All-metallic electromagnetic absorbing structure for eliminating the influence of multipath effects on a directional beacon system

Abstract

The application discloses a full-metal electromagnetic absorption structure for eliminating the influence of multipath effect on a course beacon system, and belongs to the technical field of aviation.The full-metal electromagnetic absorption structure comprises a metal back plate, an intermediate air layer and an upper resonant layer which are arranged in layers from bottom to top; the upper resonant layer is composed of periodically arranged resonant units; each resonant unit is composed of four square metal radiation patches with fan-shaped hollows; the outer ring of each square metal radiation patch is connected by a lumped capacitance element, and the internal cross structure is connected by a lumped resistance element; each resonant unit is provided with a first pin interface at each corner, and a second pin interface is arranged at the center of each resonant unit, wherein the pins at the four corners of each unit are connected with the metal back plate through a metal column.The full-metal electromagnetic absorption structure solves the problem that the course beacon system is subjected to multi-angle and multi-direction interference signal incidence in a complex multi-obstacle environment, and effectively eliminates the influence of multipath effect on the course beacon system.

Description

Technical Field

[0001] This invention belongs to the field of aerospace technology, specifically relating to an all-metal electromagnetic absorption structure that eliminates the influence of multipath effects on the heading beacon system. Background Technology

[0002] With the development of my country's civil aviation industry, more and more airports are being built, and many existing airports are undergoing upgrades and renovations. Both new and renovated airports face challenges such as increased building density and a more complex electromagnetic environment around them. The Instrument Landing System (ILS) is the most widely used precision approach and landing guidance system for aircraft. It guides aircraft to a safe landing by radiating specific waveforms through the localizer system. However, buildings, tall trees, control towers, and uneven ground near the runway can cause multipath reflections of navigation signals. Multipath reflections distort the antenna radiation pattern, affecting the accuracy of navigation information. In fact, as airport functions and services continue to upgrade and improve, more building space is needed. The demand for new building complexes near runways is constantly increasing. However, building complexes near runways poses a significant challenge to flight safety. This is because buildings close to the runway and the localizer system are prone to large-angle reflections between the localizer signal and the buildings, exacerbating the complexity of multipath effects. Therefore, suppressing or eliminating the multipath effects caused by the terrain and features around the airport runway, especially the impact on the electromagnetic environment of the localizer system under large angle incidence conditions, is of great significance for ensuring flight safety and maximizing the development of airport space resources.

[0003] Microwave absorbers are a commonly used method for eliminating or suppressing electromagnetic interference. Compared with traditional absorbers, artificial electromagnetic absorption structures based on subwavelength structures offer significant advantages, including thinner thickness, wider bandwidth, higher absorption, and greater flexibility. In existing technologies, by designing the shape, size, and combination of artificial electromagnetic absorption structure units, their equivalent dielectric constant and permeability can be controlled, achieving near-uniform absorption efficiency across very small or very wide frequency bands. It is worth noting that metamaterials, as subwavelength structures, exhibit a certain correlation between their size and operating wavelength. For heading beacon signals, the operating frequency is 108MHz-112MHz, corresponding to a wavelength of approximately 2.7 m. Therefore, reducing material thickness and designing ultra-thin unit structures is a primary challenge for the engineering application of metamaterial microwave absorbers in this frequency band. Furthermore, considering the complexity of the terrain and features surrounding airport runways, absorbers used at airports need to maintain good absorption characteristics under different incident angles. Additionally, when applied to building surfaces, the absorbers will operate in outdoor environments, facing various extreme temperatures. Therefore, metamaterial absorbers used for multipath effects caused by the terrain around airport runways also need to have good environmental adaptability.

