From: Ray Anderson (firstname.lastname@example.org)
Date: Wed Feb 23 2000 - 13:27:46 PST
Have you put your boards under a scope and measured the critical
dimensions on your filters?
This would tell you if the dimensions of your boards are different
from your original design. If the dimensions are off then it may be
that the freq shift is a function of a process problem as you have surmised.
If the dimensions look OK then you need to investigate material issues
(error in Er assumption, anistropy, delta in substrate thickness etc.)
and design issues (is Touchstone giving you the right answer, etc.).
Question: besides the center frequency being off, how is the bandwidth,
shape factor and ripple ? Are they what you expected??
Are the stripline filters being made as a multi-layer board, or are you
etching as microstrip and then attaching the top layer afterwards?
(microwave designer in years past)
> Yesterday a colleague told me that it is common with many circuit boards
> to shrink when a layer of copper is removed from a single side. This
> particular colleague even claimed that a board will shrink around 100
> mils or so after etching. Has anyone else observed or heard of an
> effect such as this? This definitely would explain why my center
> frequencies are off.
> Craig Deibele
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