Active frequency selective surface with polarization independence and angle stability

Abstract

The invention provides an active frequency selective surface with polarization independence and angle stability, which comprises a dielectric substrate and cross-shaped metal rings arranged on the dielectric substrate periodically, the tail end of each arm of each cross-shaped metal ring is provided with a notch, each notch is bridged with a PIN diode, and the PIN diode is connected with the dielectric substrate. The cross-shaped metal ring and the four PIN diodes symmetrically arranged on the cross-shaped metal ring jointly form a 90-degree rotational symmetric structure, so that the active frequency selective surface has highly consistent frequency response characteristics for incident electromagnetic waves in different polarization directions; by synchronously controlling the on-off states of all PIN diodes, the resonant frequency of the active frequency selective surface is switched between two frequencies in a Ku wave band, the problem of polarization sensitivity caused by anisotropy of a traditional adjustable structure is fundamentally solved, and excellent polarization independence is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of frequency selective surface design, and in particular to an active frequency selective surface with polarization independence and angle stability. BACKGROUND

[0002] In the fields of modern wireless communication, radar, satellite communication and electromagnetic compatibility, frequency selective surface (FSS) as a two-dimensional periodic structure with frequency filtering characteristics plays a crucial role. It can selectively transmit or reflect electromagnetic waves in a specific frequency range, so it is widely used in antenna covers, electromagnetic shielding, stealth technology and radio frequency front-end filtering, and has become one of the core technologies to improve system performance and optimize electromagnetic environment.

[0003] Traditional frequency selective surfaces 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 processed, the filtering performance is fixed and cannot be dynamically adjusted according to actual work requirements. However, with the rapid development of communication technology towards multi-band, multi-function and reconfigurable direction, higher requirements are put forward for the dynamic adaptability of frequency selective surfaces. For example, in the Ku band (12-18GHz) communication system, this frequency band is widely used in satellite television broadcasting, fixed satellite communication, radar detection and other fields. The demand for working frequency varies significantly in different application scenarios, and a single fixed frequency passive FSS cannot meet the flexible requirements of frequency switching, bandwidth adjustment and electromagnetic compatibility of the system in different working modes, so it is urgent to develop new frequency selective surface technology with dynamic frequency adjustable capability.

[0004] To realize the dynamic regulation and control of FSS performance, researchers began to introduce active devices (such as diodes, varactor diodes, micro-electro-mechanical system (MEMS) switches, etc.) into the frequency selective surface unit structure to form an active frequency selective surface (AFSS). By changing the working state (such as on or off) of the active device through an external control signal, the equivalent electromagnetic parameters of the unit structure can be dynamically adjusted, and the resonant frequency and filtering state (bandpass / bandstop) can be switched in real time. Among them, PIN diode has the advantages of fast switching speed, low insertion loss, high isolation and stable performance in microwave frequency band, etc., and becomes one of the ideal active devices for building active frequency selective surface, which is widely used in the design of various reconfigurable FSS.

[0005] At present, the research on PIN diode-based active frequency selective surface has made some progress, but in specific application frequency bands such as Ku band, it still faces many technical challenges. On the one hand, the resonance frequency shift of the existing structure is generally small, it is difficult to realize wide range of frequency adjustment, and it cannot fully cover the frequency requirements of different application scenarios in the Ku band; on the other hand, while realizing the frequency adjustment, some structures often sacrifice the polarization stability and angle stability, when the polarization mode or the incident angle of the incident electromagnetic wave changes, the filtering performance will be significantly deteriorated, which limits its application in actual complex electromagnetic environment. In addition, the design flexibility of the traditional unit structure (such as square ring, circular ring) is insufficient, it is difficult to realize the coordinated improvement of the frequency adjustment range and stability through simple structure optimization. Therefore, developing an active frequency selective surface with large resonance frequency shift, good polarization independence and angle stability in the Ku band has become a key technical problem to be solved in the current field, which has important significance for promoting the performance upgrade of Ku band communication, radar and other systems. SUMMARY

[0006] The application provides an active frequency selective surface with polarization independence and angle stability, and solves the problems of small resonance frequency shift, poor polarization stability and angle stability of the active frequency selective surface in the prior art.

