Wide-angle radar cross section reduction millimeter wave circularly polarized antenna

Abstract

This invention provides a millimeter-wave circularly polarized antenna with reduced radar cross-section in a wide-angle domain, belonging to the field of antenna technology. It includes a first dielectric substrate, a second dielectric substrate, and a third dielectric substrate stacked together. A metal grating strip layer is sandwiched between the first and second dielectric substrates. The metal grating strip layer includes four rotationally symmetric metal grating strip subarrays. Each metal grating strip subarray includes multiple equally spaced parallel metal strips. The angle between the metal strips and the side of the second dielectric substrate is 45 degrees. A metal ground layer is sandwiched between the second and third dielectric substrates. Four rotationally symmetric microstrip feed lines are disposed on the side of the third dielectric substrate facing away from the metal ground layer. Each microstrip feed line corresponds to a rectangular slot on the metal ground layer. This design achieves effective reduction of the radar cross-section in a wide-angle domain while ensuring excellent radiation performance of the millimeter-wave circularly polarized antenna.

Description

Technical Field

[0001] This invention relates to the field of antenna technology, and in particular to a millimeter-wave circularly polarized antenna with a reduced radar cross section in a wide-angle domain. Background Technology

[0002] Circularly polarized antennas possess characteristics such as resistance to polarization mismatch, strong signal stability, and resistance to multipath interference, thus they are widely used in modern communication systems such as satellite communications, global navigation systems, and 5G millimeter-wave communications. In the increasingly complex environment of modern electronic warfare, stealth technology plays a crucial role in information reconnaissance and counter-reconnaissance, and reducing the radar cross section (RCS) is an important means of achieving electromagnetic stealth. Therefore, researching circularly polarized antennas with low RCS characteristics has crucial strategic significance.

[0003] Traditional methods for reducing antenna RCS generally fall into two categories: modifying the shape and structure of the target object, and coating the surface of the target object with absorbing materials. Both methods utilize the conversion of electrical energy into heat to reduce RCS. However, each traditional method has its drawbacks. First, modifying the target shape can easily affect the antenna's radiation performance. Furthermore, these methods are costly and can only measure the RCS at a single station, with significant limitations on angular range, making them unsuitable. Coating the surface with absorbing materials absorbs some radiated energy, affecting antenna gain and other performance characteristics. In recent years, the integration of antennas with metasurfaces has been considered a crucial technological path to achieving low-RCS antennas. However, most existing designs are highly sensitive to the incident angle of the wave, and their RCS reduction performance often decreases significantly with increasing incident angle. Because electromagnetic waves do not always originate from a single direction in complex real-world environments but often come from multiple angles, a millimeter-wave circularly polarized antenna with wide-angle RCS reduction is urgently needed.

[0004] In the prior art, Chinese invention patent application CN116722370A, entitled "A Low RCS Circular Polarization Slot Array Antenna with Metasurface," includes an upper dielectric substrate and a lower dielectric substrate. The upper dielectric substrate has a polarization conversion metasurface printed on its upper surface, and the lower dielectric substrate has a metal ground plane printed on its upper surface. A feeding structure is printed on the lower surface of the lower dielectric substrate. The polarization conversion metasurface is composed of passive resonant polarization conversion elements arranged in an N×N checkerboard pattern. The metal ground plane is etched with a checkerboard-patterned slot array antenna. The polarization conversion metasurface is distributed clockwise around its center. Utilizing the phase reversal characteristics between adjacent metasurfaces, the scattered energy can be reflected in the non-threatening angular region, achieving effective RCS reduction. In this antenna, the resonant state of the polarization conversion metasurface is changed by altering the size of the metal patch, thereby obtaining different reflection phases. The metal patch of the polarization conversion element needs to have a physical size approximately equal to half the operating wavelength to achieve strong resonance with the incident electromagnetic wave. This mechanism strongly binds size to frequency; the lower the operating frequency, the larger the metal patch needs to be. This results in a large overall aperture of the metasurface array, making miniaturization extremely difficult and limiting the potential for improving aperture efficiency. In terms of structural characteristics, the polarization-conversion metasurface in this antenna is composed of discrete, discontinuous periodic units, leading to discontinuous electric field distribution and phase changes, and inducing inter-unit coupling and higher-order diffraction effects, which may degrade device performance. Summary of the Invention

[0005] The technical problem to be solved by this invention is: how to effectively reduce the radar cross section in a wide-angle domain while ensuring the excellent radiation performance of millimeter-wave circularly polarized antennas.

