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Antennas and Propagation, IEEE Transactions on

Issue 11  Part 2 • Date Nov. 2007

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Displaying Results 1 - 25 of 44
  • Table of contents

    Page(s): C1 - 3113
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  • IEEE Transactions on Antennas and Propagation publication information

    Page(s): C2
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  • An Offset Linear-Array-Fed Ku/Ka Dual-Band Reflectarray for Planet Cloud/Precipitation Radar

    Page(s): 3114 - 3122
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1766 KB) |  | HTML iconHTML  

    A Ku/Ka band dual-frequency offset array-fed microstrip reflectarray antenna using thin membranes has been developed. This antenna is a demonstration model for the next generation titan cloud precipitation radar and altimeter (TCPRA) and is intended to enhance the capability of the future cloud and precipitation remote sensing system for Earth and other planets. The reflectarray has a dimension of 0.5-m square and a flat aperture that emulates a cylindrical reflector antenna. Two sets of linear arrays with linearly polarized microstrip elements and having low cross polarization and low sidelobe levels (SLL) are placed along the focal line to illuminate the reflectarray. One set is for Ku-band, while the other is for Ka-band. Within each set, the wide-swath scanning capability of the antenna is provided by the two fixed-beam feed arrays with one for broadside beam and the other one for a 20deg tilted beam. The unique feature of this paper is that this is the first offset-fed reflectarray that has ever been practically developed to emulate a cylindrical/parabolic type of reflector antenna. In addition, new dual-concentric-ring elements and ring-patch elements are uniquely applied here to achieve the desirable wide phase variation characteristics. Tests of feed arrays and the reflectarray in the anechoic chamber of Texas A&M University result in good pattern performance and the successful demonstration of beam scanning at both frequency bands. View full abstract»

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  • Design and Test of a Mobile Antenna System With Tri-Band Operation for Broadband Satellite Communications and DBS Reception

    Page(s): 3123 - 3133
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    The tri-band mobile antenna system for broadband multimedia services in the Ka/K-band and a simultaneous direct broadcast service in the Ku-band has been developed. The radiating part of the antenna consists of a shaped dual reflector system and a tri-band feed of circular polarization. The low-profile offset main reflector has an aperture size of 60 cm 20 cm; therefore, a fan beam is formed which is sharp in azimuth and wide in elevation. The feed system contains a protruding dielectric rod for Ka/K-band and 2 2 active phased array. The latter provides the beam for Ku-band along with four fast electrical beams for stable satellite tracking. The new tracking algorithm based on a fusion technique involving various sensors and fast electrical beams has also been introduced. The antenna system was mounted on a large ship and a test car, and successfully operated via Koreasat-3. View full abstract»

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  • Design of Circularly Polarized Annular-Ring Slot Antennas Fed by a Double-Bent Microstripline

    Page(s): 3134 - 3139
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    A novel design of a circularly polarized annular-ring slot antenna is discussed. The circular polarization is attained through a newly proposed double-bent microstripline that feeds the antenna at two different positions. Several structural parameters were experimentally studied with care to establish a design procedure, which was subsequently drawn into a design flow chart. Validation was carried out using the antennas designed at 3.5 and 1.59 GHz. The measured 3-dB axial-ratio bandwidth (ARBW) for the former is 10.5% and for the latter, 10.0%, which is larger than the 8.5% 3-dB ARBW required by an Inmarsat application. View full abstract»

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  • Gain Enhancement of a Microstrip Patch Antenna Using a Cylindrical Electromagnetic Crystal Substrate

    Page(s): 3140 - 3145
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    The performance of a circular microstrip patch antenna is improved using a new cylindrical electromagnetic bandgap (EBG) substrate. The microstrip patch antenna is fed by a coaxial probe and is integrated within a cylindrical electromagnetic bandgap substrate, based on the mushroom-like substrate, to increase the antenna gain. The cylindrical electromagnetic bandgap structure is a combination of two periodic structures with different periods. One is made of metallic rings and the other of grounding vias, which are disposed such as to form a radially and circularly periodic structure. A parametric analysis using a full-wave method was carried out in order to design the EBG structure. With the proposed concept, an antenna prototype was fabricated and tested. The radiation patterns and return loss obtained from measurements show a good impedance matching and a gain enhancement of the proposed antenna. View full abstract»

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  • Convolution Constraints for Broadband Antenna Arrays

