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  • Other Sources  (12)
  • NASA Technical Reports  (12)
  • Communications and Radar  (5)
  • Numerical Analysis  (5)
  • ELECTRONIC COMPONENTS AND CIRCUITS  (2)
  • 1995-1999  (12)
  • 1950-1954
  • 1
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    Technique for Extension of Small Antenna Array Mutual-Coupling Data to Larger Antenna Arrays (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A technique is presented whereby the mutual interaction between a small number of elements in a planar array can be interpolated and extrapolated to accurately predict the combined interactions in a much larger array of many elements. An approximate series expression is developed, based upon knowledge of the analytical characteristic behavior of the mutual admittance between small aperture antenna elements in a conducting ground plane. This expression is utilized to analytically extend known values for a few spacings and orientations to other element configurations, thus eliminating the need to numerically integrate a large number of highly oscillating and slowly converging functions. This paper shows that the technique can predict very accurately the mutual coupling between elements in a very large planar array with a knowledge of the self-admittance of an isolated element and the coupling between only two-elements arranged in eight different pair combinations. These eight pair combinations do not necessarily have to correspond to pairs in the large array, although all of the individual elements must be identical.
    Keywords: Communications and Radar
    Type: NASA-TP-3603 , L-17553 , NAS 1.60:3603
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  • 2
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    The Quest for Pi (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: This article gives a brief history of the analysis and computation of the mathematical constant Pi=3.14159 ..., including a number of the formulas that have been used to compute Pi through the ages. Recent developments in this area are then discussed in some detail, including the recent computation of Pi to over six billion decimal digits using high-order convergent algorithms, and a newly discovered scheme that permits arbitrary individual hexadecimal digits of Pi to be computed.
    Keywords: Numerical Analysis
    Type: NASA-TM-112037 , NAS 1.15:112037 , NAS-96-015
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  • 3
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    On the Rapid Computation of Various Polylogarithmic Constants (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: We give algorithms for the computation of the d-th digit of certain transcendental numbers in various bases. These algorithms can be easily implemented (multiple precision arithmetic is not needed), require virtually no memory, and feature run times that scale nearly linearly with the order of the digit desired. They make it feasible to compute, for example, the billionth binary digit of log(2) or pi on a modest workstation in a few hours run time. We demonstrate this technique by computing the ten billionth hexadecimal digit of pi, the billionth hexadecimal digits of pi-squared, log(2) and log-squared(2), and the ten billionth decimal digit of log(9/10). These calculations rest on the observation that very special types of identities exist for certain numbers like pi, pi-squared, log(2) and log-squared(2). These are essentially polylogarithmic ladders in an integer base. A number of these identities that we derive in this work appear to be new, for example a critical identity for pi.
    Keywords: Numerical Analysis
    Type: NASA-TM-112039 , NAS 1.15:112039 , NAS-96-016
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  • 4
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    Closed-Form Evaluation of Mutual Coupling in a Planar Array of Circular Apertures (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The integral expression for the mutual admittance between circular apertures in a planar array is evaluated in closed form. Very good accuracy is realized when compared with values that were obtained by numerical integration. Utilization of this closed-form expression, for all element pairs that are separated by more than one element spacing, yields extremely accurate results and significantly reduces the computation time that is required to analyze the performance of a large electronically scanning antenna array.
    Keywords: Communications and Radar
    Type: NASA-TP-3552 , L-17493 , NAS 1.60:3552
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  • 5
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    Design of a Foldable Low-loss Microstrip Array Antenna (1999)
    In:  Other Sources
    Details
    Publication Date: 2018-06-05
    Description: The design and analysis of a series-fed, foldable microstrip array antenna for radiometer applications is presented. The array antenna is composed of two equal sub arrays. Each sub array consists of a series of patches connected together through segments of microstrip lines. The sub arrays are fed 180 degree out of phase to ensure a symmetric radiation pattern. The design approach, is accomplished using the IE3D code that utilizes the method of moments. All experimental and simulated data are presented and discussed.
