"Dave Platt" wrote in message
...

In article uoD1e.110018$Ze3.66917@attbi_s51,
wrote:

There is a harsh limit, imposed by physics, as to how much gain that
approach can give you.

Agreed... Do you know what those limits are ?

Sure. The simplest way to state it is "the total amount of power
delivered by the antenna, summed over all of the possible angles of
radiation, must equal the total amount of power radiated by the
antenna."


If all of the energy from one hemisphere is redirected into the other
hemisphere, and if the forward-direction pattern shape does not change
(the forward lobe is not narrowed), then you have a forward gain of 3
dB

But the forward pattern DOES change with a YAGI design. In fact it inferes
unequal pressures within the pattern. I would have no problem with a lot of
what you say
BUT the YAGI does not follow the theoretical aproach that you supplied thus
what you say regarding a yagi is based on a straw man augument.
My question was for the Yagi pattern which does not follow your aproach
You cannot relate gain and power since with a yagi tho power is an all
encompasing term
(three dimensional) gain is not. What you stated earlier regarding gain as a
ratio
is correct but for a Yagi its parameters must be defined which is not by the
term power.
as you have used it.


(2:1 power ratio increase). You *cannot* have more, as this would
require that the antenna be radiating more power than it receives from
its input.

Absolutely incorrect. If I place the air of two balloons ,which reflect
the
figure
eight,into one single balloon and where the laws of partial pressures do
not
intervene
then you will have a balloon that is round and not elongated as the
antenna
books
would have you suggest. "Gain" is a term used to to quantify a small
portion of the
energy contained in the mythical ball of energy. Since the collection of
energy comes
from different directions and phases the energy collection is layered
depending on
the influence of the earth. Thus the layers of radiation are distorted
where one layer
can be squeezed outwards further than other layers, thus the terminology
of "gain"

Jeez, Art, do you have any idea of just how thoroughly your response
qualifies as "Authentic frontier gibberish" (as a Mel Brooks character
once said)?

I'm sorry, guy, but I believe that you are trying to stretch analogies
far beyond the point where they actually apply to the physical
phenomena we're discussing. Your concept of "layers of radiation" (as
applied to the gain pattern of an antenna) simply doesn't add up.

If you are going to interelate the terms of "gain" and "power" then you
must
define
the parameters used to allow that.

OK, let's do just that.

"Power" is very well defined - it's the rate at which energy is
delivered. Pick your units for energy and time as you choose. It's
conventional to use watts for power, joules for energy and seconds for
time. One watt, equals a rate of energy delivery of one joule per
second.

"Gain" is a ratio. In discussions dealing with antennas, the gain
describes the ratio between the amount of power delivered by a given
antenna in a given direction, to the amount of power delivered in that
same direction by a "reference" antenna (a dipole in the case of a dBd
gain number, and an "isotropic" antenna in the case of a dBi gain
number). The gain figures in dB are logarithmic.

Those are the definitions everyone uses, I believe.

I can go along with that


If you, personally, are using different definitions than these, then
our discussion (you vs. everyone else) should probably stop right here.

Here's my rationale behind the statement I made about the limitations
of your approach:

- An isotropic antenna has a gain of 0 dBi, by definition.

- If you "cut off" the entire rear side of an isotropic antenna's
pattern (so that it radiates no power backwards), and precisely
overlay this power (energy flow) onto the forward half, you'll end
up with a "half-isospheric" antenna. It's radiating exactly the
same amount of power, but over only half as much target area. The
power (energy flow) towards each point in that targeted hemisphere
will be exactly twice as much as in the isotropic antenna.

This antenna has a gain of 3 dBi plus a hair.

As you say, when you are refering to isentropic


It cannot have *more* gain in any direction (more power into a
sub-portion of the hemisphere) unless it has *less* gain in another
portion of that hemisphere...
For the isotropic aproach which has little relationship to the real world of
yagis
that some how narrows not only the main lobe but also the other lobes all
of which have seperate gains created by the movement of energy from the rear
and not constrained by your theoretical 3 db aproach


in other words, unless is starts
exhibiting some form of lobing/nulling.

