Re: NEC-LIST: DECT Coverage in Metal Tunnel

This is a reply to Kwan Meng Chong (mdeng1_at_hotmail.com) regarding his
question for the NEC-LIST.

Kwan Meng,

Your message concerning DECT coverage in a metal tunnel was forwarded
to me. I have done some work with ray methods in large cavities, so I
may be able to answer your questions.

You are correct that there will be terrible multipath problems in a
closed metal tunnel. With the tunnel closed on both ends, and there
being no loss mechanism, it doesn't matter what kind of an antenna you
choose. Rays will bounce around through many reflections from the
walls and form a standing wave pattern. If the tunnel is not closed on
the ends, the multipath problem may still be noticeable but not nearly
as severe. The bi-directional yagi should work fine for this case.

If you are stuck with a closed tunnel, then you need to introduce a
loss mechanism to kill the higher order reflected fields. It may also
be possible to break up or "roughen" the metal walls so the reflection
from them is diffuse. It would probably be sufficient to treat only
the closed ends of the tunnel.

NEC-BSC could be used for the analysis, but it is limited in the
number of reflections which can be included. It can also account for
reflections from lossy planar walls, but not diffuse reflections. We
are planning to study cellular propagation inside tunnels in the
future, but we currently don't have funding for this problem. As part
of the study we would increase the number of reflections included in
NEC-BSC.

Please let me know if I may be of further assistance.

Best regards,
Bob

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                        Robert J. Burkholder
Adjunct Associate Professor Research Scientist
The Ohio State University ElectroScience Laboratory
Department of Electrical Engineering 1320 Kinnear Road
Phone: (614) 292-4597, FAX: (614) 292-7297 Columbus, Ohio 43212
E-mail: burkhold_at_ee.eng.ohio-state.edu
Web site: http://esl.eng.ohio-state.edu/
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Received on Sun Apr 09 2000 - 12:25:08 EDT