Dual-band multi-polarization flexible transparent leaky-wave antenna based on artificial surface plasmons

Abstract

Disclosed is a dual-band multi-polarization flexible transparent leaky-wave antenna based on artificial surface plasmons, which comprises, from bottom to top, a flexible transparent dielectric substrate and a metal pattern layer attached thereto, and the metal pattern layer comprises, from left to right, a first coplanar waveguide feed structure, a first transition structure, an SSPP transmission line, a radiation patch, a second transition structure and a second coplanar waveguide feed structure.The basic mode and high-order mode of the SSPP transmission line are controlled, left-handed and right-handed dual-circularly polarized wave beam scanning is realized through Archimedes spiral lines in a low-frequency band of 4.5-7GHz, and linearly polarized wave beam continuous scanning is realized in a high-frequency band of 8.5-12.7GHz.The overall optical transmittance and visual transmittance of the antenna are both above 90%, and the antenna can be conformally attached to a curved surface.The present application is used to solve the problems of low radiation efficiency, single frequency band and incomplete visual transparency of traditional transparent antennas, and has important application value in the fields of satellite communication, intelligent building glass and vehicle-mounted radar.

Description

Technical Field

[0001] This invention relates to the fields of antenna technology and artificial electromagnetic materials, specifically to a dual-band multi-polarization flexible transparent leaky wave antenna based on artificial surface plasmons. Background Technology

[0002] Artificial surface plasmons (SSPPs) can simulate the propagation characteristics of natural surface plasmons in the microwave and terahertz bands, exhibiting high field confinement and slow wave characteristics. The emergence of two-dimensional planar SSPP structures provides a new approach for designing low-profile, lightweight, and easily integrated microwave devices and antennas. Among them, SSPP leaky-wave antennas have shown great application potential in target detection, beam tracking, and satellite communications.

[0003] With the increasing complexity of the electromagnetic environment and the development of next-generation wireless communication systems, higher demands are being placed on the functional integration and environmental adaptability of SSPP leaky wave antennas. Firstly, compared to single-band antennas, dual-band designs that enable two independent frequency band beam scanning within the same physical structure can significantly improve spectrum utilization. Secondly, in scenarios such as mobile terminals, vehicle radar, and the Internet of Things (IoT), polarization multiplexing technology is crucial for improving link reliability and suppressing multipath effects, requiring antennas to possess multi-polarization radiation capabilities. In existing technologies, the literature “SY Lei, G. Wei, KK Han, TC Qiu, and M. Wang, Dual circularly polarized and linearly sweeping leaky-wave antenna. IEEE Trans. Antennas Propag., vol. 23, no. 1, pp. 369-372, Jan.2024.” achieves dual circularly polarized radiation by loading a single-arm Archimedean spiral, but cannot generate linearly polarized waves. Another literature, “M. Wang, HC Wang, SC Tian, ​​HF Ma, and TJ Cui, Spatial multi-polarized leaky-wave antenna based on spoof surface plasmon polaritons. IEEE Trans. Antennas Propag., vol. 68, no. 12, pp. 8168-8173, Dec. 2020.” employs an orthogonal skew slot structure, which can achieve polarization reconstruction by adding an external metal reflector, but has a single operating frequency band and a complex system. On the other hand, optically transparent antennas can transmit and receive microwave signals without affecting visible light transmission, thus overcoming the installation limitations of traditional antennas and achieving stealthy integration with environments such as building windows and vehicle glass. However, traditional transparent conductive materials such as indium tin oxide (ITO) inherently suffer from high resistance and low radiation efficiency. The recently proposed quasi-one-dimensional SSPP structure composed of fine metal wires provides a new approach for highly transparent and efficient antennas, but its feed section (such as the coplanar waveguide) still uses continuous metal patches, creating visual obstruction and impairing the overall visual transparency. Moreover, most of these antennas can only achieve end-fire radiation, limiting their application scenarios.

