An active frequency selective surface with polarization independence and angular stability

Abstract

The application provides an active frequency selective surface with polarization independence and angle stability, which comprises a dielectric substrate and a periodic arrangement of cross-shaped metal rings arranged on the dielectric substrate, wherein a notch is formed at the end of each arm of the cross-shaped metal ring, and a PIN diode is connected across each notch, and the cross-shaped metal ring and the four symmetrically arranged PIN diodes form a 90-degree rotational symmetry structure, so that the active frequency selective surface has highly consistent frequency response characteristics for incident electromagnetic waves with different polarization directions; by synchronously controlling the on-off state of all the PIN diodes, the resonant frequency of the active frequency selective surface is switched between two frequencies in the Ku band, thereby fundamentally solving the polarization sensitivity problem caused by anisotropy of a traditional adjustable structure and achieving excellent polarization independence.

Description

Technical Field

[0001] This invention relates to the field of frequency selective surface design technology, and more particularly to an active frequency selective surface with polarization independence and angular stability. Background Technology

[0002] In modern wireless communication, radar, satellite communication, and electromagnetic compatibility, frequency selective surfaces (FSS), as two-dimensional periodic structures with frequency filtering characteristics, play a crucial role. They can selectively transmit or reflect electromagnetic waves within a specific frequency range, and are therefore widely used in critical scenarios such as radomes, electromagnetic shielding, stealth technology, and RF front-end filtering, becoming one of the core technologies for improving system performance and optimizing the electromagnetic environment.

[0003] Traditional frequency selective surfaces (FSS) are mostly passive structures, whose resonant frequency is determined by the geometric parameters of the unit structure, the characteristics of the substrate, and the surrounding dielectric environment. Once designed and fabricated, their filtering performance is fixed and cannot be dynamically adjusted according to actual operating requirements. However, with the rapid development of communication technology towards multi-band, multi-functional, and reconfigurable directions, higher demands are placed on the dynamic adaptability of FSS. For example, in Ku-band (12-18GHz) communication systems, this band is widely used in satellite television broadcasting, fixed satellite communication, radar detection, and other fields. Different application scenarios have significantly different requirements for operating frequencies. A single fixed-frequency passive FSS can no longer meet the flexible requirements of frequency switching, bandwidth adjustment, and electromagnetic compatibility in different operating modes. There is an urgent need to develop new frequency selective surface technologies with dynamic frequency adjustability.

[0004] To achieve dynamic control of FSS performance, researchers have begun to incorporate active devices (such as diodes, varactor diodes, and microelectromechanical systems (MEMS) switches) into the frequency selective surface unit structure, forming an Active Frequency Selective Surface (AFSS). By changing the operating state of the active devices (such as on or off) through external control signals, the equivalent electromagnetic parameters of the unit structure can be dynamically adjusted, thereby achieving real-time switching of resonant frequency and filtering state (band-pass / band-stop). Among these, PIN diodes have become one of the ideal active devices for constructing active frequency selective surfaces due to their advantages such as fast switching speed, low insertion loss, high isolation, and stable performance in the microwave band, and are widely used in the design of various reconfigurable FSSs.

[0005] Currently, research on active frequency selective surfaces based on PIN diodes has made some progress, but it still faces many technical challenges in specific application frequency bands such as the Ku band. On the one hand, the resonant frequency offset of existing structures is generally small, making it difficult to achieve wide-range frequency adjustment and failing to fully cover the frequency requirements of different application scenarios within the Ku band. On the other hand, some structures, while achieving frequency tunability, often sacrifice polarization stability and angular stability. When the polarization or incident angle of the incident electromagnetic wave changes, the filtering performance deteriorates significantly, limiting its application in complex electromagnetic environments. In addition, the design flexibility of traditional unit structures (such as square rings and circular rings) is insufficient, making it difficult to achieve a synergistic improvement in frequency adjustment range and stability through simple structural optimization. Therefore, developing an active frequency selective surface with a large resonant frequency offset, good polarization independence, and angular stability in the Ku band has become a key technical problem that urgently needs to be solved in this field, and it is of great significance for promoting the performance upgrade of Ku-band communication, radar, and other systems. Summary of the Invention

[0006] This invention proposes an active frequency selective surface with polarization independence and angle stability, which solves the problems of small resonant frequency offset, poor polarization stability and angle stability of active frequency selective surfaces in the prior art.

