Generation of Multiple High-Order Bessel Beams Carrying Different Orbital-Angular-Momentum Modes through an Anisotropic Holographic Impedance Metasurface

Conventional multiple vortex beams carrying different orbital-angular-momentum (OAM) modes propagating in different directions suffer from beam divergences along with the increasing transmission distance, which greatly limits their practical applications. This article presents a diffraction-resisting dual high-order Bessel-beam (DHOBB) generator based on an anisotropic holographic impedance metasurface (AHIM) operating at 30 and 30.5 GHz. By virtue of leaky-wave theory and the optical holographic principle, surface waves excited by a monopole antenna welded on the back of the metasurface can be modulated into nondiffractive DHOBBs. Different geometric parameters of the subwavelength meta-atoms can be mapped by the interference patterns between the reference surface waves and the desired beams. Furthermore, this designed single-layer anisotropic metasurface can be equivalent to the functionalities of spiral-phase-plate, refractive-hyperbolic, and axicon lenses synthetically utilized in the popular air-fed metasurface to generate HOBBs. Compared with the most popular air-fed metasurface, this design results in predominant performances of ultralow profile, easy fabrication, and integration with other electronic components and avoids alignment errors. Both simulated and measured results demonstrate that nondiffractive DHOBBs carrying different OAM modes can be generated by this designed AHIM. Nondiffractive DHOBBs with different Bessel orders with distinctive properties may open a window for wireless communications with multiarea coverage and multitarget radar detection.

Figure 1

Schematic diagram of the physical mechanism in the ultralow-profile AHIM developed to realize DHOBB multiplexing.

Figure 2

(a) Geometrical structure of the tensor impedance meta-atom in simulation. (b) Effective scalar impedance versus surface-wave propagation angle, ${\theta }_k$, on the tensor impedance surface with ${\theta }_s={60}^{\circ }$ and $g_a=0.2\mathrm{mm}$.

Figure 3

Tensor impedance components of position function: (a) $Z_{xx}$, (b) $Z_{xy}$.

Figure 4

Geometrical parameters of the tensor impedance meta-atoms distributed on the AHIM to launch nondiffractive dual HOBBs. (a) Gap of $g_a$. (b) Slot angle of ${\theta }_s$.

Figure 5

Far-field radiation pattern at 30 GHz. (a) Dual diffraction vortex beams. (b) Dual HOBBs.

Figure 6

Far-field radiation pattern at 30.5 GHz. (a) Dual diffraction vortex beams. (b) Dual HOBBs.

Figure 7

Near-field distributions of the horizontally polarized E field for the launched dual HOBBs and dual diffraction vortex beams with two different OAM modes, $\pm 1$, at 30 GHz. (a) Simulated amplitude distributions on the x-o-z plane with a rotated angle of $+{30}^{\circ }$ with OAM mode $l_1=+1$ for the dual diffraction vortex beams. (b) Simulated amplitude distributions on the x-o-z plane with a rotated angle of $+{30}^{\circ }$ with Bessel order $n_1=+1$. (c) Simulated amplitude distributions on the x-o-z plane with a rotated angle of $-{30}^{\circ }$ with OAM mode $l_2=-1$ for one of the dual diffraction vortex beams. (d) Simulated amplitude distributions on the x-o-z plane with a rotated angle of $-{30}^{\circ }$ with Bessel order $n_2=-1$.

Figure 8

Near-field distributions of the horizontally polarized E field for the launched dual HOBBs and dual diffraction vortex beams with two different OAM modes, $\pm 1$, at 30.5 GHz. (a) Simulated amplitude distributions on the x-o-z plane with a rotated angle of $+{30}^{\circ }$ with OAM mode $l_1=+1$ for the dual diffraction vortex beams. (b) Simulated amplitude distributions on the x-o-z plane with a rotated angle of $+{30}^{\circ }$ with Bessel order $n_1=+1$. (c) Simulated amplitude distributions on the x-o-z plane with a rotated angle of $-{30}^{\circ }$ with OAM mode $l_2=-1$ for one of the dual diffraction vortex beams. (d) Simulated amplitude distributions on the x-o-z plane with a rotated angle of $-{30}^{\circ }$ with Bessel order $n_2=-1$.

