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Antennas and Propagation, IEEE Transactions on

Issue 2 • Date Feb 2002

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Displaying Results 1 - 22 of 22
  • Broadband dual-polarized aperture-coupled patch antennas with modified H-shaped coupling slots

    Publication Year: 2002 , Page(s): 188 - 191
    Cited by:  Papers (27)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (219 KB)  

    This paper presents a new design of aperture-coupled patch antennas with modified H-shaped coupling slots for achieving dual-polarization radiation with high isolation over a wide bandwidth. By using the proposed coupling slots, whose two upper side arms are bent inward with a proper angle, the isolation between the two feeding ports of the patch antenna can. greatly be improved, compared to the case with conventional H-shaped coupling slots. Also, when using a pair of modified H-shaped coupling slots for each feeding port, the isolation can further be improved; a high degree of isolation (< -34 dB) over the entire impedance bandwidth greater than 15% and good cross-polarization level (> 20 dB) for the two polarizations can be achieved. Details of the proposed design and experimental results are presented and discussed View full abstract»

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  • Wideband 3D characterization of mobile radio channels in urban environment

    Publication Year: 2002 , Page(s): 233 - 243
    Cited by:  Papers (49)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    This paper describes three-dimensional (3D) radio channel measurements at the base station site in an urban environment. We introduce a measurement concept which combines an RF switched receiver array and a synthetic aperture technique and allows full 3D characterization of the channel. Additionally, dual-polarized patch antennas as array elements enable full determination of the polarization properties of the impinging signals. We describe measurements at over 70 different transmitter positions and three receiver array sites with different sectors and antenna heights. Our results show that the received energy is concentrated within identifiable clusters in the azimuth-elevation-delay domain. We demonstrate that the observed propagation mechanisms are mainly determined by the environment close to the base station. Street canyon propagation dominates also when the receiver array is at or even above rooftop level with the studied measurement distances. Thus, the azimuth spectrum at the BS site is fairly independent of the location of the mobile. Signal components propagating over the rooftop are often related to reflections from high-rise buildings in the surroundings View full abstract»

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  • Measurement and analysis of miniature multilayer patch antenna

    Publication Year: 2002 , Page(s): 244 - 250
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (293 KB)  

    Although the microstrip patch antenna has a number of advantages such as low-cost and light weight, its physical size is quite large at low microwave frequencies. The designs of multilayer miniature patch antennas with coaxial feed are presented. The first design is a rectangular two-layer patch antenna. Measured results and the results of a preliminary analysis are presented. The projection area of the two-layer patch antenna is kept the same as the single-layer rectangular patch antenna. The resonant frequency of the two-layer antenna is reduced by 50% and has bandwidth of 5%, which is wider than the single-layer rectangular patch antenna. In the second design, the upper patch is cut into a bow-tie shape. This results in a 60% reduction in resonant frequency and a 12% bandwidth. Both the two-layer rectangular and the two-layer bow-tie antennas have good radiation patterns, with cross-polarization level lower than the copolarization level by more than 20 dB View full abstract»

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  • Computation of the scattering from inhomogeneous objects with a discrete rotational symmetry and a nonsymmetric part

    Publication Year: 2002 , Page(s): 168 - 174
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    Using a specific solver for circulant matrices can reduce the cost of computing the scattering from a discrete rotational symmetric object by up to several orders of magnitude. A solver is developed for symmetric objects with a nonsymmetrical part (such as an antenna on a body of revolution). This solver has been implemented in a finite-element code based upon a hybrid formulation. The hybrid formulation combines integral equations and partial differential equations; it can handle inhomogeneous anisotropic objects of arbitrary shape. Results on inhomogeneous objects with defects are shown. The solver can also be used to perform a parametric study of the defects View full abstract»

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  • Broadband dual polarization patch element for cellular-phone base stations

    Publication Year: 2002 , Page(s): 251 - 253
    Cited by:  Papers (35)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (202 KB)  

