Impact of the Antenna on the Sub-Terahertz Indoor Channel Characteristics: An Experimental Approach

TL;DR

This work addresses how sub-THz antennas reshape indoor channels by conducting a measurement campaign at 130–150 GHz with multiple receiver beam widths. It demonstrates that path loss, K-factor, RMS delay spread, and angular spread depend on antenna directivity in ways that standard antenna-agnostic models fail to capture, due to near-field and waveguide-tunneling effects. The authors provide simple parametric relations linking path loss exponent, K-factor, and delay spread to antenna gain, and offer a Gaussian-beam interpretation to explain effective aperture effects. The findings highlight the need for antenna-aware channel models and real-time beam adaptation in 6G/sub-THz systems, and motivate extending datasets to diverse indoor/outdoor/aerial scenarios for robust THz link design.

Abstract

Terahertz-band (100 GHz-10 THz) communication is a promising radio technology envisioned to enable ultra-high data rate, reliable and low-latency wireless connectivity in next-generation wireless systems. However, the low transmission power of THz transmitters, the need for high gain directional antennas, and the complex interaction of THz radiation with common objects along the propagation path make crucial the understanding of the THz channel. In this paper, we conduct an extensive channel measurement campaign in an indoor setting (i.e., a conference room) through a channel sounder with 0.1 ns time resolution and 20 GHz bandwidth at 140 GHz. Particularly, the impact of different antenna directivities (and, thus, beam widths) on the channel characteristics is extensively studied. The experimentally obtained dataset is processed to develop the path loss model and, subsequently, derive key channel metrics such as the path loss exponent, delay spread, and K-factor. The results highlight the multi-faceted impact of the antenna gain on the channel and, by extension, the wireless system and, thus, show that an antenna-agnostic channel model cannot capture the propagation characteristics of the THz channel.

Figures (7)

• Figure 1: The NU Channel Sounder System with a) transceiver hardware, b) rotatory table hardware, c) signal processing backend, and d) THz frequency absorption meterial. The conference room details, i.e., the sounding environment, including e) layout, f) picture, and g) legend.
• Figure 2: Path Loss with varying antenna gain (beam width) with experimental (EXP) and curve fitted (CF) value.
• Figure 3: Experimental and curve-fitted channel parameters with varying antenna gains for the conference room.
• Figure 4: Beam profile from a 15 dBi antenna: (a) propagation; (b) cross-sectional amplitude; and (c) cross-sectional phase. The cross-sectional cut is at 1 m.
• Figure 5: CDF of K-factor with different antenna gain for EXP result (dotted line) and its CF (solid line) with $\mu$, and $\sigma$ of log-normal distribution.