Antenna physical size
 

On Mar 26, 11:04 am, (Richard Harrison)
wrote:
Cecil Moore wrote:

"But the Method Of Moments used by NEC for antenna radiation patterns
calculates the interference at a point in space based on radiation from
different elementary dipole sections of the antenna."

Completely logical and it works. Interference or vector sum?

Terman illustrates radiation from an elementary doublet (dipole) , and
it is mostly at right angles to the antenna axis, on page 865 of his
1955 opus. On page 866 he shows an actual antenna consisting of numerous
elementary doublets and on page 867 he says:
"The result is that the fields radiated from different elementary
sections of a long wire add vectorially to give a sum that depends on
direction."

Kraus devotes Chapter 14 in the 3rd edition of "Antennas" to: "The
Cylindrical Antenna and the Moment Method (MM)."

Best regards, Richard Harrison, KB5WZI

Richard,
Surely you are aware of the two vectors which represent the electrical
field and the magnetic field
If the current carrying member is a diamagnetic material both of thes
vectors will be in the same direction.
But the diamagnetic material is just a myth of mine right ? So I will
go along with you and say the vectors are at right angles to each
other
just like all your books say. But later in your books they then refer
to the vector "curl. This vector must be added to the two vectors at
right angles to each other so a resultant vector can be found. Now you
and the books state that radiation is at right angle to the axis of
current flow.
So the question becomes'Where must the 'curl' vector be placed in
general terms to justify the right angle radiation statment that all
your books
apparently parrot? Simple question isn't it? Did all your learning get
discarded because of books because you are unwilling to challenge
them?
Terman was not made a saint, nor was Kraus or Feldman or even
Einstein. None of these would state that they never have made a
mistake.
Stop imitating Andy Capp and draw on your own thoughts for once
Art

Antenna physical size
 

Richard Clark wrote:
But you don't know how, and have never seen one either.

Dear Richard - some people contribute to human knowledge
through their optimism regarding things to come that are
presently out of reach. Some people would prefer that we
live forever in the dark ages. Which one are you?
--
73, Cecil http://www.w5dxp.com

Antenna physical size
 

Antenna physical size
 

On Mon, 31 Mar 2008 23:47:00 +0100, "Mike Kaliski"
wrote:

Hi Richard,

I have a pair of computer speakers sitting on my desk that completely out
perform the so called ultimate hi-fi floor mounted tower system speakers I
bought 35 years ago for the equivalent of several thousand dollars in
today's money.

Hi Mike,

I have a set of 30 year old Pioneers that still kick ass. The Pioneer
amp feeding any other set drives them into distortion where the
Pioneer speakers still have more range to go.

Never needed to push the amp above 4 to be heard outside.

OK, so much for the merits of qualitative reports, otherwise known as
testimonials. Proves nothing.

The old speakers still work just fine but the audio experts
have learned how to squeeze that performance out of a speaker that old audio
theory predicted couldn't possibly work.

Magnetics got better, and theory stayed the same. Performance
followed the theory's prediction of new magnetics is all. This isn't
a mystery is it?

Care to name your speakers' model and manufacturer, or did you form
the cone and wind the voice coils around a selected magnet by hand?

73's
Richard Clark, KB7QHC

Antenna physical size
 

Mike Kaliski wrote:

Hi Richard,

I have a pair of computer speakers sitting on my desk that completely
out perform the so called ultimate hi-fi floor mounted tower system
speakers I bought 35 years ago for the equivalent of several thousand
dollars in today's money. The old speakers still work just fine but the
audio experts have learned how to squeeze that performance out of a
speaker that old audio theory predicted couldn't possibly work. Just how
does a 3 inch speaker in a cabinet the size of a couple of books manage
to produce notes from 20 Hz - 20 kHz? To be fair, the small speakers
can't fill a room with sound in the same smooth way that a larger
speaker cabinet can, but for everyday use in a small modern house or
apartment they are more than adequate for the majority of people.

It seems to me that Art and others are pursuing a similar path at RF.
The aim being to produce an antenna that punches out a signal from a
physically small area. It may not perform quite as well as a full size
half or full wavelength antenna, but it will work well enough for most
people with small gardens or limited real estate for an antenna farm.