[0007] The technical solution of this invention is implemented as follows: The first aspect of this invention provides an active frequency selective surface with polarization independence and angular stability, comprising a dielectric substrate and periodically arranged cross-shaped metal rings disposed thereon. Each arm of the cross-shaped metal rings has a slot at its end, and a PIN diode is connected across each slot. The cross-shaped metal rings and the four symmetrically arranged PIN diodes thereon together constitute a 90-degree rotationally symmetrical structure. By synchronously controlling the on / off state of all PIN diodes, the resonant frequency of the active frequency selective surface can be switched between two frequencies in the Ku band.

[0008] Preferably, the dielectric substrate is made of resin material with a dielectric constant of 4.2 to 4.6 and a loss tangent of 0.018 to 0.022.

[0009] Preferably, the cross-shaped metal ring has an arm length of 7mm, a line width of 0.2mm, and an inner width of 0.5mm.

[0010] Preferably, the periodic dimension P of the cross-shaped metal ring takes values ​​ranging from [value missing]. ,in, The free-space wavelength corresponding to the Ku band. It is 18.3-25mm.

[0011] Preferably, the PIN diode is equivalent to a 2Ω resistor when it is turned on and equivalent to a 0.04pF capacitor when it is turned off.

[0012] Specifically, when all PIN diodes are in the on state, the active frequency selective surface resonates at the center of the cross-shaped metal ring with a resonant frequency of 12.0 GHz; when all PIN diodes are in the off state, the active frequency selective surface resonates at the PIN diodes at the upper and lower ends of the cross-shaped metal ring with a resonant frequency of 16.4 GHz.

[0013] A second aspect of the present invention provides a method for preparing an active frequency selective surface, which is prepared by 3D printing and includes the following steps: S1, Dielectric substrate forming: Using a polymer material with a matching dielectric constant, the dielectric substrate is formed by printing through photopolymerization or fused deposition additive manufacturing process, and a cross-shaped metal ring filling groove and a PIN diode mounting groove are reserved on the surface of the dielectric substrate. S2, Conductive structure forming: In the filling groove area, conductive paste is deposited by direct writing printing, and after curing or sintering, a cross-shaped metal ring is formed; S3, Active device integration: Place the PIN diode in the mounting slot and use conductive adhesive material to electrically connect its electrode to the corresponding part of the cross-shaped metal ring; S4, Insulated Encapsulation: The area where the PIN diode is integrated is covered with insulating encapsulation material.

[0014] Preferably, the polymer material is a modified epoxy acrylate photocurable resin or a polylactic acid composite material filled with glass fiber.

[0015] Preferably, the conductive paste is prepared by mixing copper powder and photosensitive resin at a mass ratio of 7:3 and adding 0.5% dispersant, and has a viscosity of 800-1500 CP at room temperature.

[0016] Preferably, the conductive adhesive material is conductive silver paste, and its resistivity is less than or equal to... Ω cm; the insulating encapsulation material is an insulating protective resin with a dielectric constant of 3.0~3.5.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) This invention achieves a novel active frequency selective surface with a wide range of resonant frequencies in the Ku band by symmetrically loading PIN diodes at the end slots of each arm of the cross-shaped metal ring and synchronously controlling their on / off states; by constructing the cross-shaped metal ring and four PIN diodes together into a 90-degree rotationally symmetrical structure, the active frequency selective surface has a highly consistent frequency response characteristic to incident electromagnetic waves with different polarization directions, fundamentally solving the polarization sensitivity problem caused by anisotropy of traditional tunable structures and achieving excellent polarization independence. (2) By designing the periodic size of the unit structure to a specific ratio range that matches the working wavelength, the present invention significantly suppresses the performance degradation caused by the mutual coupling effect and phase difference between the units when electromagnetic waves are incident at large angles, so that the surface can still maintain a stable resonant frequency and filtering characteristics in a wide range of incident angles, and obtains good angular stability. (3) By selecting a PIN diode with specific on-resistance and off-resistance as an active control element, this invention ensures that it exhibits drastically different impedance characteristics in the on and off states, thereby achieving significant frequency shift and significantly improving the product's adaptability in complex electromagnetic environments. Attached Figure Description

[0018] 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 these drawings without creative effort.

