Wideband low rcs antenna and terminal based on frequency selective reflection hybrid structure

Abstract

The application belongs to the technical field of wireless communication and antenna design, and particularly relates to a wideband low RCS antenna and terminal based on a frequency selective reflection hybrid structure. The antenna comprises a low-frequency wave-absorbing layer, a three-dimensional frequency selective reflection structure and a circularly polarized antenna layer. The low-frequency wave-absorbing layer is composed of a dielectric substrate and two curved metal strips respectively etched on the upper and lower sides of the dielectric substrate, and the two curved metal strips are perpendicular to each other. A patch resistor is embedded at the perpendicular point of the curved metal strip. The three-dimensional frequency selective reflection structure is composed of a hollow cuboid dielectric plate with metal etched on the adjacent inner side surface. The circularly polarized antenna layer is composed of dielectric layers and metal layers arranged alternately from top to bottom. The first metal layer and the second metal layer are different rectangular shapes with the same cut corner position. The antenna can radiate with high efficiency within the working band, suppress the out-of-band RCS, maintain the circularly polarized antenna performance and ensure the high gain and wideband characteristics.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wireless communication and antenna design, and particularly relates to a wideband low RCS antenna and terminal based on a frequency selective reflection hybrid structure. BACKGROUND

[0002] With the rapid development of stealth technology and wireless communication technology, the radar cross section (RCS) can measure the strength of the stealth ability and represent the echo intensity of the object after being irradiated by the radar. Therefore, reducing the radar cross section of the target can reduce the exposure degree of the target in the enemy radar detection, thereby reducing the probability of being discovered by the enemy. According to the position and number of the receiving and transmitting radar, it can be divided into single station RCS and double station RCS. The RCS measured by the receiving and transmitting radar at the same position is single station RCS, at this time, the scattering observation direction and the incident direction always keep reverse. Circularly polarized antenna is a kind of antenna used for wireless communication, which can send or receive electromagnetic waves in the form of two orthogonal components in the rotating plane. This kind of antenna has the ability to handle multipath interference and signal reflection, thereby providing more stable communication quality.

[0003] The method of realizing RCS reduction is generally using metamaterial wave absorber, polarization conversion super surface and artificial magnetic conductor. However, in a wider frequency band, the realization of low RCS performance will often affect the radiation performance of the antenna in its working frequency band. Therefore, it is necessary to design a new structure to suppress the out-of-band RCS without affecting the radiation efficiency in the working band of the antenna, and maintain the performance of the circularly polarized antenna. SUMMARY

[0004] The purpose of the application is to provide a wideband low RCS antenna and terminal based on a frequency selective reflection hybrid structure. The wideband low RCS antenna suppresses the out-of-band RCS while maintaining the radiation efficiency in the working band, and maintains the performance of the circularly polarized antenna. The three-dimensional frequency selective reflection structure of the wideband low RCS antenna can act as a reflector in the working frequency band of the antenna to ensure the high gain and wide frequency band characteristics of the circularly polarized antenna.

[0005] In order to achieve the above purpose, the application provides the following technical scheme:

[0006] In a first aspect, the present application provides a wideband low RCS antenna based on a frequency selective reflection hybrid structure, comprising a low-frequency wave-absorbing layer, a three-dimensional frequency selective reflection structure, and a circularly polarized antenna layer. The low-frequency wave-absorbing layer comprises a dielectric substrate, a first curved metal strip is arranged at a first diagonal position on the upper surface of the dielectric substrate, a second curved metal strip is arranged at a second diagonal position on the lower surface of the dielectric substrate, and the first curved metal strip and the second curved metal strip are perpendicular to each other but do not intersect. A patch resistor is arranged at the perpendicular point of the first curved metal strip and the second curved metal strip. The three-dimensional frequency selective reflection structure comprises at least a dielectric plate. The dielectric plate is a hollow cuboid with metal etched on the adjacent inner side. The upper side of the dielectric plate is a curved metal strip with two open metal rings connected in series, and the lower side is only connected with one open metal ring. The circularly polarized antenna layer is composed of N×N circularly polarized antenna units arranged in a regular matrix. Each circularly polarized antenna unit is composed of metal layers and dielectric layers arranged alternately from top to bottom. The first metal layer and the second metal layer are both cut-corner rectangles, and the sizes of the rectangles are different but the cut-corner positions are the same.

