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Antennas and Propagation, IEEE Transactions on

Issue 1 • Date Jan 1997

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Displaying Results 1 - 25 of 31
  • Evidence for the presence of turbulent attenuation on low-elevation angle Earth-space paths. I. Comparison of CCIR recommendation and scintillation observations on a 3.3° path

    Publication Year: 1997 , Page(s): 73 - 84
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    This paper presents the results of and conclusions drawn from two experimental studies of low-elevation slant-path scintillation. The paper describes observations made on an 11.2 GHz, 3.3° path over a two and a half year period. Received signal strength and a variety of concurrent meteorological parameters were recorded. The resulting database has enabled the veracity of the 1990 International Telecommunications Union-Radio [(ITU-R)-formerly International Consultative Radio Committee (CCIR)] model to be determined. An interesting discrepancy between the CCIR prediction procedure and the experimental data suggests an as yet unmodeled scintillation mechanism operating in wet summer weather View full abstract»

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  • Evidence for the presence of turbulent attenuation on low-elevation angle Earth-space paths. 2. Frequency scaling of scintillation intensity on a 10° path

    Publication Year: 1997 , Page(s): 85 - 92
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    For pt.1 see ibid., vol.45, no.1, p.73-84 (1997). This paper presents the results of and conclusions drawn from two experimental studies of low-elevation, slant-path scintillation. Part I related to 11.2-GHz measurements at an elevation angle of 3.3°. Part II describes 14- and 11-GHz observations made on a (nominal) 10° path over a four year period. The resulting time-series data have enabled frequency scaling to be investigated in some depth. Scintillation occurring during periods unassociated with fading is found to be well modeled in its frequency scaling behavior by classical theories of clear air turbulence (CAT). This is not the case, however, for scintillation that occurs during, just before, or just after rain-induced fading. A rapidly fluctuating attenuation mechanism, not separable from CAT-induced scintillation on the basis of its spectrum alone, is thought to be responsible for this anomalous frequency-scaling result View full abstract»

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  • Equivalence between physical optics and aperture integration for radiation from open-ended waveguides

    Publication Year: 1997 , Page(s): 183 - 185
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (88 KB)  

    The eigen-mode radiation from an open-ended waveguide of arbitrary cross section is considered. The following theorem is demonstrated: the Kirchhoff-Kottler aperture integration for the radiated field is equivalent to the physical-optics (PO) approach applied to the wall currents. This theorem allows one to resort to aperture integration for those structures involving complicated PO integration. On the other hand, based on the same theorem the aperture integration may be reduced to a line integral along the edge of the waveguide for those configurations that allow a simple PO integration. It can also be useful in developing more efficient solutions in the framework of incremental theories View full abstract»

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  • Compact range reflector edge treatment impact on antenna and scattering measurements

    Publication Year: 1997 , Page(s): 57 - 65
    Cited by:  Papers (3)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    Compact range measurements with a serrated edge and a blended, rolled edge reflector are compared. This is done by using simulated antenna pattern and backscattered field measurements. The measurement errors caused by stray signals emanating from the edge termination of reflector are discussed. It has been found that different stray signal sources impact on the measurement accuracy from different aspect angles. In addition, the measurement accuracy achievable with different reflector systems is dependent on the characteristics of the antenna or scatterer under test. From these findings, one will be better able to understand how well these two types of reflectors will perform in terms of accurately providing the proposed measurements. Consequently, one will be able to choose the best reflector design for his/her application View full abstract»

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  • Diffraction of electromagnetic wave on multielement diffraction grating

    Publication Year: 1997 , Page(s): 15 - 19
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    The problem of plane-wave diffraction on a multielement grating of arbitrarily shaped cylindrical screens is rigorously solved using the integral equations technique. An integral representation of the Green's function of the problem is suggested. It substantially allows improvement of the calculation accuracy and effectiveness of solving. In the case of illumination by a normal E-polarized wave, a resonance penetration of it through the array is analyzed View full abstract»

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  • Modeling radiation with an efficient hybrid finite-element integral-equation waveguide mode-matching technique

    Publication Year: 1997 , Page(s): 34 - 39
    Cited by:  Papers (6)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    A method is presented to model electromagnetic radiation, combining the finite-element technique in the penetrating portion of a three-dimensional (3-D) radiating structure with an integral equation on the outer surface of the computational domain, and with a waveguide mode-matching technique on a cross section of the feeding waveguide. The antenna can be of general shape, provided a portion of the surrounding medium up to a surface of revolution is chosen as part of the computational domain. This truncation scheme and the accurate source representation are more general than those existing in the literature for radiation modeling. An open-ended waveguide and a waveguide with a choke ring are analyzed and their radiation patterns are obtained and compared with available measurements View full abstract»

