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S-Parameters Calculation - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement

Post subject: S-Parameters Calculation Posted: Sun Aug 13, 2006 3:51 pm


Joined: Fri Aug 11, 2006 6:07 am
Posts: 5
Is there a way to find the S-Parameters of a system without doing all the calculations to get them? Assume that I have a passive R network, is there a simulation program I can put this circuit into and have it calculate the S-Parameters for it?


Post subject: Posted: Tue Aug 15, 2006 5:59 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany

Basically any known RF simulation program will be able to calculate the S-Paramaters of a passive R network (I assumre it is an attenuator). You can try: Microwave Office and Genesys for example.

Best regards,

- IR


Post subject: RF SimulatorPosted: Tue Aug 15, 2006 11:28 am


Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104

Just a note on simulators:

Virtually every SPICE-based simulator can be convinced to give you an impedance R+jX, which can relatively easily be converted to S11 and S12.
Free versions are readily available - for example, NGSpice.

Linear Technology provides a remarkably good version of SPICE for free download, called "SwitcherCAD" or "LTSpice". (Their angle: they provide models only for Linear Technology's products. I can't criticize them for that, because many device models are available online).

For small circuits, many providers will give you free "crippleware" - which is good enough for small circuits. (PSpice from Mentor Graphics/OrCad and TopSpice from Penzar Research, for example).

S12 and S21 can be gotten with not much more effort with the AC simulation facility in SPICE. If you've got a pocket calculator, you can get S parameters from Z or Magnitude/Angle.

A free/open source RF simulator is "qucs", available online from SourceForge. It's still relatively undeveloped, compared to Genesys or Microwave Office, but if you're not yet to the point where those programs pay for themselves, it's a way to get started.

Good Luck!


Post subject: Posted: Tue Aug 15, 2006 4:54 pm


Joined: Wed Aug 20, 2003 11:47 am
Posts: 47
Location: Santa Barbara, CA
There is a free RF simulator called RFSim99 that is pretty nice that outputs S-Parameters directly. One link to get it is here:


Post subject: SimulatorPosted: Tue Aug 15, 2006 8:39 pm


Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104
KPainter -

RFSim99.exe - I forgot about that one! It has the advantage of being a Windows program, so easy to use and install. While it's not being updated anymore as far as I know, it's a good piece of work.


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