opinions on an antenna idea
 

Roy Lewallen wrote:
Ed Cregger wrote:

You appear to be extrapolating, if I see this correctly, that since
all of the radiation is believed to come from one end of the dipole,
then the rest of the antenna is merely acting as the necessary
reactances and resistance needed to obtain the proper feedpoint
impedance at a given frequency. True?

No. It's not true that all the radiation "comes from one end of the
dipole". Extrapolation from that mistaken premise will lead to invalid
conclusions.

Following that line of reasoning, if the need for the aggregate
reactances/resistances can be eliminated via superconducting elements,
one will have just a single point source of radiation. Or, what is
commonly known as an isotropic radiator. I suspect that the plasma
antenna fellows are contemplating this too.

And there's the first one. . .

Roy Lewallen, W7EL


-------------


You are the acknowledged expert here (we're not worthy!!!).

What is the flaw in the proposed thinking? You have to admit that lots
of the commercial antenna companies and ham publications either do, or
used to, emphasize the point that "most of the radiation of a 1/4 wave
ground plane antenna (half of a half wave) occurs near the feed point".

Instead of just saying, no, this thinking is incorrect, how about
teaching your students (includes me) precisely what is wrong with this
line of thinking. Not at the engineering level necessarily (oodles of
formulas), but in the analog/real world level.

Please?

Be merciful, oh great one. I'm on enough prescription drugs to put half
a football team to sleep, so, occasionally, I get quite tangential to
the topic at hand. I hope this isn't one of those times. G

Thank you, oh merciful one.


Ed, NM2K

opinions on an antenna idea
 

Ed Cregger wrote:

You are the acknowledged expert here (we're not worthy!!!).

What is the flaw in the proposed thinking? You have to admit that lots
of the commercial antenna companies and ham publications either do, or
used to, emphasize the point that "most of the radiation of a 1/4 wave
ground plane antenna (half of a half wave) occurs near the feed point".

Instead of just saying, no, this thinking is incorrect, how about
teaching your students (includes me) precisely what is wrong with this
line of thinking. Not at the engineering level necessarily (oodles of
formulas), but in the analog/real world level.

Please?

Be merciful, oh great one. I'm on enough prescription drugs to put half
a football team to sleep, so, occasionally, I get quite tangential to
the topic at hand. I hope this isn't one of those times. G

Thank you, oh merciful one.

C'mon, now, I'm not the Great Guru. I'm just somebody who's interested
in antennas and has spent a lot of time thinking and learning about
them. As I said when I was in the service (as an enlisted man), "Don't
call me 'sir'! My parents were married."

The question of where radiation "comes from" is really a complicated
one. Not long ago I came across a recent paper in the IEEE Transactions
on Antennas and Propagation which addresses the issue, and it's one of
many. One of the conclusions of the paper is that it's really not
possible to assign any part or parts of an antenna as being responsible
for a particular share of the radiation.

A lot of people confuse the field generated by a current-carrying
conductor with far field radiation. It's very well known and established
that a field is created which is proportional to the current flowing on
a conductor -- antenna analysis programs use this principle to produce
very accurate results. This is certainly the source of claims that the
middle of a half wave dipole or the bottom of a quarter wave monopole
does most of the "radiating", because those points are where the current
is highest and therefore the field most intense.

However, the fields all parts of the antenna add together to become the
radiation which "escapes" beyond the region close to the antenna. You
can, for example, have two different parts of an antenna which each
produce intense fields, but out of phase in some directions so they
cancel completely or partially out of phase in such a way that they
nearly cancel in all directions. If you could somehow make the field
from one of those parts disappear without affecting the other, the
contribution to the overall radiation from the other would increase.
(However, the law of conservation of energy requires that radiation from
somewhere else would have to decrease to keep the total the same.) So
the radiation is the result of contributions from all parts of the
antenna, but in a way that's not easy to apportion to individual parts.
In the example, the two parts of the antenna, in combination, contribute
little to the radiated field. But each one, by itself, would contribute
quite a bit if it weren't for the other. An antenna has an infinite
number of radiating parts which all sum together to produce the radiated
field, so you can hopefully see the problem here.

