RE: NEC-LIST: E-M demos/simulations/animations

Hi all,

There still seems to exist the wrong picture, that one electron
travels from one end of a 1/2-wavelength dipole to the other one
during 1/2 period. If this would really be the case, then the
acceleration was independent of the field strength, which would
contradict a = Q*E/m.

Instead, each charge oscillates around its center position. This
oscillation is nearly synchronous along the antenna (standing wave)
and the polarization of the whole dipole is the sum of these
simultaneous displacements. Excitation and radiation of the charges
contribute to the standing wave which is guided by the wire and
reflected at the ends of the dipole, where the radiation takes place.

To avoid confusion, we first should answer the following questions
before forming suitable thinking models and pictures:

1. Is it in time-domain (e.g. pulse propagation) or in frequency
   domain (stationary solutions)?

2. Do we think of a receiving or transmitting antenna? Of course, we
   normally have reciprocity, but the energy flow is opposite which
   may necessitate different illustrations and explanations.
 
Attached is a figure of the power flow (real part of the complex
Poynting vector in the stationary case)in the near field of a small
transmitting patch radiator without excitation (complex
eigensolutions). It is nearly equivalent to a dipole on a grounded
dielectric layer. The results have been obtained using a
finite-difference procedure in space domain (frequency domain).

The radiating edges are clearly to locate.

Regards,

Achim

_________________________________________________________
Dr.-Ing. Achim Dreher Tel.: +49-8153-28-2314
Deutsches Zentrum fuer Fax: +49-8153-28-1135
Luft- und Raumfahrt e. V. E-Mail: achim.dreher_at_dlr.de
Oberpfaffenhofen

D-82234 Wessling

GERMANY
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Received on Tue Apr 25 2000 - 05:09:00 EDT