    A broadband dual polarization patch antenna double fed by an L-shaped probe and a near-resonant aperture is presented. The proposed antenna achieves a 1.5:1 standing wave ratio bandwidth of >20% at the two ports. Input isolation exceeding 25 dB has been obtained in the wide bandwidth. Thus, it can potentially be used as a base station antenna for cellular-phone networks View full abstract»

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  • Effect of canopy-air interface roughness on HF-VHF wave propagation in forest

    Publication Year: 2002 , Page(s): 111 - 121
    Cited by:  Papers (34)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (530 KB)  

    The problem of electromagnetic wave propagation in a realistic forest environment in the high-frequency and very high-frequency bands is considered. In particular, the effect of the nonplanar interface between the air and the canopy, which has been ignored in previous models, is examined. An analytical formulation is obtained for the mean field when both the transmitter and the receiver are within the foliage. This formulation is based on distorted Born approximation and accounts for the surface roughness that exists between the canopy and air interface. It is shown that the surface roughness attenuates the so-called lateral wave slightly, which is the dominant source of the field at receiver locations far from the transmitter. It is also shown that this attenuation rate increases when the RMS height of the surface roughness is increased View full abstract»

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  • FDTD simulation of radiation characteristics of half-volume HEM and TE-mode dielectric resonator antennas

    Publication Year: 2002 , Page(s): 175 - 179
    Cited by:  Papers (16)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (301 KB)  

    Cylindrical and rectangular dielectric resonator antennas (DRAs) using HEM11δ, TE11δ, and TE01δ mode were examined to see the radiation pattern, impedance, field distribution and resonant frequency that were achieved when the DRAs were bisected through an image plane by a conducting sheet. The resultant half DRAs are smaller in volume and have a more directional radiation pattern. The elevation angle of maximum radiation was lowered in some cases. Finite-difference time-domain simulation techniques were used View full abstract»

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  • A hybrid moment method solution for TEz scattering from large planar slot arrays

    Publication Year: 2002 , Page(s): 145 - 156
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (435 KB)  

    This paper develops a hybrid moment method (MM) based numerical model for electromagnetic scattering from large finite-by-infinite planar slot arrays. The model incorporates the novel concept of a physical basis function (PBF) to reduce dramatically the number of required unknowns. The model can represent a finite number of slot columns with slots oriented along the infinite axis, surrounded by an arbitrary number of coplanar dielectric slabs. Each slot column can be loaded with a complex impedance to tailor the array's edge currents. An individual slot column is represented by equivalent magnetic scattering currents on an unbroken perfectly conducting plane. Floquet theory reduces the currents to a single reference element. In the array's central portion, where the edge perturbations are negligible, the slot column reference elements are combined into a single basis function. Thus, one PBF can represent an arbitrarily large number of slot columns. A newly developed one-sided Poisson sum formula is used to calculate the mutual coupling between the PBF and the slot columns in the presence of a stratified dielectric media. The array scanning method (ASM) gives the mutual coupling between the individual slot columns. The hybrid method is validated using both numerical and experimental reference data. The results demonstrate the method's accuracy as well as its ability to handle array problems too large for traditional MM solutions View full abstract»

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  • A novel design method for Blass matrix beam-forming networks

    Publication Year: 2002 , Page(s): 225 - 232
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    A novel design method for lossy Blass matrix beam-forming networks (LBNMFNs) is presented. Compared to those formerly developed, the new method allows the design of an LBMBFN in order to generate not only two simultaneous beams but also an arbitrary number of them. This skill is obtained by means of a new approach to minimize losses that allows one to transform a nonlinear multivariable programming problem into a linear one-variable problem. The solution of such a design problem, then, can be carried out in a very straightforward way by applying Gram-Schmidt orthogonalization. Such a design method takes into account also the limited availability of coupling values of directional couplers. Numerical results obtained through the application of such a design method are then presented. The ease, accuracy, and efficiency of this novel method for the design of LBMBFN make it very useful in modern applications of multibeam antenna arrays View full abstract»

