Transmission type metasurface based on pin diode polarization and independent adjustable phase

Abstract

The invention discloses a transmission type metasurface based on pin diode polarization and independent adjustable phase, and the metasurface is composed of n * n metasurface units which are periodically arranged, and the metasurface units are arranged along the Z-axis direction, a polarization regulation and control layer, an upper substrate, a radio frequency grounding layer, a bonding substrate, a feed network layer, a lower substrate and a phase regulation and control layer are sequentially arranged from top to bottom. Electromagnetic waves enter from the phase regulation and control layer and exit from the polarization regulation and control layer to form a transmission type metasurface. The polarization regulation and control layer is used for realizing transmission wave polarization switching, the polarization regulation and control layer comprises a square-like patch, and two PIN diodes are integrated in the middle of the square-like patch. According to the invention, polarization and phase regulation are completely decoupled without crosstalk, the common-caliber integration degree is high, the polarization isolation degree is excellent, the phase regulation precision is high, the working states are rich, the structural process is simple, and the cost is controllable.

Description

Technical Field

[0001] This invention belongs to the field of reconfigurable smart metasurface technology, specifically relating to a transmissive metasurface based on pin diode polarization and phase independently adjustable. Background Technology

[0002] Most current metasurfaces are single-function metasurfaces, capable of controlling only one of the electromagnetic properties: phase, polarization, or amplitude, thus limiting their applications. While a 1-bit phase-controlled transmissive metasurface was designed in BAI X, ZHANG F, SUN L, et al. Time-Modulated Transmissive Programmable Metasurface for Low Sidelobe Beam Scanning[J / OL]. Research, 2022, 2022: 2022 / 9825903. DOI:10.34133 / 2022 / 9825903, its functionality is limited to the phase dimension and cannot meet the multi-dimensional requirements of dual-polarization communication.

[0003] To expand application scenarios, researchers designed a transmissive-reflective dual-mode polarization conversion metasurface. Its unit cell employs a multilayer composite structure of "metal-dielectric-functional material." While this design achieves efficient polarization control, its temperature-driven control method has a response speed in the millisecond range, far below the microsecond-level dynamic requirements of communication systems. Furthermore, its functionality only covers polarization conversion and absorption, lacking phase control capabilities, thus limiting its practicality. In JING L, ZHANG D, SONG K, et al. Reconfigurable chiral radiation enabled by origami metasurface [J / OL]. Laser&Photonics Reviews: e01474. DOI:10.1002 / lpor.202501474, a deformable polarization-controlled metasurface was designed. Its unit cell uses a polyimide film as a substrate, with cross-shaped copper foil patches etched on the surface. Polarization state switching is achieved by mechanically folding to change the three-dimensional configuration, converting incident ray-polarized waves into left-handed or right-handed circularly polarized waves. Although the design offers a wide range of polarization control dimensions, it relies on mechanical drives and cannot achieve real-time control of electrical signals. Furthermore, it lacks an integrated phase control module. Additionally, the support and fixing structures of the folding mechanism increase the overall design complexity and manufacturing costs.

[0004] In addition, although some existing solutions attempt to achieve joint control of polarization and phase, they adopt a separate aperture design, which leads to an increase in the size of the metasurface and a decrease in integration. Furthermore, the two affect each other during the control process, making it impossible to achieve truly independent control.

[0005] In summary, existing reconfigurable metasurfaces still have the following drawbacks: Severe coupling of control: Existing schemes do not effectively isolate the polarization control and phase control circuits. The two interfere with each other when they are working and cannot be switched independently, which limits the functional flexibility of the metasurface.

[0006] Low integration: Some solutions adopt a separate aperture design, with polarization and phase control modules laid out separately, resulting in a large overall size of the metasurface, which is not conducive to the miniaturization and integration of the equipment.

[0007] Insufficient polarization isolation: The polarization control structure design of the existing scheme is unreasonable. The transmission amplitude difference between different polarization modes is small, and the isolation is generally lower than 18dB, which affects the signal purity.

[0008] Low phase modulation accuracy: The equivalent electrical length design of the phase modulation unit is not optimized enough, resulting in a 180° phase jump error of more than 8°, which cannot meet the application requirements of high-precision beamforming.

[0009] Limited operating states: Most existing solutions can only achieve two or fewer operating states, which cannot meet the electromagnetic wave control needs in multiple scenarios. Summary of the Invention

[0010] In order to overcome the shortcomings of the existing technology, the present invention aims to provide a transmissive metasurface based on pin diode polarization and phase independently adjustable. This metasurface has the characteristics of complete decoupling of polarization and phase control without crosstalk, high common aperture integration, excellent polarization isolation, high phase control accuracy, rich operating states, simple structure and process, and controllable cost.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A transmissive metasurface based on pin diode polarization and phase-independent adjustable is proposed, which is composed of n×n metasurface units arranged periodically.

[0012] Along the Z-axis, the metasurface unit consists of, from top to bottom, a polarization control layer, an upper substrate, an RF ground layer, an adhesive substrate, a feed network layer, a lower substrate, and a phase control layer. Electromagnetic waves are incident from the phase modulation layer and emitted from the polarization modulation layer, forming a transmissive metasurface; The polarization control layer is used to switch the polarization of the transmitted wave. The polarization control layer includes a square patch, and two PIN diodes are integrated in the middle of the square patch.

[0013] The metasurface unit maintains resonant characteristics in the 6.0GHz~6.6GHz frequency band, enabling the metasurface to operate stably in the 6.0GHz~6.6GHz range; the upper substrate, bonding substrate, and lower substrate are Rogers RO4350 dielectric substrates; The polarization control layer, RF ground layer, feed network layer, and phase control layer are all copper metal layers, which are alternately arranged with the Rogers RO4350 dielectric substrate.

[0014] The RogersRO4350 dielectric has a dielectric constant of 3.48 and a loss tangent of 0.0037, exhibiting low microwave loss and structural stability.

[0015] The periphery of the quasi-square patch has four rectangular metal pieces respectively arranged along the positive X-axis, negative X-axis, positive Y-axis, and negative Y-axis, maintaining a gap between them and the quasi-square patch. Each rectangular metal piece is independent of the quasi-square patch and is centrally symmetrically distributed. The "quasi-square patch" mentioned in this invention does not refer to a complete square in a geometric sense. Its overall outline is approximately square, maintaining the central symmetry of the square structure. At the same time, it adopts a composite design of "square ring + internal nested square", which combines the symmetrical characteristics of a square with the impedance regulation function of a ring. Therefore, "quasi-square" is used to describe its structural attributes of "approximately square and functionally composite".

[0016] Based on the center of the polarization control layer (1), short rod-shaped metal feed plates are provided in the negative X-axis and negative Y-axis regions. The short rod-shaped metal feed plates are located in the top polarization control layer and are connected to the feed network layer (5) through a metallized via perpendicularly along the negative Z-axis. This is used to introduce external bias signals. The short rod-shaped metal feed plates are electrically connected to the outer edge of the square patch (square ring structure) through an inductor. This is used to transmit the bias signals required for polarization control and to achieve impedance matching with the inductor. Four rectangular metal plates are respectively set in the positive X-axis, negative X-axis, positive Y-axis, and negative Y-axis directions around the square patch. They maintain independent gaps with the square patch and the short rod-shaped metal feed plates and have no direct electrical connection. This is used to assist the electromagnetic boundary conditions of the control unit and enhance polarization isolation and resonance stability.

[0017] The anodes of both PIN diodes are electrically connected to the inner edge of the square ring metal sheet, and the cathodes are electrically connected to the centrally nested square chip. The positive and negative directions of the two diodes are consistent. The model is SMP1340-040LF, which serves as a polarization selection switch. With the center of polarization control layer 1 as the reference, a capacitor of model GCM1555C1H101JA16D is also configured in the positive X-axis and positive Y-axis regions as a structure for polarization control function. At the center of the square patch, which is the origin of the coordinate system, another metallized via extends along the negative Z-axis and directly connects to the phase control layer. This metallized via provides a stable conduction path for the radio frequency signal and ensures that the bias signal is uniformly loaded onto the PIN diode of the top polarization control layer, providing key structural support for the coordinated realization of independent polarization and phase control functions.

[0018] The power supply plate is electrically connected to the central square metal plate through a surface-mount high-frequency inductor, LQW15AN9N1G8ZD, manufactured by Murata.

