CN113054439B - Curved surface conformal frequency selection surface cover, design method and application - Google Patents
Curved surface conformal frequency selection surface cover, design method and application Download PDFInfo
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- CN113054439B CN113054439B CN202110218149.7A CN202110218149A CN113054439B CN 113054439 B CN113054439 B CN 113054439B CN 202110218149 A CN202110218149 A CN 202110218149A CN 113054439 B CN113054439 B CN 113054439B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
- H01Q15/0026—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective said selective devices having a stacked geometry or having multiple layers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/42—Housings not intimately mechanically associated with radiating elements, e.g. radome
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/0013—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices working as frequency-selective reflecting surfaces, e.g. FSS, dichroic plates, surfaces being partly transmissive and reflective
- H01Q15/0046—Theoretical analysis and design methods of such selective devices
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q17/00—Devices for absorbing waves radiated from an antenna; Combinations of such devices with active antenna elements or systems
Abstract
The invention belongs to the technical field of frequency selection surfaces, and discloses a curved surface conformal frequency selection surface mask, a design method and application. The invention is suitable for the design scheme of the miniaturized low-profile band-pass FSR unit pattern projected by the curved surface; modeling and actual structural scheme of the curved FSS cover body. Different patterns are designed in different projection directions of an inductance part in the FSR unit so as to ensure communication after projection; the invention provides a projection mode combining local deformation and parameter compensation, and ensures the consistency of the FSR electrical performance after the curved surface projection. The unit pattern is adapted to the projection mode, thereby realizing the comprehensive design of the curved FSR cover.
Description
Technical Field
The invention belongs to the technical field of frequency selective surfaces, and particularly relates to a curved surface conformal frequency selective surface mask, a design method and application.
Background
At present: the antenna housing is an important component of an aircraft radar system, is used for protecting a radar antenna or the whole microwave system from working normally in a severe environment, and is a pneumatic, structural and wave-transmitting function integrated part. Traditional antenna house is when satisfying the high transmissivity requirement of own side's antenna electromagnetic wave, can't prevent that enemy surveys inside the electromagnetic wave gets into the antenna house, and inside guidance equipment often has great radar scattering cross section (RCS), causes very big echo signal. Frequency Selective Surfaces (FSS) are widely used in radome designs for antenna performance and aircraft stealth. The FSS is a periodic metal structure, and a specific periodic cell pattern generates capacitance and inductance when electromagnetic waves pass through the FSS. The working principle of the filter is similar to that of a filter in a circuit, and when a capacitive part and an inductive part are in parallel resonance, the filter shows a band-pass characteristic; when the capacitive part and the inductive part are in series resonance, the band stop characteristic is achieved. The FSS itself does not absorb electromagnetic waves and is essentially a spatial filter.
The band-pass FSS radome allows transmission of electromagnetic waves with low insertion loss within the passband, exhibits the electromagnetic properties of a metal radome outside the passband, and totally reflects the electromagnetic waves. The shape of the radome causes the electromagnetic waves to be reflected in different directions from the incident waves, thereby reducing their single station RCS. But the out-of-band reflected waves typically cause increased scattering in other directions and are thus received by the multi-station radar. To solve this problem, the concept of a frequency selective surface absorber (FSR) is proposed, which absorbs the reflected wave outside the pass band to reduce the dual station RCS of the antenna. The FSR is essentially a microwave absorbing structure based on Salisbury, the upper layer is a resistance layer, the lower layer is a metal layer, electromagnetic waves are respectively reflected on the two layers to generate two beams of electromagnetic waves with opposite phases, the two beams of electromagnetic waves interfere with each other and are emitted and offset, and energy is consumed by a resistive part on the resistance layer, so that the wave absorbing effect is achieved.
In the existing unit design of the FSR, the transmissivity of the FSR in a passband is determined by a multilayer structure, and when the impedance of a wave absorbing layer is infinite, the wave absorbing layer shows a full-transmission characteristic. Therefore, researchers insert LC parallel resonators on the current loop of the absorbing layer to increase the wave-transmissivity at the pass band. A circular spiral inductor is inserted into the current loop as a resonator, and the design units are shown in the following figures. It is divided into two parts: a resistive layer and a bandpass layer. The upper layer is an impedance layer, the basic pattern is a hexagonal ring, a circular spiral inductor is inserted into a loop to serve as a parallel LC resonator, and a resistor is inserted into the loop; the lower layer is a band-pass layer and is composed of three layers of patterns, namely a capacitive hexagonal patch unit, a sensitive hexagonal groove and a capacitive hexagonal patch unit. Both the two have parallel resonance at 10GHz, infinite impedance and high wave-transmitting rate.