[0007] The technical scheme of the application is as follows: The application provides an active frequency selective surface with polarization independence and angle stability, and solves the problems of small resonance frequency shift, poor polarization stability and angle stability of the active frequency selective surface in the prior art.

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

[0009] Preferably, the arm length of the cross-shaped metal ring is 7 mm, the line width is 0.2 mm, and the internal width is 0.5 mm.

[0010] Preferably, the period size P of the cross-shaped metal ring is in the range of 18.3-25 mm. wherein, is the free space wavelength corresponding to the Ku band, is 18.3-25 mm.

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

[0012] Specifically, when all the 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 12.0GHz; when all the 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 16.4GHz.

[0013] The second aspect of the present application provides a preparation method of an active frequency selective surface, which is prepared by a 3D printing method, comprising the following steps: S1, medium substrate forming: using a polymer material with matched dielectric constant, printing the medium substrate by a light curing or fused deposition additive manufacturing process, and reserving a filling groove of the cross-shaped metal ring and a mounting groove of the PIN diode on the surface of the medium substrate; S2, conductive structure forming: in the filling groove area, depositing conductive paste by direct writing printing, and forming the cross-shaped metal ring after curing or sintering; S3, active device integration: placing the PIN diode in the mounting groove, and electrically connecting the electrode of the PIN diode and the corresponding part of the cross-shaped metal ring using conductive adhesive material; S4, insulation packaging: covering the area integrated with the PIN diode with insulation packaging material.

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

[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 the viscosity at room temperature is 800-1500CP.

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

[0017] Compared with the prior art, the present application has the following advantages: (1) The application realizes a novel active frequency selective surface with a large range of switchable resonant frequencies in Ku band by symmetrically loading PIN diodes at the end notches of each arm of the cross-shaped metal ring and synchronously controlling the on-off state of the PIN diodes; the active frequency selective surface has a highly consistent frequency response characteristic to incident electromagnetic waves of different polarization directions by forming a 90-degree rotational symmetric structure with the cross-shaped metal ring and the four PIN diodes, thus fundamentally solving the polarization sensitivity problem caused by anisotropy of the traditional adjustable structure and realizing excellent polarization independence; (2) The application significantly suppresses the performance deterioration caused by the mutual coupling effect and phase difference between units when electromagnetic waves are incident at a large angle by designing the period size of the unit structure to be in a specific proportional range matching the working wavelength, so that the surface can still maintain stable resonant frequency and filtering characteristics within a wide range of incident angles, and good angle stability is obtained; (3) The application selects a PIN diode with specific on-resistance and off-capacitance as an active control element to ensure that it has completely different impedance characteristics in the on and off states, thereby realizing significant frequency shift and significantly improving the adaptability of the product in a complex electromagnetic environment. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 It is a schematic diagram of the three-dimensional structure of the active frequency selective surface of the application.

[0020] Figure 2 It is a schematic diagram of the front structure of the active frequency selective surface of the application.

[0021] Figure 3 It is a schematic diagram of the electric field distribution of the active frequency selective surface in the embodiment of the application. Figure 3 In the figure, (a) represents the electric field distribution schematic diagram of the PIN diode in the on state; (b) represents the electric field distribution schematic diagram of the PIN diode in the off state.

[0022] Figure 4 It is a transmission characteristic curve diagram of the active frequency selective surface in the embodiment of the application under different polarized wave incidence.