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  • Application of maximum likelihood estimation to radar imaging

    Publication Year: 1997 , Page(s): 20 - 27
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    An efficient maximum likelihood (ML) estimator to obtain the scattering center locations of a target and the relative scattering level of these scattering centers from the scattered field data is described. In the proposed method, ML estimation is carried out in the image domain rather than in the frequency-aspect domain. A two-dimensional (2-D) inverse Fourier transform is used to transfer the scattered field data from frequency-aspect domain to the image domain (down-range/cross-range). As expected, the scattered field data in the image domain has some regions with high energy. The samples in the high-energy regions are used to obtain the initial guess for the ML estimator as well as for ML estimation. The ML estimator in the image domain is applied to both simulated and experimental scattered fields of some targets View full abstract»

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  • Pattern optimization of a reflector antenna with planar-array feeds and cluster feeds

    Publication Year: 1997 , Page(s): 93 - 97
    Cited by:  Papers (14)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    We study pattern optimization of a parabolic reflector with planar-array feeds and cluster feeds. The optimization is carried out within the conjugate gradient method (CGM) in which the optimum weight vector of a linearly constrained minimum variance (LCMV) beam former is used as the initial condition. Optimization with the CGM to determine element weights is found to yield better sidelobe suppression and true settlement of desired scan direction compared to the LCMV beam former and conjugate field matching (CFM) techniques for the continuous beam-scanning case. The proposed method is also applied to multibeam reflector-antenna design View full abstract»

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  • Photonic band-gap materials for high-gain printed circuit antennas

    Publication Year: 1997 , Page(s): 185 - 187
    Cited by:  Papers (81)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    It is found through a vector integral-equation analysis and the reciprocity theorem that the gain of a microstrip antenna can be greatly enhanced with a photonic band-gap material layer either as the substrate or the superstrate. The beam angle is found to coincide with that of a leaky-wave mode of a planar-grating structure. This observation suggests that high gain is due to the excitation of strong leaky-wave fields View full abstract»

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  • Extrapolation of time-domain responses from three-dimensional conducting objects utilizing the matrix pencil technique

    Publication Year: 1997 , Page(s): 147 - 156
    Cited by:  Papers (50)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    In this paper, we use the matrix pencil approach to extrapolate time-domain responses from three-dimensional (3-D) conducting objects that arise in the numerical solution of electromagnetic field problems. By modeling the time functions as a sum of complex exponentials, we can eliminate some of the instabilities that arise in late times for the electric-field integral equation in the time domain. However, this method can also be utilized for extending the responses obtained using a finite-difference time-domain (FDTD) formulation View full abstract»

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  • Removal of surface-wave induced radiation nulls for patch antennas integrated with vehicle windscreens

    Publication Year: 1997 , Page(s): 176 - 177
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (64 KB)  

    A solution to the problem of radiation nulls for patch antennas integrated with vehicle windscreens is presented. The nulls, attributable to surface waves within the windscreen superstrate, are removed by the addition of a thin resistive film to the windscreen surface. Analysis of the surface-wave modes at 5.8 GHz within two typical laminated windscreen structures coated with a resistive film shows a sheet resistance value of 50 Ω/sq to be appropriate. Polar-pattern results demonstrate the effectiveness of the technique in removing the radiation nulls without significantly reducing the forward gain View full abstract»

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  • An approximation of the radiation integral for distorted reflector antennas using surface-error decomposition

    Publication Year: 1997 , Page(s): 5 - 10
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    The physical optics/aperture integration (PO/AI) formulation is often used to analyze the radiation patterns of reflector antennas. In this study, the PO/AI radiation integrals for distorted reflector antennas are addressed. The surface error of the antennas is approximated by a series of surface expansion functions. The radiation integral is decomposed into a series of radiation-type integrals, each of which corresponds to one of the surface expansion functions. Each of these radiation-type integrals is then weighted by amplitude coefficients. The advantage of performing the decomposition is that each of the radiation-type integrals can be computed and the pattern data stored. The computation of the pattern for a distorted reflector antenna with a changing error profile is performed by recalling the pattern data for each perturbation term and weighting it with the amplitude coefficient. This facilitates rapid evaluation of the radiation integral in cases where the error profile is changing (for example, time-varying errors). The superposition of integrals presented in this paper was shown to be valid for surface-error profiles up to 0.1 λ rms amplitude View full abstract»

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  • Transparent boundary conditions for parabolic equation solutions of radiowave propagation problems

