Elementary question about S parameters!!!

Hello all,

As far as I know, the S parameters of any N-port network, is a matrix describes the relation between the peak of incedent voltage wave and reflected voltage wave i.e. V+ and V- ...
For low frequency, i.e. 100MHz and below, is the definition also applicable? i.e. can i use S11 simulation to express power transfer and perrform matching using Smith chart at these low frequencies, or this is theoritically wrong?
Please comment,
Thanks,
Ahmad,

S parameters can be for DC. There is no frequency limit.

Agree. However, S parameters are not very useful for designing something like an audio system, however. You microphone input impedance will be around 10,000 to 1 Mohm, so you are NOT trying to do a power match, but instead just amplify the voltage. At the output you have the opposite problem, you are trying to match to a 4 ohm output impedance, where you ARE trying to do a power match.

S parameters work very well in a system where the input and output impedance WANT to be matched to 50 or 75 ohms.

what about Smith chart usage in general for frequencies less than 100MHz? is it correct?

Thanks,
Ahmad,

S parameters can have any base-reference impedance just as the smith chart can have any impedance be the center value.

As a matter of history, the "smith" chart was published in full form in Japan 13 months prior to the publishing by Smith. The circular nature of the chart was published in the 1920s by Campbell of filter fame of Bell Labs.

This is similar to the so called Gilbert mixer going back to the days of valves/tubes when Gilbert was wearing diapers.

Another example was spread spectrum being publicly disclosed by a German language book in 1913 and a German patent in 1924 and English language books in 1915 and 1917. This was reduced to Practice by the German X-Fritz air weapons during the 1930-1940 build up to the war. The German-Ameican film star getting a patent for it in 1940 was a fraud.

ahmad_abdulghany said:

what about Smith chart usage in general for frequencies less than 100MHz? is it correct?

Thanks,
Ahmad,

Click to expand...

Yes - I use for a long time ago smithchart in design of phone line interface with fork/hybrid in range 200Hz - 5000 Hz. Smithchart was great to visible not so easy to grasp complex measure of line and try to make line eqvivalent for canceling of outgoing voice in hearphone via active OP-amp bridge . In this time (later 80's) simulate program was for me unknow/not exist or very expensive and I doing most of this by hand (and much help from hp42S complex capability in all calculation...)

Smitchart and S-parameter is not depend of used frequency or impedance. only relation between measured impedance in complex notation and used reference impedance as reference point.


It's say S-parameters only working for high frequency and specific impedance as 50 Ohm is near same as told excel only working to counting money.... both can lot more if you have knowledge how this work and use for rigth type of problem.