[0019] The radio frequency grounding layer is a complete metal foil covering the entire area of ​​the unit. It serves as a radio frequency reference ground and is used to isolate electromagnetic crosstalk between the top polarization control circuit and the lower phase control circuit. The bonding substrate below it is used to support the feed network layer and to achieve a stable bond between the radio frequency grounding isolation layer and the lower structure. The main body of the phase control layer is a U-shaped metal patch, which is based on the unit center and extends along the Y-axis with the unit coordinate origin as the center. A rectangular hollow area is opened in the middle of the patch along the Y-axis. Within the aforementioned cutout area, a PIN diode is integrated at each end of the patch along the positive and negative X-axis directions. A short rod-shaped metal feed plate is positioned along the positive Y-axis direction. This feed plate is electrically connected to the feed network layer via a metallized via along the positive Z-axis direction. It is connected to the center position via a high-frequency inductor and also connected to the center of the top layer via a metallized via, in order to optimize impedance matching of the signal transmission path and suppress parasitic losses. With the center as the reference, a short rod-shaped metal feed plate is also positioned in the positive X-axis and negative Y-axis directions. This feed plate is also connected to the feed network layer via a metallized via along the positive Z-axis direction.

[0020] The core function of the two short rod-shaped metal feed plates mentioned above is to receive the phase modulation bias signal transmitted from the feed network layer, thereby driving the switching of the on and off states of the two PIN diodes at the bottom layer, providing power support for the 180° phase jump function.

[0021] The power supply network layer uses a strip metal power supply line, one end of which is connected to the polarization control layer through a metallized via, and the other end extends to the pad at the edge of the cell to receive the power supply signal and realize the on / off drive of the PIN diode.

[0022] When the metasurface is in operation, a 2-18 GHz dual-ridge broadband horn is selected as the feed source, with a gain of 6-12 dBi. When a 15x15 metasurface is selected and operates at 6.3 GHz, the feed gain is approximately 10 dBi; the horn is fixed at a position 300 mm from the center of the metasurface, and the focal diameter ratio is set to 0.8.

[0023] The beneficial effects of this invention are: This invention employs a common-aperture integrated design, using the XY plane (25mm×25mm) of a single metasurface unit as the unified aperture boundary. Polarization and phase modulation functions are integrated within the same unit space, eliminating the need for additional lateral aperture expansion. The design features a quasi-square metal patch for the top polarization modulation layer and a U-shaped metal patch for the bottom phase modulation layer, both symmetrically arranged around the unit coordinate origin, ensuring no misalignment or offset within the XY plane and fully utilizing the vertical space of the same aperture. An alternating stack of an RF ground layer, bonding substrate, and feed network layer along the Z-axis achieves physical isolation and independent operation of the two modulation circuits while avoiding lateral volume redundancy caused by separate apertures. Ultimately, by optimizing the unit structure layout, the metasurface volume is reduced, improving integration density. A quasi-square resonant patch structure is designed, enabling incident wave polarization modulation through switching states.

[0024] This invention achieves complete isolation between polarization and phase control circuits through a metallic ground layer, ensuring that the control processes do not interfere with each other and solving the coupling problem of existing technologies. It features high integration and small size: the common aperture design integrates polarization and phase control functions into a single unit, and the compact 15×15 array structure facilitates miniaturized deployment of the device.

[0025] This invention employs a quasi-square resonant patch design for the polarization control layer. A high-frequency inductor is connected in series between the top short rod-shaped metal feed plate and the quasi-square metal plate to form an impedance matching link, which can reduce signal reflection and cross-polarization coupling. By combining the on and off states of the two PIN diodes on the top layer, the equivalent impedance distribution of the quasi-square patch along the X / Y axis is precisely changed, so that the transmitted electric field is concentrated in the target polarization direction (X polarization or Y polarization). In conjunction with the RF ground isolation layer, electromagnetic crosstalk between the top and bottom circuits is blocked. Polarization crosstalk is suppressed from three aspects: impedance matching, polarization orientation control, and structural isolation. Ultimately, a polarization isolation of over 20dB is achieved in the X / Y polarization mode, ensuring signal purity.

[0026] The phase modulation layer primarily consists of a U-shaped metal patch. A high-frequency inductor is connected in series between the bottom short-rod metal feed plate and the U-shaped metal patch to optimize impedance matching of the signal transmission path and suppress parasitic losses. By switching on and off two PIN diodes symmetrically distributed along the Y-axis at the bottom layer, the effective current path length of the U-shaped patch along the X-axis is precisely adjusted, achieving 0° and 180° phase switching based on the principle of "equivalent electrical length change." Furthermore, the unit size parameters (such as the U-shaped patch opening width and arm length) are precisely optimized to perfectly match the 6.3GHz resonance requirements, avoiding the introduction of additional phase deviations during the switching process and ensuring the stability and accuracy of phase transitions. The error is controlled within 5°, meeting the requirements of high-precision beamforming. The signal purity and modulation accuracy are significantly superior to existing solutions.

[0027] It adopts the mature PIN diode SMP1340-040LF and a low-loss dielectric substrate, with a simple structure and process, making it suitable for mass production. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the overall reconfigurable metasurface of the present invention.

[0029] Figure 2 This is a three-dimensional schematic diagram of the unit structure of the present invention.

[0030] Figure 3 These are bottom views, top views, and top views of the power supply network layer of the present invention.

[0031] Figure 4 for Figure 1 The s-parameter response curve of the unit under a given PIN diode state sequence when operating in x-polarization mode.

[0032] Figure 5 This represents the transmission phase response of the underlying PIN diode under different conditions.

[0033] Figure 6 The electric field distribution on the metal patch surface of the diode unit in two states is shown; (a) pin value is 01 (b) pin value is 10.

[0034] Figure 7 The current distribution on the metal patch of the diode under two states is shown; (a) pin value is 01 (b) pin value is 10.

[0035] Figure 8 (a) is the radiation pattern under x-polarization mode; Figure 8 (b) is the radiation pattern in the y-polarization mode; Figure 8 (c) is the radiation pattern in the 45° linear polarization mode. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings.

[0037] like Figure 1 As shown, this invention designs a 1-bit reconfigurable metasurface with independent tunable phase and polarization based on PIN diodes. The metasurface is composed of 15×15 periodically arranged units. The patch structure is designed so that the units resonate at 6.3 GHz, enabling the metasurface to operate at 6.3 GHz.

[0038] Metasurface unit structure such as Figure 2As shown, the cell has a periodicity of 25 mm. The core structure consists of three layers of Rogers RO4350 dielectric substrate and four layers of copper metal layers stacked alternately. The Rogers RO4350 dielectric has a dielectric constant of 3.48 and a loss tangent of 0.0037, exhibiting low microwave loss and structural stability. Along the Z-axis, the copper layers from top to bottom are, in order: polarization control layer 1, RF ground layer 3, feed network layer 5, and phase control layer 7.

[0039] The top layer of the unit serves as polarization control layer 1, as shown in the top view below. Figure 3 As shown, the square-shaped metal patch is centrally symmetrically distributed with the origin of the unit coordinate system as the center. The corresponding size parameter is w4. Its outer contour is an octagonal structure formed by chamfering the four right angles on the basis of a square (the opposite sides along the X and Y axes are parallel and of the same length). Another metallized via is perpendicularly penetrating the center of the square-shaped patch along the negative Z half axis, which is connected to the bottom bias circuit to ensure uniform loading of the bias signal. Four rectangular metal pieces are respectively set along the positive X-axis, negative X-axis, positive Y-axis, and negative Y-axis directions on the periphery of the square patch. The width of each piece is w1 and the length is L1. They are separated from the patch body by a gap d. Each rectangular metal piece is independent of the square patch and is centrally symmetrically distributed. With the origin of the unit coordinate system as the reference, a PIN diode, model SMP1340-040LF, is placed in the patch area corresponding to the negative half-axis of the Y-axis and the positive half-axis of the X-axis, serving as a polarization selection switch. The width of the area where the PIN diode is located is indicated by the label w2 in the attached figure. Both PIN diodes maintain a stable electrical connection with the patch body. In the patch area along the positive X-axis and positive Y-axis, a capacitor, model GCM1555C1H101JA16D, is configured as an auxiliary impedance matching structure for the polarization control function. With the center of the top layer of the unit as a reference, a short rod-shaped metal feed plate is set in the negative X-axis direction and the negative Y-axis direction. The feed plate is connected to the feed network layer 5 through a metallized via perpendicularly through the negative Z-axis direction. It is used to introduce an external bias signal to achieve the switching of transmitted wave polarization. The feed plate is electrically connected to the square-like metal patch in the center through a high-frequency inductor LQW15AN9N1G8ZD manufactured by Murata. This arrangement of component positions serves two purposes. First, the symmetrical layout of the four rectangular metal plates on the periphery enhances the electromagnetic structure symmetry of the unit, preventing additional signal distortion introduced by asymmetrical layouts. Second, placing the PIN diodes in the negative Y-axis and positive X-axis regions and matching the size design of w2 allows for precise control of the equivalent impedance distribution of the patch along the X / Y axes. Combined with the deployed capacitors and inductors, this optimizes the impedance matching characteristics of polarization control layer 1. The adaptive design of various dimensional parameters (w1, w2, a, etc.) further ensures the resonant performance of the unit in the 6.3GHz frequency band. At the same time, the independent layout of the two PIN diodes ensures that their on / off states do not interfere with each other, achieving a polarization isolation of over 20dB and improving the signal purity and functional stability of the unit.