    Publication Year: 1997 , Page(s): 66 - 72
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    Perfectly transparent boundary conditions are derived for truncating the integration domain when solving radiowave propagation problems with a parabolic equation (PE) method. The boundary conditions are nonlocal: they are expressed as a convolution integral involving the field at all previous ranges. The convolution kernel is matched to the refractive index vertical gradient at the boundary. The boundary conditions include an incoming energy term which can model an arbitrary incident field. In particular, they may be used with plane-wave incidence, or with a point-source located below or above the domain boundary. If required, the solution can be extended to heights above the boundary with a generalized horizontal PE method. Closed-form solutions for the incoming energy term are given for plane-wave incidence and for Gaussian sources when the refractive index above the boundary is constant or linear. The resulting finite-difference algorithms provide efficient solutions to problems involving airborne sources. Numerical examples are given, showing excellent agreement with a pure split-step/Fourier PE algorithm View full abstract»

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  • The complex bi-conjugate gradient solver applied to large electromagnetic scattering problems, computational costs, and cost scalings

    Publication Year: 1997 , Page(s): 140 - 146
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB)  

    The complex bi-conjugate gradient iterative method is applied to an isoparametric boundary integral equation formulation for frequency-domain electromagnetic scattering problems. It is demonstrated to work well on large and geometrically complex examples, including a 20 wavelength slender dipole, the NASA almond, and a resonant cavity. On such problems, with asymmetric curvilinear irregular meshes and nontrivial geometries, the number of iterations required seems to increase rather more than linearly with body size, indicating an overall ~sixth power cost scaling. This scaling is essentially as for direct methods, but with costs still a small fraction of the direct approach. A method is proposed for the selection of a termination condition designed to avoid seeking the approximate answer too precisely; it typically permits a further halving of costs View full abstract»

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  • A hybrid FE-FMM technique for electromagnetic scattering

    Publication Year: 1997 , Page(s): 180 - 181
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (64 KB)  

    The authors apply a version of the fast multipole method (FMM) to reduce the storage and computational requirement of the boundary integral in the finite-element boundary-integral method. By virtue of its O(N1.5) operation count, the application of the single-stage FMM results in substantial speedup of the boundary-integral portion of the code, independently of the shape of the boundary-integral contour. They discuss the efficiency of the method and present an application of the technique to electromagnetic scattering from large grooves recessed in a ground plane View full abstract»

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  • An SBR/image approach for radio wave propagation in indoor environments with metallic furniture

    Publication Year: 1997 , Page(s): 98 - 106
    Cited by:  Papers (62)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (424 KB)  

    In this paper, we propose a deterministic approach to model the radio wave propagation channels in complex indoor environments. This technique applies the modified shooting-and-bouncing-ray (SBR) method to find the equivalent sources (images) for each launched ray tube. In addition, the first-order wedge diffraction from furniture is included and the diffracted rays also can be attributed to the corresponding images. By summing the contributions of all these images coherently, we can obtain the total received field at a receiver. Besides, the vector-effective height (VEH) of an antenna is introduced to consider the polarization coupling effect resulting from multiple reflection inside the rooms. We verify this approach by comparing the numerical results in three canonical examples where closed-form solutions exist. The good agreement indicates that our method can provide a good approximation of high-frequency radio propagation inside rooms where multiple reflection is dominant. Work reported in this paper has shown that the propagation loss in indoor environments varies considerably according to furniture and polarizations View full abstract»

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  • A comparison of anisotropic PML to Berenger's PML and its application to the finite-element method for EM scattering

    Publication Year: 1997 , Page(s): 40 - 50
    Cited by:  Papers (41)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    The use of an anisotropic material for the boundary truncation of the finite-element method is considered. The anisotropic material properties can be chosen such that a plane-wave incident from free space into the anisotropic halfspace has no reflection. Because there is no reflection, the material is referred to as a perfectly matched layer (PML). The relationship between the anisotropic PML and the original PML proposed by Berenger (see J. Comp. Phys., vol.114, p.185-200, October 1994) is considered. The anisotropic PML is applied to the finite-element solution of electromagnetic (EM) scattering from three-dimensional (3-D) objects. Numerical results are presented to demonstrate the accuracy of the PML View full abstract»

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  • Power densities in the near field of a large antenna focused to infinity

    Publication Year: 1997 , Page(s): 181 - 183
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (84 KB)  

    At low-beam elevation angles, measurements of microwave propagation from satellite to ground have exhibited large variations in signal strength under clear weather and cloudy conditions. Large nonuniformities in the three-dimensional (3-D) near-field region of an antenna focused to infinity have been computed. These field nonuniformities interacting with a dynamic turbulent troposphere can introduce phase errors at the antenna aperture, resulting in signal scintillation and loss View full abstract»

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  • Scattering by an indentation satisfying a dyadic impedance boundary condition

