One-way / two-way radiation reconfigurable antenna based on fresnel lens and super surface

Abstract

The application discloses a one-way / two-way radiation reconfigurable antenna based on a Fresnel lens and a metasurface, and belongs to the technical field of antennas.The antenna is based on a Fresnel lens, and a novel metasurface unit is proposed and combined into a metasurface; the polarization selection characteristic and phase control ability of the metasurface are utilized, and the rotation of a feed antenna is combined to further realize one-way / two-way radiation reconfigurability.The polarization direction of a normal beam is the same as that of the feed antenna when the antenna radiates in one-way; when the antenna radiates in two-way, the polarization direction of the normal beam is the same as that of the feed antenna, the polarization direction of a back radiation beam is orthogonal to that of the feed antenna, and the back radiation beam can deviate from the normal direction.

Description

Technical Field

[0001] This invention belongs to the field of antenna technology, specifically relating to a unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces. Background Technology

[0002] Antennas, as key components for converting guided waves and free-space waves, play a crucial role in wireless communication systems. High-gain antennas with unidirectional radiation effectively compensate for path loss during electromagnetic wave propagation, significantly improving signal quality and reducing the burden on the RF front-end. Bidirectional radiation antennas have important applications in micro base stations, tunnel relay communication, indoor wireless communication, and RFID systems. Fresnel lenses illuminated by a single point source are typically used for unidirectional radiation; compared to source antennas, the directionality and gain of electromagnetic waves are greatly improved after passing through a Fresnel lens. However, Fresnel lens antennas without reflectors or back cavities often exhibit significant back radiation, which is usually not effectively utilized. Furthermore, with the trend towards highly integrated communication equipment, antennas with reconfigurable unidirectional / bidirectional radiation capabilities are highly attractive in terms of miniaturization, weight reduction, and high integration.

[0003] The existing technology "Pattern Reconfigurable Antenna Array With CircularPolarization, IEEE Transactions on Antennas and Propagation, vol.64, no.4, 2016" discloses an antenna operating in the 1.9 to 2.3 GHz range. This antenna achieves reconfigurability for unidirectional and bidirectional radiation by controlling a PIN diode to change the state of the feed network. However, the gain of this antenna in each reconfiguration state is only 1.6 to 7.1 dBi; and its large feed network introduces a significant amount of insertion loss, resulting in a deterioration of the overall antenna performance.

[0004] The prior art, "Electronically Controlled Beam Steerable Dual-Band Star-Shaped DRA for UAS and Wi-Fi Data Link Applications," IEEE Transactions on Antennas and Propagation, vol. 68, no. 10, 2020, discloses a unidirectional and bidirectional reconfigurable antenna operating in the S and C bands. This antenna consists of a star-shaped dielectric resonator antenna, several single-pole double-throw switches, and control circuitry. Beam reconfiguration is achieved by controlling the on / off states of the single-pole double-throw switches. However, this antenna has a relatively wide beamwidth, and its average gain in different radiation modes is only 6 dBi.

[0005] The existing technology "Reconfigurable Bidirectional Beam-Steering Aperture With Transmitarray, Reflectarray, and Transmit-Reflect-Array Modes Switching," IEEE Transactions on Antennas and Propagation, vol.71, no.1, 2023, discloses a metasurface antenna capable of reconfigurable unidirectional and bidirectional radiation, operating at a center frequency of 9.5 GHz. This metasurface antenna consists of several metasurface units loaded with a pair of PIN diodes. Reconfigurable unidirectional and bidirectional radiation is achieved by controlling the conduction state of the two PIN diodes. However, even a small change in the equivalent capacitance of the PIN diodes significantly affects the transmission and reflection performance of the metasurface units, placing extremely high demands on device consistency and hindering practical applications.

[0006] In addition to the aforementioned technical issues, these antennas all require the use of PIN diodes and single-pole double-throw switches, which leads to problems such as high cost and high loss. At the same time, these devices inevitably have parasitic effects, which will pose a great challenge to millimeter-wave and even higher frequency applications. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces.