[0007] As a possible implementation manner, the outer ring of the open metal ring is downwardly open, the inner ring is upwardly open, and the opening gap widths are equal.

[0008] As a possible implementation manner, the gap width is determined by the resonant frequency, the equivalent capacitance, and the equivalent inductance of the open metal ring.

[0009] As a possible implementation manner, the metal layer is four layers, and the materials of each metal layer are the same, being one of copper, aluminum, tungsten, titanium, tantalum, molybdenum, or platinum.

[0010] As a possible implementation manner, the third metal layer is a metal plate with a circular hole opened upward.

[0011] As a possible implementation manner, the fourth metal layer is a metal power divider.

[0012] As a possible implementation manner, for each circularly polarized antenna unit, a first blind hole penetrates the second dielectric layer, the second metal layer, and the third dielectric layer of the circularly polarized antenna, and is used to connect the second metal layer and the fourth metal layer.

[0013] As a possible implementation manner, the diameter of the circular hole is 3-4 times the diameter of the first blind hole.

[0014] As a possible implementation manner, a second blind hole penetrates the third dielectric layer of the circularly polarized antenna layer, and is used to connect the third metal layer and the fourth metal layer.

[0015] In a second aspect, the present application provides a terminal applying the wideband low RCS antenna based on the frequency selective reflection hybrid structure provided in the first aspect.

[0016] Compared with the prior art, the present application has the following effects:

[0017] 1. The wideband low RCS antenna provided by the present application has the advantage of high integration degree, and the wideband low RCS antenna adopts the mode of electromagnetic stealth surface cooperating with circularly polarized antenna to realize the integration of array antenna radiation stealth performance.

[0018] 2. The wideband low RCS antenna provided by the present application has the advantage of good independence, and the wideband low RCS antenna is divided into three parts, i.e. a low-frequency wave-absorbing layer, a three-dimensional frequency selective reflection structure and a circularly polarized antenna layer. The three parts can work independently and have the characteristic of polarization insensitivity, so that the performance is stable.

[0019] 3. The wideband low RCS antenna provided by the present application has the advantage of good stealth performance, i.e. can realize ultra-wideband RCS reduction. The RCS reduction bandwidth provided by the prior art is usually in the range of 10-30 GHz, and the wideband low RCS antenna provided by the present application expands the bandwidth to S band, C band and X band, which can meet different application requirements in the fields of communication and radar. BRIEF DESCRIPTION OF DRAWINGS

[0020] The drawings described herein are used to provide further understanding of the present application, and constitute a part of the present application. The schematic embodiments of the present application and the descriptions thereof are used to explain the present application, and do not constitute improper limitation on the present application.

[0021] Figure 1 A three-dimensional exploded view of the wideband low RCS antenna based on the frequency selective reflection hybrid structure provided for the embodiment of the present application;

[0022] Figure 2 A reflection coefficient and absorption rate result graph of the wideband low RCS antenna provided for the embodiment of the present application;

[0023] Figure 3 A structure diagram of the low-frequency wave-absorbing layer provided for the embodiment of the present application;

[0024] Figure 4 A top view of Figure 3 ;

[0025] Figure 5 Reflection coefficient result graphs of the low-frequency wave-absorbing layer under vertical incidence TE and TM polarization modes provided for the embodiment of the present application;

[0026] Figure 6 A unit structure diagram of the three-dimensional frequency selective reflection structure provided for the embodiment of the present application;

[0027] Figure 7 A partial enlarged view of Figure 6 ;

[0028] Figure 8A reflection coefficient result chart of a three-dimensional frequency selective reflection structure provided by the embodiment of the present application in TE polarization mode under different layers in the case of perpendicular incidence;