    Page(s): 3146 - 3154
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    Directional constraints are imposed on the weights of an antenna array to obtain solutions of some constrained beamforming problems. For broadband antenna arrays, formulation of a constrained beamforming problem typically requires presteering the array using steering delays. These delays create implementation problems and cause loss of system performance in the presence of implementation errors. This paper presents new kind of constraints referred to as convolution constraints, which are easy to implement, eliminate the need for presteering the array and can be used for broadband pattern synthesis. Examples are presented to demonstrate many applications of these constraints on an array weights. View full abstract»

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  • Dualband Split Dielectric Resonator Antenna

    Page(s): 3155 - 3162
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    A dualband dielectric resonator antenna (DRA) is designed by splitting a rectilinear dielectric resonator (DR) and carving notches off the DR. It is observed that notches engraved at different positions affect different modes. Removal of dielectric material from where the electric field is strong incurs a significant increase in resonant frequency. The abrupt change of normal electric field across the discontinuities reduces the -factor and increases the impedance bandwidth. Both the and modes incur broadside radiation patterns on the -plane. The proposed DRA can cover both the worldwide interoperability for microwave access (WiMAX, 3.4-3.7-GHz) and the wireless local area network (WLAN, 5.15-5.35-GHz) bands. View full abstract»

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  • Analysis of the Equiangular Spiral Antenna on a Dielectric Substrate

    Page(s): 3163 - 3171
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    While the first equiangular spiral antennas were slots cut from a thin conductive sheet, the widespread availability of cheap photoetching fabrication has made it more common for the spiral to be printed on a dielectric substrate. This paper examines the effects of the substrate on the spiral's performance. The finite-difference time-domain (FDTD) technique is used to model the spiral over a range of configurations. The results are used to construct a design graph that shows that the substrate significantly affects the impedance of the antenna. The results also show that the substrate can negatively impact the bore-sight gain and radiation patterns. Measurements from two spirals are used to verify the accuracy of the numerical model. View full abstract»

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  • Approximate Expansion of a Narrow Gaussian Beam in Spherical Vector Wave Functions

    Page(s): 3172 - 3177
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    The expansion of electromagnetic sources is fundamental to the analysis of field propagation and scattering. Of these electromagnetic sources, one of the most commonly used optical sources is the narrow Gaussian beam. It is, therefore, useful to find an expansion of the narrow Gaussian beam that could be used in applications such as scattering and propagation studies in free-space and materials. The approximate method of expansion here is based on an exact expansion that was obtained for a vector plane wave in terms of spherical vector wave functions. Since the simpler vector plane wave representation that previously enabled an exact solution is replaced here by the more complicated narrow Gaussian beam representation, an approximation of the associated Legendre function will be applied in order to obtain an approximate expansion of a narrow Gaussian beam in terms of spherical vector wave functions. Although the expansion is taken about the source point, field points close to the beam axis located at distances near and far from the source are found to have good accuracy. View full abstract»

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  • EM Field Induced in Inhomogeneous Dielectric Spheres by External Sources

    Page(s): 3178 - 3190
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (638 KB) |  | HTML iconHTML  

    The electromagnetic field induced in the interior of inhomogeneous dielectric bodies by external sources can be evaluated by solving the well-known electric field integrodifferential equation (EFIDE). For spheres with constant magnetic permeability but variable dielectric constant , a direct, mainly analytical solution can be used even in case when the inhomogeneity in renders separation of variables inapplicable. This approach constitutes a generalization of the hybrid (analytical-numerical) scalar method developed by the authors in two recent papers, for the corresponding acoustic (scalar) field induced in spheres with variable density and/or compressibility. This extension, by no means trivial, owing to the vector and integrodifferential nature of the equation, is based on field-vector expansions using the set of three harmonic surface vectors, orthogonal and complete over the surface of the sphere, for their angular dependence, and Dini's expansions of a general type for their radial functions. The use of the latter has been shown to be superior to other possible sets of orthogonal expansions and as far as its convergence is concerned it may further be improved by properly choosing a crucial parameter in their eigenvalue equation. The restriction to the spherical shape is imposed here to allow use of the well-known expansion of Green's dyadic in spherical eigenvectors of the vector wave equation. View full abstract»

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  • A Transmission Line Method to Compute the Far-Field Radiation of Arbitrary Hertzian Dipoles in a Multilayer Structure Embedded With PEC Strip Interfaces