[0023] Figure 5 It is a transmission characteristic curve diagram of the active frequency selective surface in the embodiment of the application under different incident angles. DETAILED DESCRIPTION

[0024] The technical solutions of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0025] Referring to Figure 1 , 2 The first aspect of the embodiment provides an active frequency selective surface with polarization independence and angle stability, comprising a dielectric substrate and a periodic arrangement of cross-shaped metal rings arranged on the dielectric substrate, wherein each end of each arm of the cross-shaped metal ring is provided with a notch, and each notch is connected with a PIN diode, and the cross-shaped metal ring and the four symmetrically arranged PIN diodes form a 90-degree rotational symmetry structure; the resonant frequency of the active frequency selective surface is switched between two frequencies in the Ku band by synchronously controlling the on-off state of all PIN diodes.

[0026] The present application adopts the mode of loading one PIN diode on each leg of the cross-shaped ring unit to form a tunable "switching type" active frequency selective surface (AFSS). The PIN diode is in an on / off state when the external voltage bias direction is different, and the filtering characteristic can be controlled by controlling the direction of the externally loaded bias voltage to realize frequency reconstruction. The whole structure is composed of an extremely thin metal film and a dielectric substrate, and a two-dimensional periodic arrangement is performed to form the required AFSS. Figure 1 、 2 The unit structure is shown, in which the gray color is a copper metal film, the blue color is a dielectric substrate, and the orange color is a PIN diode.

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

[0028] In a preferred embodiment of the present application, the dielectric substrate material is a resin material with a dielectric constant of 4.4 and a loss tangent of 0.02, and the thickness is 1mm. The dielectric constant of the substrate is stable, and the equivalent dielectric constant can be fixed to avoid additional interference on 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 resonant peak in the on / off state, and further highlight the frequency shift effect.

[0029] Preferably, the arm length of the cross-shaped metal ring is 7mm, the line width is 0.2mm, and the internal width is 0.5mm. Table 1 below lists the key geometric parameters of the cross-shaped metal ring unit in the embodiment: Table 1 Cross-shaped metal ring unit geometry parameter table

[0030] Preferably, the period size P of the cross-shaped metal ring is in the range of , wherein, is the free space wavelength corresponding to the Ku band, is 18.3-25mm. The period size design principle ensures that the unit size is much smaller than the working wavelength of the Ku band. This is the key to achieving good angle stability: when the electromagnetic wave is incident at a large angle, the small size unit can effectively suppress the strong mutual coupling effect and phase difference change between adjacent units, thereby ensuring that the filtering performance remains stable within a wide range of incident angles.

[0031] Angle stability refers to the stable resonant frequency and bandpass / bandstop characteristics of the AFSS for electromagnetic waves at different incident angles (usually 0°-60°). The reason why the AFSS of the present application has good angle stability is that the unit size is much smaller than the working wavelength: The working frequency band of the AFSS of the present application is the Ku band (12-16.4GHz), and the corresponding free space wavelength is about 18.3-25mm; the period size of the cross-shaped ring unit is designed to be (e.g. 5-8mm), which is much smaller than the working wavelength. When the electromagnetic wave is incident at a large angle (e.g. 60°), the "mutual coupling effect" between adjacent units is weak (the mutual coupling strength is positively correlated with the ratio of the unit spacing to the wavelength, and the smaller the spacing, the weaker the mutual coupling), and the unit equivalent parameters (such as equivalent capacitance and equivalent inductance) will not change dramatically due to the change in incident angle. At the same time, small size units can reduce the "angle-dependent phase difference" - when the electromagnetic wave is incident at a large angle, the phase difference on adjacent units is small, and the overall array has higher frequency response consistency, avoiding resonance frequency shift or bandpass / bandstop state disorder.

