Design method of electromagnetic shielding air-inlet grille

Abstract

The invention discloses a design method of an electromagnetic shielding air inlet grille, which comprises the following steps: step 1, establishing a group of straight cavity air inlet duct models, each model in the group of straight cavity air inlet duct models having different grille parameters; step 2, calculating a radar cross section (RCS) of each model in the group of straight cavity air inlet duct models in simulation software so as to obtain electromagnetic shielding effects of different grille parameters on the air inlet grille, namely an RCS value of each model changing along with a radar wave incident angle; and step 3, manufacturing a test piece of each model in the group of straight-cavity air inlet duct models, performing an RCS test on each model in the radar darkroom, and further verifying a simulation calculation result through an RCS test result. According to the technical scheme, the problem that an existing air inlet grille with the electromagnetic shielding effect is large in design difficulty when applied to a helicopter air inlet channel is solved.

Description

Technical Field

[0001] The present invention relates to, but is not limited to, the technical field of helicopter structural design and radar stealth design, and in particular to a design method for an electromagnetic shielding air intake grille. Background Art

[0002] Radar stealth technology has an increasingly important impact on the survivability and combat effectiveness of future aircraft. For helicopters, radar stealth has also become a trend in future development. Unlike fixed-wing aircraft, helicopters have more complex shapes and stronger radar scattering characteristics. As one of the strong scattering sources of helicopters, the engine inlet is crucial to the RCS (radar cross section) control of the entire aircraft, and special treatment of the engine inlet is usually required.

[0003] In order to prevent radar waves from irradiating the engine blades and forming mirror reflection, a grille can be installed at the air inlet. The principle of the grille shielding radar waves is: on the one hand, radar waves will be scattered when irradiated on the grille, most of the radar waves cannot enter the air inlet, and are reflected in the direction that the radar cannot receive; on the other hand, the installation of the grille will form a cavity between the air inlet and the air inlet, and a small part of the radar waves entering the air inlet will be reflected multiple times in the cavity, and the radar wave energy will continue to attenuate, greatly reducing the echo intensity.

[0004] Air intake grilles have been used on fixed-wing aircraft for a long time. As early as the 1970s, the F-117A developed achieved electromagnetic shielding of the air inlet by setting a grille at the air inlet. However, there are currently no grilles used on helicopter air inlets, and there is no typical design method for reference for the selection of grille parameters and size definition. Summary of the invention

[0005] The purpose of the present invention is: in order to solve the above-mentioned problem, an embodiment of the present invention provides a design method for an electromagnetic shielding air intake grille to solve the problem that the existing air intake grille with electromagnetic shielding effect is usually used in fixed-wing aircraft. Since the shape of the helicopter is more complex and the radar scattering characteristics are stronger, the design of the air intake grille for use on the helicopter air inlet is difficult.

[0006] The technical solution of the present invention is as follows: An embodiment of the present invention provides a design method for an electromagnetic shielding air intake grille, comprising:

[0007] Step 1, establishing a group of straight cavity air intake models, each model in the group of straight cavity air intake models has different grille parameters;

[0008] Step 2, calculating the radar cross section RCS of each model in the set of straight cavity air intake models in the simulation software, so as to obtain the electromagnetic shielding effect of different grille parameters on the air intake grille, that is, the RCS value of each model changing with the incident angle of the radar wave;

[0009] Step 3: manufacture test pieces for each model in this set of straight cavity air inlet models, conduct RCS test on each model in a radar darkroom, and then verify the simulation calculation results through the RCS test results.

[0010] Optionally, in the design method of the electromagnetic shielding air intake grille as described above, the straight cavity air intake duct model established in step 1 includes: an air intake duct cavity and an air intake grille located at the air inlet; the bottom surface of the air intake duct cavity is closed, and the inclined port formed by the front air inlet is provided with an air intake grille.

[0011] Optionally, in the design method of the electromagnetic shielding air intake grille as described above, in step 1, the grille parameters of each straight cavity air intake duct model established include:

[0012] Grid hole size a, in-plane grid thickness b, normal grid thickness c, grid surface inclination α;

[0013] In the step 1, a control variable strategy is used to design grille parameters corresponding to multiple straight cavity air intake duct models.

[0014] Optionally, in the above-mentioned design method of the electromagnetic shielding air intake grille, the step 2 comprises:

[0015] Each model in a set of straight cavity inlet duct models that have been completed is meshed, and each mesh model that has completed meshing is imported into the simulation software, and RCS simulation calculation is performed on each model by setting the simulation parameters of the simulation software.

