Re: NEC-LIST: Use of CP for multiple dipoles antennas

>Hello,
>I am currently studying a solution under NEC2 permitting the mesurement of
>the decoupling between 2 antennas: a Yagi and a GSM type. I have indeed
>tried everything using the CP function. But the difficulty comes from the
>fact that the GSM antenna is made of several radiating elements.
>Now the CP function permits the measurement of the decoupling only between
>two unique segments. The solution that I envision at the moment is to
>distribute a unique supply (on one of the dipoles) for all of the GSM
>antenna. So I can use the one unique CP function between the radiating
>segment of the GSM antenna and the radiating segment of the Yagi.
>Only, the obtained results do not return a correct outcome in the case.
>Indeed, according to the place of excitement on which dipole on the GSM
>antenna, the decoupling value is variable. I hope to have formulated my
>problem in a rather clear manner and that you will be able to reply with
>some elements of explanation.
>In this case, I sincerely thank you.
>Cordially, Etienne LEROUX-GIRARD.
>
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>http://www.gweep.ca/mailman/listinfo.cgi/nec-list

Hello. If you ultimately want to know how the antennas interact with
one another with respect to their feedpoints, you can model your
situation as a passive two-port. The feedpoints of the Yagi and GSM
antennas are ports 1 and 2, respectively. For example you can use
z-parameters (z11, z22, z21=z12) and then use NEC to establish the
relationships between the driving point voltages and currents at each
port by using open and short circuit terminations as required. You
will have to compute a set of z-parameters at each frequency that you
are interested in. Once you have the z-parameters for each frequency
you can put NEC aside. Now you will know the effect of a termination
on port 2 on the driving point impedance seen at port 1 and
vice-versa. If the antennas are decoupled sufficiently the effect
should be minimal.

I and my colleagues have taken vector network analyzers aboard USN
ships to characterize the local coupling channels existing between
shipboard antennas, so what I have described above is useful for both
modeling and measurement. Hope this helps. Sincerely,

-- 
John Wood                               (202) 767-2608
Code 5550                               (202) 767-3377 (FAX)
U.S. Naval Research Laboratory          e-mail: wood_at_itd.nrl.navy.mil
4555 Overlook Avenue, SW                WWW: http://server5550.itd.nrl.navy.mil
Washington, DC 20375-5337
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