Correction for line length errors and center-conductor-gap variation in the coaxial multiline through-reflect-line calibration

We present an extension of the coaxial multiline through-reflect-line calibration method which allows to correct for line length errors and center-conductor-gap variation. Our approach is based on the multi-frequency formulation of the vector-network-analyzer calibration problem which accounts for the physical relationships between calibration standard S-parameters at different frequencies. We illustrate our approach with experimental results for the coaxial multiline through-reflect-line calibration in the 7 mm standard. We show that our calibration method yields an improved measurement accuracy as compared with the classical multiline through-reflect-line calibration method.