[0016] Optionally, in the design method of the electromagnetic shielding air intake grille as described above, the simulation parameters in step 2 are set as follows:

[0017] The simulation algorithm adopts the multi-layer fast multipole (MLFMM) algorithm. The incident radar wave is set to a plane wave to simulate the incident radar wave from an infinitely far position. The radar wave receiving mode is set to the far-field condition to simulate the radar wave incident from an infinitely far position and reflected to an infinitely far position. The radar wave frequency is set to 10 GHz, the polarization mode of the radar wave is set to horizontal polarization, the direction along the cavity is set to 0°, the radar wave incident angle is set to -30°~30° and 0°~30°, and the step angle of the point frequency test is 0.1°.

[0018] Optionally, in the above-mentioned design method of the electromagnetic shielding air intake grille, step 3 comprises:

[0019] Step 31, using 3D printing to manufacture a test piece of a model corresponding to each set of grid parameters;

[0020] Step 32, each test piece is placed on a turntable bracket in a radar darkroom in two placement methods to perform a point frequency RCS test, and a set of RCS values ​​varying with the incident angle corresponding to each placement method of each test piece is obtained.

[0021] Optionally, in the above-mentioned design method of the electromagnetic shielding air intake grille, in step 3,

[0022] Placement method 1 is used to simulate the air intake method on the top of a helicopter. The test piece is placed horizontally on the turntable bracket in the radar darkroom, and the air intake grille surface faces the incident direction of the radar wave. The radar wave is incident horizontally, the radar azimuth angle is -30°~30°, and the step angle of the point frequency test is 0.1°.

[0023] Optionally, in the above-mentioned design method of the electromagnetic shielding air intake grille, in step 3,

[0024] Placement method 2 is used to simulate the air intake method on both sides of the helicopter. The test piece is placed sideways on the turntable bracket of the radar darkroom, and the air intake grille surface faces the incident direction of the radar wave. The radar wave is incident horizontally, the radar wave azimuth angle is 0°~30°, and the step angle of the point frequency test is 0.1°.

[0025] The beneficial effects of the present invention are as follows: an embodiment of the present invention provides a method for designing an electromagnetic shielding air intake grille. Aiming at the complex appearance of helicopters and the stronger radar scattering characteristics, taking a conventional square grille as an example, the grille parameters include grille hole size, grille normal thickness, grille tangential thickness, and grille surface inclination angle; the design method provided by the present invention establishes a set of straight cavity air intake duct models with different grille parameters, and calculates the RCS of this set of models in the simulation software, thereby considering the influence of different grille parameters on the electromagnetic shielding effect of the air intake grille. In addition, this set of straight cavity air intake duct models is easy to implement, and test pieces can be quickly manufactured by 3D printing, and tested in a radar darkroom, and then the simulation calculation results are verified by experimental results. The design method provided by the present invention has the following beneficial effects:

[0026] First, due to the limitation of structure and appearance, the RCS index of helicopter is generally much higher than that of fixed wing, so the proportion of helicopter air inlet in the whole aircraft RCS index will also be lower than that of fixed wing; if the whole aircraft model is established for simulation or experiment according to the traditional method, not only the modeling is difficult and the feasibility is poor, but also the influence of the change of air inlet grille parameters on the whole aircraft RCS will be difficult to reflect, and it is difficult to intuitively and effectively examine the influence of changing grille parameters on the electromagnetic shielding effect of the grille; the method of the present invention establishes an independent straight cavity air inlet model, and the influence of the change of a single grille parameter on the electromagnetic shielding effect of the grille can be examined by the control variable method;

[0027] Second, the design method provided by the present invention equivalently examines the electromagnetic shielding effect of the grid by simulating and testing the radar cross section of the established straight cavity inlet model; if the model RCS is small, it means that most of the radar waves irradiated on the grid are reflected, and a small part passes through the grid into the cavity, that is, the grid reflectivity is high, and the grid electromagnetic shielding effect is better, otherwise it means that the grid electromagnetic shielding effect is worse;

[0028] Third, the straight cavity air intake model established in the present invention is easy to implement, and the test piece can be quickly manufactured by 3D printing, thus shortening the research and development cycle;

[0029] Fourthly, the present invention only needs to manufacture one set of test pieces during the test phase, and by changing the placement of the test pieces, two common helicopter air inlet layouts, namely, helicopter top air intake and helicopter side air intake, are simulated, thereby reducing R&D costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0031] Figure 1 A schematic diagram of a flow chart of a design method for an electromagnetic shielding air intake grille provided in an embodiment of the present invention;

