Presentazioni e Articoli Tecnici

Metasurface (MTS) antennas are based on the use of special types of scattering surfaces patterned at a sub-wavelength scale with electrically small metallic dielectric inclusions, usually called unit cells [O. Quevedo-Teruel et al., Journal of Optics, vol. 21, 2019]. The radiation mechanism of a MTS antenna is based on the modulation of the surface impedance, which is obtained by varying the geometrical parameters of the unit cell. The metasurfaces having a spatially modulated equivalent impedance transform a surface wave (SW) propagating across them into a leaky wave, i.e., a wave with a complex propagation wavenumber, which radiates energy away from the surface. MTS-based leaky-waves antennas (LWAs) are attractive solutions, whose main characteristics are the simple structure, the high gain, and the possibility to have a simple feeding. However, some drawbacks characterize this kind of structures and need to be mitigated in the design process. The open stopband at broadside is the biggest challenge for LWAs (where “open stopband” indicates the range of frequencies where radiation is stopped in a particular direction). Moreover, sidelobe level is difficult to control for all scan angles. A newly developed current-based numerical technique for the synthesis of metasurface antennas radiating at broadside with low side lobe level is presented in [M. Zucchi, F. Vernì, M. Righero, and G. Vecchi, IEEE Trans. Antennas Propag., vol. 71, no. 6, 2023]. The numerically retrieved impedance pattern obtained with this method is translated in a proper MTS antenna geometry which needs to be modelled in a full-wave simulation software for the validation of the predicted behaviour.

In this context, the COMSOL Multiphysics® software proved to be an optimal tool to reproduce the complex structure of the MTS antennas radiating at broadside designed using the above-mentioned technique. The RF module was employed, and the Far-Field domain environment activated, to analyze the radiation pattern of the simulated antennas and verify the correctness of the predicted behaviour. For the different structures, the feeding has been simulated by modeling a coaxial connector and using a Coaxial Lumped port. The possibility to use different geometries for the PML structure allowed to analyze the antenna performance using the PML shape that best fits the geometry of the antenna and corresponds to a good trade-off between the precision of the results and the computational time. Moreover, an S-parameter comparison between the Adaptive Frequency Sweep and the results obtained with a regular discrete sweep has been performed for the different antennas considered.