Terahertz transmission array metasurface antenna based on continuous phase modulation

Abstract

The invention relates to a terahertz transmission array metasurface antenna based on continuous phase modulation, which is formed by arranging N * N metasurface units, and each unit structure comprises a top arc metal corner structure, a middle polyimide dielectric layer and a bottom arc metal strip, the transmission amplitude gt of the 2THz-frequency linearly polarized electromagnetic waves is realized by adjusting the distance between the top-layer metal strips, the length of the bottom-layer metal strips and the corresponding central angle of the arc-shaped structure; and the continuous phase modulation of 0.8 is realized. The unit structure parameters are determined through collaborative design of a neural network and a genetic algorithm, when N is equal to 25 and the focal diameter ratio is 1, the antenna can efficiently convert spherical waves emitted by a feed source at the focal point into plane waves, the far-field gain of the antenna reaches 29.6 dBi, and the aperture efficiency is 52%. The invention has the characteristics of simple structure, easiness in manufacturing and high transmission efficiency, and can be widely applied to the fields of terahertz communication, imaging and the like.

Description

Technical Field

[0001] This invention belongs to the field of antenna technology, specifically relating to a terahertz transmission array metasurface antenna based on continuous phase modulation. Background Technology

[0002] Terahertz waves (0.1~10THz), as a "blank band" in the electromagnetic spectrum between microwaves and infrared, have shown great application potential in high-speed communication, high-resolution imaging, and security detection due to their short wavelength, large bandwidth, and strong penetration. However, the high atmospheric absorption loss, material dispersion effect, and the complex and bulky feeding structure in traditional antenna designs of the terahertz band severely restrict their practical application.

[0003] Metasurface technology, through subwavelength artificial microstructures, allows for flexible manipulation of the amplitude, phase, and polarization of electromagnetic waves, providing a novel approach to terahertz antenna design. Traditional terahertz antennas often rely on three-dimensional bulk materials or complex feeding networks, resulting in large system sizes and low integration. In contrast, transmissive array metasurface antennas achieve beam collimation and focusing through planar structures, offering significant advantages such as thin profiles, light weight, and ease of conformal design. For example, gradient phase modulation-based metasurfaces can convert spherical waves into plane waves, significantly improving antenna gain and directivity.

[0004] Existing technologies still face the challenge of insufficient phase control accuracy. Most metasurfaces rely on 1-bit or finite phase quantization, which leads to increased beam sidelobes and decreased focusing quality, making it difficult to meet the requirements of terahertz systems for high directionality and high focusing accuracy. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a terahertz transmission array metasurface antenna based on continuous phase modulation. By optimizing the unit structure design, a continuous phase gradient distribution from the center to the edge is achieved, which can efficiently convert the spherical wave emitted by the feed into a plane wave, significantly improving the antenna gain and beam quality. At the same time, the use of low-loss dielectric materials and layered manufacturing process reduces the processing complexity and cost, providing a feasible solution for the miniaturization and integration of terahertz communication, imaging and other systems.

[0006] The technical problem solved by this invention is achieved through the following technical solution: A terahertz transmission array metasurface antenna based on continuous phase modulation is composed of N×N unit structures. Each unit structure includes a top layer, a middle layer, and a bottom layer arranged from top to bottom. The top layer consists of arc-shaped metal corner structures distributed at the four corners of the unit structure. The middle layer is a polyimide dielectric layer. The bottom layer consists of arc-shaped metal strips distributed at the edges of the unit structure. Continuous electromagnetic wave phase modulation under high transmission conditions is achieved by adjusting the spacing of the arc-shaped metal corner structures in the top layer, the length of the arc-shaped metal strips in the bottom layer, and the corresponding central angles of the arcs of the upper and lower metal layers.

[0007] Moreover, the top-layer arc-shaped metal corner structure and the bottom-layer arc-shaped metal strip are both made of gold with a thickness of 0.2μm and a width of 5μm, the thickness of the middle layer polyimide dielectric layer is 20μm, and the dimensions of the unit structure in the x and y directions are 80μm.

[0008] Furthermore, the spacing between the top-layer arc-shaped metal corner structures is 4–60 μm, the length of the bottom-layer arc-shaped metal strip is 8–64 μm, the corresponding central angles of the top-layer arc-shaped metal corner structures and the bottom-layer arc-shaped metal strips are 0–60°, where 0° corresponds to a straight line segment, and the top-layer arc-shaped metal corner structures and the bottom-layer arc-shaped metal strips are symmetrical about the x-axis and y-axis, forming a centrally symmetrical structure.

