Re: NEC-LIST: Large Model Problems....

Hi Ken et. al.,

Are you aware of any non commercial TLM software that my student might
apply?

Your rough calculation is correct, however, by eliminating most
elements that are not in the correct direction for the polarization he
is using, I think he comes closer to meeting the requirements of NEC
for number of segments needed. I admit, he is on the outer limits of
the program. Fortunately, my other students have stuck to more
reasonable size antennas. This particular student's reason for
modeling and building this antenna, (besides for my class) is that he
lives about 20 miles from campus, and can see the building where our
wireless access points are located with a telescope, and once in a
while he can connect with a 24 dbi dish. He has this old TVRO dish
sitting around, and would like to use it to connect to the campus. It
will be interesting to see how well the NEC simulation pans out
assuming he gets it going. He will measure the pattern and input
impedance experimentally, so we will have something to look at.

And to everyone, thanks for all the suggestions. I have passed them on
to my student. We will see what he comes up with.

As a matter of interest, his simulation is taking roughly 7 hours to
compute.

Again, thanks for the help!

Rob

On Feb 19, 2004, at 11:21 AM, Carrigan, Ken wrote:

> Rob,
> Just from calculating the ratio of a quarterwave 2.4GHz
> dipoles (2-180 degree wires) with a 10 foot dish (3.4 meters)
> the ratio suggests over 11,000:1. NEC usually needs not less
> then 10:1 length vs wavelength to be somewhat accurate. This
> is one major problem with modeling microwave frequencies with
> NEC on larger structures. For situations like this, I would
> using something like TLM, which instead of N^2 matrix's it's
> more like N computations. I seen some good results with using
> this on X-Band radar EMI - modeling RAM and Navy Mast
> structures. Amazing results with larger structures and
> microwave frequencies.
> v/r
>
> Kenneth Carrigan
> Electromagnetic Engineer,
> Anteon, Systems Engineering Group
> 1100NJ Ave, Washington, DC
>
>>> -----Original Message-----
>>> From: D. B. Miron [mailto:dbmiron_at_paulbunyan.net]
>>> Sent: Thursday, February 19, 2004 8:40 AM
>>> To: nec-list_at_gweep.ca
>>> Subject: Re: NEC-LIST: Large Model Problems....
>>>
>>>
>>> Good day Rob,
>>>
>>> Without seeing either the wire list or the source code used
>>> to generate it, I can't help you. There are just too many
>>> ways to mess up.
>>>
>>> Doug Miron
>>>
>>> "Rob Frohne" <frohro_at_wwc.edu> writes:
>>>
>>> Hi All,
>>>
>>> I have a student who is trying to model a 10 foot parabolic
>>> dish at 2.4
>>> GHz. He has around 11,000 segments, though using symmetry,
>>> he has
>>> reduced the matrix dimensions by a factor of four. He is
>>> getting gains
>>> that are -999.99 for every direction. The electric fields
>>> are not all
>>> the same, and may make sense. I didn't get a chance to see
>>> that.
>>>
>>> Does anyone have any advice for my student?
>>>
>>> Thanks,
>>>
>>> Rob
>>> --
>>> Rob Frohne, Ph.D., P.E.
>>> E.F. Cross School of Engineering
>>> Walla Walla College
>>> http://www.wwc.edu/~frohro/
>>>
>>> --
>>> The NEC-List mailing list <nec-list_at_gweep.ca>
>>> http://www.gweep.ca/mailman/listinfo.cgi/nec-list
>>>
>>> --
>>> The NEC-List mailing list <nec-list_at_gweep.ca>
>>> http://www.gweep.ca/mailman/listinfo.cgi/nec-list
>>>
>>
>
> --
> The NEC-List mailing list <nec-list_at_gweep.ca>
> http://www.gweep.ca/mailman/listinfo.cgi/nec-list
>

--
Rob Frohne, Ph.D., P.E.
E.F. Cross School of Engineering
Walla Walla College
http://www.wwc.edu/~frohro/
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