sci.physics.electromag

"Szczepan Bia³ek" < @ > wrote in message
news:fcapul$1pj$1@ ...
>
> "Bill Miller"
>> "Benj" <
>>> Szczepan Bialek wrote:
>>>>
>>
>> In "real" antennas (disregarding "long" antennas that are multiples of a
>> wavelength) radiation is broadside to the conductor and near zero off the
>> ends.
>
> In "real" antennas radiation is from the ends of the OPEN circuit. How
> much from the broadside vs tip top it is shape dependent.

I wonder where you are getting this idea?

Let me back up a bit and make sure we are talking about the same structure.
For simplicity, I want to discuss antennas made of "thin," straight
conductors in the form of a dipole. My discussion antennas are of the same
order of magnitude as that of the source wavelength. In these antennas, (and
unlike "small" dipole antennas) the current and/or voltage in the
antennas is NOT constant. Most antenna elements contain a feed point that is
usually but not necessarily located at or near the centre.

I am deleting from consideration any "long" antennas whose length is > a
wavelength or two, because these exhibit a traveling wave kind of behaviour
that allows radiation in the area surrounding the ends that may be mistaken
as being radiation from OFF OF the ends.

With the above definition in mind, I have never seen or heard of such an
antenna with significant amounts of radiation off of the ends.

If this antenna model is sufficiently close to your model, then can you
please amplify on your claim that antennas radiate off their ends?


>>
>> Generally, balls on the end of an antenna seem most useful in reducing or
>> eliminating corona discharge -- an important issue at higher power
>> levels.
>
> OK
>
>> They seem to have little or nothing to do with the function of radiating
>> signals.
>
> Here are the two possibilities:
> 1. In charge method - the higher voltage (charge density) the stronger
> signal,

This might be correct if the antenna consisted entirely of a ball fed with
very high voltage radio frequency energy. A friend has built such a device
and it seems to have some very unconventional characteristics. But it is
definitely not a "mainstream" method of radiating signals.

> 2. In field method - I do not know. It seams that the corona discharge
> should increase the current.

Generally, antenna designers try to eliminate corona discharge. Corona
discharge is -- in effect - a process by which the antenna is manufacturing
high energy plasma (and heat!) rather than high energy radio frquency
signals.

>In your field method the stronger current the stronger signal. Could you
>comment this?

It is empirically true. But why it is empirically true is still a mystery.

We understand that the acceleration of electrons is accompanied by
radiation. But this acceleration of electrons does not appear to be the
mechanism by which antennas radiate. Instead, the metal conductors seem to
be "guiding" the radio frequency signals along a path that encourages
radiation. The electrons in the metal seem to have nothing to do with the
actual radiation process. (An exception MAY be the "high voltage ball"
antenna that my friend built. I hope to build one myself and learn more.)

I wish I could comment further. I wish *anybody* could!

Bill


> S*
>