Mismatch uncertainty evaluation in precision RF attenuation measurement

A practical technique to apply the mismatch loss correction in radio frequency (RF) attenuation measurements of fixed attenuators as well as variable attenuators as devices under test is presented. The correction factor is obtained by measuring the reflection coefficients of the source and load testing ports, and the devices under test using a vector network analyzer. The formula to express the residual uncertainty of this correction is derived by implementing the law of error propagation after modifying the general mismatch loss equation. The solution is also given; hence the uncertainty of the obtained mismatch correction is simply estimated and used. Experimental results on a 10-dB step attenuator measurements at frequencies of 1 GHz to 18 GHz show good agreement with measurements where the source and load are impedance matched. © 2011 The Institute of Electrical Engineers of Japan.