If it *could*, it would be trivial to demonstrate that the antenna
was delivering more power (more energy over time) into its loads,
than it was accepting from its transmitter.

The same line of logic applies even if you start with a dipole. If
you begin with a dipole, and then magically "deflect" all of the power
from the rear towards the front and overlay the patterns exactly,
you'll exactly double the power in each forward-lying half of the
sphere, and create a gain of 3 dB over the dipole. In order to have
*more* forward gain in any direction in the forward direction, you
must necessarily have *less* in another, and this either narrows the
pattern in the forward direction or creates partial or complete nulls.

To claim otherwise, is to claim an antenna which can be shown to
deliver more power than it accepts as input... in other words, one
which violates the conservation of energy.

The same basic rule applies for any situation in which you take a
bidirectional antenna (one which has a symmetrical forward-and-
backward gain pattern) and then "deflect" all of the rearward energy
into a forward direction. This will gain you at most 3 dB over the
basic gain pattern of the antenna you started with. Any further
maximum forward gain, over the antenna you were starting with, can
*only* be achieved by decreasing the gain somewhere in the pattern
(narrowing or weakening the main lobe or one of the sidelobes).

A Moxon antenna is, to a first approximation, a pretty good example of
this approach - it has very little energy in the rear hemisphere, and
a broad forward lobe. There are various two-driven-element array
designs which achieve a similar pattern and result.

And the resulting "gain" is ....what?

According to Cebik's web site, a 2-meter Moxon shows a maximum forward
gain of about 10.7 dBi, or a bit more than 8 dB over a dipole. One
could gain at most 3 dB due to the forward "deflection" of rear-
hemisphere energy, and hence the remaining 5 dB or so of gain over a
dipole must come from a narrowing of the antenna's pattern in either
azimuth or elevation or both.

Yes I agree because of conservation laws e.t.c . When cancellation occurs
then energy creats energy in another direction similar to pulling steel
apart in tension
(or using compression) the steel becomes narrower before severing occurrs.
This thinning or "waisting" is created by the additional forces created at
90 degrees
to the tensile forces and where the break actually occurrs at 45 degrees
and not at right angles.

Art, I think your analogies between radiation patterns, balloons,
stretching metal, etc. are leading you astray more than they are
helping you.

Conservation of energy *requires* that the main lobe be narrowed, if
you wish to achieve more gain than you can get by simply redistibuting
the rear-ward energy in the forward direction.

This is what you alluded to before and it is still incorrect
What "requires" what ? And how is this conclusion generating
an elongated lobe?

A super-high-gain antenna *cannot* have a wide, uniform beam-width in
both azimuth and elevation.

Don't know how you can say that

I say that because the opposite case would contradict the law of
conservation of energy.

If you have an antenna which puts all of its power, uniformly, into a
forward beam which covers only 1/10 of the sphere, then that forward
beam will carry 10 times as much power per angle, for a gain of 10
dBi.

If you squeeze the beam down in size so that it covers only 1/100 of
the sphere, it will carry 100 times as much power per angle, for a
gain of 20 dB.

You can't have a broad forward lobe (say, one which covers a full 1/10
of the sphere), and achieve a high gain of 20 dB (100 times as much
power per angle) without violating the law of conservation of energy.

*THAT* is the fundamental limit I'm talking about, Art.


As usual for your postings, Art, it's impossible to tell whether your
claims for your antenna are plausible, because you refuse to disclose
*anything* (either the invention, or the results you claim) in any
halfway-tanglible form (e.g. models, specific numbers, etc.).


My antenna is somewhat related

You DID IT AGAIN, Art. You said "is somewhat related", you didn't say
related to *what*, you didn't give any details whatsoever.

Oh come on Dave, don't twist things around. I have stated that my antenna,
which is not a yagi, when transposing pattern volume from the rear to the
front
does it in an orderly fashion by expansion of the receiving vessel in a
circular form.
.. Thus the gain increased as the rear volume decreased with a diminishing
increase in gain.
The yagi does something different as other vectorial interferences is
creating
"outward pressures" on the so called balloon to NARROW the beam width.
Disregarding any effects that can be attributed to other antennas my
question is
related to the YAGI design which actually creates a narrowing beam as
progress is made
in transposing energy from the front to the rear. This is a fact , thus the
question "why"
a question that is pertinent to the YAGI design and not any other design or
multiple
arrangements of such..
You have supplied plenty of dots regarding antennas but none that remotely
relates to the question





The question however, is specifically related to Yagi's
and its narrowed lobes.
Do you know what it is that creats an elongated lobe
on a high gain yagi i.e not totally round.?
Nothing more, nothing less.

