[TowerTalk] S21 to Rp & Cp - Equivalent Circuit

[jimlux]

On 1/12/18 7:57 AM, Steve Hunt wrote:
> Yes!!!! - S11 Magnitude and Phase are quite different from S21 Magnitude 
> and Phase.
> 
> If you are interested, here's how I derive the choke's complex impedance 
> from S21 Magnitude and Phase:
> http://www.karinya.net/g3txq/chokes/s21.pdf
> 


The conversion of Mag/Phase to complex values is the same, but the 
conversion of the measurement to Z is different...

in the 1 port measurement, the unknown is in series with the 50 ohm 
impedance of the source, so you're looking at the ratio of the 
voltage/current across the Z compared to the voltage/current across the 
series combination (with some math to turn it into gamma/S11)

In the 2 port measurement, the unknown is between the ports, so you're 
looking at the voltage/current across the port 2 load, compared with the 
voltage/current at the port 1 source (with some math to turn it into S21)

Steve's website has the equations.