Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: How an antenna launches its input power into radiation: the pattern of
  the Poynting vector at and near an antenna   In this paper I first address the question of whether the seat of the power
radiated by an antenna made of conducting members is distributed over the
``arms'' of the antenna according to -J . E, where J is the specified current
density and E is the electric field produced by that source. Poynting's theorem
permits only a global identification of the total input power, usually from a
localized generator, with the total power radiated to infinity, not a local
correspondence of -J . E dv with some specific radiated power, r^2 S . n dO. I
then describe a model antenna consisting of two perfectly conducting
hemispheres of radius a separated by a small equatorial gap across which occurs
the driving oscillatory electric field. The fields and surface current are
determined by solution of the boundary value problem. In contrast to the first
approach (not a boundary value problem), the tangential electric field vanishes
on the metallic surface. There is no radial Poynting vector normal to the
surface. Numerical examples are shown to illustrate how the energy flows from
the input region of the gap and is guided near the antenna by its ``arms''
until it is launched at larger r/a into the radiation pattern determined by the
value of ka.

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The categories of this paper are: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: cond-mat
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The categories of this paper are: q-fin
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The categories of this paper are: nlin
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-ph
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The categories of this paper are: econ
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The categories of this paper are: funct-an
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The categories of this paper are: math-ph
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The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-ex
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The categories of this paper are: eess
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The categories of this paper are: patt-sol
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The categories of this paper are: q-bio