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Antennas and Propagation, IEEE Transactions on

Issue 11  Part 2 • Date Nov. 2006

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  • Table of contents

    Page(s): C1 - 3329
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  • IEEE Transactions on Antennas and Propagation publication information

    Page(s): C2
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  • Naval Structural Antenna Systems for Broadband HF Communications—Part II: Design Methodology for Real Naval Platforms

    Page(s): 3330 - 3337
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    Recently, it was shown how to make a multipurpose broadband HF antenna system out of existing naval super-structures such as the funnel or a big mast. The idea was discussed by means of canonical structures, e.g., a cylindrical body of circular or square cross-section, placed onto an infinite ground plane. This paper investigates the critical aspects concerning the extension of naval structural antenna concept to real ship platforms with the aim to define a general design methodology for impedance matching and radiation pattern control. The method is described with reference to a realistic frigate model, whose big mast is transformed into a broadband HF antenna system able to perform communications by both sea-wave and sky-wave links. It is demonstrated that, even in a real environment, the multiport strategy permits to increase the system efficiency and to moderately shape the radiation pattern in order to overcome the shadowing effect due to other large objects View full abstract»

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  • Broadband/Multiband Conformal Circular Beam-Steering Array

    Page(s): 3338 - 3346
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    A new approach for a broadband/multiband conformal circular beam-steering array is presented with both theory and experimental data. The array is low-profile, suitable for conformal mounting on a platform. It has an omnidirectional coverage with a unidirectional beam that aims at a moderate directivity of 5 to 15 dBi. It consists of a center driven element and parasitic surface waveguide elements symmetrically positioned in the periphery, for electronic beam steering and beam forming to enhance RF connectivity and/or spectral efficiency. This array can achieve ultrawideband multiband performance and low-profile conformability unattainable by conventional array approaches. In addition, its cost is estimated to be an order of magnitude lower than that of conventional beam-steering arrays. Breadboard and brassboard development efforts for the array have essentially achieved a bandwidth of 1.0-2.5 GHz. A larger bandwidth is feasible since its driven element has achieved a continuous 10:1 bandwidth, and since the surface waveguide elements could achieve a multioctave bandwidth similar to the broadbanding path from the Yagi-Uda array to the LP array View full abstract»

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  • Operating Modes and Dynamic Range of Active Space-Fed Arrays With Digital Beamforming

    Page(s): 3347 - 3355
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    Narrow band space-fed (lens) scanning arrays have played a major role in many military and commercial applications. However, wider bandwidth space-fed arrays with phase shifters in the objective aperture, and subarrayed time delay have not found many ready applications because of network losses, complexity, and more recently because of a perceived incompatibility with active solid state module technology. This paper demonstrates that a feed array with transmit/receive (T/R) modules and digitally reconfigured control, can accommodate both narrow band and radiation with relatively efficient use of the active sources View full abstract»

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  • Design of a Near Field Protective Dielectric Radome “Window” for a Curved Phased Array Antenna-Circumferential Polarization Case

    Page(s): 3356 - 3366
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    A systematic design method of near field dielectric windows for two-dimensional conformal fed arrays has been previously developed. The developed design yielded simultaneously well-behaved element patterns in each polarization. This method utilized dimensioning of the window thickness to maximize the radial decay rate of the radome induced surface waves and inclusion of a sufficiently large gap to decouple the surface waves from the array face. In the present paper, these ideas are extended further to arrays scanning in both planes for which the coupling between the two cross polarizations due to the dielectric layer is taken into consideration View full abstract»

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  • Broadband Triple-Frequency Microstrip Patch Radiator Combining a Dual-Band Modified Sierpinski Fractal and a Monoband Antenna

    Page(s): 3367 - 3373
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    A triple-frequency antenna combining a dual-band and a monoband antenna with broadside radiation patterns is presented. The dual-band antenna is inspired in the Sierpinski fractal. Such a dual-band antenna is stacked over a monoband antenna. The antenna presents a broadband behavior at each band thanks to parasitic patches. The antenna has been designed using a MoM commercial code and has been experimentally tested, obtaining three bands with a broad bandwidth, high efficiency, and similar radiation patterns View full abstract»