[0040] The RF ground layer 3 is located below the upper substrate 2. It is a complete metal foil covering the entire area of ​​the unit and serves as an RF reference ground. It is used to isolate electromagnetic crosstalk between the top polarization control circuit and the lower phase control circuit. The bonding substrate below it is used to support the feed network layer 5 and to achieve a stable bond between the RF ground isolation layer and the lower structure. The power supply network layer 5 uses a strip-shaped metal power supply wire. One end is connected to the top-layer power supply structure through a metallized via, and the other end extends to the pad at the edge of the cell for receiving the power supply signal to drive the PIN diodes on and off. A top view of power supply network layer 5 is shown below. Figure 3 As shown.

[0041] The fourth metal layer of the unit is the bottom phase modulation functional layer, such as Figure 3 As shown.

[0042] The main body of the bottom phase control layer 7 is a U-shaped metal patch (with the origin of the unit coordinate as the center and extending along the Y-axis direction) (the whole is centrally symmetrically distributed). The total length of the patch along the Y-axis direction corresponds to the number m1 in the attached figure, and the width along the X-axis direction corresponds to the number n1. A rectangular cutout area is opened in the middle of the patch along the Y-axis direction. The width of this area along the X-axis direction corresponds to the number n2, and the length along the Y-axis direction corresponds to the number m2.

[0043] Within the aforementioned cutout area, with the unit center as the reference, one PIN diode is integrated at each end of the patch along the positive and negative X-axis directions. A short rod-shaped metal feed plate is provided along the positive Y-axis direction. This feed plate is electrically connected to the feed network layer 5 through a metallized via along the positive Z-axis direction. It is connected to the center position along the X-axis direction through a high-frequency inductor with an extension length corresponding to the label m3. It is also connected to the center of the top layer through a metallized via to optimize the impedance matching of the signal transmission path and suppress parasitic losses. With the center as the reference, a short rod-shaped metal feed plate is also set in the positive X-axis direction and the negative Y-axis direction. This feed plate is also electrically connected to the feed network layer 5 through a metallized via along the positive Z-axis direction. The core function of the above two short rod-shaped metal feed plates is to receive the phase modulation bias signal transmitted from the third feed network layer 5, thereby driving the switching of the on / off state of the two PIN diodes at the bottom layer.

[0044] This arrangement of component positions ensures, on the one hand, the symmetrical layout of the main U-shaped patch and the central hollow area guarantees electromagnetic symmetry during phase modulation, avoiding additional phase deviations introduced by asymmetrical structures. On the other hand, integrating the PIN diode and inductor into the central hollow area allows for precise adjustment of the effective current path length of the patch. Combined with the extended layout of the inductor (corresponding to the m3 size), it optimizes the impedance matching characteristics of signal transmission and reduces parasitic losses. Meanwhile, the directional extension design of the short rod-shaped feed plate facilitates a stable electrical connection with the feed network layer 5. The adaptive design of dimensions such as n1 and n2 further guarantees the resonance requirements of the unit in the 6.3GHz frequency band, ultimately achieving a high-precision modulation effect with a phase jump error of less than 5°, ensuring the stability and accuracy of the unit's phase modulation.

[0045] The main dimensions of the unit are shown in Table 1.

[0046] Table 1 Dimensional parameters (unit: mm) For clarity and conciseness, the four PIN diodes in the unit are functionally divided into "Top-level Polarization Control Layer 1" and "Bottom-level Phase Control Layer 7," and numbered sequentially in a counter-clockwise direction: the two PIN diodes in the center of the top-level square patch are numbered 1 with the center of the square patch as the symmetrical point, starting from the negative Y-axis and moving counter-clockwise to the second PIN diode, which is numbered 2; the two PIN diodes at both ends of the bottom-level U-shaped patch are numbered 3 along the negative x-axis and 4 along the positive x-axis. For example, when the top-level polarization control needs to switch to Y-polarization (PIN diode 1 is off, PIN diode 2 is on), and the bottom-level phase control needs to achieve 0° phase (PIN diode 3 is on, PIN diode 4 is off), the corresponding state sequence number is "01 / 10"; when the top-level switch is to X-polarization (PIN diode 1 is on, PIN diode 2 is off), and the bottom-level switch is to 180° phase (PIN diode 3 is off, PIN diode 4 is on), the state sequence number is "10 / 01". By adjusting the on / off states of the four PIN diodes, this unit can achieve four independent operating states. The functions implemented are shown in Table 2.

