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Antennas and Propagation, IEEE Transactions on

Issue 7 • Date Jul 1999

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Displaying Results 1 - 15 of 15
  • Single-feed slotted equilateral-triangular microstrip antenna for circular polarization

    Publication Year: 1999 , Page(s): 1174 - 1178
    Cited by:  Papers (40)  |  Patents (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    Novel designs of single-feed equilateral-triangular microstrip antennas for circular polarization (CP) are proposed and studied experimentally. It is demonstrated that by embedding a narrow slot or a cross slot of unequal slot lengths in the triangular patch, circularly polarized radiation of microstrip antennas can easily be achieved using a single probe feed. Furthermore, results show that for the design with a cross slot, the proposed antenna can perform CP radiation with a reduced antenna size at a given frequency (denoted as compact CP operation here); that is, the required antenna size is smaller for the proposed antenna for performing CP radiation as compared to a conventional circularly polarized triangular microstrip antenna at a fixed operating frequency. Details of the proposed CP designs are described, and typical experimental results are presented and discussed View full abstract»

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  • Beam scan using the quasi-optical antenna mixer array

    Publication Year: 1999 , Page(s): 1160 - 1166
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    The quasi-optical antenna mixer system transforms an RF signal into an intermediate frequency signal just after it spatially receives the RF signal and the local oscillator's (LO) signal. In this paper, we present a novel beam scanning system using the quasi-optical antenna mixer array and describe its principle of operation and the experimental results in the microwave band. The arrival direction of RF signals can be controlled by adjusting the LO incident angle and/or the LO frequency without implementing RF circuits such as phase shifters. Therefore, the novel beam-scanning system has no loss due to RF circuits and can be easily designed because of its simple composition View full abstract»

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  • Three-dimensional FDTD simulation of electromagnetic wave transformation in a dynamic inhomogeneous magnetized plasma

    Publication Year: 1999 , Page(s): 1146 - 1151
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    A three-dimensional (3-D) finite-difference time domain (FDTD) algorithm is developed to study the transformation of an electromagnetic wave by a dynamic (time-varying) inhomogeneous magnetized plasma medium. The current density vector is positioned at the center of the Yee cube to accommodate the anisotropy of the plasma medium due to the presence of a static magnetic field. An appropriate time-stepping algorithm is used to obtain accurate solutions for arbitrary values of the collision frequency and the electron cyclotron frequency. The technique is illustrated by calculating the frequency shifts in a cavity due to a switched magnetoplasma medium with a time varying and space-varying electron density profile View full abstract»

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  • Cross-polarization characteristics of a probe-fed hemispherical dielectric resonator antenna

    Publication Year: 1999 , Page(s): 1228 - 1230
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (92 KB)  

    The cross-polarization characteristics of a probe-fed hemispherical dielectric resonator antenna are studied theoretically. The mode-matching method was used to find the exact antenna Green's functions rigorously. The effects of the dielectric constant, probe length, and probe displacement on the cross-polarization level are examined View full abstract»

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  • Cross-floor signal propagation inside a contemporary ferro-concrete building at 434, 862, and 1705 MHz

    Publication Year: 1999 , Page(s): 1230 - 1232
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (44 KB)  

    Cross-floor signal propagation characteristics at 434, 862, and 1705 MHz were assessed from measured data in a building similar to a hospital as a first step toward maximizing electromagnetic compatibility (EMC) between wireless radiators within a hospital and medical equipment. Certain transmitter-receiver configurations resulted in 1/r d signal attenuation (d=2, and 3<4<4), while other configurations exhibited quasi-constant signal levels over increasing transmitter-receiver separations View full abstract»

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  • A high-gain 58-GHz box-horn array antenna with suppressed grating lobes

    Publication Year: 1999 , Page(s): 1125 - 1130
    Cited by:  Papers (14)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    A low-profile high-gain antenna array of box horns for the frequency band 57.2-58.2 GHz is presented. The antenna consists of 256 radiating elements divided into two subgroups of 128 elements fed by a rectangular waveguide feed network. The radiating elements are fed in parallel and the waveguides are connected with T-junctions. The matching of the T-junctions is improved with a matching pin and a splitter. Because of the waveguide feed network, the element spacing is larger than one wavelength, which causes grating lobes. The grating lobes and sidelobes in the H-plane have been suppressed by the use of a combination of subarrays, a special characteristic of the box horn, and an array amplitude tapering. The measured sidelobe levels in the H-plane are below -30 dB at angles larger than 8° from boresight. A gain higher than 35.7 dBi and a return loss higher than 14.4 dB have been measured for the antenna over the band 57.2-58.2 GHz View full abstract»

