Art,

OK, here is my contribution.

Short antennas are quite thoroughly understood. Most of the analytical
treatments of antenna theory I have seen start with short dipoles and then
expand to longer dipoles and other types of antennas.

There have been any number of segmented antennas proposed and built, including
multiple trap antennas, multiple capacitor antennas, curtain antennas, fractal
antennas, and so on. Do you have some new idea that has not already been tried?

Short antennas radiate just fine, IF one can feed the power into the antenna and
avoid losing too much to non-radiative losses.

It has already been pointed out that all parts of a dipole antenna contribute to
the radiation. Sure, it is possible to shorten the antenna and even maintain the
same total radiated power. However, the pattern will change and the antenna may
become more difficult to feed.

It is not clear what issue you find with Yagi antennas. Keep in mind that it is
unlikely that one can achieve high directionality and gain from an antenna with
a size that is a tiny fraction of the wavelength. This is the case for radio
waves, optics, or any other wave phenomena. The reason people choose to use
large Yagi antennas is gain, not efficiency or cost.

Soooo, the bottom line is that there are large antennas, and there are small
antennas. Different applications favor one type over others.

Do you expect to develop some new antenna design concepts or even some new
science? If the former, then the field is well-plowed, even if it is
theoretically still infinite. If the latter, well, good luck.

73,
Gene
W4SZ


Art Unwin KB9MZ wrote:

Gene,
Brian is a fellow Brit why would I trash a fellow 'G'
Come to think of it why are you trashing me when you contributed nothing ?
Just try to get along and you are home free
Art

(Art Unwin KB9MZ) wrote in message om...
I found it interesting to read on a particular
antenna page that the antenna future will revolve
around what the person was presenting.

This does not compute to me...
He may well be correct if we are all lemmings but
people who piddle with antennas are a different breed.
Personaly I see antennas gyrating towards smaller
antennas where radiation per unit length will finish
at the top of the heap

Belly dancing antennas? I've never actually seen an antenna gyrate,
but it sounds interesting...

Antenna engineers have become so focussed on the half
wave patterns that they have completely ignored the
low efficiency portions at the ends of a half wave
antenna.

Says who? BTW, there are no low efficiency portions of a dipole.

Future antennas most surely will remove these
low efficient radiator parts

Why remove something that doesn't exist?

together with the addition
of coupling techniques that will help to move away
from the Yagi syndrome,

What is the "Yagi syndrome"? A disdain for antennas that fail to
compete with yagi's?
together with resolving the
of a "lossless" coupling direct to the transmitter

Of all your wishes, to me, this is the most foolish . I think you
should erase this "lossless coupling" from your mind, when it applies
to very small antennas. It doesn't exist, and never will. I don't know
if superconductivity could change this or not....I don't have the
superconductive materials needed for such a test..

that will obsolete the need of matching interface.

You wish...

Ofcourse this is where my intersts lie, but does this
vision of the future match yours or am I thinking
of the impossible?

Well, let me give you a hint....I prefer the largest antennas I can
get away with...I doubt anything will be changing that anytime soon.

One noted Russion scientist stated
that theoretically radiation can come from a single point,
is this part of our future or just an impossible dream ?

How does this relate to small antenna's? I don't get your point
here...

Best regards, and please put your pea shooters aside
and try to get along rather than looking for
ten seconds of cheap glory.

I don't have a pea shooter. I can pee a long ways though, if I go into
a holding pattern for about 5 hours after drinking about 14 cups of
coffee...Maybe we should have a rraa peeing contest....I don't want
any glory, if it's cheap. :/ MK

Art, KB9MZ wrote:
"Personally, I see antennas gyrating towards smaller antennas where
radiation per unit length will finish at the top of the heap."

Kraus, W8JK is somewhat famous among many reasons for his experience
with close-spaced antenna elements.

On page 184 of the 3rd edition of Kraus` "Antennas for All
Applications", is Figure 6-12 containing an ordinarily-spaced broadside
driven-array of two dipoles and a driven array radiating in the plane of
the two dipoles (an end-fire array), the W8JK array.

