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Microstrip TRL Calibration in E8363B PNA

Question asked by mikekoba on Sep 28, 2009
Latest reply on Oct 10, 2010 by mark521
Hello,

I am trying to conduct a TRL calibration in order to measure some power transistors for load-pull testing.  I have constructed my microstrip line with a taper to transition smoothly from 50ohms to 6ohms to accommodate for the transistor tab size. However, after I set up my TRL cal kit and conduct the calibration, I find a strange resonance for the LINE standard as seen in the plot.  This resonance is apparent on all the TRL standards, but it is the most abnormal with the LINE.

I have constructed three standards for this TRL cal. All connectors are APC 7mm and the transmission lines are made on microstrip.
1. THRU (two identical tapers connected abut)
2. LINE (two identical tapers connected abut with a piece of 1/4-wave line placed inline)
3. SHORT (the taper is shorted to ground)

I believe the resonance is not real, and that it is an artifact of the TRL algorithm because I am a bit confused at how to set up the cal kit properly in the PNA.  I know the fixtures do not resonate because I have calibrated to the APC 7mm connector planes and I have looked at each of the standards, and they behave just like how I expected them to and it conforms to simulated results.  Can somebody outline the steps necessary for setting up the PNA cal kit correctly?  These are the steps I took, but I have a feeling that I am doing it incorrectly:

1. Created new Cal Kit with APC 7mm connectors by going to Calibration > Advanced Modify Cal Kit
2. Added a THRU standard with 0 delay, 0 loss, and 6ohm impedance; named THRU.
3. Added a SHORT standard with 0 delay, 0 loss, and 6ohm impedance; named REFLECT.
4. Added a THRU standard with 187.12ps delay, 0.18248 Gohm/s loss, and 6ohm impedance; named LINE.
5. Changed the pull down menu to TRL in the Class Assignments to edit the tables
6. Calibration Reference Z0 is set to LINE Z0, and Testport Reference Plane is set to THRU STANDARD.
7. For Cal Kit Class TRL THRU, I selected the THRU label standard and moved it to the Selected Standards Table.
8. For Cal Kit Class TRL REFLECT, I selected the REFLECT label standard and moved it to the Selected Standards table.
9. For Cal Kit Class TRL LINE/MATCH, I selected the LINE Label standard and moved it to the Selected Standards table.

I save this cal kit and use it with the smart Cal method by going to Calibration > Calibration Wizard > SmartCal, but after doing these steps, I get this funny resonance as seen in the plot for the LINE standard.  Can anyone help to clarify what I am doing incorrectly?  

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