A broadband lens for generating deflected Bessel multi-beams and a control method thereof

Abstract

The present invention discloses a broadband lens and a control method for generating deflected Bessel multi-beams, comprising a feed source and N metasurface units, wherein the feed source generates a spherical wave to illuminate the metasurface unit and forms multiple Bessel beams on one side of the metasurface unit, wherein the metasurface unit is phase-adjustable, and comprises a first polarization grid, a first dielectric plate, a polarization conversion surface, a second dielectric plate and a second polarization grid stacked in sequence, wherein the polarization conversion surface is mirror-symmetric along the y-axis to achieve a 180-degree phase difference, and a 180-degree phase change is obtained by size transformation of the polarization metasurface, and a 360-degree transmission phase change is further obtained. The transmission-type Bessel beam antenna provided by the present invention has the characteristics of planarization, broadband, multi-beams and adjustable beam energy.

Description

Technical Field

[0001] The present invention relates to the field of communications, and in particular to a broadband lens for generating a deflected Bessel multi-beam and a control method thereof. Background Art

[0002] Since it was proposed by Durnin in 1987, Bessel beam has attracted widespread attention due to its non-diffraction characteristics. It can concentrate the energy of electromagnetic waves in a certain direction and keep the energy unchanged at a certain distance when propagating in free space. It has the potential to be applied in high-speed communication, wireless energy transmission, laser micromachining, etc.

[0003] In the field of microwave and millimeter waves, there are two common methods for generating Bessel beams. One is to design an antenna with an aperture field similar to the Bessel function, such as a waveguide leaky wave antenna or a radial slot array. However, it is very difficult for the electric field to form a good Bessel function distribution characteristic on the aperture surface, and the antenna structure is generally complex. The other is to convert the incident wave into a Bessel beam structure such as an axicon or a metasurface. However, the axicon system has high requirements for the relative position and coaxiality of the three devices: the feed horn, the convex lens, and the axicon. Metasurfaces are mainly divided into reflective metasurfaces and transmissive metasurfaces. Transmissive metasurfaces do not have the problem of feed source shielding of reflective metasurfaces, but in order to achieve 360° phase coverage, four or more metal layers are often required, and the frequency band is narrow.

[0004] At present, there are not many antennas that use metasurfaces to form Bessel beams. They mainly generate single-frequency single beams, and there is little research on broadband multi-beams. Bessel beams can be used for wireless energy transmission. In order to achieve efficient use and flexibility of energy, it is necessary to distribute the energy of Bessel multi-beams. There is almost no research on this in the existing literature. Summary of the invention

[0005] In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides a broadband lens for generating deflected Bessel multi-beams and a method for controlling beams with unequal power distribution. The lens can operate in a broadband mode, carry deflected multi-Bessel beams, and realize unequal power distribution of beams.

[0006] The present invention adopts the following technical solution:

[0007] A broadband lens for generating deflected Bessel multi-beams comprises a feed source and N metasurface units, wherein the feed source generates a spherical wave to illuminate the metasurface unit and form multiple Bessel beams on one side of the metasurface unit, wherein the metasurface unit is phase-adjustable and comprises a first polarization grid, a first dielectric plate, a polarization conversion surface, a second dielectric plate and a second polarization grid stacked in sequence, wherein the polarization conversion surface is mirror-symmetric along the y-axis to achieve a phase difference of 180 degrees, and a 180-degree phase transformation is obtained by size transformation of the polarization metasurface, and further a 360-degree transmission phase change is obtained.

[0008] Furthermore, the first polarization grid and the second polarization grid are both composed of microstrip straight lines arranged at equal intervals, and the microstrip straight lines in the first polarization grid and the microstrip straight lines in the second polarization grid are orthogonal to each other.

[0009] Furthermore, the polarization conversion surface includes an I-type metal patch and a square metal patch with cut corners, wherein the I-type metal patch is symmetrical about the center of the second dielectric plate and is arranged along a diagonal line of the second dielectric plate, and the square metal patch is arranged at the center of the I-type metal patch and is symmetrical about its center.

[0010] Furthermore, the first dielectric plate and the second dielectric plate are completely identical.

[0011] Furthermore, the feed source is a horn antenna or a microstrip antenna.

[0012] Furthermore, the I-shaped metal patch includes two arc-shaped patches, and the two arc-shaped patches are connected by a strip patch.

[0013] Furthermore, the two arc patches are formed by subtracting a rectangle from an arc structure with the center point of the second dielectric substrate as the center, an outer radius R2 and an inner radius R1.

[0014] Furthermore, the length of the rectangle is l1 and the width is R2. When the length of the rectangle varies between 0.5 and 4.3 mm, a 180° phase shift is achieved.

