Recommend me a tutorial about S parameters

Hi!
Anyone has a good Tutorial for learn S parameters ?
May be some book to read. I have one, but it is very dificult to follow and not too clear.

Thanks in advance

u may take a look here:

Electromagnetic Waves & Antennas: S-Parameters
S. J. Orfanidis

From www.ece.rutgers.edu/SJrfanidi/ewa

Regards,

I think the one from HP is good.
Try
http://www.sss-mag.com/pdf/an-95-1.pdf

ludwig's RF design

Gonzalez "Microwave Amplifier Design "

Also worthwhile Appl.Note from Agilent. AN 154 S parameter design.
http://cp.literature.agilent.com/lit.../5952-1087.pdf