[SI-LIST] Re: Microstrip Loss Correlation
- From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
- To: <Christopher.Crowley@xxxxxxxxxxxxxxxxx>, "Mark Burford" <Mark_Burford@xxxxxxxxxxx>
- Date: Fri, 21 Oct 2005 12:23:18 -0700
You should be able to do much better bandwidth on FR4 than you are seeing
here for that length trace.
Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
tom@xxxxxxxxxxxxx
www.teraspeed.com
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of
Christopher.Crowley@xxxxxxxxxxxxxxxxx
Sent: Friday, October 21, 2005 11:16 AM
To: Mark Burford
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Microstrip Loss Correlation
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Hello Mark,
I have attached a copy of the insertion loss plot, but basically you can
see that there is a small rise, than a
cliff after the 2.4Ghz. The gnd plane under the trace is a full plane.
The board is shaped like a stop sign
that is nearly 3"X3", so there is plenty of gnd under the trace. The area
where the gnd is cut away is only
just under the top layer pad for the signal conductor of the sma. The pad
itself is 40 mils wide, but the GND
underneath is 50 mils wide. I have attached a .bmp for reference.
Thanks,
Chris
"Mark Burford" <Mark_Burford@xxxxxxxxxxx>
10/21/2005 12:31 PM
To: Christopher Crowley/Corporate/FSC@Fairchild,
<si-list@xxxxxxxxxxxxx>
cc:
Subject: RE: [SI-LIST] Microstrip Loss Correlation
Is this loss a continuing attenuation i.e. does loss increase past 2.4GHz
or are you experiencing a 'notch' type attenuation at the frequency you
stated where past 2.4GHz less loss is seen?
You are right in saying that the superior quality material should give
less attenuation at this frequency but then it all depends on rise time of
you signal, trace width (a wider trace will increase dielectric loss per
length), around this frequency dielectric losses should be dominating skin
depth (conductor) losses so perhaps reducing the line width if poss may
reduce your attenuation. Obvioulsy reducing trace length would help too.
How wide is the ground plane under the trace? Is it at least 2.5 - 3 times
the trace width where you have cut it away (not sure exactly what you have
done so couldn;t comment further) because this would affect the return
current if the return plane was not continuous at about 3 times the trace
width. Also this would cause reflections and affect your measurement.
I hope these simple questions and reminders are of use to you.
Regards
Mark
--
Mark R Burford M.Eng M.I.E.E.
EngD Research Engineer
School of Electronics and Computer Science
University of Southampton
________________________________
From: si-list-bounce@xxxxxxxxxxxxx on behalf of
Christopher.Crowley@xxxxxxxxxxxxxxxxx
Sent: Fri 21.10.2005 16:53
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Microstrip Loss Correlation
Hello All,
I am working on measuring the bandwidth of a couple fixtures and am
surprised
by the results. I am hoping that someone may be able to help shed some
light on
the subject. I have two fixtures that are identical other than the
materials. One board
is made of Isola's FR406 and the other is Arlon 25N. The only minor
difference is
that the stackup may have been changed slightly to accommodate for 50
ohm's on
12 mil trace widths. Four layer board, 2.8" total length traces, routed
only on the
top layer microstrip.
I have used edge launch sma's to interconnect to the network analyzer.
Johnson
Components 142-0701-801 PN. The issue is that when making an S21
measurement
across the 2.8" trace I see both boards have a 3db loss at approximately
2.4GHz.
Since I would obviously expect the Arlon 25N board to perform much further
out in
frequency one thing I am suspect of is the sma interconnect. I know that
the sma
footprint should be optimized and we have tried to do that by cutting away
some
GND under the signal conductor of the sma. It seems like it is still
causing an issue
though. Does anyone have any footprint or other recommendations?
Thank you,
Chris
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