[0015] Furthermore, a 180-degree phase shift is obtained by a y-axis mirror symmetric transformation of the polarized metasurface. Specifically, a 360-degree phase coverage adjustment is obtained by adjusting the length of the two arc-shaped patches and the symmetry with the y-axis.

[0016] A method for controlling a broadband lens comprises the following steps:

[0017] Obtain the phase values ​​required to generate m arbitrarily deflected Bessel beams, labeled ph1, ph2, ... ph m ; Set the amplitude allocation ratio s of each beam;

[0018] The distribution of electric field is obtained by using phase weighting and Green's function;

[0019] According to the characteristics of the non-diffraction beam, a focal point of the beam is selected to optimize the energy, so as to maximize the efficiency while ensuring the distribution of energy.

[0020] Beneficial effects of the present invention:

[0021] (1) The radiation unit of the present invention adopts an I-type and a square microstrip structure with a cut corner. The phase coverage is adjusted by adjusting the length of the branches on both sides of the I-type and the y-axis symmetry of the unit. The introduction of the square patch with a cut corner improves the transmittance and widens the bandwidth. The phase shift curve of the radiation unit has similar characteristics in the frequency range of 10 GHz to 18 GHz, indicating that the structure has broadband characteristics.

[0022] (2) The antenna can be used to generate Bessel multi-beams in any deflection direction. As a verification, the present invention provides (θ = 30°, With θ=-30°, ) and (θ=30°, With θ=-30°, )Two Bessel multi-beam embodiments.

[0023] (3) The antenna can perform unequal power distribution of energy. The present invention provides θ = 30°, With θ=-30°, An embodiment in which the allocation ratio of two beams is 1:0.8.

[0024] (4) The planar transmission type Bessel beam antenna overcomes the shortcomings of the difficult processing of parabolic antennas, the feed source shielding of reflective antennas, and the narrow bandwidth of transmission antennas. The antenna has a planar structure and is easy to process and assemble. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the structure of the present invention;

[0026] Figure 2 is a schematic structural diagram of a super surface unit of the present invention;

[0027] Figure 3(a) to Figure 3(c) They are respectively top views of the first polarization grid, the polarization conversion surface and the second polarization grid of the present invention;

[0028] FIG. 4( a ) is a diagram showing the size transformation of the polarization conversion surface of the present invention;

[0029] FIG4( b ) is a schematic diagram of the amplitude and phase of the present invention at a frequency of 14 GHz as the size of FIG4( a ) is changed;

[0030] Figure 5 is an amplitude-phase curve diagram of the polarization conversion surface of the present invention at 10 GHz to 18 GHz;

[0031] Figure 6(a) to Figure 6(c) They are respectively the phase of the broadband lens at 14 GHz, whether the unit is mirrored, and the unit size distribution diagram of Example 1 of the present invention, 1 means no mirroring, and 2 means mirroring;

[0032] Figure 7(a) to Figure 7(e) They are respectively the Bessel beam electric field distribution simulation diagrams of the broadband lens described in Example 1 of the present invention at 10 GHz, 12 GHz, 14 GHz, 16 GHz, and 18 GHz;

[0033] Figure 8(a) to Figure 8(c) They are respectively the phase at 14 GHz, whether the unit is mirrored, and the unit size distribution diagram of Example 2 of the present invention;

[0034] Figure 9(a) to Figure 9(e) They are respectively the Bessel beam electric field distribution simulation diagrams of the broadband lens described in Example 2 of the present invention at 10 GHz, 12 GHz, 14 GHz, 16 GHz and 18 GHz;

[0035] Figure 10(a) to Figure 10(c) They are respectively the phase at 14 GHz, whether the unit is mirrored, and the unit size distribution diagram of Example 3 of the present invention;

[0036] Figure 11(a) to Figure 11(e) They are respectively the Bessel beam electric field distribution simulation diagrams of the broadband lens described in Example 3 of the present invention at 10 GHz, 12 GHz, 14 GHz, 16 GHz and 18 GHz. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0038] Example 1

[0039] like Figure 1-Figure 2 As shown, a broadband lens for generating deflected Bessel multi-beams includes a feed source 1 and N metasurface units 2, wherein the N metasurface units can be arranged in a circular or rectangular array. The feed source generates a spherical wave to illuminate the metasurface unit, and forms a plurality of Bessel beams on one side of the metasurface unit. In this embodiment, the feed source 1 is located at a certain distance to the left of the metasurface unit 2, generates a spherical wave to illuminate the metasurface, and forms a plurality of Bessel beams 3 on the right side of the metasurface.