For curved conformal FSS covers, a method for creating a curved frequency-selective surface based on HFSS-Matlab is proposed, which utilizes Matlab to control the command execution of HFSS through HFSS script interface. The conformal flow is as follows: the method comprises the steps of firstly determining the central position of each band unit according to a bus, carrying out bending projection on the central position of the plane-designed unit, carrying out one-time rotation array on each annular band, and obtaining a curved surface frequency selection surface radome model after multiple cycles.
When the curved surface FSR cover is manufactured, the manufacturing difficulty can be reduced by the design of a low section, the conformality of metal patterns can generate great difference with a plane design, and in order to realize the feasibility of manufacturing the cover body and ensure the electromagnetic performance, the following technical problems are solved: the problem that large-angle incident high wave-transmitting rate and low profile design are contradictory is ensured; and the problems of pattern continuity and electrical property consistency are ensured after the curved surface is conformal.
Through the above analysis, the problems and defects of the prior art are as follows:
(1) for the design of the band-pass FSR, only structural and functional innovations are concerned, and the importance of high wave-transmitting rate under the condition of large angle in actual engineering is ignored.
(2) The multi-layer miniaturized design results in an enlarged cross section and is difficult to machine on a curved surface.
(3) The design of the unit is only suitable for planar and not for curved mask projection.
(4) The electrical performance changes caused by cell deformation and cell distribution non-uniformity are not considered when projecting the array.
The difficulty in solving the above problems and defects is:
(1) the performance of the planar unit pattern and the unit pattern after curved surface projection needs to be considered at the same time, and the thickness of the actually manufactured soft board needs to be considered not to be thick, so that the low-profile design needs to be carried out at the same time, and the difficulty of unit design is increased.
(2) The projection method needs to ensure that the projection does not change the electrical property, so that the deformation of local patterns and the compensation of parameters need to be carried out, and the difficulty of the projection scheme is increased.
The significance of solving the problems and the defects is as follows:
(1) and provides reference for the design of the curved FSR cover, and illustrates the engineering realizability of the curved FSR cover.
(2) The wave absorbing material can be applied to the head of an aircraft, so that the wave absorbing material meets the high wave-transmitting characteristic at the working wave band, the wave absorbing material absorbs waves outside the working wave band, the multi-station RCS is reduced, and the stealth is better realized.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a curved surface conformal frequency selection surface cover, a design method and application.
The curved conformal frequency selective surface cover is sequentially provided with a lumped component, a solder mask layer, an impedance layer metal, a first polyimide PI, an adhesive layer, PMI foam, a band-pass layer upper layer metal, a second polyimide PI, a band-pass layer upper layer metal, an adhesive layer and high-temperature-resistant resin from top to bottom.
Furthermore, the miniaturized band-pass FSR of the curved conformal frequency selective surface mask consists of a layer of impedance layer and a layer of band-pass layer, the middle of the impedance layer and the band-pass layer are separated by PMI foam, and the dielectric constant epsilon of the PMIr1.05, loss tangent tan δ 0.0003; the 0805 resistor of 200 omega and the square spiral resonator are inserted into each edge of the impedance layer unit, the outer ring is directly connected with one edge, and the inner ring penetrates through the lower layer through a metalized through hole and a jumper wire to be connected with the other edge.
Furthermore, the dielectric plate of the impedance layer is Rogers 4350B with the thickness of 0.254mm, and the dielectric constant epsilonr3.48, loss tangent tan δ 0.0027; the band-pass FSS is a double-layer coupling structure, the upper layer is rectangular ring metal, the lower layer is bent metal wires which are arranged in a square shape,the period was 18mm, two layers were printed on a 0.254mm thick sheet of Rogers 4350B;
the shape parameters are as follows: t is t1＝t3＝0.254mm，t2＝5.0mm，la＝2.7mm，a＝12mm，w＝1.6mm，ax＝8.5mm，ay＝8mm，wx＝1.25mm，wy＝1.5mm，s＝0.4mm，g＝0.2mm，p＝18mm。
Further, the conformal frequency selective surface of curved surface face mask bottommost is the high temperature resistant resin who prints with 3D, thickness is 1.5mm, the medium substrate of soft board is the polyimide, thickness 0.0254mm, use PCB etching technique to form the FSS pattern on the surface, the band pass layer is pasted on high temperature resistant branch, use 3M467 glue, thickness is 0.02mm, the centre is the PMI foam cover with milling machine processing, thickness is 5mm, paste the impedance layer on the PMI foam, medium substrate and band pass layer are unanimous, the upper surface covers has DuPont FR0110 as the group solder mask, thickness is 0.0254 mm.