[0032] Figure 2 Schematic diagram of a straight cavity air intake model established in an embodiment of the present invention, wherein FIG a is an overall schematic diagram of the straight cavity air intake model, and FIG b is a specific enlarged schematic diagram of grille parameters;

[0033] Figure 3 Schematic diagram of the RCS test method of the straight cavity air intake model in the embodiment of the present invention; Figure a shows the placement method 1, and Figure b shows the placement method 2;

[0034] Figure 4 It is a schematic diagram of RCS curves obtained by simulating test pieces 1 to 6 in arrangement mode 2 in an embodiment of the present invention;

[0035] Figure 5 Schematic diagram of RCS curves obtained by testing test pieces 1 to 6 in placement mode 2 in an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0037] The above background technology has already explained the important role of radar stealth in helicopter design. Existing air intake grilles with electromagnetic shielding effect are usually used in fixed-wing aircraft. Since helicopters have more complex shapes and stronger radar scattering characteristics, it is more difficult to design air intake grilles for use in helicopter air intakes.

[0038] In view of the above problems, an embodiment of the present invention provides a design method for an electromagnetic shielding air intake grille.

[0039] The present invention provides the following specific embodiments which can be combined with each other. The same or similar concepts or processes may not be described in detail in some embodiments.

[0040] The design method of the electromagnetic shielding air intake grille provided by the embodiment of the present invention takes a conventional square grille as an example, and the grille parameters include the grille hole size, the grille normal thickness, the grille tangential thickness, and the grille surface inclination angle; the design method provided by the present invention establishes a group of straight cavity air intake duct models with different grille parameters, and calculates the RCS of this group of models in the simulation software, so as to consider the influence of different grille parameters on the electromagnetic shielding effect of the air intake grille. In addition, this group of straight cavity air intake duct models is easy to implement, and the test pieces can be quickly manufactured by 3D printing means, and tested in a radar darkroom, and then the simulation calculation results are verified by experimental results.

[0041] Figure 1 A schematic diagram of a design method for an electromagnetic shielding air intake grille provided by an embodiment of the present invention. Figure 1 As shown, the design method of the electromagnetic shielding air intake grille provided in the embodiment of the present invention includes the following steps:

[0042] Step 1, establishing a group of straight cavity air intake models, each model in the group of straight cavity air intake models has different grille parameters;

[0043] Step 2, calculating the radar cross section (RCS) of each model in the set of straight cavity inlet duct models in the simulation software, so as to obtain the electromagnetic shielding effect of different grille parameters on the air intake grille, that is, the RCS value of each model changing with the incident angle of the radar wave;

[0044] Step 3: manufacture test pieces for each model in this set of straight cavity air inlet models, conduct RCS test on each model in a radar darkroom, and then verify the simulation calculation results through the RCS test results.

[0045] In one implementation of an embodiment of the present invention, the straight cavity air intake duct model established in the above step 1 includes: an air intake duct cavity and an air intake grille located at the air intake port; the bottom surface of the air intake duct cavity is closed, and the inclined port formed by the front air intake port is provided with an air intake grille.

[0046] In one implementation of the embodiment of the present invention, in the above step 1, the grille parameters of each straight cavity air intake model established include: grille hole size a, in-plane grille thickness b, normal grille thickness c, grille surface inclination angle α; Figure 2 As shown, it is a schematic diagram of the straight cavity air intake duct model established in an embodiment of the present invention, wherein Figure a is an overall schematic diagram of the straight cavity air intake duct model, and Figure b is a specific enlarged schematic diagram of the grille parameters.

[0047] In this implementation, in step 1, a control variable strategy is used to design grille parameters corresponding to multiple straight cavity air intake duct models.

[0048] In an implementation of the embodiment of the present invention, the implementation of step 2 may include:

[0049] Each model in a set of straight cavity inlet duct models that have been completed is meshed, and each mesh model that has completed meshing is imported into the simulation software, and RCS simulation calculation is performed on each model by setting the simulation parameters of the simulation software.

[0050] In this implementation, the simulation parameters in step 2 can be set to:

[0051] The simulation algorithm adopts the multi-layer fast multipole (MLFMM) algorithm. The incident radar wave is set to a plane wave to simulate the incident radar wave from an infinitely far position. The radar wave receiving mode is set to the far-field condition to simulate the radar wave being incident from an infinitely far position and reflected to an infinitely far position. The radar wave frequency is set to 10 GHz, and the polarization mode of the radar wave is set to horizontal polarization (the cavity can be more sensitive to horizontally polarized radar waves). The direction along the cavity is set to 0°, the radar wave incident angle is set to -30°~30° and 0°~30°, and the step angle of the point frequency test is 0.1°.