[0006] The present invention solves the above-mentioned technical problems through the following technical solution: a millimeter-wave circularly polarized antenna with reduced radar cross-section in a wide-angle domain, comprising a first dielectric substrate, a second dielectric substrate, and a third dielectric substrate stacked together, wherein a metal grating strip layer is sandwiched between the first dielectric substrate and the second dielectric substrate, the metal grating strip layer comprising four sets of rotationally symmetric metal grating strip subarrays, each grating strip subarray comprising multiple equally spaced parallel metal strips, the metal strips forming an angle of 45 degrees with the side of the second dielectric substrate, a metal ground layer is sandwiched between the second dielectric substrate and the third dielectric substrate, and four rotationally symmetric microstrip feed lines are provided on the side of the third dielectric substrate away from the metal ground layer, each microstrip feed line corresponding to a rectangular slot on the metal ground layer.

[0007] Beneficial Effects: This invention employs an integrated design of an artificial electromagnetic metasurface and a circularly polarized antenna. A first dielectric substrate, a metal grating strip layer, a second dielectric substrate, and a metal ground layer together form a low-RCS metasurface structure. By loading this low-RCS metasurface structure onto the slot array antenna, the radar cross-section is reduced while maintaining the antenna's radiation characteristics. The low-RCS metasurface is constructed from a single set of metal grating strip polarization conversion metasurfaces arranged in a checkerboard pattern. The metal grating strip polarization conversion metasurface structure converts incident electromagnetic waves into orthogonally polarized waves. The incident wave generates reflected waves with equal amplitude and a 180-degree phase difference in its mirror-symmetric polarization conversion metasurface. These reflected waves cancel each other out, achieving RCS reduction by deflecting the scattered energy away from the normal direction. The slot array antenna can be considered as consisting of a metallic ground layer, a third dielectric substrate, microstrip feed lines, and feed ports. Four equal-amplitude excitation signals with a 90-degree phase difference are input through four feed ports. After transmission through four microstrip feed lines, circular polarization is generated through corresponding rectangular slot coupling excitation, ultimately reducing the antenna's radar cross-section while maintaining good radiation characteristics. By placing the first dielectric substrate above the metallic grating strip layer, electromagnetic waves are induced to undergo multiple reflections within the substrate, exciting multiple modes and improving the operating bandwidth of the metallic grating strip polarization conversion metasurface. Placing the first dielectric substrate above the metallic grating strip layer eliminates coupling effects between adjacent elements and provides a unique path difference phase response mechanism, exhibiting low sensitivity to the incident angle and giving the metallic grating strip polarization conversion metasurface good angular stability.

[0008] Preferably, each metal strip extends to the edge of the second dielectric substrate at both ends.

[0009] Preferably, when the electric field direction of the electromagnetic wave is parallel to the metal strip, the electromagnetic wave will induce a current in the metal strip, and each metal strip is equivalent to an inductor; when the electric field direction of the electromagnetic wave is perpendicular to the metal strip, charge will accumulate in the gap between the two metal strips, and the two metal strips are equivalent to a capacitor. At this time, the phase control becomes the control of the equivalent circuit parameters, and the phase is controlled by changing the local equivalent inductance and capacitance.

[0010] Preferably, the first dielectric substrate, the metal grating strip layer, the second dielectric substrate, and the metal ground layer together form a low RCS metasurface structure. The low RCS metasurface structure includes four sets of rotationally symmetric metal grating strip polarization conversion metasurfaces. When an electromagnetic wave is incident, two adjacent metal grating strip polarization conversion metasurfaces generate reflected waves with equal amplitude and a phase difference of 180 degrees, thereby achieving phase cancellation of the reflected waves.

[0011] Preferably, each microstrip feed line has a power supply port at one end, the power supply port is located at the edge of the third dielectric substrate, and the rectangular slot corresponding to each microstrip feed line is located directly above the end of the microstrip feed line.

[0012] Preferably, four rectangular slots are etched on the metal formation. The four rectangular slots are distributed in a 90-degree rotational symmetry with the geometric center of the metal formation as the origin. Two of the rectangular slots extend in the horizontal direction, and the other two extend in the vertical direction. The four rectangular slots are orthogonal to each other and centrally symmetrical.

