David González Ovejero

Gradient and Modulated Metasurfaces for mm-Wave and Sub-Terahertz Antennas

Millimeter-wave and sub-terahertz (sub-THz) frequency bands offer access to large unlicensed bandwidths and can therefore address the ever-increasing demand for higher data rates. However, fully exploiting these large bandwidths requires overcoming the increased free-space path loss, which generally becomes more challenging at higher carrier frequencies and can significantly constrain the link budget in the sub-THz regime. Moreover, generating sufficient output power at room temperature in the sub-THz frequency range remains technologically demanding. These challenges call for the use of high-gain antennas capable of generating narrow, highly directive pencil beams. Sub-THz frequency bands are also of considerable interest for Earth and atmospheric observation, particularly for detecting molecular absorption lines associated with the rotational transitions of molecules such as ClO, HNO₃, H₂O, and H₂O₂. These spectral signatures enable the monitoring of the spatial and temporal dynamics of such species and can ultimately contribute to assessing the state of our planet. In this context as well, highly directive beams are essential to achieve high spatial resolution in the resulting images. Typical high-gain antenna architectures rely on scalar horns used as feeds for large reflector or lens systems. Although these architectures can provide high efficiency and wide bandwidth, they are inherently bulky and difficult to reconcile with emerging paradigms that envision the massive deployment of compact, low-profile nodes and small satellites. As an alternative to electrically large reflectors and lenses, this presentation will discuss gradient and modulated metasurfaces as low-profile and lightweight architectures capable of providing comparable gain while maintaining substantial relative bandwidth. The architectures considered will include folded configurations, such as folded transmitarrays, which can significantly reduce the overall profile of conventional transmitarrays, in some cases by a factor of three. This profile reduction is enabled by the use of gradient metasurfaces, which provide the required ray reflection and phase compensation. Alternatively, the feed can be integrated within the plane of the metasurface by exploiting surface-wave-based metasurface antennas. In these architectures, radiation is generated through the interaction between a guided surface wave and a periodically modulated reactive surface implemented using subwavelength elements. The advantages and limitations of these different architectures will be discussed, with particular emphasis on the trade-offs among gain, bandwidth, efficiency, profile, and integration potential.

David González Ovejero (Senior Member, IEEE) received the M.Sc. degree in telecommunication engineering from the Universidad Politécnica de Valencia, Valencia, Spain, in 2005, the Ph.D. degree in electrical engineering from the Université catholique de Louvain, Leuven, Belgium, in 2012, and the Habilitation á Diriger des Recherches degree from the Université de Rennes, Rennes, France, in 2024. From 2012 to 2014, he was a Research Associate with the University of Siena, Siena, Italy. In 2014, he joined the Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA, where he was a Marie Curie Post-Doctoral Fellow. Since 2016, he has been a tenured Researcher with the French National Center for Scientific Research (CNRS), Institut d’Électronique et des Technologies du numéRique (IETR), Rennes. His current research interests include computational electromagnetics, large phased arrays, periodic structures, metasurfaces, and submillimeter-wave antennas. Dr. González Ovejero was awarded the Marie Curie International Outgoing Fellowship from the European Commission in 2013 the Sergei A. Schelkunoff Transactions Prize Paper Award from the IEEE Antennas and Propagation Society in 2016 the Best Paper Award in Antenna Design and Applications at the 11th European Conference on Antennas and Propagation (EuCAP) in 2017 the Best Paper Award in Electromagnetics at the 15th EuCAP in 2021 the Best Paper Award at the International Workshop on Antenna Technology in 2023 and the Médaille Blondel from the SEE in 2025. From 2019 to 2025, he served as an Associate Editor for IEEE Transactions on Terahertz Science and Technology and IEEE Transactions on Antennas and Propagation, receiving the Outstanding Associate Editor recognition for the latter in 2022, 2023, and 2025. He currently serves as a Track Editor for IEEE Transactions on Antennas and Propagation.