[0052] In an implementation of the embodiment of the present invention, the implementation process of the above step 3 may include:

[0053] Step 31, using 3D printing to manufacture a test piece of a model corresponding to each set of grid parameters;

[0054] Step 32, each test piece is placed on a turntable bracket in a radar darkroom in two placement methods to perform a point frequency RCS test, and a set of RCS values ​​varying with the incident angle corresponding to each placement method of each test piece is obtained.

[0055] In step 3 of the embodiment of the present invention, the following two placement methods can be used:

[0056] Placement method 1 is used to simulate the air intake method on the top of a helicopter. The test piece is placed horizontally on the turntable bracket in the radar darkroom, and the air intake grille surface faces the incident direction of the radar wave. The radar wave is incident horizontally, the radar azimuth angle is -30°~30°, and the step angle of the point frequency test is 0.1°.

[0057] Placement method 2 is used to simulate the air intake method on both sides of the helicopter. The test piece is placed sideways on the turntable bracket of the radar darkroom, and the air intake grille surface faces the incident direction of the radar wave. The radar wave is incident horizontally, the radar wave azimuth angle is 0°~30°, and the step angle of the point frequency test is 0.1°.

[0058] like Figure 3 As shown, it is a schematic diagram of the RCS test method of the straight cavity air intake duct model in an embodiment of the present invention; Figure a illustrates placement method 1, and Figure b illustrates placement method 2.

[0059] An embodiment of the present invention provides a design method for an electromagnetic shielding air intake grille. In view of the complex appearance of helicopters and the stronger radar scattering characteristics, taking a conventional square grille as an example, the grille parameters include grille hole size, grille normal thickness, grille tangential thickness, and grille surface inclination angle; the design method provided by the present invention establishes a set of straight cavity air intake duct models with different grille parameters, and calculates the RCS of this set of models in simulation software, thereby considering the influence of different grille parameters on the electromagnetic shielding effect of the air intake grille. In addition, this set of straight cavity air intake duct models is easy to implement, and test pieces can be quickly manufactured by 3D printing, and tested in a radar darkroom, and then the simulation calculation results are verified by experimental results. The design method provided by the present invention has the following beneficial effects:

[0060] First, due to the limitation of structure and appearance, the RCS index of helicopter is generally much higher than that of fixed wing, so the proportion of helicopter air inlet in the whole aircraft RCS index will also be lower than that of fixed wing; if the whole aircraft model is established for simulation or experiment according to the traditional method, not only the modeling is difficult and the feasibility is poor, but also the influence of the change of air inlet grille parameters on the whole aircraft RCS will be difficult to reflect, and it is difficult to intuitively and effectively examine the influence of changing grille parameters on the electromagnetic shielding effect of the grille; the method of the present invention establishes an independent straight cavity air inlet model, and the influence of the change of a single grille parameter on the electromagnetic shielding effect of the grille can be examined by the control variable method;

[0061] Second, the design method provided by the present invention equivalently examines the electromagnetic shielding effect of the grid by simulating and testing the radar cross section of the established straight cavity inlet model; if the model RCS is small, it means that most of the radar waves irradiated on the grid are reflected, and a small part passes through the grid into the cavity, that is, the grid reflectivity is high, and the grid electromagnetic shielding effect is better, otherwise it means that the grid electromagnetic shielding effect is worse;

[0062] Third, the straight cavity air intake model established in the present invention is easy to implement, and the test piece can be quickly manufactured by 3D printing, thus shortening the research and development cycle;

[0063] Fourthly, the present invention only needs to manufacture one set of test pieces during the test phase, and by changing the placement of the test pieces, two common helicopter air inlet layouts, namely, helicopter top air intake and helicopter side air intake, are simulated, thereby reducing R&D costs.

[0064] The following is a schematic illustration of the implementation of the design method of the electromagnetic shielding air intake grille provided by the present invention through an implementation example.

[0065] Implementation Example

[0066] The design method of the electromagnetic shielding air intake grille provided in this implementation example includes the following steps:

[0067] Step 1: A set of straight cavity inlet duct models with different grille parameters were established, a total of 12; their composition is shown in Table 1. The cavity cross-sectional size is 200mm*200mm, the cavity length is 800mm, the cavity thickness is 2mm, the cavity bottom is closed, and the front of the cavity is a grille bevel with square openings, such as Figure 2 shown.