[0004] In summary, existing SSPP leaky wave antennas suffer from problems such as limited functionality, incomplete transparency, and insufficient flexible integration capabilities. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention proposes a dual-band multi-polarization flexible transparent leaky wave antenna based on artificial surface plasmon resonance (ASPR), hereinafter referred to as the "antenna". The antenna comprises, from bottom to top, a flexible transparent dielectric substrate 1 and a metal pattern layer 2 attached to the upper surface of the dielectric substrate. The flexible transparent dielectric substrate 1 is hereinafter referred to as substrate 1. The metal pattern layer 2 comprises, from left to right, the following: a first coplanar waveguide feeding structure 21, a first transition structure 22, an SSPP transmission line 23, a radiating patch 24, a second transition structure 25, and a second coplanar waveguide feeding structure 26. Taking the plane where the dielectric substrate 1 is located as the reference plane, the direction along the electromagnetic wave propagation direction is defined as the transverse direction, and the direction perpendicular to the transverse direction in the reference plane is defined as the longitudinal direction. The first coplanar waveguide feeding structure 21 is divided into left and right halves with the antenna central axis as the axis of symmetry. The left and right halves are arranged back to back in the same shape of a quarter circle. One right-angled side of the two quarter circles coincides with the left edge of the substrate 1, and the other right-angled side is parallel to the antenna central axis and symmetrical about it. A certain distance is maintained between the two quarter circles. The lower quarter circle includes a rectangular ground layer adjacent to the left edge of substrate 1 and a curved shape on its right, which are integrally formed; The first transition structure 22 comprises a rectangular strip-shaped central conductor adjacent to the left edge of the substrate 1 and a tower-shaped body that widens from narrow to wide on its right side. The central conductor and the tower-shaped body are integrally formed. The length of the central conductor and the rectangular ground layer of the first coplanar waveguide feed structure 21 along the antenna's central axis is equal. The left edge of the central conductor coincides with the left edge of the substrate 1. The length from the left edge of the central conductor to the widest point on the right side of the tower-shaped body is equal to the maximum length of a quarter circle along the antenna's central axis. The first transition structure 22 is quantified into several rectangles. Therefore, the first transition structure 22 is composed of multiple rectangles from left to right. The first transition structure 22 is symmetrical about the antenna's central axis. Each rectangle is a hollow metal frame. The central conductor includes several rectangles of the same shape. The rectangles included in the tower-shaped body have the same height in the lateral direction and their width in the longitudinal direction gradually increases in an arithmetic progression. The SSPP transmission line 23 is a planar single-layer structure composed of multiple quasi-one-dimensional SSPP units arranged periodically along the transmission direction. Each quasi-one-dimensional SSPP unit is a centrally symmetrical double-L-shaped pattern, which consists of a left L-shaped frame and a right L-shaped frame. The left L-shaped frame is a hollow frame composed of six metal wire segments connected end to end, and is the shape of a vertical L-shaped frame rotated 90° clockwise. The right L-shaped frame is the shape of the left L-shaped frame rotated 180° with its lower right corner as the center. The left and right L-shaped frames are electrically connected, and adjacent quasi-one-dimensional SSPP units are electrically connected. The left and right sides of the SSPP transmission line 23 are electrically connected to the first transition structure 22 and the second transition structure 25, respectively. Radiating patches 24 consist of multiple pairs of spirals arranged in pairs on both sides of the SSPP transmission line 23. The starting position of the radiating patches 24 is located after most of the high-frequency leakage radiation energy on the SSPP transmission line 23 has leaked out. The leftmost spiral starts from the Mth element of the SSPP transmission line 23, with the starting point being the point closest to the SSPP transmission line 23, and extends inward in a rotating manner. The first spiral on the lower left side extends inward in a rotating manner from the midpoint of the quasi-one-dimensional SSPP element, and the first spiral on the upper left side extends inward in a rotating manner from the starting line of the next quasi-one-dimensional SSPP element on the right. These two are a pair of spirals. The second spiral on the lower left side is arranged with a quasi-one-dimensional SSPP element between it and the first spiral on the lower left side, and the second spiral on the upper left side is arranged with a quasi-one-dimensional SSPP element between it and the first spiral on the upper left side. Multiple pairs of spirals are arranged along the antenna's central axis until the last quasi-one-dimensional SSPP element. The spirals are arranged in pairs. The outer rings of adjacent spirals do not touch, maintaining electrical insulation. The spirals do not touch the SSPP transmission line 23. The second transition structure 25 is symmetrical to the first transition structure 22 about the central axis of the width direction of the substrate 1; The second coplanar waveguide feeding structure 26 is symmetrical to the first coplanar waveguide feeding structure 21 about the central axis of the width direction of the substrate 1. The first coplanar waveguide feeding structure 21 and the second coplanar waveguide feeding structure 26 adopt a periodic silver grid pattern.

[0006] In one specific embodiment of the present invention, 15 quasi-one-dimensional SSPP units are used, with the leftmost spiral line starting from the eighth SSPP unit of SSPP transmission line 23.

[0007] In one embodiment of the present invention, the left L-shaped frame includes a "horizontal part" and a "vertical part". The width of the "horizontal part" can be adjusted to change the groove depth h and change the operating frequency band. The width of the "vertical part" is narrower than that of the "horizontal part" to ensure that the groove width a is large enough.

[0008] In another embodiment of the invention, a spatial rectangular coordinate system is established, with the x-axis pointing in the direction of electromagnetic wave propagation, the y-axis pointing upwards, and the z-axis perpendicular to the XY plane and pointing outwards. The curved edge of the shape is expressed as a function of the curve profile. ,in, x Let be the coordinates along the x-axis. y Let C1 and C2 be the coordinates along the y-axis, and C1 and C2 be constants determined based on the initial coordinates. is the curvature factor.

[0009] In another specific embodiment of the present invention, the first coplanar waveguide feeding structure 21 and the second coplanar waveguide feeding structure 26 adopt a periodic silver grid pattern, with a period gm=200μm and a linewidth Wm=20μm; the period gm=200μm of the central conductor of the first transition structure 22 and the second transition structure 25 is 200μm.

[0010] In another embodiment of the present invention, the tower-shaped body of the first transition structure 22 and the second transition structure 25 is provided with a depth gradient structure of 3 to 7 levels, the width of the starting end along the longitudinal direction is 3 to 6 mm, and the width of the ending end along the longitudinal direction is 0.5 to 2 mm.

[0011] In another specific embodiment of the present invention, the metal branches of the transition structures 22 and 25 are provided with a total of 5 levels of depth from the starting end to the end end, namely: h1=5mm, h2=4mm, h3=3mm, h4=2mm, and h5=1mm.