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  • Experimental Proof of Electrically Invisible State of Inductively Loaded Dipole and Proposal of Electrically Invisible Meander-Lines

    Page(s): 3374 - 3382
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    We examine that an inductively loaded dipole becomes electrical invisible showing that the influence on a nearby antenna's input impedance and on its radiation pattern (scattering) are minimized. We also verify that the direction of the current reverses on the electrically invisible dipole so that the integral of the dipole current becomes zero. By making an inductive load with a distributed constant line, we fabricate an electrically invisible dipole without using chip devices and evaluate its performance. Furthermore, we propose electrically invisible conductor lines formed by connecting these electrically invisible dipoles in series using open stubs as connectors, and analytically examine their invisible state View full abstract»

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  • Control of Leaky-Mode Propagation and Radiation Properties in Hybrid Dielectric-Waveguide Printed-Circuit Technology: Experimental Results

    Page(s): 3383 - 3390
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    Experimental results are presented to show how a planar circuit, printed on a laterally shielded dielectric waveguide, can induce and control the radiation from a leaky-mode. By studying the leaky-mode complex propagation constant, a desired radiation pattern can be synthesized, controlling the main radiation characteristics (pointing direction, beamwidth, sidelobes level) for a given frequency, This technique leads to very flexible and original leaky-wave antenna designs. The experiments show to be in very good agreement with the leaky-mode theory View full abstract»

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  • Magnetodielectric Substrates in Antenna Miniaturization: Potential and Limitations

    Page(s): 3391 - 3399
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    We discuss patch antenna miniaturization using magnetodielectric substrates. Recent results found in the literature reveal that with passive substrates advantages over conventional dielectric substrates can only be achieved if natural magnetic inclusions are embedded into the substrate. This observation is revised and the physical background is clarified. We present a detailed discussion concerning magnetic materials available in the microwave regime and containing natural magnetic constituents. The effects of magnetic dispersion and loss are studied: constraints on the microwave permeability are used to estimate the effect of magnetic substrates on the achievable impedance bandwidth. Microwave composites filled with thin ferromagnetic films are considered as a prospective antenna substrate. We calculate the impedance bandwidth of a lambda/2-patch antenna loaded with the proposed substrate, and challenge the results against those obtained with conventional dielectric substrates. The results are verified using full-wave simulations, and it is shown that the radiation quality factor is strongly minimized with the proposed substrate even in the presence of realistic losses. Estimates for the radiation efficiency are given as a function of the magnetic loss factor View full abstract»

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  • Planar Differential Elliptical UWB Antenna Optimization

    Page(s): 3400 - 3406
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    A recently proposed optimization procedure, based on the time domain characteristics of an antenna, is exploited to design a planar differential elliptical antenna for ultrawideband (UWB) applications. The optimization procedure aims at finding an antenna not only with low VSWR but also one exhibiting low-dispersion characteristics over the relevant frequency band. Furthermore, since in pulse communications systems the input signal is often of a given form, suited to a particular purpose, the optimization procedure also aims at finding the best antenna for the given input signal form. Specifically, the optimized antenna is designed for high temporal correlation between its electric field intensity signal and the given input signal. The optimization technique followed in this work makes use of genetic algorithm (GA) search concepts. The electromagnetic analysis of the antenna is done by means of a finite-difference time-domain method using the commercially available CST Microwave Studio software View full abstract»

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  • Multiple Phase Center Performance of Reflector Antennas Using a Dual Mode Horn

