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Antennas and Propagation, IEEE Transactions on

Issue 7 • Date July 2003

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Displaying Results 1 - 25 of 35
  • Comments on "Pattern characteristics of harmonic and intermodulation products in broad-band active transmit arrays"

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    [Comments and authors' reply] Active array antenna patterns at harmonic and intermodulation (IM) frequencies have been studied (for original paper see ibid., vol. 50, p. 858-865 (2002)). In particular, the beam directions have been found at IM and harmonic frequencies for different scenarios. Multiple beams may also exist at IM and harmonic frequencies. [Author's reply] Pointing out that a multiple signal transmit array with grating lobes will have intermodulation (IM) lobes associated with the grating lobes, as well as with the main lobe, is an important point. In some array applications, this can be very significant. Also, an array with significant energy radiated at a harmonic could support "harmonic grating lobes" even if the fundamental pattern does not have grating lobes. View full abstract»

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  • Authors' reply [to comments on "Pattern characteristics of harmonic and intermodulation products in broad-band active transmit arrays"]

    Page(s): 1683 - 1684
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (158 KB)  

    The author replies to the comments of Loyka see ibid., vol.51, no.7, p.1683 (2003), Pointing out that a multiple signal transmit array with grating lobes will have intermodulation (IM) lobes associated with the grating lobes, as well as with the main lobe, is an important point. In some array applications, this can be very significant. Also, an array with significant energy radiated at a harmonic could support "harmonic grating lobes" even if the fundamental pattern does not have grating lobes. View full abstract»

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  • A hybrid evaluation method for the full-wave analysis of microstrip structures

    Page(s): 1656 - 1658
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (230 KB) |  | HTML iconHTML  

    A hybrid evaluation method using both the spectral- and the spatial-domain techniques is proposed for the evaluation of the Sommerfeld-type integrals resulting from the full-wave analysis of microstrip structures. This method combines the advantages of the spectral-domain for the evaluation of near fields and the spatial-domain method for the evaluation of far-fields. This method is simple and needs no additional formulations. It also provides an easy alternative method to handle the inefficiency of calculation with the singularity of the Green's function. Numerical results are used to demonstrate the simplicity and the accuracy of this method. View full abstract»

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  • A stabilized resistive voltage source for FDTD thin-wire models

    Page(s): 1615 - 1622
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB) |  | HTML iconHTML  

    The von Neumann analysis is applied to investigate the stability of a source connected on a wire described by a thin-wire model. Both a soft source and a resistive voltage source (RVS) are shown to limit the stable range of values for wire radius or time step. Using the von Neumann analysis, a stable RVS model for thin wires is developed. The proposed model is verified by comparison with a hard source, an original RVS and NEC-generated reference data. The stabilized RVS introduces no additional stability constraints on those of the wire model while maintaining fast decay of incident fields of the original RVS model. View full abstract»

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  • Resonant frequency of circular microstrip antenna covered with dielectric superstrate

    Page(s): 1649 - 1652
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (349 KB) |  | HTML iconHTML  

    A simple design formulation to compute accurate resonant frequencies of circular microstrip antennas covered with dielectric superstrates is proposed. It alleviates the rigorous mathematical analyzes and large computational time of some earlier works. This theory is widely applicable to both high and low dielectric constant superstrates as verified with the experiments and other theoretical models. Of all theories, the present one shows the closest approximation with the measurements revealing average percent error as low as 0.52%. The extension of this formulation to predict the accurate design data for conventional microstrip circular antennas are also verified with different experiments and available improved theories for various sets of antenna parameters. View full abstract»

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  • On the possibility of aperture synthesis with a single mobile antenna in radio astronomy

    Page(s): 1658 - 1662
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (449 KB) |  | HTML iconHTML  

    The classic aperture synthesis widely used in radio astronomy, synthetic aperture radar, and remote sensing is based on the measurement of the degree of spatial coherence in the diffraction pattern of a radio emission source. All these applications imply correlation with a coherent reference signal. The possibility of obtaining the same information from the autocorrelation of a signal recorded on a single, mobile antenna is considered. Comparison of the output of an ordinary cross-correlation two-element radio interferometer and the autocorrelation output of a mobile antenna shows a similarity that allows extraction of information about the radio source spatial coherence in the latter case. The limitations of this method of aperture synthesis are considered. View full abstract»