[0029] Figure 9 A structure chart of a circularly polarized antenna layer provided by the embodiment of the present application;

[0030] Figures 10-11 A partial enlarged view of Figure 9 ;

[0031] Figure 12 A standing wave ratio simulation result of a wideband low RCS antenna provided by the embodiment of the present application in a working frequency band;

[0032] Figure 13 A gain and axial ratio simulation result of a wideband low RCS antenna provided by the embodiment of the present application in a working frequency band;

[0033] Figure 14 A result of RCS reduction of an array structure composed of 8x8 after the embodiment of the present application in the case of TE polarization with the change of incident angle;

[0034] Figure 15 A result of RCS reduction of an array structure composed of 8x8 after the embodiment of the present application in the case of TE polarization with the change of incident angle;

[0035] Figure 16 A result of array RCS reduction of an array structure composed of 8x8 after the embodiment of the present application in the case of TM polarization with the change of angle.

[0036] Reference signs

[0037] 10-low frequency wave absorbing layer, 101-medium substrate, 102-first curved metal strip, 103-second curved metal strip, 104-patch resistor, 20-three-dimensional frequency selective reflection structure, 201-medium plate, 202-curved metal strip, 203-open metal ring, 30-circularly polarized antenna layer, 301-first metal layer, 302-first dielectric layer, 303-second metal layer, 304-second dielectric layer, 305-third metal layer, 306-third dielectric layer, 307-fourth metal layer. DETAILED DESCRIPTION

[0038] In order to clearly describe the technical solutions of the embodiments of the present application, in the embodiments of the present application, the terms of "first", "second", etc. are used to distinguish the same or similar items with basically the same functions and effects. For example, the first threshold and the second threshold are only used to distinguish different thresholds, and the order is not limited. Those skilled in the art can understand that the terms of "first", "second", etc. do not limit the quantity and execution order, and the terms of "first", "second", etc. do not necessarily mean different.

[0039] It should be noted that in the present application, the words "exemplary" or "for example" are used to mean serving as an example, instance, or illustration. Any embodiment or design described as "exemplary" or "for example" in the present application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of the words "exemplary" or "for example" is intended to present concepts in a particular manner.

[0040] In the present application, "at least one" means one or more, and "multiple" means two or more. The association relationship of the associated objects is described, which means that there can be three relationships, for example, A and / or B, which can represent the following three cases: A exists alone, A and B exist together, and B exists alone, where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the front and rear associated objects. "At least one of the following" or similar expressions means any combination of these items, including any combination of single or multiple items. For example, at least one of a, b, or c can represent: a, b, c, the combination of a and b, the combination of a and c, the combination of b and c, or the combination of a, b, and c, where a, b, and c can be single or multiple.

[0041] The frequency-selective reflection hybrid structure-based wideband low-RCS antenna provided by the present application will be described in detail below in combination with the drawings and examples.

[0042] Referring to Figure 1 The frequency-selective reflection hybrid structure-based wideband low-RCS antenna provided by the present application comprises a low-frequency wave-absorbing layer 10, a three-dimensional frequency-selective reflection structure 20, and a circularly polarized antenna layer 30 stacked together from top to bottom.

[0043] The frequency-selective reflection hybrid structure-based wideband low-RCS antenna provided by the present application has the following effects: the low-frequency wave-absorbing layer 10 serves as the first part and has the function of low-frequency wave absorption; the three-dimensional frequency-selective reflection structure 20 serves as the second part, which opens a reflection band window in the middle of the absorption band, and can act as a reflector to improve the in-band gain of the antenna when the antenna is working, and act as a wave-absorbing body to reduce the scattering characteristics of the antenna structure when the antenna is working out of the band; and the circularly polarized antenna layer 30 serves as the third part.