Nope.. there's a significant difference between the speakers and the
antenna, and that's the fact that the amateur user of the antenna is
power limited (by regulation). In the speaker case, they trade off
efficiency (acoustic watts out for electrical watts out) because
electrical watts are cheap these days (not so back in McIntosh tube amp
days...) You can tolerate a 1% efficient design that puts out 100mW of
acoustic power with 10W electrical power in. (note that 120dB SPL = 1
Watt.. a symphony orchestra, at full tilt, is about a watt of acoustic
power, and I daresay you couldn't tolerate a whole orchestra in your office)


OTOH, a 1% efficient antenna design is pretty crummy. A dipole is
probably on the order of 70% efficient (RF power radiated into the far
field vs RF power at the feedline). A mobile antenna (which everyone
will agree is not particularly efficient, even if you argue about the
actual magnitude) might be 5-10% efficient (10dB down).



As a practical matter, you can get away with a 1% efficient antenna,
particularly if you're not looking for "link reliability"... The
propagation loss between you and some arbitrary point could easily vary
by 100 dB, so you just wait until propagation is "good enough" to work
the guy with the 0.1W you radiate. Of such are "worked 300 countries on
two bedsprings" sorts of stories made. Folks work around the world on
less than a watt radiated, just not "on demand".. they keep trying until
conditions are just right and they "get lucky".

So, on that basis, you could probably fire up your 1500W amplifier into
a compact loop antenna that's a meter in diameter, and work the world,
eventually.





Clearly there are considerable differences in dealing with sound waves
and RF but I believe that a principle has been established that it is
possible to 'simulate' the performance of a larger system using
physically small components. Art may not be the first to get there, but
he seems to be having a damn good try and someone, somewhere will
eventually succeed.

Mike G0ULI

Antenna physical size
 

On Mar 31, 7:52 pm, Jim Lux wrote:
wrote:
I find this topic very interesting, including the mandrill part :)

We all want to have small, broadband, eficient antennas. I believe Art
is right in his original post, today we can have all these
characteristics in the same package. There is no law of physics
forbidding that.

Uhhh. actually there ARE laws of physics putting some pretty severe
constraints on it, if not actually forbidding it, if you also accept the
constraint that the material of which you make the antenna has finite
resistance.

Through advances in computation power we can achieve

today in months what took decades in the past and there is much
research directed at these kinds of new antennas. Eventually
everyone will be able to choose and model his own antenna based on the
characteristics one wants, but without the cumbersome dimensions,
without significant bandwith limitations, without major efficiency
compromises. I believe the tradeoff (for it has to exist one) will be
ease of manufacturing.

Where ease might be defined in terms of being able to be made of
actually realizable materials?



Incidentally these new antennas have a lot to do with what Art
defines as equilibrium although I don't think he has a clear enough
definition. But it's all related to patterns, patterns which can be
found everywhere in nature an which can be expressed almost entirely
through matemathical formulas. Scaling of antennas is clearly
possible, despite of what the Chu-Harrington limit states ( or to be
fair, by applying them in a new way ).

Chu and, later, Harrington said nothing about bandwidth, by the way.
They were more concerned with directivity and size and stored energy
(the latter of which ties to efficiency and bandwidth).

Also, even if you created a very small antenna with high efficiency
(e.g. with superconductors), the fields around such an antenna will be
quite intense, so while the antenna may be small, its near field will be
pretty much the same size as the dipole it replaces, so you'll need to
put that tiny antenna way up in the air with a non-conductive, non-lossy
support to get it away from everything else. Finding a feedline might be
a bit of a challenge. One has to be careful when one draws "the
boundary" of the antenna.

In practical terms, the size of an antenna isn't just the dimensions of
the metal, but the "keepout" area within which you can't tolerate any
intrusions and still keep the same antenna performance (i.e. a 40m
dipole laying on the ground doesn't work nearly as well as a dipole
suspended 10 feet off the ground)

For that matter, avoiding the breakdown of air might be a problem.
Consider a tesla coil, which is basically a fairly inefficient (in terms
of radiated power for RF input power) small antenna for 100 kHz or so.
The limit on performance for the tesla coil isn't thermal heating of the
coil, but HV breakdown. Even a few hundred watts into a "shoebox" sized
coil will have breakdown problems (and this is fully predicted by Chu's
analysis... it's that "energy stored in the field" problem)

I eagerly await the day when the 80 meter dipole will be replace by a
small device the size of a shoe box ( although it might be a bit
larger in the beginning :) ).

