Directivity, with smooth sidelobes
 

What sort of antenna offers narrow beamwidth, combined with smooth
sidelobes?
I'm not too concerned with F/B ratio, or the magnitude of the sidelobes,
(smaller is better obviously) but I'm more concerned that they not be a mess
of deep spiky notches.

This is a somewhat special application above the 440 band, but I could scale
a 440/900/1296 design appropriately. Gain, per se, isn't really an issue,
and negative gain may in fact be acceptable.

--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet?

What sort of antenna offers narrow beamwidth, combined with smooth
sidelobes?

I don't know what you mean by 'smooth sidelobes'.

Sidelobes are artifacts of truncation and/or lack of continuity, in the spatial
frequency spectrum of the aperture.

There are lots of ways, in hardware, to mitigate sidelobes. In an array this is
done, conventionally, by amplitude weighting of elements. There are
non-conventional ways of course, that are beyond the scope of this NG.

As elelemnts, there are moderate gain dipoles that have no sidelobes. A
conventional solution, for example, is a Landstorfer element, which is a curved
wire antenna that looks like a Gaussian in outline.

Perhaps a bit more specificity would help.

73,
Chip N1IR

I don't know what you mean by 'smooth sidelobes'.

I would rather have a higher sidelobe amplitude, if I can also not have deep
notches in it, than lower sidelobes with deep notches, unless of course the
sidelobes can be made to be insignificant.
And at this point, I'm not sure how low they would have to be, to be
insignificant.

A small dish is possible, but given the wavelength, "small" is not really
all that small.
I don't get a choice on wavelength.
In order of importance, tight beamwidth, low sidelobes, "smooth" sidelobes,
and gain.

Sidelobes are artifacts of truncation and/or lack of continuity, in the
spatial
frequency spectrum of the aperture.

There are lots of ways, in hardware, to mitigate sidelobes. In an array
this is
done, conventionally, by amplitude weighting of elements. There are
non-conventional ways of course, that are beyond the scope of this NG.

As elelemnts, there are moderate gain dipoles that have no sidelobes. A
conventional solution, for example, is a Landstorfer element, which is a
curved
wire antenna that looks like a Gaussian in outline.

Perhaps a bit more specificity would help.

It probably would, but I'm just at the back of napkin stage on this project.
I won't know what I need really, till I do some testing.

"Dave VanHorn" wrote in message
...


What sort of antenna offers narrow beamwidth, combined with smooth
sidelobes?
I'm not too concerned with F/B ratio, or the magnitude of the sidelobes,
(smaller is better obviously) but I'm more concerned that they not be a
mess
of deep spiky notches.

This is a somewhat special application above the 440 band, but I could
scale
a 440/900/1296 design appropriately. Gain, per se, isn't really an issue,
and negative gain may in fact be acceptable.

--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet?
Because I don't want to read the same damn message 26 times.

Dave VanHorn wrote:
What sort of antenna offers narrow beamwidth, combined with smooth
sidelobes?
I'm not too concerned with F/B ratio, or the magnitude of the sidelobes,
(smaller is better obviously) but I'm more concerned that they not be a mess
of deep spiky notches.

An Extended Double Zepp has a relatively narrow beamwidth
(~35 deg) and four side lobes about -13 dB down. I vaguely
remember a magazine article that told how to virtually
eliminate the EDZ side lobes.
--
73, Cecil http://www.qsl.net/w5dxp

On Fri, 21 May 2004 10:25:10 -0400, "Tam/WB2TT"
wrote:
Q: Why is top-posting such a bad thing?
....
Because I don't want to read the same damn message 26 times.

Hi Tam,

You prove to be an example of your own grief. The poorest response
style is the one that does not edit the point responded to.

73's
Richard Clark, KB7QHC

You prove to be an example of your own grief. The poorest response
style is the one that does not edit the point responded to.

I am fairly mystefied as well.. Maybe he got a ton of copies somehow, but
there was only one on my server, and I only sent one.

Oh well.

An Extended Double Zepp has a relatively narrow beamwidth
(~35 deg) and four side lobes about -13 dB down. I vaguely
remember a magazine article that told how to virtually
eliminate the EDZ side lobes.

