# Thevenin and S parameters - RF Cafe Forums

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Camelot

Post subject: Thevenin and S parameters... Posted: Fri Jan 26, 2007 11:18 am

Captain

Joined: Fri Jan 19, 2007 10:36 am

Posts: 7

Hello,

I'm have “little” doubt about s-parameter simulations . My question is very simple but I do not know if the answer is the same .

The Thevenin theorem can be applied to a s-parameter simulation?

That is, if I do a simulation using a port P1 with 50 ohm where at valley of the port I've connected 2 impedences, one in parallel Z1 and one in series Z2. Supposing I obtained S11 at frequency f1. Then, if I incorporate the impedence Z2 (at frequency f1) in the port 1 impedence (using Thevenin), can I obtain the same S11 parameters for f1 fequency?

Camelot

Top

IR

Post subject: Posted: Fri Jan 26, 2007 3:18 pm

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hi Camelot,

In S-parameters you can short voltage sources, but you can't create an open circuit which is required to create the equivalent resistance for Thevenin. You can only connect the network characteristic impedance to derive each of the S-parmaters.

Hence Thevenin theorem applies only at DC and low frequency networks where it is possible to use open-circuit, but not to RF/Microwave networks.

_________________

Best regards,

- IR

Posted  11/12/2012