaction problem

    Page(s): 43 - 45
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (223 KB)  

    The use of numerical phantoms is a common way to attack complex dosimetric problems, such as the near-field human-antenna interaction. The human exposure to the near-field of radiobase antennas is numerically studied using a parallel finite-difference time-domain (FDTD) method, comparing results attained with eight different human numerical phantoms. The effects of the phantom shape and structure on specific absorption rate (SAR) calculation are studied, as well as the error induced by the use of homogeneous phantoms, instead of accurate heterogeneous ones. Results demonstrate that substantial differences can be observed in peak-SAR calculations. View full abstract»

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  • A low-profile wide-band (5:1) dual-pol array

    Page(s): 46 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (657 KB) |  | HTML iconHTML  

    A low profile egg-crate array with wide-band printed flared dipole ("bunny-ear") elements was developed for dual-pol applications. A small test array of 9/spl times/9 elements was built and tested in a 1-5 GHz experiment. Gain and scan element patterns in E-, H-, and diagonal cuts were measured. Excellent results including low cross-pol were observed. View full abstract»

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  • A quadrature-sampled precorrected FFT method for the electromagnetic scattering from inhomogeneous objects

    Page(s): 50 - 53
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    A fast iterative solution for the electromagnetic scattering from inhomogeneous objects computed via the quadrature sampled precorrected fast Fourier transform (QSPCFFT) algorithm is presented. The method is based on a locally corrected Nystrom solution of the volume electric field integral equation. The discontinuous FFT is applied to accelerate the computation of all far interactions. The method preserves the high-order properties of the Nystrom solution, and has a complexity that can scale as O(N log N) and memory that scales as O(N), where N is the number of unknowns. View full abstract»

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  • Hardware implementation of a three-dimensional finite-difference time-domain algorithm

    Page(s): 54 - 57
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    In order to take advantage of the significant benefits afforded by computational electromagnetic techniques, such as the finite-difference time-domain (FDTD) method, solvers capable of analyzing realistic problems in a reasonable time frame are required. Although software-based solvers are frequently used, they are often too slow to be of practical use. To speed up computations, hardware-based implementations of the FDTD method have recently been proposed. Although these designs are functionally correct, to date, they have not provided a practical and scalable solution. To this end, we have developed an architecture that not only overcomes the limitations of previous accelerators, but also represents the first three-dimensional FDTD accelerator implemented in physical hardware. We present a high-level view of the system architecture and describe the basic functionality of each module involved in the computational flow. We then present our implementation results and compare them with current PC-based FDTD solutions. These results indicate that hardware solutions will, in the near future, surpass existing PC throughputs, and will ultimately rival the performance of PC clusters. View full abstract»

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  • Acceleration of the convergence of series containing Mathieu functions using Shanks transformation

    Page(s): 58 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (293 KB) |  | HTML iconHTML  

    A modification of the standard application of Shanks transformation is shown to improve the convergence rate in certain cases where the straightforward application of Shanks transformation fails. Here, the straightforward application of Shanks transformation to a well known series expansion containing Mathieu functions failed to improve the convergence rate. However, convergence was achieved by a new method of applying Shanks transformation. This new method requires analysis of the behavior of the series terms to determine the cause of the slow or failing convergence. Then, the Shanks transformation was applied only to the slowly convergent part of the series. This work is important because, with this new method, convergence may be achieved in cases where the standard application of Shanks transformation fails to improve the convergence rate. The paper takes as a case study the electromagnetic problem of the expansion of a cylindrical wave in a series of Mathieu functions. View full abstract»

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  • Adaptive eigen-projection beamforming algorithms for 1D and 2D antenna arrays

    Page(s): 62 - 65
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    We develop one-dimensional (1D) and two-dimensional (2D) adaptive algorithms that use gradient projections in selected subspaces for use in antenna beamforming. The 1D algorithm is essentially a significantly enhanced version of an eigenspace projection algorithm (EPA) that was previously developed for controls. The 2D algorithm is new and is based on a stacked configuration of the enhanced 1D algorithm. Both algorithms are applied to antenna beamforming in uniform linear and planar arrays. Simulation results show faster convergence as well as improved beam properties. In addition, results for a more realistic scenario, with a BPSK signal and antenna coupling effects, are also quite promising. View full abstract»

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  • The effect of rain attenuation on orthogonally polarized LMDS systems in tropical rain regions

    Page(s): 66 - 67
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    The effect of rainfall is to reduce the link reliability of local multipoint distribution service (LMDS) systems. We study the effects of rain attenuation on the microwave channel in two heavy rainfall tropical cites in Asia for wideband signals using a line-of-sight LMDS link with orthogonal polarizations. This is performed by transmitting signals with horizontal and vertical polarizations with carrier frequencies commonly used in LMDS systems. It is noted that the effect of depolarization due to rain is minimal at around 10 GHz; it is also observed that the rainfall rate has little effect on the difference in attenuation with different polarizations. View full abstract»

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  • Shorting strap tunable single feed dual-band stacked patch PIFA

