Max F/b and max gain at same freq.
 

I have just come to realise that if one drew a polygon of element phases in
a array
and all elements were 180 degrees to its companion element and excluding the
driven element, the max gain and max front to back will occur at the SAME
frequency!
Until now I was of the understanding that these two max figures could not
occur at
the same frequency. Is there anything written about this possibility?
Regards
Art

On Fri, 04 Mar 2005 05:41:29 GMT, "
wrote:

I have just come to realise that if one drew a polygon of element phases in
a array
and all elements were 180 degrees to its companion element and excluding the
driven element, the max gain and max front to back will occur at the SAME
frequency!
Until now I was of the understanding that these two max figures could not
occur at
the same frequency. Is there anything written about this possibility?
Regards
Art

OK Art,

This posting has been swinging in the wind for a couple of days now.
Given that you threw your frustration in my face that no one shows any
interest in it. Stop blaming them for their failure to recognize your
genius and get down from Calvary - blame me instead! ;-)

WTF do you mean by
if one drew a polygon of element phases in a array
and WTF should we care?

73's
Richard Clark, KB7QHC

On Mon, 07 Mar 2005 01:02:18 GMT, "
wrote:

It would appear that I have come across something new.

No wonder no one came to this party.

73's
Richard Clark, KB7QHC

On Sun, 06 Mar 2005 17:21:26 -0800, Richard Clark
wrote:

|On Mon, 07 Mar 2005 01:02:18 GMT, "
wrote:
|
|It would appear that I have come across something new.
|
|No wonder no one came to this party.

It could be new, but he can't tell us about, so how do we know?

Wes,
I described a polygon of element phases where pairs of elements were equal
and opposite and where the director was either alone or was joined by
another
element of the same phase. This polygon aproach was used often before the
computor era A polygon as described above not only makes for a wide single
direction lobe but enforces among other things the same frequency for both
parameters i.e. gain and f/b
If such a polygon can be drawn as stated above it shows that it is possible.
I don't see how anything can be added to the above to emphasise the point
I am making which is why I asked if anybody knew of any book references to
the above.
If you are not aware of the phase polygon aproach I can find you a
reference. or, if you prefer;
a simulated diagram of a polygon that illustrates my point .
If that is beyond your ken I could also mail to you a computor compilation
of
phase and currents of an array that also illustrates my point.
But my main question still remains a pointer to a technical article that
discusses the possibility or impossibility of what I have stated.
If you have a deeper interest in the subject I could supply
to you alone the whole computor model of such an antenna
and a photograph of the actual antenna which is for 20 meters.
All I would ask for is complete privacy of what I provide as I
have a further pursuit connected with the above.
Regards
Art


Stewart" *n7ws*@ yahoo.com wrote in message
...
On Sun, 06 Mar 2005 17:21:26 -0800, Richard Clark
wrote:

|On Mon, 07 Mar 2005 01:02:18 GMT, "
wrote:
|
|It would appear that I have come across something new.
|
|No wonder no one came to this party.

It could be new, but he can't tell us about, so how do we know?

Art Unwin wrote:
"But my main question still remains a pointer to a technical article
that discusses the possibility or impossibility of what I have stated."

I don`t get the question, but it seems to me, Art wants to know if
anyone has written of a method to make maximum gain correspond with
maximum front-to-back ratio in a Yagi.

I haven`t seen it. There is a third factor in the compromise, 50-ohm
feedpoint (or some other convenient impedance).

Kraus gives the Yagi-Uda story in "Antennas" There has been much
experimentation and the tradeoffs still exist. Don`t close the patent
office yet. Almost everything can be improved. Art may be implying that
he thinks he has a way to make a better Yagi. I hope so.

The "ARRL Antenna Book" is a good place to see where the art was at the
time of publication. The Antenna Book devotes a chapter to the Yagi, No.
11 in my 19th edition. The directional patterns show a pair of
troublesome sidelobes in addition to the mainlobe. It`s the sidelobes
which are suppressed at the sacrifice of a little gain. Parasitic
arrays are close-spaced for significant excitation. Close-spacing means
close-coupling which lowers the drivepoint impedance. It`s a tradeoff
again because low impedance eventually limits the antenna`s efficiency.

Best regards, Richard Harrison, KB5WZI

There's yet another tradeoff -- bandwidth, of both the pattern and the
impedance. Close spacing, in particular, reduces the range of
frequencies over which the pattern is acceptable ("acceptable" being in
itself subject to compromise) and over which the SWR is acceptable. But
close spaced or not, it's much easier to tweak a design to work
perfectly at a single frequency than make one that will retain some
semblance of that perfection over a wider range of frequencies.