[0019] Figure 1 This is a three-dimensional structural diagram of the active frequency selective surface of the present invention.

[0020] Figure 2 This is a schematic diagram of the front structure of the active frequency selective surface of the present invention.

[0021] Figure 3 This is a schematic diagram of the electric field distribution of the active frequency selective surface in an embodiment of the present invention; Figure 3 In the diagram, (a) shows the electric field distribution of the PIN diode in the on state; (b) shows the electric field distribution of the PIN diode in the off state.

[0022] Figure 4 This is a transmission characteristic curve of an active frequency selective surface under different polarization wave incident conditions in an embodiment of the present invention.

[0023] Figure 5 This is a transmission characteristic curve of the active frequency selective surface under different incident angles in an embodiment of the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all 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.

[0025] Reference Figure 1 , 2 The first aspect of this embodiment provides an active frequency selective surface with polarization independence and angular stability, including a dielectric substrate and a periodically arranged cross-shaped metal ring disposed thereon. Each arm of the cross-shaped metal ring has a slot at its end, and a PIN diode is connected across each slot. The cross-shaped metal ring and the four symmetrically arranged PIN diodes thereon together form a 90-degree rotationally symmetrical structure. By synchronously controlling the on / off state of all PIN diodes, the resonant frequency of the active frequency selective surface can be switched between two frequencies in the Ku band.

[0026] This invention employs a method of loading a PIN diode on each of the four legs of a cross-shaped ring unit to construct a tunable "switch-type" active frequency selective surface (AFSS). The PIN diodes are in an on / off state depending on the direction of the applied voltage bias. By controlling the direction of the externally applied bias voltage, their filtering characteristics can be controlled, achieving frequency reconstruction. The entire structure consists of an extremely thin metal film and a dielectric substrate, arranged in a two-dimensional periodic pattern to form the desired AFSS. Figure 1 , 2 The unit structure is shown, where gray represents a copper metal film, blue represents a dielectric substrate, and orange represents a PIN diode.

[0027] Preferably, the dielectric substrate is made of resin material with a dielectric constant of 4.2 to 4.6 and a loss tangent of 0.018 to 0.022.

[0028] In a preferred embodiment of the present invention, the dielectric substrate material is a resin material with a dielectric constant of 4.4 and a loss tangent of 0.02, and a thickness of 1 mm. The substrate has a stable dielectric constant, which can fix the equivalent dielectric constant and avoid it from causing additional interference to the resonant frequency; at the same time, the low loss characteristic can reduce the energy loss of electromagnetic waves in the substrate, ensure the clear resonance peak in the on / off state, and further highlight the frequency shift effect.

[0029] Preferably, the cross-shaped metal ring has an arm length of 7mm, a line width of 0.2mm, and an internal width of 0.5mm. Table 1 below lists the key geometric parameters of the cross-shaped metal ring unit in this embodiment: Table 1 Geometric Parameters of Cross-Shaped Metal Ring Unit

[0030] Preferably, the periodic dimension P of the cross-shaped metal ring takes values ​​ranging from [value missing]. ,in, The free-space wavelength corresponding to the Ku band. The period size is 18.3-25mm. This period size design principle ensures that the unit size is much smaller than the Ku-band operating wavelength. This is key to achieving good angular stability: when electromagnetic waves are incident at large angles, the small-sized unit can effectively suppress the strong mutual coupling effect and phase difference change between adjacent units, thereby ensuring that the filtering performance remains stable over a wide incident angle range.

[0031] Angular stability refers to the fact that the AFSS maintains a stable resonant frequency and bandpass / bandstop characteristics for electromagnetic waves at different incident angles (typically 0°-60°). The reason why the AFSS of this invention has good angular stability is due to the fact that "the unit size is much smaller than the operating wavelength": The operating frequency band of the AFSS of this invention is the Ku band (12-16.4 GHz), corresponding to the free space wavelength. Approximately 18.3-25mm; the periodic dimension of the cross-shaped ring unit is designed as follows: (For example, 5-8mm), much smaller than the operating wavelength. When electromagnetic waves are incident at large angles (e.g., 60°), the "mutual coupling effect" between adjacent units is weak (mutual coupling strength is positively correlated with the ratio of unit spacing to wavelength; the smaller the spacing, the weaker the mutual coupling), and the equivalent parameters of the units (such as equivalent capacitance and equivalent inductance) will not change drastically due to changes in the incident angle. At the same time, small-sized units can reduce "angle-related phase differences"—when incident at large angles, the phase difference of electromagnetic waves on adjacent units is small, resulting in higher frequency response consistency of the overall array and avoiding resonant frequency shifts or bandpass / bandstop state disturbances.

