A low scattering characteristic radar infrared composite radome system

Abstract

The present invention proposes a low-scattering characteristic radar infrared composite radome system, comprising a composite material radome (including FSS), an optical window (including metal grid FSS), and an optical window mounting interface. Through the integrated design of the composite material radome and FSS structure, the optical window and metal grid FSS structure, the optical window mounting interface, etc., the radar in-band transmission, out-of-band shielding effect and infrared working band wave transmission characteristics are solved, the wave transmission difficulty and strong scattering echo problems caused by the discontinuity of the material, structure and thickness of the radome are overcome, the wave transmission performance of the radar infrared composite radome is improved, and its RCS is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of low-scattering radomes, and in particular relates to a radar infrared composite radome system with low-scattering characteristics. Background Art

[0002] The radar infrared composite radome must first take into account the high wave transmittance performance of both radar and infrared working bands to meet the requirements of use; secondly, outside the working band, it is required to have shielding properties and use its shape to reflect enemy detection signals to non-threatening corners to improve the aircraft's penetration capability.

[0003] The commonly used RCS reduction measure for radomes is frequency selective surface (FSS) technology, that is, designing an FSS with bandpass filtering characteristics on the inner surface, outer surface or interlayer of the radome to achieve in-band wave transmission and out-of-band reflection, and using the shape of the radome to deflect threat waves to the non-threat angle area, thereby achieving forward RCS reduction.

[0004] At present, the research on RCS reduction technology of radar / infrared composite radome is mainly focused on the low RCS design of optical windows. For example, the patents "High Performance Radar / Infrared Dual-Band Bandpass Frequency Selective Surface" (application number: 201310385578.9) and "Radar / Infrared Dual-Band Bandpass Frequency Selective Surface" (application number: 201310385579.3) only describe the design of a metal grid frequency selective surface (FSS) with infrared transparency, radar in-band transmission, and out-of-band shielding characteristics on the MgF2 window. Since the above scheme does not consider the influence of the installation mechanism, the discontinuity in material, structure, and thickness will inevitably cause inconsistency in electromagnetic wave transmission performance during specific application, causing the radar antenna radiation pattern to be distorted, the sidelobe level to be raised, the aiming error to surge, and the forward RCS to increase, which brings major difficulties to the application of radar infrared composite radomes and greatly restricts their comprehensive performance. Summary of the invention

[0005] The purpose of the present invention is to propose a low-scattering characteristic radar infrared composite radome system, to improve the wave transmission and RCS reduction performance of the radar infrared composite radome, and to overcome the wave transmission difficulties and scattered echo enhancement problems caused by the discontinuity of the material, structure and thickness of the radome.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A low-scattering characteristic radar infrared composite radome system, the radome is composed of a composite material radome, an optical window, a composite material gasket, and a composite material bolt, and the optical window is fixed between the composite material radome and the composite material gasket by the composite material bolts, and the outer surface is kept flush; the composite material radome contains an FSS layer, and the outer surface of the optical window is plated with a metal grid FSS; the dielectric constant of the composite material radome is the same as or close to that of the optical window material in the radar working band; the dielectric constants of the composite material gasket, the composite material bolt and the composite material radome are the same or made of the same material; the electrical thickness of the composite material radome in the radar working band differs from that of the optical window by an integral multiple of half the wavelength of the radar working frequency.

[0008] Preferably, the composite material cover FSS and the optical window metal grid FSS have the same shape and are made of the same type of conductive material.

[0009] Preferably, when the optical window is plated with the metal grid FSS, a circle of metal electrodes with a width of 0.1 to 5 mm is prepared at the edge of the FSS to ensure the electrical continuity of the entire radome, increase the shielding effect of the metal grid FSS, and reduce RCS.

[0010] Preferably, the optical window material is magnesium fluoride with a dielectric constant of 4 to 5, and the composite material cover is made of fiberglass with a dielectric constant of 4 to 5.

[0011] Preferably, when the electrical thickness of the optical window is N times the half wavelength of the radar operating frequency, N is an integer, and the electrical thickness of the composite material cover is also designed to be N times the half wavelength of the radar operating frequency.