[0004] Using high-refractive-index media such as barium titanate, rutile, and magnetic material composites as substrates is beneficial for miniaturizing metamaterial absorbers. However, non-magnetic high-dielectric materials, when used as metamaterial substrates, cause a severe narrowing of the absorption peak of the absorber, making it difficult to meet practical requirements. Furthermore, compared to traditional dielectric materials such as FR4 and PTFE, the introduction of magnetic dielectric substrates significantly increases manufacturing costs. In addition, since the relative permeability of most dielectric materials is relatively low in the microwave band, the miniaturization effect achieved by this approach is extremely limited. The combination of dielectric substrates and distributed electronic components offers advantages such as low processing costs, dynamic tunability, and ultra-thin structures. However, low-cost dielectric substrates are significantly affected by environmental factors, making them difficult to meet the practical application requirements of airports. Summary of the Invention

[0005] In response to the unique working conditions of airports, this invention proposes a low-profile all-metal electromagnetic absorption structure to eliminate the impact of multipath effects on the localizer system. By employing an all-metal resonant unit with integrated lumped elements, a high-performance all-metal electromagnetic absorption structure for eliminating the impact of multipath effects on the localizer system is obtained.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The all-metal electromagnetic absorption structure provided by the present invention for eliminating the influence of multipath effects on the heading beacon system includes a metal back plate, an intermediate air layer and an upper resonant layer stacked from bottom to top;

[0008] The upper resonant layer is composed of periodically arranged resonant units, each of which consists of four fan-shaped hollow square metal radiating patches. The four fan-shaped hollows form a cross structure. The outer ring of each square metal radiating patch is connected by lumped capacitor elements, and the inner cross structure is connected by lumped resistor elements. A first pin interface is provided at each of the four corners of the resonant unit, and a second pin interface is provided at the center of the resonant unit. The pins at the four corners of the unit are connected to the metal back plate through metal pillars.

[0009] The square metal radiating patch is divided into four equally sized 90° sector-shaped cutouts, with each sector's 90° right angle pointing towards the center of the absorbing structure unit; the spacing between the 90° sectors is related to the required absorption frequency.

[0010] The square metal radiating patch is made of a copper plate with high conductivity.

[0011] Furthermore, the lumped capacitor element is located at the center of the outer unit side of the square metal radiating patch, and the outer ring of the radiating patch forms a resonant current path.

[0012] Furthermore, the lumped resistor element is located at 1 / 3 of the diagonal length of the square metal radiating patch, connecting the inner cross structure of the square metal radiating patch to the outer ring. The position of the lumped resistor element is related to the resonant frequency and the absorption efficiency.

[0013] Furthermore, the intermediate air layer contains four circular metal pillars located at the four corners of the resonant unit, with their tops connected to the upper resonant layer and their bottoms connected to a metal backplate. The radius of the metal pillars is related to the absorption frequency and absorption efficiency; the radius of the metal pillar with the optimal absorption efficiency is selected during the design process.

[0014] Furthermore, the side length of the periodic resonant unit is much smaller than the wavelength related to the operating frequency band of the resonant unit, approximately 0.014. λ 0 ( λ 0 represents the wavelength corresponding to the operating frequency band, satisfying the metamaterial periodic unit size condition.

[0015] Furthermore, the thickness of the periodic resonant unit is 13.14 mm (approximately 0.0048 mm). λ 0), achieving the low profile characteristics of the absorption unit in the VHF band where the heading beacon system is located, which is helpful for practical engineering applications.

[0016] This invention incorporates a metal backplate at the bottom of the absorbing structure as a total internal reflection mirror to prevent the transmission of input electromagnetic waves. The absorbing structure is supported by metal pillars. A dielectric equivalent circuit model is used to find the equivalent impedance of the absorbing structure and the characteristic impedance of the surrounding environment. Z The perfect match of 0 and the control relationship between it and the incident angle.

[0017] When electromagnetic waves are obliquely incident on an absorbing structure, the polarization can be divided into perpendicular polarization (TE polarization) and parallel polarization (TM polarization). The relationship between the electric and magnetic field vector directions and the stealth structure under TE and TM polarization is as follows: θ Indicates the angle of incidence. k 0 represents the propagation direction of the plane wave, and E and H represent the electric and magnetic field vectors of the incident wave, respectively. The relationship between the directions of the electric and magnetic field vectors under TE and TM polarization and the absorbing structure is as follows: Figure 1 As shown. Treating the medium as a uniform transmission line, its ABCD matrix is ​​as follows:

[0018]

[0019] in

[0020]