    Page(s): 3191 - 3198
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    A transmission line (TL) method was proposed to compute the far-field radiation of Hertzian dipoles in a multilayer dielectric structure previously. This method is generalized here to deal with a structure embedded with perfectly electric conducting (PEC) strip interfaces. The problem is solved by analyzing an equivalent network, where each PEC strip interface is mapped into a four-port network, and each dielectric layer is mapped into two two-port networks for transverse electric (TE) and transverse magnetic (TM) modes. The S matrix of a four-port network is obtained analytically by applying the asymptotic boundary conditions. As an application, the PEC strip interfaces are used to reduce the cross polarization or rotate the polarization of a dielectric resonator antenna (DRA). In addition, the TL method is valid for a structure with any type of homogeneous and reciprocal layers whose S matrices are known. It is also able to solve two kinds of problems which cannot be done by a full-wave analysis equipped with a periodic boundary condition. Furthermore, the investigation of the system matrix singularity helps us to avoid the cavity mode in designing a radiating structure. View full abstract»

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  • Revisiting the Stability of Crank–Nicolson and ADI-FDTD

    Page(s): 3199 - 3203
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    The stability properties of Crank-Nicolson (CN) and alternating direction implicit finite-difference time-domain ADI-FDTD methods to solve Maxwell's equations are investigated. Since the ADI-FDTD scheme can be formulated in many cases as an approximation to a CN-FDTD scheme, we start by analyzing the stability of CN-FDTD and, from it, we try to derive conditions on ADI-FDTD. We first recall the von Neumann analysis, and then we present a matrix-norm analysis. We show that the matrix-norm stability of CN-FDTD is a necessary condition to find matrix-norm stable conditions for ADI-FDTD. View full abstract»

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  • On the Use of the Geometric Mean in FDTD Near-to-Far-Field Transformations

    Page(s): 3204 - 3211
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    Near-to-far-field transformations require the tangential electric and magnetic fields over a surface, which we call the integration boundary. However, the staggered nature of the finite-difference time-domain grid is problematic in that the electric and magnetic fields are not collocated in either space or time. For harmonic transformations, i.e., ones which rely upon a Fourier transform of the time-domain near-fields, one can account for the temporal offset with a simple phase correction in the frequency domain. To account for spatial offsets, previously an arithmetic mean of the time-domain fields to either side of the integration boundary has been used. Here we show that superior results are obtained by instead using a geometric mean of the harmonic fields to either side of the integration boundary. View full abstract»

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  • A New Spatial Interpolation Algorithm to Reduce the Matrix Fill Time in the Method of Moments Analysis of Planar Microstrip Structures

    Page(s): 3212 - 3219
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    A new spatial interpolation scheme is proposed to reduce the matrix fill time in the method of moments implementation of planar microstrip structures. The approach is based on the division of the distance between the basis and the testing functions into three, namely near, intermediate and far regions. The matrix entries in the near region are computed directly. The entries corresponding to both intermediate and far regions are evaluated in two steps: (1) choosing an adequate number of sampling points in these regions and computing the associated entries directly and (2) interpolating the remaining entries by using cubic spline or bicubic spline algorithms. To demonstrate the efficiency and accuracy, the technique is applied to a planar microstrip low-pass filter and a microstrip-line fed patch antenna problems. It is shown that the interpolation scheme can result in significant savings with high accuracy. View full abstract»

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  • Fast Direct Solution of Method of Moments Linear System

    Page(s): 3220 - 3228
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    A novel algorithm, the compressed block decomposition (CBD), is presented for highly accelerated direct (noniterative) method of moments (MoM) solution of electromagnetic scattering and radiation problems. The algorithm is based on a block-wise subdivision of the MoM impedance matrix. Impedance matrix subblocks corresponding to distant subregions of the problem geometry are not calculated directly, but approximated in a compressed form. Subsequently, the matrix is decomposed preserving the compression. Examples are presented of typical problems in the range of 5000 to 70000 unknowns. The total execution time for the largest problem is about 1 h and 20 min for a single excitation vector. The main strength of the method is for problems with multiple excitation vectors (monostatic RCS computations) due to the negligible extra cost for each new excitation. For radiation and scattering problems in free space, the numerical complexity of the algorithm is shown to be N 2 and the storage requirements scale with N 3/2 . View full abstract»

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  • Spectral Properties of the EFIE-MoM Matrix for Dense Meshes With Different Types of Bases

