Vector Network Analyzer Calibration Options For Ensuring Measurement Accuracy In The Field

By Afsi Moaveni, Agilent Technologies

Installation, troubleshooting, and maintenance of RF and microwave systems and components requires measurement of their reflection and transmission characteristics within a variety of indoor and outdoor environments and conditions, some of which can be quite extreme. One day the measurements may need to be taken in an area with freezing temperatures, the next, at very high elevation, such as on top of an outdoor tower and mast installation. Even measurements taken in shipboard, aircraft, or vehicle applications can be problematic, as they may require the engineer or technician to operate in small, confined spaces. Typically, these measurements are made using a handheld vector network analyzer (VNA) having a user calibration that is performed in the field.

Calibration is necessary to remove the effects of cables and adapters placed between the instrument and the device under test (DUT) when measuring the S-parameters of components and systems. Selection of the appropriate calibration type is often a trade-off between measurement accuracy, speed, and complexity of the calibration process. Making the right decision is critical, since the VNA’s measurement accuracy is directly influenced by the type of user calibration selected. Luckily, recent advances in VNA calibration now present operators (engineers and technicians) with a number of compelling options.

The Basics
Due to the extreme conditions under which engineers and technicians must often make their measurements in the field, measurement accuracy, calibration convenience, sweep speed, and analyzer portability must all be considered when selecting an infield measurement solution. When using a VNA, the measurement accuracy will be dependent on the user calibration selected, as well as the associated test configuration. The VNA hardware determines how the DUT is measured, either in the forward direction only using a transmission/reflection (T/R) hardware configuration, or in both the forward and reverse directions using a full two-port configuration.