[0021]

[0022] Where f is the frequency, j is the imaginary unit, and d n where c is the material thickness and c is the grating. Since it's an air layer, it's approximately equal to 1. When... As the angle increases, it approaches 90°, and the TE polarization... Z n The gradual increase in TE polarization leads to a gradual mismatch and a gradual decrease in absorption efficiency, while the TM polarization... Z n As the angle of incidence increases, it gradually approaches... Z 0, achieving perfect matching with the characteristic impedance of the surrounding environment, thereby achieving perfect absorption.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The all-metal electromagnetic absorption structure proposed in this invention eliminates the influence of multipath effects on the heading beacon system, which can be adjusted by changing the incident angle of electromagnetic waves. θ The absorption efficiency of electromagnetic waves with different linear polarizations at 112 MHz was adjusted. For TE polarization, the absorption rate decreased with increasing incident angle. For TM polarization, the absorption efficiency gradually increased with increasing incident angle. For TM incident angles, the absorption efficiency exceeded 90% when the incident angle was greater than 70°. This excellent absorption efficiency at large incident angles solves the problem of multi-angle and multi-directional interference signals encountered by the heading beacon system in complex multi-obstacle environments, and can effectively eliminate the impact of multipath effects on the heading beacon system.

[0025] 2. The all-metal electromagnetic absorption structure proposed in this invention for eliminating the influence of multipath effects on the heading beacon system, under circularly polarized incident conditions, achieves a circular polarization conversion efficiency that gradually increases to 52% at 112 MHz by adjusting the oblique incident angle. This demonstrates that, under circularly polarized incident conditions, this invention can control the circular polarization operating mode of the structure by adjusting the oblique incident angle, thus meeting the application requirements of VHF circularly polarized multimode operation.

[0026] 3. The all-metal metamaterial absorbing structure proposed in this invention, compared to other absorbing structures, is fabricated entirely from metal, eliminating the intermediate dielectric layer. This not only reduces processing costs but also provides a high power capacity characteristic that is difficult to achieve with other metamaterial absorbing structures. Furthermore, because the absorbing structure used in this invention is fabricated entirely from metal, it exhibits higher stability compared to other absorbing structures that use non-magnetic high-dielectric materials and microwave substrate fabrication.

[0027] 4. The thickness of the all-metal metamaterial absorbing structure proposed in this invention is 13.14 mm (approximately 0.0048 mm). λ 0) achieves the low profile characteristics of the absorption unit, which facilitates conformal application in complex environments and effectively improves the overall system compactness. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the polarization mode.

[0029] Figure 2 This is a schematic diagram of the structural units of an embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram of a multi-period array according to an embodiment of the present invention.

[0031] Figure 4 This is a side view of a structural unit according to an embodiment of the present invention.

[0032] Figure 5(a) is a schematic diagram of the incident angle adjustment for TE absorption efficiency.

[0033] Figure 5(b) is a schematic diagram of the incident angle adjustment for TM absorption efficiency.

[0034] Figure 6 This is a schematic diagram illustrating the effect of incident modulation on circular polarization conversion efficiency.

[0035] The names corresponding to the reference numerals in the attached figures are:

[0036] Among them, 1-metal backplate, 2-intermediate air layer, 3-upper resonant layer, 4-square metal radiating patch, 5-fan-shaped cutout, 6-metal pillar, 7-pin No. 1 interface, 8-pin No. 2 interface, 9-lumped capacitor element, and 10-lumped resistor element. Detailed Implementation

[0037] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0038] As attached Figure 2-4 As shown, the all-metal electromagnetic absorption structure proposed in this embodiment for eliminating the influence of multipath effects on the heading beacon system adopts an all-metal structure different from the existing wave-absorbing structures. The all-metal electromagnetic absorption structure of the present invention includes a metal back plate 1, an intermediate air layer 2, and an upper resonant layer 3 stacked from bottom to top.

[0039] The upper resonant layer 3 is composed of four square metal radiating patches 4 with four equally sized fan-shaped cutouts 5. The four fan-shaped cutouts 5 of the square metal radiating patches 4 are rotationally symmetrical and separated by metal rectangular strips. The corner of each fan-shaped cutout 5 points to the center of the wave-absorbing structure unit.

[0040] As a preferred embodiment, the angle of the fan-shaped cutout 5 is 90°, and the 90° right angle of each fan-shaped cutout 5 points to the center of the wave-absorbing structure unit.

[0041] The resonant unit has a first pin interface 7 at each of its four corners and a second pin interface 8 at its center.

[0042] The upper resonant layer 3 and the metal backplate 1 are connected vertically and vertically to the four corners of the wave-absorbing structure unit via metal pillars 6 located in the middle air layer 2. The metal pillars 6 around the perimeter are connected to pins to form a resonant current path.

[0043] The upper resonant layer 3 can be obtained by directly processing the metal material. Compared with other microwave absorbing structures based on dielectric substrates, this invention does not require chemical etching, the materials are inexpensive, and the processing cost of the microwave absorbing structure is greatly reduced.

[0044] The choice of intermediate air layer 2 was obtained through analysis using the equivalent medium theory. When choosing air as the intermediate medium, the incident angle can be used to determine the equivalent medium. Z n By controlling the process, the matching between the absorbing structure and the surrounding environment can be effectively regulated, thereby achieving the goal of controlling the absorbing efficiency of the absorbing structure.

[0045] The metal backplate 1 and the intermediate air layer 2 are both 30.5mm × 30.5mm in size, and the thickness of the air layer is 13.14mm, which is 4.8 per thousand of the working wavelength.

[0046] The upper resonant layer 3 is formed into a periodic pattern with a specific unit shape in this invention through metal processing. The square metal radiating patch 4 of the upper resonant layer 3 is rectangular with an aspect ratio of 1, and the size of the fan-shaped cutout 5 is related to the resonant frequency. A schematic diagram of the structural unit in this embodiment is shown below. Figure 2 As shown.

[0047] The square metal radiating patch 4 is a rectangular metal patch with dimensions of 29.5 mm × 29.5 mm × 0.035 mm and an aspect ratio of 1. The radius of the 90° circular fan-shaped cutout is 11.46 mm. The cross structure between the four circular fan-shaped cutouts 5 is composed of metal rectangular strips, with each metal rectangular strip being 2 mm wide.

[0048] The diameter of each of the four No. 1 pin interfaces is 2.43 mm, and the height is 1.5 mm; the diameter of the No. 2 pin interface is 1.6 mm, and the height is 1 mm. The four No. 1 pin interfaces are located at the four corners, each 1.55 mm from the four sides of the square metal radiating patch.

[0049] The four metal pillars 6 are located 1.55 mm away from the four corners of the metal back plate 1, and their radii are 1.6 mm.

[0050] The lumped capacitor element 9 is a 1080 48pF metal film chip capacitor. The lumped capacitor element 9 is soldered to the outside of the square metal radial patch 4 and is used to connect the upper metal resonant layer 3 into an LC resonant circuit.

[0051] The lumped resistor element 10 is a CR1812F105RE04Z, 1.5Ω metal film chip resistor, used to adjust the absorption efficiency of the absorbing structure.

[0052] The high-power all-metal metamaterial absorbing structure proposed in this invention was analyzed by full-wave electromagnetic simulation using the commercial electromagnetic simulation software CST. The absorbing structure unit was set as a periodic boundary around its perimeter, and the upper and lower ports adopted the Floquet port mode to obtain the S-parameter curves of the absorbing structure.

[0053] Its absorption efficiency is shown in Figures 5(a) and 5(b). The polarization mode of the incident electromagnetic wave and the incident angle of the incident wave are changed respectively. θ The influence of incident angle on absorption efficiency of the absorbing structure was analyzed for 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, and 80°. Simulation results show that under TE polarized incident angle, the absorption efficiency gradually decreases by 14.1% from 58.9% to 98.6% as the incident angle gradually increases; while under TM polarized incident angle, the absorption efficiency gradually increases from 58.9% to 98.6% as the incident angle gradually increases.

[0054] The above results demonstrate that the absorbing structure of this invention can control the absorption efficiency of different polarizations under both TE and TM polarization modes by adjusting the oblique incident angle. The control effect is most significant at 112 MHz, while the control range and absorption efficiency of TM polarization are slightly better than those of TE polarization. The absorption frequency and absorption efficiency of the absorbing structure can be adjusted by controlling the key geometric parameters of the absorbing structure. These geometric parameters include the radius of the circular fan cutout, the radius of the metal column, and the electrical parameters of the lumped element.

[0055] As attached Figure 6 As shown, the polarization of the incident wave is changed to circular polarization, and the incident angle of the incident wave is set separately. θ The electromagnetic performance of the absorbing structure under circularly polarized oblique incidence was observed at angles of 0°, 10°, 20°, 30°, 40°, 50°, 60°, 70°, and 80°. Simulation results show that as the incident angle increases, the absorbing structure gradually exhibits circular polarization conversion functionality; furthermore, the circular polarization conversion efficiency gradually increases with increasing angle, rising from 0 to 52.1% at 112 MHz. These results demonstrate that the absorbing structure of this invention can control the polarization conversion efficiency of circularly polarized wave incident incident by adjusting the incident angle.

[0056] The simulation results above demonstrate that the high-power all-metal metamaterial absorbing structure proposed in this invention has the function of adjusting the linearly polarized wave (TE / TM) polarization absorption efficiency by adjusting the incident angle in the VHF band. Furthermore, the proposed high-power all-metal metamaterial absorbing structure also has the function of converting the incident wave into a circularly polarized wave. In addition, since this absorbing structure uses an all-metal material, its processing cost and power capacity are significantly optimized compared to other absorbing structures. Any changes to the parameters mentioned in this invention, as well as the design shape of the various resonant structures, fall within the scope of protection of this invention.

Claims

1. An all-metal electromagnetic absorption structure for eliminating the influence of multipath effects on a heading beacon system, characterized in that, It includes a metal back plate (1) stacked from bottom to top, an intermediate air layer (2) and an upper resonant layer (3); The upper resonant layer (3) is composed of periodically arranged resonant units. Each resonant unit is composed of a square metal radiating patch (4) with four fan-shaped cutouts (5). The four fan-shaped cutouts (5) form a cross structure. The outer ring of the square metal radiating patch (4) is connected by a lumped capacitor element (9), and the inner cross structure is connected by a lumped resistor element (10). The four corners of the resonant unit are respectively provided with a first pin interface (7), and the center of the resonant unit is provided with a second pin interface (8). The pins at the four corners of the unit are connected to the metal back plate (1) through metal pillars. The lumped capacitor element (9) is located in the center connection direction of the outer unit side length of the square metal radiating patch (4), and the outer ring of the square metal radiating patch (4) forms a resonant current path. The side length of the resonant unit is 0.

014. λ 0, unit thickness is 0.0048 λ 0, λ 0 represents the wavelength corresponding to the operating frequency band.

2. The all-metal electromagnetic absorption structure for eliminating the influence of multipath effects on the heading beacon system according to claim 1, characterized in that, The square metal radiation patch (4) is hollowed out by four equally sized 90° fan-shaped cutouts, and the 90° right angle of each fan-shaped cutout points to the center of the resonant unit.

3. The all-metal electromagnetic absorption structure for eliminating the influence of multipath effects on the heading beacon system according to claim 1 or 2, characterized in that, The square metal radiation patch (4) is made of a copper plate with high conductivity.

4. The all-metal electromagnetic absorption structure for eliminating the influence of multipath effects on the heading beacon system according to claim 1, characterized in that, The lumped resistor element (10) is located at 1 / 3 of the diagonal length of the square metal radiating patch (4), connecting the internal cross structure to the outer ring of the square metal radiating patch (4).

5. The all-metal electromagnetic absorption structure for eliminating the influence of multipath effects on the heading beacon system according to claim 4, characterized in that, The intermediate air layer (2) is provided with four circular metal pillars (6), which are located at the four corners of the resonant unit. The top of the circular metal pillars (6) is connected to the upper resonant layer (3), and the bottom is connected to the metal back plate (1).

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