Another object of the present invention is to provide a projection method of the curved conformal frequency selective surface mask, wherein the projection method includes: dividing the bus into several ring zones according to the period length according to the bus equation, calculating the length s and total length s of ab curve segmenttotalExcess length s0And the number n of zones:
origin of coordinates to(s)00) dividing the divided area at intervals of the period d, obtaining an abscissa of the divided surface for each division, and determining the abscissa x as the abscissaiThe equation of (a) is:
calculating the horizontal coordinate of the division surface of the ring beltThen, each separated girdle band is approximately equivalent to a conical surface, analysis is carried out on the same generatrix, the distance between two tangent planes of the ith girdle band is the period d, the distance between the intersection point of the two tangent planes and the generatrix of the girdle band is calculated, the taper of the equivalent conical surface is calculated, and the small radius and the large radius are calculated according to a generatrix formula and are riAnd RiDetermining all parameters of the conical surface, approximately unfolding the curved surface into n sectors, establishing a local coordinate system by utilizing a circumferential equally-divided unit of the conical surface, establishing a plane unit on the local coordinate system and then projecting;
before projection, parameters are compensated by utilizing triangular transformation, and the compensation principle for structure and parameters is as follows:
(1) for the capacitive part, the space distance of the opposite metal strips is consistent with that of the plane unit;
(2) for the inductive part, the width and the length of the inductance line in the unit area on the curved surface are consistent with those of the plane.
Another object of the present invention is to provide a radome comprising the curved conformal frequency selective surface mask.
By combining all the technical schemes, the invention has the advantages and positive effects that: the invention designs a low-profile FSR unit with high wave transmittance under large-angle incidence suitable for curved surface projection; improving a projection method, and performing structural compensation on unit deformation and unit uneven distribution; the design of the prior art for band-pass FSR is realized by only paying attention to structural and functional innovation and neglecting the importance of high wave transmittance under the condition of a large angle in the actual engineering, the section is enlarged due to the multi-layer miniaturized design, the processing and forming on a curved surface are difficult, the design of a unit is only suitable for a plane and is not suitable for the projection of a curved mask, and the problems of electrical property change caused by unit deformation and uneven unit distribution are not considered during the projection of an array.
The invention is suitable for the design scheme of the miniaturized low-profile band-pass FSR unit pattern projected by the curved surface; modeling and actual structural scheme of the curved FSS cover body. The period of the band-pass layer is only 0.12 times of the wavelength, and the period in the prior art is 0.4 times of the wavelength, so that the stability of the incident angle is better. The invention adopts square units, which are matched with a projection mode, and an inductance part in a band-pass layer is provided with different patterns in different projection directions in order to ensure communication. The conformal method in the prior art does not consider the deformation of unit projection, and the invention respectively considers the pattern structure of a capacitive part and the compensation of parameters of an inductive part, so that the electrical properties before and after projection are kept consistent.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained from the drawings without creative efforts.
Fig. 1 is a schematic 3D overall structure diagram of a miniaturized bandpass FSR according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of simulation results under the condition that electromagnetic waves are incident at different angles according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of a design using coupling of a capacitive layer and an inductive layer according to an embodiment of the present invention.
Fig. 4 is a schematic diagram illustrating S parameters calculated by comparing equivalent circuits and S parameters obtained by simulation according to an embodiment of the present invention.
Fig. 5 is a schematic diagram of a square spiral inductor according to an embodiment of the present invention.
FIG. 6 is the equivalent circuit model of FIG. 6(a) of a resistive layer provided by an embodiment of the present invention; FIG. 6(b) compares the results with HFSS simulations; fig. 6(c) values for the real and imaginary parts.
Fig. 7 is a schematic diagram of dividing the divided regions according to the embodiment of the present invention.
