[SI-LIST] Re: CPWG
- From: "D G" <dgun@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 31 Jul 2003 16:00:46 +0800
From: Bob Patel <whizplayer@xxxxxxxxx>
> Hi! I had a question regarding CPWG:
> For Edge coupled CPWG in Wadell book it is mentioned
> that to gurantee coplanar propagation:
> s+2.0w+2.0d<h
> where s=spacing between the traces
> w=width
> d=distance from trace to gnd trace
> h=height of dielectric.
> I want to know why I need to meet that equation and
> what if I don't?
> THanks in advance.
> Bob
Bob,
When the ground plane at the bottom of the dielectric gets too close to the
traces (smaller h), then there is coupling to this plane. This coupling does
two things: it changes the impedance of the lines, and it can introduce
parasitic modes.
On the other hand, if h is too big, parallel-plate waveguide modes will show up
at certain frequencies.
--
Daniel
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