You're acting as though the lobe were a physical object, and that
something is "putting pressure" on it to squeeze it out of shape like
a physical balloon.

That is a FALSE ANALOGY, Art. It's meaningless.

The "shape" of the lobe is simply a way of plotting numbers on a
graph. It depends on the scaling of the graph, and it's a *relative*
scale. A dipole's lobes may look perfectly round on one sort of
graph, elliptical on another, and lumpy on a third, depending on
whether the plot's axes are logarithmic, linear, or somewhere in
between the two.

Fundamentally, the reason that the shape of the lobe (on a
conventional plot) changes from somewhat-circular to more-eliptical is
due to the fact that the antenna is sending more of its power in a
favored direction (to achieve gain), at the expense of sending less in
other directions. Period.

The *mechanism* by which this is done, in a Yagi (or an actively-
driven set of phased radiators), is simply one of dividing up the
power being radiated so that it's radiated (or re-radiated) from
multiple points, in different spatial and phase relationships, so that
the resulting waves cancel out in certain directions and reinforce in
others.

If you really want to know the details, I suggest that you dig up and
read the original papers by Uda and Yagi.
Until you do, I really think it would be to everyone's relief if you'd
follow through with your recent statement that you were going to stop
posting. You're achieving no good result for yourself by contining as
you are.

I have not posted as you have inferred. The question is about Yagi design

It all seems to come down to the same thing with you, Art.

I suppose I should just killfile you and completely ignore your
postings. I'm sorry, I've tried my best to steer you in directions
that I think will actually help your efforts, but it seems quite futile.

By all means put me on your kill file. I asked a simple question and you
want to reply to a different question of your liking and place your
question
as one preferable to mine.
No one has been able to supply the answer to my question,
Using your words ,what steers the pattern away from a circular
form from a natural circular form. I am not asking for the extraneious
information
that all feel they are compelled to supply to make their posting look
informative.
Regards
Art





--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Great! I would disagree with respect to "any other type of directional array
but I would like a further insight to the mechanics of vector array that
produces
this phenomina. I would like to reproduce this effect else where if I could.
Regards
Art



"Richard Fry" wrote in message
...
" wrote:
The shape changes can come from squeezing the balloon (pattern)
horizontally, vertically, or in combination -- which, in antenna
hardware is accomplished by an appropriate array of, and feed system
for, its radiating elements.

Right..... so what creats it, this "squeezing" that you talk about and
from where does this "squeezing force come from in an "appropiate"array?
That's what I was asking not a discussion of what the Yagi array
produces. Why does the lobe narrow?
______________

Narrowing is the natural result of the vector addition of the separate EM
waves radiated from the individual sources comprising the Yagi (or any
other kind of directional array).

RF

" wrote
Great! I would disagree with respect to "any other type of directional
array' but I would like a further insight to the mechanics of vector
array that produces this phenomina. I would like to reproduce this
effect else where if I could.
___________

Suggest you get this background from a good read of just about any of the
many antenna textbooks available. It's a bit much to deal with in a NG
forum.

RF

Hal I think you are right
It is magic!.
I think that this subject has been pushed to one side during the last
century in the event
anybody should come along and say all is known about antennas
so we can put them in their place.
Someday, someone will come along with an answer and then we can all jump on
him
and ask him to prove it so the monkey is not on our backs.
The post did attract a lot of interest tho even if there was not a cigar
supplied.
It really is amazing what photons can do when they become all entangled.
Time to get back to what SWR really entails when all can put their two
pennies
worth in.
I've got to now draw a circle with a compass and observe how the shape
changes when
replotted with logrithmic and other types of graph paper

Regards
Art

"Hal Rosser" wrote in message
. ..

"Cecil Moore" wrote in message
...
wrote:
So to the gurus of this group, what actualy creates
the narrowing of the forward lobes ?

