Yasaman Ghasempour

Wireless networks operating in the millimeter-wave and sub-terahertz regimes typically rely on highly directional pencil beams to overcome severe path loss, making initial access and link discovery a critical bottleneck in the control plane. Existing approaches either employ iterative beam scanning, which incurs substantial latency, or create angle-dependent spectral signatures, which require large bandwidths and additional hardware complexity. Here, we introduce a fundamentally new paradigm for link discovery: single-shot, narrowband beam acquisition enabled by space–polarization encoding. The key insight is to harness anisotropic electromagnetic scattering in a carefully engineered metasurface to encode spatial directions into distinct polarization signatures. Specifically, a transmissive metasurface radiates angle-dependent polarization patterns while a dual-polarized receiver extracts lightweight features from a single narrowband measurement to directly infer the optimal beam direction without any beam sweeping. We establish a physics-grounded framework that links electromagnetic wave manipulation and polarization transformation to link discovery performance, enabling the systematic design of metasurfaces that generate robust and distinguishable polarization signatures across space. We validate this framework through full-wave simulations and extensive over-the-air experiments at 140 GHz, demonstrating accurate localization. Our results show how a deep understanding of electromagnetic can be translated into practical metasurface designs and establish a new pathway for low-latency link adaptation in high-frequency mobile wireless networks.

The ever-growing demand for ultra-high data rates, massive connectivity, and joint communication-sensing capabilities in future wireless networks is driving research into sub-terahertz (sub-THz) communications. While these frequency bands offer abundant spectrum, they also pose severe propagation and hardware design challenges, motivating the search for alternative antenna solutions beyond conventional antenna arrays. Leaky-wave antennas (LWAs) have emerged as a promising candidate for sub-THz systems due to their simple feed structure, low fabrication cost, and inherent angle-frequency coupling, which enables frequency-controlled beamsteering with simple hardware. In this article, we review the fundamentals of the LWA technology, highlight their unique properties, and showcase their potential in multi-user wideband sub-THz wireless communications. We present representative studies demonstrating that LWAs can simultaneously support high-rate multi-user communications and accurate localization using only a single antenna element. Finally, several key open challenges are outlined, spanning algorithm design, signal processing, information theory, standardization, and hardware implementation, that need to be addressed to fully harness LWAs as a cost-effective and scalable enabler of next-generations of wireless systems.

In sub-Terahertz (sub-THz) wireless networks, the radiative near-field regime can no longer be ignored. Indeed, this less-explored electromagnetic regime can provide unprecedented opportunities to tackle the long-standing challenges of sub-THz wireless communication, including using focused beams to combat higher propagation losses and self-healing beams that offer enhanced resilience against line-of-sight blockage. Nevertheless, our mathematical modeling and experimental study find that such favorable near-field properties can be observed only within a smaller range of the nominal near-field Fresnel regime. To extend the functioning range where the use of near-field beams is advantageous, prior literature advocates the use of transmit arrays with larger form factors; however, such arrays may be impractical in real-world environments and are often difficult and costly to fabricate. In this study, we present the mathematical modeling and experimental demonstration of distributed near-field beam shaping using multiple coordinated transmitting apertures, hence, increasing the effective near-field regime. Our modeling is built on a detailed understanding of near-field electromagnetics, Fourier optics, and wave optics.

Electromagnetic beams carrying orbital angular momentum (OAM) exhibit helical phase structures and doughnut-shaped intensity profiles, offering a promising basis for mode-division multiplexing and for fine-grained sensing in millimeter wave and sub-terahertz regimes. The simultaneous use of multiple OAM modes in joint communication and sensing systems has nevertheless remained unexplored due to conflicting requirements. While concurrent transmission of multiple orthogonal modes maximizes throughput in favor of communication, sensing relies on obtaining location-dependent scattering signatures by probing individual modes. In this work, we exploit the flexibility of OAM multiplexing to reconcile these requirements, based on the core insight that communication capacity depends primarily on the number of active modes, rather than the specific mode indices. Hence, by reconfiguring subsets of OAM modes, we generate diverse composite field distributions, whose reflections from sensing targets encode rich spatial information, while maintaining orthogonality for data multiplexing. We derive the theoretical limits of joint sensing performance and validate our approach through extensive over-the-air experiments at 120 GHz, demonstrating accurate target localization alongside high-speed data transmission. Our modeling and design are built on a deep understanding of the physics of OAM-carrying beams and the fundamentals of multiple-input multiple-output wireless propagation channels.

Orbital Angular Momentum (OAM)-based communication systems offer high-capacity multiplexing in line-of-sight (LOS) scenarios; yet, their performance is sensitive to nodal misalignment, which disrupts modal orthogonality, hindering the data multiplexing gain. To tackle this challenge, we present OrthoVortex, a novel framework that estimates the misalignment angles and applies the appropriate phase correction to restore orthogonality between modes. Unlike purely theoretical prior efforts that rely on impractical fully digital arrays or exhaustive beam scans, OrthoVortex introduces and leverages the cross-modal phase, as a unique signature for identifying the misalignment angles from the received signal. OrthoVortex is a few-shot alignment technique, making it feasible for real-world implementations. Our key contributions include: (i) a robust angle estimation and phase correction framework based on the physics of OAM propagation that estimates the misalignment and restores modal orthogonality, (ii) the first-ever experimental validation of OAM beam alignment with RF transceivers, and (iii) a comprehensive analysis of practical constraints, including the impact of antenna count and bandwidth. Simulations and over-the-air measurements using low-cost, rapidly prototyped metasurfaces operating at 120 GHz demonstrate that OrthoVortex achieves fast and precise misalignment estimation (mean absolute error of 0.69° for azimuth and 2.54° for elevation angle). Further, OrthoVortex can mitigate the inter-modal interference, yielding more than 12 dB increase in signal-to-interference ratio and more than 4.5-fold improvement in link capacity. Lastly, we experimentally demonstrate how the proposed phase correction scheme improves the link quality in the presence of misalignment.

The real-time knowledge of mmWave device orientation offers dual benefits for wireless networks and Internet of Things (IoT) applications: it enhances communication and localization performance through link diagnosis, and it enables context inference with asset and wearable tracking. This article presents metasurface-assisted polarization sensing (MetaPol), a novel system architecture that augments commodity mmWave access points (APs) with a carefully designed ultralow-cost anisotropic metasurface to noninvasively extract the orientation of client devices, without hindering data reception or modifying hardware. MetaPol leverages the polarization of transmitted electromagnetic (EM) waves as an accurate indicator of the orientation of linearly polarized antenna arrays, prevalent in commercial mmWave mobile and IoT devices. Yet, polarization sensing is rarely supported by commodity APs due to the need for two orthogonally polarized antenna arrays to capture the incident electric field. Instead, MetaPol creates virtual polarization channels to characterize impinging electric fields, through the conversions of wave polarization on the fly as it interacts with the metasurface. To design MetaPol, we model and exploit the properties of a unique anisotropic metamaterial based on C-shaped split-ring resonators (SRRs). We discover that, when grouped in certain configurations, these meta-elements can convert the incident polarization in a deterministic way. We show that three polarization channels are sufficient for unambiguous orientation sensing, and we provide a corresponding three-shot noncoherent protocol that extracts user orientation by comparing the power received from distinct surface areas. Through extensive over-the-air experiments with more than 1000 measurements in the mmWave band, we demonstrate that MetaPol achieves a mean error of 2.6° across practical settings with negligible compromise to the underlying data communication link.