Hi All, I'm looking for help from someone who has gone through the in-fixture calibration routine for a Vector Network Analyzer. For this discussion, I would like to use as a reference Agilent application note 1287-9, "In-Fixture Measurements Using Vector Network Analyzers". This application note can be found on the Agilent web site: www.agilent.com.
I am using a test fixture that looks like the one in Figure 10 of the application note. The fixture card was designed using the design guides recommended by Agilent. All traces are 50 ohms. The short standard is terminated in the center of the board. The open and load standards are the same length as the short. The thru trace is twice as long as the short. The load is designed with two 100 ohm resistors in parallel. The Network Analyzer I am using is the Agilent(HP) 8753D. My problem is in trying to determine the coefficients for the polynomial equation that describes the fringing capacitance of the open standard as described on page 13 of the application note. The polynomial equation is C0 + C1*F + C2*F(squared) + C3*F(cubed) where C0, C1, C2, and C3 are the coefficients and F is frequency. The units of C0 are 1e-15 farads. The units of C1 are 1e-27 farads/Hz. The units of C2 are 1e-36 farads/Hz(squared). The units of C3 are 1e-45 farads/Hz(cubed). Per the instructions on pages 13 and 14 of the application note, I measured the following capacitances in femto farads (1e-15) from the Smith Chart. The format of the data below is frequency in MHz followed by capacitance in femto farads. 10, 380 50, 324 100, 307 200, 300 400, 270 600, 246 1000, 214 1500, 150 2000, 70 2500, 23 3000, 2 3500, 14 4000, 86 4500, 165 5000, 279 5500, 208 6000, 148 I created an Excel file that uses the polynomial equation mentioned earlier to try to curve-fit the data. (I can forward the Excel file to anyone who would like to see it.) From the Excel file, I arrived at the following numbers for the coefficients: C0 = 350 C1 = -200,000 C2 = 22,000 C3 = 2000 These coefficients did not provide and exact fit but it was close. I then entered the coefficients into the calibration table of the Network Analyzer. When I entered the values for C1 and C2, the Network Analyzer truncated the entries to 10,000. This leads me to believe there is something wrong with my numbers. If anyone can find a flaw in my approach, I would greatly appreciate your comments. The calibration did not work with the truncated numbers. After my attempted calibration, when I looked at the open standard on the Smith Chart of the Network Analyzer, it looked inductive. There was an arc on the perimeter of the Smith Chart above the horizontal center line. Thanks in advance. Allen Tudor _________________________________________________________________ Is your PC infected? Get a FREE online computer virus scan from McAfee® Security. http://clinic.mcafee.com/clinic/ibuy/campaign.asp?cid=3963 - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Jim Bacher: [email protected] David Heald: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