[0012] In another specific embodiment of the present invention, the specific geometric parameters of the quasi-one-dimensional SSPP unit are: period P = 13.9 mm, metal line width w = 0.1 mm, slot width a = 6.5 mm, slot depth h = 3 mm, unit width d = 7 mm, and substrate thickness t = 0.125 mm; the cutoff frequency is changed by adjusting the value of h, thereby controlling the range of the two frequency bands.

[0013] In another specific embodiment of the present invention, a total of 8 spirals are symmetrically arranged on both the upper and lower sides of the latter half of the SSPP transmission line, 4 on the top and 4 on the bottom. The trajectory of the Archimedean spiral is derived from the polar coordinate equation. Defined as follows: initial radius r0 = 2 mm, outer radius r1 = 13 mm, line width w = 0.1 mm. The Archimedean spiral spirals from the inside out along the trajectory, with a total number of rotations denoted as T = 7.5. The rotation angle represents the polar coordinates; the correspondence between the above parameters and the geometric position of the helix is ​​as follows: r0 corresponds to the radius of the starting point of the innermost loop of the helix; r1 corresponds to the radius of the outermost loop of the helix; w corresponds to the width of the thin metal wire that makes up the helix pattern; T corresponds to the total number of loops from the starting point of the inner loop to the ending point of the outer loop; the spacing between adjacent Archimedean spirals along the transmission direction is P1 = 27.8 mm, corresponding to the spacing between the center points of two adjacent spirals along the antenna axis; the spacing between the spiral and the SSPP transmission line 23 is gr = 0.1 mm, corresponding to the vertical spacing between the starting end of the outermost loop of the spiral and the edge of the SSPP transmission line 23.

[0014] In another specific embodiment of the present invention, the grounding layer width W0 of the coplanar waveguide feeding structures 21 and 26 is 33 mm, the width of the center conductor h5 is 1 mm, and the height of both the grounding layer and the center conductor is... The distance between the grounding layer and the center conductor is gs=0.1mm.

[0015] The advantages of this invention are as follows: First, the leaky antenna of this invention has the advantages of both flexibility and optical transparency. It adopts a silver grid and fine silver wire structure to achieve visual stealth of the antenna. At the same time, the overall structure is based on a flexible PET substrate, which can be conformally attached to complex curved surface devices such as building glass, car windows, and aircraft radomes.

[0016] Secondly, this invention simultaneously achieves dual-band independent beam scanning and multi-polarization radiation within a single antenna structure. By simultaneously manipulating the basic and higher-order modes of the SSPP transmission line, left-hand and right-hand circular polarization beam scanning is achieved in the low-frequency band, and continuous linear polarization beam scanning is achieved in the high-frequency band. This dual-band multi-polarization characteristic enables it to flexibly adapt to complex electromagnetic environments such as satellite communication, mobile communication, and radar detection, significantly improving the system's anti-interference and spectrum utilization capabilities.

[0017] This invention effectively solves the contradictory problems of low radiation efficiency, single frequency band, fixed polarization mode and incomplete visual transparency of traditional transparent antennas. It has excellent flexibility and high transparency, and therefore has high application value. Attached Figure Description

[0018] Figure 1 This invention presents a schematic diagram of the overall structure and application scenarios of a dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons (hereinafter referred to as "leaky antenna"). Figure 1 (a) shows the main structure of the antenna and a partial enlarged view. Figure 1 (b) illustrates a dual-circularly polarized radiation scenario used for satellite communications. Figure 1 (c) Shows a linearly polarized radiation scenario for wireless communication attached to building glass; Figure 2 The diagram shows the principle of dual-band leaky wave radiation of a leaky wave antenna, in which... Figure 2 (a) shows the Brillouin diagram of the slow-wave structure. Figure 2 (b) shows a schematic diagram of the radiation mode of the loaded patch; Figure 3 The diagram shows a schematic and characteristic diagram of a quasi-one-dimensional SSPP element structure, in which... Figure 3 (a) shows the unit design process. Figure 3 (b) Shows the dispersion curves of the fundamental mode and the -1st spatial harmonic of the quasi-one-dimensional SSPP element, and compares them with the dispersion curve of the fundamental mode of the two-dimensional SSPP element. Figure 3 (c) and (d) show the energy binding properties of quasi-one-dimensional SSPP elements and two-dimensional SSPP elements, respectively. Figure 4The diagram shows a comparison of the electric field amplitudes of quasi-one-dimensional SSPP elements and two-dimensional SSPP elements at different cross sections, where... Figure 4 (a) shows a comparison diagram of the electric field amplitude at section 1. Figure 4 (b) Shows a comparison diagram of the electric field amplitude at section 2; Figure 5 The diagram shows the geometric parameters of a quasi-one-dimensional SSPP element and the dispersion curves at different groove depths h. Figure 5 (a) shows the annotation diagram of the element geometric parameters. Figure 5 (b) Shows the dispersion curves corresponding to different groove depths; Figure 6 The diagram shows the structural schematic and simulation results of a single-band leaky wave antenna. Figure 6 (a) shows a schematic diagram of the structure. Figure 6 (b) Shows the simulation S-parameters; Figure 7 The electric field distribution of the single-band radiation structure at 4 GHz, 5.4 GHz, 6.8 GHz, and 10 GHz is shown. Figure 8 The diagram shows the structure and electric field distribution of the leaky antenna. Figure 8 (a) shows a schematic diagram of the structure. Figure 8 (b) shows the electric field distribution at 5.4 GHz; Figure 9 The graph shows the variation of the S-parameters of the leaky wave antenna under different r1 values, where Figure 9 (a) shows a graph illustrating the variation in the reflectance coefficient. Figure 9 (b) shows a graph illustrating the variation of the transmission coefficient; Figure 10 The simulated radiation performance of the leaky wave antenna is shown, in which... Figure 10 (a) shows the simulation results of the S-parameters. Figure 10 (b) shows the simulation results of the shaft ratio. Figure 10 (c) and (d) show the simulation results of radiation efficiency and actual gain for circular and linear polarization, respectively; Figure 11 The normalized two-dimensional radiation pattern of the antenna at a selected frequency is shown, where Figure 11 (a) shows a two-dimensional radiation pattern with left-handed circular polarization. Figure 11 (b) shows a two-dimensional radiation pattern with right-hand circular polarization. Figure 11 (c) Shows a two-dimensional radiation pattern with linear polarization; Figure 12 The diagram shows the three-dimensional radiation pattern and electric field distribution of the antenna at a selected frequency. Figure 12 (a) shows the three-dimensional radiation pattern and electric field distribution of circular polarization. Figure 12 (b) shows the three-dimensional radiation pattern and electric field distribution of linear polarization. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0020] This invention proposes a dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons (hereinafter referred to as "leaky antenna"), such as... Figure 1 As shown in (a), the antenna comprises, from bottom to top, a flexible transparent dielectric substrate 1 (hereinafter referred to as substrate 1) and a metal pattern layer 2 attached to the upper surface of the dielectric substrate, as follows: Figure 1 (a) As shown in the enlarged view, the metal pattern layer 2 includes, from left to right, the following components: coplanar waveguide feeding structure 21, transition structure 22, SSPP transmission line 23, radiating patch 24, transition structure 25, and coplanar waveguide feeding structure 26.

