# How an antenna launches its input power into radiation: thepattern of the Poynting vector at and near an antenna

### Description

In this paper I first address the question of whether theseat of the power radiated by an antenna made of conducting members isdistributed over the "arms" of the antenna according to $- \bf J \cdotE$, where $\bf J$ is the specified current density and $\bf E$ is theelectric field produced by that source. Poynting's theorem permits only aglobal identification of the total input power, usually from a localizedgenerator, with the total power radiated to infinity, not a localcorrespondence of $- \bf J \cdot E\ d^3x$ with some specific radiatedpower, $r^2 \bf S \cdot \hat r\ d\Omega$. I ... continued below

### Creation Information

Jackson, J.D. May 18, 2005.

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## What

### Description

In this paper I first address the question of whether theseat of the power radiated by an antenna made of conducting members isdistributed over the "arms" of the antenna according to $- \bf J \cdotE$, where $\bf J$ is the specified current density and $\bf E$ is theelectric field produced by that source. Poynting's theorem permits only aglobal identification of the total input power, usually from a localizedgenerator, with the total power radiated to infinity, not a localcorrespondence of $- \bf J \cdot E\ d^3x$ with some specific radiatedpower, $r^2 \bf S \cdot \hat r\ d\Omega$. I then describe a modelantenna consisting of two perfectly conducting hemispheres of radius\emph a separated by a small equatorial gap across which occurs thedriving oscillatory electric field. The fields and surface current aredetermined by solution of the boundary value problem. In contrast to thefirst approach (not a boundary value problem), the tangential electricfield vanishes on the metallic surface. There is no radial Poyntingvector at the surface. Numerical examples are shown to illustrate how theenergy flows from the input region of the gap and is guided near theantenna by its "arms" until it is launched at larger \emph r/a into theradiation pattern determined by the value of \emph ka.

### Source

• Journal Name: American Journal of Physics; Journal Volume: 74; Journal Issue: 4; Related Information: Journal Publication Date: 04/2006

### Identifier

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• Report No.: LBNL--57623
• Grant Number: DE-AC02-05CH11231
• Office of Scientific & Technical Information Report Number: 919923

### Collections

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Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

## When

• May 18, 2005

### Added to The UNT Digital Library

• Sept. 27, 2016, 1:39 a.m.

### Description Last Updated

• Oct. 31, 2016, 4:11 p.m.

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