    Page(s): 3229 - 3238
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    The relationship between the properties of the basis functions employed to discretize the electric field integral equation (EFIE) and the eigenvalue spectrum of the resulting method of moments (MoM) matrix is studied. We concentrate on dense meshes, i.e., on complex geometries with large number of unknowns per wavelength, and/or disparate mesh cells sizes, and/or low frequency. These are typical occurrences in antennas, packaging and microwave circuits. We show that if the basis functions have separated Fourier spectra, the diagonal MoM matrix entries are close to the eigenvalues, and explain it in terms of the Fourier spectrum of the Green's function. For such a basis, diagonal preconditioning drastically reduces the condition number. This does not happen with sub-domain basis functions like the Rao-Wilton-Glisson (RWG), or with their linear combination into loop-tree or loop-star bases that are employed to solve low-frequency problems. Finally we analyze the properties of a multiresolution (MR) basis formed by linear combinations of RWG, but whose functions possess some degree of (Fourier) spectral resolution. We show that there is still correspondence between matrix diagonal, Green's function (Fourier) spectrum, and matrix eigenvalues. Diagonal preconditioning of the MR-MoM matrix causes the eigenvalues to cluster around 1, as it happens with the MoM matrix for the magnetic field integral equation. This strongly impacts on the EFIE matrix condition number and the speed of convergence of iterative solvers. View full abstract»

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  • Exponentially Converging NystrÖm Methods Applied to the Integral-Integrodifferential Equations of Oblique Scattering/Hybrid Wave Propagation in Presence of Composite Dielectric Cylinders of Arbitrary Cross Section

    Page(s): 3239 - 3250
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    Systems of singular integral-integrodifferential equations are studied that pertain to 2-D oblique scattering and to hybrid-wave propagation in presence of a dielectric cylinder with arbitrarily shaped smooth boundary. These systems, having the tangential to the surface of the cylinder components of the electric and magnetic fields as the unknowns, are solved via fast, highly accurate algorithms that rely on the Nystrom method (NM). Because of our specialized treatment, the present solution technique has the following characteristics: (1) it fully accounts for the singular nature of the kernels, (2) it appears to converge exponentially, and (3) it yields simple closed-form expressions for all matrix elements. In addition, an extension of the analysis is presented to account for composite dielectric cylinders that contain arbitrarily shaped dielectric or conducting cylindrical inclusions. Numerical examples and case studies illustrate the simplicity, flexibility, and efficiency of the algorithms. Exhaustive comparisons with available results for several special cases serve to test the correctness of the implementation and bring to light the extremely high accuracy of our algorithms. View full abstract»

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  • Hybrid Periodic Boundary Condition for Particle Swarm Optimization

    Page(s): 3251 - 3256
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (788 KB) |  | HTML iconHTML  

    A molecular dynamics (MD) formulation of particle swarm optimization (PSO) is established formally. Based on this analogy, the periodic boundary condition (PBC) is introduced to the PSO method by postulating that the swarm environment is similar to crystal bulk materials studied using MD. A combination of soft and hard boundary modes is employed in the formulation of the hybrid version of the proposed PBC. The hybrid version represents a substantial modification of the scenario assumed in theoretical physics but is allowed here to suit the PSO environment. The hybrid PBC proved to be superior to previously established boundary conditions when applied to standard test functions and the practical problem of linear antenna array synthesis. View full abstract»

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  • Calculation of the Dynamic Input Parameter for a Stochastic Model Simulating Rain Attenuation: A Novel Mathematical Approach

    Page(s): 3257 - 3264
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (621 KB) |  | HTML iconHTML  

    The Maseng-Bakken model simulates rain attenuation induced on a microwave link, and it accepts as input three parameters: the first two coincide with the parameters belonging to the conditional lognormal cumulative distribution of rain attenuation while the third one-called the dynamic parameter hereafter-should be assigned appropriately so that the model reflects some particular dynamic properties of rain attenuation. Thus far, the dynamic parameter has been calculated with emphasis on the simulation of the spectral density function of rain attenuation. This in turn, does not necessarily imply that the Maseng-Bakken model also simulates other crucial statistical features of rain attenuation such as Fade/Inter-Fade Duration Statistics. In this paper, we demonstrate a novel mathematical algorithm that gives the optimum value for the dynamic parameter so that the Maseng-Bakken model approximates simultaneously both second-order and hitting time statistics, with the latter being quite similar to Fade/Interfade durations. The algorithm is exemplified through the simulation of rain attenuation affecting a satellite channel which operates at 20 GHz and connects Athens with Hellas-Sat 2. The results show that the optimum value for the dynamic parameter is much more "sensitive" to hitting time statistics-and probably to fade durations statistics as well-than it is to the spectral density function of rain attenuation. View full abstract»