[0013] Preferably, four equal-amplitude excitation signals with a phase difference of 90 degrees are input through four feed ports. After the four equal-amplitude excitation signals are transmitted through four microstrip feed lines, each rectangular slot is coupled and excited by the microstrip feed line to generate a linearly polarized radiation field. The radiation fields generated by the four rotationally symmetrical rectangular slots are finally synthesized into a circularly polarized wave.

[0014] Preferably, each metal grating strip polarization conversion metasurface comprises multiple metal grating strip units, and the side length of each metal grating strip unit is... The width of the metal strip on the metal grating strip unit is w The distance between the edge of the metal strip and the edge of the metal grating strip unit is The first intermediate structure is obtained by laterally translating and replicating the metal grating strip units. The spacing between adjacent metal strips in the first intermediate structure is... s The first intermediate unit is vertically translated and copied to obtain the second intermediate structure. The metal grating strip polarization conversion metasurface arranged at an angle of 45° is selected in the second intermediate structure.

[0015] Preferably, the thickness of the first dielectric substrate is the same as the thickness of the second dielectric substrate, and the thickness of the third dielectric substrate is less than the thickness of the first dielectric substrate.

[0016] Preferably, the first and second dielectric substrates are both made of F4B material, and the third dielectric substrate is made of Rogers 5880 material.

[0017] The advantages provided by this invention are:

[0018] 1. Traditional metasurfaces change the resonant state by altering the size of the surface metal patches, thereby obtaining different reflection phases. This mechanism strongly binds size to frequency; the lower the operating frequency, the larger the metal patches need to be. This results in a large overall aperture of the array, making it extremely difficult to miniaturize the device and limiting the potential for improving aperture efficiency.

[0019] The metal grating strip polarization-to-metasurface in the millimeter-wave circularly polarized antenna of this invention is not constrained by half-wavelength limitations. When the electric field direction of an electromagnetic wave is parallel to the continuous metal strips, the electromagnetic wave induces a current in the strips, which is equivalent to an inductor L. When the electric field direction is perpendicular to the metal strips, charge accumulates in the gaps between the metal strips, which is equivalent to a capacitor C. At this time, phase modulation becomes the modulation of equivalent circuit parameters, and the phase can be controlled by changing the local equivalent inductance and capacitance. This makes the metal grating strip polarization-to-metasurface insensitive to frequency and aperture size, thereby enabling miniaturization and customized dimensions.

[0020] 2. The polarization conversion rate of the metal grating strip polarization conversion metasurface in the millimeter-wave circularly polarized antenna of the present invention is greater than 0.9 in the frequency range of 16.6GHz-43.2GHz, indicating that the polarization conversion metasurface structure has good polarization conversion capability and completely covers the working frequency band of the antenna.

[0021] 3. Regarding the wide operating bandwidth, the present invention provides a first dielectric substrate above the metal grating strip layer, which allows electromagnetic waves to be reflected multiple times within the dielectric substrate and excite multiple modes, thereby improving the operating bandwidth of the metal grating strip polarization conversion metasurface and ultimately enabling the low RCS metasurface to achieve radar cross section reduction in a wide frequency band.

[0022] Regarding angular stability, under oblique incidence conditions, more complex unit coupling and multiple reflections often occur inside the metasurface, which in turn destroys its resonant mode and leads to performance degradation. However, the metal grating strip polarization conversion metasurface in the antenna of this invention eliminates the coupling effect between adjacent units by setting a dielectric substrate on top of the metal grating strip layer, and has a unique path difference phase response mechanism. It has low sensitivity to the incident angle, which makes the polarization conversion metasurface have good angular stability, and ultimately enables the antenna to achieve wide-angle radar cross-section reduction.

[0023] In terms of structural characteristics, metasurfaces are usually composed of discrete discontinuous periodic units, which leads to discontinuities in electric field distribution and phase changes, and induces inter-unit coupling and higher-order diffraction effects, which may reduce device performance. In contrast, the metal grating strip polarization conversion metasurface in the antenna of this invention adopts a continuous grating strip structure, which ensures the continuity of the reflected field and phase changes, effectively eliminates inter-unit coupling and higher-order diffraction, and has extremely high efficiency.