[0008] The technical problem addressed by this invention is solved as follows:

[0009] A unidirectional / bidirectional reconfigurable antenna based on a Fresnel lens and a metasurface includes a Fresnel lens 1, a metasurface 2, and an open waveguide feed antenna 3; the Fresnel lens 1 and the metasurface 2 are parallel and have an air gap in between; the open waveguide feed antenna 3 is located at the center of the metasurface 2 and its open end is flush with the upper surface of the metasurface 2.

[0010] The Fresnel lens 1 includes a metal concentric circle-ring structure 4 and a first dielectric substrate 5; the metal concentric circle-ring structure 4 is located on the lower surface of the first dielectric substrate 5; the first dielectric substrate 5 is square, and the metal concentric circle-ring structure 4 includes a metal circular patch and three metal ring patches; the center of the metal circular patch and the center of the three metal ring patches coincide with the center of the first dielectric substrate 5.

[0011] Metasurface 2 consists of two PCB layers, which are bonded together by a prepreg. The upper PCB includes a first metal grid 6, a second dielectric substrate 10, and umbrella-shaped metal units 7. The lower PCB includes a second metal grid 9 and a third dielectric substrate 11. The first metal grid 6 is located on the upper surface of the second dielectric substrate 10 and consists of 2M periodically parallel first metal strips. The first metal strips are parallel to the edges of the second dielectric substrate 10 and parallel to the y-axis. M×M periodically arranged umbrella-shaped metal units 7 are located on the lower surface of the second dielectric substrate 10. The second metal grid 9 is located on the lower surface of the third dielectric substrate 11 and consists of 2M periodically parallel second metal strips. The second metal strips are perpendicular to the first metal strips and parallel to the x-axis, with the same width, where M is a positive integer.

[0012] A cross-shaped through-hole 8 is opened at the center of the metasurface 2. The size of the cross-shaped through-hole 8 is the same as that of the two orthogonal open waveguide feed antennas 3.

[0013] The open waveguide feed antenna 3 is a standard waveguide located in the cross-shaped through-hole 8 of the metasurface 2, and its open end is kept flush with the upper surface of the metasurface.

[0014] Furthermore, an air gap is formed between the Fresnel lens 1 and the metasurface 2 by nylon pillars or foam support.

[0015] Furthermore, the metasurface 2 can be divided into M×M metasurface units, the period of which is 1 / 3 of the free space wavelength corresponding to the antenna center frequency; from top to bottom, it consists of a first metal grid 6, a second dielectric substrate 10, an umbrella-shaped metal unit 7, a three-dielectric substrate 11, and a second metal grid 9; in one metasurface unit, the first metal grid 6 and the second metal grid 9 are two metal strips respectively; the umbrella-shaped metal unit 7 includes a metal arc and a metal parallel double-line structure, the metal arc is axially symmetric about the metal parallel double-line structure; the center of the metal arc coincides with the center of the metasurface unit; the metal parallel double-line structure is located on the diagonal of the lower surface of the second dielectric substrate 10, with an angle of 45° to both the x-axis and y-axis, one end is in contact with the metal arc, and the other end extends towards the corner of the second dielectric substrate 10.

[0016] Furthermore, in the umbrella-shaped metal unit 7 of the metasurface unit, the angle between the end of the metal arc and the center is denoted as the half-arc angle α. The transmission phase of the electromagnetic wave is changed by controlling the half-arc angle α. The metal grid 6 on the upper surface of the metasurface 2 is along the y-axis, and the metal grid 9 on the lower surface is along the x-axis. Near the center frequency, the first metal grid 6 of the metasurface 2 can only transmit x-polarized electromagnetic waves, while the second metal grid 9 can only transmit y-polarized electromagnetic waves. The metasurface 2 can realize the transmission and conversion of x-polarized waves reflected by the Fresnel lens into y-polarized waves.

