Abstract
In this paper the focusing capability of a radiating aperture implementing an inward cylindrical traveling wave tangential electric field distribution directed along a fixed polarization unit vector is investigated. In particular, it is shown that such an aperture distribution generates a non-diffractive Bessel beam whose transverse component (with respect to the normal of the radiating aperture) of the electric field takes the form of a zero-th order Bessel function. As a practical implementation of the theoretical analysis, a circular-polarized Bessel beam launcher, made by a radial parallel plate waveguide loaded with several slot pairs, arranged on a spiral pattern, is designed and optimized. The proposed launcher performance agrees with the theoretical model and exhibits an excellent polarization purity.
Highlights
In recent years growing interest has been gained by the so-called diffractionless beams, among which Bessel beams assume a relevant importance, since their early introduction by Durnin [1]
It is shown that such an aperture distribution generates a non-diffractive Bessel beam whose transverse component of the electric field takes the form of a zero-th order Bessel function
We extend the results obtained in [13], showing that a tangential electric field aperture distribution polarized along a fixed unit vector pgenerates a Bessel beam with the same arbitrary transverse polarization p
Summary
In recent years growing interest has been gained by the so-called diffractionless beams, among which Bessel beams assume a relevant importance, since their early introduction by Durnin [1]. Whereas Bessel beam launchers usually adopt a standing wave (Bessel function) aperture distribution [10], in [11, 12, 13] it has been shown that Bessel beams can be alternatively generated synthesizing an inward cylindrical traveling wave (Hankel functions) aperture distribution. In [13] a tangential electric field polarized along the radial unit vector ρand shaped as an inward cylindrical traveling wave H1(1)(kρaρ) produces a Bessel beam with the longitudinal component (i.e. normal to the radiating aperture) of the electric field shaped as J0(kρaρ)e− jkzaz, in a well-defined conical region centered on the axis of symmetry of the radiating aperture. To implement a circular-polarized (CP) Bessel beam launcher with a transverse inward cylindrical traveling wave equivalent aperture distribution, a radial parallel plate waveguide (PPW) loaded with several slot pairs arranged on a spiral is designed and optimized. The presented low profile launcher can profitably find practical application in the field of medical imaging and of ground penetrating radars (GPR), both at millimeter waves and at Terahertz
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