From: C Deibele (firstname.lastname@example.org)
Date: Wed Feb 23 2000 - 12:48:23 PST
I have a question about something that I've heard about recently.
I am making FIR stripline filters - circa 4 GHz, and the physical
dimension of the filter is 5"x30". The filter is manufactured using
Arlon 2.33 LX material, eps_r=2.31 (Arlon measured the dielectric and
loss tangent), and is put together using an etch/acid wash.
I designed the circuit using Agilent's Touchstone package.
My problem: The center frequency of each filter is off by 70 MHz. My
filters are rather narrow band, so this was a problem for me. I simply
made individual sections of my filter a bit longer to accomodate this
frequency offset. Each coupled line in my design was originally 460
mils, I extended each to 465 mils. This implies that the overall length
increase is proportional to 3/460 or about .5%.
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.
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