How to identify incorrect S-parameter?

[ruwan2]

Hi,
I know S-parameter basics. I was asked a question on S-parameter recently. If the S-parameter is not correct, how to identify it?

I just came to cross that the pass through energy plus the reflect energy should be equal to the incoming energy. Is it right?

Please give me your answer to me. Thanks,

 

[reidintransit]

1. gain in passive system is a good sign something is wrong.
2. |S11|^2 + |S21|^2 should be close to but less than 1 for a lossy system and = 1 for a lossless system. sometimes referred to as "energy balance"

 

[ruwan2]

Thank you very much. Your answer does reply me well. I am not clear about the passive device gain here. Does it account for the ratio of pass through power to input power, or to the reflected power? Please teach me more.

 

[reidintransit]

A passive device by definition can have no gain. you can't get more power out of a passive system than you put into it. On a smith chart anything outside the unit circle would be gain.