The narrowing of the forward lobes is
caused by constructive interference
during superposition of EM waves.
--
73, Cecil http://www.qsl.net/w5dxp

Darn - I thought it was pure magic.
Now we hear all about induced currents and interference patterns
cancelling
in the rearward and the sides, but constructively interferring in the
forward direction. All in an attempt to become the chosen guru of the
original poster.
If nominated, I will not run - if elected - I will not serve.

I've got to now draw a circle with a compass and observe how the shape
changes when
replotted with logrithmic and other types of graph paper

Regards
Art

Be sure to give us a report on creating the logarithmic graph paper.
If I heard someone was looking to replot circles on log graph paper, I would
say he must be a ham.
Then I would think about writing a Java program to do it, as I slipped into
sleep while listening to 'Coast-to-coast-AM' on the radio.

Dave, you are amazing. Such a well-reasoned and complete post. Too
bad it was a total waste of your time.

Regards,

Wes


On Sun, 27 Mar 2005 20:41:24 -0000, (Dave Platt)
wrote:


In article uoD1e.110018$Ze3.66917@attbi_s51,
wrote:

There is a harsh limit, imposed by physics, as to how much gain that
approach can give you.

Agreed... Do you know what those limits are ?

Sure. The simplest way to state it is "the total amount of power
delivered by the antenna, summed over all of the possible angles of
radiation, must equal the total amount of power radiated by the
antenna."


If all of the energy from one hemisphere is redirected into the other
hemisphere, and if the forward-direction pattern shape does not change
(the forward lobe is not narrowed), then you have a forward gain of 3
dB (2:1 power ratio increase). You *cannot* have more, as this would
require that the antenna be radiating more power than it receives from
its input.

Absolutely incorrect. If I place the air of two balloons ,which reflect the
figure
eight,into one single balloon and where the laws of partial pressures do not
intervene
then you will have a balloon that is round and not elongated as the antenna
books
would have you suggest. "Gain" is a term used to to quantify a small
portion of the
energy contained in the mythical ball of energy. Since the collection of
energy comes
from different directions and phases the energy collection is layered
depending on
the influence of the earth. Thus the layers of radiation are distorted
where one layer
can be squeezed outwards further than other layers, thus the terminology
of "gain"

Jeez, Art, do you have any idea of just how thoroughly your response
qualifies as "Authentic frontier gibberish" (as a Mel Brooks character
once said)?

I'm sorry, guy, but I believe that you are trying to stretch analogies
far beyond the point where they actually apply to the physical
phenomena we're discussing. Your concept of "layers of radiation" (as
applied to the gain pattern of an antenna) simply doesn't add up.

If you are going to interelate the terms of "gain" and "power" then you must
define
the parameters used to allow that.

OK, let's do just that.

"Power" is very well defined - it's the rate at which energy is
delivered. Pick your units for energy and time as you choose. It's
conventional to use watts for power, joules for energy and seconds for
time. One watt, equals a rate of energy delivery of one joule per
second.

"Gain" is a ratio. In discussions dealing with antennas, the gain
describes the ratio between the amount of power delivered by a given
antenna in a given direction, to the amount of power delivered in that
same direction by a "reference" antenna (a dipole in the case of a dBd
gain number, and an "isotropic" antenna in the case of a dBi gain
number). The gain figures in dB are logarithmic.

Those are the definitions everyone uses, I believe.

If you, personally, are using different definitions than these, then
our discussion (you vs. everyone else) should probably stop right here.

Here's my rationale behind the statement I made about the limitations
of your approach:

- An isotropic antenna has a gain of 0 dBi, by definition.

- If you "cut off" the entire rear side of an isotropic antenna's
pattern (so that it radiates no power backwards), and precisely
overlay this power (energy flow) onto the forward half, you'll end
up with a "half-isospheric" antenna. It's radiating exactly the
same amount of power, but over only half as much target area. The
power (energy flow) towards each point in that targeted hemisphere
will be exactly twice as much as in the isotropic antenna.

This antenna has a gain of 3 dBi plus a hair.