Roy Lewallen, W7EL

Richard Harrison wrote:
Art Unwin wrote:
"But my main question still remains a pointer to a technical article
that discusses the possibility or impossibility of what I have stated."

I don`t get the question, but it seems to me, Art wants to know if
anyone has written of a method to make maximum gain correspond with
maximum front-to-back ratio in a Yagi.

I haven`t seen it. There is a third factor in the compromise, 50-ohm
feedpoint (or some other convenient impedance).

Kraus gives the Yagi-Uda story in "Antennas" There has been much
experimentation and the tradeoffs still exist. Don`t close the patent
office yet. Almost everything can be improved. Art may be implying that
he thinks he has a way to make a better Yagi. I hope so.

The "ARRL Antenna Book" is a good place to see where the art was at the
time of publication. The Antenna Book devotes a chapter to the Yagi, No.
11 in my 19th edition. The directional patterns show a pair of
troublesome sidelobes in addition to the mainlobe. It`s the sidelobes
which are suppressed at the sacrifice of a little gain. Parasitic
arrays are close-spaced for significant excitation. Close-spacing means
close-coupling which lowers the drivepoint impedance. It`s a tradeoff
again because low impedance eventually limits the antenna`s efficiency.

Best regards, Richard Harrison, KB5WZI

Yes Richard that is exactly the case.
I have a case where F/B is at
the same frequency as max gain and I have not come across that before
so I asked those well versed in antenna design if this had been discussed
before,
Yes, it is an alternative to a yagi but nowhere as simplistic to build, for
that the yagi is hard to beat, As it happens the feed point impedance of
less than 2:1
at 50 ohms is easily obtained across the 20 meter band , the primary design
It compares to a 60 foot boom yagi and change of feed point can produce
higher impedance
but its beam width is not as narrow , the
elevation angle for max gain (TOA) is 10 degrees which is some what lower
than the norm
.. I have been working on this design for some time now and have all the
parts
made for a actual antenna, The winter has been
very harsh in the midwest but with good weather tomorrow I should be able
to put it together and put it up as there is no need to use the prop pitch
rotor
which is hard to install in cold or blustery weather as I get older.
.. The turning radius by the way is somewhat less
than a tight two element yagi and is of a design where frontal side lobes
have not
come into play. Because of mechanical difficulties I do not see it replacing
a yagi
but that was not the intent in the first place, I just like to explore and
experiment
and try to work from first principles rather than be tied to well known
paths of the past
As a point of interest Roy I use 300 segments per halfwave length. to double
check
my designs but who knows ,it may still be a case of garbage! If the antenna
is not
broken then I have not tried hard enough and I have broken many antennas in
my time
As a point of interest I would direct you to past postings where I describe
close coupling
to the driven element to attain for an impedance of choice and can be
adapted
for use in any array.You may remember Roy checking out one of my designs on
his page
( 13 elements on a 60 or 80 foot boom ) ere coupling achieved the 50 oihm
feed
as desired

Regards
Art

Roy
I understand where you are coming from but your points are all based
around a Yagi with standard feeds !. In my past postings over the years
I have pointed out other methods of feeds that not only broaden the
bandwidth
but uses a high impedance, this done by extreme "close" coupling,
in the order of a inch or so upwards to about 12 inches which I also wrote
up
in a patent some years ago just for kicks.
I myself ,choose not to go less than 26 ohms when designing. and tho I can
make them with very high impedance it is not really required as the ham
bands
are quite narrow. Where I really concentrate upon is to move away
from "mutual" coupling ( what ever that means) which is commonly described
with yagi antennas, to "close" coupling designs which is an entirely new
world when
dealing with feed impedances, as Richards post on coupling some months ago
described so much better than I have done.

Regards
Art



"Roy Lewallen" wrote in message
...
There's yet another tradeoff -- bandwidth, of both the pattern and the
impedance. Close spacing, in particular, reduces the range of frequencies
over which the pattern is acceptable ("acceptable" being in itself subject
to compromise) and over which the SWR is acceptable. But close spaced or
not, it's much easier to tweak a design to work perfectly at a single
frequency than make one that will retain some semblance of that perfection
over a wider range of frequencies.

Roy Lewallen, W7EL

Richard Harrison wrote:
Art Unwin wrote:
"But my main question still remains a pointer to a technical article
that discusses the possibility or impossibility of what I have stated."

I don`t get the question, but it seems to me, Art wants to know if
anyone has written of a method to make maximum gain correspond with
maximum front-to-back ratio in a Yagi.
I haven`t seen it. There is a third factor in the compromise, 50-ohm
feedpoint (or some other convenient impedance).

snip.

Best regards, Richard Harrison, KB5WZI