[0024] 4. The antenna of this invention adopts a stacked integrated structure, which is compact and has a low profile, making it easy to process, manufacture, and integrate into various millimeter-wave communication terminal devices. Each layer has a clear function: the metasurface layer provides stealth functionality, and the antenna layer provides communication functionality. The two do not interfere with each other, thus balancing both communication and stealth performance. Attached Figure Description

[0025] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0026] Figure 1 This is a schematic diagram of the structure of a millimeter-wave circularly polarized antenna with reduced radar cross-section in a wide-angle domain, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of a low RCS metasurface structure in a millimeter-wave circularly polarized antenna with reduced radar cross section in a wide-angle domain, provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the structure of the metallic ground layer in the millimeter-wave circularly polarized antenna with reduced radar cross-section provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the microstrip feed line in a millimeter-wave circularly polarized antenna with reduced radar cross-section in a wide-angle domain, provided in an embodiment of the present invention. Figure 5 This is a schematic diagram of the return loss S11 parameter of the millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain provided in an embodiment of the present invention. Figure 6 This is a schematic diagram of the axial ratio parameters of a millimeter-wave circularly polarized antenna with reduced radar cross-section in a wide-angle domain, provided in an embodiment of the present invention. Figure 7 This is a schematic diagram of the gain parameters of a millimeter-wave circularly polarized antenna with reduced radar cross-section in a wide-angle domain, provided in an embodiment of the present invention. Figure 8 This is a schematic diagram of the gain pattern of the millimeter-wave circularly polarized antenna with reduced radar cross section in the wide-angle domain at 30.2 GHz, provided in an embodiment of the present invention. Figure 9 This is a schematic diagram of the gain pattern of the millimeter-wave circularly polarized antenna with reduced radar cross section in the wide-angle domain at 30.2 GHz, provided in an embodiment of the present invention. Figure 10 This is a schematic diagram of the polarization conversion rate parameters of the metal grating strip element in the millimeter-wave circularly polarized antenna with reduced wide-angle radar cross-section provided in an embodiment of the present invention. Figure 11 This is a schematic diagram comparing the monostatic RCS of a millimeter-wave circularly polarized antenna with reduced wide-angle radar cross section and a metal plate of the same size as frequency, provided in an embodiment of the present invention. Figure 12 This is the 3D bistatic RCS scattering pattern of the millimeter-wave circularly polarized antenna with reduced radar cross section in the wide-angle domain at 30.2 GHz, provided in an embodiment of the present invention. Figure 13The 3D bistatic RCS scattering pattern of a metal plate of the same size as the millimeter-wave circularly polarized antenna with reduced wide-angle radar cross section provided in the embodiments of the present invention at 30.2 GHz; Figure 14 This is a schematic diagram comparing the bistatic RCS of a millimeter-wave circularly polarized antenna with reduced radar cross section in the wide-angle domain and a metal plate of the same size under oblique incident wave illumination, provided in an embodiment of the present invention. Figure 15 This is a schematic diagram of the process of obtaining a metal grating strip polarization conversion metasurface by translating and replicating a metal grating strip unit in a millimeter-wave circularly polarized antenna with reduced wide-angle radar cross section provided in an embodiment of the present invention. In the figure: 1 First dielectric substrate, 2 Metal grating strip layer, 21 Metal grating strip polarization conversion metasurface, 210 Metal strip, 3 Second dielectric substrate, 4 Metal ground layer, 5 Rectangular slot, 6 Third dielectric substrate, 7 Microstrip feed line, 8 Feed port.

[0027] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0029] like Figure 1 As shown, this embodiment provides a millimeter-wave circularly polarized antenna with a reduced radar cross-section over a wide angle range, comprising a first dielectric substrate 1, a second dielectric substrate 3, and a third dielectric substrate 6 stacked together. The first dielectric substrate 1 and the second dielectric substrate 3 are both made of F4B material, and the third dielectric substrate 6 is made of Rogers 5880 material. The thickness of the first dielectric substrate 1 is the same as the thickness of the second dielectric substrate 3, and the thickness of the third dielectric substrate 6 is less than the thickness of the first dielectric substrate 1. In this embodiment, the length of the first dielectric substrate 1 is... It is 15mm wide. It is 15mm thick. The length is 1.5mm. (This refers to the length of the second dielectric substrate 3.) It is 15mm wide. It is 15mm thick. The length is 1.5mm. (This refers to the length of the third dielectric substrate 6.) It is 15mm wide. It is 15mm thick. The length is 0.254 mm. The dimensions of the millimeter-wave circularly polarized antenna are: length 15 mm, width 15 mm. (Establishment) Figure 1 The spatial rectangular coordinate system o-xyz shown includes the origin o, x-axis, y-axis, and z-axis. The first dielectric substrate 1, the second dielectric substrate 3, and the third dielectric substrate 6 are all parallel to the xy plane of the spatial rectangular coordinate system o-xyz.