[0021] To facilitate an accurate description of the structure, the plane containing the dielectric substrate 1 is taken as the reference plane. In the reference plane, the direction along the electromagnetic wave transmission direction (i.e., the length direction of the dielectric substrate) is defined as the transverse direction, and the direction perpendicular to the transverse direction (i.e., the width direction of the dielectric substrate) in the reference plane is defined as the longitudinal direction.

[0022] The coplanar waveguide feeding structure 21 is divided into left and right halves with the central axis of the substrate 1 (hereinafter referred to as the "antenna central axis") as the axis of symmetry. The left and right halves are arranged back to back in the same shape of a quarter circle. One right-angled side of the two quarter circles coincides with the left edge of the substrate 1, and the other right-angled side is parallel to the antenna central axis and symmetrical about it. A certain distance is maintained between the two quarter circles.

[0023] The following description uses a square-shaped quarter-circle as an example. The square-shaped quarter-circle includes a rectangular ground layer immediately adjacent to the left edge of substrate 1 and a curved edge on its right side, both integrally formed. For example... Figure 1 As shown, a spatial rectangular coordinate system is established, with the x-axis pointing in the direction of electromagnetic wave propagation (the horizontal direction mentioned above), the y-axis pointing upwards (the vertical direction mentioned above), and the z-axis perpendicular to the paper and pointing outwards. The curved edges of the shape adopt a specific curve profile, the function expression of which is: ,in, x Let be the coordinates along the x-axis. y Let C1 and C2 be the coordinates along the y-axis, and C1 and C2 be constants determined based on the initial coordinates. The curvature factor is optimized to a value of, for example, 0.26.

[0024] The first transition structure 22 comprises a rectangular elongated central conductor adjacent to the left edge of the substrate 1 and a tower-shaped body that widens from narrow to wide on its right side. The central conductor and the tower-shaped body are integrally formed. The length of the central conductor and the rectangular ground layer of the coplanar waveguide feed structure 21 along the antenna's central axis is equal. The left edge of the central conductor coincides with the left edge of the substrate 1, and the length from the left edge of the central conductor to the widest point on the right side of the tower-shaped body is equal to the maximum length of the aforementioned quarter-circle along the antenna's central axis. The first transition structure 22 is quantified into several rectangles; therefore, the transition structure 22 is composed of multiple rectangles from left to right. The transition structure 22 is symmetrical about the antenna's central axis, and each rectangle is a hollow metal frame. The central conductor comprises several rectangles of the same shape, and the rectangles included in the tower-shaped body have the same horizontal height and their vertical widths gradually increase in an arithmetic progression, i.e., the width difference between each subsequent rectangle and the preceding rectangle is equal.

[0025] The SSPP transmission line 23 is a planar single-layer structure. It consists of multiple quasi-one-dimensional SSPP units arranged periodically along the transmission direction. The number of units can be odd or even, and the specific number can be flexibly adjusted according to the actual size requirements and gain requirements of the antenna. In a preferred embodiment of the present invention, 15 quasi-one-dimensional SSPP units are used. Each quasi-one-dimensional SSPP unit is a centrally symmetrical double-L-shaped pattern. This double-L-shaped structure consists of a left L-shaped frame and a right L-shaped frame. The left L-shaped frame is a hollow frame, formed by six metal wire segments connected end to end in sequence, and is the shape of a vertical L-shaped frame rotated 90° clockwise. The right L-shaped frame is also a hollow frame, and is the shape of the left L-shaped frame rotated 180 degrees with its lower right corner as the center. The left and right L-shaped frames are electrically connected, and adjacent quasi-one-dimensional SSPP units are electrically connected. The left and right sides of the SSPP transmission line 23 are electrically connected to the first transition structure 22 and the second transition structure 25, respectively.