[0047] Table 2. Pin values ​​under different operating conditions Work status Top PIN tube (1 / 2) status Bottom PIN tube (3 / 4) status Function Description Y polarization 01 01 / 10 The top-layer PIN diode is locked in a Y-polarized emission state, while the bottom-layer state switching achieves a 180° phase difference in the transmitted wave. X polarization 10 01 / 10 The top-layer PIN diode is locked in X-polarized emission, while the bottom-layer state switching achieves a 180° phase difference in the transmitted wave. The decoupling of polarization and phase is achieved through a collaborative design of "structural isolation, response independence, and signal independence": the RF ground layer 3, as a complete metal foil structure, physically separates the top polarization control layer 1 and the bottom phase control layer 7, blocking the electromagnetic crosstalk path between the two circuit layers; polarization control is based on the principle of equivalent electromagnetic boundary condition control, changing the equivalent impedance distribution of the square patch by switching the top PIN diode 1 / 2 on and off, thereby controlling the polarization direction of the transmitted electric field, while phase control is based on the principle of "equivalent electrical length change", adjusting the effective current path length of the U-shaped patch by switching the bottom PIN diode 3 / 4 on and off, thereby achieving a 180° phase jump. The physical mechanisms and implementation paths of the two control methods are completely independent; the feed network layer 5 provides bias signal channels for the top and bottom PIN diodes respectively, and the driving signals for polarization and phase control are transmitted separately to avoid cross-interference at the electrical signal level, thus jointly ensuring the decoupling effect.

[0048] Figure 4 The transmission and reflection coefficient response diagrams for X-polarized incident signal clearly verify the high polarization isolation and crosstalk-free characteristics. When the incident signal is an X-polarized wave propagating from the -Z axis, if the top PIN diode 1 / 2 is in the "10" state (X-polarization mode), the equivalent impedance distribution of the square patch causes the transmitted electric field to be mainly distributed along the X direction. In the attached diagram, the X-polarized transmission coefficient (S21-X) curve is significantly higher than the Y-polarized transmission coefficient (S21-Y) curve. The Y-polarized transmission amplitude is more than 20dB lower than that of X-polarization, and the two curves do not overlap significantly, indicating that the purity of the X-polarized outgoing signal is extremely high, and the Y-polarized crosstalk is negligible. The same applies when Y-polarization is working. The simulation results demonstrate the efficient isolation between the X and Y polarization modes. The orange curve in the attached figure represents the reflection coefficient (S11). This curve reaches its lowest value at the center frequency of 6.3 GHz, indicating that the incident signal reflection loss is minimal at this point, and most of the energy is converted into a transmitted signal. This effect is due to the characteristics of the top-layer impedance matching network (the synergistic effect of high-frequency inductors and capacitors) and the low-loss dielectric substrate, which effectively avoids signal attenuation during the modulation process.

[0049] Figure 5 The phase response diagrams under different polarization states verify the independence and stability of phase modulation. Regardless of whether the top PIN diode 1 / 2 is in the "01" (Y polarization) or "10" (X polarization) state, when the bottom PIN diode 3 / 4 switches between "01" and "10", the corresponding transmission phase in the attached diagram produces a stable 180° phase difference, and the phase modulation error is less than 5°. This indicates that phase modulation is not affected by the polarization state, further confirming the complete decoupling of polarization and phase, and that there is no significant fluctuation in the amplitude of the transmitted signal during the modulation process. This stability is also due to the optimized design of the feed line (short path, reasonable line width to reduce transmission loss) and the configuration of the parallel high-frequency inductor of the bottom PIN diodes (suppressing parasitic losses and avoiding additional attenuation introduced by diode switching), which together ensure signal integrity.

[0050] Furthermore, the current distribution can better reflect changes in the transmission phase. Figure 6 The diagram shows the current distribution on the lower surface when the top pin remains unchanged and the bottom pin switches states. Observing the current direction at the varactor diode loading point, it can be seen that the current direction on the lower surface has reversed, indicating a 180° phase reversal. This is consistent with... Figure 5 The transmission phase curves shown are consistent. The electric field distribution on the unit metal patch changes with different polarization states. This is because the equivalent impedance introduced by the diode under different voltage regulation states differs, causing changes in this part of the electric field. The electric field distribution of the top layer of the unit under different operating states is as follows: Figure 7 As shown.

