From: c deibele (firstname.lastname@example.org)
Date: Mon Feb 28 2000 - 18:36:59 PST
If you can correctly characterize your TDR head, and your
connectors/cables to connect to your DUT, then either measurement
technique will work well.
In my opinion, it is easier to get accurate measurement using frequency
domain. This is a result of several assumptions.
a) a VNWA can be calibrated to extract extraneous effects that are
difficult to extract in the time domain. These effects are connectors,
cables, gain slope of the VNWA, etc.
b) the VNWA can run a relatively pure sinusoid. This means that the
effective bandwidth is very low, and therefore noise becomes a
nonissue. The only way to combat this in the time domain is to sample
your result for a very "long time". This is of course not true if what
you are measuring is a very high Q and then resonances can be missed
because of a poor choice of frequency sampling.
I've gotten excellent results using circa 12 psec pulseheads to get
relatively good results out to 30 GHz. I compared these results with
calibrated VNWA results and observed the time domain results are simply
more noisy. additionally, depending on the impedance of the DUT
compared to your measurement system, reflection and/or transmission
measurements in the time domain can be next to impossible because of the
noise considerations in b)
Of course, if you wish to characterize your results using some microwave
tools (like touchstone or ADS or other simulator), then you'll most
likely have to go to the frequency domain.
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