A Circular Multipass Cell-Based Measurement Platform for Characterizing Atmospheric Propagation Attenuation in the Terahertz Band

This paper proposes a closed experimental platform based on a Circular Multipath Cell (CMC) to quantitatively measure terahertz (THz) atmospheric attenuation characteristics under various environmental conditions. The proposed system realizes a long propagation path of 16.61 m through 26 internal reflections within a compact chamber, thereby simultaneously overcoming the spatial constraints of existing long-path experiments and the sensitivity limitations of small cells. Measurement results in the 330–490 GHz band under precisely controlled relative humidity (20–90%, ±0.5%) showed high agreement with the ITU-R P.676-13 model and demonstrated that stable measurements are possible even at high attenuation levels, which are difficult to implement in open environments. With its structural flexibility and precise environmental control capabilities, the CMC platform is expected to serve as a key tool for future 6G channel modeling and atmospheric propagation research.