Abstract Bessel beams (BBs) generated by leaky-wave resonant cavities are here studied beyond their nondiffractive limit through a fully vectorial approach. The transition from the near- to the far-field region reveals interesting intermediate features of the pattern between a near-field limited-diffraction BB and a scanned far-field conical beam. The latter interestingly shows a beam angle which shifts with respect to that expected from the leaky-wave theory due to the significant truncation of the resonant cavity. This correction may have important consequences on the accurate design of such devices for establishing wireless links based on highly focused beams.