Beam shift effects in resonant focusing devices

Planar radiating structures that exploit the generation of leaky waves can be used to realize conical beams in the far field or focused beams in near field. In the latter case, Bessel beams are usually created by truncating structures with a metallic rim at a radial resonance. The radiated Bessel beams are maintained up to a distance which is determined by the angle of the radiation in near field, also known as axicon angle. In this work, we relate the axicon angle to the angle of maximum radiation in the far field and show how these angles are affected by the lateral truncation. When the structure is truncated to work as a Bessel-beam launcher, results show that the beam angle is considerably shifted with respect to the ideal, infinite aperture case. This analysis is thus important to accurately determine the performance of a wireless link based on Bessel beams.