[0044] Referring to Figure 2 , the unit structure is simulated by using ANSYS HFSS full-wave simulation software, and the boundary conditions are set as periodic boundary conditions and Floquet port so that the unit structure is periodically arranged along the x direction and the y direction. The reflection coefficient and the absorption rate of the structure are shown in Figure 2 , it can be seen that the absorption rate is greater than 90% at 2-12.08 GHz and 14.32-19.76 GHz. The fractional bandwidth is 143.2% and 31.9%, respectively. The thickness of the entire structure is only 0.1296λ L , where λ L is the lowest frequency of the operating frequency band.

[0045] Referring to Figure 3 and Figure 4 , the low-frequency wave-absorbing layer 10 can be a broadband absorber, which includes a dielectric substrate 101, a first curved metal strip 102 formed on the upper surface of the dielectric substrate by etching process, and a second curved metal strip 103 formed on the lower surface of the dielectric substrate. The first curved metal strip 102 is located on the first diagonal line of the upper surface. The second curved metal strip 103 is located on the second diagonal line of the lower surface. The first curved metal strip 102 and the second curved metal strip 103 are perpendicular to each other but do not intersect on different surfaces. A patch resistor 104 is arranged at the perpendicular point of the first curved metal strip 102 and the second curved metal strip 103. The resistance of the patch resistor 104 is R=200Ω. The dielectric constant of the dielectric substrate 101 is 2.2, and the loss tangent angle is 0.009. The first curved metal strip 102 and the second curved metal strip 103 are metal dipoles, which are processed by bending for the purpose of miniaturization. Based on this, better angular stability can be obtained while shortening the unit period. The unit period p of the low-frequency wave-absorbing layer 10 is 12.5 mm, and the low-frequency wave-absorbing layer is placed above the metal floor at a distance h of 19 mm, which is about one quarter of the corresponding wavelength at the center frequency of the absorption frequency band.

[0046] Referring to Figure 4 , the first curved metal strip 102 and the second curved metal strip 103 have the same structure and equal dimensions. Specifically, l1=2mm, l2=1.2mm, l3=1mm, l4=3mm, and w=0.5mm.

[0047] Referring to Figure 5 , from the simulation results of the frequency and the reflection coefficient of the low-frequency wave-absorbing layer 10, it can be seen that the electromagnetic waves incident in TE or TM polarization mode have approximately the same parameter variation trend. In the frequency band of 1.94-5.46 GHz, the reflection coefficient is below -10 dB. The relative bandwidth is 79%. Two resonance points appear at 2.46 GHz and 4.87 GHz, forming a low-frequency electromagnetic stealth surface.

[0048] Referring to Figure 6 and Figure 7 , the three-dimensional frequency selective reflection structure 20 at least comprises a dielectric plate 201; the dielectric plate 201 is a hollow cuboid with metal etched on the adjacent inner side; the upper side of the dielectric plate 201 is a curved metal strip 202 with two open metal rings 203 connected in series, and the lower side is only connected with one open metal ring 203.

[0049] The dielectric plate 201 adopts a Rogers RO5880 hollow cuboid with a relative dielectric constant of 2.2 and a loss tangent angle of 0.009. Two groups of the same metal are printed on the adjacent surfaces as dipole resonators, which belong to three-dimensional lossy layers. Compared with the previous two-dimensional structure, the three-dimensional structure has better stability, better frequency selection performance and wider high-frequency absorption band. The printing on the adjacent surfaces helps to achieve dual-polarization absorption. Each group of dipole resonators is composed of two dipoles on the top and bottom, respectively, to control the absorption of low and high frequency bands. The top dipole is connected in series with two open resonant rings, and the bottom dipole is connected in series with one open resonant ring. The three resonant rings have the same radius. The application of resonant rings helps to produce a reflection window in the absorption band, reducing the loss in the transmission band. The position of the reflection frequency point is mainly controlled by the radius of the open resonant ring, and the position of the absorption frequency point is mainly controlled by the length of the dipole metal strip. H and R L represent the resistance loaded on the top and bottom dipoles, respectively, with resistance values of 125Ω and 75Ω, respectively.