Regards,
Robert

Antenna physical size
 

On Mar 31, 7:52 pm, Jim Lux wrote:
wrote:
I find this topic very interesting, including the mandrill part :)

We all want to have small, broadband, eficient antennas. I believe Art
is right in his original post, today we can have all these
characteristics in the same package. There is no law of physics
forbidding that.

Uhhh. actually there ARE laws of physics putting some pretty severe
constraints on it, if not actually forbidding it, if you also accept the
constraint that the material of which you make the antenna has finite
resistance.

Through advances in computation power we can achieve

today in months what took decades in the past and there is much
research directed at these kinds of new antennas. Eventually
everyone will be able to choose and model his own antenna based on the
characteristics one wants, but without the cumbersome dimensions,
without significant bandwith limitations, without major efficiency
compromises. I believe the tradeoff (for it has to exist one) will be
ease of manufacturing.

Where ease might be defined in terms of being able to be made of
actually realizable materials?



Incidentally these new antennas have a lot to do with what Art
defines as equilibrium although I don't think he has a clear enough
definition. But it's all related to patterns, patterns which can be
found everywhere in nature an which can be expressed almost entirely
through matemathical formulas. Scaling of antennas is clearly
possible, despite of what the Chu-Harrington limit states ( or to be
fair, by applying them in a new way ).

Chu and, later, Harrington said nothing about bandwidth, by the way.
They were more concerned with directivity and size and stored energy
(the latter of which ties to efficiency and bandwidth).

Also, even if you created a very small antenna with high efficiency
(e.g. with superconductors), the fields around such an antenna will be
quite intense, so while the antenna may be small, its near field will be
pretty much the same size as the dipole it replaces, so you'll need to
put that tiny antenna way up in the air with a non-conductive, non-lossy
support to get it away from everything else. Finding a feedline might be
a bit of a challenge. One has to be careful when one draws "the
boundary" of the antenna.

In practical terms, the size of an antenna isn't just the dimensions of
the metal, but the "keepout" area within which you can't tolerate any
intrusions and still keep the same antenna performance (i.e. a 40m
dipole laying on the ground doesn't work nearly as well as a dipole
suspended 10 feet off the ground)

For that matter, avoiding the breakdown of air might be a problem.
Consider a tesla coil, which is basically a fairly inefficient (in terms
of radiated power for RF input power) small antenna for 100 kHz or so.
The limit on performance for the tesla coil isn't thermal heating of the
coil, but HV breakdown. Even a few hundred watts into a "shoebox" sized
coil will have breakdown problems (and this is fully predicted by Chu's
analysis... it's that "energy stored in the field" problem)

I eagerly await the day when the 80 meter dipole will be replace by a
small device the size of a shoe box ( although it might be a bit
larger in the beginning :) ).

Regards,
Robert

Jim,
With all due respect a discussion is futile if you stray from the
concept of
a small FULL WAVE antenna and use the ELECTRICALLY SMALL antenna
as a straw man. The electrically small antenna is a fractional wave
antenna
which is represented by a series circuit. This is totally different
to a parallel
tank circuit. This correlates to a pendulum being cast as a weight
that comes
to a abrupt stop and instead of swinging up goes back from the bottom
to the
top from whence it came! A electrical small antenna assumes an
awefull lot
as to the mechanics of action involved in a full period. The tank
circuit is a
good example that shows that all segments of a period in terms of area
are exactly the same
where the tank circuit clearly shows that radiation occurres only in
the last
quarter of a period! The idea or concept of a fractional wave antenna
came
from the assumption that a sino soidal pattern can be seen as four
areas
under a line which can be considered the same as four times a quarter
segment,
a concept around which the NEC programs were formed. You NEVER get
radiation
at every quarter segment of a period. The concept implicit in Maxwells
laws is
that equilibrium is a given which means that the root C L portion is
that of a
full wave antenna as a minimum.
All the laws of the masters are based on a stable boundary at the
beginning and
at the time for a period of time., Time has removed a lot of memory of
the human race.
I suspect that the NEC programs around the current flow OUTSIDE the
arbitary boundary
that allowed them the successes they have gained without having to
consider
the mechanics of the innards within the boundary.
Regards
Art Unwin