It was in the vol. 4 Compendium, and it is also in my latest ARRL antenna
book. The technique involves placing about 2500 ohms capacitive reactance on
each leg of EDZ at a strategic location. You can reduce the side lobes, and
provide a better match to 50 ohm coax.
I have been playing around with a 3 element 2 meter EDZ beam that is
currently 17 dbi gain @ 3 deg. elevation with 12 dbi F/B. I used side lobe
reduction on all 3 elements. Be interesting to see if the actual antenna
matches the model.
73 Gary N4AST

"Richard Clark" wrote in message
...
On Fri, 21 May 2004 10:25:10 -0400, "Tam/WB2TT"
wrote:
Q: Why is top-posting such a bad thing?
...
Because I don't want to read the same damn message 26 times.

Hi Tam,

You prove to be an example of your own grief. The poorest response
style is the one that does not edit the point responded to.

Precisely, I think you got the point.

Tam

73's
Richard Clark, KB7QHC

You have too much time on

Tam/WB2TT wrote:

"Dave VanHorn" wrote in message
...


What sort of antenna offers narrow beamwidth, combined with smooth
sidelobes?
I'm not too concerned with F/B ratio, or the magnitude of the sidelobes,
(smaller is better obviously) but I'm more concerned that they not be a

mess

of deep spiky notches.

This is a somewhat special application above the 440 band, but I could

scale

a 440/900/1296 design appropriately. Gain, per se, isn't really an issue,
and negative gain may in fact be acceptable.

--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet?

Because I don't want to read the same damn message 26 times.



your hands.

;)

tom
K0TAR

"Tom Ring" wrote in message
...
You have too much time on

Random text generator?

I'd suggest one or two antennas, a dipole with a plane reflector or a
corner reflector. Both offer excellent bandwidth, good beamwidth,
clean pattern and usually arount 10DbI gain. Go to www.cebic.com
for details (and polar plots!).

Just not my day today.. This is an internet security company?

Dave VanHorn wrote:

"Tom Ring" wrote in message
...

You have too much time on


Random text generator?



You needed to read the whole post. It was a joke about the joke that is
the thread.

tom
K0TAR

Dave VanHorn wrote:
I'd suggest one or two antennas, a dipole with a plane reflector or a
corner reflector. Both offer excellent bandwidth, good beamwidth,
clean pattern and usually arount 10DbI gain. Go to www.cebic.com
for details (and polar plots!).


Just not my day today.. This is an internet security company?

http:www.cebik.com should get you to the right place, Dave.


- Mike KB3EIA -

"Tom Ring" wrote in message
...
Dave VanHorn wrote:

"Tom Ring" wrote in message
...

You have too much time on


Random text generator?

You needed to read the whole post. It was a joke about the joke that is
the thread.

The thread isn't a joke.
It's a serious question.

Just not my day today.. This is an internet security company?


Rah futz, lizdexia kicked in... it's www.cebik.com

Do check out the commentary on plane and corner reflectors.

I see Much better. I need to read and understand.
From what I see at the moment, the corner reflector gives me the smooth and
minimal sidelobes I wanted, but not as much directivity as I'd like.
Still, it's a start.

From the site;not closely related to the thread, but to a common topic
in this group:

"Magical antennas.

I'm not looking for magic. I'm well aware of the total BS that's out there.

I have compromises I'm willing to make, and indeed it looks like a corner
reflector will do what I want. Engineering is the art of compromise.

I have compromises I'm willing to make, and indeed it looks like a corner
reflector will do what I want. Engineering is the art of compromise.



Corner reflectors are good, but keep in mind that it will challenging to
maintain similar SWR, not to mention gain, over the multiple bands of
interest.

My standard question: what problem are you trying to solve? At this point it
seems a bit open ended to help more specifically.

Unlike other fields of engineering, antennas are one of the few where expertise
is acheived by doing, rather than a mere degree. For example, Dr. Cebik is a
retired philosphy of aesthetics professor. Most of what I have seen from his
antenna work is especially useful to amateurs, which is the audience target of
this NG.

73,
Chip N1IR

"Fractenna" wrote in message
...
I have compromises I'm willing to make, and indeed it looks like a corner
reflector will do what I want. Engineering is the art of compromise.



Corner reflectors are good, but keep in mind that it will challenging to
maintain similar SWR, not to mention gain, over the multiple bands of
interest.

I'm only interested in a small frequency range. I said that I could scale
designs on ham bands to what I want.

My standard question: what problem are you trying to solve? At this point
it
seems a bit open ended to help more specifically.

I want to minimize signals from off-axis, and then achieve minimum beamwidth
(maximum directivity).
Gain and bandwidth are compromise points.