Speaker: Professor Stefano Maci, University of Siena, Siena, Italy

Time: 14:00 to 17:00, October 12, 2026

Place: B1-c101

Abstract  

Recent developments in gradient-index (GRIN) and metasurface-based antennas are enabling low-cost, compact, and highly directive multibeam solutions without the need for traditional beamforming networks (BFNs). By replacing complex RF feeding systems with passive spatial field control, these approaches provide substantial reductions in hardware complexity, size, and overall cost. This talk highlights efficient GRIN lens synthesis techniques tailored for multifocal and multibeam operation. A generalized design methodology—going beyond classical ray-based assumptions—enables accurate refractive-index profiles that maintain stable radiation characteristics over wide frequency ranges. Supported by a fast geometrical optics solver based on the Fast Sweeping Method, this approach allows the direct computation of spatial index distributions required to produce prescribed field patterns, enabling precise passive beam shaping and steering. In addition, we present several metasurface (MTS) antenna solutions based on both space-wave manipulation and surface-wave excitation by multiple point sources. These planar architectures employ engineered impedance or phase profiles to efficiently transform guided or incident waves into multiple directive free-space beams, entirely without BFNs. The proposed MTS antennas are inherently thin, low-profile, and compatible with low-cost fabrication techniques.  Overall, the talk presents a comprehensive set of MTS antenna solutions spanning multiple architectures and operating over large frequency ranges, demonstrating the versatility and effectiveness of GRIN and metasurface concepts for next-generation multibeam antenna systems.

Biography

Stefano MACI is a Professor at the University of Siena (UNISI). Since 2000, he has been P.I. of 10 research projects funded by the European Union (EU) and by the European Space Agency (ESA). He is a Fellow of IEEE since 2004. In 2004 he founded the European School of Antennas (ESoA), a PhD school that presently comprises 35 courses on Antennas, Propagation, and Electromagnetic Theory, and 200 teachers, among them 20 IEEE Fellow. He graduated more than 40 PhD students. He has been former member of IEEE Antennas and Propagation Society (AP-S) AdCom, the Chair of the Award Committee of the IEEE AP-S, member of the AP Executive Board of IET (UK), Distinguished Lecturer of IEEE and of EurAAP. He was recipient of several prizes and awards, among which the EurAAP Award 2014, the Chen-To Tai Distinguished Educator award 2016, of the Shelkunoff Transaction Prize in 2015, and of the URSI Dellinger Gold Medal in 2020. He is presently Director of ESoA. He has been TPC Chair of the METAMATERIAL 2020 and and General Chair of EuCAP 2023. He was the president of the IEEE Antennas and Propagation Society 2023.  In the last ten years he has been invited 60 times as key-note speaker in international conferences. His research activity is documented in 200 papers published in international journals, (among which 100 on IEEE journals), 10 book chapters, and about 450 papers in proceedings of international conferences.