[0017] Furthermore, the antenna operates in both unidirectional and bidirectional radiation modes;

[0018] The wide side of the open waveguide feed antenna 3 is set along the y-direction, and its open end is kept flush with the upper surface of the metasurface. At this time, the open waveguide feed antenna 3 is x-polarized. Part of the x-polarized wave generated by the open waveguide feed antenna 3 is transmitted through the even-number Fresnel zone to form a normal pen beam; the other part is reflected by the metal concentric circle-ring structure of the odd-number Fresnel zone, and then refracted and polarized by the metasurface 2 to form a y-polarized back-deflected beam. At this time, the antenna operates in a bidirectional radiation mode.

[0019] The wide side of the open waveguide feed antenna 3 is set along the x-direction, and its open end is kept flush with the upper surface of the metasurface. At this time, the open waveguide feed antenna 3 is y-polarized. Part of the y-polarized wave generated by the open waveguide feed antenna 3 is transmitted through the even-number Fresnel zone, and the other part is reflected by the metal concentric circle-ring structure of the odd-number Fresnel zone. Since the upper surface of the metasurface 2 only transmits x-polarized electromagnetic waves, the metasurface 2 has polarization selectivity. The electromagnetic waves reflected by the Fresnel lens 1 cannot pass through the metasurface 2, forming a cavity effect between the Fresnel lens 1 and the metasurface 2. After multiple reflections, the electromagnetic waves finally obtain a unidirectional radiating pencil beam. At this time, the antenna operates in unidirectional radiation mode.

[0020] Furthermore, the number of Fresnel zones is set to 7, and the radius of each Fresnel zone is calculated using the following formula:

[0021]

[0022] Where, r n Let λ represent the nth Fresnel zone, 1≤n≤7, λ represent the free space wavelength corresponding to the antenna center frequency, and F represent the focal length of the Fresnel lens.

[0023] Furthermore, the specific process of changing the transmission phase of electromagnetic waves by controlling the half-circle angle α is as follows:

[0024] In electromagnetic simulation software, the metasurface unit is modeled, periodic boundary conditions are set, the half-arc angle α of the umbrella-shaped metal unit 7 is parameter scanned, and the mapping relationship between the half-arc angle α and the transmission phase is established and saved as a half-arc angle-transmission phase mapping database for future use.

[0025] Let the deflection angle θ of the reflected beam of the antenna in the bidirectional radiation mode of this embodiment be set, and let the phase of the metasurface elements in the same row or column be the same. Calculate the phase difference Δφ between two adjacent rows or columns of metasurface elements as follows:

[0026]

[0027] Where p is the period length of the metasurface unit;

[0028] Let the phase of the first row or column of metasurface units be 0°. Calculate the phase of each row or column of metasurface units using the phase difference Δφ. Based on the phase information of each row or column of metasurface units, find the half-arc angle corresponding to each position of the metasurface unit in the half-arc angle-transmission phase mapping database.

[0029] Furthermore, the first dielectric substrate 5 is made of Arlon Diclad 880 with a thickness of 0.762 mm and a side length of 123 mm; there is a 30 mm air gap between the Fresnel lens 1 and the metasurface 2.

[0030] Furthermore, both the second dielectric substrate 10 and the third dielectric substrate 11 are made of Arlon Diclad 880 and have a thickness of 0.762 mm; the two PCBs are bonded together by a 0.102 mm thick prepreg RO4450F.

[0031] Furthermore, the open waveguide feed antenna 3 is a standard waveguide WR-28, with an inner cross-section width of 7.12 mm and a short side of 3.556 mm, and an outer cross-section width of 9.14 mm and a short side of 5.59 mm.

[0032] Furthermore, the period length of the metasurface unit is p = 3.5 mm; in the first metal grid 6 and the second metal grid 9, the width of the metal strips is w1 = 0.8 mm, and the spacing between the metal strips is w2 = 0.95 mm; the parallel double-line structure strips of the umbrella-shaped metal unit 7 have a width t = 0.3 mm and a length l sh =3.15mm, gap g=0.1mm.

