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Use of Offset Load when Building TRL Cal Kit

Question asked by VNA123 on Aug 11, 2015
Latest reply on Aug 17, 2015 by Dr_joel
Wish I had AFR. Maybe soon.

Until then, I'm using TRLM calibration to eliminate a 42.5Ohm test fixture the best I can. I use a zero length Load standard to take care of frequencies 10MHz-400MHz. Problem is my s-parameters at that frequency region are complete junk. VNA -> 50Ohm Coax Lines -> 50Ohm SMA -> 50Ohm Via -> 42.5Ohm Trace -> 42.5Ohm Load. That's the Measurement. There's another Load on the board. So it's like this (x are smas)

(1) X---------------------------------------------------X                                                  =  Primary Thru 2xTHRU
(2) X-----------------------Load                                                                               = Load Standard I use  (Has a trace 1x Trace Length from SMA to load)
(3) X------------------------------------------------------------------------------Load           = Load Standard that is that has length of (1)+(2)

Never have issues with LRM for 50Ohm fixtures. I read in Dr. Joels book about using offset loads as a way of fixing these kinds of situations (I think), since fixed loads are suppose to be close to perfect (I think). I have noooo clue what I'm doing in this situation and assuming makes an.... well you know.

Is there any way I can use this extra standard on the cal board provided to me to get decent cal in this region (10MHz-400MHz)?

Thanks,
KTB  

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