A feature of the W8JK array is close-spacing (1/8-wavelength). Gain of
the W8JK array is a tiny bit more than that of the 4X wider-spaced
broadside array. It`s a pity if you don`t have a copy of Kraus
available.

Kraus says in his earl;ier 1950 edition of "Antennas" on page 295:
"The end-fire array of two side-by-side out-of-phase 1/2-wavelength
elements discussed in Sec. 11-3 produces substantial gains even when the
spacing is decreased to small values."

To my eye, the W8JK array resembles the Adcock antenna if so spaced and
polarized. The 1955 edition of Terman has the Adcock on page 1050.

Terman has a comment on page 906 of his 1955 edition regarding
"Close-spaced Arrays-Super-gain Antennas. A review of the behavior of
broadside and end-fire arrays make it appear that in order to achieve
high gain it is necessary that the antenna system be distributed over a
considerable space. However, the antennas of Figs. 23-35 and 23-39
obtain enhanced directivity by employing antennas that are closely
spaced. Moreover, it can be shown that an end-fire (like a Yagi) type of
array that is short compared with a wavelength can theoretically achieve
any desired directive gain provided enough radiators are employed and
they are suitably phased. Such antennas which give great gain using
small over-all dimensions are referred to as super-gain antennas."

Read on. There is a fly in the ointment. Terman says:

" A characteristic of all close-spaced arrays is that as the ratio of
size to antenna gain is reduced, the radiation resistance also goes
down; this is illustrated by Fig. 23-36. The result is a practical limit
to the amount of gain that can be achieved in compact antenna systems,
since as the radiation resistance goes down the fraction of the total
power dissipated in the antenna loss resistance goes up. The Yagi
antenna of Fig.23-39 andf the corner reflector represent about the best
that can be achieved----."

So, Art may be on to something to some extent.

Best regards, Richard Harrison, KB5WZI

(Richard Harrison) wrote in message ...


Terman has a comment on page 906 of his 1955 edition regarding
"Close-spaced Arrays-Super-gain Antennas. A review of the behavior of
broadside and end-fire arrays make it appear that in order to achieve
high gain it is necessary that the antenna system be distributed over a
considerable space. However, the antennas of Figs. 23-35 and 23-39
obtain enhanced directivity by employing antennas that are closely
spaced. Moreover, it can be shown that an end-fire (like a Yagi) type of
array that is short compared with a wavelength can theoretically achieve
any desired directive gain provided enough radiators are employed and
they are suitably phased. Such antennas which give great gain using
small over-all dimensions are referred to as super-gain antennas."

Read on. There is a fly in the ointment. Terman says:

" A characteristic of all close-spaced arrays is that as the ratio of
size to antenna gain is reduced, the radiation resistance also goes
down; this is illustrated by Fig. 23-36. The result is a practical limit
to the amount of gain that can be achieved in compact antenna systems,
since as the radiation resistance goes down the fraction of the total
power dissipated in the antenna loss resistance goes up. The Yagi
antenna of Fig.23-39 andf the corner reflector represent about the best
that can be achieved----."

This is the fly I refer to when he keeps talks about "lossless
matching" for small antennas or arrays..

So, Art may be on to something to some extent.

Not anything really new though. There is no free lunch. Many have
tried to find it, but it's almost always spoiled by the time they
do...:/ I've modeled close spaced arrays that had loads of gain, but
to feed them efficiently in the real world is not going to be easy.
I'm not sure what the most efficient fed "very small" antenna is.
Maybe a magloop? Dunno...But even a magloop's efficiency will be lucky
to be over 70%?? or so. Not exactly what I'd call a lossless feed. MK

Mark
Let me only respond to the technical things that you are mistaken on
Radiators do have parts that are inefficient which you
apparently do not accept.
Radiation is created by current. If current was uniform over a radiator
length then the length of the radiator is reduced from 1/2 wave to
wavelength over pi.
This is because voltage becomes more dominant than current at the ends of a
radiator.
If you divide the current curve into uniform radiator length
it should become clear to you that the area under the current curve per unit
length diminishes as the curve moves to zero. This is fundermental but if
you still have problems with this concept by all means continue a technical
dialogue.