[0009] Moreover, the design steps of the unit structure are as follows: S1. Establish a neural network model. The input is the spacing of the top arc metal corner structure, the length of the bottom arc metal strip and the central angle. The output is the real part and imaginary part of the corresponding complex transmission coefficient. The amplitude and phase can be calculated. S2. The parameters of the neural network model are optimized using a genetic algorithm, with the objective functions of maximizing transmission efficiency and minimizing phase error, to determine the optimal parameter combination for each unit structure. S3. Based on the target phase distribution (forming a continuous gradient change from the center of the array to the edge), the parameters of the N×N unit structures are independently adjusted so that the units at different positions generate specific phase values, thereby converting the spherical wave emitted by the feed at the focal point into a plane wave.

[0010] Moreover, the antenna operates at a frequency of 2THz. When N=25 and the focal diameter ratio is 1, the spacing between the top arc metal corner structures and the length of the bottom arc metal strips of each unit structure are independently adjusted according to the target phase distribution to form a gradient phase distribution. This converts the spherical wave emitted by the feed at the focal point into a plane wave, achieving a far-field gain of 29.6dBi and an aperture efficiency of 52%.

[0011] Moreover, the gradient phase distribution is dynamically adjusted according to the position r of the distance from the center of the array, so that the phase value of each unit structure changes continuously from the center to the edge, and the spherical wave emitted by the feed at the focal point is converted into a plane wave.

[0012] The advantages and beneficial effects of this invention are as follows: 1. Achieve continuous phase modulation: By finely adjusting the metal structure parameters, the limitations of traditional metasurface 1-bit or limited phase quantization are overcome, and the phase modulation range covers 0 to 2π, significantly reducing beam sidelobes and improving focusing quality; 2. High transmission efficiency and high gain: With an optimized three-layer structure design and a low-loss polyimide dielectric layer, the transmission amplitude is greater than 0.8 in the 2THz frequency band. Combined with gradient phase distribution, it achieves efficient conversion of spherical waves to plane waves, with a far-field gain of 29.6dBi. 3. Highly efficient and accurate design method: Combining the phase prediction capability of neural networks with the global optimization capability of genetic algorithms, the unit structure parameters are quickly determined, reducing design complexity; 4. Simple structure and easy to process: It adopts a planar layered structure, and both the metal layer and the dielectric layer are compatible with existing nano-manufacturing processes, making it suitable for mass production and reducing costs; 5. Strong application adaptability: It can be directly used in terahertz communication, imaging and other systems, providing core component support for highly directional and miniaturized terahertz devices. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the three-dimensional structure and feed source location of the present invention; Figure 2 These are front and rear views of the metasurface unit structure of the present invention; Figure 3 This is a cross-sectional view of the three-layer structure of the metasurface unit of the present invention; Figure 4 This is a flowchart illustrating the reverse design steps of the genetic algorithm combined with a neural network in this invention. Figure 5 This is a schematic diagram of the phase theory arrangement of the metasurface antenna of the present invention; Figure 6 This is a simulation comparison of the far-field gain of the metasurface antenna of this invention; Figure 7 The figure shows the simulation results of the beam gain and aperture efficiency of the metasurface antenna of the present invention near the 2THz frequency. Detailed Implementation

[0014] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0015] A terahertz transmission array metasurface antenna based on continuous phase modulation, such as Figure 1 The diagram shows the overall three-dimensional structure and feed position of the present invention, illustrating the relative position of the N×N element array arrangement and the feed at the focal point. Its innovation lies in the fact that the antenna is composed of N×N metasurface elements arranged periodically on a plane perpendicular to the electromagnetic wave transmission direction. A terahertz feed (such as a point source feed) is set at the focal point. The feed is placed at position 1 in front of the metasurface and is perpendicularly aligned with the center of the metasurface array at a distance of the focal length F, forming a cooperative structure of "feed-metasurface array" to convert the spherically linearly polarized electromagnetic waves emitted by the feed into plane waves.