Fig. 8 is a schematic diagram of creating a plane unit on a local coordinate system and then projecting according to an embodiment of the present invention.
Fig. 9 is a schematic diagram of compensation of parameters by using trigonometric transformation according to an embodiment of the present invention.
FIG. 10 is a schematic diagram of a post-projection model provided by an embodiment of the invention; (a) the structure is an upper layer square ring structure of a band-pass part, (b) the structure is a lower layer bending inductance structure of the band-pass part, (c) the whole structure of the band-pass layer, (d) a local graph after impedance layer projection, and (e) the whole structure after FSR projection; 1. lumped components; 2. a solder resist layer; 3. a resistance layer metal; 4. a first polyimide PI; 5. a glue layer; 6. PMI foam; 7. a band-pass layer upper layer metal; 8. a second polyimide PI; 9. a band-pass layer upper layer metal; 10. a glue layer; 11. and (3) high-temperature resistant resin.
Fig. 11 is a schematic structural diagram of a sample FSR cone cover manufactured by a method of attaching a flexible board according to an embodiment of the present invention.
FIG. 12 is a graphical representation of the results of S21 for an own space launch test FSR shroud provided by an embodiment of the invention.
Fig. 13 is a schematic diagram of a test result of the wave absorbing effect (RCS reduction capability) of the FSR cover in the X-band by using the compact range method according to the embodiment of the present invention.
FIG. 14 is another schematic view of a housing construction provided in accordance with an embodiment of the present invention; in the figure: 1. lumped components; 6. PMI foam; 11. a high temperature resistant resin; 12. nano silver; 13. and (3) UV resin.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In view of the problems in the prior art, the present invention provides a curved conformal frequency selective surface mask, a design method and an application thereof, which are described in detail below with reference to the accompanying drawings.
The technical solution of the present invention is further described below with reference to the accompanying drawings.
Frequency selective surface of the invention: the periodic metal pattern structure is a periodic metal pattern structure, the capacitive part and the inductive part of the periodic metal pattern structure generate resonance at a resonance point, and the periodic metal pattern structure is a spatial filter with band-pass or band-stop characteristics. And (3) S wave band: 2-4 GHz; and (3) X wave band: 8-12 GHz; when the S21 is-0.7 dB, the wave transmittance is 85 percent, and when the S11 is-10 dB, the wave absorption rate is 90 percent.
1. FSR cell design
The 3D overall structure of the miniaturized bandpass FSR is shown in fig. 1. It consists of a resistance layer and a band-pass layer, which are separated by PMI foam, the dielectric constant epsilon of PMIr1.05, and a loss tangent tan δ of 0.0003. The impedance layer unit is improved from a basic square ring FSS unit, a 0805 resistor of 200 omega and a square spiral resonator are inserted into each edge, the outer ring is directly connected with one edge, and the inner ring penetrates through the lower layer through a metalized through hole and a jumper wire to be connected with the other edge.
The dielectric plate of the impedance layer is 0.254mm thick Rogers 4350B, and has a dielectric constant of ∈r3.48, and a loss tangent tan δ of 0.0027. The band-pass FSS is a double-layer coupling structure, the upper layer is made of rectangular ring metal, the lower layer is made of bent metal wires which are arranged in a square shape with a period of 18mm, and the two layers are printed on a Rogers 4350B plate with the thickness of 0.254 mm.
The shape parameters are as follows: t is t1＝t3＝0.254mm，t2＝5.0mm，la＝2.7mm，a＝12mm，w＝1.6mm，ax＝8.5mm，ay＝8mm，wx＝1.25mm，wy＝1.5mm，s＝0.4mm，g＝0.2mm，p＝18mm。
The simulation results of the electromagnetic waves under different incident angles are shown in the following figure 2, when the electromagnetic waves are incident at 0 degree, the pass band range with the wave transmittance of more than 85 percent is 2.84GHz-3.4GHz, and the wave absorbing band range with the wave absorbing rate of more than 90 percent is 8.79GHz-11.8 GHz; at 50 DEG oblique incidence, the passband is 3.04GHz-3.38GHz, and the absorption band is 8.91GHz-12.0 GHz.
(1) For the design of the band-pass layer, attention needs to be paid to the wave-transmitting rate of large-angle incidence, the frequency of the wave-absorbing band is 3 times of the wave-transmitting band, and the difficulty of manufacturing.
