Re: NEC-LIST:Modeling a conductive surface in NEC2

As long as the water tower is very large compared to the wavelength of
the emission, you should just be able to use Mininec. It can handle an
antenna being driven against a solid metal ground plane. On my website
is ASAP, another free program which will model antennas where one side
of the driving point is at ground. The differences in radiation pattern
you will get versus some ridiculously complicated simulation should be
very small indeed. And you will save a bundle of money:) Rob. N3FT

Alan Robert Clark wrote:
>
> On Tue, 1 Oct 2002, Brandon Orchard wrote:
>
> > In my previous e-mail I mentioned that you can model any surface using wire
> > segments in NEC. By that I meant any metal surface of course.
> >
>
> As they say in South Africa: ``JaNee''. (Yes-No, a non-committal response
> :-) We have used SuperNEC to model non-metallic surfaces very effectively:
>
> A R Clark and A P C Fourie and J Dresel ``Modelling lossy surfaces using a
> wire Method-of-Moments code'' IEE Proceedings---Microwaves, Antennas and
> Propagation, pp247--248, June 2000. Vol 147, No 3.
>
> Subsequent work has proved the article's concluding assertion that this
> method can be extended to dielectric surfaces, but has not been published.
>
> >
> >
> > > Hi Jerry
> > >
> > > You can model any surface using wire segments that are about a 1/10 of a
> > > wavelength in length.
> > > I don't think that the diameter of the wires would be of such importance
> > in
> > > such a case as long as they satisfy the general rules for NEC with regards
> > > to Segment length to radius ratios etc.
> > > This same technique of modeling surfaces by a wire mesh can even be used
> > to
> > > model very complex structures such as aircraft, boats, cars etc.
> > >
> > > If you are looking for a easy to use, professional program to quickly
> > model
> > > this problem, why don't you try using SuperNEC. It has a full 3D graphical
> > > interface so you won't have to write any text .nec files, and a really
> > great
> > > output interface for plotting 3D radiation patterns, smith chart plots etc
> > > etc. It also has a number of predefined structure and antenna assemblies
> > > such as wire mesh plates, cylinders, spheres, yagi's, helices, lpda's etc
> > > etc. With the antenna assemblies, by changing your model frequency in
> > > SuperNEC, the assemblies are automatically re-segmented so that your model
> > > remains valid. Another great feature of this product is the structure
> > > checker which checks your model to see that all the nec rules to produce
> > > accurate results have been followed.
> > > I am sure that these features of SuperNEC will considerably reduce the
> > time
> > > taken to model your specific problem.
> > >
> > > You can download SuperNEC from www.supernec.com and get a 30day evaluation
> > > license file for running the software.
> > >
> > > Regards
> > > Brandon Orchard
> > > ----- Original Message -----
> > > From: "Jerry Flanders" <jeflanders_at_comcast.net>
> > > To: <nec-list_at_gweep.ca>
> > > Sent: Friday, September 27, 2002 11:42 PM
> > > Subject: NEC-LIST:Modeling a conductive surface in NEC2
> > >
> > >
> > > > I am trying to evaluate a few ideas for a replacement antenna for my
> > ham
> > > > radio club's 2 Meter repeater.
> > > >
> > > > The new antenna will be mounted on one of our city's water tanks. I
> > would
> > > > like to take into account the effect of this nearby reflective surface
> > in
> > > > the model calculations.
> > > >
> > > > I understand NEC2 cannot model the surface, but that I can simulate the
> > > > surface with a wire grid. I need help with some specifics on the grid
> > > > structure.
> > > >
> > > > I have a copy of Arie's "Build" to actually generate a grid of the right
> > > > size and shape, but I don't know what mesh size (size of the openings)
> > is
> > > > appropriate. If I use too large a mesh opening, I suspect it would not
> > > > represent a plane surface accurately, but if I just use an
> > > > arbitrarily fine mesh, I will cripple this 384MB computer. Is there a
> > > rule
> > > > of thumb for adequate mesh "pore" sizes in terms of wavelength?
> > > >
> > > > I could also use advice on what diameter "wire" to use for the grid, and
> > > > what conductivity, if conductivity is important. I assume it is a steel
> > > tank.
> > > >
> > > > Anybody?
> > > >
> > > > Jerry Flanders
> > > >
> > > > W4UK
> > > > --
> > > > The NEC-List mailing list <nec-list_at_gweep.ca>
> > > > http://www.gweep.ca/mailman/listinfo.cgi/nec-list
> > >
> >
>
> --
> Alan Robert Clark, Pr Eng Computational Electromagnetics
> Associate Professor Wits University
> School of Electrical and Information Engineering
> Wits; Gauteng ``Bugs are later known as features''
> 2050 South Africa Ps 111:10; Ps 37/150
> Fax (+27 11)403-1929 clark_at_YingTongDiddleIPo.ee.wits.ac.za(Pref)
> Tel (+27 11)717-7223(24hr) <http://YingTongDiddleiPo.ee.wits.ac.za/>
> **Linux 2.4pl7(RH7.2)---the choice of a GNU generation.**
> --
> The NEC-List mailing list <nec-list_at_gweep.ca>
> http://www.gweep.ca/mailman/listinfo.cgi/nec-list

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