  This paper documents a simple parametric polynomial line-of-sight channel
model for 100-450 GHz band. The band comprises two popular beyond fifth
generation (B5G) frequency bands, namely, the D band (110-170 GHz) and the
low-THz band (around 275-325 GHz). The main focus herein is to derive a simple,
compact, and accurate molecular absorption loss model for the 100-450 GHz band.
The derived model relies on simple absorption line shape functions that are
fitted to the actual response given by complex but exact database approach. The
model is also reducible for particular sub-bands within the full range of
100-450 GHz, further simplifying the absorption loss estimate. The proposed
model is shown to be very accurate by benchmarking it against the exact
response and the similar models given by International Telecommunication Union
Radio Communication Sector (ITU-R). The loss is shown to be within $\pm$2 dBs
from the exact response for one kilometer link in highly humid environment.
Therefore, the its accuracy is even much better in the case of usually
considered shorter range future B5G wireless systems.