[0033] The beneficial effects of this invention are:

[0034] The antenna described in this invention is based on a Fresnel lens, and proposes a novel metasurface unit to form a metasurface; by utilizing the polarization selectivity and phase modulation capability of the metasurface, combined with the rotation of the feed antenna, unidirectional / bidirectional radiation reconfigurability is further realized;

[0035] The antenna described in this invention does not require the use of PIN diodes or single-pole double-throw switches, thus reducing research and development costs and complexity. At the same time, it also reduces the introduction of device insertion loss and parasitic effects, which is beneficial to the development of high-performance antennas and enables them to operate in millimeter wave or even higher frequency bands.

[0036] When the antenna of the present invention radiates in one direction, the polarization direction of the beam is the same as that of the feed antenna; when radiating in two directions, the polarization direction of the normal beam is the same as that of the feed antenna, the polarization direction of the back-radiating beam is orthogonal to that of the feed antenna, and the back-radiating beam can deviate from the normal direction. Attached Figure Description

[0037] Figure 1 These are side views and perspective views of the overall antenna structure described in this invention;

[0038] Figure 2 This is a schematic diagram of the metal concentric circle-ring structure in the antenna described in this invention;

[0039] Figure 3 This is a schematic diagram of the metasurface structure in the antenna described in this invention;

[0040] Figure 4 This is a schematic diagram of the metasurface unit in the antenna described in this invention;

[0041] Figure 5 The antenna described in the embodiment operates in bidirectional radiation mode. Simulation results of radiation pattern at the center frequency of the YOZ plane and the dual-beam gain as a function of frequency;

[0042] Figure 6 The antenna described in the embodiment operates in unidirectional radiation mode. Simulation results of radiation pattern of center frequency of YOZ plane and normal pen beam gain as a function of frequency. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0044] This embodiment provides a unidirectional / bidirectional reconfigurable antenna based on a Fresnel lens and a metasurface. The side view (left) and perspective view (right) of its overall structure are shown below. Figure 1 As shown, it includes a Fresnel lens 1, a metasurface 2, and an open waveguide feed antenna 3; the Fresnel lens 1 and the metasurface 2 are parallel and have an air gap in the middle. In actual use, the air gap can be formed by supporting materials such as nylon pillars and foam; the open waveguide feed antenna 3 is located at the center of the metasurface 2 and its open end is flush with the upper surface of the metasurface 2.

[0045] The Fresnel lens 1 includes a metal concentric circle-ring structure 4 and a first dielectric substrate 5; as shown Figure 2 As shown, the metal concentric circle-ring structure 4 is located on the lower surface of the first dielectric substrate 5; the first dielectric substrate 5 is square, and the metal concentric circle-ring structure 4 includes a metal circular patch and three metal ring patches; the center of the metal circular patch and the center of the three metal ring patches coincide with the center of the first dielectric substrate 5.

[0046] A schematic diagram of the structure of metasurface 2 is shown below. Figure 3As shown, the PCB consists of two PCB layers, which are bonded together by a prepreg. The upper PCB includes a first metal grid 6, a second dielectric substrate 10, and umbrella-shaped metal units 7. The lower PCB includes a second metal grid 9 and a third dielectric substrate 11. The first metal grid 6 is located on the upper surface of the second dielectric substrate 10 and consists of 2M periodically parallel first metal strips, which are parallel to the edges of the second dielectric substrate 10 (parallel to the y-axis). M×M periodically arranged umbrella-shaped metal units 7 are located on the lower surface of the second dielectric substrate 10. The second metal grid 9 is located on the lower surface of the third dielectric substrate 11 and consists of 2M periodically parallel second metal strips, which are perpendicular to the first metal strips (parallel to the x-axis) and have the same width, where M is a positive integer.

[0047] A cross-shaped through-hole 8 is opened at the center of the metasurface 2. The size of the cross-shaped through-hole 8 is the same as that of the two orthogonal open waveguide feed antennas 3, so that the open waveguide feed antennas 3 can be excited by illuminating the Fresnel lens 1 above through the cross-shaped through-hole 8.

