I. Introduction
Microcalorimeters were proposed in the late 1950s to realize the electromagnetic power standard at high frequency [1]. This primary level measurement system is used to measure a temperature change due to the power loss of a thermistor mount as a dc voltage, and to measure the radio frequency (RF) power of the applied electromagnetic field using a thermistor mount and Wheatstone bridge. The effective efficiency of the thermistor mount is calculated from these two measurements [2].