    Publication Year: 1997 , Page(s): 28 - 33
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    We derive a pair of boundary integral equations for the problem of scattering of an electromagnetic wave by an indentation in a perfectly conducting screen. The wall of the indentation obeys a dyadic impedance boundary condition. The unknowns are the electric current density on the wall of the indentation and the total tangential magnetic field in the opening of the indentation. We also derive integral representations for the fields everywhere in free space, including the far-field region. In all cases, the integrals involved extend over finite surfaces only View full abstract»

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  • Design of a loaded monopole having hemispherical coverage using a genetic algorithm

    Publication Year: 1997 , Page(s): 1 - 4
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (80 KB)  

    A genetic algorithm is used to design a monopole loaded with a modified folded dipole so that it radiates uniform power over the hemisphere. Each of the wires that make up the antenna are given a range of possible lengths. The genetic algorithm randomly selects a sample population of possible antenna configurations from the total population of all configurations. The radiation pattern of each sample configuration is computed using the numerical electromagnetics code (NEC). The solutions are compared with the desired pattern and ranked in terms of performance. The best solutions are retained and mated with one another and the process is repeated until an optimal solution is obtained. The genetic algorithm quickly produced an antenna that has a nearly uniform power over the hemisphere. Although the antenna was designed to operate at a frequency of 1.6 GHz, it performed satisfactorily over the frequency range from 1.4 to 1.8 GHz. The antenna was fabricated and the computational results were verified experimentally. We have shown that the genetic algorithm is a very powerful tool for designing wire antennas; it is expected that this process can be used to design any antenna that can be analyzed using an electromagnetic code View full abstract»

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  • Robust adaptive array beamforming under steering vector errors

    Publication Year: 1997 , Page(s): 168 - 175
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (284 KB)  

    This paper considers adaptive array beamforming in the presence of random steering vector errors. We first formulate the problem of finding an optimal steering vector as an optimization problem. The cost function to be minimized consists of two terms which utilize a posteriori information due to the received signal data and a priori information due to the probabilistic distribution of steering errors, respectively. Two methods are then presented to find the optimal steering constraint vector. It is shown that each method yields a closed-form optimal solution if the steering error vector is an additive Gaussian random vector. We also investigate the performance for each method. Modification of the proposed methods and an implementation algorithm for dealing with the case of steering vector errors due to phase perturbation are also presented. Finally, several computer simulation examples are presented for illustration View full abstract»

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  • Exact solution for a penetrable wedge structure

    Publication Year: 1997
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (32 KB)  

    A structure consisting of four penetrable wedges with a common edge is considered. For a certain polarization and direction of incidence of the primary plane wave, the edge does not scatter and geometrical optics is the exact solution. Two derivative structures are described that also do not scatter-one consisting of two parallel edges and the other of the junction of two parallel-plate waveguides View full abstract»

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  • Forbidden directions for TM waves in anisotropic conducting media

    Publication Year: 1997 , Page(s): 133 - 139
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB)  

    We investigate the wave propagation properties of nonuniform plane waves in an (unbounded homogeneous) anisotropic conducting material. Such waves (for which amplitudes vary across surfaces of constant phase) characterize the refracted field in an imperfect dielectric, like the earth when a uniform electromagnetic plane wave is incident from the air. The results, presented in terms of polar diagrams of the attenuation, slowness, energy velocity, and quality factor predict the existence of “stopbands” beyond a given degree of nonuniformity (i.e., combinations of propagation and attenuation directions where there is no wave propagation). This is a peculiar, effect due to the joint presence of anisotropy and conductivity that may have application in the design of synthetic materials acting as absorbers of electromagnetic radiation View full abstract»

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  • The tab monopole

    Publication Year: 1997 , Page(s): 187 - 188
    Cited by:  Papers (42)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (60 KB)  

    A new, compact, broadband printed antenna called the tab monopole is described. The tab monopole is a small antenna designed primarily for applications requiring antennas that can be readily integrated with printed circuit boards. The tab monopole is smaller than a quarter wavelength in size but provides a 2:1 VSWR bandwidth of greater than 50%. Measured S11 and gain patterns are provided View full abstract»

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  • Calculation of radiation patterns of microstrip antennas on cylindrical bodies of arbitrary cross section

    Publication Year: 1997 , Page(s): 126 - 132
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    A simplified approach based on reciprocity is presented to calculate the radiation patterns of microstrip patch antennas or arrays on a cylindrical body having an arbitrary cross section. In this approach, the microstrip patch antennas are characterized using the finite-element method, and their radiation patterns are then calculated using a two-dimensional method of moments in conjunction with the reciprocity theorem. The validity of the calculation is demonstrated by comparison with measured data for a microstrip patch antenna on a circular cylinder attached to a plate. Other numerical examples are also presented to show the capability of the method as well as various effects of the host cylinder on radiation patterns 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