An adjustable frequency RIS structure based on interlayer air gap distance adjustment

Abstract

The application discloses a tunable frequency RIS structure based on interlayer air gap distance adjustment, which comprises a patch layer, a metal reflection layer, a distance adjustment component and a programmable control module. The patch layer is provided with an RIS unit array composed of a main resonant patch, an auxiliary resonant patch and a PIN diode. The distance adjustment component is used for mechanically adjusting the thickness of the adjustable air layer between the patch layer and the metal reflection layer to continuously change the central working frequency. The programmable control module realizes 1-bit phase modulation by controlling the on-off of the PIN diode. The structure utilizes the characteristics that the resonant frequency of the PIN diode in two states changes in the same direction with the layer thickness, maintains the stable phase difference between the two reflection states in the whole frequency adjustment process, thereby achieving the efficient cooperation of wideband frequency adjustment and beamforming with a simple mechanical structure, and significantly improving the link reliability and adaptability in a non-line-of-sight communication scene.

Description

Technical Field

[0001] This invention relates to the field of radio frequency communication and electromagnetic wave control hardware design technology, and in particular to a frequency-tunable RIS structure based on interlayer air gap adjustment. Background Technology

[0002] Reconfigurable Intelligent Surfaces (RIS), as planar structures capable of flexibly controlling the phase and amplitude of incident electromagnetic waves, can achieve electromagnetic beam redirection, spatial propagation environment reconstruction, and wireless link enhancement, showing broad application prospects in wireless communication and radio frequency sensing. Existing reflective RIS typically employs a reflective structure composed of a patch layer and a metal reflective layer, combined with semiconductor switching devices such as PIN diodes to achieve phase modulation, thereby completing beamforming or energy redirection.

[0003] However, existing RIS structures generally suffer from a fixed operating frequency. Their electromagnetic response characteristics are determined after the design is finalized, making it difficult to adjust the center operating frequency according to the needs of actual application scenarios, thus failing to meet the requirements of multi-band adaptation. While some existing technologies have proposed frequency-tunable solutions, they typically rely on complex electrical tuning (such as varactor diodes) or optical tuning structures, resulting in complex hardware structures, high dependence on external control circuits, difficulties in bias network design, and high engineering implementation costs. Furthermore, in large-scale arrays, poor coordination between the frequency modulation mechanism and the 1-bit phase control mechanism can easily lead to deterioration of cell amplitude and phase consistency due to factors such as bias network parasitic effects and uneven interlayer pitch, thereby affecting the overall beam control performance of the array.

[0004] Therefore, there is an urgent need to propose a tunable frequency RIS structure based on interlayer air gap adjustment that is simple in structure, easy to implement in engineering, and can take into account both continuous adjustment of the center frequency and high-precision discrete phase control. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a frequency-tunable RIS structure based on interlayer air gap adjustment, so as to solve the technical problems of fixed operating frequency, complex frequency modulation structure, and inefficient coordination between frequency modulation and phase control in existing reflective reconfigurable smart surfaces.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a frequency-tunable RIS structure based on interlayer air gap adjustment, comprising: A patch layer on which a RIS unit array consisting of multiple RIS units is formed; A metal reflective layer is disposed behind the RIS cell array and opposite to the patch layer; An adjustment component, mechanically connected to the patch layer and / or the metal reflective layer, is used to adjust the thickness of the adjustable air layer between the patch layer and the metal reflective layer, thereby continuously adjusting the center operating frequency of the RIS cell array; A programmable control module is electrically connected to each of the RIS units; Each RIS unit includes a main resonant patch, an auxiliary resonant patch, a PIN diode, and a bias line network. The PIN diode is connected in series between the main resonant patch and the auxiliary resonant patch. The programmable control module applies a bias voltage to the PIN diode through the bias line network to control the PIN diode to switch between a conducting state and a cutoff state, thereby enabling the RIS unit to switch between two reflection states with a preset phase difference, achieving 1-bit phase modulation. When the thickness of the adjustable air layer changes, the resonant frequency of the PIN diode in the on state and the resonant frequency in the off state have the same trend of shifting with the thickness change, so that the preset phase difference between the two reflection states remains stable within the tuning range of the center operating frequency.

