10,705 research outputs found
Charlie May Simon materials
No full textThis collection contains materials relating to Arkansas author Charlie May Simon
Fundamental directivity limitations of dense array antennas: a numerical study using Hannan ́s embedded element efficiency
No full textHannan introduced in 1964 an embedded element efficiency concept that explains the so-called element -gain paradox in antenna arrays, i.e., that the array gain always is smaller than the sum of the element gains. In the present letter, we show for the first time the usefulness of his approach by evaluating directivities and aperture efficiencies of an array of open-ended waveguides by commercial full -wave electromagnetic (EM) solvers for a large range of element spacing. The results show also that by using embedded element analysis, the realized gain of regular arrays actually becomes equal to the sum of the realized gains of the embedded elements. Thus, the embedded element efficiency is more practical to use in design and numerical analysis than the more commonly used active element pattern approach. We also show that the embedded element efficiency can be approximated by a simple formula when the element spacing is smaller than half -wavelength
Degrees of freedom and maximum directivity of antennas: a bound on maximum directivity of nonsuperreactive antennas
No full textWe derive a general fundamental directivity limitation formula that applies to nonsuperreactive antennas of any size that fit within a minimum sphere of any given radius rmin. The derivation is done by using a new concept: the degrees of freedom (DoF) of the field radiated by arbitrary sources within the minimum sphere must be twice the maximum directivity. The formula converges to the known bound of the directivity for large rmin. For small spheres, it becomes equal to three, i.e., 4.8 dBi, which is the directivity of the Huygens source. The transition region between these two limiting cases is determined by counting the most significant spherical modes at the surface of the minimum sphere. This is not trivial, because spherical modes have a gradual cutoff when their order approaches krmin. Therefore, we use a weighted summation where the weighting factor is inversely proportional to the radiation-Q of the modes. This extends the DoF from a discrete to continuous function of the minimum sphere radius. The final maximum directivity is similar to a previously published heuristic limit. The formulas are compared to results for measured antennas with large directivity and superdirectivity
"Dispersion Characteristics of a Metamaterial-Based Parallel-Plate Ridge Gap Waveguide Realized by Bed of Nails"
No full textThe newly introduced parallel-plate ridge gap waveguide consists of a metal ridge in a metamaterial surface, covered by a metallic plate at a small height above it. The gap waveguide is simple to manufacture, especially at millimeter and sub-millimeter wave frequencies. The metamaterial surface is designed to provide a frequency band where normal global parallel-plate modes are in cutoff, thereby allowing a confined gap wave to propagate along the ridge. This paper presents an approximate analytical solution for this confined quasi-TEM dominant mode of the ridge gap waveguide, when the metamaterial surface is an artificial magnetic conductor in the form of a bed of nails. The modal solution is found by dividing the field problem in three regions, the central region above the ridge and the two surrounding side regions above the nails. The fields within the side regions are expressed in terms of two evanescent TE and TM modes obtained by treating the bed of nails as an isotropic impedance surface, and the field in the central ridge region is expanded as a fundamental TEM parallel-plate mode with unknown longitudinal propagation constant. The field solutions are linked together by equalizing longitudinal propagation constants and imposing point-continuity of fields across the region interfaces, resulting in a transcendental dispersion equation. This is solved and presented in a dispersion diagram, showing good agreement with a numerical solution using a general electromagnetic solver. Both the lower and upper cutoff frequencies of the normal global parallel-plate modes are predicted, as well as the quasi-TEM nature of the gap mode between these frequencies, and the evanescent fields in the two side regions decay very rapidly away from the ridge. © 2010 IEEE
Special issue on artificial magnetic conductors, soft/hard surfaces, and other complex surfaces - Guest Editorial
No full textSimon Nyakot
No full textabstract: Simon Nyakot left his village when he was six years old.
“Lost Boys Found” is an ongoing, interdisciplinary project that is collecting, recording and archiving the oral histories of the Lost Boys/Girls of Sudan. The collection is a work-in-progress, seeking to record the oral history of as many Lost Boys/Girls as are willing, and will be used in a future book.Age: 27Region: LakeThis picture and bio was donated to the Lost Boys Found project from The Arizona Lost Boys Cente
Cahiers Saint-Simon
No full texthttps://www.persee.fr/renderCollectionCover/simon.pngThe Société Saint-Simon was founded in 1972 in order to promote studies about the Duke of Saint-Simon (1675-1755), namely about the work, life, and thinking of the Mémoires’s author. Each year it issues a Cahier Saint-Simon. It contains the Acts of the annual Journée d’étude in Versailles, but also Notes and Documents, News of the Society and Book reviews.Fondée en 1972, la Société Saint-Simon a pour but de développer les études concernant l'oeuvre, la personne et la pensée du duc de Saint-Simon (1675-1755), l’auteur des Mémoires. Chaque année, paraît un numéro de Cahiers Saint-Simon contenant les actes de la journée annuelle de Versailles, ainsi que des Mélanges, des Notes et Documents et une Chronique bibliographique détaillée
Cahiers Saint-Simon
No full texthttps://www.persee.fr/renderCollectionCover/simon.pngThe Société Saint-Simon was founded in 1972 in order to promote studies about the Duke of Saint-Simon (1675-1755), namely about the work, life, and thinking of the Mémoires’s author. Each year it issues a Cahier Saint-Simon. It contains the Acts of the annual Journée d’étude in Versailles, but also Notes and Documents, News of the Society and Book reviews.Fondée en 1972, la Société Saint-Simon a pour but de développer les études concernant l'oeuvre, la personne et la pensée du duc de Saint-Simon (1675-1755), l’auteur des Mémoires. Chaque année, paraît un numéro de Cahiers Saint-Simon contenant les actes de la journée annuelle de Versailles, ainsi que des Mélanges, des Notes et Documents et une Chronique bibliographique détaillée
Investigation of the Distribution of the Random LOS Component in a Reverberation Chamber [Elektronisk resurs]
No full textIn the previous measurement uncertainty work by Kildal, et al. (2012), the random line-of-sight (LOS) component in a reverberation chamber (RC) was assumed to be Gaussian distributed without quantitative justification. In the present paper, we apply goodness-of-fit (GOF) test to the measured LOS component samples to check its Gaussianity. It is shown that the Gaussianity hypothesis of the distribution of the random LOS component is accepted at most of the frequencies, which justifies the Gaussian LOS component assumption
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