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  • An efficient method for attaching thin wire monopoles to surfaces modeled using triangular patch segmentation

    Page(s): 1623 - 1629
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (411 KB) |  | HTML iconHTML  

    A general method is described for attaching thin wires to surfaces segmented with triangular patches which allows significant versatility in their positioning, whilst maximizing computational efficiency by preserving all of the surface segmentation when wires are added or moved, apart from at the connection patch. Variations on the general methodology of single patch subsegmentation are investigated by introduction of convergence metrics and comparisons with controls for input impedances at the monopole bases. View full abstract»

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  • Design of a frequency selective surface (FSS) with very low cross-polarization discrimination via the parallel micro-genetic algorithm (PMGA)

    Page(s): 1664 - 1668
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (402 KB) |  | HTML iconHTML  

    We discuss the design of a frequency selective surface (FSS) with low cross-polarization discrimination. In the past, FSS screens have been employed to improve the cross-polarization performance. The objective of this paper is to synthesize an FSS subreflector with low cross-polarization via the application of a parallel binary coded micro-genetic algorithm (PMGA). The PMGA optimizes the metallization pattern and the periodicity of the FSS screen in both the x- and y-directions to maintain a low cross-polarization level for a wide band of frequencies and a range of incident angles. View full abstract»

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  • Evaluation of the Green's function for the mixed potential integral equation (MPIE) method in the time domain for layered media

    Page(s): 1559 - 1571
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (867 KB)  

    In the use of the time-domain integral equation (TDIE) method for the analysis of layered media, it is important to have the time-domain layered medium Green's function computed for many source-to-field distances ρ and time instants t. In this paper, a numerical method is used that computes the mixed potential Green's functions Gv(ρ,t) and GA(ρ,t) for a multilayered medium for many ρ's and t's simultaneously. The method is applicable to multilayered media and for lossless or lossy dispersive media. Salient features of the method are: 1) the use of complex ω so that the surface wave poles are lifted off the real kρ axis such that pole extractions are not required; 2) the use of half-space extraction so that the integrand for the Sommerfeld integral decays exponentially along the kρ axis to obtain fast convergence of the integral; and 3) the use of the fast Hankel transform so that the Green's function is calculated for many values of ρ simultaneously. For a four-layer medium, we illustrate the numerical results by a three-dimensional plot of ρGv(ρ,t) versus ρ and t and demonstrate the space-time evolution of these Green's functions. For a maximum frequency range of 8 GHz, the method requires only a few CPU minutes to compute a table of 100 (points in ρ) × 168 (points in t) uniformly spaced values of Gv(ρ,t) on an 867-MHz Pentium PC. View full abstract»

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  • Broadband design of three-layer printed reflectarrays

    Page(s): 1662 - 1664
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (307 KB) |  | HTML iconHTML  

    A method is proposed to design three-layer printed reflectarrays with patches of variable size for broadband operation. The patch dimensions are adjusted by an optimization routine to achieve the required phase distribution in a given frequency band. A 1-meter reflectarray was designed, and significant bandwidth and gain stability improvements were obtained. View full abstract»

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  • Rectangular and zonal slots on a sphere with a backing shell: theory and experiment

    Page(s): 1434 - 1442
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (683 KB) |  | HTML iconHTML  

    A rectangular slot antenna on a spherical cavity with a conducting backing shell is investigated rigorously. The Green's function approach is used to formulate an integral equation for the magnetic slot current, which is solved using the moment method. Two previously developed methods to evaluate the admittance integrals are used and compared with each other. Both methods use recurrence formulas and analytical integration to speed the computation. The slot and cavity resonances of the structure are studied. In particular, two simple formulas for the first two natural resonances of the cavity structure are given. The effects of the shell size, slot length, and cavity dielectric constant on the input impedance are discussed. Measurements were carried out to verify the theory, and very good agreement between theory and experiment is obtained. In addition, the zonal slot antenna on a spherical cavity with a conducting backing shell is studied. The effect of the shell radius on the input impedance is investigated and, again, very good agreement between theory and experiment is found. View full abstract»

