Hi Jan, My 2 cents: As you noted, the spatial resolution is different for 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 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. Windowing options may include flat, Hamming-like and Bessel-like windows. Their leakage is different, and it will directly affect the spatial resolution. With a 'typical' windowing, the first approximation of BW=0.35/tr is a good start, and you could substitute the upper frequency end of the sweep to BW, and get the equivalent tr. 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. regards Istvan novak SUN Microsystems ----- 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 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 (=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 > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > http://www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List archives are viewable at: > http://www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: http://www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: http://www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu