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Antennas and Propagation, IEEE Transactions on

Issue 9 • Date Sept. 2003

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Displaying Results 1 - 25 of 60
  • Well-conditioned asymptotic waveform evaluation for finite elements

    Page(s): 2442 - 2447
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (321 KB) |  | HTML iconHTML  

    The frequency-domain finite-element method (FEM) results in matrix equations that have polynomial dependence on the frequency of excitation. For a wide-band fast frequency sweep technique based on a moment-matching model order reduction (MORe) process, researchers generally take one of two approaches. The first is to linearize the polynomial dependence (which will either limit the bandwidth of accuracy or require the introduction of extra degrees of freedom) and then use a well-conditioned Krylov subspace technique. The second approach is to work directly with the polynomial matrix equation and use one of the available, but ill-conditioned, asymptotic waveform evaluation (AWE) methods. For large-scale FEM simulations, introducing extra degrees of freedom, and therefore increasing the length of the MORe vectors and the amount of memory required, is not desirable; therefore, the first approach is not alluring. On the other hand, an ill-conditioned AWE process is unattractive. This paper presents a novel MORe technique for polynomial matrix equations that circumvents these problematic issues. First, this novel process does not require any additional unknowns. Second, this process is well-conditioned. Along with the presentation of the novel algorithm, which is called well-conditioned AWE (WCAWE), numerical examples modeled using the FEM are given to illustrate its accuracy. View full abstract»

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  • Comments on "Wide-band E-shaped patch antennas for wireless communications"

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    For original paper see Yang, F. et al., ibid., vol.49, p.1094-1100 (2001). The writer disputes the novelty claimed by Yang et al. for the E-shaped patch antenna in wireless communications. He points out that it is a special case of the double C-patch antenna which he invented in 1994 (Sanad, M. Proc. IEEE AP-S Symp., p.2116-19, 1995). He refers to papers and patents which describe the further development of the double C-patch antenna and also its application as the basis of internal integrated antennas for portable wireless communication equipment, including cellular phones. View full abstract»

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  • On the relationship between fractal dimension and the performance of multi-resonant dipole antennas using Koch curves

    Page(s): 2296 - 2303
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (806 KB) |  | HTML iconHTML  

    This paper relates for the first time, multiple resonant frequencies of fractal element antennas using Koch curves to their fractal dimension. Dipole and monopole antennas based fractal Koch curves studied so far have generally been limited to certain standard configurations of the geometry. It is possible to generalize the geometry by changing its indentation angle, to vary its fractal similarity dimension. This variation results in self-similar geometry which can be generated by a recursive algorithm. Such a variation is found to have a direct influence on the input characteristics of dipole antennas. The primary resonant frequency, the input resistance at this resonance, and the ratio of first two resonant frequencies, have all been directly related to the fractal dimension. Curve-fit expressions can also be obtained for the performance of antennas at their primary resonance, in terms of fractal iteration and fractal dimension. The antenna characteristics have been studied using extensive numerical simulations and are experimentally verified. These findings underscore the significance of fractal dimension as an important mathematical property of fractals that can be used as a design parameter for antennas. The use of these ideas would not only reduce the computational intensity of optimization approaches for design of fractal shaped antennas, but also help antenna designers approach the problem systematically. Design formulation for antennas based on other fractal geometries can be similarly obtained after identifying suitable parameters of variation. This would therefore help analytical design of multiband and multifunctional antennas using fractal geometries. View full abstract»

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  • A dual-band dual-polarized nested Vivaldi slot array with multilevel ground plane

    Page(s): 2168 - 2175
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1264 KB)  

    In this paper, we present a systematic approach to the design, optimization and characterization of a broadband 5:1 bandwidth (0.8 to 4.0 GHz) antenna subarray. The array element is an optimized-taper antipodal Vivaldi slot with a bandwidth of 2.5:1. Two such elements of different sizes and with 0.4 GHz (10% of the highest frequency) overlapping bandwidths are arrayed in a nested lattice above a multilevel ground plane that shields the feeds and electronics. Return loss, radiation patterns, cross-polarization and mutual coupling are measured from 0.5-5.0 GHz. This array demonstrates E plane patterns with 50° and 45° 3-dB beamwidths in the lower and upper frequency bands, respectively. The coupling between the elements is characterized for different relative antenna positions in all three dimensions. View full abstract»

