[SI-LIST] spatial resolution and effective rise time of VNA with TDR time-domainoption

Hello SI-list,

I have a question about the saptial resolution of vector network analysers
(VNA)
with time-domain TDR option, that is, to resolve discontinuitites in
space (=length dimension)

Is there a rule of thumb for estimating the spatial resolution of a VNA
with a
TDR time-domain option from knowlegde of its bandwith BW.

I have found one rule in an application note: 15cm/BW(Ghz). For example,
for a 6GHz
BW the spatial resolution is about 2.5cm for an effective dielectric
(dkeff) of 1.0.
You probably get better resolution for PCB or cable measurments. The rule
of thumb would become: 15cm/(sqrt(dkeff) BW(GHz).

Another question concerns the relation between the VNA bandwith and the
available
effective rise time of the step or pulse of the time domain signals. I
assume that one
cannot use the rule trise=0.35/Bw because there BW refers to the 3dB
breakpoint
(the effective BW is bigger). A VNA bandwith is its upper limit.

-1- Is the above spatial resolution rule correct?
-2- Is there a rule of thumb to convert bandwith (BW) into an effective
rise time (10-90%)
      of a VNA with a time-domain option?




Kind regards,

Jan Vercammen


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