[0068] The main difference between the models with different grille parameters lies in the grille parameters of the oblique section of the front of the cavity. The grille parameters mainly include: grille hole size a, tangential grille thickness b, normal grille thickness c, and grille surface inclination angle α.

[0069] Table 1 Test piece grid parameters

[0070]

[0071] The above 12 groups of grid parameters are set using the control variable strategy:

[0072] 1~6, b~α are the same, a is a variable;

[0073] 2, 7, 8, b is a variable;

[0074] 2, 9, 10, c is a variable;

[0075] 2, 11, 12, α is a variable.

[0076] Step 2: In the simulation stage, after the CATIA modeling is completed, each model is meshed using Hypermesh software. The RCS simulation calculation uses FEKO software, the mesh model is imported into FEKO software, and the simulation parameters are set as follows:

[0077] The simulation algorithm adopts the multi-layer fast multipole (MLFMM) algorithm. The incident radar wave is set to a plane wave (simulating the incident radar wave incident from an infinitely far position), and the radar wave receiving mode is set to the far-field condition (simulating the radar wave incident from an infinitely far position and reflected to an infinitely far position). The radar wave frequency is set to 10 GHz, and the polarization mode of the radar wave is set to horizontal polarization (the fine cavity is more sensitive to horizontally polarized radar waves). The direction along the cavity is set to 0°, the incident angle is set to -30°~30°, and the step angle is 0.1°.

[0078] like Figure 3 Schematic diagram of the RCS test method of the straight cavity inlet model shown in FIG. Figure 3 Arrangement 1 shown in Figure a is used to simulate the air intake on the top of the helicopter, with the radar wave incident horizontally at an azimuth angle of -30°-30°; Arrangement 2 shown in Figure b is used to simulate the air intake on both sides of the helicopter. Since one side of the helicopter air intake is usually close to the fuselage and blocked by the fuselage, it cannot be illuminated by the radar wave. It is only necessary to examine the radar wave incident at an azimuth angle of 0°-30°.

[0079] Step three, verify the simulation results;

[0080] The simulation results are as follows: Taking test pieces 1 to 6 and placement 2 as an example, the RCS value of each model as the incident angle of the radar wave changes is obtained through simulation calculation, and a curve with the horizontal axis as the incident angle and the vertical axis as the RCS is generated based on the data. Figure 4 As shown, Figure 4 This is a schematic diagram of the RCS curve obtained by simulating the test pieces 1 to 6 in the arrangement mode 2 in the implementation example of the present invention. Figure 5 Schematic diagram of RCS curves obtained by testing test pieces 1 to 6 in placement mode 2 in an embodiment of the present invention.

[0081] Reference Figure 4 and Figure 5 Comparison of the RCS curves obtained by simulation and test shows the following conclusions:

[0082] Compared with simulation, the data obtained from the test is more real and reliable. Although there are differences, the general trend is consistent, which is reflected in that as the grille hole size a continues to decrease, the smaller the RCS of the test piece, that is, the better the electromagnetic shielding effect of the grille.

[0083] Since specimen 5 has no grille, its RCS is the largest.

[0084] Since it is impossible to seal the air inlet of test piece 6 in actual application, it is only used as a comparative test under ideal conditions.

[0085] By comparing the simulation results of test pieces 1 to 4, it can be found that as the grid hole size a continues to decrease, the smaller the RCS of the test piece, that is, the better the electromagnetic shielding effect of the grid.

[0086] The RCS of test pieces 3 and 4 is quite different from that of test pieces 1 and 2, indicating that when the grid hole size a is greater than 8 mm, the electromagnetic shielding of the grid is poor, and the electromagnetic shielding effect of the grid must be improved by further reducing the grid hole size a.

[0087] The RCS of test pieces 1 and 2 are relatively close, indicating that when the grid hole size a is reduced to 5 mm, it can basically meet the electromagnetic shielding requirements. Continuing to reduce the grid hole size a has little significance for improving the electromagnetic shielding effect of the grid.

[0088] In this implementation example, the control variable method is used to reasonably set the test piece grid parameters, and the influence of four grid parameters on the grid electromagnetic shielding effect is comprehensively examined. By comparing the experimental data of test pieces 1-6, the influence of the grid hole size can be examined; by comparing the experimental data of test pieces 2, 7, and 8, the influence of the tangential grid thickness can be examined; by comparing the experimental data of test pieces 2, 9, and 10, the influence of the normal grid thickness can be examined; by comparing the experimental data of test pieces 2, 11, and 12, the influence of the grid surface inclination angle can be examined.