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  • On the use of Coifman intervallic wavelets in the method of moments for fast construction of wavelet sparsified matrices

    Publication Year: 1999 , Page(s): 1189 - 1200
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    Orthonormal wavelets have been successfully used as basis and testing functions for the integral equations and extremely sparse impedance matrices have been obtained. However, in many practical problems, the solution domain is confined in a bounded interval, while the wavelets are originally defined on the entire real line. To overcome this problem, periodic wavelets have been described in the literature. Nonetheless, the unknown functions must take on equal values at the endpoints of the bounded interval in order to apply periodic wavelets as the basis functions. We present the intervallic Coifman wavelets (coiflets) for the method of moments (MoM). The intervallic wavelets release the endpoints restrictions imposed on the periodic wavelets. The intervallic wavelets form an orthonormal basis and preserve the same multiresolution analysis (MRA) of other usual unbounded wavelets. The coiflets possesses a special property that their scaling functions have many vanishing moments. As a result, the zero entries of the matrices are identified directly, without using a truncation scheme with an artificially established threshold. Further, the majority of matrix elements are evaluated directly without performing numerical integration procedures such as Gaussian quadrature. For an n×n matrix, the number of actual numerical integrations is reduced from n2 to the order of 3n(2L-1), when the coiflets of order L is employed. The construction of intervallic wavelets is presented. Numerical examples of scattering problems are discussed and the relative error of this method is studied analytically View full abstract»

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  • A parametric model for synthetic aperture radar measurements

    Publication Year: 1999 , Page(s): 1179 - 1188
    Cited by:  Papers (39)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (936 KB)  

    We present a parametric model for radar scattering as a function of frequency and aspect angle. The model is used for analysis of synthetic aperture radar measurements. The estimated parameters provide a concise, physically relevant description of measured scattering for use in target recognition, data compression and scattering studies. The scattering model and an image domain estimation algorithm are applied to two measured data examples View full abstract»

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  • An implementation of a direction-finding antenna for mobile communications using a neural network

    Publication Year: 1999 , Page(s): 1152 - 1159
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB)  

    Direction-finding systems for radio signals are mostly used in mobile communications and avionics applications for antenna tracking or navigation purposes. In general, such systems require accurate calibration and may be sensitive to noise and external interference. In this paper, we investigate the performance of a neural network-based direction-finding system under such conditions. The proposed topology is a hybrid one, combining a simple RF signal beamformer with a neural network. The training of the neural network is accomplished experimentally with a three-element antenna array by varying the beam's direction and the carrier frequency. The error on the estimated direction of arrival caused by the environment and training limitations are investigated View full abstract»

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  • Differences between the narrow-angle and wide-angle propagators in the split-step Fourier solution of the parabolic wave equation

    Publication Year: 1999 , Page(s): 1131 - 1140
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2780 KB)  

    For tropospheric electromagnetic propagation, Maxwell's equations can be reduced to a parabolic wave equation, which is solved by marching over range steps. In each step, the solution is split into a product of three operators. The first and third account for atmospheric and surface variation, while the center operator propagates the field as though in vacuum. This center operator is the object of interest here. Older versions of the method used the narrow-angle propagator, while more recent versions use the wide-angle propagator. It was thought that the wide-angle propagator was entirely superior to the narrow-angle propagator, but some artifacts observed in experiments have led to the present investigation. The two propagators are examined numerically and analytically and found to exhibit subtle differences at large angles from the horizontal. This has required modifications to the way in which sources are created for starting the split-step solution. The narrow- and wide-angle propagators are also compared on two problems with analytic solutions to quantify the improvement of the wide-angle over the narrow-angle View full abstract»

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  • Local spectral analysis of short-pulse excited scattering from weakly inhomogeneous media. II. Inverse scattering