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  • A novel TLM-based time-domain wave propagator

    Page(s): 1679 - 1680
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (723 KB) |  | HTML iconHTML  

    In this letter, a novel time-domain wave propagator, based on the transmission line matrix (TLM) technique, is introduced. A two-dimensional (2-D) TLM algorithm is modified and the sliding window technique is applied to analyze ground wave propagation characteristics. The longitudinal propagation region over the Earth's surface is covered by a finite-size TLM computation space, as if the space slides from source to observation point. A short pulse is injected into the TLM computation space as a vertical initial source distribution near the left end and is traced within an adjustable window while propagating towards the right. Perfectly matched layer (PML) blocks on the left, top and right terminate the TLM computation space to simulate the semi-open propagation region. The ground at the bottom is a perfect electrical conductor (PEC). The PML blocks absorb field components that scatter back and top. The ground wave components (i.e., the direct, ground-reflected and surface waves) are traced longitudinally towards the right. Transient propagation can be observed at any range/altitude by accumulating the time history of the desired field components and any steady-state vertical and/or horizontal field profile at a desired frequency can be extracted by applying the off-line discrete Fourier transformation (DFT). View full abstract»

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  • Accurate and efficient numerical integration of weakly singular integrals in Galerkin EFIE solutions

    Page(s): 1630 - 1637
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (453 KB)  

    A Galerkin descretization of the electric field integral equation for perfectly conducting surfaces using Rao-Wilton-Glisson (1982) basis functions requires the numerical evaluation of integrals with singular kernels over triangular regions. These singularities have been traditionally handled by utilizing a "singularity extraction" procedure to produce a regular integral and an analytic function to replace the original singular integral. A new approach is presented here in which the four-dimensional (4-D) weakly singular integrals unique to the Galerkin Rao-Wilton-Glisson electric field integral equation solution for perfectly conducting surfaces are transformed into integrals with regular integrands. The transformations allow some of the integrations to be performed analytically, in some cases reducing the original 4-D integral into a 1-D numerical integration. The accuracy and convergence properties of the new method are demonstrated by evaluating the scalar potential function over a unit triangle. View full abstract»

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  • Acoustic and electromagnetic wave interaction: estimation of Doppler spectrum from an acoustically vibrated metallic circular cylinder

    Page(s): 1499 - 1507
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (611 KB) |  | HTML iconHTML  

    The idea of using acoustically induced Doppler spectra as a means of target detection and identification is introduced. An analytical solution for the calculation of the bistatic scattered Doppler spectrum from an acoustically excited, vibrating, metallic, circular cylinder is presented. First, the electromagnetic scattering solution of a slightly deformed circular cylinder is obtained using a perturbation method. Then, assuming the vibration frequency is much smaller than the frequency of the incident electromagnetic wave, a closed form expression for the time-frequency response of the bistatic scattered field is obtained which can be used directly for estimating the Doppler spectrum. The acoustic scattering solution for an incident acoustic plane wave upon a solid elastic cylinder is applied to give the displacement of the cylinder surface as a function of time. Results indicate that the scattered Doppler frequencies correspond to the mechanical vibration frequencies of the cylinder, and the sidelobe Doppler spectrum level is, to the first order, linearly proportional to the degree of deformation and is a function of bistatic angle. Moreover, the deformation in the cylinder, and thus the Doppler sidelobe level, only becomes sizeable near frequencies of normal modes of free vibration in the cylinder. Utilizing the information in the scattered Doppler spectrum could provide an effective means of buried object identification, where acoustic waves are used to excite the mechanical resonances of a buried object. View full abstract»

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  • Electromagnetic diffraction from metallic deep cross-gratings

    Page(s): 1669 - 1670
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (277 KB) |  | HTML iconHTML  

    In order to have a benchmark solution for the electromagnetic scattering from a rough metallic surface, the particular case of a metallic plate hollowed with identical and regularly spaced cavities of sufficiently simple shape was studied. Hemispheroidal cavities allow us to carry out a rigorous theoretical statement (modal method) which particularly may be applied to very deep irregularities (strong ellipticity). Our numerical results are compared with previous ones obtained with a cross-grating of hemispherical cavities and mainly with an experimentation we have specially performed in the microwave range. View full abstract»

