When using noiseParameters functions, why do I have to set the impedance to 1 and not 50.

I have created a cascade of S-Parameter files using the RF Toolbox. When I use the noiseParameters function for the active elements to calculate the noise figure, I notice that to get a noise figure close to what I have calculated manually, I need to set the impedance to 1 Ohm.

However, I am certain that these S-Parameter files represent 50 Ohm systems. This discrepancy is concerning, and I would appreciate any insights or suggestions on how to resolve this issue.

Thank you!

[Anmol]

Hi James,

I understand that you are facing a discrepancy in the impedance while generating a noise figure from the cascaded S-parameter files. You can check if the value used to set Rn is normalised or in Ohms.

You can see from the documentation link the requirement: https://www.mathworks.com/help/releases/R2025a/rf/ref/noiseparameters.html

You can also look into these for debugging:

https://www.mathworks.com/help/releases/R2025a/phased/ref/noisefigure.html

Rf budget Analysis: https://www.mathworks.com/help/releases/R2025a/rf/rf-budget-analysis.html

MATLAB answer: https://www.mathworks.com/matlabcentral/answers/2145514-rf-budget-analyzer-calculating-noise-figure-incorrectly?s_tid=srchtitle

I hope, it helps.

[James]

Hi Anmol,

Thank you for all of those resources. They have led me to realize that the only function I am using that does not specify impedence is the below:

nport('mysparameters.s2p, "MYS2P");

Am I unable to check and/or set the nport function's impedence?

Thank you for your time,

James