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  • A finite-difference time-domain algorithm optimized for arbitrary propagation angles

    Page(s): 2456 - 2463
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (706 KB)  

    We present a two-dimensional higher order FDTD algorithm to minimize the numerical dispersion error at arbitrary, preassigned angles. Filtering schemes are further employed to optimize the FDTD frequency response at a given frequency range. A stability analysis of the resulting FDTD algorithms is included. Numerical dispersion properties are compared against Yee's scheme and a higher order (2,4) FDTD scheme. Numerical results demonstrate that the dispersion error around a preassigned angle (and, with filtering, around a frequency band of choice) can be significantly reduced. View full abstract»

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  • Improvement of prompt response from impulse radiating antennas by aperture trimming

    Page(s): 2158 - 2167
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (632 KB) |  | HTML iconHTML  

    Reflector impulse radiating antennas (IRA) traditionally have been constructed by terminating a self-reciprocal, transverse electromagnetic (TEM) transmission-line feed structure into a paraboloidal reflector. The section of the paraboloid used is usually circular in cross-section, with the outer boundary coinciding with the circle of symmetry of the TEM feed. The reflector converts the spherical TEM mode on the feed line into an approximate plane wave in the near field by geometric optics. The prompt radiated electric field in the direction of focus is given in the physical optics approximation in terms of the integral of the electric field of the TEM mode over the aperture plane inside the reflector boundary. Balanced feed structures have TEM modes that provide both positive and negative contributions to this integral in the aperture plane. Determination of the contour where the principal component of the electric field in the TEM mode is zero identifies portions of the aperture that contribute destructively to the integral. These portions are removed, thereby increasing the prompt radiated field without altering the feed structure or the applied voltage waveform. Furthermore, decreasing the size of the TEM feed relative to the aperture size, followed by appropriate aperture trimming, allows an even greater increase in radiated field. Results are presented that predict an increase in prompt radiated fields for all electrode configurations. Improvements are largest for electrode angles that are large (with respect to the vertical). The trends predicted by the numerical results are verified by an experiment conducted on a time-domain antenna range. View full abstract»

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  • Calculation of the RCS from the double reflection between planar facets and curved surfaces

    Page(s): 2509 - 2512
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (327 KB) |  | HTML iconHTML  

    A method to obtain the contribution to the monostatic radar cross section (RCS) due to double reflections between plane facets and curved surfaces is presented. This method is applied to arbitrary targets modeled by NURBS (non-uniform rational B-spline) surfaces. The method developed is a combination of geometrical optics (GO) and the stationary phase method (SPM). View full abstract»

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  • Mutual coupling between patch antennas recessed in an elliptic cylinder

    Page(s): 2489 - 2492
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (470 KB) |  | HTML iconHTML  

    Cavity-backed microstrip patch antennas are often used in aircraft applications because of their ability to conform to the vehicle surface. For arrays of patches, it is important to be able to predict the dependence on surface curvature of the coupling between patches. The mutual impedance between two rectangular patch antennas recessed in an elliptic cylinder is computed using a finite element-boundary integral method. Results show that the coupling between the antennas is dependent on the curvature of the cylinder surface. For H-plane coupling, the coupling decreases as the radius of curvature increases. For E-plane coupling, the strongest coupling occurs for a specific curvature. View full abstract»

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  • Intersector correlations: a quantitative approach to switched beams' diversity performance in wireless communications

    Page(s): 2238 - 2243
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (575 KB) |  | HTML iconHTML  

    We show that intersector correlations may be used as a convenient way to analyze diversity in switched beam antennas, with particular emphasis on the elevation dependence of the received power spectrum. In addition to their experimental characterization, such correlations can be computed from first principles according to the radio environment. The expected diversity performance can then be used as an input to antenna design and optimization. View full abstract»

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  • Printed double-T monopole antenna for 2.4/5.2 GHz dual-band WLAN operations

    Page(s): 2187 - 2192
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (666 KB) |  | HTML iconHTML  

