Sub-Terahertz Channel Sounder: Review and Future Challenges

Due to the large amount of unused and unexplored spectrum resources, the so-called sub-Terahertz (sub-THz) frequency bands from 100 to 300 GHz are seen as promising bands for the next gen-eration of wireless communication systems. Chan-nel modeling at sub-THz bands is essential for the design and deployment of future wireless communi-cation systems. Channel measurement is a widely adopted method to obtain channel characteristics and establish mathematical channel models. Channel mea-surements depend on the design and construction of channel sounders. Thus, reliable channel sounding techniques and accurate channel measurements are re-quired. In this paper, the requirements of an ideal channel sounder are discussed and the main chan-nel sounding techniques are described for the sub-THz frequency bands. The state-of-the-art sub-THz channel sounders reported in the literature and re-spective channel measurements are presented. More-over, a vector network analyzer (VNA) based channel sounder, which supports frequency bands from 220 to 330 GHz is presented and its performance capability and limitation are evaluated. This paper also discussed the challenge and future outlook of the sub-THz chan-nel sounders and measurements.