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[SI-LIST] Re: Microstrip/Stripline

From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
To: "Hassan O. Ali" <hassan@xxxxxxxx>, babid_a@xxxxxxxxx, si-list@xxxxxxxxxxxxx
Date: Tue, 13 Dec 2005 09:03:33 -0800
The higher skin effect loss for the same width microstrip transmission line
over the same width stripline is more likely due to the fact that most of
the current in the microstripline is confined to the side of the trace exst
to the plane over which it runs while the stripline trace has current
distributed over both sides.  The under side of a surface microstripline is
roughened in order to make it bond to the prepreg layer, increasing the
loss.

This is offset, somwhat, by the fact that a surface microstripline has air
on one side which has a lower loss tangent that the dielectrics of the
stripline version.

As someone pointed out, there isn't a simple answer to this question.  I
rarely use surface microstriplines because the impedance control on outer
layers is so poor, so this question doesn't come up. 

Lee W. Ritchey
Speeding Edge
P. O. Box 2194
Glen Ellen, CA 95442
Phone- 707-568-3983
FAX-    707-568-3504

I just used the energy it took to be angry to write some blues.
Count Basie


> [Original Message]
> From: Hassan O. Ali <hassan@xxxxxxxx>
> To: <babid_a@xxxxxxxxx>; <si-list@xxxxxxxxxxxxx>
> Date: 12/12/2005 10:45:38 PM
> Subject: [SI-LIST] Re: Microstrip/Stripline
>
> Babid, 
>
> You can always find a microstrip line that is more lossy than a
stripline. You can also 
> find a stripline that is more lossy than a microstrip line. You'll have
to fix some 
> parameters of interest and then ask the same question.
>
> For example, you can fix the trace width, trace thickness, dielectric
constant, electric 
> loss tangent, metal conductivity, and characteristic impedance for both
line types 
> (allowing the trace height to vary to give rise to the required
characteristic 
> impedance). You may also need to specify whether or not the stripline is
symmetric, i.e. 
> the center strip is the same distance from the two reference planes. You
should also fix 
> a frequency band of interest - low frequency loss behavior can be
different from high 
> frequency loss behavior.
>
> In general though, a microstrip is more lossy than a stripline. The
fundamental reason is 
> that a stripline provides two planes through which the return currents
could pass, hence 
> less resistive loss (two resistors in parallel). But at higher
frequencies where 
> dielectric loss dominates over skin-effect (resistive) loss, the story
can be different. 
> That's pretty much material-dependent.
>
> Now go find a book if you need more info.
>
> Best regards.
>
> Hassan. 
>
>
>
> On Dec 12, "Tom Dagostino" <tom@xxxxxxxxxxxxx> wrote:
> > 
> > There are many good books that describe this.  I would suggest you try
the
> > "Transmission Line Design Handbook" by Brian C. Wadell as a good source.
> > 
> > Tom Dagostino
> > Teraspeed(R) Labs
> > 13610 SW Harness Lane
> > Beaverton, OR 97008
> > 503-430-1065
> > tom@xxxxxxxxxxxxx
> > www.teraspeed.com
> > 
> > Teraspeed Consulting Group LLC
> > 121 North River Drive
> > Narragansett, RI 02882
> > 401-284-1827
> > 
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Babid A
> > Sent: Monday, December 12, 2005 5:44 PM
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Microstrip/Stripline
> > 
> > 
> > Which is more lossy between microstrip and stripline? why?
> > 
> >   Thanks,
> >   -Babid
> > 
>
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[SI-LIST] Re: Microstrip/Stripline

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