Antenna physical size
 

On Mar 31, 7:00 pm, Richard Clark wrote:

Hi Robert,

50 years ago they said Electricity would be so easy to produce they
would pay us to use it. They ignored Hiroshima and discovered
Chernobyl.

I believe ease of production is a subjective term. To obtain energy
one must consume energy, there's no free lunch. But ease may be
considered 'convenience' to us, i.e. what suits our production
capability better.


40 years ago they said DNA and genetics would allow us to design our
own babies. They ignored Thalidomide and discovered Dolly the sheep
that died before her time.

Genetics have indeed contributed to most important advances in our
understanding of the human body. Instead of relying only on physiology
and anatomy, we can now have a glimpse at the 'programming language'
at the core. What use do we put it to, that's a different problem.


30 years ago they invented modeling software that would allow us to
create the Gaussian dipole (or whatever) and discovered every dipole
that came before it performed better.

That's a bit of devil's advocate stance, isn't it? :) You can't
seriously say that modelling software didn't bring something to the
table.


Nearly 20 years ago Johnny Carson retired and we are still getting
jokes.

Not nearly 10 years ago with the Dow at 11658 and a budget surplus at
230 billion, the Republicans promised prosperity was around the corner
and their voters are now living in cardboard boxes with the Dow at
12176 and the national debt up 50%.

Scaling of antennas is clearly
possible, despite of what the Chu-Harrington limit states ( or to be
fair, by applying them in a new way ).

But you don't know how, and have never seen one either.

That's true, I am not an expert in this field, I only try to stay up
to date with the technology, feel free to correct me if I'm wrong, but
I have seen many advancements in this direction lately.


73's
Richard Clark, KB7QHC

Best regards,
Robert

Antenna physical size
 

On Mar 31, 8:04 pm, Jim Lux wrote:
Mike Kaliski wrote:
Hi Richard,

I have a pair of computer speakers sitting on my desk that completely
out perform the so called ultimate hi-fi floor mounted tower system
speakers I bought 35 years ago for the equivalent of several thousand
dollars in today's money. The old speakers still work just fine but the
audio experts have learned how to squeeze that performance out of a
speaker that old audio theory predicted couldn't possibly work. Just how
does a 3 inch speaker in a cabinet the size of a couple of books manage
to produce notes from 20 Hz - 20 kHz? To be fair, the small speakers
can't fill a room with sound in the same smooth way that a larger
speaker cabinet can, but for everyday use in a small modern house or
apartment they are more than adequate for the majority of people.

It seems to me that Art and others are pursuing a similar path at RF.
The aim being to produce an antenna that punches out a signal from a
physically small area. It may not perform quite as well as a full size
half or full wavelength antenna, but it will work well enough for most
people with small gardens or limited real estate for an antenna farm.

Nope.. there's a significant difference between the speakers and the
antenna, and that's the fact that the amateur user of the antenna is
power limited (by regulation). In the speaker case, they trade off
efficiency (acoustic watts out for electrical watts out) because
electrical watts are cheap these days (not so back in McIntosh tube amp
days...) You can tolerate a 1% efficient design that puts out 100mW of
acoustic power with 10W electrical power in. (note that 120dB SPL = 1
Watt.. a symphony orchestra, at full tilt, is about a watt of acoustic
power, and I daresay you couldn't tolerate a whole orchestra in your office)

OTOH, a 1% efficient antenna design is pretty crummy. A dipole is
probably on the order of 70% efficient (RF power radiated into the far
field vs RF power at the feedline). A mobile antenna (which everyone
will agree is not particularly efficient, even if you argue about the
actual magnitude) might be 5-10% efficient (10dB down).

