A comparative analysis of Bessel and Gaussian beams beyond the paraxial approximation

The use of Bessel and Gaussian beams for focusing applications has long been debated. The former are attractive for their diffraction-resistant and self-healing character, whereas the latter notably exhibit higher efficiency. In previous works, efforts have been made to clarify whether Bessel or Gaussian beams are more suitable for wireless power transfer. However, the theoretical discussions proposed so far did not attract a general consensus from the community, the arguments often being based on restrictive, arbitrary hypotheses under the frame of the ray optics and paraxial approximations. On the other hand, especially at microwaves, nonparaxial Bessel beams have found important applications. This work aims at providing an engineering perspective on the focusing properties of both Bessel and Gaussian beams by introducing significant figures of merit. The latter are defined taking into account the beam features that are of greatest interest in focusing applications, namely the beam efficiency, the maximum cover distance, and the beam resolution. Analytical expressions are provided, and results are shown for comparing the Bessel and Gaussian beam features when their beam waists are allowed to freely vary in a range of physical realizability.