[0050] Referring to Figure 7 , the height of the dielectric plate h1=15mm, the length of the metal strip bending part is L H1 =1.7mm, L l1 =1.2mm, the length of the metal strip horizontal part is L H =3mm, L l =2.2mm, the resistance placement position is d H =2.7mm, d L =1.5mm, the width of the metal strip w H =0.6mm, the width of the open resonant ring w1=0.2mm, the ring spacing d=0.1mm, the open g=0.3mm, the inner ring radius r1=1.15mm, and the outer ring radius r2=0.85mm.

[0051] As a possible implementation, the outer opening of the open metal ring is downward, the inner opening is upward, and the gap widths are equal.

[0052] As a possible implementation, the gap width is determined by the resonant frequency, equivalent capacitance and equivalent inductance of the open metal ring.

[0053] The simulation results of the frequency and reflection coefficient of the three-dimensional frequency selective reflection structure under the condition of the period boundary (master-slave boundary) and the excitation of the Floquet port are shown in Figure 8 Figure 8 The dashed line in the figure is the bottom dipole printed with only one SSR in the hollow cuboid medium plate, and the dotted line is the top dipole printed with two SSRs. It can be seen that the lower layer produces absorption peaks at two frequency points of 9.98 GHz and 18.90 GHz, and the absorption peaks of the upper layer are at 6.50 GHz and 18.30 GHz. The SSR can be equivalent to an inductor and a capacitor in parallel, and the dipole loaded with a lumped resistor is equivalent to an inductor, a capacitor and a resistor in series. Two SSRs in series are equivalent to two parallel LC circuits in series, which can obtain larger virtual impedance and thus achieve a wider passband. By connecting two SSRs in series while keeping the SSR radius and the gap width unchanged, a wider transmission band can be obtained at the same center frequency. The 3dB transmission frequency band is 11.98-15.04 GHz, and the fractional bandwidth is 45.3%. The combination of the upper and lower layers enables the three-dimensional frequency selective reflection structure to produce the performance of absorption-transmission-absorption.

[0054] Referring to Figures 9 to 11 The circularly polarized antenna layer 30 is composed of three layers of dielectric and four layers of metal arranged alternately from top to bottom. The first layer of metal and the second layer of metal are both cut-corner rectangles, which differ in size but have the same cut-corner position. Each of the four layers of metal is made of one of copper, aluminum, tungsten, titanium, tantalum, molybdenum or platinum. The third layer of metal is a metal plate with a circular hole. The diameter of the circular hole is 3-4 times the diameter of the blind hole. The fourth layer of metal is a metal power divider. There are blind holes penetrating the second layer of dielectric of the circularly polarized antenna, the metal plate and the third layer of dielectric, which are used to connect the second layer of metal and the fourth layer of metal. There are blind holes penetrating the third layer of dielectric of the circularly polarized antenna, which are used to connect the third layer of metal and the fourth layer of metal.

[0055] In a specific application, the circularly polarized antenna layer is a single-feed circularly polarized antenna layer, which can realize uplink and downlink communication and further cover the allocated uplink and downlink frequencies. The design of circular polarization can avoid strict antenna alignment requirements and reduce polarization loss.

[0056] As an example, the first blind hole has a diameter of 0.6 mm.

