"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

" 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

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

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
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