Coding metasurface dual-channel asymmetric digital transmission system based on weighted theorem optimization

Abstract

The invention discloses a coding metasurface dual-channel asymmetric digital transmission system based on weighted theorem optimization, and relates to the technical field of communication and artificial electromagnetic materials. The system adopts a two-dimensional programmable coding metasurface, the unit structure of the system is formed by loading two PIN diodes in a metal pattern, and the system has 2-bit four-phase regulation and control capability. The metasurface array adopts a column control mode, and dynamic control over the reflected wave beam phase is achieved at the 6.1 Ghz frequency. In order to improve the directivity of the space beam, the Chebyshev weighting theorem is adopted to adjust the amplitude distribution of the array unit, and the sidelobe gain is effectively suppressed. And a coding matrix is designed in combination with an addition theorem, so that reflection beams in two directions are formed independently at the same time. According to the method, the main and side lobe gain difference (in a dual-beam communication experiment, the main and side lobe gain difference is 2.34 dB under an unweighted condition and is increased to 5.52 dB after weighting) is remarkably improved, and the space channel isolation capacity is enhanced. And synchronous transmission and receiving of image information in asymmetric directions are realized in an experiment, so that a dual-channel digital transmission system is constructed. The invention has the advantages of simple structure, strong directivity, high anti-interference capability, clear coding design physical mechanism and the like, and is suitable for the fields of high-density spatial multiplexing communication, millimeter wave radar imaging, low-power-consumption passive information modulation and the like.

Description

Technical Field

[0001] The present invention relates to the field of communications and artificial electromagnetic material technology, and in particular to a coded metasurface dual-channel asymmetric digital transmission system optimized based on weighted theorem, which is suitable for multi-user information modulation, transmission and decoding in spatial multiplexing wireless communications. Background Art

[0002] As 5G, 6G, and next-generation communication systems continue to increase their requirements for spectrum efficiency, channel capacity, and power consumption, traditional wireless communication architectures are facing physical bottlenecks. While Multiple-Input Multiple-Output (MIMO) and beamforming technologies can improve channel reuse capabilities, they are complex and energy-intensive, making them difficult to adapt to large-scale deployments.

[0003] In recent years, artificial electromagnetic structures, particularly two-dimensional programmable metasurfaces, have been widely studied. Their advantages include low cost, flat structure, and controllable phase and amplitude, offering new hardware solutions for novel wireless communication systems. Metasurfaces utilize subwavelength-scale units. By precisely designing their geometric parameters, circuit structure, or loading elements (such as PIN diodes and varactor diodes), they can dynamically control reflected and transmitted waves in space, thereby adjusting beam direction, polarization state, and amplitude response, demonstrating a high degree of programmability.

[0004] Currently, mainstream research focuses on applications such as metasurface reflection beam steering, coded modulation, and imaging radar, while research in the communications field has been relatively late. Traditional metasurface communication systems mostly use a single beam approach, supporting only directional data transmission between a pair of transmitters and receivers. This suffers from low communication capacity and low spatial efficiency. In terms of spatial multiplexing communications, although some research has attempted to utilize multi-beam strategies, these generally face technical challenges such as low beam separation, severe sidelobe interference, and difficult channel reconstruction.

[0005] In addition, some work has attempted to introduce artificial intelligence algorithms into metasurface coding optimization. While this has improved adaptability, it relies on training sets and computational resources, making it difficult to respond to communication needs in real time. However, the use of mathematical weighting theories such as Chebyshev's can directly control far-field radiation patterns. This has the advantages of clear physics and universal structure, making it particularly suitable for beam sidelobe control and spatial channel isolation tasks.

[0006] Therefore, developing a coded metasurface communication architecture that supports multi-directional independent control, has a simple structure, good beam performance and strong scalability has great theoretical significance and application value, especially in scenarios such as the next generation of intelligent wireless networks, the Internet of Things, intelligent transportation and millimeter wave security imaging. Summary of the Invention

[0007] The purpose of the present invention is to provide a coded metasurface dual-channel asymmetric digital transmission system based on weighted theorem optimization to solve the problems of poor beam directivity, severe multi-user signal interference and insufficient control capability in existing communication systems.

[0008] The present invention is achieved through the following technical solutions:

[0009] The present invention provides a dual-channel asymmetric digital transmission system based on a coded metasurface, comprising the following modules:

[0010] The coded metasurface array module consists of M×N phase-programmable units. Each unit consists of two PIN diodes loaded on a metal structure. Different switch combinations can form four reflection phases (0°, 90°, 180°, and 270°), achieving 2-bit control capability.

[0011] The specific structural parameters of the metasurface unit are as follows: the size of each unit is 14mm×14mm, the metal layer is a copper pattern with a thickness of 0.035mm, the spacing is 1mm, the dielectric substrate material is FR4 with a thickness of 1mm, the relative dielectric constant εr is 2.65, and the loss tangent value is 0.002.

[0012] The PIN diode selected is Skyworks SMP1320-079LF, and its equivalent electrical parameters are: the equivalent circuit parameters in the on state are RON=0.17Ω, LON=0.89nH, CON=2.75pF; in the off state, ROFF=0.06Ω, LOFF=0.45nH, COFF=0.25pF.

[0013] The FPGA control module is used to convert the input image information stream into a metasurface state control signal according to a preset mapping relationship, and output a 3.3V control voltage to drive the switching state of the PIN diode;

[0014] The image coding mapping module is used to convert the two images into binary data streams and generate 2-bit wide coding units in an interleaved reorganization manner. The data is mapped to four states (M0 to M3), which correspond to the metasurface modulation response of a specific beam direction.

[0015] The coding matrix design module is based on the far-field scattering formula and the addition theorem, combined with Chebyshev weighting to design the optimal metasurface coding matrix, achieving beam energy concentration and sidelobe suppression in a specific direction;

[0016] The signal source module, a vector network analyzer (VNA), is used to transmit a carrier signal of a specific frequency and receive a scattered signal modulated by the metasurface;

[0017] The dual receiving antenna modules are arranged in two preset directions to receive the reflected information of user 1 and user 2 respectively.

[0018] The system workflow of the present invention includes:

[0019] The step 1 is to convert the input image 1 and image 2 into binary code streams respectively;

[0020] The second step is to combine the two coded streams into a new coded stream in an interleaved order;

[0021] In step 3, the coded stream is divided into groups of 2 bits each, forming four coding states of "00", "01", "10", and "11";

[0022] The fourth step is to establish a mapping relationship between the "coding state" and the "metasurface control state", wherein "00" corresponds to the M3 state, "01" corresponds to the M2 state, "10" corresponds to the M1 state, and "11" corresponds to the M0 state;

[0023] In step five, the metasurface coding sequence corresponding to the unidirectional reflected light beam is obtained according to the far-field scattering theorem, and then the dual-beam coding sequences in the -15° and +18° directions are generated according to the addition theorem. Subsequently, the Chebyshev weighting theorem is used to obtain the weighted coding sequences for the single and dual beams.

[0024] In step 5, the FPGA generates a control sequence according to the mapping relationship, drives the PIN diode state, and causes the metasurface to generate a reflected beam in a specified direction;

[0025] In step six, the receiving antenna collects the reflected signal and demodulates it to complete image reconstruction.

[0026] The coding design method of the present invention comprises:

[0027] The array pattern is constructed using the far-field scattering formula;

[0028] The Chebyshev weighting is applied to the unit amplitude to meet the minimum sidelobe gain condition;

[0029] The dual-beam solution is designed in combination with the addition theorem to optimize the directional pattern performance.

[0030] Before the weighted theorem is adopted, the gain difference between the main lobe and side lobe of the beam formed by the metasurface in the target direction is relatively small, for example, it is only 3.69dB in the +18° direction, 5.18dB in the +28° direction, and 2.44dB in the +45° direction, resulting in strong energy leakage in non-target directions.

[0031] After introducing Chebyshev weighting, the mainlobe and sidelobe gain differences were significantly improved, reaching 8.68dB, 6.68dB, and 9.77dB in the aforementioned directions, respectively. This weighting process adjusts the amplitude distribution of each element of the metasurface to focus the beam more closely in the desired direction while suppressing sidelobe energy.

[0032] The experiments further validated the effectiveness of this optimization strategy. In a dual-beam communication experiment, the mainlobe and sidelobe gain difference was 2.34dB under unweighted conditions, but increased to 5.52dB after weighting, significantly improving the dual-beam separation capability and spatial independence.

[0033] Furthermore, in an image transmission experiment, user 1 and user 2 received reflected signals at -15° and +18°, respectively. Through amplitude-shift keying (OOK) demodulation, the corresponding image information was fully recovered. The demodulated images were highly consistent with the originals, with clear image structure and well-preserved edges, and a transmission bit error rate of less than 5%.

[0034] The present invention verifies that the combination of spatial multiplexing coding and Chebyshev weighting method can significantly improve beam directivity, reduce interference in non-target directions, and enhance image transmission quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings in the specification, which constitute a part of this application, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0036] Figure 1 Schematic diagram of the system for realizing asymmetric beam direct digital transmission using the programmable metasurface based on the weighted theorem.

[0037] Figure 2 A top view of the unit structure of the programmable metasurface.

[0038] Figure 3 3D structural diagram of the unit structure of the programmable metasurface.

[0039] Figure 4 is the reflection coefficient of the unit structure of the coding metasurface at a frequency of 6.1 GHz. The reflection coefficients of the four states of the metasurface unit are all greater than 0.8, indicating that it has good electromagnetic wave reflection characteristics.

[0040] Figure 5 is the reflection phase of the unit structure of the coding metasurface at a frequency of 6.1 GHz, and the four reflection phases of the metasurface unit differ by 90°.

[0041] Figure 6 The far-field direction of the metasurface array composed of 24×24 metasurface units in the +18° direction Figure 3 D(left), 2D(right).

[0042] Figure 7 The far-field direction of the metasurface array composed of 24×24 metasurface units in the +28° direction Figure 3 D(left), 2D(right).

[0043] Figure 8 The far-field direction of the metasurface array composed of 24×24 metasurface units in the +45° direction Figure 3 D(left), 2D(right).

[0044] Figure 9 The far-field direction of the metasurface array composed of 24×24 metasurface units at -15° Figure 3 D(left), 2D(right).

[0045] Figure 10 The far-field direction of the metasurface array composed of 24×24 metasurface units at -35° Figure 3 D(left), 2D(right).

[0046] Figure 11 The far-field direction of the metasurface array composed of 24×24 metasurface units at -40° Figure 3 D(left), 2D(right).

[0047] Figure 12 3D diagram (top), 2D diagram (left), two unidirectional beams and one

[00047] bidirectional beam (right) of the far-field direction of the metasurface array composed of the 24×24 metasurface units in the +18° and -15° directions.

[0048] Figure 13 These are the far-field experimental diagrams of the metasurface array. The left diagram is the normalized far-field 2D diagram of the front and rear beams with +18° beam weighting, the middle diagram is the normalized far-field 2D diagram of the front and rear beams with +28° beam weighting, and the right diagram is the normalized far-field 2D diagram of the front and rear beams with +45° beam weighting.

[0049] Figure 14 These are the far-field experimental diagrams of the metasurface array. The left diagram is the normalized far-field 2D diagram of the front and rear beams after -15° beam weighting, the middle diagram is the normalized far-field 2D diagram of the front and rear beams after -35° beam weighting, and the right diagram is the normalized far-field 2D diagram of the front and rear beams after -40° beam weighting.

[0050] Figure 15 Figure 2 is a diagram of the far-field experimental setup of the metasurface array.

[0051] Figure 16 This is a physical picture of the metasurface array.

[0052] Figure 17 Phase diagrams of the metasurface array under four different encoding conditions.

[0053] Figure 18 Graphs showing the far-field experimental results of the two unidirectional beams and bidirectional beams of the metasurface array.

[0054] Figure 19 This is the transmission result diagram of the wireless communication system built based on the programmable metasurface, which is the image information received in the -15° direction.

[0055] Figure 20 This is the transmission result diagram of the wireless communication system built on the programmable metasurface, which is the image information received in the +18° direction.

[0056] Figure 21 The wireless communication system based on the programmable metasurface transmits image information in the -15° direction, before transmission (left) and after reception (right).

[0057] Figure 22 The wireless communication system based on the programmable metasurface transmits image information in the +18° direction, before transmission (left) and after reception (right). DETAILED DESCRIPTION

[0058] The present invention will be further described below with reference to the accompanying drawings. It should be understood that the specific embodiments described are only used to illustrate the present invention and do not limit the scope of protection of the present invention.

[0059] The metasurface of the present invention is composed of 24×24 units, and a column control structure is used to control the state of the PIN diode. Each unit can form four phase states through two PIN diodes, achieving 2-bit control capability.

[0060] The copper pattern of the unit structure is two symmetrically loaded U-shaped circuits, connecting PIN diodes at both ends and coupling with a hexagonal common mode structure to form an adjustable reflection phase characteristic; the back metal is grounded to enhance reflection efficiency.