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  • An Adaptive Multiscaling Imaging Technique Based on a Fuzzy-Logic Strategy for Dealing With the Uncertainty of Noisy Scattering Data

    Page(s): 3265 - 3278
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    Inverse scattering data, even though collected in a controlled-environment, are usually corrupted by noise, which strongly affects the effectiveness of the reconstruction techniques because of the intrinsic ill-positioning of the problem. In order to limit the effects of the noise on the retrieval procedure and to fully exploit the information content available from the measurements, an innovative inversion scheme based on the integration of an adaptive multiscale procedure and a fuzzy-logic (FL)-based strategy is proposed. The main goal of the approach is to reduce the complexity of the problem as well as to improve the robustness of the inversion procedure allowing an accurate retrieval of the profile under test. The approach is based on an adaptive, coarse-to-fine successive representation of the unknown object obtained through a sequence of reconstructions where suitable weighting coefficients are defined through a FL. Key elements of the theoretical analysis are given and several numerical examples, concerned with synthetic and experimental test cases, illustrate the consequences of the proposed approach in terms of both resolution accuracy and robustness as well as computational costs. View full abstract»

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  • Full-Wave Three-Dimensional Microwave Imaging With a Regularized Gauss–Newton Method— Theory and Experiment

    Page(s): 3279 - 3292
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    A reconstruction algorithm is detailed for three-dimensional full-vectorial microwave imaging based on Newton-type optimization. The goal is to reconstruct the three-dimensional complex permittivity of a scatterer in a homogeneous background from a number of time-harmonic scattered field measurements. The algorithm combines a modified Gauss-Newton optimization method with a computationally efficient forward solver, based on the fast Fourier transform method and the marching-on-in-source-position extrapolation procedure. A regularized cost function is proposed by applying a multiplicative-additive regularization to the least squares datafit. This approach mitigates the effect of measurement noise on the reconstruction and effectively deals with the non-linearity of the optimization problem. It is furthermore shown that the modified Gauss-Newton method converges much faster than the Broyden-Fletcher-Goldfarb-Shanno quasi-Newton method. Promising quantitative reconstructions from both simulated and experimental data are presented. The latter data are bi-static polarimetric free-space measurements provided by Institut Fresnel, Marseille, France. View full abstract»

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  • Calculation of the Transient Plane-Wave Reflection From an N-Layer Medium by the Method of Subregions

    Page(s): 3293 - 3299
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    The transient reflected-field response of an arbitrarily incident plane wave from planarly-layered, dispersive materials is investigated. The reflection coefficient for the layered media is first determined in the frequency domain as a ratio of functions and a series solution is derived. Each partial sum of this series represents the reflection coefficient for a layered material consisting of a subregion of the problem of interest. It is shown that the transient reflected field may be written as a sequence of events, each of which is the late-time response of a subregion. This result can be used in time-domain methods to determine the properties of layered materials. View full abstract»

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  • A Five-Band Reconfigurable PIFA for Mobile Phones

    Page(s): 3300 - 3309
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    We describe the design of a small microelectromechanical systems (MEMS) switched planar inverted F antenna capable of operation in five cellular radio frequency bands. Both simulated and measured results are shown using MEMS devices fabricated in an industrialized process based on high-ohmic silicon. Results show that the antenna bandwidth (or size) and specific absorption rate can be significantly improved using such devices. View full abstract»

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  • Electrically Small Frequency-Agile PIFA-as-a-Package for Portable Wireless Devices

    Page(s): 3310 - 3319
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    A reconfigurable electrically small capacitively loaded PIFA-as-a-package (PIFA-AAP) is developed to demonstrate the potential utility of reconfigurable antenna technologies to miniature and/or portable UHF wireless devices. The scalable PIFA-AAP concept involves simply integrating the antenna and the device package to maximize the effective area of the antenna given the physical constraints of the application. An elegant approach to frequency-agility is developed using commercial-off-the-shelf solid state switches, overcoming the key weakness of extreme environmental sensitivity inherent to any electrically small antenna. The measured performance of a 25 times 50 times 9-mm PIFA-AAP includes near-contiguous tuning coverage between 407.8 and 463.1 MHz with a total realized gain of better than -10 dBi across the tuning range. The measured bandwidth of our proof-of-concept frequency-agile PIFA-AAP is benchmarked against the Wheeler-Chu-Mclean fundamental limit. 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