Improvement in the evaluation of a rectangular waveguide microcalorimeter correction factora

The correction factor of the National Institute of Standards and Technology´s WR-15 (50 to 75 GHz) microcalorimeters has been re-evaluated. Use of modeled values for the reflection coefficient of a flat short and offset short instead of measured values results in lower uncertainties in the evaluation of the calorimeter correction factor obtained with these artifacts. The uncertainties are now comparable to that of an evaluation technique in which two calorimeter cores are directly connected to each other. Improvements in a fourth technique were also achieved with an improved measurement of the transmission coefficient of a line section. The differences in the derived correction factors are a little larger than would be expected based on the uncorrelated uncertainties. The source of the discrepancy has not been determined.