    A novel and simple printed dual-band double-T monopole antenna is proposed. The antenna comprises two stacked T-shaped monopoles of different sizes, which generate two separate resonant modes for the desired dual-band operation. The proposed antenna has a low profile and can easily be fed by using a 50 Ω microstrip line. Prototypes of the proposed antenna designed for WLAN operations in the 2.4 and 5.2 GHz bands have been constructed and tested. Good radiation characteristics of the proposed antenna have been obtained. Effects of varying the monopole dimensions and the ground-plane size on the antenna performance have also been studied. View full abstract»

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  • A fast volume integral equation solver for electromagnetic scattering from large inhomogeneous objects in planarly layered media

    Page(s): 2393 - 2401
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    A newly developed iterative method, the stabilized biconjugate gradient fast Fourier transform (BCGS-FFT) method is applied to simulate electromagnetic scattering from large inhomogeneous objects embedded in a planarly layered medium. In this fast solver, the weak-form formulation is applied to obtain a less singular discretization of the volume electric field integral equation. Several techniques are utilized to speed up the dyadic Green's function evaluation. To accelerate the operation of the dyadic Green's function on an induced current (i.e., the "Green's operation"), the Green's function is split into convolutional and correlational components so that FFT can be applied. The CPU time and memory cost of this BCGS-FFT method is O(NlogN) and O(N), respectively, where N is the number of unknowns, significantly more efficient than the method of moments (MoM). As a result, this method is capable of solving large-scale electromagnetic scattering problems in a planarly layered background. A large-scale scattering problem in a layered medium with more than three million unknowns has been solved on a Sun Ultra 60 workstation with 1.2 GBytes memory. View full abstract»

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  • Finite-difference time-domain model of interfaces with metals and semiconductors based on a higher order surface impedance boundary condition

    Page(s): 2448 - 2455
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (748 KB)  

    A new numerical finite-difference time-domain (FDTD) model of interfaces with metals and semiconductors is developed. The model uses a higher order impedance boundary condition to simulate the fields in conductive media. The approach has been found to be considerably more accurate than the known models based on the simple Leontovich impedance boundary condition. This is because the new model takes the incidence angle of the incident waves into account, and it is valid for all values of conductivity. The derivation of the method is presented in the two-dimensional (2D) case, and the performance is studied over a wide range of conductivity. The validation of the method is made by comparing with the exact results in a 2D example problem. The proposed method is also compared with some other methods available in the literature. View full abstract»

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  • A patch antenna with a rectangular-loop feed

    Page(s): 2464 - 2468
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (373 KB) |  | HTML iconHTML  

    The characteristics of a rectangular-loop fed patch antenna with radiation patterns similar to a 2 × 1 monopole array are presented. The loop is equivalent to a L-probe with the end shorted to ground. The proposed antenna consists of two patches which are excited by two rectangular-loops respectively. It is designed to operate at both GSM and PCS bandwidths, with resonant frequencies of 870.75 and 1773 MHz, respectively. The distance between each patch and the ground plane is 0.1 free space wavelength at their resonant frequencies. Foam is used as the dielectric substrate. Each patch radiates with a in the direction normal to the patch, and an elliptical pattern on the horizontal plane. This antenna can be used for indoor wireless communication systems. The commercial simulation software IE3D was used to predict the characteristics of this antennas such as the resonant frequencies, impedance bandwidth and radiation patterns. Experimental and simulation results are shown to be in good agreement. View full abstract»

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  • Dual-beam microstrip leaky-wave array excited by aperture-coupling method

    Page(s): 2496 - 2498
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    The paper describes the design of a microstrip leaky-wave array excited by the aperture-coupling technique. The microstrip first higher order leaky mode is employed as the radiation source. Separating the radiators from other components by ground planes provides an optimal design of radiators and other devices so that the inherent broadband, high gain and frequency-scanning properties of the leaky-wave antenna can be exploited. Four kinds of feeding arrangements to excite dual beams are experimented in K band. Markedly reducing the required elements compared to a patch-array for high gain design can simplify the complexity of the feeding layout. Versatile designs combining the merits of multilayer technology offer simplicity and efficient design for practical wireless applications. View full abstract»

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  • Limit and application range of the slope-diffraction method for wireless communications

    Page(s): 2512 - 2514
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (283 KB) |  | HTML iconHTML  

