[SI-LIST] Re: Insertion Loss, Return Loss, ILD, UNi versus Dual stripline

  • From: Scott McMorrow <scott@xxxxxxxxxxxxx>
  • To: Ken Cantrell <Ken.Cantrell@xxxxxxxxxxxxxxxx>
  • Date: Thu, 05 Aug 2010 11:33:18 -0400

With 4-ports as follows

1 ----- 2
3 ----- 4


Create the stackups in an accurate solver, or better yet make high 
quality measurements.  Model the dielectric layering such that each 
layer has a different Dk, since they will be different in a real build.  
Of course the measurements will naturally see this.

Look at S14 across the manufacturing variations.
Look at S12 across a long length of trace.

Both of these will tell you just how non-uniform your dielectric is, 
which will ultimately have some impact on overall return loss.  Once you 
have this down, then you can use the worst case to determine overall 
variation in IL, RL, and ILD

don't forget to model the layer between the Plus and Minus side of the 
traces correctly. (Where the core and prepreg materials interface.)  
This region is resin rich, and has a different Dk than the surrounding 
material layers.  It's value will impact differential coupling and 
resistive losses between the trace edges.

Scott


On 8/5/2010 10:59 AM, Ken Cantrell wrote:
> Robert,
> Interesting question.  S11 is dependent on impedance matching between the
> source and the input port, and S21 is dependent on impedance matching
> between the load and the ouput port, and the associated line loss.  S11
> should be identical, but S21 should vary slightly between the two
> configurations.  For the dual strip configuration, given no coupling between
> the pairs, and the same permittivity and height on all layers concerned, the
> dual strip trace width would be>  than the stripline width, and have less
> resistive loss.  The dielectric loss would be constant.  Conversely the dual
> strip would be harder to manufacture, and the deviation would be greater.
>
> my guess,
>
> Ken
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx
> [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Haller, Robert
> Sent: Thursday, August 05, 2010 8:07 AM
> To: Katkoria, Deepak; si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: Insertion Loss, Return Loss, ILD, UNi versus Dual
> stripline
>
>
> ASCI Graphics did not come through correctly- will try again. I know the
> first option is preferable, and I know I can (and have) measured the Loss.
> What I am trying to quantify is Specifically Which S parameter(s) I can
> use/measure to quantify the difference;
> Insertion loss, Return Loss, or insertion loss deviation
>
> GND -----------------
> Sig        -  -
> GND -----------------
>
> GND -----------------
> SIG     - -
> SIG           - -
> GND -----------------
>
>
> -----Original Message-----
> From: Katkoria, Deepak [mailto:Katkoria.Deepak@xxxxxxxxxxx]
> Sent: Thursday, August 05, 2010 9:58 AM
> To: Haller, Robert; si-list@xxxxxxxxxxxxx
> Subject: RE: [SI-LIST] Insertion Loss, Return Loss, ILD, UNi versus Dual
> stripline
>
> Yes you would get a loss in both cases..
> First option is more preferable...
>
> Otherwise in second option, overlap the differential signal in opposite
> polarity. i.e 2 layer +- 3 later -+
>
> Cheers,
> Deepak
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
> Behalf Of Haller, Robert
> Sent: Thursday, August 05, 2010 3:49 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Insertion Loss, Return Loss, ILD, UNi versus Dual
> stripline
>
> I have 2 Diff pairs in the same dielectric Material (ISO370HR). One is Uni
> Stripline, One is Dual Stripline. Aside from the potentially different
> core/Prepreg material, resin content, glass weave (etc), and they are the
> Same Copper Geometry (say 4 mil line/7 mil space) and have the same
> impedance, same DC resistance  will I be able to observe a difference in
> Insertion Loss, Return Loss, or Insertion Loss Deviation ?
> GND ---------------                    GND --------------
> Sig        -  -                                     SIG      -  -
> GND ----------------                   SIG                -  -
>                                                          GND ---------------
>
>
> Regards
> Bob
>
> Robert Haller
> Architect Engineer, Switching
> Enterasys Networks
>
> Phone: +1 978 684 1340
> Fax:     +1 978 684 1499
> E-mail:  rhaller@xxxxxxxxxxxxx<mailto:gnigg@xxxxxxxxxxxxx>
> Web:     www.enterasys.com<http://www.enterasys.com/>
>
>
>
>
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-- 
Scott McMorrow
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