That being said, some professional papers do establish some sort of
criteria for apportioning it. In ones I've seen, the radiation from half
a dipole as a function of position looks sort of tub-shaped, with
considerable radiation arising from all parts of the antenna, but having
a somewhat larger amount coming from the center and ends. As far as I
can tell, though, this depends on exactly how you define in what way a
particular part of the antenna is responsible for each fraction of the
total radiated power.

The bottom line is that any simplified assignment of radiation as coming
from one part of the antenna or another is too much of a simplification
and will lead to erroneous conclusions.

All I can say about what antenna publications and commercial antenna
manufacturers say is that a very large fraction of it is just plain
wrong. Consequently, they're very poor sources of information. Good
information can be found in textbooks and professional publications, and
very few other places. One exception (that is, one good source not in
these categories) is the _ARRL Antenna Book_, since when Jerry Hall
overhauled it (15th Edition if I recall correctly). The current editor,
Dean Straw, is knowledgeable about antennas and very conscientious about
correcting errors and misinformation. So it's become the only reference
I know of which is fundamentally accurate while keeping explanations at
a level which is easily understood by non-professionals.

Hope this helped.

Roy Lewallen, W7EL

opinions on an antenna idea
 

Roy Lewallen wrote:
Alan Peake wrote:


If one were to find lossless material (superconductors?) for the short
antenna and it's corresponding matching network, what would happen as
the antenna became shorter and shorter compared with the half-wave
dipole? Would it simply approach an isotropic radiator?
Alan


No. The answer can be found in any antenna textbook,
....
etc.

Roy Lewallen, W7EL


Thanks Roy. Unfortunately, since I retired, I no longer have access to
Jasik, Kraus etc. So, thanks for the answer. I should have realised that
a dipole of any length is still a dipole and as such will not radiate
off it's ends. Mind you, Eznec shows the average dipole, less than
half-wave above ground, goes pretty close to an isotropic radiator for
all practical purposes :)
Alan

opinions on an antenna idea
 

John Smith wrote:
Alan Peake wrote:

If one were to find lossless material (superconductors?) for the short
antenna and it's corresponding matching network, what would happen as
the antenna became shorter and shorter compared with the half-wave
dipole? Would it simply approach an isotropic radiator?
Alan


If room temperature super-conductors were available, do you even realize
the shape antennas would take? My gawd man, share some of that material
here! The thought alone is inspiring!

Regards,
JS
Don't know what shape it would be but I'm sure I wouldn't recognize it!
Alan

opinions on an antenna idea
 

Roy Lewallen wrote:
Ed Cregger wrote:

You are the acknowledged expert here (we're not worthy!!!).

What is the flaw in the proposed thinking? You have to admit that lots
of the commercial antenna companies and ham publications either do, or
used to, emphasize the point that "most of the radiation of a 1/4 wave
ground plane antenna (half of a half wave) occurs near the feed point".

Instead of just saying, no, this thinking is incorrect, how about
teaching your students (includes me) precisely what is wrong with this
line of thinking. Not at the engineering level necessarily (oodles of
formulas), but in the analog/real world level.

Please?

Be merciful, oh great one. I'm on enough prescription drugs to put
half a football team to sleep, so, occasionally, I get quite
tangential to the topic at hand. I hope this isn't one of those times.
G

Thank you, oh merciful one.

C'mon, now, I'm not the Great Guru. I'm just somebody who's interested
in antennas and has spent a lot of time thinking and learning about
them. As I said when I was in the service (as an enlisted man), "Don't
call me 'sir'! My parents were married."

The question of where radiation "comes from" is really a complicated
one. Not long ago I came across a recent paper in the IEEE Transactions
on Antennas and Propagation which addresses the issue, and it's one of
many. One of the conclusions of the paper is that it's really not
possible to assign any part or parts of an antenna as being responsible
for a particular share of the radiation.

