RE: NEC-LIST: Low angle radiation?

Hi Jack,

I do not quite agree with your explanation of radiation. The
acceleration of charges happens along the whole antenna. The drift
velocity of charges in metals is very low (some mm/s or maybe cm/s).

So if the antenna is excited with a source of e.g. 1 MHz, each charge
oscillates around its position of rest with 1 MHz and very low
amplitude. It never sees the end of the dipole. Since the oscillation
is harmonic, the same holds for the acceleration (second derivative
w.r.t time). To inquire as to the causes of radiation from the
viewpoint of charges is not easy, since the cause for the oscillation
of the charges is the guided wave along the antenna and all the
charges themselves cause radiation.

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
_________________________________________________________

......

> I have asked myself, and others, in particular Ed Miller, the
> question: how does an antenna radiate? Radiation results from the
> acceleration of charge. Where does this happen? Near the ends of the
> antenna, since here the velocity of a current element comes to zero,
> and accelerates very quickly again to its velocity on the center part
> of the antenna. So the ends of a dipole are important. The
> expectation that "maximum radiation results from the parts of the
> dipole where current is a maximum" is not true. Model a drooping
> dipole, centre higher than the ends --- and reverse the droop; ends
> higher than the centre. The latter gives this the most gain.
>
>.......
>
> _____________________________________________
> John S. (Jack) Belrose, PhD Cantab, VE2CV
Received on Thu Feb 17 2000 - 04:31:58 EST