Comparison Between Two National Metrology Institutes of Diameters and Characteristic Impedance of Coaxial Air Lines

This paper summarizes a bilateral comparison of the measurements of the diameters of two precision coaxial air lines with a line size of 3.5 mm. These mechanical measurements were independently made by two national metrology institutes, i.e., the National Metrology Institute of Japan (NMIJ) and the National Physical Laboratory (NPL). The laboratories also calculated the characteristic impedance of each air line based on the measured diameter values. The difference between the characteristic impedances calculated by the two laboratories for both lines was less than 0.020 Omega. The uncertainty of this difference, at a 95% level of confidence for each line, was 0.084 and 0.307 Omega.