Re: NEC-LIST: S11 to Z

So...you didn't give us any hard numbers to work with, besides the
fact that you used an "82 ohm" resistor. First off, if your Z0
reference impedance is 50 ohms, and the resistor is actually 82 ohms,
non-reactive (highly unlikely...), I'd expect S11 to be
(82-50)/(82+50) = 32/132 = 0.2424...+j0 . Is that what your network
analyzer says? When I put that into your formula, I get Zin =
50*(1.2424/0.7575) = 50*1.64 = 82. So...that all looks good to me.
Perhaps by comparing those numbers with the numerical results you got
from your measurement you'll be able to see what's wrong...or perhaps
nothing is wrong!

Cheers,
Tom

"Richeson, Peter D" wrote:
>
> 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?
Received on Thu Apr 12 2001 - 20:41:46 EDT