The current commonly used miniaturization design methods include bending interdigital, coupling of a capacitive layer and an inductive layer, loading of passive lumped elements, loading of active adjustable lumped elements and the like. Too much passive device loading can increase the manufacturing difficulty, is difficult to make into the antenna house moreover, and the interdigital technique only is applicable to the plane, and FSS becomes the quasiperiodic and arranges when projection and curved surface, is difficult to guarantee that the interdigital part of every unit all exists. Therefore, the present invention adopts the design of coupling the capacitive layer and the inductive layer to divide the inductor and the capacitor into two layers, thereby avoiding the limitation of the wavelength on the period, and the design pattern is as shown in fig. 3. The capacitance layer uses a square ring and can be equivalent to an LC series circuit, and L3 and C3 generate resonance at high frequency to ensure that the FSS is in a total reflection state at 8-12 Ghz; the inductance layer adopts a bending technology, bending is concentrated on the middle blank part of the square ring to reduce the dead area between the two layers, and no new parasitic parameter is introduced when large-angle incident TE polarization is ensured, so that a low section is realized, in order to ensure that inductance lines are connected and equal in inductance after projection on the antenna cover, a transverse inductance line is not bent, the interval is increased to ensure that the inductance is the same as the longitudinal direction, the inductance is equivalent to the inductance and is connected with the capacitance layer in parallel, and C3 and L4 are in parallel resonance at the position of 3GHz to generate a passband.
Impedance ZF of band-pass FSS2Expression:
when in use
Time, ZF2Infinity, showing total transmission of electromagnetic waves; when in use
Time, ZF2And 0, representing total reflection of the electromagnetic wave. In FSS, the equivalent inductance and capacitance per unit length is:
calculated to obtain L3＝1.1nH,L4＝14.1nH,C30.216pF, at this time f1＝3.31Ghz，f2The calculated S-parameters and the simulated S-parameters were compared in the equivalent circuit at 10.33GHz, and the two parameters matched as shown in fig. 4.
(2) For the design of the resistive layer, the spiral inductor is used as an LC parallel resonator.
Common spiral inductors are: circular, square, hexagonal and octagonal spiral inductors need to resonate around 3GHz, so that higher inductance and parasitic capacitance values are needed, and square spiral inductors have relatively higher parasitic capacitances, so that a square spiral inductor is selected as shown in fig. 5.
The inductance value is empirically expressed as:
the coil is three turns, the line width is 0.1mm, the gap is 0.1mm, the outer diameter is 2.1mm, the diameter of the metallized via hole is 5mm, and the jump line width is 0.3 mm. The inductance L can be calculated2When 20.518nH is obtained, parasitic capacitance distribution is complicated and there is no fixed calculation formula, and parasitic capacitance value C can be obtained from simulationpIt was calculated to resonate at 2.97GHz, 0.14 pF.
The equivalent circuit model of the impedance layer is shown in fig. 6(a), and L can be calculated from the equivalent inductance and capacitance formula1＝3.09nH，C3The above calculated value was substituted into the ADS simulation and compared with the HFSS simulation at 0.067pF, and as a result, (b) in fig. 6, it can be seen that the single-layer resistance layer exhibits a fully transmissive state at 3 GHz. The total impedance of the resistive layer is expressed as:
the values of the real part and the imaginary part are shown in (c) of fig. 6, and the impedance at the full wave-transparent position is infinite. The optimization can be realized, when the metal plate is added at a position 5mm away from the impedance layer, the wave-absorbing effect is good, and the stable wave-absorbing frequency band is 8.8GHz-11.8GHz at the incident angle of 0-50 degrees.
2. Projection method and structural design of curved FSR shroud
The conformal projection basic method of the surface of the curved surface rotator comprises the following steps: dividing the bus into several ring zones according to the period length according to the bus equation, calculating the length s and total length s of ab curve segmenttotalExcess length ofs0And the number n of zones:
as shown in fig. 7, the coordinate origin is(s)00) dividing the divided area at intervals of the period d, obtaining an abscissa of the divided surface for each division, and determining the abscissa x as the abscissaiThe equation of (a) is:
after calculating the horizontal coordinate of the zone dividing surface, each separated zone is approximately equivalent to a conical surface, analysis is carried out on the same bus at the moment, the distance between two tangent planes of the ith zone is the distance, the distance between the intersection point of the two tangent planes and the zone bus is the period d, so that the taper of the equivalent conical surface can be calculated, and the small circle radius and the large circle radius are calculated according to a bus formula and are riAnd RiSo that all the parameters of the conical surface are determined, the curved surface can be approximately spread out into n sectors. (approximation is not needed for the conical surface), a local coordinate system is established by equally dividing the unit by the circumference of the conical surface, and a plane unit is established on the local coordinate system and then projected.