[0016] like Figure 2 The diagram shows a three-dimensional schematic, a front view, and a rear view of unit structure 1. The front view shows the distribution of the top layer arc-shaped metal corner structure, and the rear view shows the distribution of the bottom layer arc-shaped metal strips. Figure 3 The diagram shows a three-layer cross-section of the metasurface unit, clearly illustrating the thickness and layering relationship between the top-layer arc-shaped metal corner structure, the middle polyimide dielectric layer, and the bottom arc-shaped metal strip.

[0017] Top layer 2: Circular metal corner structures distributed at the four corners of the unit structure, with the center of the circle located on the x-axis or y-axis, and symmetrically distributed along the x-axis and y-axis; Intermediate layer 3: Polyimide dielectric layer, serving as a support and insulating layer; Bottom layer 4: The arc-shaped metal strips distributed at the edge of the unit are circular arcs, symmetrical along the x and y axes, and consistent with the central angle of the top layer circular arc metal corner structure.

[0018] The core parameters for each layer are as follows: Both the top-layer arc-shaped metal corner structure and the bottom-layer arc-shaped metal strip are made of gold material, with a thickness of 0.2μm and a line width of 5μm; The intermediate polyimide dielectric layer has a thickness of 20 μm, a dielectric constant of 3.5, and a loss tangent of 0.0027. The unit structure has a size of 80μm in both the x and y directions, ensuring subwavelength characteristics (the wavelength corresponding to 2THz is 150μm, and the unit size is close to half a wavelength).

[0019] Unit structure parameters and phase modulation principle: This invention achieves continuous phase modulation by adjusting the spacing of the top-layer arc-shaped metal corner structure, the length of the bottom-layer arc-shaped metal strip, and the central angle between the two. Specific parameter ranges are as follows: Distance between top-level arc-shaped metal corner structures: 4–60 μm (straight-line distance between the edges of adjacent corner structures); The length of the bottom arc-shaped metal strip is 8 to 64 μm (corresponding to the straight-line distance between the two ends of the arc). Central angle: 0~60° (0° corresponds to a straight line segment, 60° corresponds to a one-sixth arc, and the curvature of the metal structure is adjusted by changing the central angle).

[0020] The core principle of phase modulation is: when a terahertz wave is incident perpendicularly on the unit structure, the top arc-shaped metal corner structure and the bottom arc-shaped metal strip generate a phase delay through electromagnetic resonance. By continuously changing the above parameters, continuous phase modulation in the range of 0 to 2π can be achieved and the transmission amplitude can always be greater than 0.8 (operating frequency is 2THz).

[0021] Reverse design process based on neural networks and genetic algorithms: like Figure 4 As shown in the flowchart (inverse design steps combining genetic algorithm and neural network), the unit structure parameters are determined through the following steps: (1) Neural network modeling: Input: top layer spacing l1 and l2 (4~60μm), bottom layer length g1 and g2 (8~64μm), central angle (0~60°); Output: real and imaginary parts of transmission complex parameters at 2THz frequency; Training data: 10,000 sets of simulation results with different parameters were generated by electromagnetic simulation software (CST Microwave Studio), and the training set (80%) and validation set (20%) were divided. A 6-layer fully connected neural network (5 neurons in the input layer, 64 neurons in the hidden layer, and 2 neurons in the output layer) was used and trained until the mean square error was less than 0.0001.

[0022] (2) Genetic algorithm optimization: Objective function: min(1-transmission efficiency) + min(phase error), where transmission efficiency = |transmission amplitude|², phase error is the absolute value of the difference between the target phase and the predicted phase, and the predicted transmission amplitude and transmission phase are calculated from the complex transmission parameters; Optimization process: Initialize 100 parameter populations, and iterate through selection, crossover (probability 0.8), and mutation (probability 0.8) for 200 generations to output the optimal parameter combination.

[0023] (3) Array phase arrangement: Based on the phase compensation requirement from spherical wave to plane wave, the target phase distribution satisfies "continuous gradient change from center to edge" (e.g. Figure 5 The diagram shown is a phase theory layout heatmap. The phase value at a distance r from the array center needs to compensate for the optical path difference between the spherical wave and the plane wave. Finally, the parameters of each unit are determined using the above design method.

[0024] Performance verification: Verification Example 1: N=25, focal diameter ratio 1, operating frequency: 2THz; Simulation results (such as) Figure 6 , Figure 7 As shown): Far-field gain: 29.6 dBi ( Figure 6For the gain comparison between the addition and absence of the metasurface (gain is only 17.5 dBi without metasurface); aperture efficiency: 52%; beamwidth: 3 dB; beamwidth 4.8°; sidelobe level –17.2 dB (better than the -10.5 dB of the traditional 1-bit quantized metasurface).

