Re: NEC-LIST: Mutual Coupling Impedance from S parameters

At 04:59 PM 8/18/2004 -0500, Mohammad Amin wrote:
>Hi All,
>
>The mutual coupling impedance between two antennas can be calculated by
>representing these with an equivalent two port network. With active
>impedance of antenna #1(Z1), while terminating antenna #2 with a passive
>impedance ( Zp, say 0 or 50 ohms), the mutual coupling impedance can be
>found using the formula Z1 = Z11-(Z12)^2/ (Z22+Zp). Here Z11 and
>Z22 are self impedance ( For identical antennas, Z11 = Z22).
>With two port network analyzer measurements, Z1 can be calculated from
>S11, Zp is 50. If Z11, Z22 are known, Z12 can be calculated. (Likewise
>admittances can be used)
>
>However there is another formula for Z12 which uses directly S
>parameters, that is:- Z12 = 2S12/{(1-S11)(1-S22)-(S12)^2}. I,m not
>getting the same results from this formula as from the formula given
>above.
>
>(1) CAN SOMEONE POINT OUT THE DIFFERENCE BETWEEN THE TWO?
>(2) GIVE REFERENCE WHERE ONE FORMULA IS DERIVED FROM ANOTHER?
>(3) HAS SOMEONE USED SECOND FORMULA FOR MUTUAL IMPEDANCE CALCULATION?
>
>Regards
>MAM

There is an HP/Agilent Applications note that gives conversions among
Y,Z,T,ABCD,S, etc. I'll see if I can find the number (you might try
searching for AN95-1)

James Lux, P.E.
Spacecraft Telecommunications 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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