It cannot have *more* gain in any direction (more power into a
sub-portion of the hemisphere) unless it has *less* gain in another
portion of that hemisphere... in other words, unless is starts
exhibiting some form of lobing/nulling.

If it *could*, it would be trivial to demonstrate that the antenna
was delivering more power (more energy over time) into its loads,
than it was accepting from its transmitter.

The same line of logic applies even if you start with a dipole. If
you begin with a dipole, and then magically "deflect" all of the power
from the rear towards the front and overlay the patterns exactly,
you'll exactly double the power in each forward-lying half of the
sphere, and create a gain of 3 dB over the dipole. In order to have
*more* forward gain in any direction in the forward direction, you
must necessarily have *less* in another, and this either narrows the
pattern in the forward direction or creates partial or complete nulls.

To claim otherwise, is to claim an antenna which can be shown to
deliver more power than it accepts as input... in other words, one
which violates the conservation of energy.

The same basic rule applies for any situation in which you take a
bidirectional antenna (one which has a symmetrical forward-and-
backward gain pattern) and then "deflect" all of the rearward energy
into a forward direction. This will gain you at most 3 dB over the
basic gain pattern of the antenna you started with. Any further
maximum forward gain, over the antenna you were starting with, can
*only* be achieved by decreasing the gain somewhere in the pattern
(narrowing or weakening the main lobe or one of the sidelobes).

A Moxon antenna is, to a first approximation, a pretty good example of
this approach - it has very little energy in the rear hemisphere, and
a broad forward lobe. There are various two-driven-element array
designs which achieve a similar pattern and result.

And the resulting "gain" is ....what?

According to Cebik's web site, a 2-meter Moxon shows a maximum forward
gain of about 10.7 dBi, or a bit more than 8 dB over a dipole. One
could gain at most 3 dB due to the forward "deflection" of rear-
hemisphere energy, and hence the remaining 5 dB or so of gain over a
dipole must come from a narrowing of the antenna's pattern in either
azimuth or elevation or both.

Yes I agree because of conservation laws e.t.c . When cancellation occurs
then energy creats energy in another direction similar to pulling steel
apart in tension
(or using compression) the steel becomes narrower before severing occurrs.
This thinning or "waisting" is created by the additional forces created at
90 degrees
to the tensile forces and where the break actually occurrs at 45 degrees
and not at right angles.

Art, I think your analogies between radiation patterns, balloons,
stretching metal, etc. are leading you astray more than they are
helping you.

Conservation of energy *requires* that the main lobe be narrowed, if
you wish to achieve more gain than you can get by simply redistibuting
the rear-ward energy in the forward direction.

This is what you alluded to before and it is still incorrect
What "requires" what ? And how is this conclusion generating
an elongated lobe?

A super-high-gain antenna *cannot* have a wide, uniform beam-width in
both azimuth and elevation.

Don't know how you can say that

I say that because the opposite case would contradict the law of
conservation of energy.

If you have an antenna which puts all of its power, uniformly, into a
forward beam which covers only 1/10 of the sphere, then that forward
beam will carry 10 times as much power per angle, for a gain of 10
dBi.

If you squeeze the beam down in size so that it covers only 1/100 of
the sphere, it will carry 100 times as much power per angle, for a
gain of 20 dB.

You can't have a broad forward lobe (say, one which covers a full 1/10
of the sphere), and achieve a high gain of 20 dB (100 times as much
power per angle) without violating the law of conservation of energy.

*THAT* is the fundamental limit I'm talking about, Art.


As usual for your postings, Art, it's impossible to tell whether your
claims for your antenna are plausible, because you refuse to disclose
*anything* (either the invention, or the results you claim) in any
halfway-tanglible form (e.g. models, specific numbers, etc.).


My antenna is somewhat related

You DID IT AGAIN, Art. You said "is somewhat related", you didn't say
related to *what*, you didn't give any details whatsoever.

The question however, is specifically related to Yagi's
and its narrowed lobes.
Do you know what it is that creats an elongated lobe
on a high gain yagi i.e not totally round.?
Nothing more, nothing less.

You're acting as though the lobe were a physical object, and that
something is "putting pressure" on it to squeeze it out of shape like
a physical balloon.

That is a FALSE ANALOGY, Art. It's meaningless.