[0032] Preferably, in the present embodiment, the MEST2G-010-20 type PIN diode manufactured by MACOM Company is selected, which can be equivalent to a resistance of about 2Ω in the on state (forward bias) and a capacitance of about 0.04pF in the off state (reverse bias). The significant impedance difference is the physical basis for achieving a large shift in resonant frequency. The specification parameters of the PIN diode in the present embodiment are shown in Table 2: Table 2 PIN diode specification parameter table

[0033] Specifically, in order to determine the working mechanism of the active frequency selective surface structure of the application, the distribution of the electric field on the surface of the structure is calculated. The surface electric field distribution results of the active frequency selective surface structure under different states (i.e. on or off) of the PIN diode and two resonance frequencies (i.e. 12.0 GHz and 16.4 GHz) are shown in Figure 3 ; when all the PIN diodes are in the on state, the active frequency selective surface resonates at the center of the cross-shaped metal ring, and the resonance frequency is 12.0 GHz; when all the 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, and the resonance frequency is 16.4 GHz.

[0034] In order to verify the filtering characteristics of the active frequency selective surface of the application with respect to frequency changes, the transmission characteristics of the structure under the TE wave and TM wave incidence, respectively, in the on and off states of the PIN diode are calculated by simulation, as shown in Figure 4 , the structure has good polarization independence.

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

[0036] Take the transmission characteristics under TM wave incidence as an example for analysis: when the PIN diode is on, the active frequency selective surface has a -3dB passband of 9.9GHz~14.7GHz, a relative bandwidth of 39.0%, a resonance frequency of 12.0GHz, a -10dB stopband of 7.2GHz~8.8GHz and 15.9GHz~16.6GHz, and a relative bandwidth of 20% and 4.3%; when the PIN diode is off, the active frequency selective surface has a -3dB passband of 14.1GHz~20.2GHz, a relative bandwidth of 35.6%, a resonance frequency of 16.3GHz, and a -10dB stopband of 11.3GHz~13.0GHz, a relative bandwidth of 14.0%.

[0037] From the above analysis, for TE wave and TM wave, the active frequency selective surface can produce a resonance frequency shift of about 4.3~4.4GHz in Ku band, and the switching of bandpass / bandstop state is realized near 12GHz and 16.3GHz.

[0038] In order to verify the angle stability of the active frequency selective surface of the application, the transmission characteristics of the structure under the on and off states of the PIN diode when the incident angle θ 0°~ 60° are calculated by simulation, and the results are shown in FIGS. 2 and 3. Figure 5 When the PIN diode is on, θ= the resonance frequencies of the active frequency selective surface at 60° and 0° are both 12.0GHz, and the-3dB passband bandwidths only differ by 4.7%, and the-10dB stopband bandwidths only differ by 6.4% and 2.8%; when the PIN diode is off, θ= the resonance frequencies of the active frequency selective surface at 60° and 0° are 16.2GHz and 16.4GHz respectively, only differ by 0.2GHz, and the-3dB passband bandwidths only differ by 2.9%, and the-10dB stopband bandwidths only differ by 3.5%. This shows that the active frequency selective surface has very stable transmission characteristics when the incident angle θ= 0°~ 60°. θ= θ

[0039] The frequency shift of the active frequency selective surface of the application is essentially that the on / off state of the PIN diode changes the equivalent impedance and equivalent electrical length of the cross-shaped ring unit, and then adjusts the resonance frequency (the resonance frequency is inversely proportional to the equivalent electrical length). The specific mechanism is as follows: On state (forward bias): the PIN diode presents low impedance characteristics, at this time the diodes on the four legs of the cross-shaped ring are equivalent to "wires", which short-circuit the "notch" of the ring unit. The cross ring legs divided by the notch form a complete conductive path, the equivalent electrical length is lengthened, and the resonance frequency is reduced.

[0040] Off state (reverse bias): the PIN diode presents high impedance characteristics, at this time the diodes are equivalent to "open circuit", the notch of the cross-shaped ring remains open, the effective conductive length of the ring unit is shortened, and the resonance frequency is increased.

