Broadband wide-angle single-layer substrate linear circular polarization conversion device based on metasurface

Abstract

The invention belongs to the technical field of wireless communication, and particularly provides a broadband wide-angle single-layer substrate linear circular polarization conversion device based on a metasurface, which is used for realizing efficient circular polarization conversion of K / Ka wave band linear polarization waves and meeting the requirements of the fields of satellite communication and the like on broadband and high-stability polarization converters. The periodic polarization conversion device is formed by splicing a plurality of periodic polarization conversion units which are arranged in a matrix mode, each polarization conversion unit comprises a single-layer dielectric substrate, a top metal layer and a bottom metal layer, and through the structural design of a cross-shaped metal structure and a semicircular metal structure in the top metal layer and a bottom horizontal metal strip in the bottom metal layer, the polarization conversion efficiency is improved. On the premise that the number of layers is not increased, broadband and wide-angle performance is achieved; in conclusion, the high-efficiency linear circular polarization conversion in the K / Ka wave band is realized; moreover, due to the compact sub-wavelength unit, low loss and broadband characteristics, the antenna has a wide application prospect in satellite communication, a 5G millimeter wave system and a multi-beam antenna.

Description

Technical Field

[0001] The present invention belongs to the field of wireless communication technology, and specifically provides a wide-bandwidth and wide-angle single-layer substrate linear circular polarization conversion device based on a metasurface, which is particularly suitable for wide-bandwidth and wide-angle circular polarization conversion scenarios in K / Ka band satellite communication systems. Background Art

[0002] With the growing demand for high-speed, large-scale data transmission, satellite communication systems need to expand their operating bandwidth to meet future communication requirements. As a key frequency band for satellite communications, the K / Ka band (16-32 GHz) is increasingly in need of broadband equipment. Circularly polarized waves, with their resistance to multipath fading and Faraday rotation effects, are widely used in wireless communications. Compared to directly designed circularly polarized antennas, the solution using linearly polarized antennas combined with linear-to-circular polarization converters (LCPCs) offers significant advantages. The linearly polarized antenna feed network is simple, and mature linear polarization antenna technology can be leveraged to convert its broadband, dual-band, or single-pulse characteristics into circularly polarized antennas. This provides a new technical means for achieving superior upgrades in the communications field.

[0003] Traditional single-layer LCPCs mostly use a single resonant structure, such as the Jerusalem cross or hybrid meander line loop, resulting in a narrow bandwidth (usually <50%) and high insertion loss. For example, in the literature "I. Sohail, Y. Ranga, K. Esselle, and S. Hay, "A linear to circular polarization converter based on Jerusalem-Cross frequency selective surface," in Proc. 7th Eur. Conf. Antennas Propag. (EuCAP), April 2013, pp. 2141–2143," Sohail et al. used a single-layer Jerusalem cross unit and only achieved a narrow axial ratio bandwidth and high insertion loss. Another example is the literature "P. Fei, Z. Shen, X. Wen, and F. Nian, "A single-layer circular polarizer based on hybrid meander line and loop configuration," IEEE Trans. Antennas Propag., vol.63, no.10, pp.4609–4614, Oct.2015. ", Fei et al. improved the bandwidth to 46.8% by using a hybrid structure, but the angular stability was only up to 30°.

[0004] Building on this, multilayer LCPCs have expanded bandwidth through composite structures (such as combining split-rings with metal strips, and zigzag lines with patches), partially achieving an axial ratio bandwidth exceeding 35% and 45° angular stability. However, the multilayer structure increases manufacturing complexity and error, and is thicker. For example, in the paper "D. Blanco and R. Sauleau, "Broadband and broad-angle multilayer polarizer based on hybrid optimization algorithm for low-cost Ka-band applications," IEEE Trans. Antennas Propag., vol. 66, no. 4, pp. 1874–1881, April 2018," Blanco and Sauleau's five-layer structure achieves 50° angular stability, but the bandwidth is only 19.6%. Another example is the paper "H. Li, B. Li, and L. Zhu, "Wideband linear-to-circular polarizer based on orthogonally inserted slot-line structures," IEEE Antennas Wireless Propag. Lett., vol. 18, no. 6, pp. 1169–1173, Jun. 2019. ”, Li et al.’s three-dimensional orthogonal slot line structure is bulky and difficult to assemble.