[0030] A metal grating strip layer 2 is sandwiched between a first dielectric substrate 1 and a second dielectric substrate 3, and the metal grating strip layer 2 is located on the upper surface of the second dielectric substrate 3. (See also...) Figure 2 The metal grating strip layer 2 comprises four sets of rotationally symmetric metal grating strip subarrays. The metal grating strip layer 2 can be viewed as being formed by sequentially rotating a metal grating strip subarray around the antenna center by 90 degrees, 180 degrees, and 270 degrees, and then splicing them together, exhibiting strict fourfold rotational symmetry. Each metal grating strip subarray includes multiple equally spaced parallel metal strips 210, the width of which is... The spacing between adjacent metal strips 210 is 0.3 mm. The metal strips 210 are 0.7 mm thick and arranged obliquely. Each metal strip 210 extends to the edge of the second dielectric substrate 3 at both ends. The angle between the metal strip 210 and the side of the second dielectric substrate 3 is 45 degrees; that is, one end of the metal strip 210 and the other end of the metal strip 210 form a 45-degree angle with one side of the second dielectric substrate 3, and the other end of the metal strip 210 forms a 45-degree angle with the other side of the second dielectric substrate 3. In this embodiment, the metal grating strip layer 2 is made of copper and has a thickness of... It is 0.035mm.

[0031] See also Figure 1 A metal ground layer 4 is sandwiched between the second dielectric substrate 3 and the third dielectric substrate 6, and a metal grating strip layer 2 is located on the upper surface of the third dielectric substrate 6. (See also...) Figure 3 Four rectangular slots 5 are etched on the metal formation 4. These four slots 5 are distributed with 90-degree rotational symmetry about the geometric center of the metal formation 4. Two of the slots 5 extend horizontally, and the other two extend vertically. The four slots 5 are orthogonal to each other and centrally symmetrical. The length of each rectangular slot 5 is... It is 2.6mm wide. The horizontal distance between the center of the rectangular slot 5 and the center of the metallic stratum 4 is 0.4 mm. and vertical distance All are 3.75mm thick. In this embodiment, the metal substrate 4 is made of copper, with a thickness of... It is 0.035mm.

[0032] See Figure 4 Four rotationally symmetric microstrip feed lines 7 are disposed on the side of the third dielectric substrate 6 opposite to the metal ground layer 4, and the microstrip feed lines 7 are located on the lower surface of the third dielectric substrate 6. Each microstrip feed line 7 corresponds to a rectangular slot 5 on the metal ground layer 4. Each rectangular slot 5 is coupled and excited by the microstrip feed line 7 to generate a linearly polarized radiation field. The radiation fields generated by the four rotationally symmetric rectangular slots 5 are finally synthesized into a circularly polarized wave. In this embodiment, the microstrip feed lines 7 are made of copper, and the length of the microstrip feed lines 7 is... It is 4mm wide. It is 0.78mm thick. The thickness is 0.035 mm. Each microstrip feed line 7 has a feed port 8 at one end, located at the edge of the third dielectric substrate 6. Electromagnetic energy is input from the feed port 8 and coupled into the antenna interior via the microstrip feed line 7. The rectangular slot 5 corresponding to each microstrip feed line 7 is located directly above the end of the microstrip feed line 7. Four equal-amplitude excitation signals with a phase difference of 90 degrees are input through the four feed ports 8. After being transmitted through the four microstrip feed lines 7, each rectangular slot 5 is coupled and excited by the microstrip feed line 7 to generate a linearly polarized radiation field. The radiation fields generated by the four rotationally symmetrical rectangular slots 5 are ultimately synthesized into a circularly polarized wave.

[0033] When the electric field of the electromagnetic wave is parallel to the metal strip 210, the electromagnetic wave induces a current in the metal strip 210, and each metal strip 210 is equivalent to an inductor. When the electric field of the electromagnetic wave is perpendicular to the metal strip 210, charge accumulates in the gap between two metal strips 210, and the two metal strips 210 are equivalent to a capacitor. In this case, phase control becomes the control of equivalent circuit parameters, which can be controlled by changing the local equivalent inductance and capacitance. When the electromagnetic wave is incident, the polarization conversion metasurface 21 of two adjacent metal grating strips generates reflected waves with equal amplitude and a phase difference of 180 degrees, achieving phase cancellation of the reflected waves.