The "shape" of the lobe is simply a way of plotting numbers on a
graph. It depends on the scaling of the graph, and it's a *relative*
scale. A dipole's lobes may look perfectly round on one sort of
graph, elliptical on another, and lumpy on a third, depending on
whether the plot's axes are logarithmic, linear, or somewhere in
between the two.

Fundamentally, the reason that the shape of the lobe (on a
conventional plot) changes from somewhat-circular to more-eliptical is
due to the fact that the antenna is sending more of its power in a
favored direction (to achieve gain), at the expense of sending less in
other directions. Period.

The *mechanism* by which this is done, in a Yagi (or an actively-
driven set of phased radiators), is simply one of dividing up the
power being radiated so that it's radiated (or re-radiated) from
multiple points, in different spatial and phase relationships, so that
the resulting waves cancel out in certain directions and reinforce in
others.

If you really want to know the details, I suggest that you dig up and
read the original papers by Uda and Yagi.
Until you do, I really think it would be to everyone's relief if you'd
follow through with your recent statement that you were going to stop
posting. You're achieving no good result for yourself by contining as
you are.

I have not posted as you have inferred. The question is about Yagi design

It all seems to come down to the same thing with you, Art.

I suppose I should just killfile you and completely ignore your
postings. I'm sorry, I've tried my best to steer you in directions
that I think will actually help your efforts, but it seems quite futile.

In article P2G1e.110904$Ze3.11791@attbi_s51,
wrote:

By all means put me on your kill file. I asked a simple question and you
want to reply to a different question of your liking and place your
question
as one preferable to mine.

Art, in cases like this, you keep asking "simple questions" which
imply, by their very wording, a whole bunch of assumptions about how
things work which just ain't so.

The fact that you keep getting answer after answer, from a lot of
knowledgeable people, which you either don't understand or "blow past"
or that you feel evade the point of your question, ought to be saying
something to you: that there's something wrong with the questions you
ask.

No one has been able to supply the answer to my question,
Using your words ,what steers the pattern away from a circular
form from a natural circular form.

That depends on what you mean by "a natural circular form."

If you're referring to the fact that the main lobe of a dipole tends
to look circular on many of the commonly-used plots, then the pattern
isn't "circular" in any cosmic sense of the word. It's just as
correct to say that it's elliptical, or bumpy, or squashed, because
that's exactly how it will look on plots which use different circular
axes (linear, logarithmic, etc).

To try it again, though: you're asking why the pattern appears to be
compressed, as the gain increases. Fundamentally, it's due to the
fact that the antenna is sending more power out in the desired
directions (more gain), at the expense of sending less in other
directions. This is done by creating multiple radiators, which are
offset in power and location and phase so that their individual
radiation wavefronts reinforce in the desired directions, and cancel
in the undesired directions.

When we plot the resulting RF strengths, the RF in the desired
direction is stronger (we got the gain that we want). Let's assume
that (as is common practice) we continue to plot the signal in the
strongest direction on the outer circle of the graph.

Now, one of two things will have to be true:

[1] Every other direction in the main lobe had its power "scaled up"
by the same amount... the increase in gain worked the same for all
directions within the main lobe. In this case, the shape of the
main lobe will not change at all.

In this case, the additional power required to achieve the
increase in gain in the main lobe will have had to come for
somewhere. Since it didn't come from the main lobe, it will have
had to come either from the sidelobes, or from the rear half of
the antenna's pattern.

There's a limit to how far you can take approach [1]. It stops
working when your sidelobes and rear half of the pattern drop to
zero... and it becomes rather ineffective some time before that,
when the largest of the side/rear lobes is maybe 10-15 dB down.
Beyond that point, there just isn't enough power left in those
backlobes to be useful.

[2] The other possibility is that you didn't manage to boost the gain,
uniformly, in the entire main lobe.

In this case, if you're still plotting the strongest signal on the
outermost circle of the graph, you'll notice that the shape of the
main lobe has changed. Any direction in which the gain increase
was less than the maximum you achieved, will be closer to the
center of the circle than before. [Another way of looking at this
is that by increasing your maximum directional gain, you've
"enlarged the circle" on which you're plotting it, but that some
points didn't move outwards by the same ratio.]

