Introduction to the Metrology of VNA Measurement

A Vector Network Analyzer (VNA) makes RF measurements of reflection coefficients. To be very meticulous, each measurement should be accompanied by an uncertainty with a specified statistical confidence interval. A typical reflection measurement might be -32 dB ± 0.5 dB (95% confidence interval). To understand the measurement uncertainty, or accuracy, it is important to understand the factors which contribute to it. A VNA measurement will be affected by both systematic and random errors.The process of user calibration mostly corrects systematic errors but leaves some residual errors.Random factors cannot be corrected by calibration but may be minimized through careful measurement methodology.

This paper will describe the types of calibration that might be employed,the errors which these methods correct, the residual errors which remain, the mitigation of random errors, and how to estimate the uncertainty of a measurement taking all of these things into account.