A Calorimeter for Power Measurements at Millimeter Wavelengths

A calorimeter for measuring low-level power at millimeter wavelengths is described. This is a broadband device capable of measuring power levels of the order of one milliwatt with an estimated accuracy of plus or minus 1/4 db. The calorimeter utilizes the substitution principle by matching the temperature rises of two identical power absorbers, in one of which is dissipated the unknown high frequency power while the other is heated by a measured amount of direct current power.