Efficient wireless near-field links between bessel-beam launchers

The focused nature of Bessel beams allows for secure and efficient wireless links in the near-field region. Still, at millimeter waves, few studies analyze the transmission efficiency between devices in a systematic way. In addition, present studies only analyze links between launchers of the same kind, which is here demonstrated to be a restricting hypothesis. For this purpose, in this work, we consider two kinds of launchers: a compact resonant cavity and a partially open radial waveguide. The transmission efficiency between two identical devices is first analyzed at various distances, showing that an optimum range exists. The link efficiency is then evaluated while reducing the size of one device. Remarkably, it is shown that there is an operating point for which the link efficiency dramatically increases if the partially open radial waveguide of reduced size is replaced by a compact resonant cavity. Ray-optics interpretations and leaky-wave analysis are used to provide qualitative and quantitative design rules for all kinds of links. The results here reported - all corroborated with full-wave simulations - may revolutionize the concept of wireless links based on Bessel beams at millimeter waves.