[0040] Furthermore, the metasurface unit includes a first polarization grid 4, a first dielectric plate 5, a polarization conversion surface 6, a second dielectric plate 7 and a second polarization grid 8 stacked in sequence from top to bottom. The polarization conversion surface is mirror-symmetric along the y-axis to achieve a phase difference of 180 degrees. The 180-degree phase transformation is obtained by the size transformation of the polarization metasurface, and a 360-degree transmission phase change is further obtained.

[0041] The first polarization grid 4 and the second polarization grid 8 are both composed of microstrip straight lines arranged at equal intervals, and the microstrip straight lines of the first polarization grid 4 and the microstrip straight lines of the second polarization grid 8 are orthogonal to each other.

[0042] The polarization conversion surface is the radiation unit of the broadband lens. The polarization conversion surface is mirror-symmetric along the y-axis, and can achieve a phase difference of 180 degrees. Combined with the size transformation, a 180-degree phase change is obtained, thereby obtaining a 360-degree transmission phase change.

[0043] Specifically, the polarization conversion surface includes an I-type metal patch and a square metal patch with cut corners. The introduction of the square patch with cut corners improves the transmittance, increases the bandwidth, and works at different frequencies.

[0044] The I-type metal patch includes two arc patches, the two arc patches are connected by a strip patch, the strip patch is arranged along one of the diagonals of the second dielectric plate, and is symmetrical about the center of the second dielectric plate. The center point of the square metal patch is the center point of the second dielectric plate, and the square metal patch is symmetrical about the center point. A diagonal line of the square metal patch coincides with a diagonal line of the second dielectric plate.

[0045] The two arc-shaped patches are constructed as follows:

[0046] With the center point of the second dielectric plate as the center, draw an arc with an outer radius of r2 and an inner radius of r1. Then, subtract a rectangular patch with a length of l1 and a width of r2 from the arc. The resulting figure is rotated 45 degrees counterclockwise around the center to form the arc patch shown in Figure 3(b).

[0047] Furthermore, the two arc-shaped patches are symmetrical about the center of the second dielectric plate and have the same size.

[0048] Furthermore, in this embodiment, the structural dimensions of the first dielectric plate 5 and the second dielectric plate 7 are completely the same. The material of the two dielectric plates is F4B with a dielectric constant of 2.55, and the length and width are both 5.5 mm, and the height is 2 mm.

[0049] As shown in FIG. 3(a), FIG. 3(b) and FIG. 3(c), the preferred dimensions of each part in this embodiment 1 are:

[0050] P=5.5mm, R1=2.1mm, R2=2.5mm, W=0.35mm, W1=1.5mm, g1=0.3mm, S1=0.2mm, S2=0.5mm, t=0.2mm, l1=0.5~4.3mm.

[0051] A control method for Bessel multi-beam unequal power allocation combines Green's function with genetic algorithm to achieve weighted optimization of phase. The specific steps are as follows:

[0052] (1) Obtain the phase values ​​required to generate m arbitrarily deflected Bessel beams, labeled ph1, ph2, ... ph m ; Set the amplitude allocation ratio s of each beam.

[0053] (2) Using phase weighting (3) and Green's function (1), the distribution of the electric field (2) can be obtained, which is expressed as

[0054]

[0055]

[0056]

[0057] Among them, in (x n ,y n , there are N units at 0) to form a transmission metasurface, and the phase of the unit can be expressed as E(x p ,y p , z p ) is defined as the position (x) generated by the transmission array. p ,y p , z p ) is the electric field at .

[0058] (3) Based on the characteristics of the non-diffraction beam and simplified calculation, a focal point of the beam can be selected to optimize the energy.

[0059] Under the premise of ensuring energy distribution, the efficiency is maximized. The optimization formula is as follows

[0060] St

[0061] Among them, Mag E p = abs(E opt (x p ,y p , z p )) indicates that the weighted optimization process is located at (x p ,y p , z p ) is the value of the electric field amplitude at .

[0062] like Figure 4(a) to Figure 4(b) As shown in the figure, when l1 varies between 0.5 and 4.3 mm, the corresponding phase shift range is greater than 180°, and the 180° phase difference is generated by the unit mirror symmetry, which satisfies the 360° phase adjustment. The phase shift curve trend of the radiating unit at 10 to 18 GHz is the same, as shown in the figure below. Figure 5 As shown, it is demonstrated that the unit has broadband characteristics.

