[SI-LIST] Re: spatial resolution and effective rise time of VNA with TDR time-domain option

  • From: "D G" <dgun@xxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Fri, 01 Nov 2002 01:27:51 +0800


I've used Agilent (HP) VNAs and have not had a problem with the Time-Domain 
option.  When the cables are calibrated, then the response begins at time 0 and 
is easy to follow.  If you memorize the discontinuity signatures (shunt c,l; 
series c,l; loss; short, open) then it's easy to see what's going on if you 
have enough spatial resolution.  It's also useful to be able to switch between 
impulse and step response at the touch of a button.

I use time-domain in both production and design.  In production it helps to 
locate the problem area for troubleshooting.  In design it helps to minimize 
discontinuities, improving signal transmission.

The gating feature is useful for mathematically removing fixtures.

Of course, your rise time is limited by bandwidth, and bandwidth is expensive 
in a VNA.

- Daniel

From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
> This brought up a question I have:
> Does anybody routinely use the "TDR option" of a VNA?
> I already had a TDR when I got our VNA.  I tried the "TDR option" of the =
> VNA, but found it cumbersome, awkward, etc. (not to mention the sloooow =
> rise-time it forced).  Kinda like using a 2x4 for a hammer - it works in =
> a pinch, but just barely, and not for everything.  So, I'm real glad I =
> have both the TDR and VNA.  I can't imagine using just the TDR option of =
> the VNA.
> Am I missing something?  Have others had different experiences?
> Jeff Loyer
> -----Original Message-----
> From: Jan Vercammen [mailto:jan.vercammen.jv1@xxxxxxxxxxxxxxxx]
> Sent: Wednesday, October 30, 2002 4:58 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] spatial resolution and effective rise time of VNA
> with TDR time-domain option
> 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 (=3Dlength 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=3D0.35/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

(remove the Z-'s to reply--they're what I do when I read spam)

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