The auto calibration process represents both a calibration kit and an algorithm that can be used to speed up the calibration process with extremely high accuracy and a minimal number of manual steps.

The 36585X AutoCal module calibrates the VNA by a process known as “transfer calibration.” There are a number of impedance and transmission states in the module designed to be extremely stable in time and these states are carefully “characterized,” generally by the Anritsu factory but also in a customer laboratory in certain cases. When the same states are re-measured during an actual calibration, and the results compared to the characterization data, an accurate picture can be generated of the behaviors and error terms of the VNA and setup being calibrated.

A very high calibration accuracy is maintained through the use of certain principles:

The resulting accuracy can exceed that obtained with a typical mechanical calibration performed in a laboratory. The AutoCal results may not be better than that of an exotic manual calibration (such as is performed during factory characterization) but will be far better than that done typically. Since it is a very high performance calibration, connector care is of the utmost importance and is discussed in detail later in this chapter.

The AutoCal consists of the calibration module itself, a separate external power supply, a control cable that runs to the VNA, and the characterization data provided on a USB memory device.

Of the various calibration types described for the instrument, most are available with the AutoCal unit. Frequency response calibrations are omitted since the AutoCal unit would provide no benefit in these cases (since only a through or high reflect standard is needed for these calibrations). Available calibrations include: