Agilent Technologies 87075C manual Test Set Cal and SelfCal Theory of Operation, Chapter

Test Set Cal and SelfCal

Test Set Cal and SelfCal: Theory of Operation

Test Set Cal and SelfCal: Theory of Operation

Adding a multiport test set to the analyzer degrades raw performance of the test system as well as introduces drift. Test Set Cal provides the vector error correction that allows the system to achieve good performance. A Test Set Cal is a calibration that is performed on a regular, but infrequent basis. The results of the Test Set Cal are used by the SelfCal feature to remove the drift associated with the hardware of the test set and analyzer to return the multiport system to an accurately calibrated state.

There are two steps to the Test Set Cal:

•The first step requires you to connect calibration standards (from a calibration kit) and your own through-cables to the calibration reference plane. The analyzer measures the known reference standards and uses those measurements to compute error correction coefficients.

•The second step occurs once you are done measuring the calibration standards and store the Test Set Cal data. The multiport test set contains electronically switched open, short, load, and through standards behind each port. (See Figure 3-3. This illustration depicts a two-port test set. The same internal standards are also included behind every port of your test set.) These standards are very stable, yet their calibration definitions are not known like the mechanical standards. During this second step, the analyzer makes a measurement of each internal standard and then, using the error coefficients that were computed from the measurements of the external standards, derives a very accurate calibration definition for each internal standard. Once this has been done, the internal standards act as “transfer standards” for future automatic calibrations called SelfCals.

Chapter 3 45