[0007] Furthermore, the programmable control module includes a main control unit and multiple shift registers cascaded with the main control unit; the main control unit is used to convert beamforming codebook data into serial control signals and transmit them bit by bit along the cascaded shift registers, loading the status data of each group of RIS units into the shift registers in a serial shift transmission manner; each shift register is configured to output control levels in parallel to the corresponding group of RIS units when the latch signal is valid, so as to synchronously update the working status of all units in the RIS unit array.

[0008] Furthermore, the RIS units in the RIS unit array are connected in groups by bias lines of equal length to form the bias line network; the bias lines of all the RIS units in the same group have the same length, and the bias lines of each group are respectively connected to the corresponding interface of the programmable control module.

[0009] Furthermore, the pitch adjustment component is used to continuously adjust the thickness of the adjustable air layer within the range of 2.5 mm to 5.5 mm, so that the center operating frequency of the RIS unit array is correspondingly continuously adjustable within the range of 3.86 GHz to 4.56 GHz.

[0010] Furthermore, throughout the entire thickness adjustment range of the adjustable air layer, the phase difference between the first reflection phase corresponding to the PIN diode in the off state and the second reflection phase corresponding to the PIN diode in the on state is maintained at 180°±20°.

[0011] Furthermore, the main resonant patch and the auxiliary resonant patch are disposed on the front side of the patch layer; the bias line network includes at least one radio frequency choke element, which is used to block the interference of radio frequency signals on the DC bias circuit and to block the interference of DC bias signals on the radio frequency path.

[0012] Furthermore, the metal reflective layer is a continuous copper-clad layer formed on one side surface of a substrate; the other side surface of the substrate is an exposed dielectric surface to avoid introducing parasitic coupling.

[0013] Furthermore, the programmable control module's storage unit pre-stores multiple 1-bit beamforming codebooks generated collaboratively based on distance compensation and direction compensation; each beamforming codebook corresponds one-to-one with different center operating frequencies and target beam pointing angles; each beamforming codebook is composed of binary phases obtained by quantizing the continuous compensation phases of each RIS unit under the corresponding center operating frequency and target beam pointing angle, and the binary phases correspond to the cutoff and on states of the PIN diode, respectively.

[0014] Furthermore, after the pitch control component changes the thickness of the adjustable air layer to adjust the center operating frequency, the programmable control module is configured to call the corresponding beamforming codebook that matches the current center operating frequency and the target beam pointing angle, and load the beamforming codebook into the shift register to achieve beam pointing reconstruction under broadband adjustable frequency.

[0015] Furthermore, the RIS unit array is arranged in a 16×16 planar rectangular grid array; the patch layer is a high-frequency dielectric substrate made of Rogers RT / duroid 6010 material.

[0016] The beneficial effects of this invention are as follows: By using an adjustable air layer disposed between the patch layer and the metal reflective layer, and an adjustable spacing component mechanically connected to both, the center operating frequency of the RIS unit array can be continuously adjusted by mechanically changing the interlayer spacing. This completely avoids the engineering problems of complex bias network parasitic effects and high control circuit dependence in existing electrical or optical tuning schemes. It achieves broadband frequency tunability while significantly simplifying the hardware architecture and reducing implementation costs. Furthermore, through structural design, the resonant frequency of the PIN diode in both the on and off states moves in the same direction as the air layer thickness changes, thereby stably maintaining the preset phase difference between the two reflection states throughout the frequency adjustment process. This achieves a high degree of synergy between mechanical frequency tuning and 1-bit phase control, solving the technical pain point of difficulty in balancing frequency tuning and phase control in traditional tunable schemes. This allows the structure of this invention to maintain stable beamforming performance across the entire frequency tuning range, significantly improving the scene adaptability and link reliability of reconfigurable smart surfaces in complex non-line-of-sight communication scenarios. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram illustrating the application of the present invention in non-line-of-sight communication scenarios; Figure 2 This is a schematic diagram of the RIS unit structure and dimensions of the present invention; Figure 3 This is a schematic diagram of the working state of the RIS unit of the present invention, wherein... Figure 3 (a) represents the cutoff state of the RIS cell. Figure 3 (b) is the RIS cell on state; Figure 4 This is a schematic diagram of the interlayer structure of the RIS architecture in this unit; Figure 5 The graph shows the reflection amplitude characteristics of the RIS unit PIN diode in two working states, ON and OFF, under different interlayer spacings according to the present invention. Figure 6 This is a schematic diagram of the planar structure of the RIS cell array of the present invention; Figure 7 This is a schematic diagram of the 1-bit beamforming codebook for different target orientations in this invention. Figure 8 This is a schematic diagram of the hierarchical hardware structure of the RIS architecture of the present invention, wherein... Figure 8 (a) is a schematic diagram of the upper patch layer. Figure 8 (b) is a schematic diagram of the lower metal reflective layer; Figure 9 This is a block diagram illustrating the control architecture principle of the programmable control module of the present invention. Figure 10 This is a schematic diagram of a microwave anechoic chamber test scenario for the RIS architecture of this invention. Figure 11 The figure shows the measured results of the relationship between different interlayer spacings and center frequencies in this invention. Figure 12 This is a comparison chart of the simulation and measured results of the normalized radiation pattern for different target deflection angles at different representative frequencies according to the present invention. Figure 12 (a) is 3.86 GHz. Figure 12 (b) is 4.56 GHz.

[0019] In the diagram, the component names corresponding to each label are: 1. Main resonant patch, 2. Auxiliary resonant patch, 3. PIN diode, 4. RF choke inductor, 5. Bias line, 6. Patch layer, 7. Metal reflective layer, 8. Transmitting horn antenna, 9. Receiving horn antenna, 10. Turntable, 11. RIS architecture main body, 12. Support bracket, 13. Keysight N5247A vector network analyzer. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that the descriptions involving "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0022] like Figure 1 As shown, an embodiment of the present invention is: a frequency-tunable RIS structure based on interlayer air gap adjustment, mainly applied to Sub-6GHz band non-line-of-sight wireless communication scenarios. The RIS performs amplitude and phase coordinated modulation of the incident electromagnetic wave, reflecting the signal to the target user area to compensate for transmission loss due to obstructed links and improve the coverage and reliability of the communication system. The structure includes: The patch layer 6 has a RIS unit array consisting of multiple RIS units formed on it; A metal reflective layer 7 is disposed behind the RIS cell array and opposite to the patch layer 6; An adjustment component, mechanically connected to the patch layer 6 and / or the metal reflective layer 7, is used to adjust the thickness of the adjustable air layer between the patch layer 6 and the metal reflective layer 7, thereby continuously adjusting the center operating frequency of the RIS cell array. A programmable control module is electrically connected to each of the RIS units; Each RIS unit includes a main resonant patch 1, an auxiliary resonant patch 2, a PIN diode 3, and a bias line network. The PIN diode 3 is connected in series between the main resonant patch 1 and the auxiliary resonant patch 2. The programmable control module applies a bias voltage to the PIN diode 3 through the bias line network to control the PIN diode 3 to switch between a conducting state and a cutoff state, thereby enabling the RIS unit to switch between two reflection states with a preset phase difference, achieving 1-bit phase modulation. When the thickness of the adjustable air layer changes, the resonant frequency of the PIN diode 3 in the conducting state and the resonant frequency in the cut-off state have the same trend of shifting with the thickness change, so that the preset phase difference between the two reflection states remains stable within the tuning range of the center operating frequency.

[0023] In this embodiment, a reflective layered architecture is adopted, and its core structure is as follows: Figure 4 As shown. The 1-bit phase control of the RIS unit is achieved by switching the PIN diode 3 between its on and off states. For example... Figure 3 As shown in (a), when PIN diode 3 is cut off, the current path of the resonant structure is relatively long, corresponding to the first reflection state; as Figure 3 As shown in (b), when PIN diode 3 is turned on, the main and auxiliary patches form a coupling path, and the current path and resonance characteristics change, corresponding to the second reflection state. The reflection phase difference between the two states is stable in the range of 180°±20°, which meets the two-state phase modulation requirements for beamforming.

[0024] The core mechanism of this frequency-adjustable invention is as follows: by changing the air gap spacing d through the spacing adjustment component, the equivalent electrical thickness of the RIS cell to ground and the equivalent inductance of the current loop are adjusted. When the spacing d increases, the transmission path between the surface mount current and the mirror current becomes longer, the equivalent inductance increases accordingly, and the resonant point shifts towards lower frequencies; when the spacing d decreases, the transmission path shortens, the equivalent inductance decreases, and the resonant point shifts towards higher frequencies. Figure 4 As shown, the interlayer air gap spacing is denoted as d, and its adjustable range is 2.5 mm to 5.5 mm. (From...) Figure 5 The simulation results show that the interlayer pitch adjustment has an approximately parallel trend in the resonant curve shift of the PIN diode in both on and off states. Therefore, it can stably maintain a phase difference of approximately 180° within the effective pitch range, which meets the design requirements of 1-bit phase control and frequency modulation.

[0025] In a specific embodiment, the programmable control module includes a main control unit and multiple shift registers cascaded with the main control unit; the main control unit is used to convert beamforming codebook data into serial control signals and transmit them bit by bit along the cascaded shift registers, loading the status data of each group of RIS units into the shift registers in a serial shift transmission manner; each shift register is configured to output control levels in parallel to the corresponding group of RIS units when the latch signal is valid, so as to synchronously update the working status of all units in the RIS unit array.

[0026] In this embodiment, as Figure 9 As shown, to achieve the loading and execution of the aforementioned binary beamforming codebook, the control system uses an STM32F103C8T6 minimum system board as the main control module, in conjunction with a multi-level cascaded 74HC595 shift register to form a serial control link. The beamforming codebook is pre-frozen in the on-chip memory of the main control module, and the corresponding codebook data can be called according to the actual communication scenario and target pointing requirements. During operation, the main control module converts the codebook data into serial control signals and transmits them bit by bit along the cascaded shift register link. Each shift register completes codeword shifting under the drive of the synchronous clock signal, and outputs control levels in parallel when the latch signal is valid, driving the PIN diode 3 of the corresponding RIS unit to work in the cutoff or conduction state respectively. Through the above cascaded control method, the synchronous configuration and rapid update of all array units can be achieved with fewer I / O interface resources, ensuring the real-time performance and state consistency of beam switching. At the same time, the control system is powered by a 3.3V DC regulated power supply, with low overall power consumption and stable and reliable operation. The control architecture and the inter-layer frequency modulation mechanism of this invention are independent of each other and work together. When the air gap between the patch layer 6 and the metal reflective layer 7 is changed to adjust the working frequency, the beam pointing reconstruction can be completed simply by calling the beamforming codebook at the corresponding frequency. No changes are required to the control architecture and hardware circuit, which improves the applicability and engineering practicality of the system in broadband adjustable communication scenarios.

[0027] In a specific embodiment, the RIS units in the RIS unit array are connected in groups by bias lines of equal length to form the bias line network; the bias lines 5 of all the RIS units in the same group have the same length, and the bias lines 5 of each group are respectively connected to the corresponding interface of the programmable control module.

[0028] In this embodiment, the RF choke inductor 4 and the bias line 5 of the RIS unit form a DC bias network, which can realize diode state control and block mutual interference between RF signals and DC circuits, ensuring stable RF performance.

[0029] In a specific embodiment, the pitch adjustment component is used to continuously adjust the thickness of the adjustable air layer within the range of 2.5 mm to 5.5 mm, so that the center operating frequency of the RIS unit array is correspondingly continuously adjustable within the range of 3.86 GHz to 4.56 GHz.

[0030] In this embodiment, the effective adjustment range of the air gap spacing d is 2.5mm to 5.5mm. Through unit simulation under periodic boundary conditions, a precise mapping relationship between the interlayer spacing d and the center frequency fc can be established, providing a reliable basis for actual engineering tuning.

[0031] In a specific embodiment, the phase difference between the first reflection phase corresponding to the PIN diode 3 in the off state and the second reflection phase corresponding to the on state is maintained at 180°±20° throughout the entire thickness adjustment range of the adjustable air layer.

[0032] In this embodiment, as Figure 5 As shown, as the gap increases, the equivalent inductance of the RIS unit increases, and the resonant frequency shifts towards lower frequencies; conversely, as the gap decreases, the equivalent inductance decreases, and the resonant frequency shifts accordingly towards higher frequencies. Throughout the entire pitch range, the resonant curves corresponding to the two operating states of the PIN diode shift approximately in parallel, while the 1-bit phase difference remains essentially constant, achieving coordinated operation of frequency modulation and phase control.

[0033] In a specific embodiment, the main resonant patch 1 and the auxiliary resonant patch 2 are disposed on the front side of the patch layer 6; the bias line network includes at least one radio frequency choke element, which is used to block the interference of radio frequency signals on the DC bias circuit and to block the interference of DC bias signals on the radio frequency path.

[0034] In this embodiment, as Figure 2 As shown, the RIS unit adopts a square structure. PIN diode 3 is a BAV-02L type switching device, which has low parasitic parameters and fast switching speed, meeting the fast switching requirements of 1-bit phase modulation. The substrate of patch layer 6 uses Rogers RT / duroid 6010 high-frequency dielectric material with a thickness D1 of 1.6mm. Its dielectric constant is stable and its loss is low, ensuring good electromagnetic response consistency in the Sub-6GHz band. The geometric parameters and corresponding values ​​of the RIS unit are shown in Table 1, in mm.

[0035] Table 1 In a specific embodiment, the metal reflective layer 7 is a continuous copper-clad layer formed on one side surface of a substrate; the other side surface of the substrate is an exposed dielectric surface to avoid introducing parasitic coupling.

[0036] In this embodiment, the metal reflective layer 7 adopts a 35μm thick high conductivity copper-clad structure, with an FR4 substrate underneath as a mechanical support. The total thickness D2 of this layer is 3.0mm to improve the overall structural rigidity and assembly stability.

[0037] In a specific embodiment, the storage unit of the programmable control module pre-stores multiple 1-bit beamforming codebooks generated collaboratively based on distance compensation and direction compensation; each beamforming codebook corresponds one-to-one with different center operating frequencies and target beam pointing angles; each beamforming codebook is composed of binary phases obtained by quantizing the continuous compensation phases of each RIS unit under the center operating frequency and target beam pointing angle corresponding to the codebook, and the binary phases correspond to the cutoff state and the on state of the PIN diode 3, respectively.

[0038] In this embodiment, a 1-bit beamforming codebook is generated using a combination of range compensation and direction compensation. By rationally configuring the phase of each unit, the reflected waves achieve in-phase superposition in the target direction. Let the operating wavelength be... The space wavenumber is The first in the array The coordinates of each unit are The beam pitch angle is The beam azimuth angle is The desired beam pointing angle is Then the direction compensation phase can be expressed as: (1) To eliminate the spatial phase difference introduced by the incident wave from the feed at each element, a range compensation term is further introduced, the expression of which is: (2) in For feed to the first The straight-line distance between units This represents the distance from the feed to the array center. To facilitate subsequent quantization, the direction compensation phase is first phase-constrained, limiting it to... Within the interval, that is: (3) and with the maximum phase value in the array Normalization was performed for reference: (4) The normalized direction compensation phase and range compensation terms are... Linear superposition yields the final compensated phase: (5) To ensure the total phase after superposition Always in Within the interval, phase wrap-around processing is performed: (6) Finally, the continuous phase is quantized into a 1-bit two-state. Let the quantization threshold interval be... The quantification rules are as follows: (7) in, , , This is the optimal value selected after traversing different cutoff points. The two quantized states correspond to the cutoff and conduction states of the PIN diode, respectively, and a binary beamforming codebook is generated through the above process. Figure 7 A schematic diagram of the binary codebook distribution under different target orientations is presented, where different gray levels correspond to two states of the PIN diode. This type of codebook exhibits a "striped / blocky" structure, and its spatial frequency is determined by the target deflection angle. The larger the deflection angle, the greater the phase gradient, and the more frequent the codebook flips. This codebook generation method is compatible with inter-layer frequency modulation mechanisms, enabling stable and precise beam pointing control at different operating frequencies.

[0039] In a specific embodiment, after the pitch control component changes the thickness of the adjustable air layer to adjust the center operating frequency, the programmable control module is configured to call the corresponding beamforming codebook that matches the current center operating frequency and the target beam pointing angle, and load the beamforming codebook into the shift register to achieve beam pointing reconstruction under broadband adjustable frequency.

[0040] In this embodiment, as Figure 6 As shown, to achieve wide-range beam control, the RIS unit array adopts a 16×16 array layout, with an effective electromagnetic aperture of 430mm×430mm and an overall assembly size of 450mm×450mm. The array uses a grouping method with equal-length bias lines, with 8 units per group. The bias lines within each group have consistent lengths to ensure control signal synchronization, while also reducing the number of external interfaces and lowering the complexity of the control system. Figure 8 As shown in (a), the surface mount layer 6 is designed with high precision PCB layout according to the above parameters. The main resonant patch 1 and auxiliary resonant patch 2 are printed on the front side of the 6010 substrate using high precision photolithography to ensure pattern accuracy. The PIN diode 3, micro-strip lines, and bias network are integrated into a single design. Figure 8 As shown in (b), a continuous copper layer is printed on the back of the FR4 support substrate as a metal reflective layer 7, and no traces are laid on the front to avoid introducing unnecessary coupling. A uniform and adjustable air gap is formed between the two layers through a support component. The control circuit is integrated on the back of the RIS architecture and electrically connected to the array unit, and drives the conduction and cutoff states of the PIN diodes 3 of each unit through the aforementioned serial cascade control method.

[0041] After the RIS architecture was assembled, to pre-verify the beamforming effect of the array in a broadband tunable frequency scenario, full-wave simulation was performed using HFSS software based on the previously generated beamforming codebook. A simulation model of the RIS units and the array was built, material parameters and boundary conditions were accurately set, and the radiation characteristics of the RIS array were simulated and analyzed. In the simulation, for each typical frequency point, the corresponding beamforming codebook pointing to the target was loaded, and the on / off states of the PIN diodes in each RIS unit were configured. The normalized radiation pattern of the array was obtained through simulation. For example... Figure 12 As shown in the simulation results, under different frequency points and different target pointing conditions, the array can form a main lobe beam with clear direction and concentrated energy. The main lobe direction is consistent with the preset target angle, the side lobe level is controlled within a reasonable range, and the beamforming effect meets the design expectations.