[0089] The design method provided by the embodiment of the present invention, on the one hand, establishes a separate straight cavity air inlet model; its simulation and test results are universal and not affected by the fuselage structure;

[0090] On the other hand, by calculating and testing the radar cross section of the established straight cavity inlet model, the effect of the change of the grid parameters on the grid reflectivity and electromagnetic shielding effect is equivalently investigated.

[0091] On the other hand, by changing the placement of the test pieces, two common helicopter air intake layouts, top air intake and side air intake, are simulated.

[0092] Although the embodiments disclosed in the present invention are as above, the contents are only embodiments adopted to facilitate understanding of the present invention and are not intended to limit the present invention. Any technician in the field to which the present invention belongs can make any modifications and changes in the form and details of implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A design method for an electromagnetic shielding air intake grille, characterized in that: include: Step 1, establishing a group of straight cavity air intake models, each model in the group of straight cavity air intake models has different grille parameters; Step 2, calculating the radar cross section RCS of each model in the set of straight cavity air intake models in the simulation software, so as to obtain the electromagnetic shielding effect of different grille parameters on the air intake grille, that is, the RCS value of each model changing with the incident angle of the radar wave; Step 3: manufacture test pieces for each model in this set of straight cavity air inlet models, conduct RCS test on each model in a radar darkroom, and then verify the simulation calculation results through the RCS test results.

2. The design method of the electromagnetic shielding air intake grille according to claim 1, characterized in that: The straight cavity air intake model established in step 1 includes: an air intake cavity and an air intake grille located at the air intake port; the bottom surface of the air intake cavity is closed, and the inclined port formed by the front air intake port is provided with an air intake grille.

3. The design method of the electromagnetic shielding air intake grille according to claim 2, characterized in that: In step 1, the grille parameters of each straight cavity air intake model established include: Grid hole size a, in-plane grid thickness b, normal grid thickness c, grid surface inclination α; In the step 1, a control variable strategy is used to design grille parameters corresponding to multiple straight cavity air intake duct models.

4. The design method of the electromagnetic shielding air intake grille according to claim 1, characterized in that: The step 2 comprises: Each model in a set of straight cavity inlet duct models that have been completed is meshed, and each mesh model that has completed meshing is imported into the simulation software, and RCS simulation calculation is performed on each model by setting the simulation parameters of the simulation software.

5. The design method of the electromagnetic shielding air intake grille according to claim 4, characterized in that: The simulation parameters in step 2 are set as: The simulation algorithm adopts the multi-layer fast multipole (MLFMM) algorithm. The incident radar wave is set to a plane wave to simulate the incident radar wave from an infinitely far position. The radar wave receiving mode is set to the far-field condition to simulate the radar wave incident from an infinitely far position and reflected to an infinitely far position. The radar wave frequency is set to 10 GHz, the polarization mode of the radar wave is set to horizontal polarization, the direction along the cavity is set to 0°, the radar wave incident angle is set to -30°~30° and 0°~30°, and the step angle of the point frequency test is 0.1°.

6. The design method of the electromagnetic shielding air intake grille according to claim 1, characterized in that: The step 3 comprises: Step 31, using 3D printing to manufacture a test piece of a model corresponding to each set of grid parameters; Step 32, each test piece is placed on a turntable bracket in a radar darkroom in two placement methods to perform a point frequency RCS test, and a set of RCS values ​​varying with the incident angle corresponding to each placement method of each test piece is obtained.

7. The design method of the electromagnetic shielding air intake grille according to claim 6, characterized in that: In step 3, Placement method 1 is used to simulate the air intake method on the top of a helicopter. The test piece is placed horizontally on the turntable bracket in the radar darkroom, and the air intake grille surface faces the incident direction of the radar wave. The radar wave is incident horizontally, the radar azimuth angle is -30°~30°, and the step angle of the point frequency test is 0.1°.

8. The design method of the electromagnetic shielding air intake grille according to claim 6, characterized in that: In step 3, Placement method 2 is used to simulate the air intake method on both sides of the helicopter. The test piece is placed sideways on the turntable bracket of the radar darkroom, and the air intake grille surface faces the incident direction of the radar wave. The radar wave is incident horizontally, the radar wave azimuth angle is 0°~30°, and the step angle of the point frequency test is 0.1°.

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