How to read S Parameter's graph ?

[hasan_fneish]

for example if the S11 and S22 is the same along the frequency, what does it mean ?
If the S12 suddenly drop and then rise again in a small range of frequency ,what does it mean ?
If the S21 suddenly drop and then rise again in a small range of frequency ,what does it mean ?
If S12 is bigger than S21 , what does it mean ?
If S21 is bigger than S12 , what does it mean ?

 

[Ow@i$]

S11 and S22 same means you will have same amount of reflection back from both ports 1 & 2.
Normally S21 is more important since it means forward gain , S12 means gain when from output to input.
if drops means it is not properly matched around that frequency, it can be seen from S21 that the frequency where gain is low is the same frequency where reflection will be high that can be verified from S11 or S22.
S12 greater means gain will be high if input is given at the port 2 as compared to port 1.
S21 greater means gain will be high if input is given at the port 1.

Read following i see you have to read the basics of S parameter than you could answer all related question yourself it is not that difficult.
http://en.wikipedia.org/wiki/Scattering_parameters#Two-Port_S-Parameters
**broken link removed**