[0026] The left L-shaped border includes a wider "horizontal section" and a narrower "vertical section," as shown below. Figure 5 As shown in (a), the width of the "horizontal section" can be adjusted to change the groove depth h and thus the operating frequency band; the narrower width of the "vertical section" ensures that the groove width a is large enough to confine the energy to the unit surface. This is not the only option and can be adjusted according to the needs of different frequency bands.

[0027] The radiating patch 24 consists of multiple pairs of spirals arranged in pairs on both sides of the SSPP transmission line 23. To avoid mutual interference between high-frequency leakage radiation and low-frequency radiation, the initial position of the radiating patch 24 should be located after most of the high-frequency leakage radiation energy has leaked out on the SSPP transmission line 23. In a preferred embodiment of the invention, the leftmost spiral starts from the eighth unit of the SSPP transmission line 23, with the starting point being the point closest to the SSPP transmission line 23, and extends inward in a rotating manner. If the total number of units in the SSPP transmission line 23 changes, the specific starting unit position of the radiating patch 24 can be determined through simulation based on the aforementioned principle of "the position where most of the high-frequency energy has leaked out". The first spiral on the lower left side extends from the midpoint of the quasi-one-dimensional SSPP element inwards, and the first spiral on the upper left side extends from the starting point of the next quasi-one-dimensional SSPP element on the right inwards. These two are considered a pair of spirals. The second spiral on the lower left side is arranged with a gap of one quasi-one-dimensional SSPP element between it and the first spiral on the lower left side, and the second spiral on the upper left side is arranged with a gap of one quasi-one-dimensional SSPP element between it and the first spiral on the upper left side. Multiple pairs of spirals are arranged along the antenna's central axis until the last quasi-one-dimensional SSPP element, with the spirals arranged in pairs. The outer rings of adjacent spirals do not touch, maintaining electrical insulation.

[0028] The spiral line does not contact the SSPP transmission line 23.

[0029] The second transition structure 25 is symmetrical to the transition structure 22 about the central axis of the width direction of the substrate 1.

[0030] The coplanar waveguide feeding structure 26 is symmetrical to the coplanar waveguide feeding structure 21 about the central axis of the width direction of the substrate 1.

[0031] In one embodiment of the present invention: the substrate 1 is a flexible transparent polyethylene terephthalate (PET) substrate with a thickness of 0.125 mm. The dielectric constant of the substrate 1 is 3.3 and the loss tangent is 0.003. In another embodiment of the invention, the coplanar waveguide feeding structures 21 and 26 as a whole, and the transition structures 22 and 25 adopt a periodic silver grid pattern to replace the traditional continuous metal patch. The period of the silver grid is gm=200μm and the linewidth is Wm=20μm.

[0032] In another specific embodiment of the present invention, the grounding layer height W0 of the coplanar waveguide feeding structures 21 and 26 is 33mm, the height of the center conductor h5 is 1mm, and the width of both the grounding layer and the center conductor is... The distance between the grounding layer and the center conductor is gs=0.1mm.

[0033] In another embodiment of the invention, the depth of the tower-shaped structures 22 and 25 decreases in a stepped manner from the end near the coplanar waveguide feed structure to the end near the SSPP transmission line. The tower-shaped structure has multiple levels (e.g., 3 to 7 levels) of depth gradient, with the initial depth preferably ranging from 3 to 6 mm and the final depth preferably ranging from 0.5 to 2 mm, to achieve a smooth transition and impedance matching from the coplanar waveguide mode to the SSPP mode. Specifically, a total of 5 depth levels are provided from the initial to the final, in the following order: h1 = 5 mm, h2 = 4 mm, h3 = 3 mm, h4 = 2 mm, and h5 = 1 mm.

[0034] like Figure 1 As shown in (b), the leaky wave antenna can be used in scenarios such as satellite communication, mobile communication and drone tracking.

[0035] Figure 2 (a) is a Brillouin diagram of a slow-wave structure. The region below the free-space ray (black dashed line) is the slow-wave region, and the region above it is the fast-wave region. The fundamental mode (solid line on the right) of the quasi-one-dimensional SSPP unit is always located in the slow-wave region and cannot be directly radiated. However, due to the periodicity of the transmission line, the quasi-one-dimensional SSPP unit generates spatial harmonics. When the -1st harmonic (solid line on the left) enters the fast-wave region, the leakage radiation condition is met, resulting in beam scanning. In this invention, the high-frequency band (8.5-12.7 GHz) utilizes this principle to achieve linearly polarized leakage radiation. Figure 2 (b) is a schematic diagram of the radiation mode after the radiating patch is loaded. In the low-frequency band (4.5-7GHz), the fundamental mode of the quasi-one-dimensional SSPP unit is in the slow-wave region and cannot be radiated through spatial harmonics. At this time, the SSPP transmission line 23 acts as a slow-wave transmission line, transmitting energy to the Archimedean spiral radiating patch 24. Beam scanning is achieved through the phase difference between adjacent patches, generating circularly polarized radiation.