[0032] Preferably, in this embodiment, a MACOM MEST2G-010-20 PIN diode is selected. In the forward bias state, it is equivalent to a resistor of approximately 2Ω, and in the reverse bias state, it is equivalent to a capacitor of approximately 0.04pF. This significant impedance difference is the physical basis for achieving a large shift in the resonant frequency. The specifications of the PIN diode in this embodiment are shown in Table 2 below: Table 2 PIN Diode Specifications

[0033] Specifically, to determine the operating mechanism of the active frequency selective surface structure of this invention, the distribution of the electric field on the structure surface was calculated. The surface electric field distribution of the active frequency selective surface structure at two resonant frequencies (12.0 GHz and 16.4 GHz) under different states of the PIN diode (i.e., on or off) is shown below. Figure 3 As shown; when all PIN diodes are in the on state, the active frequency selective surface resonates at the center of the cross-shaped metal ring, with a resonant frequency of 12.0 GHz; when all PIN diodes are in the off state, the active frequency selective surface resonates at the PIN diodes at the upper and lower ends of the cross-shaped metal ring, with a resonant frequency of 16.4 GHz.

[0034] To verify the filtering characteristics of the active frequency selective surface of this invention as a function of frequency, this embodiment simulates and calculates the transmission characteristics of the structure under TE and TM wave incident conditions, with the PIN diode in the on and off states, respectively. Figure 4 As shown, this structure exhibits good polarization independence.

[0035] Taking the transmission characteristics under TE wave incident as an example for analysis: When the PIN diode is turned on, the active frequency selector surface has a -3dB passband of 10.0GHz~14.9GHz with a relative bandwidth of 39.4% and a resonant frequency of 12.0GHz, and a -10dB stopband of 7.3GHz~8.9GHz and 16.1GHz~16.8GHz with relative bandwidths of 19.8% and 4.3%, respectively; when the PIN diode is turned off, there is a -3dB passband of 14.0GHz~20.2GHz with a relative bandwidth of 36.3% and a resonant frequency of 16.4GHz, and a -10dB stopband of 11.3GHz~13.0GHz with a relative bandwidth of 14.0%.

[0036] Taking the transmission characteristics under TM wave incident light as an example for analysis: When the PIN diode is turned on, the active frequency selector surface has a -3dB passband of 9.9GHz~14.7GHz with a relative bandwidth of 39.0% and a resonant frequency of 12.0GHz, and a -10dB stopband of 7.2GHz~8.8GHz and 15.9GHz~16.6GHz with relative bandwidths of 20% and 4.3%, respectively; when the PIN diode is turned off, there is a -3dB passband of 14.1GHz~20.2GHz with a relative bandwidth of 35.6% and a resonant frequency of 16.3GHz, and a -10dB stopband of 11.3GHz~13.0GHz with a relative bandwidth of 14.0%.

[0037] The above analysis shows that for TE and TM waves, the active frequency selective surface can generate a resonant frequency shift of about 4.3~4.4 GHz in the Ku band, and achieves bandpass / bandstop switching near 12 GHz and 16.3 GHz.

[0038] To verify the angular stability of the active frequency selective surface of this invention, simulation calculations were performed on the structure at the incident angle. θ The transfer characteristics of the PIN diode in the on and off states when the angle is 0° to 60° are as follows: Figure 5 As shown. When the PIN diode is turned on, θ= 60° and θ= The resonant frequency at 0° is 12.0GHz for both, with a -3dB passband bandwidth difference of only 4.7% and a -10dB stopband bandwidth difference of only 6.4% and 2.8%, respectively; when the PIN diode is cut off, θ= 60° and θ= The resonant frequencies at 0° are 16.2 GHz and 16.4 GHz, differing by only 0.2 GHz; the -3 dB passband bandwidth differs by only 2.9%; and the -10 dB stopband bandwidth differs by only 3.5%. This indicates that the active frequency selector surface... θ It has very stable transmission characteristics from 0° to 60°.