[0042] To further verify the actual performance of the RIS architecture of this invention, a microwave anechoic chamber test platform was built. The assembled RIS architecture was subjected to experimental verification of its broadband tunable characteristics and beamforming. The experimental conditions were strictly consistent with the aforementioned simulation parameters to ensure the comparability of the simulation and experimental results. A schematic diagram of the test platform is shown below. Figure 10 As shown, the system mainly includes a transmitting horn antenna 8, a receiving horn antenna 9, a motorized turntable 10, a RIS architecture main body 11, a support bracket 12 for the RIS architecture, and a Keysight N5247A vector network analyzer 13. The RIS architecture is fixed on the motorized turntable 10. The transmitting and receiving horns are respectively arranged on the incident and reflecting sides. The distance R from the feed to the RIS strictly satisfies the far-field condition. Where D is the maximum physical size of the array. The test frequency band is defined as the electromagnetic wave wavelength, and the test coordinate system is defined as the RIS array located at... The plane is aligned with the positive direction of the angle and the desired reflection direction, enabling accurate calibration of the test angle.

[0043] The actual tests were conducted in two parts: broadband tunable performance testing and beamforming performance testing. In the broadband tunable performance testing, the operating state of the RIS unit PIN diodes was kept constant, and the interlayer air gap spacing was gradually adjusted. The resonant frequency of the RIS architecture under different gap thicknesses was recorded, obtaining the correspondence between the interlayer air gap spacing and the operating frequency. The results are as follows: Figure 11 As shown. Experimental results show that when the interlayer air gap thickness is adjusted within the range of 2.5mm to 5.5mm, the operating frequency of the RIS architecture can be continuously and smoothly tuned within the range of 3.8GHz to 4.6GHz. The tuning law is consistent with the simulation results, verifying the practical feasibility of the broadband tunable mechanism of this invention.

[0044] In beamforming performance testing, the interlayer air gap spacing was fixed to determine typical operating frequencies. Beamforming codebooks corresponding to different target orientations, consistent with simulations, were loaded. The on / off states of the PIN diodes in each RIS unit were controlled. The array reflection normalized radiation patterns under different orientation conditions were acquired through the receiving antenna and compared with the simulated radiation patterns. The results are as follows: Figure 12 As shown in the figure. The actual test results show that the main lobe of the array beam points in line with the preset target angle. The deviations of the main lobe gain and side lobe level from the simulation results are within acceptable range. Even with the inherent error introduced by 1-bit phase quantization, the beam pointing accuracy and energy concentration are not affected. This further verifies the cooperative reliability of the beamforming codebook generation method, the control system and the array structure.

[0045] Furthermore, through repeated testing and verification, the RIS device demonstrated stable operation under different frequency points and beam pointing configurations. The switching between the on and off states of the PIN diodes was reliable, and the interlayer air gap adjustment was smooth. It can stably achieve broadband frequency tunable beamforming functions over a long period, meeting the practical application requirements for link enhancement in non-line-of-sight communication scenarios. A slight deviation exists between the measured and simulated results, primarily due to three factors: first, the inherent phase error caused by 1-bit phase quantization, which, using only two discrete states (on and off), cannot achieve continuous phase control and introduces some sidelobe rise; second, structural errors caused by the uniformity of interlayer air gaps, PCB processing tolerances, and parasitic parameters of components during physical assembly; and third, multipath reflections, antenna alignment deviations, and instrument measurement errors present in the test environment. Overall, the impact of these errors on the main lobe pointing is relatively small, and the array can still achieve stable and reliable beamforming, meeting the application requirements of practical communication scenarios.

[0046] In a specific embodiment, the RIS unit array is arranged in a 16×16 planar rectangular grid array; the patch layer 6 is a high-frequency dielectric substrate made of Rogers RT / duroid 6010 material.

[0047] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A frequency-tunable RIS structure based on interlayer air gap adjustment, characterized in that, include: A patch layer on which a RIS unit array consisting of multiple RIS units is formed; A metal reflective layer is disposed behind the RIS cell array and opposite to the patch layer; An adjustment component, mechanically connected to the patch layer and / or the metal reflective layer, is used to adjust the thickness of the adjustable air layer between the patch layer and the metal reflective layer, thereby continuously adjusting the center operating frequency of the RIS cell array; A programmable control module is electrically connected to each of the RIS units; Each RIS unit includes a main resonant patch, an auxiliary resonant patch, a PIN diode, and a bias line network. The PIN diode is connected in series between the main resonant patch and the auxiliary resonant patch. The programmable control module applies a bias voltage to the PIN diode through the bias line network to control the PIN diode to switch between a conducting state and a cutoff state, thereby enabling the RIS unit to switch between two reflection states with a preset phase difference, achieving 1-bit phase modulation. When the thickness of the adjustable air layer changes, the resonant frequency of the PIN diode in the on state and the resonant frequency in the off state have the same trend of shifting with the thickness change, so that the preset phase difference between the two reflection states remains stable within the tuning range of the center operating frequency.

