  There is a growing interest in exploiting the terahertz frequency band for
future communication systems that demand high data rates. Given the complex
propagation behavior of this frequency band, various researchers have developed
channel models that can be utilized in the development of communication
systems. These models however do not include a crucial aspect of terahertz
propagation at short distances: the presence of standing waves. Our
measurements show that at specific distances, the effect of standing waves is
significant. In this paper, we extend previous terahertz channel models to
include the effect of standing waves and show a good fit with our measurements.
Our measurements and modeling cover the five most promising terahertz frequency
bands: 140, 220, 340, 410, 460 GHz.