[0039] The frequency shift of the active frequency selective surface of this invention is essentially achieved by changing the equivalent impedance and equivalent electrical length of the cross-shaped ring unit through the on / off state of the PIN diode, thereby controlling the resonant frequency (the resonant frequency is inversely proportional to the equivalent electrical length). The specific mechanism is as follows: In the forward bias state (conduction state), the PIN diode exhibits low impedance characteristics. At this time, the diodes on the four legs of the cross-shaped ring act as "wires," short-circuiting the "slots" of the ring unit. The cross-shaped ring legs, which were originally divided by the slots, form a complete conductive path, increasing the equivalent electrical length and reducing the resonant frequency.

[0040] Cut-off state (reverse bias): The PIN diode exhibits high impedance characteristics. At this time, the diode is equivalent to an "open circuit". The slot of the cross-shaped ring remains open. The effective conductive length of the ring unit is shortened and the resonant frequency increases.

[0041] In the on-state, the equivalent electrical length increases, leading to a decrease in resonant frequency to 12 GHz; in the off-state, the equivalent electrical length decreases, leading to an increase in resonant frequency to 16.4 GHz. The frequency difference between these two states (16.4 GHz - 12 GHz = 4.4 GHz) represents the resonant frequency shift within the Ku-band, and this shift is determined by both the change in equivalent electrical length corresponding to the slot width and the difference in switching impedance of the PIN diode. A larger slot width and a more significant difference in diode switching impedance result in a larger frequency shift.

[0042] Polarization independence refers to the consistent frequency response of an AFSS to electromagnetic waves with different polarization directions (such as TE polarization, TM polarization, or arbitrary linear polarization from 0° to 90°). The good polarization independence of the AFSS of this invention stems from the four-sided symmetrical structure of the cross-shaped ring unit. The cross-shaped ring consists of four mutually perpendicular "legs," and the parameters (impedance, position, and number) of the PIN diodes on the four legs are completely identical, forming a "90° rotationally symmetrical structure" (i.e., after rotating 90° around the center of the unit, the structure completely coincides with the original structure). This symmetry ensures that regardless of the polarization direction of the incident electromagnetic wave (e.g., along the x-axis, y-axis, or a 45° diagonal line), the induced current distribution excited by the electromagnetic wave on the four legs of the cross-shaped ring is completely symmetrical, and there will be no situation where "the current is strong in one direction and weak in another" due to changes in polarization direction; under different polarization directions, the equivalent impedance and equivalent electrical length of the unit remain consistent, thus the resonant frequency (12GHz / 16.4GHz) and bandpass / bandstop characteristics are indistinguishable.

[0043] If the unit structure is an asymmetric design (such as a rectangular ring or a monopole), there is a "polarization sensitive axis" (for example, the long and short sides of a rectangular ring respond differently to different polarization directions); while the four legs of a cross-shaped ring are evenly distributed and there is no obvious difference between the long and short axes. The electric field component of the incident electromagnetic wave can be uniformly coupled to the four ring legs, avoiding the influence of polarization direction on the frequency response.

[0044] The second aspect of this embodiment provides a method for preparing an active frequency selective surface, which is prepared by 3D printing and includes the following steps: S1, Dielectric substrate forming: Using a polymer material with a matching dielectric constant, the dielectric substrate is formed by printing through photopolymerization or fused deposition additive manufacturing process, and a cross-shaped metal ring filling groove and a PIN diode mounting groove are reserved on the surface of the dielectric substrate. Equipment selection: Digital light processing (DLP) photopolymerization 3D printer (resolution ≥30μm), or fused deposition modeling (FDM) printer (nozzle diameter 0.2mm); Process parameters: layer thickness 20-50μm, printing speed 10-30mm / s (DLP) or 5-15mm / s (FDM), DLP curing wavelength 405nm, single layer exposure time 8-15s; Key operations: Arrange the cross-shaped ring units periodically, and reserve "filling grooves" (5-10μm deep, matching the thickness of the metal film) and "diode mounting grooves" (0.1mm larger than the PIN diode to ensure embedding fit) at the corresponding positions on the substrate.