As a practical matter, you can get away with a 1% efficient antenna,
particularly if you're not looking for "link reliability"... The
propagation loss between you and some arbitrary point could easily vary
by 100 dB, so you just wait until propagation is "good enough" to work
the guy with the 0.1W you radiate. Of such are "worked 300 countries on
two bedsprings" sorts of stories made. Folks work around the world on
less than a watt radiated, just not "on demand".. they keep trying until
conditions are just right and they "get lucky".

So, on that basis, you could probably fire up your 1500W amplifier into
a compact loop antenna that's a meter in diameter, and work the world,
eventually.



Clearly there are considerable differences in dealing with sound waves
and RF but I believe that a principle has been established that it is
possible to 'simulate' the performance of a larger system using
physically small components. Art may not be the first to get there, but
he seems to be having a damn good try and someone, somewhere will
eventually succeed.

Mike G0ULI

Believe it or not Jim but I presently have a 160 meter antenna (full
wave)
wound on a metre loop that is resonant and can be used to work the
world.
It is hanging in the yard right now and obviously is very efficient at
what it does.
Covers the whole band to. Paid a dollar at the dollar store for the
hoola hoop!
Don't need to add capacitors and inductances evry few KHZ !
Art

Antenna physical size
 

On Mar 31, 8:52 pm, Jim Lux wrote:
wrote:


Uhhh. actually there ARE laws of physics putting some pretty severe
constraints on it, if not actually forbidding it, if you also accept the
constraint that the material of which you make the antenna has finite
resistance.


Where ease might be defined in terms of being able to be made of
actually realizable materials?


The term 'actually realizable materials' seems to shift it's
definition every time something new is discovered :)




Chu and, later, Harrington said nothing about bandwidth, by the way.
They were more concerned with directivity and size and stored energy
(the latter of which ties to efficiency and bandwidth).

True, I didn't imply that.


Also, even if you created a very small antenna with high efficiency
(e.g. with superconductors), the fields around such an antenna will be
quite intense, so while the antenna may be small, its near field will be
pretty much the same size as the dipole it replaces, so you'll need to
put that tiny antenna way up in the air with a non-conductive, non-lossy
support to get it away from everything else. Finding a feedline might be
a bit of a challenge. One has to be careful when one draws "the
boundary" of the antenna.

Ok, it was my mistake to not clarify 'high efficiency'. By that I
meant 'at the same order of efficiency as normal scale designs'.
I am currenty interested by what I have seen claimed as 'compacted
antennas', which behave similar to normal ones, except their
dimensions are smaller, X-axis wise at least. That those designs do
not perform as well or better than their counterparts is no problem
to me, as long as the figures are in the same ballpark. That would
mean they still are more efficient than previous designs which
attempted to solve the problem of physical dimensions, which is an
advancement in my book. That some other unexpected features as the
broadband factor may appear is only a bonus, because we can achieve
that with full scale antennas too.
To be more specific, I was reffering to such designs that reduce the
scale of antennas in at least one axis:
http://adsabs.harvard.edu/abs/2004ITAP...52.1945P
http://ctd.grc.nasa.gov/organization...i-antennas.htm
http://ntrs.nasa.gov/details.jsp?R=362773
http://ntrs.nasa.gov/details.jsp?R=470415
I have seen some of them described as fractal trees, but the
information is relatively scarce. I know research is continuing on
this subject and even found some info at a website somewhere but I
can't remember where. Since you probably know more about them than me,
I would appreciate some guidance here too :)


In practical terms, the size of an antenna isn't just the dimensions of
the metal, but the "keepout" area within which you can't tolerate any
intrusions and still keep the same antenna performance (i.e. a 40m
dipole laying on the ground doesn't work nearly as well as a dipole
suspended 10 feet off the ground)

For that matter, avoiding the breakdown of air might be a problem.
Consider a tesla coil, which is basically a fairly inefficient (in terms
of radiated power for RF input power) small antenna for 100 kHz or so.
The limit on performance for the tesla coil isn't thermal heating of the
coil, but HV breakdown. Even a few hundred watts into a "shoebox" sized
coil will have breakdown problems (and this is fully predicted by Chu's
analysis... it's that "energy stored in the field" problem)


I do not dispute that, however I get a feeling we're talking about
different things.

Best,
Robert