RE: [SI-LIST] : Inner vs. Outer Layer Routing

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From: sweir (weirsp@a.crl.com)
Date: Tue Dec 21 1999 - 10:26:18 PST


Andrew,

I vote phase of the moon.

I do not perceive a difference between the flux surrounding the return
current in a reflection plane, versus the current in the signal
conductor. So, I don't really like referring to reflection planes as
shields. The stripline benefit over microstrip is that the flux return
path is shorter, sic fewer total lines to intersect our antenna.

Regards,

Steve.

At 01:52 PM 12/21/99 -0500, you wrote:
> >Chris, if you are comparing differential microstrips vs differential
> >striplines it should be obvious to you that stripline, being surrounded
> >by grounds would radiate less.
>
>Wait a minute ... maybe it's just me, or the phase of the moon, but this
>isn't obvious.
>
>For the differential component, I agree. For the common-mode component, I'm
>not so sure. In microstrip, both paths of the common-mode component are
>exposed to the side of the board, both might radiate, out-of-phase, and
>cancel one another in the far field to some degree.
>
>In stripline, the common-mode component on the signal traces is shielded
>from the outside world. At high frequencies, the return path takes the
>inner surface of the return plane, and is shielded by the thickness of the
>return plane from the outside world. But at lower frequencies, the return
>path, and ONLY the return path, might be exposed to the outside world, into
>which it alone can radiate. No cancellation of radiation components as you
>could get in microstrip.
>
>There may be some leaps of faith in these assumptions, but it seems that the
>potential could exist for stripline to maybe cause more radiation than
>microstrip. This seems flawed, but I'm not sure how.
>
>Andy
>
>
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