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Antennas and Propagation Magazine, IEEE

Issue 1 • Date Feb. 1999

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Displaying Results 1 - 18 of 18
  • The Third Annual Special Session On Image Reconstruction Using Real Data, Part 1

    Publication Year: 1999 , Page(s): 34 - 36
    Cited by:  Papers (1)
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  • Quasioptical Systems: Gaussian Beam Quasioptical Propaga- Derived Results To Reveal The Underlying Physics And Implications [Book Review]

    Publication Year: 1999 , Page(s): 104 - 105
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    Freely Available from IEEE
  • Using Model-based Parameter Estimation For Estimating Data 2 Uncertainty

    Publication Year: 1999 , Page(s): 112 - 115
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  • Upon The Shoulders Of Giants

    Publication Year: 1999 , Page(s): 116
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  • Radiowave Propagation In ITU-R

    Publication Year: 1999 , Page(s): 118 - 119
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  • IEEE Engineering Management Society: A Resource For Your IEEE Responsibilities And Your Career

    Publication Year: 1999 , Page(s): 142 - 145
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  • Ethically Speaking

    Publication Year: 1999 , Page(s): 146
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  • Intellectual Property And Patent Abstracts

    Publication Year: 1999 , Page(s): 148 - 154
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  • A numerical method to solve the inverse medium problem: an application to the Ipswich data. II

    Publication Year: 1999 , Page(s): 44 - 47
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    For pt.I see ibid., vol.39, no.14-19 (1997). The following electromagnetic inverse scattering problem is considered: reconstruction of the refractive index of a cylindrically symmetric inhomogeneity from knowledge of the scattered electromagnetic fields, when the inhomogeneity is hit by known incident electromagnetic fields. Taking advantage of the cylindrical symmetry, the problem for the Maxwell equations is reduced to a boundary-value problem for the two-dimensional scalar Helmholtz equation. The inverse problem is formulated using the Born approximation for the far-field patterns of the scattered fields. The numerical algorithm proposed in Maponi et al. (1997) is used View full abstract»

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  • Linearly polarized radial-line slot-array antennas with improved return-loss performance

    Publication Year: 1999 , Page(s): 52 - 61
    Cited by:  Papers (25)
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    The standard linearly polarized radial-line slot-array (RLSA) antenna exhibits poor return loss as seen by its coaxial feed. This paper describes techniques that improve the poor return-loss performance of this antenna, by using two interchangeable methods: i) reflection-canceling slots on the front and back surface of the antenna, and ii) beam squinting. A series of 550 mm diameter linearly polarized Ku-band prototype antennas were constructed to experimentally investigate the efficiency of each of these methods. In order to cut experimental costs, initial radiation-pattern modeling was performed theoretically, and then prototypes were developed using inexpensive aluminum foil. Measurements of the developed prototypes indicated that both the reflection-canceling and beam-squinting methods provided a substantial improvement in return loss over the desired frequency band View full abstract»

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  • The orthogonal method for the geometry synthesis of a linear antenna array

    Publication Year: 1999 , Page(s): 96 - 99
    Cited by:  Papers (3)
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    The orthogonal method for geometry synthesis of a linear antenna array is presented. We start from an initial array, and we perturb the element positions by using an iterative procedure and applying the orthogonal method. Applications for arrays with uniform excitation give patterns with the desired sidelobe level View full abstract»

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  • P(MoM/MAS): an interactive environment, coupling WWW technology and parallel processing, to solve large-size electromagnetic problems

    Publication Year: 1999 , Page(s): 130 - 137
    Cited by:  Papers (4)
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    Parallel processing over the Internet is now becoming a realistic possibility. There are numerous of-the-shelf high-performance computing (HPC) platforms available with Internet access, on which to implement computationally intensive algorithms. HPC can be applied in the field of computational electromagnetics. The networking capabilities of the Internet now allow these computing resources to be used as a remote service. Additionally, the pragmatics of their utilization can be abstracted by adopting a World Wide Web (WWW) interface. A Web-based environment can provide the supportive tools for data entry, program initiation, result visualization, and even interactive modifications of the geometry and/or electromagnetic (EM) properties. For realistic interaction, the emerging question is which algorithm to use that supports the exploitation of parallelism. In order to exploit and utilize all the available performance of current and predicted HPC platforms, inherently-parallel-based algorithms have to be devised. One such algorithm is the parallel method of moments/method of auxiliary sources, P(MoM/MAS), introduced in this paper. The resulting algorithm parallelization enables the MoM/MAS method to be applied to solving electrically-large-in-size and complex EM structures on various computational platforms. This paper concentrates on the parallel-processing issues, and on the importance of adopting suitable algorithms, such as the MoM/MAS technique View full abstract»

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  • How Ewen and Purcell discovered the 21-cm interstellar hydrogen line