[0048] The open waveguide feed antenna 3 is a standard waveguide.

[0049] Metasurface 2 can be divided into M×M metasurface elements. The period of each metasurface element is 1 / 3 of the free space wavelength corresponding to the antenna center frequency. A schematic diagram of the metasurface element structure is shown below. Figure 4 As shown; from top to bottom, the components are a first metal grid 6, a second dielectric substrate 10, an umbrella-shaped metal unit 7, a third dielectric substrate 11, and a second metal grid 9; in a metasurface unit, the first metal grid 6 and the second metal grid 9 are two metal strips respectively; the umbrella-shaped metal unit 7 includes a metal arc and a metal parallel double-line structure, the metal arc is axially symmetric about the metal parallel double-line structure; the center of the metal arc coincides with the center of the metasurface unit; the metal parallel double-line structure is located on the diagonal of the lower surface of the second dielectric substrate 10, with an angle of 45° to both the x-axis and y-axis, one end is in contact with the metal arc, and the other end extends towards the corner of the second dielectric substrate 10.

[0050] Let the angle between the end of the metal arc and the center be the half-arc angle α. By controlling the half-arc angle α, the transmission phase of the electromagnetic wave can be changed. The metal grid 6 on the upper surface of the metasurface 2 is along the y-axis, and the metal grid 9 on the lower surface is along the x-axis. Near the center frequency, the first metal grid 6 of the metasurface 2 can only transmit x-polarized electromagnetic waves, while the second metal grid 9 can only transmit y-polarized electromagnetic waves. The metasurface 2 can realize the transmission and conversion of x-polarized waves reflected by the Fresnel lens into y-polarized waves.

[0051] In this embodiment, the first dielectric substrate 5 is made of Arlon Diclad 880 (relative permittivity 2.2, loss tangent tanδ = 0.0009) and has a thickness of 0.762 mm. The overall array is square with a side length of 123 mm, corresponding to 11.5 times the free-space wavelength at the 28 GHz center frequency. There is a 30 mm air gap between the Fresnel lens 1 and the metasurface 2.

[0052] The second dielectric substrate 10 and the third dielectric substrate 11 are both made of Arlon Diclad 880 (relative permittivity 2.2, loss tangent tanδ=0.0009) and both have a thickness of 0.762mm. The two PCB layers are bonded together by a 0.102mm thick prepreg RO4450F (relative permittivity 3.52, loss tangent 0.004).

[0053] The open waveguide feed antenna 3 is a standard waveguide WR-28, with an inner cross-section width of 7.12 mm and a short side of 3.556 mm, and an outer cross-section width of 9.14 mm and a short side of 5.59 mm.

[0054] The metasurface unit has a structure of three metal layers sandwiching two dielectric layers, with a period of p = 3.5 mm. In the first metal grid 6 and the second metal grid 9, the width of the metal strips is w1 = 0.8 mm, and the spacing between the metal strips is w2 = 0.95 mm. The umbrella-shaped metal unit 7 has a strip width of t = 0.3 mm and a length of l. sh =3.15mm, gap g=0.1mm, the transmission phase of electromagnetic waves is changed by controlling the half-arc angle α.

[0055] The antenna described in this embodiment operates in both unidirectional and bidirectional radiation modes.

[0056] The wide side of the open waveguide feed antenna 3 is set along the y-direction, and its open end is kept flush with the upper surface of the metasurface. At this time, the open waveguide feed antenna 3 is x-polarized. Part of the x-polarized wave generated by the open waveguide feed antenna 3 is transmitted through the even-number Fresnel zone to form a normal pen beam; the other part is reflected by the metal concentric circle-ring structure of the odd-number Fresnel zone, and then refracted and polarized by the metasurface 2 to form a y-polarized back-deflected beam. At this time, the antenna operates in a bidirectional radiation mode.