[0034] The first dielectric substrate 1, the metal grating strip layer 2, the second dielectric substrate 3, and the metal ground layer 4 together constitute a low RCS metasurface structure. The low RCS metasurface structure includes four sets of rotationally symmetric metal grating strip polarization conversion metasurfaces 21. Each set of metal grating strip polarization conversion metasurfaces 21 includes multiple metal grating strip units. Through the principle of phase modulation and phase cancellation of incident electromagnetic waves by the metasurface, a wide-angle radar cross-section reduction is achieved. (See also...) Figure 15The single-group metal grating strip polarization conversion metasurface 21 of this invention can be obtained by translating and replicating the metal grating strip unit. Specifically, the side length of the metal grating strip unit is... The width of the metal strip on the metal grating strip unit is w, and the distance between the edge of the metal strip and the edge of the metal grating strip unit is [missing value]. The first intermediate structure is obtained by laterally translating and copying the metal grating strip units. The spacing between adjacent metal strips in the first intermediate structure is 's'. The second intermediate structure is obtained by vertically translating and copying the first intermediate unit. The polarization conversion metasurface of the metal grating strips arranged at a 45° angle can then be selected within the second intermediate structure. In practical work, for ease of modeling in simulation software, it is done by... Figure 15 In the single-group model ④, copy it to the right to obtain model ⑤, and then copy it upwards from model ⑤ to directly obtain model ⑥.

[0035] The working principle of the millimeter-wave circularly polarized antenna of this invention is as follows: A low-RCS metasurface structure is formed by a first dielectric substrate 1, a metal grating strip layer 2, a second dielectric substrate 3, and a metal ground layer 4. By loading the low-RCS metasurface structure onto the slot array antenna, the radar cross-section is reduced while maintaining the antenna radiation characteristics. The low-RCS metasurface structure can be regarded as being constructed by sequentially rotating a single set of metal grating strip polarization conversion metasurfaces 21 around the antenna center by 90 degrees, 180 degrees, and 270 degrees, and then splicing them together. It has strict fourfold rotational symmetry. The polarization conversion metasurface structure can convert the incident electromagnetic wave into an orthogonally polarized wave. The single set of metal grating strip polarization conversion metasurfaces 21 are arranged in a checkerboard pattern to form a low-RCS metasurface, so that the incident wave generates reflected waves with equal amplitude and a phase difference of 180 degrees in its mirror-symmetric polarization conversion metasurface. The two reflected fields cancel each other out. By deviating the scattered energy from the normal direction, RCS reduction is achieved. The slot array antenna can be considered as consisting of a metallic ground layer 4, a third dielectric substrate 6, microstrip feed lines 7, and feed ports 8. Four equal-amplitude excitation signals with a phase difference of 90 degrees are input through the four feed ports 8. After transmission through the four microstrip feed lines 7, each rectangular slot 5 is coupled and excited by the microstrip feed line 7 to generate a linearly polarized radiation field. The radiation fields generated by the four rotationally symmetric rectangular slots 5 are combined to form a circularly polarized wave. Ultimately, this achieves a reduction in the antenna's radar cross-section while maintaining good radiation characteristics.

[0036] In traditional metasurface design, the resonant state is altered by changing the size of the metal patch, thereby obtaining different reflection phases. Therefore, the metal patch of the polarization conversion unit needs to be approximately half the operating wavelength to achieve strong resonance with the incident electromagnetic wave. This mechanism strongly binds size to frequency; the lower the operating frequency, the larger the metal patch needs to be. This results in a very large overall aperture of the metasurface array, making miniaturization extremely difficult and limiting the potential for improving aperture efficiency.

[0037] The metal grating strip polarization-to-metasurface in the millimeter-wave circularly polarized antenna of this invention is not constrained by the half-wavelength limitation. When the electric field direction of the electromagnetic wave is parallel to the continuous metal strip, the electromagnetic wave induces a current in the strip, which is equivalent to an inductor L. When the electric field direction is perpendicular to the metal strip, charge accumulates in the gaps between the metal strips, which is equivalent to a capacitor C. At this time, phase modulation becomes the modulation of equivalent circuit parameters, and the phase can be controlled by changing the local equivalent inductance and capacitance. This makes the metal grating strip polarization-to-metasurface insensitive to frequency and aperture size, thereby enabling miniaturization and customized dimensions.

