Electronics > RF, Microwave, Ham Radio
Converting Single ended to Differential Insertion Loss. Possible?
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hazuki:
Hi all,
I have a project where I am trying to measure the differential insertion loss of a pair through a system with a VNA and then compare that to the basic model of the system where insertion losses for each component (connector, microstrip lines, cables, etc) are tabulated for each frequency and then simply added up. I am at a loss however to determine how single ended insertion loss compares to differential insertion loss when generating this table. For instance, I have single ended insertion loss per inch data for a particular dielectric that I am running differential microstrip over, but how do I translate this into a differential insertion loss per inch? I feel as though I would need some more information..
Thanks
Earendil:
According to http://www.magazines007.com/pdf/DC10_Loyer_Kunze.pdf:
"Measuring differential insertion loss (SDD21) historically requires a 4 port VNA or TDT measurement, typically with 2 ports measured at one location, while the other 2 ports are measured at another location."
"SDD21 is derived from four singleended measurements as SDD21=0.5*(S21-S23-S41+S43)."
"For ideal symmetric traces, S21 ~ S43 and S41 ~ S23. The equation then simplifies to SDD21 = S21 – S41.
"In actual manufacturing, the traces won’t be perfectly symmetrical."
As for your last question in my opinion the answer depends on the differential pair's properties and cannot be answered generally.
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