[SI-LIST] Re: Microstrip Loss Correlation
- From: "Mark Burford" <Mark_Burford@xxxxxxxxxxx>
- To: <Christopher.Crowley@xxxxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 21 Oct 2005 17:31:43 +0100
=0A= =0A= =0A= =0A= =0A= =0A= [SI-LIST] Microstrip Loss Correlation
=0A= =0A= =0A= =0A= Is this loss = a continuing =0A= attenuation i.e. does
loss increase past 2.4GHz or are you experiencing = a =0A= 'notch' type
attenuation at the frequency you stated where past 2.4GHz = less loss =0A=
isseen?=0A= You are right in saying that = the superior =0A= quality
materialshould give less attenuation at this frequency but then = it all
=0A=depends on rise time of you signal, trace width (a wider trace will =
increase =0A= dielectric loss per length), around this frequency dielectric
losses = should be =0A= dominating skin depth (conductor) losses so perhaps
reducing the line = width if =0A= poss may reduce your attenuation.
Obvioulsyreducing trace length would = help =0A= too.=0A= =0A= How wide is
the ground plane = under the =0A= trace? Is it at least 2.5 - 3 times the
trace width where you have cut = it away =0A= (not sure exactly what you
havedone so couldn;t comment further) = because this =0A= would affect the
return current if the return plane was not continuous = at about =0A= 3
timesthe trace width. Also this would cause reflections and affect = your
=0A= measurement.=0A= =0A= I hope these simple questions = and reminders
=0A= are of use to you.=0A= =0A= Regards=0A= Mark=0A= =0A= =0A= -- =0A=
Mark R Burford M.Eng = M.I.E.E.
EngD =0A= Research Engineer
School of Electronics and Computer = Science
University =0A= of Southampton=0A=
=0A=
----------------------------------------------------------------------------
=0A= From: si-list-bounce@xxxxxxxxxxxxx = on behalf of =0A=
Christopher.Crowley@xxxxxxxxxxxxxxxxx
Sent: Fri 21.10.2005 =0A= 16:53
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] =0A= Microstrip Loss Correlation
=0A= =0A=
Hello All,
I am working on measuring the bandwidth = of a =0A= couple fixtures and am
surprised
by the results. I am hoping = that =0A= someone may be able to help shed
some
light on
the subject. = I have =0A= two fixtures that are identical other than the
materials. One =0A= board
is made of Isola's FR406 and the other is Arlon 25N. The = only =0A= minor
difference is
that the stackup may have been changed = slightly to =0A= accommodate for 50
ohm's on
12 mil trace widths. Four layer = board, =0A= 2.8" total length traces,
routed
only on the
top layer =0A= microstrip.
I have used edge launch sma's to interconnect to the = network =0A=
analyzer.
Johnson
Components 142-0701-801 PN. The issue is = that when =0A= making an S21
measurement
across the 2.8" trace I see both boards = have a =0A= 3db loss at
approximately
2.4GHz.
Since I would obviously expect = the Arlon =0A= 25N board to perform much
further
out in
frequency one thing I am = suspect =0A= of is the sma interconnect. I know
that
the sma
footprint = should be =0A= optimized and we have tried to do that by cutting
away
some
GND = under the =0A= signal conductor of the sma. It seems like it is still
causing = an =0A= issue
though. Does anyone have any footprint or other =0A= recommendations?
Thank =0A= you,
Chris
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