I need to add a clarifier to this post.
If the phases and and magnitudes of the paired elements
are exactly the same, then radiation to the rear is zero.
In the real world this is difficult if not impossible to do.
It certainly cannot be done with a yagi unless possibly,
when elements are contorted to ensure pure resistance
feed at the appropiate frequency
However, what is possible with a alternate design is to
have maximum front to back at max gain when the max
gain is constant over a range of frequencies such that
the max front to back which is usually a peak,
can appear at a point where the gain is still at a
maximum.

Regards
Art .........KB9MZ



" wrote in message
news:dySVd.30807$r55.174@attbi_s52...
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

Gene Fuller wrote:
Buck,

I agree with you. I too cannot figure out what Art is trying to say.

Don't feel like the lone ranger...I've been following this
thread for a week, and I still don't have a clue what he
is trying to describe.

73,
Gene
W4SZ

Buck wrote:

Art,

Your description is too vague for someone who doesn't have some
form
of reference (maybe this is a continuation of a discussion from
elsewhere?)

What he said....

In article k1FXd.109090$tl3.58979@attbi_s02,
wrote:

I need to add a clarifier to this post.
If the phases and and magnitudes of the paired elements
are exactly the same, then radiation to the rear is zero.
In the real world this is difficult if not impossible to do.
It certainly cannot be done with a yagi unless possibly,
when elements are contorted to ensure pure resistance
feed at the appropiate frequency

You might want to take a look at systems which use two or more
directly-driven radiators (rather than a driven radiator and a
parasitic element), with a chosen physical offset and phase
offset between them.

This is a classic way to get a 180-degree-only pattern. It's often
used with vertical antennas. I took a quick glance at Arnold Bailey's
"TV and other receiving antennas" text (written in 1950) and he shows
a similar sort of antenna using two horizontal half-wave dipoles,
connected together via a transmission line and fed at the center of
the rear dipole. Very clean 180-degree pattern.

This sort of arrangement might be a good starting point for your "move
all of the energy from the rear lobes into the forward half" quest.

You might be able to combine this sort of dual-driven-radiator
unidirectional beamer with additional parasisic elements, to create
more forward gain. A bunch of directors out in in the front would be
the obvious choice for a first experiment

There's a gotcha to this, though... the 180-degree pattern from a pair
of phased radiators depends on the radiators being driven with equal
currents, which (in this simple arrangement) requires that they have
equal feedpoint impedances. Stick a bunch of parasitic directors out
in front, and the feedpoint impedance of the forward radiator is going
to change (drop, most likely) and affect the current relationship
between the two radiators, and thus mess up the pattern.

I can think of a couple of possible ways to compensate for this:

- Matching network at the forward radiator (maybe shorten it a bit and
use a hairpin inductor match)?

- Tapered transmission-line section between the two radiators?

- Try installing some parasitic elements behind the rear driven
element... possibly in a corner-reflector arrangement? This might
tweak the rear element's feedpoint Z enough to make it easier to
match the two, might also help suppress any rear lobes which
develop as a result of the mismatch.

I have my doubts as to whether all of this work will pay off with
enough of an increase in forward gain, F/B ratio, cleanliness of
pattern, reduction in lobes, broadening of bandwidth, etc. to be worth
the effort over a classic Yagi, but I'm certainly willing to be proven
wrong.

--
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!

Buck
If your background is not in science then it is natural that you would
have difficulty with what I stated. If your background was in science
then this stuff would be studied in 101 i.e from first principles.
With a firm understanding of scalar quantities you are then fully armed
to deal with antenna "curl" and other interesting facets of antennas.
It would appear to me that many of this group do not have a science
background but have got by in life because of a good memory and where
knoweledge of first principles is not a requirement.
Ofcourse age can take that advantage away which appears to have happened
with past engineers of this group.........amazing!

Regards
Art



"Buck" wrote in message
news
On Tue, 08 Mar 2005 05:29:03 GMT, "
wrote:


"Buck" wrote in message
. ..
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



Art,

Your description is too vague for someone who doesn't have some form
of reference (maybe this is a continuation of a discussion from
elsewhere?) Anyway, since a polygon is any shape with more than two
sides in which all sides and angles are equal,


It does! then I have used the incorrect term.

