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De-embedding lossy transmission line - RF Cafe Forums
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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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