[0057] The wide side of the open waveguide feed antenna 3 is set along the x-direction, and its open end is kept flush with the upper surface of the metasurface. At this time, the open waveguide feed antenna 3 is y-polarized. Part of the y-polarized wave generated by the open waveguide feed antenna 3 is transmitted through the even-number Fresnel zone, and the other part is reflected by the metal concentric circle-ring structure of the odd-number Fresnel zone. Since the upper surface of the metasurface 2 only transmits x-polarized electromagnetic waves, the metasurface 2 has polarization selectivity. The electromagnetic waves reflected by the Fresnel lens 1 cannot pass through the metasurface 2, forming a cavity effect between the Fresnel lens 1 and the metasurface 2. After multiple reflections, the electromagnetic waves finally obtain a unidirectional radiating pencil beam. At this time, the antenna operates in unidirectional radiation mode.

[0058] In this embodiment, the number of Fresnel zones is set to 7, and the radius of the Fresnel zone is calculated according to the following formula:

[0059]

[0060] Where, r n Let λ represent the nth Fresnel zone, 1≤n≤7, λ represent the free space wavelength corresponding to the antenna center frequency, and F represent the focal length of the Fresnel lens (the distance from the Fresnel lens to the aperture surface of the feed antenna).

[0061] In this embodiment, the specific process of changing the transmission phase of the electromagnetic wave by controlling the half-arc angle α is as follows:

[0062] In electromagnetic simulation software, the metasurface unit is modeled, periodic boundary conditions are set, the half-arc angle α of the umbrella-shaped metal unit 7 is parameter scanned, and the mapping relationship between the half-arc angle α and the transmission phase is established and saved as a half-arc angle-transmission phase mapping database for future use.

[0063] In this embodiment, the deflection angle θ of the reflected beam in bidirectional radiation mode is set. In this embodiment, the deflection angle of the back-facing radiation beam in bidirectional radiation mode is set to -150°. The phases of the same row or column of metasurface elements are made the same. The phase difference Δφ between two adjacent rows or columns of metasurface elements is calculated as follows:

[0064]

[0065] Where p is the period length of the metasurface unit;

[0066] Let the phase of the first row or column of metasurface units be 0°. Calculate the phase of each row or column of metasurface units using the phase difference Δφ. Based on the phase information of each row or column of metasurface units, find the half-arc angle corresponding to each position of the metasurface unit in the half-arc angle-transmission phase mapping database.

[0067] When the wide side of the open waveguide feed antenna 3 is placed along the y-axis through the cross-shaped through-hole 8, the antenna is in bidirectional radiation mode. The electromagnetic waves reflected by the Fresnel lens 1 can pass through the metasurface 2 to obtain a deflected / polarized beam. Figure 5 In the bidirectional radiation mode of the antenna described in the embodiment Simulation results of beam pattern and dual-beam gain versus frequency at the center frequency of the YOZ plane. At the center frequency, the beam gain is 16.6 dBi at θ = 0°, with sidelobe levels less than -14.4 dB and cross-polarization levels less than -30.8 dB; the beam gain is 14.7 dBi at θ = -150°, with sidelobe levels less than -11 dB and cross-polarization levels less than -28.9 dB. In the frequency range of 26.5 to 29.5 GHz, the beam gain is 14.5 to 17 dBi at θ = 0° and 12.9 to 17 dBi at θ = -150°; at any frequency, the gain difference between the normal and back beams is less than 1.9 dB.

[0068] When the wide side of the open waveguide feed antenna 3 is placed along the x-axis through the cross-shaped through-hole 8, the antenna is in unidirectional radiation mode. The electromagnetic waves reflected by the Fresnel lens 1 cannot pass through the metasurface 2. A cavity effect is formed between the Fresnel lens 1 and the metasurface 2. The electromagnetic waves are reflected multiple times in the cavity and finally radiate along the normal direction to obtain a unidirectional pen beam. Figure 6 In the unidirectional radiation mode of the antenna described in the embodiment Simulation results of beam pattern and normal pen beam gain at the center frequency of the YOZ plane as a function of frequency. At the center frequency, the beam gain at θ = 0° is 19.9 dBi, the sidelobe level is less than -14 dB, and the cross-polarization level is less than -26.9 dB. In the frequency range of 26.5 to 29.2 GHz, the beam gain at θ = 0° ranges from 17 to 19.9 dBi.