[0005] In summary, it is difficult for existing technologies to simultaneously achieve a 3dB axial ratio bandwidth of more than 50% and wide-angle stability of more than 50°, which limits the application of linear circular polarization converters (LCPCs) in multi-beam or beam scanning antenna systems. Summary of the Invention

[0006] The purpose of the present invention is to provide a linear-circular polarization conversion metasurface device with a simple structure, compact size, wide bandwidth and wide-angle stability, so as to realize efficient circular polarization conversion of K / Ka band linear polarization waves and meet the demand for broadband, high-stability polarization converters in fields such as satellite communications.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A wide-bandwidth, wide-angle, single-layer substrate linear-circular polarization conversion device based on a metasurface is composed of a plurality of periodic polarization conversion units arranged in a matrix. The polarization conversion unit comprises: a single-layer dielectric substrate, a top metal layer, and a bottom metal layer. The top metal layer is arranged on the upper surface of the single-layer dielectric substrate and has an axisymmetric structure along the center line. It is composed of a cross metal structure and two semicircular metal structures. The cross metal structure is composed of a top horizontal metal strip and a top vertical metal strip arranged orthogonally. The top horizontal metal strip is arranged in the horizontal direction (x-direction). The two semicircular metal structures are arranged at both ends of the top horizontal metal strip. The semicircular metal structures of adjacent polarization conversion units in the horizontal direction are spliced ​​to form a circular metal structure. The top vertical metal strip is arranged in the vertical direction (y-direction). The top vertical metal strip of adjacent polarization conversion units in the vertical direction is interconnected. The bottom metal layer is arranged on the lower surface of the single-layer dielectric substrate and has an axisymmetric structure along the center line. It is composed of a bottom horizontal metal strip. The bottom horizontal metal strip is arranged in the horizontal direction (x-direction).

[0009] Furthermore, the dimensions of the polarization conversion unit are length×width: 0.11λ0×0.21λ0, where λ0 is the free space wavelength corresponding to the center frequency.

[0010] Furthermore, in the top metal layer, the length b1 of the top vertical metal strip of the cross metal structure is 1.4 mm, and the width a1 is 0.15 mm. The length a0 of the top horizontal metal strip of the cross metal structure is 2.08 mm, and the width b0 is 0.2 mm.

[0011] Furthermore, in the top metal layer, the radius R of the semicircular metal structure is 0.3 mm.

[0012] Furthermore, in the top metal layer, the distance between the top horizontal metal strip of the cross metal structure and the semicircular metal structure is d=0.16 mm.

[0013] Furthermore, in the bottom metal layer, the bottom horizontal metal strip has a length a3 = 2.3 mm and a width b3 = 0.2 mm.

[0014] Based on the above technical solution, the beneficial effects of the present invention are:

[0015] The present invention provides a wide-bandwidth and wide-angle single-layer substrate linear-circular polarization conversion device based on a metasurface. The device adopts a single-layer substrate structure and realizes wide-bandwidth and wide-angle performance without increasing the number of layers through the structural design of a cross metal structure and a semicircular metal structure in the top metal layer and a bottom horizontal metal strip in the bottom metal layer. In addition, the transmission characteristics of the orthogonal polarization components are utilized to independently control the passbands in the horizontal and vertical directions to generate a stable 90° phase difference, thereby resolving the contradiction between the bandwidth and angular stability of the single-layer structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the unit structure of the wide-bandwidth and wide-angle single-layer substrate linear circular polarization conversion device based on the metasurface in the present invention.

[0017] Figure 2 This is a unit structure dimension diagram of the wide-bandwidth and wide-angle single-layer substrate linear-circular polarization conversion device based on the metasurface in the present invention.

[0018] Figure 3 This is a diagram illustrating the structural topology and equivalent circuit parameters of the wide-bandwidth and wide-angle single-layer substrate linear-circular polarization conversion device based on the metasurface in the present invention.

[0019] Figure 4 This is the equivalent circuit diagram of the wide-bandwidth and wide-angle single-layer substrate linear-circular polarization conversion device based on the metasurface in the present invention.

[0020] Figure 5 This is a schematic structural diagram of the wide-bandwidth and wide-angle single-layer substrate linear-circular polarization conversion device based on the metasurface in the present invention.

[0021] Figure 6 This is the polarization conversion S-parameter diagram of the wide-bandwidth and wide-angle single-layer substrate linear-circular polarization conversion device based on the metasurface in the present invention.

[0022] Figure 7 Schematic diagram of the structure of the free space measurement system in the present invention. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0024] This embodiment provides a wide-bandwidth, wide-angle, single-layer substrate linear-circular polarization conversion device based on a metasurface, which is composed of a plurality of periodic polarization conversion units arranged in a matrix. Figure 1As shown, it includes: a single-layer dielectric substrate, a top metal layer, and a bottom metal layer; the top metal layer is arranged on the upper surface of the single-layer dielectric substrate and has an axisymmetric structure along the center line, consisting of a cross metal structure and two semicircular metal structures, the cross metal structure consisting of a top horizontal metal strip and a top vertical metal strip arranged orthogonally; the top horizontal metal strip is arranged in the horizontal direction (x direction), the two semicircular metal structures are arranged at both ends of the top horizontal metal strip, and the semicircular metal structures of adjacent polarization conversion units in the horizontal direction are spliced ​​to form a circular metal structure; the top vertical metal strip is arranged in the vertical direction (y direction), and the top vertical metal strips of adjacent polarization conversion units in the vertical direction are interconnected; the bottom metal layer is arranged on the lower surface of the single-layer dielectric substrate and has an axisymmetric structure along the center line, consisting of a bottom horizontal metal strip, and the bottom horizontal metal strip is arranged in the horizontal direction (x direction).