Figure 9

Simulated near-field propagation characteristics for the E-field amplitude distributed on different cross sections with propagation distances of 0.5, 1.0, and 1.5, perpendicular to the corresponding wave vector at 30 GHz. (a)–(c) Simulated E-field amplitude distributions for one of the dual diffraction vortex waves with OAM mode $l_1=+1$. (d)–(f) Simulated E-field amplitude distributions for one of the DHOBBs with Bessel order $n_1=+1$.

Figure 10

Simulated near-field propagation characteristic for the E-field amplitude distributed on different cross sections with propagation distances of 0.5, 1.0, and 1.5 m, perpendicular to the corresponding wave vector at 30.5 GHz. (a)–(c) Simulated E-field amplitude distributions for one of the dual diffraction vortex waves with OAM mode $l_1=+1$. (d)–(f) Simulated E-field amplitude distributions for one of the DHOBBs with Bessel order $n_1=+1$.

Figure 11

Simulated near-field propagation characteristic for the E-field amplitude distributed on different cross sections with propagation distances of 0.5, 1.0, and 1.5 m, perpendicular to the corresponding wave vector at 30 GHz. (a)–(c) Simulated E-field amplitude distributions for one of the dual diffraction vortex waves with OAM mode $l_2=-1$. (d)–(f) Simulated E-field amplitude distributions for one of the DHOBBs with Bessel order $n_2=-1$.

Figure 12

Simulated near-field propagation characteristics for the E-field amplitude distributed on different cross sections with propagation distances of 0.5, 1.0, and 1.5 m, perpendicular to the corresponding wave vector at 30.5 GHz. (a)–(c) Simulated E-field amplitude distributions for one of the dual diffraction vortex waves with OAM mode $l_2=-1$. (d)–(f) Simulated E-field amplitude distributions for one of the DHOBBs with Bessel order $n_2=-1$.

Figure 13

Prototype of the AHIM designed to generate DHOBBs.

Figure 14

Measurement environment based on the planar near-field scanning technique in a microwave anechoic chamber.

Figure 15

Measured far-field radiation pattern for the DHOBBs at 30 GHz.

Figure 16

Measured far-field radiation pattern for the DHOBBs at 30.5 GHz.

Figure 17

Measured near-field propagation characteristics for the E-field amplitude distributed on different cross sections with propagation distances of 0.5, 1.0, and 1.5 m, perpendicular to the corresponding wave vector at 30 GHz. (a)–(c) Measured E-field amplitude distributions for one of the DHOBBs with Bessel order $n_1=+1$. (d)–(f) Measured E-field phase distributions for one of the DHOBBs with Bessel order $n_1=+1$.

Figure 18

Measured near-field propagation characteristics for the E-field amplitude distributed on different cross sections with propagation distances of 0.5, 1.0, and 1.5 m, perpendicular to the corresponding wave vector at 30.5 GHz. (a)–(c) Measured E-field amplitude distributions for one of the DHOBBs with Bessel order $n_1=+1$. (d)–(f) Measured E-field phase distributions for one of the DHOBBs with Bessel order $n_1=+1$.

Figure 19

Measured near-field propagation characteristics for the E-field amplitude distributed on different cross sections with propagation distances of 0.5, 1.0, and 1.5 m, perpendicular to the corresponding wave vector at 30 GHz. (a)–(c) Measured E-field amplitude distributions for one of the DHOBBs with Bessel order $n_2=-1$. (d)–(f) Measured E-field phase distributions for one of the DHOBBs with Bessel order $n_2=-1$.

Figure 20

Measured near-field propagation characteristics for the E-field amplitude distributed on different cross sections with propagation distances of 0.5, 1.0, and 1.5 m, perpendicular to the corresponding wave vector at 30.5 GHz. (a)–(c) Measured E-field amplitude distributions for one of the DHOBBs with Bessel order $n_2=-1$. (d)–(f) Measured E-field phase distributions for one of the DHOBBs with Bessel order $n_2=-1$.