Accuracy analysis for six-port automated network analyzers

One of the assumptions made in six-port automated network analyzer (ANA) theory is that the reflection coefficient of the power detectors does not change with incident power level. This is not generally the case if diode detectors are used. Consequently, uncertainties in the measurement of the reflection coefficient of the unknown load appear because the calibration constants vary due to the variation of the detector reflection coefficients with power. Measurements of the variations of diode input impedance using commercial ANAs are used in a computer simulation to estimate their uncertainties