Generating Bessel beams using an electrically-large annular slot

This paper investigates the electromagnetic near field of an electrically large, uniformly excited annular slot. It is shown analytically that such a structure produces a Bessel beam in the reactive near field close to its axis. The theoretical predictions are verified through full-wave simulation and experiment. Furthermore, the beam excited by the plate retains an almost constant beamwidth and shape, thereby verifying the generation of a Bessel beam. Such a structure may find applications in high resolution imaging and probing, and possibly biomedical targeting devices.