    Publication Year: 1999 , Page(s): 7 - 17
    Cited by:  Papers (1)
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    The story of how Harold Irving Ewen and Edward Mills Purcell detected the first spectral line ever observed in radio astronomy, in 1951, has been told for general audiences by Robert Buderi (1996). The present article has a different purpose. The technical roots of Ewen and Purcell's achievement reveal much about the way science often depends upon “borrowed” technologies, which were not developed with the needs of science in mind. The design and construction of the equipment is described in detail. As Ewen's photographs, records, and recollections show, he and Purcell had access to an unusual combination of scientific knowledge, engineering know-how, critical hardware, and technical assistance at Harvard, in 1950 and 1951. This combination gave them a competitive edge over similar research groups in Holland and Australia, who were also striving to detect the hydrogen line, and who succeeded only weeks after the Harvard researchers did. The story also shows that Ewen and Purcell did their groundbreaking scientific work in the “small-science” style that prevailed before World War II, while receiving substantial indirect help from one of the first big-science projects at Harvard View full abstract»

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  • Imaging of unknown targets from measured scattering data

    Publication Year: 1999 , Page(s): 40 - 44
    Cited by:  Papers (1)
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    We have adopted a simple signal-processing-based approach to solving the inverse-scattering problem. We have applied these techniques to real data, measured at Rome Laboratory using microwaves, and to model targets whose structure is known a priori, the so-called Ipswich mystery data. Making these data available to the imaging community at large, but without revealing the structure of the target, has proven to be a very important exercise when it comes to comparing different inversion techniques and their claimed success. In our case, data were processed using an inversion method based on cepstral filtering. All of the so-called mystery targets were imaged, although their resolution was poor. The poor resolution results in part from the limited number of data points used in the inversion step View full abstract»

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  • A personal memoir of James R. Wait

    Publication Year: 1999 , Page(s): 62 - 65
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    Presents a biography of James Wait (1924-1998) based on the personal knowledge of the author View full abstract»

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  • Target recognition from limited-angle backscatter data

    Publication Year: 1999 , Page(s): 36 - 40
    Cited by:  Papers (1)
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    The problem of determining the nature of a target from limited backscatter data has two difficult features. The first is the problem of inverting scattered-field data when multiple scattering arises. There are few procedures to do this, and even fewer computationally feasible algorithms. The second problem lies in the fact that these methods expect to have scattering data taken all around a target, for all possible illumination directions. We have developed a spectral-estimation technique that can make use of prior knowledge about the target, to improve resolution when only limited data are available. It transpires that this approach is particularly effective at identifying support bounds on an actual target. These support bounds provide a better indicator of what the target is than the image derived from the same scattering data, especially when the data are too few to generate a meaningful image. From this we conclude that with a certain number of data points, and a certain degree of detail in one's prior knowledge of a target set, one can determine whether the best course of action is to “shape” the target using a dynamic prior function, or to form an image, in order to make the identification. These latter observations were carried out using real data acquired from a model of a cruise missile. Being a metallic target, there was little multiple scattering, and the inverse-scattering aspect of the identification step was not demanding View full abstract»

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  • Ultra-wide-band synthetic-aperture radar for mine-field detection

    Publication Year: 1999 , Page(s): 18 - 33
    Cited by:  Papers (52)
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    A full-wave model is developed for electromagnetic scattering from buried and surface land mines (both conducting and plastic), taking rigorous account of the lossy, dispersive, and potentially layered properties of soil. The (polarimetric) theoretical results are confirmed via synthetic-aperture radar (SAR) measurements, performed using the US Army Research Laboratory's BoomSAR, with which fully polarimetric ultra-wide-band (50-1200 MHz) SAR imagery is produced. The SAR system is used to acquire a large database of imagery, including a significant distribution of naturally occurring clutter. Several techniques are used for mine detection with such data, including several detectors that are based on target features gleaned from the modeling, as well as a matched-filter-like detector that directly incorporates the target signatures themselves. In addition, the theoretical model is used to predict wave phenomenology in various environments (beyond the limited range of parameters that can be examined experimentally). Since the efficacy of radar-based subsurface sensing depends strongly on the soil properties, we perform a parametric study of the dependence of such on the target RCS, and on possible landmine resonances View full abstract»

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  • Image reconstruction from the 1997 Ipswich data using a conjugate-gradient algorithm

    Publication Year: 1999 , Page(s): 48 - 51
    Cited by:  Papers (1)
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    The conjugate gradient algorithm is shown to be effective in reconstructing targets from experimental radar measurements. Enhancement, using the reciprocity relation to complete the scattered data, is also shown. The small number of iterations needed to obtain a satisfying solution (less than 50 iterations), combined with the increasing computation power of new processors (an SGI R10000 needs 30 sec to compute one iteration), make it possible for this algorithm to be used for practical applications View full abstract»

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The IEEE Antennas and Propagation Magazine covers all areas relating to antenna theory, design, and practice.

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Mahta Moghaddam