[0036] Figure 3 (a) The unit design process is given, from the traditional two-dimensional SSPP continuous metal structure, by increasing the slot width 'a', it evolves into two L-shaped metal structures connected only diagonally, and finally forms the quasi-one-dimensional fine metal wire structure of the present invention. Figure 3 The last image in (a) shows the quasi-one-dimensional fine metal wire structure ultimately adopted in this invention. The term "quasi-one-dimensional fine metal wire structure" refers to a structure that differs from traditional two-dimensional continuous metal patch structures. It is a linear border pattern formed by extremely fine metal wires with linewidths much smaller than the working wavelength. Although this linear border has a certain geometric width in the lateral direction, it does not contain a large area of ​​continuous metal surface; therefore, it is defined as a "quasi-one-dimensional" structure. The first two images serve as a comparison and transitional reference, aiming to illustrate that by increasing the slot width and refining the metal structure, the final quasi-one-dimensional structure can be evolved. The quasi-one-dimensional structure achieves high transparency while maintaining the characteristics of SSPP. Figure 3The last image in (a) shows the quasi-one-dimensional structure proposed in this invention. Both L-shaped structures are outlined with metal lines, and the middle is empty. Figure 3 (b) A comparison of the dispersion curves of the quasi-one-dimensional SSPP unit and the two-dimensional SSPP unit is given. It can be seen that the quasi-one-dimensional structure has a lower cutoff frequency and a stronger slow wave effect. Figure 3 (c) and (d) provide the electric field energy distribution diagrams. Figure 4 The electric field amplitude curves along section 1 and section 2 both show that the quasi-one-dimensional SSPP element confines the energy more tightly near the metal dendrites, resulting in a significant field enhancement effect.

[0037] Figure 5 (a) The specific geometric parameters of the quasi-one-dimensional SSPP cell are given: period P = 13.9 mm, metal line width w = 0.1 mm, groove width a = 6.5 mm, groove depth h = 3 mm, cell width d = 7 mm, and substrate thickness t = 0.125 mm. Figure 5 (b) Dispersion curves for different h values ​​are given. It can be seen that the larger the h value, the lower the cutoff frequency. Therefore, the cutoff frequency can be changed by adjusting the h value, thereby controlling the range of the two frequency bands.

[0038] Figure 6 (a) A schematic diagram of a single-band linear polarization radiation structure is given, including coplanar waveguide feeding structures 21 and 26, transition structures 22 and 25 and SSPP transmission line 23. Figure 6 (b) The simulation S-parameters are given. The results show that in the 4-6.8 GHz band, S21 is relatively high, which is the transmission state; in the 8.5-12.7 GHz band, S21 drops to below -10 dB, and S11 is also below -10 dB, indicating that the energy is effectively radiated.

[0039] Figure 7 The electric field distribution of the single-band linearly polarized radiation structure is presented. At 4 GHz, 5.4 GHz, and 6.8 GHz, energy propagates along SSPP transmission line 23, and the field confinement gradually strengthens with increasing frequency. At 10 GHz, energy significantly leaks into free space, verifying the leakage radiation mechanism.

[0040] Figure 8 (a) A diagram of the leaky antenna structure after loading the Archimedean spirals is given. The latter half of the SSPP transmission line has a total of 8 spirals symmetrically arranged on both the upper and lower sides, 4 on each side. The trajectory of the Archimedean spirals is given by the polar coordinate equation. Defined as follows: initial radius r0 = 2 mm, outer radius r1 = 13 mm, line width w = 0.1 mm. The Archimedean spiral spirals from the inside out along the trajectory, with a total number of rotations denoted as T = 7.5. Represents the rotation angle in polar coordinates. Combined with... Figure 8(a) is a partially enlarged view. The correspondence between the above parameters and the geometric position of the spiral is as follows: r0 corresponds to the radius of the starting point of the innermost spiral; r1 corresponds to the radius of the outermost spiral; w corresponds to the width of the thin metal wire that makes up the spiral pattern; T corresponds to the total number of turns from the starting point of the inner spiral to the ending point of the outer spiral; the spacing between adjacent Archimedean spirals along the transmission direction is P1 = 27.8 mm, which corresponds to the spacing between the center points of two adjacent spirals along the antenna axis; the spacing between the spiral and the SSPP transmission line 23 is gr = 0.1 mm, which corresponds to the vertical spacing between the starting end of the outermost spiral and the edge of the SSPP transmission line 23. Figure 8 (b) The electric field distribution at 5.4 GHz is given, showing that energy is coupled from the SSPP transmission line 23 to the helix and radiates outward.

[0041] Figure 9 The effect of r1 on S-parameters is shown. When r1 increases from 11.9 mm to 13 mm, the S21 in the low-frequency band shifts significantly to lower frequencies, and the operating bandwidth expands, while the S-parameters in the high-frequency band remain almost unchanged, confirming that the dual-band independent controllability is achieved.

[0042] Figure 10 The simulated radiation performance of the leaky-wave antenna is presented. Figure 10 (a) Simulation results of S-parameters are given. S11 is below -10dB in both frequency bands. Figure 10 (b) The axial ratio is given. The axial ratios of both left-handed and right-handed circular polarization in the low-frequency range are below -3dB, indicating good circular polarization performance. Figure 10 (c) and (d) give the radiation efficiency and gain of circular polarization and linear polarization, respectively. The average radiation efficiency in the low frequency band is about 90%, and the gain is 6-10.9 dBi; the radiation efficiency in the high frequency band is 78%-95%, and the peak gain is about 10 dBi.