[0012] Preferably, the optical window installation interface structure has the following technical features:

[0013] The thickness of the optical window at the interface changes gradually, and its changing rule is as follows: at the edge of the optical window, its thickness decreases from the thickness d1 in the middle of the window to the minimum thickness d4 at the edge along the window plane direction, and it is required that the surface of the window material at the edge is perpendicular to the middle of the window; the size edge of the optical window is formed between the thickness d1 and the thickness d4, and on the section perpendicular to the edge, the edge includes an outer surface transition line with a width of L1 and an inner surface transition line with a width of L2; wherein, the angle a between the outer surface transition line with a width of L1 and the outer surface of the cover is 100 degrees to 160 degrees, the angle b between the inner surface transition line L2 and the inner wall of the cover is 110 degrees to 180 degrees, and the maximum width of the L2 part does not exceed 3 times the thickness of the cover wall;

[0014] The maximum thickness of the cover material is equal to d2, the thickness difference between d2 and d1 is d6, and d2>d1, d6<3mm, the step formed by the thickness difference d6 on the cover is required to be retained on the inner surface, and the width L4 of the area with thickness d6 is 0-10mm; the composite cover at the interface position is tightly matched with the optical cover on the edge where the lengths of L2, L4 and d4 are located; the composite cover and the optical head cover are required to remain flush on the outer surface; at the same time, at the interface of the composite cover, the sunken space with unequal thickness to the outer surface transition line L1 is used for the installation of the composite gasket; the composite gasket is in close contact with the optical window in the outer surface transition line L1 area, and its outer surface is flush with the optical window and the composite cover, and the gasket width is L3>15mm;

[0015] A threaded hole of L3 size is opened in the middle of the gasket, and a composite material bolt is installed in the threaded hole.

[0016] Preferably, the optical window installation interface structure:

[0017] The thickness of the optical window at the interface changes gradually, and its changing rule is as follows: at the edge of the optical window, its thickness decreases from the thickness d1 in the middle of the window to the minimum thickness d4 at the edge along the window plane direction, and it is required that the surface of the window material at the edge is perpendicular to the middle of the window; the size edge of the optical window is formed between the thickness d1 and the thickness d4, and on the section perpendicular to the edge, the edge includes an outer surface transition line with a width of L1 and an inner surface transition line with a width of L2; wherein, the angle a between the outer surface transition line with a width of L1 and the outer surface of the cover is 100 degrees to 160 degrees, the angle b between the inner surface transition line L2 and the inner wall of the cover is 110 degrees to 180 degrees, and the maximum width of the L2 part does not exceed 3 times the thickness of the cover wall;

[0018] The maximum thickness of the cover material is equal to d2, the thickness difference between d2 and d1 is d6, and d2>d1, d6<3mm, and the step formed by the thickness difference d6 on the cover is required to be retained on the inner surface, and the width L4 of the thickness d6 area is 0~10mm; the composite material gasket is installed on the inner surface of the composite material cover; the composite material cover at the interface position is required to fit tightly with the optical window on the edge where the lengths L1 and d4 are located, and the space of unequal thickness between the inner surface of the composite material cover and the transition line of the inner surface L2 and the d6 part is used for the installation of the composite material gasket; the composite material gasket includes the part where d6 is located, and is in close contact with the optical window in the inner surface transition line area and the d6 part, and the width of the gasket is L3+L4, where L3>15mm.

[0019] A threaded hole of L3 size is opened in the middle of the gasket, and a composite material bolt is installed at the threaded hole, so that the optical window, the composite material cover body and the composite material gasket at the interface are connected as a whole through the composite material bolt.

[0020] Working principle:

[0021] In order to meet the working requirements of radar and infrared systems at the same time, the radar infrared composite antenna cover needs to open a window on the aircraft that is transparent to both radar waves and infrared light. The main materials are generally magnesium fluoride, zinc sulfide, etc. At the same time, in order to take into account the normal transmission of one's own radar working band and reduce the echo of enemy detection radar, the conventional method is to apply FSS frequency selective surface on the composite cover and metal grid FSS on the optical window.

[0022] The weakness of conventional technical solutions is that the installation interface generally contains metal frames, gaskets, and bolts, which are strong scattering structures. After taking technical measures, its radar echo is still strong, and the radar echo at this time is mainly generated by the interface; therefore, the optical window and hood must be designed as an integrated system to control the above-mentioned working band out-of-band radar echo and be compatible with the working band radar transmission.

[0023] 1. In the composite cover part, the FSS structure is adopted to realize the bandpass filtering characteristics. Within its own working frequency band, electromagnetic waves are allowed to pass through, so that the antenna system can work normally. Outside the working frequency band, it has total reflection characteristics, and the streamlined shape of the cover is used to avoid enemy detection waves to non-threatening directions.

[0024] 2. In the radar / infrared common aperture window, the metal grid FSS design is adopted to achieve infrared transparency, radar band out-of-band shielding, and in-band transmission. Figure 2 Taking the metal grid FSS unit structure shown in the figure as an example, the metal grid structure with a sub-millimeter period and a micron-level line width reflects electromagnetic waves in the radar band and exhibits electromagnetic shielding characteristics, and transmits electromagnetic waves in the infrared and visible light bands and exhibits light transmission characteristics. Therefore, the metal grid structure can efficiently transmit infrared light while efficiently shielding radar waves; and transferring FSS technology to the metal grid design can achieve the effect of in-band transmission and out-of-band shielding in the radar band without affecting the infrared transparency characteristics.

