S parameter for complex source impedance

[javier]

Hi, foremost I want to thank for all the time and effort put into developing qucstudio, which is a very useful tool in teaching and development. I am testing a quite simple circuit, it is a power source with output impedance Zg = 15+15j Ohms connected to a resistance with resistance Zl=225 Ohm. I perform S-parameter simulation over some frequencies, which do not really matter as there are no frequency-dependent elements. From the theory in Collin – Foundations of Microwave Engineering, and my own calculations comparing the power available from the source and the power delivered to the load (|S11|^2 = (Pav – Pload)/Pav), I expect the parameter S11 to be S11 = (Zl – Zg*)/(Zl+Zg), which gives -1.1547dB. However, qucstudio provides a value somewhere around -2.2 dB. Is this related to a different definition of S parameters for complex impedances or there is something to be corrected in my file/calculations, or maybe is it a bug? I place my question here since I did not really find a more appropriate topic.

Attachments:

1. RFcircuits_prj.zip

[Carsten]

in the forum post

Simulation of S-Parameter-Matrix with complex Port Impedances
(cannot post links here)

it is mentioned, that complex port impedances are not supported.

anyway, if you add a ‘*’ in the impedance definition (e.g. 15+15j  changed to 15+15*j), you get the -1,1547 dB.

btw: I would have used the formula to the right. That gives -1,23 dB. Don’t know, which is the right answer

Attachments:

1. rf_circuits_mod-1.qucs

[javier]

Thank you very much, this clarifies the situation.

While looking at these data, I seems that in my original file, when qucstudio is presented with the values Zg = 15+15j and Zl = 225+15j, it simply took Zg = 15+15 = 30 and Zl = 225+15=240; possibly a check on the number format input could help.

Best regards

JA

• This reply was modified 1 year, 1 month ago by javier.

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