[0043] Figure 11 Give a normalized two-dimensional radiation pattern. Figure 11 (a) and (b) show that, within the 4.5-7 GHz range, the left-hand circularly polarized and right-hand circularly polarized beams scan from -40° to -83° and from +40° to +83°, respectively, with a scanning range of 43°. Figure 11 (c) shows that within the range of 8.5–12.7 GHz, the linearly polarized beam gradually splits from a single beam into a symmetrical dual beam, scanning up to ±87°.

[0044] Figure 12 The three-dimensional radiation pattern and near-field electric field distribution are given. Figure 12 (a) Give the three-dimensional radiation pattern of circularly polarized radiation in the low-frequency band. Figure 12 (b) Three-dimensional radiation patterns of linearly polarized radiation in the high-frequency band are presented, all showing continuous beam scanning with frequency. The near-field distribution further verifies the energy leakage and coupling processes.

[0045] This invention achieves dual circular polarization beam scanning (left-hand and right-hand circular polarization) via an Archimedean spiral in the low-frequency band (4.5-7 GHz) using the basic and higher-order modes of the SSPP transmission line, with a scanning range of 43°. In the high-frequency band (8.5-12.7 GHz), it achieves continuous linear polarization beam scanning via the -1st spatial harmonic, achieving a radiation efficiency of 78%-95% and a peak gain of approximately 10 dBi. The antenna boasts an overall optical and visual transmittance exceeding 90% and is flexible enough to conformally attach to curved surfaces. This invention solves the problems of low radiation efficiency, single frequency band, and incomplete visual transparency inherent in traditional transparent antennas, and has significant application value in satellite communications, smart building glass, and automotive radar.

Claims

1. A dual-band multi-polarization flexible transparent leaky-wave antenna based on artificial surface plasmon resonances, hereinafter referred to as "antenna", comprising, from bottom to top, a flexible transparent dielectric substrate 1 and a metal pattern layer 2 attached to the upper surface of the dielectric substrate, the flexible transparent dielectric substrate 1 hereinafter referred to as substrate 1, characterized in that, The metal pattern layer 2 includes, from left to right, the following: a first coplanar waveguide feeding structure 21, a first transition structure 22, an SSPP transmission line 23, a radiating patch 24, a second transition structure 25, and a second coplanar waveguide feeding structure 26. Taking the plane where the dielectric substrate 1 is located as the reference plane, the direction along the electromagnetic wave propagation direction is defined as the transverse direction, and the direction perpendicular to the transverse direction in the reference plane is defined as the longitudinal direction. The first coplanar waveguide feeding structure 21 is divided into left and right halves with the antenna central axis as the axis of symmetry. The left and right halves are arranged back to back in the same shape of a quarter circle. One right-angled side of the two quarter circles coincides with the left edge of the substrate 1, and the other right-angled side is parallel to the antenna central axis and symmetrical about it. A certain distance is maintained between the two quarter circles. The lower quarter circle includes a rectangular ground layer adjacent to the left edge of substrate 1 and a curved shape on its right, which are integrally formed; The first transition structure 22 comprises a rectangular strip-shaped central conductor adjacent to the left edge of the substrate 1 and a tower-shaped body that widens from narrow to wide on its right side. The central conductor and the tower-shaped body are integrally formed. The length of the central conductor and the rectangular ground layer of the first coplanar waveguide feed structure 21 along the antenna's central axis is equal. The left edge of the central conductor coincides with the left edge of the substrate 1. The length from the left edge of the central conductor to the widest point on the right side of the tower-shaped body is equal to the maximum length of a quarter circle along the antenna's central axis. The first transition structure 22 is quantified into several rectangles. Therefore, the first transition structure 22 is composed of multiple rectangles from left to right. The first transition structure 22 is symmetrical about the antenna's central axis. Each rectangle is a hollow metal frame. The central conductor includes several rectangles of the same shape. The rectangles included in the tower-shaped body have the same height in the lateral direction and their width in the longitudinal direction gradually increases in an arithmetic progression. The SSPP transmission line 23 is a planar single-layer structure composed of multiple quasi-one-dimensional SSPP units arranged periodically along the transmission direction. Each quasi-one-dimensional SSPP unit is a centrally symmetrical double-L-shaped pattern, which consists of a left L-shaped frame and a right L-shaped frame. The left L-shaped frame is a hollow frame composed of six metal wire segments connected end to end, and is the shape of a vertical L-shaped frame rotated 90° clockwise. The right L-shaped frame is the shape of the left L-shaped frame rotated 180° with its lower right corner as the center. The left and right L-shaped frames are electrically connected, and adjacent quasi-one-dimensional SSPP units are electrically connected. The left and right sides of the SSPP transmission line 23 are electrically connected to the first transition structure 22 and the second transition structure 25, respectively. Radiating patches 24 consist of multiple pairs of spirals arranged in pairs on both sides of the SSPP transmission line 23. The starting position of the radiating patches 24 is located after most of the high-frequency leakage radiation energy on the SSPP transmission line 23 has leaked out. The leftmost spiral starts from the Mth element of the SSPP transmission line 23, with the starting point being the point closest to the SSPP transmission line 23, and extends inward in a rotating manner. The first spiral on the lower left side extends inward in a rotating manner from the midpoint of the quasi-one-dimensional SSPP element, and the first spiral on the upper left side extends inward in a rotating manner from the starting line of the next quasi-one-dimensional SSPP element on the right. These two are a pair of spirals. The second spiral on the lower left side is arranged with a quasi-one-dimensional SSPP element between it and the first spiral on the lower left side, and the second spiral on the upper left side is arranged with a quasi-one-dimensional SSPP element between it and the first spiral on the upper left side. Multiple pairs of spirals are arranged along the antenna's central axis until the last quasi-one-dimensional SSPP element. The spirals are arranged in pairs. The outer rings of adjacent spirals do not touch, maintaining electrical insulation. The spirals do not touch the SSPP transmission line 23. The second transition structure 25 is symmetrical to the first transition structure 22 about the central axis of the width direction of the substrate 1; The second coplanar waveguide feeding structure 26 is symmetrical to the first coplanar waveguide feeding structure 21 about the central axis of the width direction of the substrate 1. The first coplanar waveguide feeding structure 21 and the second coplanar waveguide feeding structure 26 adopt a periodic silver grid pattern.