[0045] S2, Conductive structure forming: In the filling groove area, conductive paste is deposited by direct writing printing, and after curing or sintering, a cross-shaped metal ring is formed; Switch the printer nozzle to a direct-write metal nozzle (50-100μm diameter), precisely inject the metal paste into the pre-reserved "filling groove" on the substrate, pre-bake at 60-80℃ for 5-10 minutes after each layer is printed, repeat printing 2-3 layers until the thickness meets the requirements, and finally sinter at 200-300℃ for 30-60 minutes to densify the metal powder (conductivity ≥ 100%). S / m); S3, Active device integration: Place the PIN diode in the mounting slot and use conductive adhesive material to electrically connect its electrode to the corresponding part of the cross-shaped metal ring; Device embedding: The PIN diode is placed into the reserved "mounting slot" by an automated picking device (such as a micro robotic arm), with the two ends of the diode aligned with the legs of the cross-shaped ring; Electrode connection: Conductive silver paste is applied to the connection between the diode terminals and the cross-shaped ring legs using inkjet printing technology, and cured at 120-150℃ for 20-30 minutes to form a reliable electrical connection (connection resistance ≤3Ω). S4, Insulated Encapsulation: The diode area is covered with insulating resin by printing, with a thickness of 50-100μm, to avoid the influence of the external environment on the device.

[0046] S5, Post-processing: Use laser cleaning (wavelength 1064nm) to remove residual slurry on the surface of the metal film, or use fine sandpaper (grit size ≥2000 mesh) to polish the substrate surface to ensure flatness ≤5μm.

[0047] Preferably, a 3D printing-specific resin with matching dielectric properties is selected as the substrate material, preferably a modified epoxy acrylate photocurable resin (dielectric constant 4.2-4.6, loss tangent 0.018-0.022), or a glass fiber-filled polylactic acid (PLA) composite material, to meet the requirements of 3D printing flowability and curing stability.

[0048] Preferably, the conductive paste is prepared by mixing copper powder (particle size 5-20μm, purity ≥99.9%) and photosensitive resin at a mass ratio of 7:3, and adding 0.5% dispersant (such as polyethylene glycol). The viscosity is controlled at 800-1500CP (25℃) to ensure that there is no particle sedimentation during printing.

[0049] Preferably, miniaturized PIN diodes (package size ≤ 0.5mm × 0.3mm) are used, paired with conductive silver paste (resistivity ≤ Ω (cm) is used for electrode connection, and insulating protective resin (dielectric constant 3.0-3.5) is prepared for diode encapsulation and fixation.

[0050] Compared to traditional active frequency selective surface treatment (substrate cutting + photolithography of metal patterns + manual soldering of PIN diodes), this invention uses 3D printing technology, which has the following significant advantages in terms of manufacturing efficiency, structural flexibility, and cost control: Traditional processes rely on photolithography to create metal patterns, which can only achieve planar or simple curved surface structures. If three-dimensional topology is required (such as active FSS with raised / hollowed-out substrates), multiple assembly steps are needed (such as bonding multilayer substrates), which can easily lead to positioning errors (≥50μm) and cause frequency response shifts. This invention uses 3D printing to directly print three-dimensional dielectric substrates (such as substrates with periodic hollowing-outs, with a hollowing-out rate of 30%-50%). The metal film and diode can be three-dimensionally integrated with the substrate topology, with a positioning error ≤10μm (based on a vision positioning system). Moreover, no assembly is required, making it suitable for the manufacturing of active FSS in complex electromagnetic scenarios.

[0051] Taking a 100mm×100mm active FSS as an example, the traditional process requires "substrate cutting (2h) → photoresist coating / exposure / development (4h) → metal coating (2h) → diode manual soldering (3h) → testing and correction (2h)", with a total cycle of about 13h. For the same size, the present invention adopts a 3D printing process (substrate printing 3h + metal film preparation 2h + diode embedding 1h + post-processing 1h) with a total cycle of about 7h, and can realize automated continuous production (no manual soldering required). The cycle advantage is more obvious for small batch customization (such as less than 10 pieces) (the traditional process requires repeated debugging of the photomask, while 3D printing only requires modification of the model).