However, in this method, the projection is performed as shown in fig. 8, and the capacitive portions are not uniformly distributed and have inconsistent pitches, thereby affecting the electrical performance.
Therefore, the unit pattern cannot be directly projected, and it needs to be compensated for the structure and parameters to ensure the consistency of the electrical properties. The compensation principle is as follows:
(1) for the capacitive part, the space distance of the opposite metal strips is ensured to be consistent with the plane unit;
(2) and for the inductive part, the width and the length of the inductance line in unit area on the curved surface are ensured to be consistent with those of the plane.
For the conical cover body, the head circumference is small, the tail circumference is large, so the unit needs to be changed into a trapezoidal unit with a small front part and a large rear part, the parameter compensation is performed by utilizing triangular transformation before projection, the distance of a capacitor part is ensured to be consistent with simulation, and the length and the width of an inductor part are ensured to be consistent with simulation. The specific flowchart is shown in fig. 9.
The design unit is projected onto the conical cover according to the projection method, and the projected model is shown in fig. 10. (a) The structure is an upper layer square ring structure of a band-pass part, (b) the structure is a lower layer bending inductance structure of the band-pass part, (c) the whole structure of the band-pass layer, (d) a local graph after impedance layer projection, and (e) the whole structure after FSR projection; the integrated circuit is characterized in that a lumped component 1, a solder mask layer 2, an impedance layer metal 3, a first polyimide PI 4, an adhesive layer 5, PMI foam 6, a band-pass layer upper layer metal 7, a second polyimide PI 8, a band-pass layer upper layer metal 9, an adhesive layer 10 and high-temperature-resistant resin 11 are sequentially arranged from top to bottom.
Finally, an FSR conical cover sample piece is manufactured by using a mode of pasting a soft board, the structure of the FSR conical cover sample piece is shown in fig. 11, the bottom layer is made of high-temperature-resistant resin printed by 3D, the thickness is 1.5mm, the medium base material of the soft board is polyimide, the thickness is 0.0254mm, an FSS pattern is formed on the surface by using a PCB etching technology, the band-pass layer is pasted on a high-temperature-resistant branch, 3M467 glue is used, the thickness is 0.02mm, the middle part is a PMI foam cover processed by a milling machine, the thickness is 5mm, an impedance layer is pasted on PMI foam, the medium base material and the band-pass layer are consistent, the upper surface is covered with DuPont FR0110 as a group welding layer, resistance welding is facilitated, and the thickness is 0.0254 mm.
The existing curved mask solution can only be used for an expandable curved surface, and for an unexpanded curved surface, a heterogeneous 3d printing technology can be used in the manufacturing process, and the mask body structure is shown in fig. 14: the method comprises the following steps: lumped component 1, PMI foam 6, high temperature resistant resin 11, nano silver 12, UV resin 13.
The lumped element 1 is arranged on the UV resin 13, the surface of the UV resin 13 is coated with the nano silver 12, the bottom of the UV resin 13 is the high temperature resistant resin 11, and the bottom of the high temperature resistant resin 11 is the PMI foam 6.
The unit design and the projection scheme are consistent with those of the prior art, but the non-extensible curved surface cannot be pasted with a flexible plate, so that 3D ink-jet printing is directly carried out on 3D printing high-temperature-resistant resin, the solidified UV resin is used as a dielectric layer, and the sintered nano silver is used as a metal layer.
The technical effects of the present invention will be described in detail with reference to the tests below.
The test result of the sample piece of the invention is as follows:
results of S21 using a self-space launch test FSR shroud are shown in FIG. 12, with a band of-0.7 dB (85% transmission) passband at 0-50 incident angles of 2.78GHz-3.13 GHz.
The wave absorbing effect (RCS reducing capability) of the FSR cover in the X wave band is tested by using a compact range method, and the test result is shown in figure 12. The average reduction in single station RCS at 0 and 30 bias angles between 8.4 and 12.4Ghz is greater than 15dB with and without capping.