2. The dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons as described in claim 1, characterized in that, Fifteen quasi-one-dimensional SSPP units are used, with the leftmost spiral starting from the eighth SSPP unit of SSPP transmission line 23.

3. The dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons as described in claim 1, characterized in that, The left L-shaped frame includes a "horizontal section" and a "vertical section". The width of the "horizontal section" can be adjusted to change the groove depth h and thus the operating frequency band. The width of the "vertical section" is narrower than that of the "horizontal section" to ensure that the groove width a is large enough.

4. The dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons as described in claim 1, characterized in that, Establish a spatial rectangular coordinate system, with the x-axis pointing in the direction of electromagnetic wave propagation, the y-axis pointing upwards, and the z-axis perpendicular to the XY plane and pointing outwards. The curvature of the shape is expressed as a function of its curve profile. ,in, x Let be the coordinates along the x-axis. y Let C1 and C2 be the coordinates along the y-axis, and C1 and C2 be constants determined based on the initial coordinates. is the curvature factor.

5. The dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons as described in claim 1, characterized in that, The first coplanar waveguide feeding structure 21 and the second coplanar waveguide feeding structure 26 adopt a periodic silver grid pattern. The period of the silver grid is gm=200μm and the linewidth is Wm=20μm. The period of the central conductor of the first transition structure 22 and the second transition structure 25 is gm=200μm.

6. The dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons as described in claim 1, characterized in that, The tower-shaped bodies of the first transition structure 22 and the second transition structure 25 are provided with a depth gradient structure of 3 to 7 levels, with the width of the starting end along the longitudinal direction ranging from 3 to 6 mm and the width of the ending end along the longitudinal direction ranging from 0.5 to 2 mm.

7. The dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons as described in claim 6, characterized in that, The metal branches of transition structures 22 and 25 are set with a total of 5 depth levels from the starting end to the end, namely: h1=5mm, h2=4mm, h3=3mm, h4=2mm, and h5=1mm.

8. The dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons as described in claim 1, characterized in that, The specific geometric parameters of the quasi-one-dimensional SSPP cell are: period P = 13.9 mm, metal line width w = 0.1 mm, slot width a = 6.5 mm, slot depth h = 3 mm, cell width d = 7 mm, and substrate thickness t = 0.125 mm. The cutoff frequency is changed by adjusting the value of h, thereby controlling the range of the two frequency bands.

9. The dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons as described in claim 3, characterized in that, The latter half of the SSPP transmission line features eight symmetrical spirals on both the top and bottom sides, four on each side. The trajectory of the Archimedean spiral is determined by the polar coordinate equation. Defined as follows: initial radius r0 = 2 mm, outer radius r1 = 13 mm, line width w = 0.1 mm. The Archimedean spiral spirals from the inside out along the trajectory, with a total number of rotations denoted as T = 7.

5. The rotation angle represents the polar coordinates; the correspondence between the above parameters and the geometric position of the helix is ​​as follows: r0 corresponds to the radius of the starting point of the innermost loop of the helix; r1 corresponds to the radius of the outermost loop of the helix; w corresponds to the width of the thin metal wire that makes up the helix pattern; T corresponds to the total number of loops from the starting point of the inner loop to the ending point of the outer loop; the spacing between adjacent Archimedean spirals along the transmission direction is P1 = 27.8 mm, corresponding to the spacing between the center points of two adjacent spirals along the antenna axis; the spacing between the spiral and the SSPP transmission line 23 is gr = 0.1 mm, corresponding to the vertical spacing between the starting end of the outermost loop of the spiral and the edge of the SSPP transmission line 23.

10. The dual-band multi-polarization flexible transparent leaky antenna based on artificial surface plasmons as described in claim 1, characterized in that, The grounding layer width W0 of coplanar waveguide feeding structures 21 and 26 is 33mm, the width of the center conductor h5 is 1mm, and the height of both the grounding layer and the center conductor is... The distance between the grounding layer and the center conductor is gs=0.1mm.

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