    Page(s): 3407 - 3417
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    A new application for reflector antennas is proposed and developed. Using the aperture theory, a phase center on the reflector aperture is determined and shown that, its location is dependent on the field distribution. The proposed concept is, initially, verified by using a symmetric reflector. It is shown that the phase center is located at the aperture geometric center, when the reflector is illuminated symmetrically about its principal planes. Then, a dual mode feed, employing TE11 and TM01 modes, is used for generating different reflector illuminations, and causing displacement of its phase center. The concept is then extended to offset reflectors, and the influence of the reflector geometry on the phase center displacement and other reflector electrical parameters is investigated. Based on the established feed radiation pattern requirements, a feed horn is designed using circular waveguide that can propagate both modes. By modifying the amplitude and phase of the modes in the horn, a controlled asymmetric reflector aperture field is achieved. A prototype feed horn is fabricated and tested for its dual mode radiation patterns. The results are in good agreement with simulations. The reflector phase center properties are then investigated, by using the designed feed. A reflector-feed assembly, with its dual phase center capability, was developed for improving the performance of the ground moving target indicator radars. The concept allows the conversion of a single reflector to two or more reflectors, simply by modifying the mode excitation amplitudes and phases, in the feed alone View full abstract»

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  • Inverse Source Problem in an Oblate Spheroidal Geometry

    Page(s): 3418 - 3428
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    The canonical inverse source problem of reconstructing an unknown source whose region of support is describable as a spheroidal (oblate or prolate) volume from knowledge of the far-field radiation pattern it generates is formulated and solved within the framework of the inhomogeneous scalar Helmholtz equation via a linear inversion framework in Hilbert spaces. Particular attention is paid to the analysis and computer illustration of flat, aperture-like sources whose support is approximated by an oblate spheroidal volume View full abstract»

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  • Relativistic Scattering of a Plane-Wave by a Uniformly Moving Half-Plane

    Page(s): 3429 - 3440
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    We discuss the effect of motion on the scattering by an edge. To this end, one considers the simplest canonical structure formed by a uniformly moving perfectly conducting half-plane illuminated by a time-harmonic plane wave and investigates the effect of the motion on the reflection and shadow zones, aberration, Doppler shift, edge-diffracted wave, etc. The cases where the velocity is parallel and normal to the half-plane are considered separately. Some of the interesting results which were obtained, in addition to the classical Doppler shift and aberration phenomena, are that (i) the edge-excited wave is never time-harmonic while the waves excited by the plane (both in the shadow and in the reflection zones) are always time-harmonic, (ii) the shadow and reflection boundaries are not parallel to the incident and reflected rays, (iii) at certain values of the velocity and incidence angle, a shadow region appears in the apparent illuminated region while a lit region appears in the apparent shadow region, (iv) the moving half-plane provides, sometimes, energy to the reflected wave. The cases of upsiLtc and upsi~c are examined in detail View full abstract»

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  • Frequency, Temperature and Salinity Variation of the Permittivity of Seawater

    Page(s): 3441 - 3448
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    With the emergence of unmanned marine robots, underwater communication systems have received much attention in recent years. To successfully develop radio wave based communication solutions, it is essential to understand properties of electromagnetic wave transmission in seawater. These properties are determined by the frequency variation of the permittivity of seawater. Existing models for the permittivity of saline water are empirical ones that best fit experimental data. We propose a physically realistic model, similar to the one used in plasma physics, for the variation of the dielectric constant of water with varying frequencies and salinities. Our model is in excellent agreement with existing empirical fits for frequencies between 1 and 256 GHz. We use this model to study the propagation of electromagnetic waves in seawater. We explain that large propagation distances would be possible at MHz frequencies if the conductivity of seawater decreases at small field strengths due to the hydrogen bonding of water molecules. However, we were unable to experimentally verify any reduction in the conductivity of seawater View full abstract»

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  • Theoretical and Experimental Investigation of Gaussian Beam Transmission and Reflection by a Dielectric Slab at 110 GHz

    Page(s): 3449 - 3457
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    Transmission and reflection properties of a Gaussian beam incident upon a dielectric slab are investigated by means the plane-wave spectrum method and compared with experimental results made at 110 GHz. The incident wave generated by a special circular horn antenna at 110 GHz is modeled as a two-dimensional Gaussian beam under the paraxial approximation and also as a simplified one-dimensional beam with a spreading factor. Measurement results are presented for the transmission and reflection of both the perpendicular and parallel polarizations. In particular, reflection measurements for a parallel-polarized beam incident at and near the Brewster angle are shown and compared to the theory. A small reflected two-lobe beam is observed even at the exact Brewster angle. Nonspecular phenomena in Gaussian beams are discussed and the relevance to a Brewster window for the output of a gyrotron is considered View full abstract»