    We investigate the limitations on the use of the uniform theory of diffraction (UTD) slope-diffraction method for propagation past knife edges. The settled field that is diffracted past rows of buildings, as computed by numerical integration, has the characteristics of amplitude and phase variation with a scale length that is large compared to the wavelength and has small amplitude near the edges. Using this field, it is shown that the error in the UTD slope-diffraction method for diffraction past a final screen is connected with the Fresnel width, as compared to the scale length of the settled field. View full abstract»

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  • Series representation of Green dyadics for layered media using PMLs

    Page(s): 2319 - 2326
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (573 KB) |  | HTML iconHTML  

    The Green dyadics for closed layered media, i.e., layered media bounded by a perfectly conducting plate at the bottom and top of the structure, can be expanded in a discrete surface wave series. For open layered media with semi-infinite layers at the top and/or bottom of the structure, the discrete series needs to be complemented by a branch-cut integral of space waves. In this paper, we present a technique to circumvent this branch-cut integral by truncating the semi-infinite layers with a perfectly matched layer (PML) that is backed by a perfect electric conductor (PEC). It is demonstrated that in this way it is possible to obtain an accurate series or closed-form representation for the Green dyadic of the open layered medium. The series allows a very efficient calculation and storage of the Green dyadic if it is needed for multiple observation and or excitation points. Very close to the source the series loses efficiency. It is shown that the determination of the surface waves in the PML truncated layered medium has the same complexity as the determination of the surface waves in a PEC truncated layered medium without a PML. View full abstract»

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  • An affordable millimeter-wave beam-steerable antenna using interleaved planar subarrays

    Page(s): 2193 - 2202
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (666 KB) |  | HTML iconHTML  

    Design and fabrication aspects of an affordable planar beam steerable antenna array with a simple architecture are considered in this paper. Grouping the elements of a phased array into a number of partially overlapped subarrays and using a single phase shifter for each subarray, generally results in a considerable reduction in array size and manufacturing costs. However, overlapped subarrays require complicated corporate feed networks and array architectures that cannot be easily implemented using planar technologies. In this paper a novel feed network and array architecture for implementing a planar phased array of microstrip antennas is presented that enables the fabrication of low-sidelobe, compact, beam-steerable millimeter-wave arrays and facilitates integration of the RF front-end electronics with the antenna structure. This design uses a combination of series and parallel feeding schemes to achieve the desired array coefficients. The proposed approach is used to design a three-state switched-beam phased array with a scanning width of ±10°. This phased array which is composed of 80 microstrip elements, achieves a gain of >20 dB, a sidelobe level of <-19 dB and a 10-dB bandwidth of >6.3% for all states of the beam. The antenna efficiency is measured at 33-36% in X band. It is shown that the proposed feeding scheme is insensitive to the mutual coupling among the elements. View full abstract»

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  • Computed SAR and thermal elevation in a 0.25-mm 2-D model of the human eye and head in response to an implanted retinal stimulator - part I: models and methods

    Page(s): 2274 - 2285
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1934 KB) |  | HTML iconHTML  

    Retinitis pigmentosa and age-related macular degeneration lead to blindness through progressive loss of retinal photoreceptors. Attempts are under way to construct a visual prosthesis to recover a limited sense of vision for these patients with the aid of implantable electronic devices. The function of these microchips is to provide electrical stimulation to existing viable retinal tissues - living ganglion and bipolar cells - using an array of on-chip stimulus circuits, while the dominant mechanism for power and data communication for these implanted devices has been wireless inductive telemetry using coils. This paper describes methods and models used to estimate the heating induced in the human eye and surrounding head tissues subject to the operation of this retinal prosthesis. A two-dimensional 0.25-mm high-resolution human head model has been developed with the aid of a new semiautomatic graphical segmentation algorithm. Finite-difference-based numerical methods for both electromagnetic and thermal modeling have been used to determine the influence of the specific absorption rate (associated with 2-MHz inductive coupling to the implant) and of stimulator integrated circuit (IC) power on tissue heating under different operational conditions and different hypothesis on choroidal blood flow and properties of the complex implanted circuitry. Results, provided in Part II of this paper, show that temperature increases of approximately 0.6 and 0.4°C are induced in the midvitreous of the human eye in the absence and presence of choroidal blood flow, respectively, for a 60-electrode retinal prosthesis chip. Correspondent temperature rises of approximately 0.19 and 0.004°C on the retina are obtained for these cases. Comparison with in vivo experimental measurements on intraocular heating in dog eyes shows good agreement. View full abstract»

