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The RI Systems have the capability to use imperfect calibration standards in their s-parameter calibration process as long as detailed s-parameter data is available for the imperfect standards. Imperfect calibration standards can be a very productive accuracy enhancement tool whenever the device under test does not interface through a standard coaxial connector. Devices on wafer or in complex packages may be more accurately measured when calibration standards in their native medium are used. These native but imperfect calibration standards must have their s-parameters measured accurately ( in an engineering lab for example ), then the RI system software can use the data in it's complex error correction mathematical routines to synthesize accuracy enhancement error correction files.

Note : The quality of these lab s-parameter measurements on the imperfect standards will completely determine the quality of the final calibration. Care should be taken to produce the best quality measurements with enough data points to accurately represent the function, including its imperfections.
The normal calibration process involves using a "near perfect" precision coaxial open, short and load standards that have been modeled and this model has been built into the RI 7100A's Calibration Kit software object. When we would like to use imperfect calibration standards, we must replace this embedded model of the calibration standards with our measured s-parameter data (which in effect is a measured "model" of that specific standard).

RI 7100

To begin we start with a new "RI Cal Kit" object from the Instruments container window, select instrument type "Ri5020A Calibration Kit"( or make a copy of an existing one) and name it so as to be understandable to users as what this calibration data includes. Place the mouse over the new Icon and click the RMB ( right mouse button ) and select Calibration Inspect.


Cassini

Click the "System" button and then the "Tester" button to get a view of the current tester. Add an existing CalKit with the menu selection "Instrument/Add CalKit...". Start with an existing cal kit and then copy it by choosing "Instrument/Retitle..." and entering a new title for the cal kit. After choosing a new title, select "Instrument/Calibration/Save" to save the new version back to Guru. Now open the calibration inspector below by choosing "Instrument/Calibration/Inspect".


All Testers

The system will list the attributes of the four standards, enr table, load, open, and short. We need to modify the attributes of the load, open and short to be s-parameter type files and then load the files with data from the measurements of the new standards. Click the LMB on the first standard ( load ) and in the window to the right of it you will see . You will need to highlight this and then replace it with the following line " RiFrVs1pS new: 2". When you are finished typing RMB and select SAVE. This statement defines a new data type of "Roos Instruments Frequency Vs 1 Port S-parameter" and it will have "2" entries to start. ( see below )



Repeat this data type redefinition procedure for all three standards, open and short as well. To load the measured s-parameter data, RMB click on the name of the standard ( load, open or sort ) and select "load Item". ( see Below )



The system will present a pick list of the different data formats that are supported ( we recommend Touchstone Format/ Sxx where the xx is replaced with either 11 or 22 depending o how your data file is structured. i.e. is the one port s-parameter data indicated as S11 or S22? ) then select the format and load your corresponding data file. ( see Below )



This then brings up a standard OS/2 file dialog box for you to pick the location and file name to be loaded. Repeat this file load procedure for all the three standards....Load, Open and Short.

After you have loaded all the s-parameter data, you should convert them to a spline. This ensures valid calibration points at any frequency as long as they fall within the start and stop frequencies of the original data. To initiate the spline interpolation, RMB click on the name of the standard (load, open or short) and select "Convert to Spline".The system will display a dialog box that asks you to chose the Independent variable, select frequency ( see Below )



Repeat this file convert to spline procedure for all the three standards....Load, Open and Short and then close the Calibration Inspect dialog box.
Now RMB click on the Cal Kit icon and select Save. The new Cal Kit is ready for use with your Imperfect Cal standards.

Remember to Save your calibration data!

The data type recommended is Touchstone format that is ascii and has a file extension .S2P or .S1P. Below is an example .S2P file:

! 1 port open data taken at 10 points
#Hz S MA R 50
! Frequency,open_s11.wfm (dBMag),open_s11.wfm (Phase)
200000000 1.005545901 -31.996 0 0 0 0 0 0
400000000 1.001188725 -66.15 0 0 0 0 0 0
600000000 1.040934733 -98.037 0 0 0 0 0 0
800000000 0.972613963 -128.62 0 0 0 0 0 0
1000000000 0.966660561 -165.69 0 0 0 0 0 0
1200000000 1.066248664 164.51 0 0 0 0 0 0
1400000000 0.982206944 135.54 0 0 0 0 0 0
1600000000 0.972372124 96.944 0 0 0 0 0 0
1800000000 1.085877914 66.803 0 0 0 0 0 0
2000000000 1.010357571 35.261 0 0 0 0 0 0


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