[SI-LIST] Re: spatial resolution and effective rise time of VNA with TDR time-domain option
- From: "Lewandowski, Bob" <blewandowski@xxxxxxxxxxxxxxxxxxxx>
- To: <istvan.novak@xxxxxxxxxxxxxxxx>,<jan.vercammen.jv1@xxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Wed, 30 Oct 2002 17:23:58 -0600
I think the bandwidth for the .35/Tr estimate is significantly narrower
than the NWA stop frequency would indicate. The end of the sweep is
effectively a filter with infinite attenuation beyond the stop
frequency. If this band shape is converted to the time domain something
called Gibbs phenomenon occurs and produces ringing artifacts in the
time domain. As a result the measured response is filtered to
essentially reduce the amplitude response at the stop frequency to have
no effect on the time domain response. I believe the filter shape can
be selected and it will dramatically effect the time response.
---Bob Lewandowski
Stratos Lightwave
> -----Original Message-----
> From: istvan novak [mailto:istvan.novak@xxxxxxxxxxxxxxxx]
> Sent: Wednesday, October 30, 2002 5:47 AM
> To: jan.vercammen.jv1@xxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: spatial resolution and effective rise=20
> time of VNA
> with TDR time-domain option
>=20
>=20
>=20
> Hi Jan,
>=20
> My 2 cents:
> As you noted, the spatial resolution is different for=20
> different Dk media,
> so probably it is more effective to stay with bandwidth/risetime. The
> complications there are that VNAs
> - do not work all the way down to DC
> - usually have a range of windowing options for IFFT
>=20
> The fact that VNAs dont include DC in their frequency range is
> less of a problem when you want to resolve closely spaced
> discontinuities, but it creates an uncertainty of baseline if you
> have to do post processing.
>=20
> Windowing options may include flat, Hamming-like and Bessel-like
> windows. Their leakage is different, and it will directly affect the
> spatial resolution.
>=20
> With a 'typical' windowing, the first approximation of BW=3D0.35/tr
> is a good start, and you could substitute the upper frequency end
> of the sweep to BW, and get the equivalent tr.
>=20
> The benefit of using VNAs for TDR is that you can do a full
> calibration up to the probe tips, if you want to, otherwise it is
> usually more limited in resolution compared to true TDR.
>=20
> regards
>=20
> Istvan novak
> SUN Microsystems
>=20
>=20
> ----- Original Message -----
> From: "Jan Vercammen" <jan.vercammen.jv1@xxxxxxxxxxxxxxxx>
> To: <si-list@xxxxxxxxxxxxx>
> Sent: Wednesday, October 30, 2002 7:57 AM
> Subject: [SI-LIST] spatial resolution and effective rise time=20
> of VNA with
> TDR time-domain option
>=20
>=20
> >
> > Hello SI-list,
> >
> > I have a question about the saptial resolution of vector=20
> 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=20
> 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).=20
> 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=20
> measurments. The rule
> > of thumb would become: 15cm/(sqrt(dkeff) BW(GHz).
> >
> > Another question concerns the relation between the VNA=20
> bandwith and the
> > available
> > effective rise time of the step or pulse of the time domain=20
> 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=20
> an effective
> > rise time (10-90%)
> > of a VNA with a time-domain option?
> >
> >
> >
> >
> > Kind regards,
> >
> > Jan Vercammen
> >
> >
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>=20
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>=20
>=20
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