2. The tunable frequency RIS structure based on interlayer air gap adjustment according to claim 1, characterized in that, The programmable control module includes a main control unit and multiple shift registers cascaded with the main control unit. The main control unit is used to convert beamforming codebook data into serial control signals and transmit them bit by bit along the cascaded shift registers, loading the status data of each group of RIS units into the shift registers in a serial shift transmission manner. Each shift register is configured to output control levels in parallel to the corresponding group of RIS units when the latch signal is valid, so as to synchronously update the working status of all units in the RIS unit array.

3. The tunable frequency RIS structure based on interlayer air gap adjustment according to claim 2, characterized in that, The RIS units in the RIS unit array are connected in groups by bias lines of equal length to form the bias line network; the bias lines of all the RIS units in the same group are of the same length, and the bias lines of each group are respectively connected to the corresponding interface of the programmable control module.

4. The tunable frequency RIS structure based on interlayer air gap adjustment according to claim 1, characterized in that, The pitch adjustment component is used to continuously adjust the thickness of the adjustable air layer within the range of 2.5 mm to 5.5 mm, so that the center operating frequency of the RIS unit array is continuously adjustable within the range of 3.86 GHz to 4.56 GHz.

5. The tunable frequency RIS structure based on interlayer air gap adjustment according to claim 4, characterized in that, Throughout the entire thickness adjustment range of the adjustable air layer, the phase difference between the first reflection phase corresponding to the PIN diode in the off state and the second reflection phase corresponding to the PIN diode in the on state is maintained at 180°±20°.

6. The tunable frequency RIS structure based on interlayer air gap adjustment according to claim 1, characterized in that, The main resonant patch and the auxiliary resonant patch are disposed on the front side of the patch layer; the bias line network includes at least one radio frequency choke element, which is used to block the interference of radio frequency signals on the DC bias circuit and to block the interference of DC bias signals on the radio frequency path.

7. The tunable frequency RIS structure based on interlayer air gap adjustment according to claim 1, characterized in that, The metal reflective layer is a continuous copper-clad layer formed on one side surface of a substrate; the other side surface of the substrate is an exposed dielectric surface to avoid introducing parasitic coupling.

8. The tunable frequency RIS structure based on interlayer air gap adjustment according to claim 1, characterized in that, The programmable control module's storage unit pre-stores multiple 1-bit beamforming codebooks generated collaboratively based on distance compensation and direction compensation; each beamforming codebook corresponds one-to-one with different center operating frequencies and target beam pointing angles; each beamforming codebook is composed of binary phases obtained by quantizing the continuous compensation phases of each RIS unit under the corresponding center operating frequency and target beam pointing angle, and the binary phases correspond to the cutoff and on states of the PIN diode, respectively.

9. The tunable frequency RIS structure based on interlayer air gap adjustment according to claim 8, characterized in that, After the pitch control component changes the thickness of the adjustable air layer to adjust the center operating frequency, the programmable control module is configured to call the corresponding beamforming codebook that matches the current center operating frequency and the target beam pointing angle, and load the beamforming codebook into the shift register to achieve beam pointing reconstruction under broadband adjustable frequency.

10. The tunable frequency RIS structure based on interlayer air gap adjustment according to claim 1, characterized in that, The RIS cell array is arranged in a 16×16 planar rectangular grid array; the patch layer is a high-frequency dielectric substrate made of Rogers RT / duroid6010 material.

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