A lot of people confuse the field generated by a current-carrying
conductor with far field radiation. It's very well known and established
that a field is created which is proportional to the current flowing on
a conductor -- antenna analysis programs use this principle to produce
very accurate results. This is certainly the source of claims that the
middle of a half wave dipole or the bottom of a quarter wave monopole
does most of the "radiating", because those points are where the current
is highest and therefore the field most intense.

However, the fields all parts of the antenna add together to become the
radiation which "escapes" beyond the region close to the antenna. You
can, for example, have two different parts of an antenna which each
produce intense fields, but out of phase in some directions so they
cancel completely or partially out of phase in such a way that they
nearly cancel in all directions. If you could somehow make the field
from one of those parts disappear without affecting the other, the
contribution to the overall radiation from the other would increase.
(However, the law of conservation of energy requires that radiation from
somewhere else would have to decrease to keep the total the same.) So
the radiation is the result of contributions from all parts of the
antenna, but in a way that's not easy to apportion to individual parts.
In the example, the two parts of the antenna, in combination, contribute
little to the radiated field. But each one, by itself, would contribute
quite a bit if it weren't for the other. An antenna has an infinite
number of radiating parts which all sum together to produce the radiated
field, so you can hopefully see the problem here.

That being said, some professional papers do establish some sort of
criteria for apportioning it. In ones I've seen, the radiation from half
a dipole as a function of position looks sort of tub-shaped, with
considerable radiation arising from all parts of the antenna, but having
a somewhat larger amount coming from the center and ends. As far as I
can tell, though, this depends on exactly how you define in what way a
particular part of the antenna is responsible for each fraction of the
total radiated power.

The bottom line is that any simplified assignment of radiation as coming
from one part of the antenna or another is too much of a simplification
and will lead to erroneous conclusions.

All I can say about what antenna publications and commercial antenna
manufacturers say is that a very large fraction of it is just plain
wrong. Consequently, they're very poor sources of information. Good
information can be found in textbooks and professional publications, and
very few other places. One exception (that is, one good source not in
these categories) is the _ARRL Antenna Book_, since when Jerry Hall
overhauled it (15th Edition if I recall correctly). The current editor,
Dean Straw, is knowledgeable about antennas and very conscientious about
correcting errors and misinformation. So it's become the only reference
I know of which is fundamentally accurate while keeping explanations at
a level which is easily understood by non-professionals.

Hope this helped.

Roy Lewallen, W7EL


------------


Thanks, Roy. Much appreciated.

Ed, NM2K

opinions on an antenna idea
 

Alan Peake wrote:
"---what would happen as the antenna became shorter and shorter compared
with the half-wave dipole?"

Terman answers that question on page 871 of his 1955 opus:
"The directive gain of the elementary doublet =1.5." For a resonant wire
of 0.5 lambda, the gain is 1.64.

There`s not much difference in directivity as the doublet shrinks to a
vanishingly small size. The gains shown are power ratios, not dB`s.

Comparison antenna is the isotropic of which Terman says:
"Although an isotropic radiator of coherent waves does not exist because
it cannot satisfy Maxwell`s equations, the properties of such an
imaginary antenna are easily visualized, and the concept of an isotropic
radiator is often found useful in the analysis of antenna systems."
(Page 871 in the 1955 opus.)

Best regards, Richard Harrison, KB5WZI

opinions on an antenna idea
 

On 4 Dec, 01:28, John Smith wrote:
Roy Lewallen wrote:
...

-- The Q of the short dipole is very high, so the reactance varies very
rapidly with frequency. A matched short antenna would have an extremely
narrow bandwidth.
...

Roy Lewallen, W7EL

And, here is where a DLM antenna is nice, keep the coils of low Q and
bandwidth is "surprisingly wide."