[0025] 3. Integrate the FSS and the metal grid FSS and select the same type of FSS pattern to ensure that the entire head cover has similar resonance filtering characteristics and polarization characteristics.

[0026] 4. The composite cover (including FSS), radar / infrared common aperture window (including metal grid FSS), and window installation interface are designed in an integrated manner in terms of materials, structure, thickness, etc. to minimize the adverse effects caused by material and structural discontinuities.

[0027] Beneficial effects of the present invention:

[0028] The present invention proposes a low-scattering characteristic radar infrared composite radome system, which solves the problems of radar in-band transmission, out-of-band shielding effect and infrared working band wave transmission characteristics through integrated design of a composite material radome body (including FSS), an optical window (including metal mesh FSS), and an optical window mounting interface, and overcomes the wave transmission difficulties and scattered echo enhancement problems caused by the discontinuity of the material, structure, and thickness of the radome. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention has 2 drawings.

[0030] Figure 1 It is a schematic diagram of the radar infrared composite radome;

[0031] Figure 2 This is a schematic diagram of the radar infrared optical window installation interface.

[0032] 1 Composite material cover (including FSS); 2 Optical window (including metal grid FSS); 3 Optical window installation interface; 4 Optical window part (including metal grid FSS). 5 Composite material part of cover (including FSS); 6 Composite material gasket; 7 Bolts; DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0034] Embodiment 1:

[0035] The optical window material is a material with a dielectric constant of 5.0 and a thickness d1 of 8 mm; the cover body, gasket and connecting bolts are made of a composite material with a dielectric constant of 4.3, and the maximum thickness d2 of the cover body is 8.6 mm.

[0036] The width of the outer transition zone L1 is 5mm, the width of the inner surface transition zone L2 is 10mm, and the minimum thickness of the optical window edge d4 = 2.6mm. At the radar operating frequency point, the thickness of the optical window with a thickness of 8mm and the thickness of the composite material with a thickness of 8.6mm are both twice the half wavelength of the radar operating band. The FSS with the same pattern of gold plating is used on the outer surface of the optical window and the cover, which can achieve better infrared wave transmission, wave transmission within the working radar wave band, and shielding effect outside the working radar wave band.

[0037] Embodiment 2:

[0038] The optical window material is a material with a dielectric constant of 4.5 and a thickness of d1 of 13mm; the cover, gasket and connecting bolts are made of composite materials with a dielectric constant of 4.2, and the maximum thickness d2 of the cover material is 13.5mm. The width of the outer transition zone L1 is 8mm, the width of the inner surface transition zone L2 is 15mm, and the L2 dimension direction is flush with the inner surface of the optical window. The minimum thickness of the optical window d4 = 5mm. In the radar working band, the thickness of the optical window with a thickness of 13mm and the thickness of the composite material with a thickness of 13.5mm are both 3 times the half wavelength of the working band. The FSS with the same pattern of gold plating is used on the outer surface of the optical window and the cover, which can achieve better infrared wave transmission and shielding effect outside the working radar wave band.

[0039] Embodiment 3:

[0040] The optical window material is selected from a material with a dielectric constant of 5.0 and a thickness of 8mm; the cover, gasket and connecting bolts are selected from a composite material with a dielectric constant of 4.3, and the maximum thickness of the cover d2 is 8.6mm. The angle between the outer surface transition line L1 and the outer surface of the optical window material is 100 degrees, the angle between the inner surface transition line and the inner surface of the optical window material is 110 degrees, and the minimum thickness of the optical window is d4 = 2.6mm. The FSS with the same pattern is plated with gold on the outer surface of the optical window and the cover, which can achieve better infrared wave transmission and shielding effect outside the working radar wave band.

[0041] Embodiment 4:

[0042] The optical window material is a material with a dielectric constant of 4.5 and a thickness of 13mm. The cover, gasket and connecting bolts are made of composite materials with a dielectric constant of 4.2, and the maximum thickness d2 of the cover material is 13.5mm. The angle between the outer surface transition line L1 and the outer surface of the optical window is 160 degrees, the inner surface transition zone width L2 is 15mm, and the L2 dimension direction is flush with the inner surface of the optical window. The minimum thickness of the optical window is d4 = 5mm. The FSS with the same pattern is plated with gold on the outer surface of the optical window and the cover, which can achieve better infrared wave transmission and shielding effect outside the working radar wave band.