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  • Topology Insensitive Location Determination Using Independent Estimates Through Semi-Directional Antennas

    Page(s): 3458 - 3472
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    We demonstrate the effect of using multiple estimations from independent single wireless motes in order to decrease network topology dependence on location estimation in a wireless sensor network. A method of determining the location of a target by using multiple compact semi-directional antennas is shown to give an independent estimate of location from each sensor mote in a network, each estimate not relying on the data from neighboring motes as in the case of traditional triangulation. We begin by demonstrating a method of using angular diversity through multiple semi-directional antennas in order to ascertain the location of a target. The estimation of both range and angle is demonstrated in the presence of a noisy and/or faded channel. An efficient and fast algorithm on a wireless sensor mote is presented through a Taylor series expansion of the simulated antenna pattern. Furthermore, using the results from the location estimation from a single node, location determination in a realistic network is explored through both theory and simulation. The results indicate that our proposed algorithm depends significantly less on the topology (spatial arrangement) of the anchor nodes. While network planning for a variety of topologies of anchor nodes is shown to be necessary when using triangulation, our proposed algorithm is insensitive to the deployments of the anchor nodes. A testbed was created in order to experimentally demonstrate that the predictions are accurate even in triangulation-adverse topologies. The experimental testbed shows that a linear arrangement of closely spaced sensors can reduce the location error to one-fourth of the location error using triangulation View full abstract»

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  • Identification of Scattering Objects in Microcell Urban Mobile Propagation Channel

    Page(s): 3473 - 3480
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    A series of measurements in two streets in a dense urban area were accomplished. The measurement scenario was small microcell line-of-sight (LoS) with low antenna height at both link ends where dipole sleeve transmitter (Tx) antenna, directive receiver (Rx) antenna, wideband pseudo-noise (PN) signal and correlator were employed. We analyze the data obtained from the measurements by careful investigation of the single-bounce scattering power distribution conforming to precise maps of the environments including all present objects. We try to identify the single-bounce scatterers for the cluster received waves appearing in the single-bounce scattering power distribution. A number of objects were identified by this method as single-bounce scatterers within the spatial resolution bins. The identified objects are signboards, traffic signs, etc. and we conclude that any metallic object visible to both Tx and Rx with dimensions in orders of tens of wavelengths can be a significant source of scattering in small cell scenarios with low antenna heights. The contribution of the scattering from these identified objects to the received power compared to other micromechanisms is evaluated. Results show that the scattering from these objects can be comparable to the wall reflections View full abstract»

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  • Improving Channel Capacity Using Adaptive MIMO Antennas

    Page(s): 3481 - 3489
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    A novel type of multiple-input multiple-output (MIMO) antenna employing parasitic elements is presented. A proper model for the parasitic-MIMO system is first discussed and then numerically and experimentally investigated. The results show that the proposed solution can significantly improve the performance of the communication system with a minimum impact on the complexity and cost of the overall system View full abstract»

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  • Modeling of Lossy Curved Surfaces in 3-D FIT/FDTD Techniques

    Page(s): 3490 - 3498
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    A conformal first-order or Leontovic surface-impedance boundary condition (SIBC) for the modeling of lossy curved surfaces in a Cartesian grid is presented for the finite-integration technique (FIT). Equivalently, the model can be derived using the contour-path formulation of the finite-difference time domain (FDTD) method. The SIBC is based on a lumped-element representation of the impedance combined with a conformal modeling scheme. The validity of the proposed model is evaluated by investigating the quality factors of rectangular, cylindrical and spherical cavity resonators. The convergence rate of the conformal SIBC model is shown to be of second order View full abstract»

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  • Rigorous, Auxiliary Variable-Based Implementation of a Second-Order ABC for the Vector FEM

