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.

Wireless backhaul links, already ubiquitous and expanding further with 5G and beyond, are employed for many critical functions, such as financial trading on Wall Street. In this work, we demonstrate for the first time that such links are acutely vulnerable to a new class of aerial metasurface attacks. In particular, we show how an adversary Eve designs and employs MetaFly to covertly manipulate the electromagnetic wavefront of the signals and remotely eavesdrop on highly directional backhaul links. Exploring the foundation of the attack, we demonstrate Eve’s strategy for generating eavesdropping diffraction beams by inducing pre-defined phase profiles at the aerial metasurface interface. We also show how Eve’s flight navigation approach can dynamically shape radiation patterns based on drone mobility via a wavefront-tailored flight refinement principle. We prototype MetaFly and demonstrate Eve’s lightweight, low-cost, transmissive, and power-free aerial metasurface. We implement the attack and perform a suite of over-the-air experiments in both a large indoor atrium and outdoor rooftops in a large metropolitan area. The results reveal that armed with MetaFly, Eve can intercept backhaul transmissions with nearly zero bit error rate while maintaining minimal impact on legitimate communication.