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  • Radar images of rough surface scattering: comparison of numerical and analytical models

    Publication Year: 2002 , Page(s): 94 - 100
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (302 KB)  

    Rough surface scattering theories are investigated through analysis of radar images. Backscatter results from 10 GHz to 14 GHz under tapered wave illumination are considered for one-dimension (1D) random rough surface realizations which satisfy an impedance boundary condition. Back-projection tomography is applied to form two-dimensional (2D) synthetic aperture radar images from deterministic surface scattered field data at multiple incidence angles and frequencies. Numerical predictions of surface backscattered fields are obtained from an accelerated forward-backward (FB) method and the resulting images are compared with those obtained from approximate scattering theories such as the physical optics (PO) approximation, the small slope approximation (SSA), and the nonlocal SSA (NLSSA). The resulting radar images illustrate scattering sources associated with single and multiple scattering on the boundary, and a ray tracing analysis confirms the locations of time-delayed image points due to double reflections. For single scattering effects, the images demonstrate excellent agreement between analytical and numerical methods in both horizontal and vertical polarizations. For surfaces with RMS height 2.0 cm and correlation length 7.5 cm at normal incidence, multiple-scattering effects are observed and successfully captured when the lowest-order NLSSA is employed View full abstract»

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  • Efficient radar signature prediction using a frequency-aspect interpolation technique based on adaptive feature extraction

    Publication Year: 2002 , Page(s): 122 - 131
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (330 KB)  

    A radar cross section (RCS) interpolation technique in both frequency and aspect is proposed for the efficient prediction of radar signatures from computational electromagnetics data. Our approach is based on a multiple-arrival model for the induced current on the target. The model parameters are determined by an adaptive feature extraction (AFE) algorithm, which uses an iterative search-and-extract procedure to find the individual model features. Random frequency and aspect sampling is used to circumvent the ambiguity in selecting the features. Numerical examples are presented to test the interpolation algorithm. It is found that sufficient accuracy in the predicted radar features can be achieved even when the original computed data is sampled at 5:1 below the Nyquist criterion in either frequency or aspect. The algorithm is also applied to efficiently predict the radar images of the benchmark VFY218 airplane at UHF band with good results View full abstract»

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  • Analysis of a circular patch antenna radiating in a parallel-plate radial guide

    Publication Year: 2002 , Page(s): 180 - 187
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (330 KB)  

    This paper investigates the use of a coaxially fed patch as a feeding element in a single-layer radial line slot antenna (RLSA) array. A field matching method is described to analyze a recessed circular cavity radiating into a radial waveguide. Using the wall impedance approach, the analysis is divided into two separate problems of the cavity and its external environment. Based on this analysis, a computer algorithm is developed for determining wall admittances as seen at the edge of the patch in the cavity, the radial admittance matrix for the two-probe feed arrangement, and the input impedance as observed from the coaxial line feeding the cavity. This algorithm is tested against the general-purpose Hewlett-Packard finite-element high frequency structure simulator as well as against measured results. Good agreement in all considered cases is noted View full abstract»

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  • Application of DCIM to MPIE-MoM analysis of 3D PEC objects in multilayered media

    Publication Year: 2002 , Page(s): 157 - 162
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (255 KB)  

    The Formulation-C Green's functions for multilayered media are reformulated in this paper to extract z-dependent part when the source and observation points are in different layers. The discrete complex image method (DCIM), is applied to obtain complex images independent on z but dependent on z´. For simulation of three-dimensional (3-D) perfectly electrical conduction (PEC) objects penetrating two or more layers, tables of complex images are built in a z´-grid. During the matrix-filling stage of the mixed-potential integral equation, together with method of moments (MPIE-MoM), the spatial-domain Green's functions are interpolated from values in the z´-grid, while these values are calculated from complex images in the z´-grid. This interpolation scheme is more efficient than those directly storing the spatial-domain Green's functions. Numerical examples are given for analyzing a dipole in a two-layered media View full abstract»