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  • A higher-order on-surface radiation condition derived from an analytic representation of a Dirichlet-to-Neumann map

    Page(s): 1607 - 1614
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB) |  | HTML iconHTML  

    On-surface radiation conditions are useful for obtaining approximate solutions to scattering problems involving compact obstacles. An analytic representation of the Dirichlet-to-Neumann map for a circle is derived and used to construct a higher-order on-surface radiation condition for a generally convex perfectly conducting body in two dimensions. This approach is based on a Hankel function in which a tangential operator appears in the index. In the high-frequency limit, this analytic representation approaches the square root of a differential operator which commonly arises in the application of parabolic equation techniques to propagation problems. Treating the scattered field propagation angle relative to the surface normal and the surface curvature as independent parameters, the representation is fit to a rational function to provide an accurate and efficient on-surface radiation condition that is tested for various examples. View full abstract»

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  • Green's function for an infinite slot printed between two homogeneous dielectrics. I. Magnetic currents

    Page(s): 1572 - 1581
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB)  

    This sequence of papers presents an analytical closed form for the Green's function of an infinite slot printed between two different homogeneous dielectrics. This first part is devoted to the derivation of the slot magnetic current and to the discussion of the relevant physical implications. The Fourier spectrum of the magnetic current is derived by solving in analytical form, under small width approximation, the integral equation (IE) representing the continuity of the magnetic field trough the slot axis. The accuracy of the result is validated trough a fine meshing Method of Moments. From the consequent spectral expression, a closed form approximation of the leaky-wave propagation and attenuation constants is derived. An asymptotic expression for the current is also obtained by steepest descent path evaluation of the pertinent spectral integral. Analytical expressions of the quasi static (reactive) contribution is given for both elementary dipole and delta gap excitations. View full abstract»

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  • Adaptive control and optimization of electromagnetic radiation, attenuation, and scattering using self-adaptive material systems

    Page(s): 1530 - 1548
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1684 KB)  

    Adaptive control of radiation and scattering by integrated antenna arrays in the long-wavelength limit is investigated. A hybrid active/passive system with embedded control logic is considered and analyzed as a synthetic composite medium with adaptive constitutive parameters. Optimal control techniques yield the transfer function of the controller for a given internal or external stimulus and cost function. The method is applied to the minimization of radiated or scattered power at large distance. A limiting condition for omnidirectional power reduction is derived. A chequered planar array of interleaved subarrays for wave conditioning in reflection and transmission is analyzed in detail. Its dyadic Green function, impedance, equivalent permittivity, and reflection, transmission and radiation coefficients for general transfer functions are calculated. For random configurations, the effective permittivity and frequency response of the reflection and transmission by a free-standing slab of the self-adaptive medium are analyzed. The results may find application in the design and operation of electromagnetic smart materials. View full abstract»

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  • A self-similar fractal radiation pattern synthesis technique for reconfigurable multiband arrays

    Page(s): 1486 - 1498
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1357 KB)  

    A novel method for designing reconfigurable multiband linear and planar antenna arrays is presented. The technique is based on a generalized Fourier series synthesis approach that exploits the self-similarity of a specified fractal radiation pattern in order to achieve the desired multiband performance. The fractal radiation patterns are composed of scaled and shifted copies of an appropriately chosen generating window function that exhibits low sidelobe levels and rapid spectral rolloffs in the transform domain. A newly developed thinning algorithm is presented which may be employed to reduce considerably both the overall physical size and the total number of elements in a synthesized multiband array. Finally, a band-switching scheme is introduced that is well-suited for implementation in the form of a reconfigurable common aperture array. View full abstract»

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  • Gain enhancement of a circularly polarized equilateral-triangular microstrip antenna with a slotted ground plane

    Page(s): 1652 - 1656
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (804 KB) |  | HTML iconHTML  

    A novel circular polarization (CP) design of a single-feed equilateral-triangular microstrip antenna with enhanced antenna gain is presented. This CP design is obtained by placing three triangular slots at properly locations below the equilateral-triangular radiating patch in the ground plane. By adjusting one of the triangular slot's side lengths slightly longer than that of the others, two orthogonal near-degenerate resonant modes for CP radiation can be excited. Measured antenna gain in this study can easily be increased by 3.3 dBi (5.1 dBi versus 1.8 dBi), as compared to the same height, substrate material, operating frequency and radiating patch shape of a regular equilateral-triangular microstrip antenna without triangular slots in the ground plane. Prototype antenna is fabricated for experimental evaluation. Simulated and measured results are presented. View full abstract»