    Page(s): 3499 - 3504
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    The finite element method (FEM) is commonly used for electromagnetic radiation and scattering analysis. When an infinite, free space exterior domain needs to be incorporated into the method, a radiation boundary condition must be enforced. An approach which has received considerable attention, is to employ approximate conditions, known as absorbing boundary conditions (ABCs), that preserve the sparsity of the original FEM system upon discretization. In the case of time-harmonic analysis based on the vector wave equation in three dimensions, the symmetric, spherical Bayliss-Turkel-type ABCs of first- and second-orders are well-established. The second-order version is expected to be more accurate, however when using the standard curl-conforming approach to FEM discretization, an implementation difficulty is encountered, relating to successive derivatives being required of the nonconforming field components. This issue is addressed here by introducing a scheme where the nonconforming first-order derivatives are projected onto a suitably conforming auxiliary field, of which another derivative can then be taken instead. Additional computational costs are minimal and the scheme retains the symmetry of the standard formulation. Numerical results demonstrate the superior performance of the rigorously implemented second-order ABC over its first-order counterpart View full abstract»

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  • Novel Explicit 2-D FDTD Scheme With Isotropic Dispersion and Enhanced Stability

    Page(s): 3505 - 3510
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    A two dimensional (2-D) finite-difference time-domain (FDTD) method based on a novel finite difference scheme is developed to eliminate the numerical dispersion errors. In this paper, the numerical dispersion and stability analysis of the new scheme are given; these show that the proposed method is nearly dispersionless and stable for a larger time step than the standard FDTD method for a monochromatic frequency. The new algorithm is also verified for two cases View full abstract»

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  • A Coupled PEC-TDS Surface Integral Equation Approach for Electromagnetic Scattering and Radiation From Composite Metallic and Thin Dielectric Objects

    Page(s): 3511 - 3516
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    The recently proposed surface electric field integral equation for thin dielectric sheets is combined with that for conductors to handle objects consisting of both dielectric and conducting materials. This leads to coupled conducting-dielectric surface integral equations which can easily be solved by the method of moments. This approach can handle both scattering and radiation problems such as coated objects, radome enclosed antennas and scatterers, and planar structures. It is observed that the normal electric field in a thin dielectric layer is indispensable when this dielectric layer resides in the vicinity of a conducting object. To validate this approach, couple numerical examples are examined. The results by this approach show agreement with other methods while it economizes on computation resource. It can be used to obtain rapid solutions in the initial phase of the design process. More importantly, it indicates the feasibility for microwave planar circuit applications View full abstract»

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  • Estimation of the Frequency-Dependent Average Dielectric Properties of Breast Tissue Using a Time-Domain Inverse Scattering Technique

    Page(s): 3517 - 3528
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    Ultrawideband (UWB) microwave radar imaging techniques for breast cancer detection typically require estimates of the spatially averaged dielectric properties of breast tissue. We propose an algorithm for estimating patient-specific, frequency-dependent average dielectric properties from scattered UWB microwave signals. The algorithm is a variation of an iterative finite-difference time-domain (FDTD) technique for solving the time-domain inverse scattering problem. The assumption is made that the breast consists of two homogeneous regions: skin and underlying tissue. This two-medium geometry results in an inverse scattering problem that is not as ill-posed as those typically encountered in microwave tomography because the number of unknowns being sought is very small. We test the performance of the algorithm on data simulated using anatomically realistic 2-D numerical breast phantoms View full abstract»

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  • Bistatic Synthetic Aperture Radar Imaging: Theory, Simulations, and Validations

    Page(s): 3529 - 3540
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    A three-dimensional "full-polarized" model for arbitrary transmitter, receiver and target motions in bistatic synthetic aperture radar configurations is proposed. Qualitative validation of this model is presented through comparison with existing results and quantitative validation is obtained from proposed general analytical resolution equations. To take into account complex targets, geometric theory of diffraction based models are considered. Some numerical results are proposed in bistatic and monostatic configurations which permit to check the performance of the proposed model and to highlight the interest of the bistatic synthetic aperture radar imaging 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