In the common case of a Yagi, when you boost the gain (say, from 10 dB
to 15 dB) there just isn't enough power available in the side and rear
lobes to make up this gain... you can't 'rob' enough directivity from
the sidelobes and rear lobe. Instead, you 'rob' the power from the
outer edges of the main lobe, and shift it in towards the center.

You do this, most commonly, by adding additional parasitic elements,
whose location and phasing are such that their radiation reinforces
that moving in the "forward" direction, and interacts destructively
with (cancels) radiation moving outwards at an angle.

When you plot the resulting pattern, and scale it so that the
strongest signal is on the outer circle of the plot, you find that the
main lobe looks narrower. Part of this is due to the actual
redirection of power, and part of it is due to the fact that you've
re-scaled the graph.a

.. I am not asking for the extraneious
information
that all feel they are compelled to supply to make their posting look
informative.

[invokes several wrathful deities...]

Art, if you continue to ask "simple questions", and you continue to
get back complicated and detailed answers, it really ought to convey
to you the possibility that your "simple" question is oversimplified.
Or, perhaps, that you've been given the actual (simple) answer three
or four or five times already, have rejected it, and people are trying
to explain to you why it's actually correct.

Goodbye, Art. This is/was my last attempt, I think. I doubt I'll try
again.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Hal
Amateur radio operators have been convinced to display radiation patterns
on logarithmic paper to make it look more directional than normal plotting
procedure.
Since I can now generate a complete circle for an non yagi antenna array
using logarithmic paper on my antenna program I thought it would be
interesting to see
what a circle would look like when using 'standard' graph paper.( a reverse
procedure)
Now, as I write this, I realise that my antenna computor program has the
ability to
make this transition.
This will be interesting as I have no pre-expectations as to what it will
show.
Best regards
Art


"Hal Rosser" wrote in message
. ..
I've got to now draw a circle with a compass and observe how the shape
changes when
replotted with logrithmic and other types of graph paper

Regards
Art

Be sure to give us a report on creating the logarithmic graph paper.
If I heard someone was looking to replot circles on log graph paper, I
would
say he must be a ham.
Then I would think about writing a Java program to do it, as I slipped
into
sleep while listening to 'Coast-to-coast-AM' on the radio.

On Sun, 27 Mar 2005 19:53:44 GMT, "
wrote:

No one has come up with a explanation

Hi Art,

As usual, I see you simply enjoy posting without corresponding.
C'mon, it is more than obvious you have no interest in any explanation
other than your own.

Roy and a couple of others qualify and have yet to respond
You've spit on them so much that is hardly surprising - is it?

73's
Richard Clark, KB7QHC

"Dave Platt" wrote in message
...
In article P2G1e.110904$Ze3.11791@attbi_s51,
wrote:

By all means put me on your kill file. I asked a simple question and you
want to reply to a different question of your liking and place your
question
as one preferable to mine.

Art, in cases like this, you keep asking "simple questions" which
imply, by their very wording, a whole bunch of assumptions about how
things work which just ain't so.

The fact that you keep getting answer after answer, from a lot of
knowledgeable people, which you either don't understand or "blow past"
or that you feel evade the point of your question, ought to be saying
something to you: that there's something wrong with the questions you
ask.

No one has been able to supply the answer to my question,
Using your words ,what steers the pattern away from a circular
form from a natural circular form.

That depends on what you mean by "a natural circular form."

If you're referring to the fact that the main lobe of a dipole tends
to look circular on many of the commonly-used plots, then the pattern
isn't "circular" in any cosmic sense of the word. It's just as
correct to say that it's elliptical, or bumpy, or squashed, because
that's exactly how it will look on plots which use different circular
axes (linear, logarithmic, etc).

To try it again, though:

I thank you for that


you're asking why the pattern appears to be
compressed, as the gain increases. Fundamentally, it's due to the
fact that the antenna is sending more power out in the desired
directions (more gain), at the expense of sending less in other
directions.

Fully agreed to


This is done by creating multiple radiators, which are
offset in power and location and phase so that their individual
radiation wavefronts reinforce in the desired directions, and cancel
in the undesired directions.

