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