In a yagi type diagram you can calculate the current and phase of each
elemrnt
but what one is interested in is the summation of the whole array and you
can do this
in the same way as you would do a vector diagram of forces.
With the yagi array you would first start with the reflector and draw to
scale a line
reflecting both phase angle and magnitude. You then add lines in
cosecutive
order for all other elements in the array. The end of this 'toe to tail'
some what
erratic line will finish up some distance from the starting point,
but this distance, if drawn, represents the phase and magnitude
of the array as a whole. As a former mechanical engineer

I am not ... You may be using a term familiar to your trade and I am
unfamiliar with. I would be a layman in respect ... that could be
the misunderstanding. I was trying to envision the antenna you were
describing... can you imagine what I was seeing in my mind?




but now nothing ,I was taught the term "polygon of forces" which is a
cumulative
vector array but the shape did not necessarily consist of "equal "sides as
you stated..
But then I am English born and it is known that Americans completely
messed
up the Elizabethan era language which a true cockney still adheres to ,
where as
others in the same country have learned to talk in such a way it sounds as
if they
are trying to retain a marble in their mouth.without swallowing it.

Actually, I like the UK accents. As I believe my misunderstanding has
nothing to do with the queen's English, but rather techno-speak for
your trade, I will pack up my octagon shaped array of dipole antennas
and gracefully move on to another topic.
Good luck and I'll catch you in another thread.

Buck


Regards
Art


--
73 for now
Buck
N4PGW

Good point ! But I have already checked this out even
wit
"Dave Platt" wrote in message
...
In article k1FXd.109090$tl3.58979@attbi_s02,
wrote:

I need to add a clarifier to this post.
If the phases and and magnitudes of the paired elements
are exactly the same, then radiation to the rear is zero.
In the real world this is difficult if not impossible to do.
It certainly cannot be done with a yagi unless possibly,
when elements are contorted to ensure pure resistance
feed at the appropiate frequency

You might want to take a look at systems which use two or more
directly-driven radiators (rather than a driven radiator and a
parasitic element), with a chosen physical offset and phase
offset between them.e phase

Good point! I tried this with a radiator that was of opposite phase
but the origanal feed method still came out best. That method has
not been tested for other bands

This is a classic way to get a 180-degree-only pattern. It's often
used with vertical antennas. I took a quick glance at Arnold Bailey's
"TV and other receiving antennas" text (written in 1950) and he shows
a similar sort of antenna using two horizontal half-wave dipoles,
connected together via a transmission line and fed at the center of
the rear dipole. Very clean 180-degree pattern.

This sort of arrangement might be a good starting point for your "move
all of the energy from the rear lobes into the forward half" quest.

You might be able to combine this sort of dual-driven-radiator
unidirectional beamer with additional parasisic elements, to create
more forward gain. A bunch of directors out in in the front would be
the obvious choice for a first experiment

But that defeats the issue where boom length can be erradicatred as an
issue.


There's a gotcha to this, though... the 180-degree pattern from a pair
of phased radiators depends on the radiators being driven with equal
currents, which (in this simple arrangement) requires that they have
equal feedpoint impedances. Stick a bunch of parasitic directors out
in front, and the feedpoint impedance of the forward radiator is going
to change (drop, most likely) and affect the current relationship
between the two radiators, and thus mess up the pattern.

I can think of a couple of possible ways to compensate for this:

- Matching network at the forward radiator (maybe shorten it a bit and
use a hairpin inductor match)?

I always require a near 50 ohm feed that does not require matching.




- Tapered transmission-line section between the two radiators?

- Try installing some parasitic elements behind the rear driven
element... possibly in a corner-reflector arrangement? This might
tweak the rear element's feedpoint Z enough to make it easier to
match the two, might also help suppress any rear lobes which
develop as a result of the mismatch.

A corner reflector does not have true reflectors as all elements
are of the same length and equaly spaced, they also carry low
but similar current flow.

I have my doubts as to whether all of this work will pay off with
enough of an increase in forward gain, F/B ratio, cleanliness of
pattern, reduction in lobes, broadening of bandwidth, etc. to be worth
the effort over a classic Yagi, but I'm certainly willing to be proven
wrong.
This cannot beat the simplicity of a yagi.

