[SI-LIST] Re: stupid VNA / TDR / TDT Measurement / Setup question

Hello Jeff

I've seen the (annoying) effects of parallel plate mode coupling on L band
(around 1 GHz) transmitter assemblies.  I think it could be seen as a deep
slot-antenna effect excited by a conducted current flowing between the
plates in one small region (e.g. thro cap and via).  You are right of
course, the wave guide is effectively below cut-off and the wave mode cannot
be sustained - the field strength decays rapidly with distance, but there
could still be enough left to show significant coupling at some distance.

Cheers
Geoff

> -----Original Message-----
> From: Loyer, Jeff [mailto:jeff.loyer@xxxxxxxxx]
> Sent: 26 November 2003 17:28
> To: engin@xxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: stupid VNA / TDR / TDT Measurement / Setup
> question
> 
> 
> Hi Ege,
> Can I get some clarification, please?  I'm probably misunderstanding =
> something...
> 
> I'm not sure what you mean by the parallel plate mode propagating in =
> this context.  Is it for the case where there is a voltage 
> difference =
> between the power and ground planes?  If that is so, wouldn't the =
> dominant frequencies propagating in that mode have as their quarter =
> wavelength the distance between the planes?  In the case cited, that =
> would be 30mils, giving a full wavelength of 0.12 inches.  
> Assuming a Tp =
> of 180ps/in, that gives a wavelength of 21.6ps, or a frequency of =
> ~46GHz, higher than we're usually concerned with in this 
> context.  And, =
> I'm not sure of the vehicle that's applying the voltage to the power =
> plane - is it the capacitance between the trace and the plane?
> 
> Of course, I may have the physics (and corresponding math) 
> completely =
> wrong.  Please correct, as needed.
> 
> Also, if I understand you correctly, when you speak of the stripline =
> mode, that's making the assumption that there is no voltage 
> differential =
> between the planes, hence a pure stripline configuration.
> 
> The actual condition will be a combination of the two modes.  
> The more I =
> think of it, the more your representation makes sense, but I 
> need some =
> help with the specifics.
> 
> Thanks for your help,
> Jeff Loyer
> 
> 
> 
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx 
> [mailto:si-list-bounce@xxxxxxxxxxxxx] =
> On Behalf Of Ege Engin
> Sent: Tuesday, November 18, 2003 1:34 AM
> To: hermann.ruckerbauer@xxxxxxxxxxxx
> Cc: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: stupid VNA / TDR / TDT Measurement / Setup =
> question
> 
> 
> Hello Hermann,
> You can think of your stripline Sig3 as a multiconductor transmission
> line (i.e., you have 3-conductors: power, ground, and signal). Two
> transmission line modes can propagate here: parallel-plate 
> and stripline
> modes. So if you launch a signal on Sig3 while referencing the ground
> plane, you excite both modes. Note that the power plane is 
> not connected
> to anything, i.e. it is floating. This can be used to reduce the
> stripline model, which can be obtained considering the two modes, to a
> single transmission line model with a slightly higher characteristic
> impedance than the stripline. In conclusion, what I would expect to
> observe in measurement is still a transmission line but with a higher
> characteristic impedance than expected. I think, Jeff Loyer's
> experiments can also be interpreted in this way. We have performed
> 4-port measurements on such stripline structures with a VNA, and have
> clearly observed the coupling between ports referenced to the 
> power and
> ground planes and got a good correlation between measurement and
> stripline model based on two modes.=20
> 
> Hope this helps.
> 
> Ege Engin
> 
> hermann.ruckerbauer@xxxxxxxxxxxx schrieb:
> >=20
> > Hello all,
> >=20
> > I do have a stupid question, maybe you can enlighten me ....
> >=20
> > Assuming a 6 layer board (Sig1 / GND / Sig2 /  / Sig3 / 
> Power / Sig4) =
> with
> > some single ended ustrip and stripline transmissionlines =
> teststructures on
> > all 4 signal layers. There are no passive components on the 
> PCB (e. g. =
> no C)
> > My probes do have a signal and a GND pin. All 
> teststructures does have =
> a
> > signal pad and a GND pad for contacting with the probe.
> > Therefor I'm fine with Sig1 and Sig2! both are nice GND referenced,
> > therefore I do not expect a problem with the measurements there!
> >=20
> > But Signal 3 and 4 are Power referenced. And so far there 
> is not too =
> much AC
> > short between PWR and GND plane. The distance between this 
> planes is > =
> 30
> > mil, therefore I would expect the most AC short coming from 
> the Vias. =
> And
> > now I'm not really sure what happens, if I'm doing a VNA / TDR / TDT
> > measurement on Sig3 and Sig4, which are Power referenced, as my =
> measurement
> > ground is connected to the GND plane on the board.....
> >=20
> > Can the results tell me something, or can I forget the results =
> completly ???
> > Is there a difference for VNA / TDR or TDT Measurments in 
> this case ?
> >=20
> > thanks
> >=20
> > Hermann
> >=20
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