[0038] Furthermore, by placing a first dielectric substrate 1 above the metal grating strip layer 2, this invention can improve the operating bandwidth of the metal grating strip polarization conversion metasurface 21. Principle analysis: Without the first dielectric substrate 1, when an x-polarized wave is completely reflected by the metal grating strip at the surface, a y-polarized wave completely penetrates the grating gap, travels downwards through the bottom dielectric layer of thickness h, and is reflected by the bottom metal ground plane. Due to the different propagation paths of the x-polarized and y-polarized waves, a phase difference is generated. To achieve a 180° phase difference, the metal grating strip is typically placed at a distance of approximately 1 / 4λ from the ground, exhibiting inherent narrow-band characteristics. This invention, by placing the first dielectric substrate 1 above the metal grating strip layer 2, allows electromagnetic waves to undergo multiple reflections within the dielectric substrate and excite multiple modes, thereby improving the operating bandwidth of the metal grating strip polarization conversion metasurface 21.

[0039] To verify the effectiveness of the present invention, the antenna of the present invention was simulated and verified. Figure 5 The present invention provides a schematic diagram of the antenna return loss S11 parameter. It can be seen that the antenna has S11≤-10dB in the 28.6GHz-31.6GHz frequency band and an impedance bandwidth of up to 3GHz, exhibiting good impedance matching characteristics.

[0040] Figure 6 The present invention provides a schematic diagram of the antenna's axial ratio parameters. The antenna's axial ratio is ≤3dB in the 28.6GHz-31.6GHz frequency band, indicating that the antenna has excellent circular polarization purity in the operating frequency band. Figure 7 The diagram shows the antenna's gain parameters. The antenna achieves a peak gain of 9.13 dBic at a frequency of 30.2 GHz. Meanwhile, the antenna's left-hand circular polarization gain is much higher than its right-hand circular polarization gain, with a difference of more than 20 dB. The circular polarization isolation is excellent and can effectively suppress cross-polarization interference.

[0041] Figure 8 , Figure 9The diagrams show the gain directions of the antenna in the xoz and yoz planes at 30.2 GHz, respectively. It can be seen that the antenna exhibits stable directional radiation characteristics in both principal planes. Figure 10 The present invention provides a schematic diagram of the polarization conversion rate parameters of the metal grating strip unit in the antenna. It can be seen that the polarization conversion rate is greater than 0.9 in the frequency range of 16.6GHz-43.2GHz, indicating that the metal grating strip unit has good polarization conversion capability and completely covers the working frequency band of the antenna.

[0042] Figure 11 The present invention provides a comparison curve of the monostatic RCS of the antenna and the metal plate of the same size with frequency. It can be seen that the monostatic RCS of the antenna provided by the present invention is significantly lower than that of the metal plate across the entire frequency band. The maximum RCS reduction is achieved at 30.2 GHz, with a reduction of up to 30 dB. The average RCS reduction exceeds 10 dB in the 28 GHz-32 GHz wide frequency band. This verifies the efficient radar cross section reduction performance of the metasurface structure under normal incidence. Moreover, the RCS reduction frequency band completely covers the working bandwidth of the antenna, realizing the synergy between radiation performance and stealth performance.

[0043] Figure 12 , Figure 13 The present invention provides 3D bistatic RCS scattering patterns of the antenna and a metal plate of the same size at 30.2 GHz. The comparison shows that the antenna with the metasurface, through phase modulation and the principle of destructive interference, scatters the energy of the illuminating radar wave beyond the normal direction, thus defocusing the antenna's scattering capability in space. This not only significantly reduces the RCS of the antenna normal but also noticeably reduces the scattering peak value of the antenna throughout space.