[0041] Under the on state, the equivalent electrical length is lengthened → the resonance frequency is reduced to 12GHz; under the off state, the equivalent electrical length is shortened → the resonance frequency is increased to 16.4GHz; the frequency difference (16.4GHz-12GHz=4.4GHz) is the resonance frequency shift in Ku band, and the shift is determined by the "equivalent electrical length change amount corresponding to the notch width" and the "switching impedance difference of the PIN diode". The greater the notch width and the more significant the switching impedance difference of the diode, the greater the frequency shift. ​​

[0042] Polarization independence means that AFSS has consistent frequency response to electromagnetic waves with different polarization directions (such as TE polarization, TM polarization, or 0°-90° arbitrary linear polarization). The reason why the AFSS of the present application has good polarization independence is that the cross-shaped ring unit has a four-face symmetric structure: The cross-shaped ring is composed of four mutually perpendicular "ring legs", and the parameters (impedance, position, number) of the PIN diodes on the four ring legs are completely consistent, forming a "90° rotational symmetry structure" (i.e. after rotating 90° around the center of the unit, the structure is completely coincident with the original structure). This symmetry ensures that no matter what the polarization direction of the incident electromagnetic wave is (such as along the x-axis, y-axis, or 45° diagonal), the induced current distribution excited by the electromagnetic wave on the four ring legs of the cross-shaped ring is completely symmetrical, and there is no situation that "the current is strong in one direction and weak in another direction" due to the change of polarization direction; the equivalent impedance and the equivalent electrical length of the unit remain consistent under different polarization directions, and thus the resonant frequency (12 GHz / 16.4 GHz) and the bandpass / stop characteristics have no difference.

[0043] If the unit structure is asymmetrically designed (such as a rectangular ring, a monopole), there will be a "polarization sensitive axis" (for example, the long side and the short side of the rectangular ring have different responses to different polarization directions); and the four legs of the cross-shaped ring are evenly distributed, without obvious differences in long and short axes, and the electric field components of the incident electromagnetic wave can be uniformly coupled to the four ring legs, avoiding the influence of the polarization direction on the frequency response.

[0044] The second aspect of the embodiment provides a preparation method of an active frequency selective surface, which is prepared by using a 3D printing method, and comprises the following steps: S1, medium substrate forming: using a polymer material with matched dielectric constant, a medium substrate is printed by a light curing or fused deposition additive manufacturing process, and a filling groove of a cross-shaped metal ring and a mounting groove of a PIN diode are reserved on the surface of the medium substrate; Equipment selection: a digital light processing (DLP) light curing 3D printer (resolution ≥ 30 μm), or a fused deposition modeling (FDM) printer (nozzle diameter 0.2 mm); Process parameters: layer thickness 20-50 μm, printing speed 10-30 mm / s (DLP) or 5-15 mm / s (FDM), DLP curing wavelength 405 nm, single layer exposure time 8-15 s; Key operations: according to the periodic arrangement of the cross-shaped ring unit, "filling grooves" (depth 5-10 μm, matched with the thickness of the metal film) and "diode mounting grooves" (0.1 mm larger than the PIN diode in size, to ensure embedding and fitting) are reserved at the corresponding positions of the substrate.

[0045] S2, conductive structure forming: in the filling groove area, deposit conductive paste by direct writing printing, and form a cross-shaped metal ring after solidification or sintering; Switch the printer nozzle to a direct writing metal nozzle (diameter 50-100 μm), accurately inject metal paste into the "filling groove" reserved on the substrate, pre-bake at 60-80°C for 5-10 min after printing each layer, repeat printing 2-3 layers until the thickness meets the standard, and finally sinter at 200-300°C for 30-60 min to densify the metal powder (conductivity ≥ S / m); S3, active device integration: place the PIN diode in the mounting groove, and use conductive adhesive to electrically connect the electrode of the diode to the corresponding part of the cross-shaped metal ring; Device embedding: use an automated pickup device (such as a micro robotic arm) to place the PIN diode into the reserved "mounting groove", and align the two poles of the diode with the leg ends of the cross-shaped ring; Electrode connection: use inkjet printing technology to coat conductive silver paste on the connection between the two poles of the diode and the leg ends of the cross-shaped ring, and cure at 120-150°C for 20-30 min to form a reliable electrical connection (connection resistance ≤3Ω); S4, insulation packaging: use insulation resin to print and cover the diode area with a thickness of 50-100 μm to avoid the influence of the external environment on the device.