Claims

1. A low scattering characteristic radar infrared composite radome system, characterized in that: The antenna cover is composed of a composite material cover body, an optical window, a composite material gasket, and a composite material bolt, and the optical window is fixed between the composite material cover body and the composite material gasket by the composite material bolts, and the outer surface is kept flush; the composite material cover body contains an FSS layer, and the outer surface of the optical window is plated with a metal grid FSS; the dielectric constant of the composite material cover body is the same or similar to that of the optical window material in the radar working band; the dielectric constants of the composite material gasket, the composite material bolts and the composite material cover body are the same or made of the same material; the electrical thickness of the composite material cover body in the radar working band differs from that of the optical window by an integral multiple of half the wavelength of the radar working frequency; The composite material cover body FSS has the same shape as the optical window metal grid FSS and is made of the same type of conductive material; when the optical window is plated with the metal grid FSS, a circle of metal electrodes with a width of 0.1 to 5 mm is prepared at the edge of the FSS to ensure the electrical continuity of the entire antenna cover, increase the shielding effect of the metal grid FSS, and reduce the RCS; when the electrical thickness of the optical window is N times the half wavelength of the radar operating frequency, N is an integer, and the electrical thickness of the composite material cover body is also designed to be N times the half wavelength of the radar operating frequency; The optical window installation interface structure has the following technical features: The thickness of the optical window at the interface changes gradually, and its changing rule is as follows: at the edge of the optical window, its thickness decreases from the thickness d1 in the middle of the window to the minimum thickness d4 at the edge along the window plane direction, and it is required that the surface of the window material at the edge is perpendicular to the middle of the window; the dimension edge of the optical window is formed between the thickness d1 and the thickness d4, and on the section perpendicular to the edge, the edge includes an outer surface transition line with a width of L1 and an inner surface transition line with a width of L2; wherein, the angle a between the outer surface transition line with a width of L1 and the outer surface of the cover is 100 degrees to 160 degrees, the angle b between the inner surface transition line L2 and the inner wall of the cover is 110 degrees to 180 degrees, and the maximum width of the L2 portion does not exceed 3 times the wall thickness of the cover; The maximum thickness of the cover material is equal to d2, the thickness difference between d2 and d1 is d6, and d2>d1, d6<3mm, the step formed by the thickness difference d6 on the cover is required to be retained on the inner surface, and the width L4 of the area with thickness d6 is 0-10mm; the composite cover at the interface position is tightly matched with the optical cover on the edge where the lengths of L2, L4 and d4 are located; the composite cover and the optical head cover are required to remain flush on the outer surface; at the same time, at the interface of the composite cover, the sunken space with unequal thickness to the outer surface transition line L1 is used for the installation of the composite gasket; the composite gasket is in close contact with the optical window in the outer surface transition line L1 area, and its outer surface is flush with the optical window and the composite cover, and the gasket width is L3>15mm; A threaded hole of L3 size is opened in the middle of the gasket, and a composite material bolt is installed in the threaded hole.

2. A low scattering characteristic radar infrared composite radome system as claimed in claim 1, characterized in that: The optical window installation interface structure is replaced with the following features: The thickness of the optical window at the interface changes gradually, and its changing rule is as follows: at the edge of the optical window, its thickness decreases from the thickness d1 in the middle of the window to the minimum thickness d4 at the edge along the window plane direction, and it is required that the surface of the window material at the edge is perpendicular to the middle of the window; the dimension edge of the optical window is formed between the thickness d1 and the thickness d4, and on the section perpendicular to the edge, the edge includes an outer surface transition line with a width of L1 and an inner surface transition line with a width of L2; wherein, the angle a between the outer surface transition line with a width of L1 and the outer surface of the cover is 100 degrees to 160 degrees, the angle b between the inner surface transition line L2 and the inner wall of the cover is 110 degrees to 180 degrees, and the maximum width of the L2 portion does not exceed 3 times the wall thickness of the cover; The maximum thickness of the cover material is equal to d2, the thickness difference between d2 and d1 is d6, and d2>d1, d6<3mm, and the step formed by the thickness difference d6 on the cover is required to be retained on the inner surface, and the width L4 of the thickness d6 area is 0~10mm; the composite material gasket is installed on the inner surface of the composite material cover; the composite material cover at the interface position is required to fit tightly with the optical window on the edge where the lengths L1 and d4 are located, and the space of unequal thickness between the inner surface of the composite material cover and the transition line of the inner surface L2 and the d6 part is used for the installation of the composite material gasket; the composite material gasket includes the part where d6 is located, and is in close contact with the optical window in the inner surface transition line area and the d6 part, and the width of the gasket is L3+L4, where L3>15mm.

3. A low scattering characteristic radar infrared composite radome system as claimed in claim 1 or 2, characterized in that: The optical window material is magnesium fluoride with a dielectric constant of 4-5, and the composite material cover is made of glass fiber reinforced plastic material with a dielectric constant of 4-5.

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