    Publication Year: 1999 , Page(s): 1218 - 1227
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    For Pt.I see ibid., vol.47, no.7, p.1208-17 (July 1999). This paper is concerned with the reconstruction of a weakly inhomogeneous scattering profile from data generated by a short-pulse incident plane wave, which is postprocessed so as to localize the interrogated region to a space-time resolved scattering cell, The phase-space localization due to postprocessing is brought about by applying local (i.e., windowed) slant-stack transforms to the time-dependent scattered fields. In the domain of the scatterer, this processing corresponds to applying windowed Radon transforms to the induced field distribution, which, in turn, generates pulsed-beam (PB) wave packets traveling toward the observer. The forward analysis parameterizing this new form of time-domain (TD) diffraction tomography has been performed in a companion paper and furnishes the framework for the investigation here. Via the forward parameterization, the three-dimensional (3-D) global scattering phenomenology has been reduced to scattering from an equivalent one-dimensional (1-D) scattering cell oriented along the bisector between the direction of the incident plane pulse and the direction of the scattered pulsed beam (PB) to the observer. For the inverse problem, this process is reversed by windowing the scattered field and backpropagating the resulting PBs so as to form local images of any selected region in the scattering domain. The phase-space signature of the scattering cell is related to the Radon transform of the medium in the cell so that the local profile function can be recovered by Radon inversion. An illustrative numerical example is included. Also discussed is the ultimate localization achieved by incident PB excitation and PB postprocessing of the scattered field View full abstract»

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  • Absorbing boundary conditions for convex object-conformable boundaries

    Publication Year: 1999 , Page(s): 1141 - 1145
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB)  

    Absorbing boundary conditions (ABCs) are developed that can be applied on object-conformable outer boundaries. The new ABCs are based on the local enforcement of the Nth order Bayliss-Turkel boundary conditions where a scattering center is defined for each outer boundary node. A demonstration of the effectiveness of the new construction is provided by considering representative numerical experiments using the finite-elements method. Results show that the new ABCs provide accuracy that compares very favorably with the method of moments solution View full abstract»

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  • A shaped-beam microstrip patch reflectarray

    Publication Year: 1999 , Page(s): 1167 - 1173
    Cited by:  Papers (69)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    This paper describes a microstrip reflectarray antenna designed to produce a shaped-beam coverage pattern using phase synthesis. The concept is demonstrated with a Ku-band linearly polarized reflectarray designed to provide coverage of the European continent and measured results are compared to those obtained for a previously designed shaped-reflector antenna designed for the same coverage specifications. Results validate the shaped-beam reflectarray concept, although there are disadvantages to the reflectarray such as narrow bandwidth and reduced aperture efficiency that may offset the mechanical and cost advantages of the flat surface of the reflectarray View full abstract»

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  • Local spectral analysis of short-pulse excited scattering from weakly inhomogeneous media. I. Forward scattering

    Publication Year: 1999 , Page(s): 1208 - 1217
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    In this two-part sequence, we extend a previously formulated pulsed plane wave (PPW)-based time-domain (TD) diffraction tomography for forward and inverse scattering from weakly inhomogeneous lossless nondispersive media to a more highly localized pulsed beam (PB) wavepacket-based diffraction tomography. In the PPW version, the incident and scattered fields have been parameterized in the space-time wavenumber domain in terms of slant-stacked TD plane waves whose wavefronts move through the scattering medium at the ambient propagation speed, thereby accumulating information along time-resolved laterally extended planar cuts. The PB parameterized localization confines the laterally sampled regions to the spatial domains of influence transverse to the relevant beam axes. These localizations are performed in two stages. The present paper implements the PB parameterization by PB post processing of the forward scattered fields excited by an incident PPW; the companion paper (Part 2, see ibid., vol.47, no.7, p.1218-27, July 1999) deals with the inverse problem by back propagation of the PB parameterized data. An “ultimate” localization of a space-time resolved scattering cell is also briefly summarized in Part 2 View full abstract»

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  • The matrix Riccati equation for scattering from stratified chiral spheres

    Publication Year: 1999 , Page(s): 1201 - 1207
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    Angular scattering from radially stratified spherical chiral objects is investigated. Based on the principles of invariant embedding, we formulate a matrix Riccati equation that can be used to examine basic scattering properties of spherical chiral structures with radial inhomogeneities in permittivity, permeability, and chirality. High- and low-frequency limits as well as weak reflection and constant impedance cases for this equation are examined. We show that in the limit of large radii of curvature, this formulation yields the planar result 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