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  • An evaluation of mixed-order versus full-order vector finite elements

    Page(s): 2430 - 2441
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (567 KB) |  | HTML iconHTML  

    Recently proposed vector finite elements are compared to previously published elements, and independently implemented and validated in the context of rectangular waveguide analysis. Both mixed-order and full-order elements up to order two are considered. The use of quadrature (cubature) to evaluate the finite element system matrices is discussed. Details of some analytical work required before quadrature is applied are presented for several types of basis functions. For many RF applications, mixed-order elements offer optimal accuracy for a given number of degrees of freedom, and an empty ("through") waveguide solution verifies this, with similar convergence rates for mixed- and full-order elements of the same order. However, a capacitive iris in the rectangular waveguide, with a solution dominated by the quasi-static electric field, motivates the use of full-order elements in such cases. Results for the electric fields in the vicinity of the iris also demonstrate the enhanced accuracy of the full-order elements here. This is further illustrated using a dielectric load in a waveguide, where complete order elements produce a better approximation of the normal jump discontinuity. Although this paper addresses guided wave problems, the results are also applicable to radiation and scattering problems. View full abstract»

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  • A novel millimeter-wave beam-steering technique using a dielectric-image line-fed grating film

    Page(s): 2203 - 2209
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (609 KB) |  | HTML iconHTML  

    This paper introduces a novel, broadband, low-cost technique for beam steering at millimeter-wave frequencies using a moveable grating film fed by dielectric image line. An excellent radiation pattern is maintained over wide scan angles across the 30-40 GHz range, with up to 53° scanning reported at 35 GHz. Theoretical calculations closely predict the observed scan angle across the entire range of measurement. View full abstract»

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  • Modal transmission-line modeling of propagation of plane radiowaves through multilayer periodic building structures

    Page(s): 2244 - 2251
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (851 KB) |  | HTML iconHTML  

    The modal transmission-line (MTL) method is used to analyze the shielding effectiveness of buildings, which is an important parameter for the accurate planning of microcellular communication networks. For that, the buildings are modeled as multilayer lossy periodic structures. After a description of the extended MTL-theory, the newly developed MTL model is applied to brick walls, reinforced-concrete walls and concrete block walls. From a comparison of the MTL-results with previously published theoretical or experimental results it is concluded that the MTL method is very well suited, because it is accurate as well as computational time-efficient. View full abstract»

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  • Reduced size, dual-polarized microstrip patch antenna for wireless communications

    Page(s): 2182 - 2186
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (423 KB)  

    A novel, compact, probe-fed microstrip patch antenna for operation in dual-polarization mode is proposed. The novel design is achieved by etching out a symmetric pattern of crossed slots from the surface of a square probe-fed patch. Reduction in patch size of up to 51% with respect to a traditional dual-polarized square patch operating at the same frequency is obtained. Results show linear polarizations in the +45 and -45° with a high isolation of 38 dB between the two ports. Moreover, the 50-Ω feed position can be achieved by moving the feed point along the diagonal of the square patch, leading to ease in fabrication. View full abstract»

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  • PIFA with a meandered and folded patch for the dual-band mobile phone application

    Page(s): 2468 - 2471
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB) |  | HTML iconHTML  

    In this communication, a novel design of the planar inverted-F antenna (PIFA) is proposed for the dual-band mobile telephone application. To reduce the antenna size, the radiating patch is meandered and folded. The studies begin with a folded-patch PIFA that has two tunable resonant modes. Next, by loading three slits on the patch, the surface current path is meandered and the antenna length is reduced significantly. The IE3D simulation software is employed for optimizing the design parameters, and the simulation results in general agree with the measured data. Results also show that, the excitation of the 900 and 1800 MHz resonant modes can be achieved for the proposed antenna with a small volume of 24×10×7.2 mm3. Radiation patterns for both resonances are measured and shown. The maximum antenna gain is estimated to be 2.5 dBi for both 900/1800 band operations. 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