[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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