alex_shrab Post subject: De-embedding lossy transmission line Posted:
Wed Jul 25, 2007 4:40 pm Lieutenant Joined: Wed Jul
25, 2007 4:23 pm Posts: 1 Hi all experts , I'm doing
the following experiment: I have a system which consists of
a pair of SMA cables, backplane with microstrip differential pair and
another pair of cables which S-parameters I'm trying to find.
Unfortunately, I can't just measure S-parameters of the second pair
of cables by using a VNA. But I have S-parameters of the whole system:
[SMA cables - backplane - cables], and S-parameters of [SMA cables]
and [backplane] separately. The backplane is relatively ‘lossy' at high
frequencies (>10GHz). I'm converting S-parameters to T-parameters,
then taking T[backplane]^-1*T[SMA-cables]^-1*T[whole system]. Then,
I'm converting back to S expecting to get "second" cables S matrix.
Beyond some frequency (~12GHz), I'm getting very high gain and obviously
wrong behavior. I used this technique in the past to de-embed NOT very
‘lossy' components... What could be wrong? Thanks a lot in advance,
Alex. Top nubbage Post subject: Posted: Thu
Jul 26, 2007 3:39 am General Joined: Fri Feb 17,
2006 12:07 pm Posts: 218 Location: London UK Hi Alex One
time I encountered something similar, where a VNA plot turned to rat
doo-dooz above a certain frequency, it turned out to be an unexpected
resonance. This produced a rapid variation in S parameters around the
resonant frequency, and at harmonics of it. Is there any chance
your set-up could exhibit a resonance?
Posted 11/12/2012
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