[0025] Furthermore, the model of the single-layer dielectric substrate is Taconic TLY-5, with a thickness of t = 1.575 mm and a dielectric constant ε r =2.2, magnetic permeability μ=1, loss tangent tanδ=0.0009, and metal patterns are printed on the upper and lower surfaces respectively.

[0026] Furthermore, the top metal layer and the bottom metal layer are made of metal copper foil, both with a thickness of 36 μm and a line width accuracy of ±5 μm. They are prepared using a photolithography etching process to ensure structural dimensional accuracy.

[0027] Furthermore, the size of the polarization conversion unit is 0.11λ0×0.21λ0 (y-direction size×x-direction size), where λ0 is the free space wavelength corresponding to the center frequency of 24.16 GHz; Figure 2 As shown, the specific dimensions of the top metal layer and the bottom metal layer are: a0 = 2.08 mm, b0 = 0.2 mm, a1 = 0.15 mm, b1 = 1.4 mm, a3 = 2.3 mm, b3 = 0.2 mm, R = 0.3 mm, d = 0.16 mm, L a =2.6mm, L b =1.4mm, t=1.575mm, tick=0.036mm.

[0028] In terms of working principle:

[0029] During operation, when a 45° linearly polarized wave is incident in the Z direction, the incident electric field is decomposed into equal amplitude and phase components through the top horizontal metal strip (x direction), so that there are components with consistent amplitude and phase in the x and y directions; then, based on the frequency response difference between the vertical metal strip on the neck (y direction) and the horizontal metal strip on the bottom (x direction), the electric field components in the above two directions are phase-adjusted, but the amplitude and direction are not affected. Since the phase adjustment strips are vertical, the amplitude balance and 90° phase difference of the two electric field components can be achieved within a wide bandwidth. Finally, the two transmitted components are vector-synthesized to generate a circularly polarized wave.

[0030] Further, such as Figure 3 and Figure 4 The figure shows the parameter identification and equivalent circuit diagram of the above-mentioned linear circular polarization conversion device. As can be seen from the figure, the y-direction is equivalent to forming a high-pass filter (L4 and C1, L1 are connected in series in parallel), providing a stopband below the cutoff frequency and a wide passband above the cutoff frequency; the x-direction is equivalent to forming a series LC resonant circuit (L3 and C3), forming a stopband above the resonant frequency and a wide passband below it; at the same time, the additional introduction of L1-C1 and L2-C2 can optimize the passband and adjust the phase difference to 90°.

[0031] In summary, the present invention has made innovative structural designs for the top metal layer and the bottom metal layer. The circular metal structure formed by splicing semicircular metal structures between adjacent polarization conversion units is loaded between the cross metal structures, which can match the equivalent impedance of the top horizontal metal strip, so that the input signal can be better coupled into the structure. On the one hand, it is conducive to achieving high transmission and low reflection performance, and on the other hand, it can further improve the polarization purity of the system; at the same time, the circular metal structure can also broaden the working bandwidth of the device, because it will introduce new structural equivalent inductance and capacitance, and the circular structure has planar symmetry, which can well achieve the stability of equivalent parameters of different input frequencies, so that the structure can stably perform the conversion function when working in a wider frequency band.

[0032] The beneficial effects of the present invention are described in detail below in conjunction with combined tests.

[0033] Taking a 3×3 array as an example, the broadband and angle-width linear-circular polarization conversion device of a single-layer substrate based on a metasurface in this embodiment is as follows: Figure 5 As shown; Figure 6 The figure shows the polarization conversion S-parameter diagram of the wide-bandwidth and wide-angle single-layer substrate linear-circular polarization conversion device based on the metasurface in this embodiment. It can be seen from the figure that the linear-circular polarization conversion device can transmit linearly polarized waves in a transmission form and ensure that the amplitudes are basically the same, thereby realizing the phase superposition of the two polarized waves to form circular polarization; and the main polarization will not change the polarization direction to produce secondary polarization, and will not produce cross-polarization phenomenon.

