[SI-LIST] 2 questions about TRL cal
- From: Mick zhou <mick.zhou@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 8 Aug 2011 10:18:54 -0400
All,
There are two simple questions about TRL calibration that papers/app
notes are not very clear about.
1. Is it necessary to enter delays of lines?
The entries are available in the GUI. I have seen people think the
delays are not necessary and use 0ps for all. The argument is: the delay is
determined as part of the process. According to the theory, S12 and
exp(-gamma*l) are determined to a sign ambiguity. Extra infomation such as
delay is needed to uniquely decide the sign (therefore the phase). However,
delay may not be a problem for engineers who don't care phases. because
they don't "see" the difference by looking at magnitudes only. But this
could be dangerous if the models without correct phases are used in time
domain simulations, the delays could be wrong unless you are lucky the
phases are always within 20-160 degrees (8:1 case).
2. Is overlap of frequencies necessary in case of multi-lines? Again it is
related to accuracy of phases. Some believe overlaps can improve phase
accuracy. Some don't believe so. The instrument picks up either the last
(unguided cal) or the prority set by Smartcal (guided cal). So how the phase
accuracy is improved?
Thanks
Mick
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