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1. Conformal leaky-wave antennas for wireless terahertz communications

   https://doi.org/10.1038/s44172-023-00067-2  

   Guerboukha, Hichem; Shrestha, Rabi; Neronha, Joshua; Fang, Zhaoji; Mittleman, Daniel M. (December 2023, Communications Engineering)

   Abstract Future generations of wireless systems are expected to combine the use of high-frequency bands (the terahertz range) with smart interconnected devices (the Internet of Things). To realize this ambitious merging, systems will require antennas that can be mounted on nonplanar objects while generating highly directional beams. Here, we study conformal THz leaky-wave antennas at THz frequencies. We find a rich set of behaviors accessible at THz frequencies dictated by the interplay among the geometrical parameters and the wavelength. We develop simple models to describe the relevant physics, which we verify by an experimental implementation. We also demonstrate data transmission using a conformal THz antenna that can generate multiple high-gain beams with low bit error rates for increased coverage of THz wireless links. 

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2. The effect of angular dispersion on THz data transmission

   https://doi.org/10.1038/s41598-022-15191-w  

   Shrestha, Rabi; Fang, Zhaoji; Guerboukha, Hichem; Sen, Priyangshu; Hernandez-Cardoso, Goretti G.; Castro-Camus, Enrique; Jornet, Josep M.; Mittleman, Daniel M. (December 2022, Scientific Reports)

   Abstract One of the key distinctions between legacy low-frequency wireless systems and future THz wireless transmissions is that THz links will require high directionality, to overcome the large free-space path loss. Because of this directionality, optical phenomena become increasingly important as design considerations. A key example lies in the strong dependence of angular radiation patterns on the transmission frequency, which is manifested in many different situations including common diffraction patterns and the emission from leaky-wave apertures. As a result of this effect, the spectral bandwidth at a receiver is nonlinearly dependent on the receiver’s angular position and distance from the transmitter. In this work, we explore the implications of this type of effect by incorporating either a diffraction grating or a leaky wave antenna into a communication link. These general considerations will have significant implications for the robustness of data transmissions at high frequencies. 

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3. Arbitrary aperture synthesis with nonlocal leaky-wave metasurface antennas

   https://doi.org/10.1038/s41467-023-39818-2  

   Xu, Gengyu; Overvig, Adam; Kasahara, Yoshiaki; Martini, Enrica; Maci, Stefano; Alù, Andrea (December 2023, Nature Communications)

   Abstract The emergence of new technological needs in 5 G/6 G networking and broadband satellite internet access amplifies the demand for innovative wireless communication hardware, including high-performance low-profile transceivers. In this context, antennas based on metasurfaces – artificial surfaces engineered to manipulate electromagnetic waves at will – represent highly promising solutions. In this article, we introduce leaky-wave metasurface antennas operating at micro/millimeter-wave frequencies that are designed using the principles of quasi-bound states in the continuum, exploiting judiciously tailored spatial symmetries that enable fully customized radiation. Specifically, we unveil additional degrees of control over leaky-wave radiation by demonstrating pointwise control of the amplitude, phase and polarization state of the metasurface aperture fields by carefully breaking relevant symmetries with tailored perturbations. We design and experimentally demonstrate metasurface antenna prototypes showcasing a variety of functionalities advancing capabilities in wireless communications, including single-input multi-output and multi-input multi-output near-field focusing, as well as far-field beam shaping. 

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4. Mobile near-field terahertz communications for 6G and 7G networks: Research challenges

   https://doi.org/10.3389/frcmn.2023.1151324  

   Petrov, Vitaly; Bodet, Duschia; Singh, Arjun (March 2023, Frontiers in Communications and Networks)

   Following the current development of the wireless technology landscape, and with respect to the constant growth in user demands, it is inevitable that next-generation mobile wireless networks will use new frequency bands located in the sub-terahertz and terahertz (THz) spectrum to complement the existing microwave and millimeter wave (mmWave) channels. The feasibility of point-to-point stationary THz communication links has already been experimentally demonstrated. To build upon this breakthrough, one of the pressing research targets is making THz communication systems truly mobile. Achieving this target is especially complicated because mobile THz wireless systems (including WLANs and even cellular access) will often operate in the near-field due to the very large (even though physically small) electrical size of the high-gain antenna systems required for making high-rate communication links feasible at such frequencies. This perspective article presents several key prospective research challenges envisioned on the way to designing efficient mobile near-field THz wireless access as a part of 6G and 7G wireless landscapes. 

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5. Security in Terahertz WLANs with Leaky Wave Antennas

   Yeh, Chia-Yi; Ghasempour, Yasaman; Amarasinghe, Yasith; Mittleman, Daniel M; Knightly, Edward W. (January 2020, Proceedings of the 13th ACM Conference on Security and Privacy in Wireless and Mobile Networks (WiSec))

   This paper presents the first security study of THz networks with Leaky Wave Antennas (LWAs). We employ a mix of analytical models and over-the-air experiments to explore the unique security properties of LWA links. We show via both models and experiments that the LWA’s angle-frequency coupling leads to non-uniform secrecy capacity across sub-channels yielding advantages to an eavesdropper at edge frequencies. Yet, because different frequencies emit energy at different angles, the eavesdropper is thwarted from easily intercepting an entire wideband transmission. The experiments diverge from the analytical model in that the model underpredicts the eavesdropper’s advantage at angles smaller than the target user and subsequent asymmetric performance across angles. Nonetheless, both the model and measurements show that increasingly wide bandwidth and correspondingly wide beams have only a modest marginal security penalty. 

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