[0034] Furthermore, a free-space measurement system is used to test the wide-bandwidth and wide-angle single-layer substrate linear circular polarization conversion device based on the metasurface in this embodiment. Figure 7 As shown, the transmitting and receiving horn antennas (operating frequency range 15GHz to 40GHz) are 2m apart, and the sample to be tested is placed at the center of the three-dimensional rotating platform with an angular accuracy of ±0.1°. During the test, the transmission coefficient is first measured without a sample to calibrate the system loss;

[0035] Then, the sample to be tested is rotated 45° and the transmission coefficients T of the x and y polarization components are measured. xx and T yy , calculate the axis ratio: in, is the phase difference;

[0036] Finally, perform an angle stability test: in the xz and yz planes, the incident angle ranges from 0° to 55°, with an interval of 10°, and record the AR and insertion loss at each angle:

[0037] The specific results are as follows:

[0038] 1. Bandwidth performance: At normal incidence, the bandwidth with an AR less than 3dB during simulation was 69% (16.2GHz to 32.4GHz), and the measured bandwidth was 74% (15.3GHz to 33.1GHz). At 55° incidence (yz plane), the measured bandwidth with an AR less than 3dB was 54% (19.2GHz to 34.3GHz). These results demonstrate that the linear-circular polarization conversion device in this embodiment maintains a wide conversion bandwidth at wide angles, indicating excellent wide-angle and wide-bandwidth stability.

[0039] 2. Insertion loss: at normal incidence, the insertion loss is less than 3dB; at 40° incidence, the insertion loss is less than 2.5dB; at 55° incidence, the insertion loss is less than 3dB, meeting the low loss requirements of actual communication systems;

[0040] 3. Polarization conversion efficiency: left-hand circular polarization transmission coefficient>-2.9dB, PER>15dB, conversion efficiency>94%, ensuring signal polarization purity.

[0041] In summary, the present invention provides a wide-bandwidth and wide-angle single-layer substrate linear-circular polarization conversion device based on a metasurface. Through innovative structural design, it breaks through the bandwidth and angular stability limitations of traditional LCPC and realizes efficient linear-circular polarization conversion in the K / Ka band. Moreover, its compact subwavelength unit, low loss and wide-bandwidth characteristics give it broad application prospects in satellite communications, 5G millimeter-wave systems and multi-beam antennas.

[0042] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A wide-bandwidth, wide-angle, single-layer substrate linear-circular polarization conversion device based on a metasurface, composed of a plurality of periodic polarization conversion units arranged in a matrix; characterized by: The polarization conversion unit includes: a single-layer dielectric substrate, a top metal layer, and a bottom metal layer. The top metal layer is disposed on the upper surface of the single-layer dielectric substrate and has an axisymmetric structure along its centerline. It is composed of a cross metal structure and two semicircular metal structures. The cross metal structure is composed of a top horizontal metal strip and a top vertical metal strip arranged orthogonally. The top horizontal metal strip is disposed in a horizontal direction (x-direction). Two semicircular metal structures are disposed at both ends of the top horizontal metal strip. The semicircular metal structures of adjacent polarization conversion units in the horizontal direction are spliced ​​together to form a circular metal structure. The top vertical metal strip is disposed in a vertical direction (y-direction). The top vertical metal strip of adjacent polarization conversion units in the vertical direction are interconnected. The bottom metal layer is disposed on the lower surface of the single-layer dielectric substrate and has an axisymmetric structure along its centerline. It is composed of a bottom horizontal metal strip. The bottom horizontal metal strip is disposed in a horizontal direction (x-direction).

2. The wide-bandwidth, wide-angle, single-layer substrate linear-circular polarization conversion device based on a metasurface according to claim 1, characterized in that: The dimensions of the polarization conversion unit are length × width: 0.11λ0 × 0.21λ0, where λ0 is the free space wavelength corresponding to the center frequency.

3. The wide-bandwidth, wide-angle, single-layer substrate linear-circular polarization conversion device based on a metasurface according to claim 1, characterized in that: In the top metal layer, the length b1 of the top vertical metal strip of the cross metal structure is 1.4 mm, and the width a1 is 0.15 mm. The length a0 of the top horizontal metal strip of the cross metal structure is 2.08 mm, and the width b0 is 0.2 mm.

4. The wide-bandwidth, wide-angle, single-layer substrate linear-circular polarization conversion device based on a metasurface according to claim 1, characterized in that: In the top metal layer, the radius of the semicircular metal structure is R = 0.3 mm.

5. The wide-bandwidth, wide-angle, single-layer substrate linear-circular polarization conversion device based on a metasurface according to claim 1, characterized in that: In the top metal layer, the distance d between the top horizontal metal strip of the cross metal structure and the semicircular metal structure is 0.16 mm.

6. The wide-bandwidth, wide-angle, single-layer substrate linear-circular polarization conversion device based on a metasurface according to claim 1, characterized in that: In the bottom metal layer, the bottom horizontal metal strip has a length a3 = 2.3 mm and a width b3 = 0.2 mm.

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