Accepted as long as you can agree that a similar vector analysis with
multiple radiators can also create a non focussing pattern



When we plot the resulting RF strengths, the RF in the desired
direction is stronger (we got the gain that we want). Let's assume
that (as is common practice) we continue to plot the signal in the
strongest direction on the outer circle of the graph.

Now, one of two things will have to be true:

[1] Every other direction in the main lobe had its power "scaled up"
by the same amount... the increase in gain worked the same for all
directions within the main lobe. In this case, the shape of the
main lobe will not change at all.

O.K. this would /could be the case I am thinking of

In this case, the additional power required to achieve the
increase in gain in the main lobe will have had to come for
somewhere.

Agreed

Since it didn't come from the main lobe, it will have
had to come either from the sidelobes, or from the rear half of
the antenna's pattern.

Agreed for over all gain but not necessarilly for the lobe becomming
focussed
which is the crux of my question

There's a limit to how far you can take approach [1]. It stops
working when your sidelobes and rear half of the pattern drop to
zero... and it becomes rather ineffective some time before that,
when the largest of the side/rear lobes is maybe 10-15 dB down.
Beyond that point, there just isn't enough power left in those
backlobes to be useful.

Using a antenna computor program the main lobe at 10 degrees does not
deviate from a circle even if the F/R is more than 30 db ( note F/R vs F/B)
and this is comprised of vector addition mode as with a yagi design.



[2] The other possibility is that you didn't manage to boost the gain,
uniformly, in the entire main lobe.

Hum!

In this case, if you're still plotting the strongest signal on the
outermost circle of the graph, you'll notice that the shape of the
main lobe has changed.

No, not always, only with a yagi design in my opinion


Any direction in which the gain increase
was less than the maximum you achieved, will be closer to the
center of the circle than before. [Another way of looking at this
is that by increasing your maximum directional gain, you've
"enlarged the circle" on which you're plotting it, but that some
points didn't move outwards by the same ratio.]

Agreed thus my question


In the common case of a Yagi, when you boost the gain (say, from 10 dB
to 15 dB) there just isn't enough power available in the side and rear
lobes to make up this gain... you can't 'rob' enough directivity from
the sidelobes and rear lobe. Instead, you 'rob' the power from the
outer edges of the main lobe, and shift it in towards the center.

Now we are getting closer to my quest. How do we "rob" from the outer
edge of the main lobe is the underpinnings of my question.


You do this, most commonly, by adding additional parasitic elements,
whose location and phasing are such that their radiation reinforces
that moving in the "forward" direction, and interacts destructively
with (cancels) radiation moving outwards at an angle.

Agreed if we are adding or subtracting on a constant plane.
Could you by any chance referring to the closing vector of the vector
analysis
to consist of two vectors and where one of these vectors is the force at
right
angles to the main lobe and which deforms it. If so I am beginning to see
the light!





When you plot the resulting pattern, and scale it so that the
strongest signal is on the outer circle of the plot, you find that the
main lobe looks narrower. Part of this is due to the actual
redirection of power, and part of it is due to the fact that you've
re-scaled the graph.a

I am lost here but if we agree on my interpretation of what you said then
I am at a point where I can generate vector diagrams of different arrays
and forecast the width of the resultant lobe .Does anybody else agree
that the main lobe width can be forecast via vector analysis.
Seems like from past posts that vector analysis is not now in vogue
for electrical engineers in the U,S and only creates blank stares
when mentioned/
..






kes several wrathful deities...]

Art, if you continue to ask "simple questions", and you continue to
get back complicated and detailed answers, it really ought to convey
to you the possibility that your "simple" question is oversimplified.
Or, perhaps, that you've been given the actual (simple) answer three
or four or five times already, have rejected it, and people are trying
to explain to you why it's actually correct.

Goodbye, Art. This is/was my last attempt, I think. I doubt I'll try
again.

But David, nobody pointed to vector analysis and the particular facet
that you referred to. You are to be congratulated in pointing to a trail
of logic that could well be the direction I was looking for.
Nobody but you presented in real terms an analysis that leads to
serious consideration and I thank you very much for that.

Best regards
Art KB9MZ.....xg



g the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!