wrote:
As gain increases with a yagi design the forward
lobe narrows. So to the gurus of this group, what
actualy creates the narrowing of the forward lobes ?
______________________

A good analogy that needs no math to understand is that of squeezing an
inflated balloon from its normally spherical shape into whatever shape is
more appropriate for the application. There is a given volume of air in
that balloon. If you want the surface of the balloon to extend further from
the origin of its original sphere, the new shape must be narrower in one or
more planes than the original shape.

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.

RF

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


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In message K3B1e.8558$NW5.7100@attbi_s02, "
writes
As gain increases with a yagi design the forward
lobe narrows . With high gain yagi's the lobe
becomes so narrow it is deemed to be a hinderence
instead of an advantage. To overcome this perceived
problem one has to know what causes it.
So to the gurus of this group, what actualy creates
the narrowing of the forward lobes ?
End effects perhaps!

My tuppence worth

It is a fundamental energy conservation effect.

There is an invariant A * Omega , where A is the capture area of the
antenna, proportional to gain and Omega is the solid angle of the lobe.

So as A goes up, Omega must come down.

One way to reduce the effect is to use a number of vertically stacked
low gain yagis. The lobe becomes narrow in the vertical plane , but
remains broad in the horizontal plane. This is fairly common technique
for VHF/UHF contesters, where a narrow horizontal beam can cause missed
contacts

Brian

--
Brian Howie

Richard.
No one has come up with a explanation BUT there are real gurus out there,
It's just that those who qualify as gurus have just thinned out a bit.
The question still pertains to Yagis and the narrowing of lobes
You have posted twice now and added nothing that relates to a possible
answer.
Tho there are many who perceive themselves as experts and then consistently
show
what they really are. I can think of one or two who can really address this
question
with a logical answer. Cecil, Roy and a couple of others qualify and have
yet to respond
You have disqualified yourself based on your responses, so like myself you
will have to wait to learn. Yagi's have been studied in depth and for many
years by many
tho apparently not by you or others that have replied so far.
Place your bets on who is the real guru of this group that comes forward
to explain with logic and to the point You Richard, can read your old QST's
in a hurry
and surely find the answer to get back into the ratings as I don't think
that new
knoweledge is around the bend, just a small manipulation of "old" knoweledge
will
surely suffice. Think "end effect" and "none- resistive residuals" along
coupled radiating
elements for starters.If that draws a blank then assuredly you wear no
clothes

Art


"Richard Clark" wrote in message
...
On Sun, 27 Mar 2005 18:59:42 GMT, "
wrote:

the problem:
My antenna is somewhat related thus my interest in what creates an
elongated lobe
the answer:
which is formed using Yagi principles.

Hi Art,

Your question already answers your question. You have a tendency to
just blow right on taking no notice of this to create the SAME
question again:
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.?
formed using Yagi principles. (to quote you)
Nothing more, nothing less.
Exactly.

Now, are we going to be treated by another round of your complaints
about Shakespeare and the quality of gurus; or are you going to stick
with technical discussion and respond to the obvious points?

73's
Richard Clark, KB7QHC

"Richard Fry" wrote in message
...
wrote:
As gain increases with a yagi design the forward
lobe narrows. So to the gurus of this group, what
actualy creates the narrowing of the forward lobes ?
______________________

A good analogy that needs no math to understand is that of squeezing an
inflated balloon from its normally spherical shape into whatever shape is
more appropriate for the application. There is a given volume of air in
that balloon. If you want the surface of the balloon to extend further
from the origin of its original sphere, the new shape must be narrower in
one or more planes than the original shape.

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?
Art




RF

Yes Cecil I can go along with that otherwise the resultant volume would be
spherical.
What is the scenario that encapsulates this "constructive interference"
event? Is it residual reactance where its underpinning reside?
Art
Art
"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


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Newsgroups
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"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.

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.


--
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!

" 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

In article bkE1e.110371$Ze3.24514@attbi_s51,
wrote:

Right..... so what creats it, this "squeezing" that you talk about and from
where
does this "squeezing force come from in an "appropiate"array?

There is no "force" in the usual sense of pressure on a physical
balloon. That's because the "balloon" is not an object. It's simply
a mathematical abstraction - a drawing of lines of equal RF power
levels on a graph having a certain set of axes.

To think that there's a specific 'force' squeezing the 'balloon', is
somewhat like trying to travel from east to west by pulling yourself
along the lines of longitude. Hey, the lines are there on the globe,
they're there on the map, why can't I just walk along the lines?

There's nothing "pushing" on the "boundaries" of the lobe, because
there is no lobe in the physical sense. It's not a separate and
distinct object.

To understand why there's a change in the shape that we visualize (and
that's all that the lobe shape is - a selective visualization), we
have to step down to the underlying phenomenon and see what's changing.

Because the conventional "lobe shape" is simply the result of plotting
the strength of the RF energy coming from the antenna, the answer is
simple. The lobe's shape is changing, because the amount of RF energy
being transmitted in the different directions is changing...

.... and *that* happens because the phase-and-location details of the
various radiators (and re-radiators) in the antenna system are being
altered.

Different radiator and re-radiator locations, intensities, and phases...

.... cause different "sum of vectors" results ...

.... which changes the strength of the RF received ...

.... which, when we walk around and try to locate the points
having equal RF field strength, means that we walk along
different paths ...

.... which means that we draw the lines on the map in
different places ...

.... which means that the "lobes" now have a different
shape.

--
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!