    Page(s): 68 - 71
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (562 KB) |  | HTML iconHTML  

    A single feed dual-band stacked patch planar inverted-F antenna (PIFA) is integrated with an RF switch array at one side of its shorting straps to make a tunable PIFA. The L-band switch yields 0.45 dB insertion loss (IL) and 10 dB isolation bandwidth (BW) of >100% at 1.2 GHz. The tunable PIFA yields >100% frequency tunability BW at the 800 MHz band and /spl sim/5% BW at the 1.9 GHz band. The measured radiation patterns are nearly omni-directional and yield a gain of 2.2 dBi at 800 MHz and 4.5 dBi at 1.9 GHz. View full abstract»

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  • The need for mixed-order representations with the locally corrected Nystrom method

    Page(s): 72 - 73
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (259 KB) |  | HTML iconHTML  

    The locally corrected Nystrom method can be used to discretize the electric field integral equation (EFIE) for scattering from conducting surfaces. Previous implementations of this technique have employed polynomial-complete representations of the surface current density. Results suggest, however, that polynomial-complete expansions yield inaccurate cross-polarization surface currents. Mixed-order expansions that provide a self-consistent representation of the equivalent charge density appear to alleviate the difficulty. View full abstract»

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  • A simple model for differential rain attenuation statistics on converging terrestrial microwave paths

    Page(s): 82 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB) |  | HTML iconHTML  

    Simple, regression-derived formulas have been generated to estimate differential rain attenuation statistics on converging microwave paths. The proposed expressions are based on a regression fitting analysis implemented on an existing analytical model. The resulting simple model is tested with experimental data taken from Brazil with very good agreement. The impact of differential rain attenuation on the interference performance of a local multipoint distribution system (LMDS) is also studied. View full abstract»

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  • A single-feeding circularly polarized microstrip antenna with the effect of hybrid feeding

    Page(s): 74 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB) |  | HTML iconHTML  

    A single series feed cross-aperture coupled microstrip antenna with the effect of hybrid feeding is proposed and demonstrated. To understand this antenna better, the characteristics according to the variation of parameters are shown. This proposed antenna has the following advantages of the effect of hybrid feeding: improved axial ratio bandwidth (4.6%); high gain (8 dBi); flat 3 dB gain bandwidth (above 16.7%). In measured radiation patterns, we have 3 dB beamwidth of /spl plusmn/30/spl deg/ and good F/B (front to back ratio) of 20 dB. View full abstract»

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  • Narrowband fading analysis of indoor distributed antenna systems

    Page(s): 89 - 92
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    The paper presents the effects of distributed antenna systems (DAS) on the Rice K factor by using practical measurements, in order to investigate the degree of possible fading degradation caused by the incoherent signal combination of the conventional DAS architecture. The measured distributions are compared with the theoretical Rice distribution and it is seen that there is no strong indication to consider any other distributions. It is found that the DAS system slightly decreases the K factor, but not sufficiently to have a detrimental effect on availability. Therefore, it is inferred that the dominant effect of DAS is to provide macro-diversity gain. View full abstract»

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  • Analysis and numerical experiments on the numerical dispersion of two-dimensional ADI-FDTD

    Page(s): 78 - 81
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (113 KB) |  | HTML iconHTML  

    The numerical dispersion relations in the literature are inconsistent for the alternate-direction-implicit finite-difference time-domain (ADI-FDTD) method. By analysis of the amplification factors, the numerical dispersion relation is rederived and verified with numerical experiments, with good agreement. The inconsistency of the numerical dispersion relation is resolved. It is shown that ADI-FDTD has some fundamental limits. For a given time step size, there is a velocity error even for zero spatial mesh. For a given spatial mesh size, the mesh does not support a numerical wave at certain time step sizes. As the Nyquist sampling limit is approached, the velocity of the wave approaches zero. At about twice the Nyquist limit, the wave does not propagate. Hence, the Nyquist criterion should be respected in choosing the time step size. View full abstract»

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  • A circular waveguide antenna using high-impedance ground plane

    Page(s): 86 - 88
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (181 KB) |  | HTML iconHTML  

    A high-impedance ground plane (HIGP) is used for a circular waveguide antenna. The benefits of using such a HIGP are related to the suppression of surface waves excited by the circular waveguide mouth, because the HIGP has a very obvious surface wave bandgap. Suppression or reduction of surface waves is expected to improve antenna efficiency and to bring a reduction of sidelobe level due to diffraction of the surface waves. In agreement with the expected result, the measured radiation patterns show that a 2 dB addition in the antenna gain and a 10 dB reduction in the back lobes, if the circular waveguide antenna working frequency is in the HIGP surface wave bandgap. View full abstract»

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Aims & Scope

IEEE Antennas and Wireless Propagation Letters is devoted to the rapid electronic publication of short manuscripts in the technical areas of Antennas and Wireless Propagation.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Yang Hao
School of Electronic Engineering and Computer Science
Queen Mary College, University of London