Bessel, Bessel-Gauss, and Gaussian beams have widely been investigated in optics in the paraxial approximation, under the frame of a scalar wave theory. Such approximations can hardly be applied in the microwave/millimeter-wave range, where the vectorial nature of the electromagnetic fields cannot be neglected, and experimental realizations for some of these beams appeared only recently. In this work, we discuss the generation of Bessel, Bessel-Gauss, and Gaussian beams through a fully vectorial electromagnetic approach. The field derivation of all these beams is first illustrated and numerical evaluations are then reported to compare their different propagation and diffractive behaviors. Finally, an innovative approach for realizing such solutions with planar microwave devices exploiting leaky waves is demonstrated through accurate numerical simulations.

Different configurations of leaky-wave antennas (LWAs) based on graphene metasurfaces are studied. The electronic properties of a graphene metasurface in the low THz range are investigated in details in order to discuss the reconfigurability features of the presented structures. Simple exact formulas for evaluating the ohmic losses related to the surface plasmon polariton (SPP) propagation along a suspended graphene sheet, and the relevant figures of merit of SPP propagating over a generic metasurface are given. Such formulas allow us to explain the low efficiency of reconfigurable antennas based on SPPs along graphene metasurfaces. Then, the radiative performance and relevant losses of graphene Fabry–Perot cavity antennas (FPCAs) based on non-plasmonic leaky waves (LWs) are investigated and compared with previous solutions based on SPPs. In particular, a single-layer structure, i.e. a grounded dielectric slab covered with a graphene metasurface, and a multilayered structure, i.e. a substrate–superstrate antenna in which the graphene metasurface is embedded at a suitable position within the substrate, are considered in detail. The results show that the proposed LW solutions in graphene FPCAs allow for considerably reducing the ohmic losses, thus significantly improving the efficiency of the proposed radiators.