Regards,
JS

Yup,
My 160M antenna came at at a resistive 200 ohm plus resonance and with
a bit of fiddling
I now connect the coax direct and cover the whole band. Not sure if I
would have been better off with keeping the high resistive impedance
and using a transformer but snow is on the way so beggars can't be
choosers.
Regards
Art KB9MZ........XG (uk)

opinions on an antenna idea
 

In article , Roy Lewallen
wrote:

All I can say about what antenna publications and commercial antenna
manufacturers say is that a very large fraction of it is just plain
wrong. Consequently, they're very poor sources of information. Good
information can be found in textbooks and professional publications, and
very few other places. One exception (that is, one good source not in
these categories) is the _ARRL Antenna Book_, since when Jerry Hall
overhauled it (15th Edition if I recall correctly). The current editor,
Dean Straw, is knowledgeable about antennas and very conscientious about
correcting errors and misinformation. So it's become the only reference
I know of which is fundamentally accurate while keeping explanations at
a level which is easily understood by non-professionals.

Hope this helped.

Roy Lewallen, W7EL

You got that right, Roy. Do marketing departments ever talk to the
engineers? At least I haven't seen a dial 1-800 TV commercial such as
"Call right now and we'll include the matching network and balun free of
charge. But call right now and we'll also include a CFA free!"

Adding to what you said above how about a little gray box that can save
you up to 25% on your electric bill (you can Google this one). Sincerely,
and 73s from N4GGO,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

opinions on an antenna idea
 

J. B. Wood wrote:
In article , Roy Lewallen
wrote:

All I can say about what antenna publications and commercial antenna
manufacturers say is that a very large fraction of it is just plain
wrong. Consequently, they're very poor sources of information. Good
information can be found in textbooks and professional publications, and
very few other places. One exception (that is, one good source not in
these categories) is the _ARRL Antenna Book_, since when Jerry Hall
overhauled it (15th Edition if I recall correctly). The current editor,
Dean Straw, is knowledgeable about antennas and very conscientious about
correcting errors and misinformation. So it's become the only reference
I know of which is fundamentally accurate while keeping explanations at
a level which is easily understood by non-professionals.

Hope this helped.

Roy Lewallen, W7EL

You got that right, Roy. Do marketing departments ever talk to the
engineers? At least I haven't seen a dial 1-800 TV commercial such as
"Call right now and we'll include the matching network and balun free of
charge. But call right now and we'll also include a CFA free!"

Adding to what you said above how about a little gray box that can save
you up to 25% on your electric bill (you can Google this one). Sincerely,
and 73s from N4GGO,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337


------------


I have quite a few engineering books on antennas (that I use G), so I
can appreciate the value of good, solid engineering text/sources.

However, the point that the OP was trying to make was that it is likely
that superconductive radiating elements could establish the need for a
serious rethinking of antenna theory. After all, superconductive
radiating elements did not exist before and the math has not been done.
Perhaps, their inclusion, will demand something more than a simple
extrapolation of existing antenna theory. I believe this to be the point
of the OP.

I added the other type of radiating element, plasma radiators, as a part
of the same discussion with the same reasoning behind it. Can you
imagine an antenna ray that only manifests itself physically when
needed? Wow!


Ed, NM2K

opinions on an antenna idea
 

On Wed, 05 Dec 2007 10:36:59 -0500, Ed Cregger
wrote:

However, the point that the OP was trying to make was that it is likely
that superconductive radiating elements could establish the need for a
serious rethinking of antenna theory.

Hi Ed,

This is uni-dimensional thinking.

"A new breakfast cereal could establish the need for a serious
rethinking of sewing machine theory."

There are probably more things possible ("could establish") than time
to consider them - and probably on file pending patent. In that
sense, patent publishing could establish the need for a serious
rethinking of replacing burning oil for heat.

"Could establish" ...this could establish a new form of gaming
entertainment in this group. [and conforms to the usage of
self-referential claims]

73's
Richard Clark, KB7QHC