[0057] Referring to Figure 9 ​As an example, from top to bottom, it includes a first metal layer 301, a first dielectric layer 302, a second metal layer 303, a second dielectric layer 304, a third metal layer 305, a third dielectric layer 306, and a fourth metal layer 307. The first metal layer is a parasitic patch, a patch antenna that is not directly fed, and achieves radiation by utilizing the electromagnetic field coupling of adjacent driving patches. The first dielectric layer has a dielectric constant of 2.2 and a thickness of 1 mm. The second metal layer is a driving patch, a patch wire used for feeding and radiating electromagnetic waves. The dimensions of the driving patch are as follows... Figure 11 As shown, the corner cutoff length C on the driver patch d =2.55mm. The parasitic patch and the driving patch are electromagnetically coupled, with no direct electrical contact. Circular polarization of the driving patch and parasitic patch is achieved by applying angular perturbations to the two patches. In practice, the driving patch, i.e., the second metal layer, is connected to the fourth metal layer (metal power divider) through a first blind via. It directly receives power and generates electromagnetic waves, which propagate through the surface current and radiated electric field of the driving patch. The second dielectric layer has a dielectric constant of 2.2, a thickness of 1.8mm, and is made of Rogers RO5880 material, on which the driving patch is etched. The third metal layer is a metal ground plane. The third dielectric layer uses Rogers RO6006 material with a dielectric constant of 6.15 and a loss tangent of 0.0019, and a thickness of 1mm. The third dielectric layer is a major factor affecting antenna impedance matching and circular polarization bandwidth. The third metal layer is placed on top of the third dielectric layer and has a circular via with a diameter of 2.4mm. The fourth metal layer is the metal power divider.

[0058] The first and second metal layers are both chamfered rectangles, and although they are different in size, the chamfer positions are the same.

[0059] In implementation, the circularly polarized antenna layer is composed of 8x8 matrix of circularly polarized antenna units, i.e. a total of 64 circularly polarized antenna units. The number of repeated circularly polarized antenna units can be a fixed value. In the embodiment, the number of circularly polarized antenna units is 64, and the 64 first blind holes penetrating the second dielectric layer, the second metal layer and the third dielectric layer correspond to each circularly polarized antenna unit, i.e. the number of first blind holes is also 64. When the array is composed of circularly polarized antenna units, the circularly polarized antenna units are first translated to form a small array of 4x4, i.e. a total of 16 circularly polarized antenna units. In order to obtain better oblique incidence performance, the small array of circularly polarized antenna units is then rotated by 90° around the vertex, i.e. a total of three rotations (a total of four small arrays of circularly polarized antenna units, which are four central symmetries, each small array has 16 circularly polarized antenna units, and the four small arrays form a large array, i.e. a total of 64 circularly polarized antenna units) to form a final central symmetric circularly polarized antenna unit array. The circularly polarized antenna array includes a total of 64 circularly polarized antenna units, and the array is a small array of 4x4, i.e. a total of 16 circularly polarized antenna units. There are a total of 8 second blind holes penetrating the third dielectric layer of the circularly polarized antenna to connect the third metal layer and the fourth metal layer. Each 4x4 small array of circularly polarized antenna units corresponds to two second blind holes, and since the final array of circularly polarized antenna units is composed of four 4x4 small arrays of circularly polarized antenna units, the number of second blind holes is 8.

[0060] The simulation tool Ansys HFSS2021 based on the finite element method is used to simulate the circularly polarized antenna layer, and the simulation results are shown in Figures 12 to 13 . The bandwidth of VSWR<2:1 is 30.9% (11.5-15.7 GHz), as shown in Figure 12 . The axial ratio and gain simulation results of the circularly polarized antenna layer are shown in Figure 13 . The bandwidth of axial ratio <3dB is 30.5% (11.4-15.5 GHz), and the gain varies between 2.78-6.36 dBc within the operating bandwidth. The driving patch works in the first frequency domain with the minimum axial ratio, the parasitic patch works in the second frequency domain with the minimum axial ratio, and the two interact to achieve wideband circular polarization.

[0061] The unit structure is arrayed in the form of Figure 14 (left), to form an 8x8 array. Figure 14 (right) is the power divider structure. The results of the array RCS reduction vary with the angle as shown in Figure 15 , Figure 16The RCS reduction is divided into three frequency bands in total, and the two sides are the RCS reduction frequency band, and 13-15 GHz is the antenna operating band. It can be seen that the RCS reduction outside the antenna operating band is greater than 10 dB in TE and TM modes, and as the incident angle gradually increases to 40°, the RCS reduction of the structure still shows excellent performance.

