This design benefited from the metamaterial that has the ability to manipulate electromagnetic waves flexibly. proposed a method to realize planar Bessel beams using artificial meta-surfaces 19. The method based on a radial line slot array was also proposed at millimeter-wave frequency to generate Bessel beams 18. Caloz and coworkers presented a method of generating Bessel beams using two-dimensional antenna array at millimeter-waves 2. Recently, Grbic and coworkers presented several new approaches for generating Bessel beams in microwave regime, including leaky-wave modes 14, near-field plates for evanescent Bessel beams 15 and metamaterial Huygens’ surfaces 16, 17. By controlling the excitation currents of the loop antennas in the waveguide, one was able to manipulate the beam intensity, spot size and modulation. that a truncated Bessel beam was set to be the aperture field at the open-end of a flanged metallic circular waveguide section 13. A new method was presented by Salem et al. By locating a circular grating-like structure in front of a subwavelength aperture, a diffraction-free beam can also be generated in microwave region 12. In 2001, a computer-generated binary amplitude hologram was used to transform an initial Gaussian electromagnetic field with spherical phase front into a non-diffracting Bessel beam 11. The microwave launcher of Bessel beams was based on the study by Mugnai in 2000 10. The first generation of Bessel beams in the millimeter-wave region of the spectrum was proposed by Monk et al. In fact, in the microwave or millimeter (mm)-wave regime, the implementation of Bessel beams is much less reported. To be remarked, it is more difficult to achieve a plane wave in a small distance to illuminate the axicon lens at microwave frequency than in optics. Recently, to help the user to avoid preliminary optical adjustments, axicon on a gradient index lens for Bessel beam generation from a point-like source was proposed by Xie 8. Pendry presented the method of localized waves to launch Bessel beams 7. Its experimental arrangement was based on a holographic optical element to generate Bessel beams efficiently 5, 6. Holograph illuminated by a laser beam is another proposal to generate Bessel beam. Later, an axicon lens as a Bessel beam launcher was proposed by Herman and Wiggins and rapidly became widely-used approach for forming Bessel beams in optical experiment 4. In optics, the first experiment for generating Bessel beam was presented by Durnin 3.
HOW TO MAKE BESSEL BEAM IN CST MICROWAVE STUDIO SERIES
In the latest decades, there have been a series of studies on the method of launching Bessel beams. In practice, a truncated Bessel beam, termed as the quasi-Bessel beam, can be realized with the diffraction-free characteristic of remaining main lobe up to a significant distance 2. However, the truth is that an ideal Bessel beam does not exist due to the fact that they are not square integrable. This is the basis idea for launching Bessel beams. An ideal Bessel beam can be thought to be a superposition of plane waves with wave vectors lying on a cone. Bessel beams are of considerable potential applications such as electromagnetic propulsion, remote power transmission and secure communication. The beam exhibits the property of remaining confined and not suffering diffractive propagating. The non-diffracting beam solutions to the free-space homogeneous Maxwell’s equations, i.e., the Bessel beams, were proposed by Durnin in 1987 1. Full-wave simulation and experiment results have proved that the generated Bessel beams can be maintained in distance larger than 1 meter within a ranging from 12 GHz to 18 GHz. To verify the approach, we have designed, fabricated and tested a metamaterial lens. In principle, this kind of metamaterial lens can produce Bessel beams at arbitrary distance by designing the refractive-index distribution. The aperture diameter of the GRIN lens is much larger than the operating wavelength to guarantee the transformation. The conical beams form quasi-Bessel beams in the near-field region. The metamaterial lens serves as a convertor which transforms the spherical beams emitted from feed into conical beams. The metamaterials are designed as dielectric plates printed with metallic patterns in the center region and drilled by air holes near the edge, which operate in wide band. The metamaterial lens is constructed with multi-layered structure and each layer is composed of GRIN metamaterials. The broadband Bessel beams are produced by a gradient index (GRIN) metamaterial lens illuminated by broadband waveguide antenna. An approach of generating broadband Bessel beams is presented.