kennycs wrote on Feb 1st, 2010, 12:28am:When I use S-parameter simulate with MCLIN(differential lines) in ADS,
the result |S11|,|S21| seems wrong.
I think |S21| should be monotone decreasing, But the result shows it is periodic
It is natural result since your line is lossless.
Frequency characteristics of lossless line is periodic.
Why do you think |S21| decrease monotonically ?
Consider |S21| of lossless single line.
Does |S21| decrease regarding frequency ?
For coupled line, if you pay attention to one line, another line acts as resonator.
So periodicity of |S21| is natural.