Loss less feed systems.
This term is used quite a lot in academia. One can relate it to such things
as household circuits where the radiation is so small it is not considered a
factor in calculations.
.. A 'loss less' feed system in say an antenna would comprise of something
short with respect to wave length and would be voltage dominated so that
radiation is minimised by the low value of current.

Regarding efficiency of magnetic loops.
It is clear in this case that we are dealing with a radiatior that is not
only one tenth of a wavelength but also has an impedance dominated by
resistive losses which means that the efficiency will be extremely low and
possibly only a tenth of what you surmised.
There are ways to ensure that low impedance
problems can be overcome, we see similar problems overcome
in very high gain yagi's which tend to have low impedances as efficiency
increases. This problem can be readily overcome in many cases by adding a
second reflector where its proximity to the driven element
reverses the decline in impedance.by adding a coupling effect.
If I have forgotton something technical that you brought up please let me
know.

Ah yes, the yagi syndrome.
Yagi gain is based on boom length assuming other requirements are met. In
the amateaur world boom length is not really a problem for half of the bands
but it is a problem in that boom length and gain have a limit in scope
as well usuitable for many bands. So I would expect that future enginners
will move away from just yagi's and explore methods where direct coupling of
radiators will occur to remove problems of fractional wavelength portions
spacings as one sees with the yagi aproach. and explore other areas, where
turning radius becomes prominent rather than boom length..
But only the future will tell.,which is the subject of this particular
thread.
Art

"Mark Keith" wrote in message
om...
(Richard Harrison) wrote in message
...


Terman has a comment on page 906 of his 1955 edition regarding
"Close-spaced Arrays-Super-gain Antennas. A review of the behavior of
broadside and end-fire arrays make it appear that in order to achieve
high gain it is necessary that the antenna system be distributed over a
considerable space. However, the antennas of Figs. 23-35 and 23-39
obtain enhanced directivity by employing antennas that are closely
spaced. Moreover, it can be shown that an end-fire (like a Yagi) type of
array that is short compared with a wavelength can theoretically achieve
any desired directive gain provided enough radiators are employed and
they are suitably phased. Such antennas which give great gain using
small over-all dimensions are referred to as super-gain antennas."

Read on. There is a fly in the ointment. Terman says:

" A characteristic of all close-spaced arrays is that as the ratio of
size to antenna gain is reduced, the radiation resistance also goes
down; this is illustrated by Fig. 23-36. The result is a practical limit
to the amount of gain that can be achieved in compact antenna systems,
since as the radiation resistance goes down the fraction of the total
power dissipated in the antenna loss resistance goes up. The Yagi
antenna of Fig.23-39 andf the corner reflector represent about the best
that can be achieved----."

This is the fly I refer to when he keeps talks about "lossless
matching" for small antennas or arrays..

So, Art may be on to something to some extent.

Not anything really new though. There is no free lunch. Many have
tried to find it, but it's almost always spoiled by the time they
do...:/ I've modeled close spaced arrays that had loads of gain, but
to feed them efficiently in the real world is not going to be easy.
I'm not sure what the most efficient fed "very small" antenna is.
Maybe a magloop? Dunno...But even a magloop's efficiency will be lucky
to be over 70%?? or so. Not exactly what I'd call a lossless feed. MK

Art Unwin KB9MZ wrote:
This is because voltage becomes more dominant than current at the ends of a
radiator.

Are you aware that the voltage is never more dominant
than the current in a terminated antenna like a rhombic?
--
73, Cecil http://www.qsl.net/w5dxp



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No Cecil I have never been fortunate to own a rombic
or even to bone up on it.
But Cecil, if it affects the validity of what I am saying please pipe up. We
certainly do not want any old wives tales to grow without dissent from those
knoweledgable in the field whose numbers are getting smaller all the time.
Best regards
Art

"Cecil Moore" wrote in message
...
Art Unwin KB9MZ wrote:
This is because voltage becomes more dominant than current at the ends
of a
radiator.