[0051] Because the top-level polarization control circuit and the bottom-level phase control circuit are completely isolated by the RF ground layer 3, and the response mechanisms of the two functional modules are independent of each other, there is no electromagnetic crosstalk during polarization switching and phase control. That is, the amplitude of the transmitted wave will not be affected by the switching of different working states of the phase control layer 7, and the control of unit polarization will not affect the phase response of the transmitted wave. The simulation results above verify that this design achieves decoupling of polarization control and phase control.

[0052] Based on the above structural design, a reconfigurable metasurface consisting of 15×15 units was constructed. During operation, a 2-18 GHz dual-ridge broadband horn with a gain of 10 dBi was selected as the feed source. The horn was fixed 300 mm from the center of the metasurface, with a focal diameter ratio of 0.8.

[0053] Transmission array antennas typically employ space feeding, with the feed source generally being a horn. Since the wave emitted by the horn is a spherical wave, the incident wave travels different paths when reaching each element of the transmission array. Therefore, according to array synthesis theory, it is necessary to compensate for the spatial phase delay from the feed source to each element of the array to achieve the conversion of the spherical wave to a plane wave and realize a high-gain beam.

[0054] To achieve beam focusing at the desired direction, phase compensation is required for each element in the array. First, the spherical wave emitted by the feed horn illuminates the array surface... mn The transmission phase of each unit is: (1) In formula (1) From the feed horn phase center to the first mn The spatial distance between the elements. The phase of each element in the array during radiation consists of two parts: the spatial path difference generated by the horn illumination and the compensation phase required by the element itself. (2) According to the transmission array pattern theory, in the desired direction The gradient phase that needs to be introduced onto the surface of the transmission array to generate the beam satisfies the following equation: (3) In the above formula As a phase constant, the design process of a transmission array requires a relative phase distribution. By selecting a phase constant, a better beam focusing effect can be achieved.

[0055] Figure 8(a), Figure 8 (b) Figure 8 (c) The three figures correspond to the beam scanning gain response of the metasurface array under different polarization configurations: Figure 8 (a) shows the beam scanning results with all elements operating in X-polarization mode. Figure 8 (b) shows the beam scanning results with all elements operating in Y-polarization mode. Figure 8 (c) Beam scanning results in a 45° linear polarization mode with half X polarization and half Y polarization of the cells.

[0056] The horizontal axis in the three figures represents the pitch angle. (Unit: degrees), the vertical axis represents the array gain (unit: dB), and different colored curves correspond to different azimuth angles. Gain characteristics.

[0057] It can be seen that, in all three polarization modes, the maximum gain beam points towards... In the vicinity of 0°, the gain peak remains above 15dB, indicating a high concentration of signal energy. When the beam is pointed towards... When deflected to both sides (-20° or 60° direction), the array gain decreases gradually with the increase of the deflection angle, without drastic gain attenuation; at the same time, the sidelobe electrical average of each polarization mode is less than -10dB, the beam energy is mainly concentrated in the main lobe region, and the sidelobe interference is weak.

[0058] Based on the phase modulation independence of the units, it can be seen that by encoding the phase state (0° / 180°) of the units at different positions, the array verifies that under different polarization configurations, the array can achieve stable beam scanning within a wide spatial angle range, and the beam directivity is good, matching the communication coverage requirements under different polarization scenarios.

Claims

1. A transmissive metasurface with independently tunable pin diode polarization and phase, characterized in that, This metasurface is composed of n×n metasurface units arranged periodically; The metasurface unit, along the Z-axis, consists of, from top to bottom, a polarization control layer (1), an upper substrate (2), a radio frequency ground layer (3), an adhesive substrate (4), a feed network layer (5), a lower substrate (6), and a phase control layer (7). Electromagnetic waves are incident from the phase modulation layer (7) and emitted from the polarization modulation layer (1), forming a transmissive metasurface; The polarization control layer (1) is used to switch the polarization of the transmitted wave. The polarization control layer (1) includes a square patch, and two PIN diodes are integrated in the middle of the square patch.

