S-parametrs definition

Hi can anyone post link where i can find detail description of s-parametrs..
Waht are s-parametrs...
What is S11 and why it should be less than -10dB?
What is s21 and what is s12 and how the graph of both should be with respect to freqency?(Because i heard that it should be almost linear no spikes)..

Hello,

Scattering parameters - Wikipedia, the free encyclopedia
http://qucs.sourceforge.net/docs/technical.pdf

Hi,

Scattering-parameters are used in high speed signal analysis to find out the reflection(S11) and insertion(S12 OR S21) losses. It depends on the no of ports we are using. lets take an example that we have 2-port network 1- input 2-output.

In s-parameter Sxy x = output y = input. if S21 then it tells input is at 1-port and output is at 2-port.

The losses are calculated in terms of DB.

say input voltage = 1V

if S11 = -3db then 0.7V will reflect back to the source port which is 1.

if s21 = -3db then only 0.7V will be available at the output port which is 2.

Thanks
Shiva