NEC-LIST: S11 to Z

This does not relate directly to NEC but... I am trying to model an
aircraft (747). I was able to take some measurements of an aircraft.
I took B-field readings on the outside and measured the S11 at the
feed point. What I am having trouble doing is converting the S11 data
that I have to Z so I can compare it with what NEC gives me. The
equation I am using is

     Zin=Zo{(1+S11)/(1-S11)}

Where:
        Zin is the drive point impedance
        Zo is the impedance of my analyzer (50 Ohms)
        S11 is a complex number

I tested this by measuring a 82 Ohm resister. When I display the data
on the network analyzer I get what looks like good answer. If I put
the S11 data into the above equation the answer does not match. If I
plot S11 on a smith chart the answer is very close to the display on
the network analyzer. What am I missing?

Thanks

Peter D. Richeson
Nuclear survivability specialist
Oklahoma City, OK
(405)739-1879

Some times He calms the Storm
Some times He calms the Child
Received on Thu Apr 12 2001 - 18:22:46 EDT