    Keywords: Communications and Radar
    Type: IEEE Antennas and Propagation Society International Symposium 1999 Digest, Volume Four; 2732-2735; IEEE-Catalog-99CH37010-Vol-4
    Format: text
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  • 6
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    Analysis of Stub Loaded Microstrip Patch Antennas (1997)
    In:  CASI
    Details
    Publication Date: 2018-06-02
    Description: A microstrip patch antenna fed by a coaxial probe and reactively loaded by a open circuited microstrip line has been used previously to produce circular polarization and also as a building block for a series fed microstrip patch array. Rectangular and circular patch antennas loaded with a microstrip stub were previously analyzed using the generalized Thevenin theorem. In the Thevenin theorem approach, the mutual coupling between the patch current and the surface current on the stub was not taken into account. Also, the Thevenin theorem approach neglects continuity of current at the patch-stub junction. The approach in this present paper includes the coupling between the patch and stub currents as well as continuity at the patch-stub junction. The input impedance for a stub loaded microstrip patch is calculated by the general planar dielectric dyadic Green's function approach in the spectral domain, as was initiated much earlier and has been extensively expanded upon and utilized successfully throughout the literature for microstrip antenna configurations. Using the spectral domain dyadic Green s function derived earlier with the electric field integral equation (EFIE), the problem is formulated by using entire domain basis functions to represent the surface current densities on the patch, the loading stub and the attachment mode at the junction. Galerkin's procedure is used to reduce the EFIE to a matrix equation, which is then solved to obtain the amplitudes of the surface currents. These surface currents are then used for calculating the input impedance of stub loaded rectangular and circular microstrip patches. Numerical results are compared with measured results and with previous results calculated by the Thevenin's theorem approach.
    Keywords: Communications and Radar
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  • 7
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    Design of a low-loss series-fed microstrip array antenna (1998)
    In:  Other Sources
    Details
    Publication Date: 2018-06-05
    Description: The design and analysis of a series-fed, low-loss, inverted microstrip array antenna, operating at 1.413 GHz is presented. The array antenna is composed of two sub arrays. Each sub array consists of an equal number of microstrip patches all connected together through a series microstrip line. The first element of each sub array is coaxially fed but 180 degree out of phase. This approach ensures a symmetric radiation pattern. The design approach, is accomplished using the IE3D code that utilizes the method of moments. All experimental and simulated data are presented and discussed.
    Keywords: Communications and Radar
    Type: IEEE Antennas and Propagation Society International Symposium 1998 Digest. Antennas: Gateways to the Global Network, Volume 2; 1146-1149; IEEE-Catalog-98CH36194-Vol-2
    Format: text
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  • 8
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    Algebraic Nonoverlapping Domain Decomposition Methods for Stabilized FEM and FV Discretizations (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: We consider preconditioning methods for convection dominated fluid flow problems based on a nonoverlapping Schur complement domain decomposition procedure for arbitrary triangulated domains. The triangulation is first partitioned into a number of subdomains and interfaces which induce a natural 2 x 2 partitioning of the p.d.e. discretization matrix. We view the Schur complement induced by this partitioning as an algebraically derived coarse space approximation. This avoids the known difficulties associated with the direct formation of an effective coarse discretization for advection dominated equations. By considering various approximations of the block factorization of the 2 x 2 system, we have developed a family of robust preconditioning techniques. A computer code based on these ideas has been developed and tested on the IBM SP2 using MPI message passing protocol. A number of 2-D CFD calculations will be presented for both scalar advection-diffusion equations and the Euler equations discretized using stabilized finite element and finite volume methods. These results show very good scalability of the preconditioner for various discretizations as the number of processors is increased while the number of degrees of freedom per processor is fixed.
    Keywords: Numerical Analysis
    Type: 10th Conference on Finite Element Methods in Fluids; Jan 08, 1998; Tucson, AZ; United States
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  • 9
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    Using Multithreading for the Automatic Load Balancing of 2D Adaptive Finite Element Meshes (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: In this paper, we present a multi-threaded approach for the automatic load balancing of adaptive finite element (FE) meshes. The platform of our choice is the EARTH multi-threaded system which offers sufficient capabilities to tackle this problem. We implement the question phase of FE applications on triangular meshes, and exploit the EARTH token mechanism to automatically balance the resulting irregular and highly nonuniform workload. We discuss the results of our experiments on EARTH-SP2, an implementation of EARTH on the IBM SP2, with different load balancing strategies that are built into the runtime system.
    Keywords: Numerical Analysis
    Type: 5th International Symposium on Solving Irregularly Structured Problems in Parallel; Aug 09, 1998 - Aug 11, 1998; Berkley, CA; United States
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  • 10
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    Electronic Compensation For Distortion Of Antenna Reflector (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Proposed method of obtaining approximately desired radiation or reception pattern from antenna that includes reflector based on concept of superposition of electromagnetic fields generated by multiple feedhorns or feed antenna elements arrayed at various positions near reflector and excited at electronically adjustable magnitudes and phases. In intended application, reflector nominally paraboloidal, feed elements N feedhorns in hexagonal array, and method used to compensate for deviations of real reflector surface from nominal paraboloidal shape. Method and concept also applicable to electronic beam steering and electronic antenna compensation in other situations.
    Keywords: ELECTRONIC COMPONENTS AND CIRCUITS
    Type: LAR-14461 , NASA Tech Briefs (ISSN 0145-319X); 19; 1; P. 32
    Format: text
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