DESIGN OF THE CALORIMETER
We have already reported a wideband calorimeter exploiting 7 mm and 2.92 mm coaxial waveguides in the frequency range from 10 MHz to 40 GHz [1]. However, an RW is more generally used at higher frequencies. Therefore, we designed a new calorimeter exploiting the WR-10 and WR-15 RWs. The combination of both RWs enables ultra-wideband operation ranging from 50 GHz to 110 GHz.
Figure 1 shows a schematic of the internal structure of the calorimeter. There is a columnar temperature reference block at the center of the calorimeter. Thermoelectric elements used for cooling RF loads and for measuring the temperature difference are mounted on the block. Absorber mounts (AMs) for the WR-10 and WR-15 RWs are attached on aluminum plates that bridge these thermoelectric elements. The RF loads are connected to the 15-mm-long WR-10 and WR-15 adiabatic lines (ALs). Then, two precision straight sections of 50 mm length are connected to the ALs. The flange of each straight section is used as an RF test port. These components are compactly installed in a double cylindrical jacket of 140 mm