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

[0047] Preferably, a 3D printing special resin with matching dielectric properties is selected as the medium substrate material, preferably a modified epoxy acrylate photocuring 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 flowability and curing stability of 3D printing.

[0048] Preferably, the conductive paste is copper powder (particle size 5-20 μm, purity ≥99.9%) mixed with photosensitive resin at a mass ratio of 7:3, with the addition of 0.5% dispersant (such as polyethylene glycol) to prepare metal paste, and the viscosity is controlled at 800-1500 CP (25°C) to ensure no particle sedimentation during printing.

[0049] Preferably, a miniaturized PIN diode (package size ≤0.5mm×0.3mm) is used, and a conductive silver paste (resistivity ≤ Ω cm) for electrode connection, while preparing the insulating protective resin (dielectric constant 3.0-3.5) for diode packaging fixation.

[0050] Compared with the processing mode of the traditional active frequency selective surface (substrate cutting + photoetching metal pattern + manual welding PIN diode), the application adopts a 3D printing processing technology, and has the following obvious advantages in manufacturing efficiency, structural flexibility, cost control and the like: The traditional process relies on photoetching technology to make a metal pattern, and can only realize a plane or a simple curved surface structure. If a three-dimensional topology (such as an active FSS with a substrate with a protrusion or a hollow) is needed, a multi-process assembly (such as multi-layer substrate bonding) is needed, and a positioning error (≥50 μm) is easy to occur, which leads to a frequency response deviation. The application adopts 3D printing to directly print a three-dimensional medium substrate (such as a substrate with a periodic hollow, with a hollow rate of 30%-50%), and the metal film and the diode can be integrated in three dimensions according to the substrate topology, with a positioning error ≤10 μm (based on a visual positioning system), and without the need for assembly, which is suitable for the manufacturing of active FSS for complex electromagnetic scenes.

[0051] Taking a 100mm×100mm active FSS as an example, the traditional process needs to go through “substrate cutting (2h) → photoresist coating / exposure / development (4h) → metal plating (2h) → diode manual welding (3h) → test correction (2h)”, and the total cycle is about 13h. Under the same size, the application adopts a 3D printing process (substrate printing 3h + metal film preparation 2h + diode embedding 1h + post-processing 1h), and the total cycle is about 7h, and automatic continuous production (without manual welding) and small-batch customization (such as within 10 pieces) can be realized. The cycle advantage is more obvious (the traditional process needs to repeat the photoetching plate, and the 3D printing only needs to modify the model).

[0052] The diode connection point manually welded by the traditional process is easy to be affected by temperature and vibration (after -40℃ to 85℃ cycle, the connection resistance may increase to more than 10Ω), and the substrate layers of multi-layer assembly are easy to peel off (the bonding strength ≤10MPa); the application adopts a 3D printing scheme to integrate the metal film and the substrate through sintering / printing (the bonding strength ≥15MPa), and the diode is packaged and fixed through insulating resin, and after -40℃ to 85℃ cycle, the connection resistance changes ≤1Ω, and the frequency deviation amount ≤0.3GHz (the deviation amount of the traditional process ≥0.8GHz), which is more suitable for aerospace and other harsh environment applications.

[0053] If the working frequency band of the active FSS needs to be adjusted, a photomask needs to be re-made (3-5 days), and the metal pattern size needs to be modified; the application only needs to adjust the cross-shaped ring size and diode position in the software, and a new printing model can be generated within 1-2 hours, so that the rapid iteration of the multi-frequency active FSS is realized.

[0054] The above merely describes preferred embodiments of the application and is not intended to limit the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

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.

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, 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 top and bottom ends of the cross-shaped metal ring, with a resonant frequency of 16.4 GHz.

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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