Re: NEC-LIST: State of the Art ?

At 08:40 AM 7/3/2005, wilfam wrote:
>Hi,
>
>Is NEC 4 considered state of the art in terms of wire antenna modelling ?

I would say so. There are a number of other products out, but essentially,
they all work the same as NEC4 internally. The differences are mostly in
the user interface, how you specify the model, etc.

As another antenna engineer at work says: MoM is MoM...

>Are there alternatives that provide similar performance ?

Performance for modeling what? In what environment? NEC4 and it's ilk
aren't as good at modeling things that have lots of dielectric scattered
around the model. In fact, it doesn't do it well at all: you get insulated
wires and you can immerse the entire thing in a dielectric, but that's it.

There are other programs/codes that use other modeling approaches (e.g.
various approximations to charge/current distributions, things like FDTD,
etc.) that handle complex structures or things like waveguide (CST, HFSS, etc.)

>We have been using wire grids to model antennas on structures. When I
>mentioned this to a non antenna modelling colleague he thought that using
>wire grids "couldn't be right". These types of questions can be challenging
>and deserve an answer.
>Wire grids provide a representation of a solid surface and here are
>guidelines for constructing them. I wondered if there were alternatives for
>non-closed surfaces.
>So, which modelling programs are considered state of the art in terms of
>modelling the influence of structures on antenna performance ?

Depends on the structure you're modeling, in particular, the presence of
dielectric materials.

There are also distinct differences in how various modeling codes "grid"
the surfaces/objects, either for wire MoM (e.g. NEC), or for other
approaches. You want fine enough gridding to cover the small scale
effects, but not so small that run time gets excessive or that you run into
numerical precision problems.

>Thanks,
>
>Michael.
>

James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875

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