Re: NEC-LIST: How does a wire antenna radiate?

Harry E Green wrote:
>
> Dear fellow NEC-lister,
>
> Schelkunoff is an author from whose clear insight much is to be
> learned.

Absolutely.
>
>
> As the impulse passes along the conductor, the charges are first
> accelerated in one direction and then immediately equally and
> oppositely in the other, so there is no NET acceleration. Two mutually
> cancellatory kinks are produced and there is therefore no net
> radiation field. This will be true everywhere except at the ends where

But the derivative of a delta-function is not zero (and it would be
by this argument!) If you give the impulse a finite width, the
two contributions will not cancel since they come from different
locations. And if your source is a sine wave, the succesive pulses
have a width of effectively half a wavelength.

> the impulse comes to a halt and is reversed (reflected). Here there is
> net acceleration and therefore radiation. The travelling impulse
> therefore radiates only from the end of the wire.

Most of its energy (if it has a large bandwidth,) but I expect this
not to hold for the low-frequency content (see above). And it also
need not be true for the usual half-wave (or full wave) dipole with
sine wave excitation. See movies on:

  http://www.iae.nl/users/bergervo/gouy/dipole.html

Greetings,
Jos

--
  Dr. Jozef R. Bergervoet                      Electromagnetism and EMC
  Philips Research Laboratories,             Eindhoven, The Netherlands
  Building WS01                                     FAX: +31-40-2742224
  E-mail: bergervo_at_natlab.research.philips.com    Phone: +31-40-2742403