[0052] Traditional hand-soldered diode connections are susceptible to temperature and vibration (after cycling from -40℃ to 85℃, the connection resistance may increase to over 10Ω), and delamination is prone to occur between substrate layers in multilayer assembly (bonding strength ≤10MPa). This invention uses a 3D printing method to integrate the metal film and substrate through sintering / printing (bonding strength ≥15MPa), and the diode is fixed by encapsulation with insulating resin. After cycling from -40℃ to 85℃, the connection resistance change is ≤1Ω, and the frequency offset is ≤0.3GHz (compared to ≥0.8GHz with traditional processes), making it more suitable for harsh environments such as aerospace.

[0053] Traditional processes require adjusting the operating frequency band of an active FSS, necessitating the creation of a new photomask (a process that takes 3-5 days) and modification of the metal graphic dimensions. This invention, using 3D printing, only requires adjusting the size of the cross-shaped ring and the position of the diode in the software, generating a new printed model within 1-2 hours, enabling rapid iteration of multi-band active FSSs.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An active frequency selective surface with polarization independence and angle stability, characterized in that, The device includes a dielectric substrate and a periodically arranged cross-shaped metal ring disposed thereon. Each arm of the cross-shaped metal ring has a slot at its end, and a PIN diode is connected across each slot. The cross-shaped metal ring and the four symmetrically arranged PIN diodes together form a 90-degree rotationally symmetrical structure. By synchronously controlling the on / off state of all PIN diodes, the resonant frequency of the active frequency selective surface can be switched between two frequencies in the Ku band. When all PIN diodes are in the ON state, the active frequency selective surface resonates at the center of the cross-shaped metal ring; when all PIN diodes are in the OFF state, the active frequency selective surface resonates at the PIN diodes at the upper and lower ends of the cross-shaped metal ring.

2. The active frequency selective surface with polarization independence and angle stability as described in claim 1, characterized in that, The dielectric substrate is made of resin material with a dielectric constant of 4.2~4.6 and a loss tangent of 0.018~0.

022.

3. An active frequency selective surface with polarization independence and angle stability as described in claim 1, characterized in that, The cross-shaped metal ring has an arm length of 7mm, a line width of 0.2mm, and an internal width of 0.5mm.

4. An active frequency selective surface with polarization independence and angle stability as described in claim 1, characterized in that, The range of values ​​for the periodic dimension P of the cross-shaped metal ring is: ,in, The free-space wavelength corresponding to the Ku band. It is 18.3-25mm.

5. An active frequency selective surface with polarization independence and angle stability as described in claim 1, characterized in that, The PIN diode is equivalent to a 2Ω resistor when it is turned on and an equivalent 0.04pF capacitor when it is turned off.

6. An active frequency selective surface with polarization independence and angle stability as described in claim 1, characterized in that, The resonant frequency is 12.0 GHz when all PIN diodes are in the ON state and 16.4 GHz when all PIN diodes are in the OFF state.

7. A method for fabricating an active frequency selective surface, used to fabricate the active frequency selective surface as described in any one of claims 1 to 6, characterized in that, The material is prepared using 3D printing and includes the following steps: S1, Dielectric substrate forming: Using a polymer material with a matching dielectric constant, the dielectric substrate is formed by printing through photopolymerization or fused deposition additive manufacturing process, and a cross-shaped metal ring filling groove and a PIN diode mounting groove are reserved on the surface of the dielectric substrate. S2, Conductive structure forming: In the filling groove area, conductive paste is deposited by direct writing printing, and after curing or sintering, a cross-shaped metal ring is formed; S3, Active device integration: Place the PIN diode in the mounting slot and use conductive adhesive material to electrically connect its electrode to the corresponding part of the cross-shaped metal ring; S4, Insulated Encapsulation: The area where the PIN diode is integrated is covered with insulating encapsulation material.

8. The method for fabricating an active frequency selective surface as described in claim 7, characterized in that, The polymer material is a modified epoxy acrylate photocurable resin or a polylactic acid composite material filled with glass fiber.

9. The method for fabricating an active frequency selective surface as described in claim 7, characterized in that, The conductive paste is prepared by mixing copper powder and photosensitive resin at a mass ratio of 7:3 and adding 0.5% dispersant, and has a viscosity of 800-1500 CP at room temperature.

10. The method for fabricating an active frequency selective surface as described in claim 7, characterized in that, The conductive adhesive material is conductive silver paste, and its resistivity is less than or equal to Ω・cm; The insulating encapsulation material is an insulating protective resin with a dielectric constant of 3.0~3.5.

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