[0062] Although the present application has been described in connection with various embodiments thereof, those skilled in the art will understand that various modifications in form and detail can be made therein without departing from the spirit and scope of the application. Accordingly, it is intended that the following claims cover all such modifications and changes as fall within the scope of the application. In this description, the word "comprising" does not exclude other components or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor or other unit can fulfill the functions of several items recited in the description. Some measures are described as being implemented in different embodiments, but this does not exclude that they could be implemented together in the same embodiment.

[0063] Although the present application has been described in connection with particular features and embodiments thereof, it is to be understood that various modifications and changes can be made thereto without departing from the spirit and scope of the application. Accordingly, the description and drawings are to be regarded as illustrative in nature and are not to be regarded as limiting the scope of the application. It will be obvious to those skilled in the art that various modifications and changes can be made thereto without departing from the spirit and scope of the application. Accordingly, the description and drawings are to be regarded as illustrative in nature and are not to be regarded as limiting the scope of the application.

Claims

1. A broadband low RCS antenna based on a frequency-selective reflection hybrid structure, characterized in that, It includes a low-frequency absorbing layer, a three-dimensional frequency-selective reflective structure, and a circularly polarized antenna layer; The low-frequency absorbing layer includes a dielectric substrate. A first bent metal strip is disposed at a first diagonal position on the upper surface of the dielectric substrate, and a second bent metal strip is disposed at a second diagonal position on the lower surface of the dielectric substrate. The first bent metal strip and the second bent metal strip are perpendicular to each other but do not intersect. A chip resistor is disposed at each perpendicular point of the first bent metal strip and the second bent metal strip. The three-dimensional frequency selective reflection structure includes at least a dielectric plate; the dielectric plate is a hollow cuboid with metal etched on its inner adjacent surfaces; the upper side of the dielectric plate has two open metal rings connected in series on a bent metal strip, and the lower side has only one open metal ring connected in series. The circularly polarized antenna layer is composed of N×N circularly polarized antenna elements arranged in a regular matrix. Each circularly polarized antenna element is composed of alternating metal layers and dielectric layers arranged from top to bottom. The first metal layer and the second metal layer are both chamfered rectangles, with different rectangle sizes but the same chamfer position.

2. A broadband low RCS antenna based on a frequency-selective reflection hybrid structure according to claim 1, characterized in that, The outer ring of the open metal ring faces downwards, while the inner ring faces upwards, and the width of the opening gaps is equal.

3. A broadband low RCS antenna based on a frequency-selective reflection hybrid structure according to claim 2, characterized in that, The gap width is determined by the resonant frequency, equivalent capacitance, and equivalent inductance of the open metal ring.

4. A broadband low RCS antenna based on a frequency-selective reflection hybrid structure according to claim 3, characterized in that, The metal layer consists of four layers, each made of the same material: copper, aluminum, tungsten, titanium, tantalum, molybdenum, or platinum.

5. A broadband low RCS antenna based on a frequency-selective reflection hybrid structure according to claim 4, characterized in that, The third metal layer is a metal plate with a circular hole on top.

6. A broadband low RCS antenna based on a frequency-selective reflection hybrid structure according to claim 5, characterized in that, The fourth metal layer is a metal power divider.

7. A broadband low RCS antenna based on a frequency-selective reflection hybrid structure according to claim 6, characterized in that, For each circularly polarized antenna element, a first blind hole penetrates the second dielectric layer, the second metal layer, and the third dielectric layer of the circularly polarized antenna to connect the second metal layer and the fourth metal layer.

8. A broadband low RCS antenna based on a frequency-selective reflection hybrid structure according to claim 7, characterized in that, The diameter of the circular hole is 3 to 4 times the diameter of the first blind hole.

9. A broadband low RCS antenna based on a frequency-selective reflection hybrid structure according to claim 8, characterized in that, A second blind hole penetrates the third dielectric layer of the circularly polarized antenna layer to connect the third metal layer and the fourth metal layer.

10. A terminal, characterized in that, The terminal uses the broadband low RCS antenna based on the frequency-selective reflection hybrid structure as described in any one of claims 1 to 9.

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