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  • Other Sources  (324)
  • COMMUNICATIONS AND RADAR  (324)
  • 2015-2019
  • 1990-1994  (324)
  • 1992  (324)
  • 1
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    Mutual coupling between parallel columns of periodic slots in a ground plane surrounded by dielectric slabs (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Arrays of slots with arbitrary orientation in a conducting plane which are infinitely periodic in one dimension and finitely periodic in another dimension are considered. The perfect conducting plane extends infinitely and is bounded on each side by dielectric slabs of finite thickness and infinite extent. Single columns of slots are represented by equivalent magnetic scattering currents, which are solved for via the moment method. The mutual coupling (admittance) between slot columns in the presence of the stratified media is found by the array scanning method (ASM), which expresses the admittance as the average of the scan admittance of an artificially constructed doubly infinite array of slots over all real scan angles. The technique avoids the use of Sommerfeld integrals, but still gives rise to singularities at scan angles corresponding to the resonant excitation of surface waves. An analytical approximation is made to remove these surface wave singularities, thus making numerical implementation of the method practical. The method is quite general and may be extended to thin slot elements of arbitrary shape and orientation.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 40; 11; p. 1324-1335.
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  • 2
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    Coplanar waveguide feed for microstrip patch antennas (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A coplanar waveguide (CPW) loop is shown to be an effective low VSWR feed for microstrip antennas. The low VSWR transition between the CPW and the antenna is obtained without the use of a matching circuit, and it is relatively insensitive to the position of the antenna and the feed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Electronics Letters (ISSN 0013-5194); 28; 25; p. 2272-2274.
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  • 3
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    Multiresolution image gathering and restoration (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: In this paper we integrate multiresolution decomposition with image gathering and restoration. This integration leads to a Wiener-matrix filter that accounts for the aliasing, blurring, and noise in image gathering, together with the digital filtering and decimation in signal decomposition. Moreover, as implemented here, the Wiener-matrix filter completely suppresses the blurring and raster effects of the image-display device. We demonstrate that this filter can significantly improve the fidelity and visual quality produced by conventional image reconstruction. The extent of this improvement, in turn, depends on the design of the image-gathering device.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Journal of Visual Communication and Image Representation (ISSN 1047-3203); 3; 4; p. 356-363.
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  • 4
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    A periodic moment method solution for TM scattering from lossy dielectric bodies with application to wedge absorber (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The periodic moment method (PMM) solution for the scattering from two-dimensional lossy dielectric bodies is developed in this paper. The purpose is to design microwave wedge absorber for low reflectivity so that one can improve the performance of anechoic chamber measurements. With PMM, the reflection and transmission coefficients of periodically distributed bodies illuminated by a plane wave have been accurately calculated using a Cray Y-MP supercomputer. Through these studies, some wedge absorber configurations have been designed, fabricated, and then tested in the OSU/ESL compact range measurement facility. Two 8 in. commercial wedges, a curved wedge, and a four-layer wedge are studied in this paper. In all cases, good agreement between calculations and measurements has been obtained.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 40; 6, Ju; 652-660
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  • 5
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    Performance of a K-band superconducting annular ring antenna (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Superconducting annular ring antennas operating in the TM12 mode at 21 GHz are designed and fabricated on a lanthanum aluminate substrate using a YBCO high-temperature superconducting thin film. The efficiencies and far-field antenna patterns are measured and compared with an identical antenna patterned with silver. The resonant frequencies and experimental far-field patterns agree well with published models, and efficiency measurements show a maximum improvement of 6 percent at 20 K in the efficiency of the HTS antenna when compared to the silver ring at the same temperature.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Microwave and Optical Technology Letters (ISSN 0895-2477); 5; 6, Ju
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  • 6
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    A unified perturbation expansion for surface scattering (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Starting with the extinction theorem, a perturbation expansion which, to first and second orders, converges over a wider domain than the small perturbation expansion and the momentum transfer expansion is presented. It is shown that, in the appropriate limits, both of these theories, as well as the two-scale expansion, are recovered. There is no adjustable parameter, such as a spectral split, in the theory. This theory is applied to random rough surfaces and derive analytic expressions for the coherent field and the bistatic cross section. Finally, a numerical test of the theory against method of moments results for Gaussian random rough surfaces with a power law spectrum is given. These results show that the expansion is ramarkably accurate over a large range of surface heights and slopes for both horizontal and vertical polarization.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Radio Science (ISSN 0048-6604); 27; 79-93
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  • 7
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    Modeling of resistive sheets in finite element solutions (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A formulation is presented for modeling a resistive card in the context of the finite element method. The appropriate variational function is derived and for variational purposes results are presented for the scattering by metal-backed cavity loaded with a resistive card.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); 40; 6, Ju; 727-731
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  • 8
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    A communication protocol for mobile satellite systems affected by rain attenuation (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A communication protocol is described that has been developed as part of a K/Ka-band mobile terminal breadboard system to be demonstrated through NASA's Advanced Communications Technology Satellite (ACTS) in 1993. The protocol is aimed at providing the means for enhancing link availability and continuity by supporting real-time data rate selection and changes during rain events. Particular attention is given to the system architecture; types of links, connections, and packets; the protocol procedures; and design rationales.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); 10; 6, Au
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  • 9
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    Comparison of the Unified Perturbation Method with the two-scale expansion (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Unified Perturbation Method (UPM) converges faster over a wider domain of surface roughness than other perturbations, such as the small perturbation method, the phase perturbation method, the Kirchhoff approximation, and the momentum transfer expansion. It can be shown that UPM intrinsically possess characteristics similar to the two-scale expansion without requiring a free parameter. This paper considers whether the UPM can be improved by applying the two-scale concept to the method. In order to do so, the unknown source current is expanded in a two-scale manner starting from the extinction theorem. Several two-scale expansions are derived and are compared with the conventional two-scale approximation. It is shown that the UPM performs best without two-scale expansions.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 30; 3, Ma; 510-515
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  • 10
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    On the decoder error probability of block codes (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: By using coding and combinational techniques, an explicit formula is derived which enumerates the complete weight distribution of decodable words of block codes using partially known weight distributions. Also an approximation formula for nonbinary block codes is obtained. These results in turn give exact and approximate expressions for the decoder error probability PE(u) of block codes.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); 40; 5, Ma; 857-859
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