[0061] To verify the performance of the present invention, a complete experimental testing platform was constructed, including a vector network analyzer (Agilent E5071C), a waveguide-horn antenna, coaxial cables, an FPGA control board, a power supply module, and a computer control system. The metasurface sample was fabricated from FR4 copper-clad laminate, soldered with 1,152 PIN diodes, and then mounted on a rotating platform to simulate different angles of incidence.

[0062] The image data is stored in binary format in the FPGA. This data is combined to generate a 2-bit control stream, which controls the FPGA's output voltage to drive the column control pins, thereby spatially modulating the metasurface. The FPGA chip model is Xilinx XC7A35T, with a control rate of 10kHz, ensuring a response speed that meets the requirements for static image transmission.

[0063] The test process is as follows: First, a VNA transmits a 6.1GHz carrier signal onto the metasurface. The reflected waves are received by receiving antennas placed at ±15° and ±18°. The VNA then measures the amplitude of the echo signal. This amplitude is then decoded with the original image bitstream (OOK modulation) to recover the image matrix.

[0064] Furthermore, to test the robustness of the system, variations in the reflected beam pattern were designed under various directional angles and environmental interference conditions (such as electromagnetic shielding and metal reflectors). Good beam retention was confirmed through near-field and far-field switching. The system achieved directional stability better than ±2° within a ±20° range, and maintained a mainlobe gain above 13dB.

[0065] This system also boasts excellent scalability. By increasing the array size and PIN control bit width, it can achieve spatial multiplexing transmission of three, four, or more channels, supporting dynamic images, video, and multi-user high-speed transmission. It can be combined with existing Wi-Fi and 5G links to build intelligent reflective communication networks and can also be used as passive modulation panels in scenarios such as millimeter-wave security inspections and radar imaging.

[0066] The system achieves excellent results in dual-beam modulation capability, sidelobe suppression effect and image transmission quality, verifying the practicality and advancement of the invention in wireless spatial modulation.

Claims

1. A coded metasurface dual-channel asymmetric digital transmission system based on weighted theorem optimization, characterized in that: The system consists of a programmable coding metasurface array, an FPGA control module, a radio frequency transceiver module, and a channel multiplexing module; The programmable coding metasurface array adopts a two-dimensional periodically arranged sub-wavelength unit structure, and each unit integrates two PIN diode control circuits; The FPGA control module controls the metasurface reflection characteristics according to the optimized coding sequence generated by the weighted theorem; The system achieves independent control of two asymmetric reflected waves by combining spatial dimension beamforming with coded modulation.

2. The dual-channel digital transmission system structure based on a coding metasurface according to claim 1 is characterized in that: The unit consists of a three-layer structure. The top radiation structure of the unit is made of copper, the middle dielectric layer is made of FR4 epoxy resin substrate, and the bottom ground structure is made of a fully covered copper reflective layer. The top radiation structure is formed by connecting a hexagonal hole structure and a rectangular strip structure; The side lengths of the hexagonal hole structure are 8 mm, 7 mm, 4.7 mm, 6 mm, 4.7 mm, 7 mm, and 8 mm, respectively, and the height is 35 microns; The hole structure has a length of 4.7 mm, a width of 1 mm, and a height of 35 μm; The rectangular strip structure is 12.8 mm long, 0.6 mm wide and 35 μm high; The small rectangles connecting the rectangular strip structures are 0.6 mm long, 0.2 mm wide, and 35 μm high; The small rectangle between the rectangular strip structure and the diode connection is 0.4 mm long, 0.3 mm wide, and 35 μm high; The intermediate dielectric layer is composed of a square structure; The material of the intermediate dielectric layer structure is FR4 (epoxy resin substrate), with a side length of 14 mm and a height of 4 mm; The relative dielectric constant ε_r of the intermediate dielectric layer material is 2.65, and the loss tangent value tanδ is 0.0019; The bottom grounding structure and the top hexagonal hole structure are connected via hollow copper columns; The bottom ground structure is a square with a side length of 14 mm; The hollow copper column connecting the bottom ground structure and the top hexagonal hole structure has a diameter of 0.3 mm, a height of 4 mm, and a thickness of 35 μm.

3. The circuit driving layer structure according to claim 1, wherein: a. Using a column-controlled circuit layout, 24 units in each column share a DC bias line; b. The control circuit includes: Level conversion module (0V to 3.3V conversion); Each unit integrates two SMP1320-079LF PIN diodes connected in reverse parallel.

4. The metasurface unit interconnect structure according to claim 1, wherein: The hexagonal radiating patch is connected to the bottom ground plane through copper plated vias (0.3mm diameter).

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