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  • A three-dimensional UTD heuristic diffraction coefficient for complex penetrable wedges

    Publication Year: 2002 , Page(s): 217 - 224
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (377 KB)  

    A three-dimensional heuristic diffraction coefficient, useful to predict the electromagnetic field scattered from penetrable wedges of complex geometry, is presented. The model, based on a modification of the exact uniform theory of diffraction (UTD) metallic wedge diffraction coefficient, allows the analysis of a large class of penetrable objects with an adequate degree of accuracy. Numerical results concerning the scattering from solid and hollow penetrable wedges show the suitability of the proposed diffraction coefficient to analyze complex structures of large practical interest. A good agreement with exact numerical results already available in the literature has been found View full abstract»

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  • Implementation and experiments of a hybrid algorithm of the MLFMA-enhanced FE-BI method for open-region inhomogeneous electromagnetic problems

    Publication Year: 2002 , Page(s): 163 - 167
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (226 KB)  

    Although the computational complexity of the finite-element boundary-integral (FE-BI) method is significantly reduced by the multilevel fast multipole algorithm (MLFMA), this MLFMA-enhanced FE-BI solution experiences a very slow convergence for some complex inhomogeneous problems. A hybrid algorithm, combining direct methods with iterative methods, is designed. to speed up the rate of convergence of this MLFMA-enhanced FE-BI solution. This hybrid algorithm is efficiently implemented with the aid of a newly developed package, SuperLU, of the LU decomposition solver. Numerical experiments are performed for scattering by a coated Northrop wing to demonstrate the efficiency of this hybrid algorithm. More importantly, the thorough investigation of the numerical experiments clearly shows the better accuracy, stability, and robustness of this hybrid algorithm over the conventional algorithms View full abstract»

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  • Fully polarimetric bistatic radar scattering behavior of forested hills

    Publication Year: 2002 , Page(s): 101 - 110
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (415 KB)  

    The bistatic radar scattering measurements of forested hills were performed at grazing incidence and at azimuth scattering angles from 28° to 66° from the forward scatter plane. Using pulse-to-pulse switching between orthogonal transmitted polarizations, the radar simultaneously measures two orthogonally polarized components of the scattered wave to obtain full polarimetric information about the scattering process. These are the first fully polarimetric terrain clutter measurements to be conducted at large bistatic angles. The complete Stokes matrix, computed by averaging successive realizations of the polarization scattering matrix, is used to examine the polarization sensitivity of the bistatic clutter. It is found that the polarization state of the EM wave scattered out of the plane of incidence strongly depends on the polarization orientation of the incident electric field. Unlike the monostatic case, these two incident wave polarization states are found to produce substantially different scattered wave behavior when trees are viewed at large bistatic angles. Scattered fields resulting from vertically oriented incident fields are found to be highly polarized and to produce bistatic clutter power levels that are strongly dependent on the polarization of the receiving antenna. In contrast, horizontally oriented incident fields are found to produce weakly polarized scattered waves with bistatic clutter power levels that are insensitive to the polarization of the receiving antenna View full abstract»

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  • Finite-element solution to electromagnetic scattering problems by means of the Robin boundary condition iteration method

    Publication Year: 2002 , Page(s): 132 - 140
    Cited by:  Papers (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (309 KB)  

    A new numerical method, called the Robin boundary condition iteration (RBCI), is proposed for the finite-element (FE) solution of electromagnetic scattering problems in open boundary domains. The unbounded domain is truncated to a bounded one by means of a fictitious boundary that contains the scatterer and on which a suitable nonhomogeneous Robin (mixed) boundary condition is assumed for the Helmholtz equation in the bounded domain. The Robin condition is expressed by means of an integral formula (the second Green identity) in terms of the field in the interior of the bounded domain, with the integration surface being a surface strictly enclosed by the truncation boundary. The discretized differential and integral equations are then coupled together to solve the problem. The formulation is completely immune from the well-known interior resonance problems. A simple and effective iterative solving scheme is described. Examples are also provided to validate RBCI and compare it with other methods View full abstract»

