Published by Eric Bogatin on 11 Dec 2012
Our newest class, Hands on Workshop for S-Parameter Measurements (HOW-SPM), was created to teach these valuable measurement and analysis skills. We just finished our first class and it was a wonderful success.
This class was limited to only 12 students and filled up in the first 2 weeks after it was posted. Our next class on March 1, will also fill quickly.
Pairs of students shared a SPARQ, Signal Integrity Network Analyzer from Teledyne LeCroy, operating up to 40 GHz. All the principles and techniques we taught applied to ANY VNA. We limited attendance to 12 students total, so that everyone would get stick time and individual attention from our expert instructors. During the course of the day, everyone measured a variety of samples, each illustrating different measurement and analysis principles.
A range of quality level 50-Ohm cables were measured to show the wide difference in bandwidth of good and bad cables, and the role of the connectors. We used port re-normalization to change the port impedances to view 75 Ohm cables and de-embedded the launches to show the impact at low frequency from the the port impedance, and the influence at high frequency from the connectors.
Don DeGroot of CNN Labs, designed and built a really cool test vehicle for the class. This board will be available for sale by CCN Labs in early 2013.
We looked at non-uniform and uniform lines with good and bad launches, in microstrip and stripline, as single ended and as differential. It was obvious looking at the first few measurements how strong a role the launches played above about 2 GHz. By de-embedding them low return loss measurements could be obtained up to 15 GHz, the limit to the $4 SMAs we used on the board.
One of the special exercises we did was to export the measurements from the test board as touchstone files and bring them into an analysis tool to extract the Dk and Df over frequency. All students saw that the Dk was strongly affected by the launches above about 2 GHz. This is one example where de-embedding is so important and why we focused an entire module just on how to perform fast and accurate de-embedding, and equally important, how to verify the quality of the de-embed file.
If you want to improve your VNA measurements, you really need to check out this class. Our next one is on March 1, in Longmont, CO. It will fill quickly so you’ll want to sign up early. Hope to see you there!