  This paper describes hardware and software improvements of the INRIM coaxial
microcalorimeter together with their outcome on the primary power standard
realization in the frequency band 0.05 - 40 GHz. A better temperature and power
stabilization turned out to provide an improved signal/noise ratio and a drift
reduction in every working condition of the microcalorimeter. The INRIM
correction model is also compared to a traditional, but faster, one in terms of
measurement uncertainty. Outcomes are presented in form of a 2.92 mm
thermoelectric power sensor calibration together with results that show the
improved stability and repeatability of the measurement system.