Are you aware that the voltage is never more dominant
than the current in a terminated antenna like a rhombic?
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

" Art Unwin KB9MZ" wrote in message news:bVUOb.100367$I06.445073@attbi_s01...
Mark
Let me only respond to the technical things that you are mistaken on
Radiators do have parts that are inefficient which you
apparently do not accept.

No, I don't accept it. To me, you are misapplying terms. All radiators
are efficient unless they are so thin, or of a material as to have a
lot of excess resistance.
All radiators are equally capable of being efficient radiators AS LONG
as you can actually transfer power to them. Efficiency is a poor term
to use for a radiator quality. A half size dipole is just as capable
of being an efficient radiator as the full size dipole. Really no
less, or more so. The fun part is actually transfering the power from
the radio/feedline to the radiator in an efficient manner. The only
thing you are altering when you shorten an antenna element is the
pattern, and gain in a certain direction. And the change is not that
drastic. The pattern is still a fig 8, and the gain has dropped to
about 1.8 dbi, instead of appx 2.1 dbi. You do not alter efficiency
per say. The efficiency is the percentage of power lost in the
transfer of power to the radiator. Or you can gauge the efficiency of
the whole system as a whole. You do not gauge efficiency of radiating
elements, except as already stated.
BTW, if I'm wrong on any of this, anyone feel free to jump in and
correct...
I don't want to create any excess old wives either...

Radiation is created by current. If current was uniform over a radiator
length then the length of the radiator is reduced from 1/2 wave to
wavelength over pi.
This is because voltage becomes more dominant than current at the ends of a
radiator.
If you divide the current curve into uniform radiator length
it should become clear to you that the area under the current curve per unit
length diminishes as the curve moves to zero. This is fundermental but if
you still have problems with this concept by all means continue a technical
dialogue.

Dunno... I'm not really getting the point of all this...

Loss less feed systems.
This term is used quite a lot in academia. One can relate it to such things
as household circuits where the radiation is so small it is not considered a
factor in calculations.
. A 'loss less' feed system in say an antenna would comprise of something
short with respect to wave length and would be voltage dominated so that
radiation is minimised by the low value of current.

I'd feel better if you dropped the "lossless" term, and changed it to
"low loss". Or maybe lower loss...

Regarding efficiency of magnetic loops.
It is clear in this case that we are dealing with a radiatior that is not
only one tenth of a wavelength but also has an impedance dominated by
resistive losses which means that the efficiency will be extremely low and
possibly only a tenth of what you surmised.

Not sure...I don't bother with such antennas, but I was under the
impression the efficiency could be fairly decent with those if the
proper techniques were used in feeding them. I could have been
mistaken on the appx 70% number...

There are ways to ensure that low impedance
problems can be overcome, we see similar problems overcome
in very high gain yagi's which tend to have low impedances as efficiency
increases. This problem can be readily overcome in many cases by adding a
second reflector where its proximity to the driven element
reverses the decline in impedance.by adding a coupling effect.
If I have forgotton something technical that you brought up please let me
know.

I'm not sure if I really agree on this, but I'll leave this for now...

Ah yes, the yagi syndrome.
Yagi gain is based on boom length assuming other requirements are met. In
the amateaur world boom length is not really a problem for half of the bands
but it is a problem in that boom length and gain have a limit in scope
as well usuitable for many bands. So I would expect that future enginners
will move away from just yagi's and explore methods where direct coupling of
radiators will occur to remove problems of fractional wavelength portions
spacings as one sees with the yagi aproach. and explore other areas, where
turning radius becomes prominent rather than boom length..

They have been, still do, and surely will continue...
MK

(Mark Keith) wrote in message . com...
" Art Unwin KB9MZ" wrote in message news:bVUOb.100367$I06.445073@attbi_s01...
Mark
Let me only respond to the technical things that you are mistaken on
Radiators do have parts that are inefficient which you
apparently do not accept.

