(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

Art,
There are several questions interspersed in your
quoted post below. These questions deal with assumptions
and/or assertions you have made.


Unfortunately Mark this is not going to happen.
Having lost so many talented people from this group
------
1. Please furnish a list of those 'talented people' who
are now missing from 'this' group. A list of present
members of the 'group' would also be appreciated.
------
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.
------
2. Please furnish a list of 'those hard questions' which
have been avoided. Also the 'quotes from books' that have
left you hanging.
------
I would like to make one point clear. I was refering to
efficiency per unit length which somehow people will not accept.
------
3. Please explain why people should accept this theory. Of
what use is it?
------
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.
------
4. Have you perhaps thought that without the 'ends' of the
dipoles
being discussed, a necessary 'part' of the antenna to produce
the
gain is missing, and that the gain is lessened or absent?
------
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
------
5. Have you ever thought that if you would explain your
thought
process, and the non-conventional terms you use, that you
might
prevent that "all hell breaking loose"?
------
Best regards
Art


- 'Doc

'Doc wrote in message ...


Doc,
you are so full of s**t

The idea of this group is to exchange and/or discuss idea's
and thoughts,and to give or receive advice in regards to antenna's,
It must be obvious to most readers of this group by now that when it
comes to postings from Art you are incapable of any of the above.
May i suggest that if you cannot resist attacking the man and not
the message then,as a better man than i said "a period of silence
from you would be very welcome".
Jaro

Art, KB9MZ wrote:
"Antenna engineers have become so focussed on the half wave patterns
that they have completely ignored the low efficiency portions at the
ends of the half wave antenna. Future antennas most surely will remove
these low efficient (sic) radiator parts together with the addition of
coupling techniques that will help to move away from the yagi syndrome."

Don`t hold your breath!

Antenna engineers are focussed on 1/2-wave antenna patterns because
those are the patterns produced by 1/2-wave antennas. A half-wave
antenna is resonant without a reflection from the earth or anything
else. Antenna system resonance is essential to remove reactive impedance
to antenna current flow. No current flow, no antenna operation.

The ends of a dipole have nearly zero radiation because current at the
ends is nearly a zero sum of incident and reflected currents.The H-field
is thus cancelled. Radiation ends where the current ends. A 1/4-wave
back from the reflection point, incident and reflected currents are
in-phase and strong radiation is possible.

What Art calls the "yagi syndrome" is a preference for an antenna which
has only one feedline attachment point and gets about as much gain per
length of wire as any. Size is important for wind loading in addition to
antenna cost and performance. The yagi is a big performer in spite of
its small size.

Yagi elements must be nearly 1/2-wave in length because that`s the
minimum length required to accept significant induced current in a
parasitic element=A0far from ground.

If you were to chop off the ends of a 1/2-wave antenna, you would have
to replace them with another mechanism to bring resonance back to the
shortened dipole. These artifices are almost always lossier than the
lost conductor removed from the antenna. A capacitance hat is an
exception, but this is hardly smaller.

At night it is often more rewarding to look for something lost, not
because the site seems probable, but because the search site is the only
illuminated spot.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:

Art, KB9MZ wrote:
"Antenna engineers have become so focussed on the half wave patterns
that they have completely ignored the low efficiency portions at the
ends of the half wave antenna. Future antennas most surely will remove
these low efficient (sic) radiator parts together with the addition of
coupling techniques that will help to move away from the yagi syndrome."

Don`t hold your breath!

Makes me wonder if Art has ever considered cutting-off the unused parts
of the tires on his car. ;-)

73, Jim AC6XG