Design of a Contactless AF-SIW Horn Antenna with Compact Size and Enhanced Directivity Biedma Pérez, Andrés Segura Gómez, Cleofás Palomares Caballero, Ángel Valenzuela Valdes, Juan Francisco Padilla De La Torre, Pablo Antenna Aperture Contactless air-filled substrate integrated waveguide (CLAF-SIW) Horn antenna This work has been supported by grant TED2021-129938B-IOO funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR. It has also been supported by grants PID2020-112545RBC54, PDC2022-133900- 100, and PDC2023-145862- 100, funded by MCIN/AEI/I0.13039/501100011033 and by the European Union NextGenerationEU/PRTR. This work presents an H-plane contactless air-filled substrate integrated waveguide (CLAF-SIW) horn antenna, whose directivity is enhanced by incorporating a metasurface along the horn flaring. CLAF-SIW structures allow efficient and cost-effective handling of the propagation zones to incorporate metasurfaces. In this way, it is possible to reduce phase errors at the aperture, a common issue in horn antennas. The metasurface is designed using substrate integrated hole (SIH) unit cells with a patch based on parallel plate waveguides (PPW). An analysis of the distribution of the unit cells along the horn antenna is conducted to obtain the equivalent effective refractive indices required in the metasurface. By varying the size of the hollow where the metal patch is located, the equivalent refractive index for the propagating mode of the PPW can be tuned. The directivity achieved is comparable to that of a horn antenna with optimal dimensions, but with a 41% reduction in length. The simulated results demonstrate an impedance bandwidth below −10 dB from 32.8 to 49.7 GHz, with a directivity above 12 dBi. 2026-02-17T12:52:56Z 2026-02-17T12:52:56Z 2025-03-30 conference output A. Biedma-Pérez, C. Segura-Gómez, á. Palomares-Caballero, J. F. Valenzuela-Valdés and P. Padilla. (2025). Design of a Contactless AF-SIW Horn Antenna with Compact Size and Enhanced Directivity. 19th European Conference on Antennas and Propagation (EuCAP). DOI: 10.23919/EuCAP63536.2025.10999573 https://hdl.handle.net/10481/111118 10.23919/EuCAP63536.2025.10999573 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional IEEE