What is the depth of the dip relative to the insertion loss curve?
Does the dip depth grow with trace length?
Are you rotating your board or angling your trace? If so what is the angle?
What fiberglass fabric are you using in your laminate?
On Fri, May 28, 2021, 6:35 AM Tommy Huang <Tommy.Huang@xxxxxxxxxx> wrote:
Hi Experts,
When I measure s-parameters of transmission line, I found S21 or Sdd21
cure with sharp dip at some frequency points, but there is no dip for
shorter trace at same layer.
I read Eric Bogatin's article "How to Read S-Parameters Like a Book",
there is a section is about "sharp dip", but its seem not match my case. In
fact we use standard Delta-L coupon design to do measurement, then
implement de-embedding. When we put Sdd21 curve together, Sdd21 of 10inch
trace have obvious dip, 5inch trace also have but not obvious, 2inch trace
no(perhaps submerged by multi-reflection?),And the dip frequency point of
10inch and 5inch trace are almost same. After de-embedding, the dip is more
obvious.
Is there any advice or experience to share? We could do some test and
study.
B&R
Tommy
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