[0025] Verification Example 2: Comparative Verification (1-bit Phase Quantization Metasurface) The same array size (N=25) is used, but the cell phase can only take 0 and π (2 states); Simulation results show a gain of 17.8 dBi, an aperture efficiency of 3%, a 3 dB beamwidth of 18.9°, and a sidelobe level of -10.5 dB, verifying the advantages of continuous phase modulation in this invention.

[0026] Processing technology description: The antenna was fabricated using standard micro / nano manufacturing processes. (1) Preparation of dielectric layer: Polyimide was spin-coated on a silicon substrate and cured at 150°C for 2 hours to form a 20μm thick dielectric layer; (2) Metal layer deposition: Electron beam evaporates gold film (thickness 0.2μm), and after photoresist coating, exposure (defining the top corner and bottom arc strip pattern), development, ion etching of gold film forms pattern; (3) Stripping and cleaning: Remove residual photoresist, ultrasonically clean with ethanol and dry to complete array fabrication.

[0027] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A continuous phase modulation based terahertz transmissive array metasurface antenna, characterized in that: The antenna is arranged by N*N unit structures, the unit structure comprises top layer, middle layer and bottom layer arranged from top to bottom, the top layer is circular arc metal corner structure distributed in four corners of the unit structure, the middle layer is polyimide dielectric layer, and the bottom layer is arc-shaped metal strip distributed in the edge of the unit structure, and the continuous electromagnetic wave phase modulation in the high transmission state is realized by adjusting the spacing of the top layer circular arc metal corner structure, the length of the bottom layer arc-shaped metal strip and the corresponding central angle of the upper and lower two metal layers.

2. The continuous phase modulation based terahertz transmissive array metasurface antenna of claim 1, wherein: The top layer circular arc metal corner structure and the bottom layer arc-shaped metal strip are both made of gold with a thickness of 0.2 μm and a width of 5 μm, the thickness of the middle layer polyimide dielectric layer is 20 μm, and the size of the unit structure in x and y directions is 80 μm.

3. The continuous phase modulation based terahertz transmissive array metasurface antenna of claim 1, wherein: The spacing between the top layer circular arc metal corner structures is 4-60 μm, the length of the bottom layer arc-shaped metal strip is 8-64 μm, and the corresponding central angle of the top layer circular arc metal corner structure and the bottom layer arc-shaped metal strip is 0-60°, wherein 0° corresponds to a straight line segment, and the top layer circular arc metal corner structure and the bottom layer arc-shaped metal strip are both symmetric about the x axis and the y axis, forming a central symmetric structure.

4. The continuous phase modulation based terahertz transmissive array metasurface antenna of claim 1, wherein: The design steps of the unit structure are: S1, establishing a neural network model, the input is the spacing of the top layer circular arc metal corner structure, the length of the bottom layer arc-shaped metal strip and the central angle, the output is the real part and the imaginary part of the corresponding complex transmission coefficient, and the amplitude and the phase can be calculated; S2, the parameters of the neural network model are optimized by using genetic algorithm, the maximum transmission efficiency and the minimum phase error are taken as the objective function, and the optimal parameter combination of each unit structure is determined; S3, according to the target phase distribution (forming a continuous gradient change from the center to the edge of the array), the parameters of N*N unit structures are independently adjusted, so that the units at different positions produce specific phase values, thereby converting the spherical wave emitted by the feed source at the focal point into a plane wave.

5. The continuous phase modulation based terahertz transmissive array metasurface antenna of claim 1, wherein: When the working frequency of the antenna is 2 THz, N=25 and the focal ratio is 1, the spacing of the top layer circular arc metal corner structure and the length of the bottom layer arc-shaped metal strip of each unit structure are independently adjusted according to the target phase distribution to form a gradient phase distribution, convert the spherical wave emitted by the feed source at the focal point into a plane wave, and the far field gain reaches 29.6 dBi and the aperture efficiency is 52%.

6. The continuous phase modulation based terahertz transmissive array metasurface antenna of claim 5, wherein: The gradient phase distribution is dynamically adjusted according to the position r from the center of the array, so that the phase values of each unit structure form a continuous change from the center to the edge, and the spherical wave emitted by the feed source at the focal point is converted into a plane wave.

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