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. Random factors cannot be corrected by calibration but may be minimized through careful measurement methodology. The process of user calibration mostly corrects systematic errors but leaves some residual errors. A VNA measurement will be affected by both systematic and random errors. To understand the measurement uncertainty, or accuracy, it is important to understand the factors which contribute to it. A full metrologically sound measurement will have all three factors the value, the uncertainty, and the confidence interval of the uncertainty. ![]() The real value will lie within a larger window. There is a 5% chance that the real value is outside of these bounds, but it is usually possible to recalculate the uncertainty for 99%, or 3σ confidence. This is to say that the real reflection is between -31.5 and -32.5 dB with 95% (2σ) confidence. A typical reflection measurement might be -32 dB ± 0.5 dB (95% confidence interval). To be very meticulous, each measurement should be accompanied by an uncertainty with a specified statistical confidence interval. A Vector Network Analyzer (VNA) makes RF measurements of reflection coefficients.
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