The conical surface FSR is made by using a PCB soft board and is adhered to high-temperature-resistant resin for 3D printing. For non-deployable curved surfaces (such as oval covers, von karman curve rotator covers and the like), soft boards cannot be pasted on the surfaces, heterogeneous 3D ink-jet printing technology can be adopted, UV resin and nano silver are printed on the substrate to form the FSS unit, and the forming process is an alternative.
The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.
Claims (4)
1. The curved conformal frequency selective surface cover is characterized in that a lumped component, a solder mask layer, impedance layer metal, first polyimide PI, an adhesive layer, PMI foam, band-pass layer upper layer metal, second polyimide PI, band-pass layer lower layer metal, an adhesive layer and high-temperature-resistant resin are sequentially arranged from top to bottom;
the miniaturized band-pass FSR of the curved conformal frequency selective surface mask consists of a resistance layerAnd a layer of bandpass layers separated by PMI foam, the dielectric constant ε of the PMIr1.05, loss tangent tan δ 0.0003; 0805 resistors of 200 omega and a square spiral resonator are respectively inserted into four edges of the impedance layer unit, the outer ring is directly connected with one edge, and the inner ring penetrates through the lower layer through a metalized through hole and a jumper wire to be connected with the other edge;
the dielectric plate of the impedance layer is Rogers 4350B with the thickness of 0.254mm and the dielectric constant epsilonr3.48, loss tangent tan δ 0.0027; the band-pass FSS is a double-layer coupling structure, the upper layer of rectangular ring metal and the lower layer of bent metal wires are in one-to-one correspondence, the rectangular ring metal and the bent metal wires are arranged in a square shape, the period is 18mm, and the two layers are printed on a Rogers 4350B plate with the thickness of 0.254 mm;
the shape parameters are as follows: t is t1＝t3＝0.254mm，t2＝5.0mm，la＝2.7mm，a＝12mm，w＝1.6mm，ax＝8.5mm，ay＝8mm，wx＝1.25mm，wy＝1.5mm，s＝0.4mm，g＝0.2mm，p＝18mm。
2. The curved conformal frequency selective surface mask of claim 1, wherein the bottom layer of the curved conformal frequency selective surface mask is a high temperature resistant resin printed in 3D, the thickness is 1.5mm, the dielectric substrate of the flexible printed circuit board is polyimide, the thickness is 0.0254mm, the surface is patterned by using a PCB etching technique, the band pass layer is adhered to a branch of the high temperature resistant resin, 3M467 glue is used, the thickness is 0.02mm, the middle part is a PMI foam cover processed by a milling machine, the thickness is 5mm, an impedance layer is adhered on the PMI foam, the dielectric substrate and the band pass layer are consistent, the upper surface is covered with dupont FR0110 as a solder mask, and the thickness is 0.0254 mm.
3. A method for projecting a curved conformal frequency selective surface mask according to any one of claims 1-2, wherein the method comprises: dividing the bus into several ring zones according to the period length according to the bus equation, calculating the length s and total length s of ab curve segmenttotalExcess length s0And the number n of zones:
s0＝mod(stotal,d),
origin of coordinates to(s)00) dividing the divided area at intervals of the period d, obtaining an abscissa of the divided surface for each division, and determining the abscissa x as the abscissaiThe equation of (a) is:
after calculating the horizontal coordinate of the zone dividing surface, approximately equating each separated zone to be a conical surface, analyzing on the same bus at the moment, calculating the taper of the equivalent conical surface by taking the distance between two tangent planes of the ith zone as the period d and the distance between the intersection point of the two tangent planes and the zone bus as the period d, and calculating the radius of a small circle and the radius of a large circle as r according to a bus formulaiAnd RiDetermining all parameters of the conical surface, approximately unfolding the curved surface into n sectors, establishing a local coordinate system by utilizing a circumferential equally-divided unit of the conical surface, establishing a plane unit on the local coordinate system and then projecting;
before projection, parameters are compensated by utilizing triangular transformation, and the compensation principle for structure and parameters is as follows:
(1) for the capacitive part, the space distance of the opposite metal strips is consistent with that of the plane unit;
(2) for the inductive part, the width and the length of the inductance line in the unit area on the curved surface are consistent with those of the plane.
4. A radome comprising the curved conformal frequency selective surface mask of any one of claims 1-2.
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