AnsweredAssumed Answered

Unknown Thru vs LRM

Question asked by jimn on Feb 1, 2011
Latest reply on Feb 3, 2011 by jimn
I have a PNA-L, N5230C Option 010, 240, Application Code A.09.20.08

I am measuring passive DUT's (connectors) and routinly use LRM calibration to 20 GHz.  My test fixture is FR-406 PCBs with on-board standards.  RL and IL of the standards are OK for LRM cal to 20 GHz and generally I get good results.

But I do see some discontinuites at the band transition frequencies, characteristic of LRM cals.  So I am motivated to check out the unknown thru cal method.

I think I need to do a Global Delta Match and I saw some guidelines on that.  For the unknown thru I was planning to use ecal for the SOL and then use the onboard thru as the unknown thru.  My expectation is that the reference plane will be located at the same location as with my LRM cal.

I saw that the assumption on the unknown thru is that it is symmetric (S11=S22).  The unknown thru can have quite a bit of loss (40 dB).

Finally - my questions...

  1. Does the above sound correct?  What am I overlooking?
  2. Have others tried this with success?
  3. Any guidelines on symmetry of the unknown thru standard?  If it has to be symetric within 0.1 dB to 20 GHz, there is no point in attempting this.