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  • Optimized basis functions for slot antennas excited by coplanar waveguides

    Page(s): 1638 - 1646
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (769 KB) |  | HTML iconHTML  

    A method is proposed for the analysis of slot antennas excited by coplanar waveguides. First, a standard integral equation for the continuity of the magnetic field is formulated. Then the appropriate equivalent magnetic currents of the method of moments are represented in terms of entire-domain basis functions which synthesize the resonant behavior of the slot and the field in proximity of the feeding source and of the bends. In order to define these basis functions, canonical geometries are identified, whose Green's functions have been found analytically. The accuracy and the effectiveness of the method in terms of convergence rate and number of unknowns is demonstrated by comparison with a standard fine meshing full-wave analysis. View full abstract»

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  • Realization of space-time adaptive filtering by employing electronically steerable passive array radiator antennas

    Page(s): 1476 - 1485
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (694 KB) |  | HTML iconHTML  

    Electronically steerable passive array radiator (ESPAR) antennas are considered to have the capability to form a beam spatially toward the desired signal with the lowest cost. We propose a method to realize space-time adaptive filtering (STAF) by employing ESPAR antennas for TDMA or CDMA signal waveforms. According to the method, the cochannel interference signals are spatially suppressed by the adaptive beamforming, and the intersymbol interference signals are suppressed by the temporal waveform-based adaptive equalization. Simulation results show the effectiveness of the proposed method in the signal environment of a local network communication system. View full abstract»

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  • New wavelet based approach for time domain simulations

    Page(s): 1590 - 1598
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (770 KB) |  | HTML iconHTML  

    A new numerical method for the time domain solution of Maxwell's equations in linear media is proposed in this paper. The field quantities derived from the spatial discretization of Maxwell's equations are expanded in the time domain by wavelets on the interval. This choice yields a new arrangement of the unknowns into a matrix (instead of the usual vector) and transforms the differential equations in time in a Sylvester (1983) matrix equation. The memory requirements are proportional to the number of spatial unknowns and the time evolution of the space quantities is obtained with better accuracy than in conventional marching-on-time techniques. View full abstract»

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  • Characteristics and design of the LAR offset system with feed-reflector

    Page(s): 1462 - 1475
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1275 KB)  

    A novel approach for analyzing the quasi-optical offset large adaptive reflector (LAR) Cassegrain system is described. In this system, a feed-reflector is used to illuminate a reconformable hyperboloid subreflector with 5-10 m diameter, located 500 m above the ground. An exact equation for the offset LAR surface is given. To scan the beam up to 60° which is one of the LAR requirements, the concept of the dual offset LAR with feed-reflector is introduced. In this design, the cross polarization is eliminated by a proper orientation of the subreflector. The parameters of the configuration are obtained by utilizing generalized Gauss-Laguerre beam modes and matrix representation of the beam mode transformation factor. The blockage effect due to the feed-reflector is totally removed. View full abstract»

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  • An inverted U-shaped patch antenna for compact operation

    Page(s): 1647 - 1648
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (298 KB) |  | HTML iconHTML  

    By using a novel inverted U-shaped radiating patch in place of the conventional planar patch, compact operation of air-substrate patch antennas is presented. The inverted U-shaped patch is formed by adding two downward rims at the two radiating edges of a planar rectangular or square patch. And owing to the added rims, the excited patch's surface current paths are lengthened, which effectively lowers the antenna's resonant frequency and results in large antenna size reduction (>50%). The proposed compact design has been successfully applied to air-substrate patch antennas fed by an aperture-coupled feed. In addition to large size reduction obtained, the proposed antenna with an air-substrate thickness about 5% the wavelength of the center operating frequency can have an impedance bandwidth (10-dB return loss) greater than 9%, a peak antenna gain of about 6.4 dBi, and good broadside radiation patterns with cross-polarization levels better than 20 dB in principal planes. 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