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  • SICS: a sensor interaction compensation scheme for microwave imaging

    Publication Year: 2002 , Page(s): 211 - 216
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (303 KB)  

    A new formulation is proposed to take into account the sensors used to measure the scattered field in microwave tomography setups. This formulation provides a way to fully compensate the perturbations resulting from the presence of an array of sensors around the target under test. A simple example is given to illustrate how this compensation can be implemented on an iterative Newton-Kantorovich reconstruction algorithm and to demonstrate its efficiency View full abstract»

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  • Application of stable FEM-FDTD hybrid to scattering problems

    Publication Year: 2002 , Page(s): 141 - 144
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    A recently developed, stable, finite-element method (FEM), finite-difference time-domain (FDTD) hybrid that eliminates the staircase approximation of complex geometries is tested by convergence studies for radar cross-sections. For a conducting sphere, 1 dB accuracy in all directions is obtained with nine cells per wavelength, whereas the NASA almond requires a higher resolution of about 15 cells per wavelength. For scatterers with a smooth boundary, the results converge quadratically with the mesh size, but for a horizontally polarized wave incident on the NASA almond, the order of convergence is lower because of singular fields at the tip View full abstract»

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  • Contoured beam reflector antenna for wireless applications

    Publication Year: 2002 , Page(s): 205 - 210
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (444 KB)  

    Wireless coverage in urban, suburban, and light industrial areas is a challenging problem for cellular network planners. This is mainly due to scattering from buildings and structures but also because area specific demographic features such as parks, streets, and sports arenas require specialized coverage. A contoured beam reflector antenna is a simple and effective solution for this problem, providing excellent control in both planes of the radiation pattern and a very sharp taper at the edge of coverage. The problem of wireless coverage planning using existing base-station antenna types is discussed, and a potential solution for these problems using contoured beam reflector antennas is demonstrated by examples. The implementation of this solution is made possible by using an inexpensive manufacturing technique involving a reconfigurable mould and a foam extrusion process View full abstract»

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  • Wideband linearly or circularly polarized monopulse tracking corrugated horn

    Publication Year: 2002 , Page(s): 192 - 197
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (321 KB)  

    A design of a wideband monopulse tracking corrugated horn, for either a linearly or a circularly polarized signal, is presented. Two types of suppressors are introduced to restrain the excitation of unwanted higher order modes. Parametric dependence curves of special points on the propagation characteristics are given for m=1 and m=2 modes in the ring-loaded corrugated horn. By using the suppressor and employing ring-loaded slots in the entire horn, the cross-polarization peak level of the horn can be reduced by a further 10 dB or more in the transmitting band, and its maximum level is less than -28 dB across C-band. The experimental results of return loss and sum and difference patterns validate that the feed possesses satisfactory wide-band communication and tracking characteristics View full abstract»

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  • A two-element horn-reflector antenna for cosmic microwave background astronomy

    Publication Year: 2002 , Page(s): 198 - 204
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (282 KB)  

    We present the design of a novel two-element horn-reflector antenna, which has been used on an interferometer built for studying the anisotropy in the cosmic microwave background at an angular scale of ≈2° and a frequency of 33 GHz. The design consists of a pair of closely packed parabolic mirrors fed by two rectangular corrugated horns, each at an offset angle of 75° to the axis of its mirror. The offset angle and the horn-reflector dimensions were chosen so that the antenna has elliptical primary beams producing a synthesized beam with circular lobes. We have designed and tested the radiation pattern of the individual antennas and the performance of the interferometer using bright radio sources. Our measurements revealed that the individual antennas have low sidelobes and that the crosstalk between the two elements of the interferometer is less than -80 dB. We therefore conclude that this design is suitable for the required astronomical application 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