[0044] Figure 14 The diagram provides a comparison of the bistatic RCS results of the antenna and a metal plate of the same size under oblique incident wave illumination along the mirror direction. It can be seen that at a 30-degree oblique incidence, the bistatic RCS of the antenna achieves a significant reduction of 10dB-21dB compared to the metal plate. It maintains excellent reduction effect across the entire frequency band of 28GHz-32GHz. At a large oblique incidence of 60 degrees, although the RCS reduction is somewhat reduced, the overall trend of RCS reduction over a wide frequency band remains good. This indicates that the RCS reduction effect of the antenna provided by the present invention has good angular stability.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A millimeter-wave circularly polarized antenna with reduced radar cross-section in a wide-angle domain, characterized in that: The substrate includes a first dielectric substrate (1), a second dielectric substrate (3), and a third dielectric substrate (6) arranged in layers. A metal grating strip layer (2) is sandwiched between the first dielectric substrate (1) and the second dielectric substrate (3). The metal grating strip layer (2) includes four sets of rotationally symmetrical metal grating strip subarrays. Each metal grating strip subarray includes multiple metal strips arranged in parallel with equal spacing. The angle between the metal strips and the side of the second dielectric substrate (3) is 45 degrees. A metal ground layer (4) is sandwiched between the second dielectric substrate (3) and the third dielectric substrate (6). Four rotationally symmetrical microstrip feed lines (7) are provided on the side of the third dielectric substrate (6) away from the metal ground layer (4). Each microstrip feed line (7) corresponds to a rectangular slot (5) on the metal ground layer (4).

2. The millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain according to claim 1, characterized in that: Each metal strip extends to the edge of the second dielectric substrate (3) at both ends.

3. The millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain according to claim 1, characterized in that: When the electric field of an electromagnetic wave is parallel to the metal strip, the electromagnetic wave induces a current in the metal strip, and each metal strip is equivalent to an inductor. When the electric field of an electromagnetic wave is perpendicular to the metal strip, charge accumulates in the gap between two metal strips, and the two metal strips are equivalent to a capacitor. At this time, phase control becomes the control of equivalent circuit parameters, and the phase is controlled by changing the local equivalent inductance and capacitance.

4. The millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain according to claim 1, characterized in that: The first dielectric substrate (1), the metal grating strip layer (2), the second dielectric substrate (3) and the metal ground layer (4) together form a low RCS metasurface structure. The low RCS metasurface structure includes four sets of rotationally symmetric metal grating strip polarization conversion metasurfaces (21). When an electromagnetic wave is incident, two adjacent metal grating strip polarization conversion metasurfaces (21) generate reflected waves with equal amplitude and a phase difference of 180 degrees, thereby achieving phase cancellation of the reflected waves.

5. The millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain according to claim 1, characterized in that: Each microstrip feed line (7) has a power supply port (8) at one end, the power supply port (8) is located at the edge of the third dielectric substrate (6), and the rectangular slot (5) corresponding to each microstrip feed line (7) is located directly above the end of the microstrip feed line (7).

6. The millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain according to claim 1, characterized in that: Four rectangular slots (5) are etched on the metal stratum (4). The four rectangular slots (5) are distributed in a 90-degree rotational symmetry with the geometric center of the metal stratum (4) as the origin. Two of the rectangular slots (5) extend in the horizontal direction, and the other two rectangular slots (5) extend in the vertical direction. The four rectangular slots (5) are arranged orthogonally to each other and centrally symmetrically.

7. The millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain according to claim 4, characterized in that: Four equal-amplitude excitation signals with phase differences of 90 degrees are input through four feed ports (8). After the four equal-amplitude excitation signals are transmitted through four microstrip feed lines (7), each rectangular slot (5) is coupled and excited by the microstrip feed line (7) to generate a linearly polarized radiation field. The radiation fields generated by the four rotationally symmetrical rectangular slots (5) are finally synthesized into a circularly polarized wave.

8. The millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain according to claim 4, characterized in that: Each metal grating strip polarization conversion metasurface (21) comprises multiple metal grating strip units, the side length of which is... The width of the metal strip on the metal grating strip unit is w The distance between the edge of the metal strip and the edge of the metal grating strip unit is The first intermediate structure is obtained by laterally translating and copying the metal grating strip unit. The spacing between adjacent metal strips in the first intermediate structure is s. The second intermediate structure is obtained by vertically translating and copying the first intermediate unit. The metal grating strip polarization conversion metasurface arranged at an angle of 45° is selected in the second intermediate structure.

9. The millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain according to claim 1, characterized in that: The thickness of the first dielectric substrate (1) is the same as that of the second dielectric substrate (3), and the thickness of the third dielectric substrate (6) is less than that of the first dielectric substrate (1).

10. The millimeter-wave circularly polarized antenna with reduced radar cross-section in the wide-angle domain according to claim 1, characterized in that: The first dielectric substrate (1) and the second dielectric substrate (3) are both made of F4B material, and the third dielectric substrate (6) is made of Rogers 5880 material.

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