Good for you Dave, you have an open mind despite the massive
studies over the years. But there is no way of convincing the masses
who demand expensive trials and measurements which if conclusive ,changes
the mode of attack to the method of testing, This is usually the method
taken
by even educated engineers who with huge experience in the field refuse to
believe
they could have passed over something.
As for this antenna it is purely to satisfy me.
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!

wrote:
If the phases and and magnitudes of the paired elements
are exactly the same, then radiation to the rear is zero.

If you rotate the elements by 90 degrees, can you make the
radiation toward the ground zero?
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

Interesting question Cecil, and I suspect the answer is yes
if you are refering to the array pointing upwards.
If you are referring to turning the array sideways i.e vertical
polarisation then I doubt
rear radiation could be zero because the earth has more influence over
vertical
polarisation compared to horizontal at one wave length high.
For instance pairs of elements could not have equality.
You can ofcourse accomplish such if the array was reflective as with a dish
but not with normal coupling and resonances where the focussing aproach
is absent.
Best regards
Art





"Cecil Moore" wrote in message
...
wrote:
If the phases and and magnitudes of the paired elements
are exactly the same, then radiation to the rear is zero.

If you rotate the elements by 90 degrees, can you make the
radiation toward the ground zero?
--
73, Cecil http://www.qsl.net/w5dxp


----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet
News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000
Newsgroups
---= East/West-Coast Server Farms - Total Privacy via Encryption =---

Dave Platt wrote:
"This is a classic way (2-element quarter-cycle phased array) to get 180
degree-only pattern. It`s often used with vertical antennas. I took a
look at Arnold Bailey`s :TV and other receiving antennas" text (written
in 1950) and he shows a similar sort of antenna using two horizontal
half-wave dipoles, connected together via a transmission line
(open-wire) and fed at the center of the rear dipole. Very clean 180
degree-only pattern."

Yes. The directional patterns on pages 477 and 478 are excellent.

This antenna also appears in Bailey`s catalog of antennas on page 521 as
"Half-Wave Antenna and Connected Reflector". Its resistance at center
frequency is 50 ohms where its gain is 4 dBd. Bandwidth is 60% for 3 dB
down.

I wonder why everybody isn`t using this antenna?

Best regards, Richard Harrison, KB5WZI

On Wed, 9 Mar 2005 20:17:04 -0600, (Richard
Harrison) wrote:

This antenna also appears in Bailey`s catalog of antennas on page 521 as
"Half-Wave Antenna and Connected Reflector". Its resistance at center
frequency is 50 ohms where its gain is 4 dBd. Bandwidth is 60% for 3 dB
down.

I wonder why everybody isn`t using this antenna?

Hi Richard,

This design (with references to the 1930s) from Bailey (given a full
chapter treatment) leads to its kin in Krauss' W8JK Antenna (which
probably answers your question, Richard).

73's
Richard Clark, KB7QHC

This sounds like a switchable three element array that I once used
for CB ( As an alien I wasn't allowed a amateur license)
I copied the design from a commercial antenna and with a switch box
was able to point it in any one of three directions. The coax between them
was a 1/4 wavelength I believe but the physical distance was much less than
that.
I believe I lost it when it iced up and broke the topsides of the vertical
dipoles..
Regards
Art



"Richard Harrison" wrote in message
...
Dave Platt wrote:
"This is a classic way (2-element quarter-cycle phased array) to get 180
degree-only pattern. It`s often used with vertical antennas. I took a
look at Arnold Bailey`s :TV and other receiving antennas" text (written
in 1950) and he shows a similar sort of antenna using two horizontal
half-wave dipoles, connected together via a transmission line
(open-wire) and fed at the center of the rear dipole. Very clean 180
degree-only pattern."

Yes. The directional patterns on pages 477 and 478 are excellent.

This antenna also appears in Bailey`s catalog of antennas on page 521 as
"Half-Wave Antenna and Connected Reflector". Its resistance at center
frequency is 50 ohms where its gain is 4 dBd. Bandwidth is 60% for 3 dB
down.

I wonder why everybody isn`t using this antenna?

Best regards, Richard Harrison, KB5WZI