[0063] In this embodiment, 32×32 metasurface units are arranged periodically. Referring to FIG. 6( a ), the phase angle to be compensated from the spherical wave to the plane wave generated by the required speaker and the phase angle to be generated are θ=30°. With θ = -30°, The phase angle required to compensate for the Bessel beam in the direction is superimposed. According to the principle of one-to-one correspondence between phase and unit size, refer to Figure 6(b) and Figure 6(c) for the change in l1 size corresponding to the required phase and whether the unit is mirrored through the y-axis (1 means no mirroring and 2 means mirroring). Figure 7(a) to Figure 7(e) As shown, in this embodiment, at 10 GHz to 18 GHz, θ = 30°, With θ = -30°, A Bessel beam is generated at .

[0064] Example 2

[0065] The difference between this embodiment and embodiment 1 is that the compensation phase required by the radiation unit is different, such as Figure 8(a) to Figure 8(c) As shown, this embodiment 2 is used to generate θ = 30°, With θ = -30°, Bessel beams of equal intensity, see Figure 9(a) to Figure 9(e) .

[0066] Example 3

[0067] The difference between this embodiment and embodiment 1 is that the required compensation phase of the radiation unit is different, such as Figure 10(a) to Figure 10(c) The figure is used to generate θ = 30°, With θ=-30°, Bessel beam with unequal intensity distribution. The amplitude distribution ratio of the Bessel beam at 14 GHz is set to 1:0.8, and the genetic algorithm is used to perform phase weighted optimization. The obtained optimized phase is superimposed on the phase that needs to be compensated from the spherical wave to the plane wave, and the phase shown in Figure 10(a) is obtained. Figure 11(a) to Figure 11(e) ,Bessel beams with unequal power distribution are obtained from 10GHz to 18GHz, and at 14GHz, the amplitude distribution ratio is 1:0.8.

[0068] The metasurface unit of the present invention is composed of N radiation units arranged in an array. The unit includes three layers of metal and two layers of dielectric substrates, wherein the upper and lower layers of metal are orthogonal metal grids, which play the role of polarization filtering. The middle layer is a polarization conversion surface, including an I-type metal patch and a square metal patch with cut corners. The unit can achieve efficient polarization conversion at 10 GHz to 18 GHz. Under the irradiation of linearly polarized electromagnetic waves, the unit can transmit most of the energy of the incident wave to the cross-polarization direction within the frequency band.

[0069] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A broadband lens for generating deflected Bessel multi-beams, comprising a feed source and N metasurface units, wherein the feed source generates a spherical wave to illuminate the metasurface unit and forms multiple Bessel beams on one side of the metasurface unit, characterized in that: The metasurface unit is phase-adjustable, and includes a first polarization grid, a first dielectric plate, a polarization conversion surface, a second dielectric plate, and a second polarization grid stacked in sequence. The polarization conversion surface is mirror-symmetric along the y-axis to achieve a phase difference of 180 degrees. The 180-degree phase change is obtained by the size change of the polarization metasurface, and a 360-degree transmission phase change is further obtained. The polarization conversion surface includes an I-type metal patch and a square metal patch with cut corners, wherein the I-type metal patch is symmetrical about the center of the second dielectric plate and is arranged along a diagonal line of the second dielectric plate, and the square metal patch is arranged at the center of the I-type metal patch and is symmetrical about the center thereof; The I-type metal patch includes two arc-shaped patches, and the two arc-shaped patches are connected by a strip patch.

2. The broadband lens according to claim 1, characterized in that: The first polarization grid and the second polarization grid are both composed of microstrip straight lines arranged at equal intervals, and the microstrip straight lines in the first polarization grid and the microstrip straight lines in the second polarization grid are orthogonal to each other.

3. The broadband lens according to any one of claims 1 to 2, characterized in that: The first dielectric plate and the second dielectric plate are completely identical.

4. The broadband lens according to claim 1, characterized in that: The feed source is a horn antenna or a microstrip antenna.

5. The broadband lens according to claim 4, characterized in that: The two arc patches are formed by subtracting a rectangle from an arc structure with the center point of the second dielectric substrate as the center, an outer radius R2 and an inner radius R1.

6. The broadband lens according to claim 5, characterized in that: The length of the rectangle is l1 and the width is R2. When the length of the rectangle varies between 0.5 and 4.3 mm, a 180° phase shift is achieved.

7. The broadband lens according to claim 5, characterized in that: Phase coverage of 360 degrees is achieved by adjusting the length of the two arc-shaped patches and the symmetry with the y-axis.

8. A method for controlling a broadband lens according to any one of claims 1 to 7, characterized in that: The steps include: Obtain the phase values ​​required to generate m arbitrarily deflected Bessel beams, labeled ph1, ph2, ... ph m ; Set the amplitude allocation ratio s of each beam; The distribution of electric field is obtained by using phase weighting and Green's function; According to the characteristics of the non-diffraction beam, a focal point of the beam is selected to optimize the energy, so as to maximize the efficiency while ensuring the distribution of energy.

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