2. The transmissive metasurface based on pin diode polarization and phase independently adjustable according to claim 1, characterized in that, The metasurface unit maintains its resonant characteristics in the 6.0 GHz to 6.6 GHz frequency band, enabling the metasurface to operate stably in the 6.0 GHz to 6.6 GHz range. The upper substrate (2), the bonding substrate (4) and the lower substrate (6) are Rogers RO4350 dielectric substrates; The polarization control layer (1), the radio frequency ground layer (3), the feed network layer (5) and the phase control layer (7) are copper metal layers, and the copper metal layers are alternately arranged with the Rogers RO4350 dielectric substrate.

3. The transmissive metasurface based on pin diode polarization and phase independently adjustable according to claim 1, characterized in that, The periphery of the square patch has four rectangular metal pieces respectively arranged along the positive X-axis, negative X-axis, positive Y-axis, and negative Y-axis. These rectangular metal pieces are spaced apart from the square patch, and each rectangular metal piece is independent of the square patch and is centrally symmetrically distributed.

4. The transmissive metasurface based on pin diode polarization and phase independently adjustable according to claim 3, characterized in that, Based on the center of the polarization control layer (1), short rod-shaped metal feed plates are provided in the negative X-axis and negative Y-axis regions. The short rod-shaped metal feed plates are connected to the feed network layer (5) through a metallized via perpendicularly along the negative Z-axis, which is used to introduce external bias signals. The short rod-shaped metal feed plates are electrically connected to the outer edge of the square patch through an inductor, which is used to transmit the bias signal required for polarization control and to achieve impedance matching with the inductor. Four rectangular metal plates are respectively set in the positive X-axis, negative X-axis, positive Y-axis, and negative Y-axis directions around the square patch. They maintain independent gaps with the square patch and the short rod-shaped metal feed plates and have no direct electrical connection. They are used to assist the electromagnetic boundary conditions of the control unit and enhance the polarization isolation and resonance stability.

5. The transmissive metasurface based on pin diode polarization and phase independently adjustable according to claim 3, characterized in that, The anodes of both PIN diodes are electrically connected to the inner edge of the square ring metal sheet, and the cathodes are electrically connected to the central nested square patch, and the positive and negative directions of the two diodes are consistent; with the center of the polarization control layer (1) as the reference, a capacitor is also configured in the positive X-axis and positive Y-axis regions as the structure for polarization control function. At the center of the square patch, i.e. the origin of the coordinate system, another metallized via is passed through along the negative Z-axis to directly connect with the phase control layer (7).

6. The transmissive metasurface based on pin diode polarization and phase independently adjustable according to claim 1, characterized in that, The radio frequency grounding layer (3) is a complete metal foil covering the entire area of ​​the unit, serving as a radio frequency reference ground to isolate electromagnetic crosstalk between the polarization control layer (1) and the phase control layer (7); The bonding substrate (4) below it serves to support the power supply network layer (5) and to achieve a stable bond between the radio frequency grounding isolation layer and the underlying structure.

7. The transmissive metasurface based on pin diode polarization and phase independently adjustable according to claim 1, characterized in that, The phase control layer (7) is mainly a U-shaped metal patch. With the unit center as the reference and the unit coordinate origin as the center, the two arms of the U-shaped metal patch extend along the Y-axis direction, and a rectangular hollow area is opened in the middle of the patch along the Y-axis direction. Within the aforementioned cutout area, one PIN diode is integrated at each end of the patch along the positive X-axis and the negative X-axis. A short rod-shaped metal feed plate is provided along the positive Y-axis. This feed plate is electrically connected to the feed network layer (5) through a metallized via along the positive Z-axis. It is connected to the center position through a high-frequency inductor and is also connected to the center of the top layer through a metallized via.

8. A transmissive metasurface based on pin diode polarization and phase independently adjustable according to claim 7, characterized in that, With the center as the reference, a short rod-shaped metal feed plate is set in the region of positive x-axis and negative y-axis. The feed plate is also connected to the feed network layer (5) through metallized via along the positive Z-axis.

9. A transmissive metasurface based on pin diode polarization and phase independently adjustable according to claim 1, characterized in that, The power supply network layer (5) adopts a strip metal power supply line. One end is connected to the polarization control layer (1) through a metallized via, and the other end extends to the pad at the edge of the unit for receiving the power supply signal to realize the on / off drive of the PIN diode.

10. The application of the metasurface according to any one of claims 1-9, characterized in that, When the metasurface is in operation, a 2-18 GHz dual-ridge broadband horn is selected as the feed source, with a gain of 6-12 dBi.

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