Bessel-beam launchers are azimuthally invariant structures characterized by a circular grounded dielectric slab with an isotropic metasurface on top. Previous works analyzed the launchers performance for some specific cases, assuming TE or TM polarizations, inductive or capacitive metasurfaces, cavities with sub-wavelength or half-wavelength height. We show here with both theoretical and full-wave results that the inductive or capacitive nature of the metasurface has a fundamental role in the radiating behavior of these devices. Results are reported for the relevant TM-polarized case, considering air-filled, halfwavelength thick cavities. The extension of this analysis to the TE-polarized and dielectric-filled case will be discussed at the conference.
Resonant Bessel-beam launchers are low-cost, planar, miniaturized devices capable of focusing electromagnetic radiation in a very efficient way in various frequency ranges, with recent increasing interest for microwave and millimeter-wave applications (i.e., 3–300 GHz). In recent years, various kinds of launchers have appeared, with different feeding mechanisms (e.g., coaxial probes, resonant slots, or loop antennas), field polarization (radial, azimuthal, and longitudinal), and manufacturing technology (axicon lenses, radial waveguides, or diffraction gratings). In this paper, we review the various features of these launchers both from a general electromagnetic background and a more specific leaky-wave interpretation. The latter allows for deriving a useful set of design rules that we here show to be applicable to any type of launcher, regardless its specific realization. Practical examples are discussed, showing a typical application of the proposed design workflow, along with a possible use of the launchers in a modern context, such as that of wireless power transfer at 90 GHz.
Bessel beams (BBs) can be generated at microwave frequencies by means of compact, planar devices based on Fabry-Perot cavity leaky-wave resonators. Most designs are based on the excitation of a single transverse magnetic/transverse electric (TM/TE) leaky mode by means of a vertical electric/magnetic dipole source. In this work, we analyze the important case of a horizontal magnetic dipole, which excites both TM and TE modes, developing an original theoretical framework suitable for resonant radiators. Analytical expressions are provided for the dominant leaky-wave aperture field. The near-field distribution is then evaluated through an accurate numerical integration of the radiating currents and validated through full-wave simulations for the relevant case of a BB launcher when excited by a waveguide-fed slot. Different designs are presented and analyzed in order to obtain TM, TE, and hybrid polarizations, finding in all cases an excellent agreement between simulations and theoretical results. Finally, we evaluate and compare the wireless-power-transfer efficiency of two coupled TM-, TE-, or hybrid-polarized BB launchers when a wireless link is established in the radiative near-field region. Interestingly, full-wave results demonstrate the superior performance of resonant BB launchers in TM or TE polarization with respect to the nonresonant hybrid case.
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