I dare to differ, my friend. ANY curved surface will have at least one
focus. Now, I must agree that it will not be a focus _point_ but never the
less, energy will be concentrated, to some extent, in a small volume of
In de case of a two dimensional cylindrical mirror surface - as the curtain
antenna- the focus area/volume will take the form of an elongated body with
the long axis vertical to the ground.
I agree that the reflector of the TH7 becomes superfluous but it does not do
any harm as the "foci" of the curtain is aimed to the driven element.
The aim of the antenna system, is not to have more gain but more F/B ratio,
As I live on the East Coast, it will cut the clutter coming from
the rest of the country. I have a feeling that if I increase the horizontal
cylindrical angle of the curtain to 180 degrees, it will
actually act as a shield against any transmission from behind. But this is
merely speculation at this time as I had not yet give it more
thought. And thank you for your reply :)
> -----Original Message-----
> From: firstname.lastname@example.org
> [mailto:email@example.com]On Behalf Of Don Havlicek
> Sent: Wednesday, June 12, 2002 1:22 PM
> To: Alex
> Cc: firstname.lastname@example.org
> Subject: Re: [Antennaware] Modeling a composite antenna
> I am very familiar with 'sperical trigonometry' as well as many other
> branches of Mathematics ... my degrees, BS & MA, are both in Math.
> [Some say I have an ABD - 'all but dissertation' - didn't see any need
> to spend $2500 for someone to call me 'doctor'].
> I reiterate .. only a parabola/paraboloid will have a true focus .. [an
> ellipse has two foci, but the unfortunate circumstance with an ellipse
> is that rays must pass through one focus to meet at the other].
> As I pointed out in my previous post, putting the TH7 at the 'focus' of
> a curved-surface reflector requires placing the driven element in the
> 'focal position', and this would disable the reflector element of the
> TH7 [unless it was within the surface of the 'new' reflector.
> All this seems quite pointless to me, as the structure would NOT be
> easily rotatable .. and, if you desire high gain in a single direction,
> a STERBA curtain would serve much better, without the requirement of
> Alex wrote:
> > I was describing the curvature of the antenna. A curtain
> antenna is never a
> > closed loop, or in this case a cylinder. But it can have a
> > specific curvature so there will be a focus!
> > I wrote "cylindrical" - please observe the quotes- as opposed
> to "spherical"
> > or "parabolic" surfaces. Please remember your spherical trigonometry :)
> > In my case the curtain has a horizontal cylindrical angle of
> about 10 to 20
> > degrees due to the limitations imposed by the trees which are used as
> > infrastructure for it.
> > Preliminary computations show a 70dB B/F ratio - for the
> composite system -
> > with a quite a wide horizontal dispersment. Forward gain is
> only improved by
> > 2.7dB. I kind's hopped to get some more. I think the curtain is to long
> > horizontally for the 20m band. I'll try to make it exactly one
> lambda for a
> > specific freq.
> > Thank you for your reply.
> > Alex
> > > -----Original Message-----
> > > From: email@example.com
> > > [mailto:firstname.lastname@example.org]On Behalf Of Don Havlicek
> > > Sent: Wednesday, June 12, 2002 9:07 AM
> > > To: Alex
> > > Cc: email@example.com
> > > Subject: Re: [Antennaware] Modeling a composite antenna
> > >
> > >
> > > A cylinder has NO focus, a parabola/paraboloid does.
> > > If you construct what you have suggested, only the RF entering the
> > > 'reflector' along the line of the boom of the TH7 will be
> reflected back
> > > to the AXIS of the cylinder .. and that is where you must place the
> > > DRIVEN ELEMENT of the TH7.
> > > A better arrangement might be to add additional reflectors to the TH7,
> > > but that would be a mechanical nightmare, as they would be trapped and
> > > placed at a distance equal to the DE/Ref distance of the TH7.
> > > Don
> > > N8DE
> > >
> > > Alex wrote:
> > > >
> > > > I am planning to erect a 60m long by 30m tall "cylindrical"
> > > curtain and in
> > > > it's foci a TH7.
> > > > What software can model this combination and where can I get it .
> > > >
> > > > TIA, Alex
> > > >
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