where Pd is the reading of the PUT, Pdm is the reading of the monitoring power meter, g is the reflection coefficient of the isolator, s is the reflection coefficient of the calorimeter and d is the reflection coefficient of the PUT.
EVALUATION OF EQUIVALENCE ERROR
A small reflection coefficient and a low equivalence error (EE) do not necessarily coexist for a waveguide calorimeter [2]. A new approach was employed to achieve a low EE by consideration of the fact that the EE is mainly caused by frequency-dependent distribution of power dissipation. Generally speaking, a small reflection coefficient is essential for most calorimeters to achieve a superior signal to noise ratio (SNR). However, we thoroughly compromised on this performance measure by employing a flat-structured mm-wave absorber (FMA). On the one hand, fully embedding this FMA in the AM makes it possible to minimize the EE. On the other hand, it makes the reflection coefficient of the calorimeter s extremely large. The absolute value of the reflection coefficient | s | typically reaches more than 0.8,