No, I don't accept it. To me, you are misapplying terms. All radiators
are efficient unless they are so thin, or of a material as to have a
lot of excess resistance.
All radiators are equally capable of being efficient radiators AS LONG
as you can actually transfer power to them. Efficiency is a poor term
to use for a radiator quality. A half size dipole is just as capable
of being an efficient radiator as the full size dipole. Really no
less, or more so. The fun part is actually transfering the power from
the radio/feedline to the radiator in an efficient manner. The only
thing you are altering when you shorten an antenna element is the
pattern, and gain in a certain direction. And the change is not that
drastic. The pattern is still a fig 8, and the gain has dropped to
about 1.8 dbi, instead of appx 2.1 dbi. You do not alter efficiency
per say. The efficiency is the percentage of power lost in the
transfer of power to the radiator. Or you can gauge the efficiency of
the whole system as a whole. You do not gauge efficiency of radiating
elements, except as already stated.

BTW, if I'm wrong on any of this, anyone feel free to jump in and
correct...
I don't want to create any excess old wives either...

Unfortunately Mark this is not going to happen.
Having lost so many talented people from this group the
tendency now for those that are left are to avoid the
hard questions, provide quotes from books that leave you
hanging afterwards or intentionaly or other wise confuse
and divert from the specific issue.
I would like to make one point clear. I was refering to
efficiency per unit length which somehow people will not accept.
In the case of the amateurs losing the ends of the dipole and not
noticing the difference is purely because the difference is not
perceptable to the ear as your figures pointed out which is why
capacity hats are so usefull.
On the ARRL question and gaps between dipoles. In all my copies
the gain curves all stop at zero gap between dipole ends which is
absolutely absurd as the ends of a dipole has nothing to do with
the situation of gain. Gain is determined as a vector addition
in combination with phase.
I also agree that less loss would be a better term but if one
moves away from convention all hell breaks loose
Best regards
Art




ie power factor or cos phi.
you have read them or


Radiation is created by current. If current was uniform over a radiator
length then the length of the radiator is reduced from 1/2 wave to
wavelength over pi.
This is because voltage becomes more dominant than current at the ends of a
radiator.
If you divide the current curve into uniform radiator length
it should become clear to you that the area under the current curve per unit
length diminishes as the curve moves to zero. This is fundermental but if
you still have problems with this concept by all means continue a technical
dialogue.

Dunno... I'm not really getting the point of all this...

Loss less feed systems.
This term is used quite a lot in academia. One can relate it to such things
as household circuits where the radiation is so small it is not considered a
factor in calculations.
. A 'loss less' feed system in say an antenna would comprise of something
short with respect to wave length and would be voltage dominated so that
radiation is minimised by the low value of current.

I'd feel better if you dropped the "lossless" term, and changed it to
"low loss". Or maybe lower loss...

Regarding efficiency of magnetic loops.
It is clear in this case that we are dealing with a radiatior that is not
only one tenth of a wavelength but also has an impedance dominated by
resistive losses which means that the efficiency will be extremely low and
possibly only a tenth of what you surmised.

Not sure...I don't bother with such antennas, but I was under the
impression the efficiency could be fairly decent with those if the
proper techniques were used in feeding them. I could have been
mistaken on the appx 70% number...

There are ways to ensure that low impedance
problems can be overcome, we see similar problems overcome
in very high gain yagi's which tend to have low impedances as efficiency
increases. This problem can be readily overcome in many cases by adding a
second reflector where its proximity to the driven element
reverses the decline in impedance.by adding a coupling effect.
If I have forgotton something technical that you brought up please let me
know.

I'm not sure if I really agree on this, but I'll leave this for now...

Ah yes, the yagi syndrome.
Yagi gain is based on boom length assuming other requirements are met. In
the amateaur world boom length is not really a problem for half of the bands
but it is a problem in that boom length and gain have a limit in scope
as well usuitable for many bands. So I would expect that future enginners
will move away from just yagi's and explore methods where direct coupling of
radiators will occur to remove problems of fractional wavelength portions
spacings as one sees with the yagi aproach. and explore other areas, where
turning radius becomes prominent rather than boom length..

They have been, still do, and surely will continue...
MK