Claims

1. A unidirectional / bidirectional reconfigurable antenna based on a Fresnel lens and a metasurface, characterized in that, It includes a Fresnel lens (1), a metasurface (2) and an open waveguide feed antenna (3); the Fresnel lens (1) and the metasurface (2) are parallel and have an air gap in the middle; the open waveguide feed antenna (3) is located at the center of the metasurface (2) and its open end is flush with the upper surface of the metasurface (2); The Fresnel lens (1) includes a metal concentric circle-ring structure (4) and a first dielectric substrate (5); the metal concentric circle-ring structure (4) is located on the lower surface of the first dielectric substrate (5); the first dielectric substrate (5) is square, and the metal concentric circle-ring structure (4) includes a metal circular patch and three metal ring patches; the center of the metal circular patch and the center of the three metal ring patches coincide with the center of the first dielectric substrate (5); The metasurface (2) consists of two PCB layers, which are bonded together by a prepreg. The upper PCB includes a first metal grid (6), a second dielectric substrate (10), and umbrella-shaped metal units (7). The lower PCB includes a second metal grid (9) and a third dielectric substrate (11). The first metal grid (6) is located on the upper surface of the second dielectric substrate (10) and consists of 2M periodically parallel first metal strips. The first metal strips are parallel to the edge of the second dielectric substrate (10) and parallel to the y-axis. M×M periodically arranged umbrella-shaped metal units (7) are located on the lower surface of the second dielectric substrate (10). The second metal grid (9) is located on the lower surface of the third dielectric substrate (11) and consists of 2M periodically parallel second metal strips. The second metal strips are perpendicular to the first metal strips and parallel to the x-axis, with the same width, and M is a positive integer. A cross-shaped through hole (8) is opened in the center of the metasurface (2), and the size of the cross-shaped through hole (8) is the same as that of the two orthogonal open waveguide feed antennas (3); The open waveguide feed antenna (3) is a standard waveguide located in the cross-shaped through hole (8) of the metasurface (2), and its open end is flush with the upper surface of the metasurface. The antenna operates in both unidirectional and bidirectional radiation modes. The wide side of the open waveguide feed antenna (3) is set along the y direction, and its open end is kept flush with the upper surface of the metasurface. At this time, the open waveguide feed antenna (3) is x-polarized. Part of the x-polarized wave generated by the open waveguide feed antenna (3) is transmitted through the even Fresnel zone to form a normal pen beam. The other part is reflected by the metal concentric circle-ring structure of the odd Fresnel zone, and then refracted and polarized by the metasurface (2) to form a y-polarized back deflection beam. At this time, the antenna operates in a bidirectional radiation mode. The wide side of the open waveguide feed antenna (3) is set along the x-direction, and its open end is kept flush with the upper surface of the metasurface. At this time, the open waveguide feed antenna (3) is y-polarized. Part of the y-polarized wave generated by the open waveguide feed antenna (3) is transmitted through the even-number Fresnel zone; the other part is reflected by the metal concentric circle-ring structure of the odd-number Fresnel zone. Since the upper surface of the metasurface (2) only transmits x-polarized electromagnetic waves, the metasurface (2) has polarization selectivity. The electromagnetic waves reflected by the Fresnel lens (1) cannot pass through the metasurface (2). A cavity effect is formed between the Fresnel lens (1) and the metasurface (2). The electromagnetic waves are reflected multiple times and finally obtain a unidirectional radiating pen beam. At this time, the antenna working mode is unidirectional radiation.

2. The unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces according to claim 1, characterized in that, An air gap is formed between the Fresnel lens (1) and the metasurface (2) by nylon pillars or foam support.

3. The unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces according to claim 1, characterized in that, The metasurface (2) can be divided into M×M metasurface units, which are, from top to bottom, the first metal grid (6), the second dielectric substrate (10), the umbrella-shaped metal unit (7), the third dielectric substrate (11), and the second metal grid (9); in a metasurface unit, the first metal grid (6) and the second metal grid (9) are two metal strips respectively; the umbrella-shaped metal unit (7) includes a metal arc and a metal parallel double line structure, the metal arc is axially symmetric about the metal parallel double line structure; the center of the metal arc coincides with the center of the metasurface unit; the metal parallel double line structure is located on the diagonal of the lower surface of the second dielectric substrate (10), with an angle of 45° with both the x-axis and the y-axis, one end is in contact with the metal arc, and the other end extends towards the corner of the second dielectric substrate (10).

4. The unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces according to claim 3, characterized in that, In the umbrella-shaped metal unit (7) of the metasurface unit, the angle between the end of the metal arc and the center is denoted as the half-arc angle α. The transmission phase of the electromagnetic wave is changed by controlling the half-arc angle α. The metal grid (6) on the upper surface of the metasurface (2) is along the y-axis, and the metal grid (9) on the lower surface is along the x-axis. Near the center frequency, the first metal grid (6) of the metasurface (2) can only transmit x-polarized electromagnetic waves, while the second metal grid (9) can only transmit y-polarized electromagnetic waves. The metasurface (2) can realize the transmission of x-polarized waves reflected by the Fresnel lens and convert them into y-polarized waves.

5. The unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces according to claim 1, characterized in that, The number of Fresnel zones is set to 7. The radius of each Fresnel zone is calculated using the following formula: Where, r n Let λ represent the nth Fresnel zone, 1≤n≤7, λ represent the free space wavelength corresponding to the antenna center frequency, and F represent the focal length of the Fresnel lens.

6. The unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces according to claim 4, characterized in that, The specific process of changing the transmission phase of electromagnetic waves by controlling the half-circle angle α is as follows: In the electromagnetic simulation software, the metasurface unit is modeled, periodic boundary conditions are set, the half-arc angle α of the umbrella-shaped metal unit (7) is parameter scanned, the mapping relationship between the half-arc angle α and the transmission phase is established, and the half-arc angle-transmission phase mapping database is saved for later use. Let the deflection angle θ of the reflected beam of the antenna in bidirectional radiation mode be set, and let the phase of the metasurface elements in the same row or column be the same. Calculate the phase difference Δϕ between two adjacent rows or columns of metasurface elements as follows: Where p is the period length of the metasurface unit; The phase of the first row of metasurface units or the first column of metasurface units is set to 0°. The phase of each row of metasurface units or each column of metasurface units is calculated using the phase difference Δϕ. Based on the phase information of each row of metasurface units or each column of metasurface units, the half-arc angle corresponding to each position of the metasurface (2) is found in the half-arc angle-transmission phase mapping database.

7. The unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces according to claim 1, characterized in that, The first dielectric substrate (5) is made of Arlon Diclad 880 with a thickness of 0.762 mm and a side length of 123 mm. There is a 30 mm air gap between the Fresnel lens (1) and the metasurface (2). The second dielectric substrate (10) and the third dielectric substrate (11) are both made of Arlon Diclad 880 with a thickness of 0.762 mm. The two PCBs are bonded together by a 0.102 mm thick prepreg RO4450F.

8. The unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces according to claim 1, characterized in that, The open waveguide feed antenna (3) is a standard waveguide WR-28 with an inner cross-section width of 7.12 mm and a short side of 3.556 mm, and an outer cross-section width of 9.14 mm and a short side of 5.59 mm.

9. The unidirectional / bidirectional reconfigurable antenna based on Fresnel lenses and metasurfaces according to claim 4, characterized in that, The period length of the metasurface unit is p = 3.5 mm; in the first metal grid (6) and the second metal grid (9), the width of the metal strips is w1 = 0.8 mm, and the spacing between the metal strips is w2 = 0.95 mm; the parallel double-line structure strip of the umbrella-shaped metal unit (7) has a width t = 0.3 mm and a length l sh = 3.15mm, gap g = 0.1 mm.

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