A triple-polarized reconfigurable metasurface antenna with low RCS characteristics

Abstract

The present invention belongs to the technical field of microwave antennas, and discloses a three-polarized reconfigurable metasurface antenna with low RCS characteristics, which includes, from top to bottom, an upper metasurface metal layer with a rotation phase slot, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer, and a bottom feed network metal layer, wherein the upper metasurface metal layer is composed of 4*4 periodically arranged metasurface units, and each of the metasurface units is provided with three congruent slots in the center obliquely, and 2*2 four metasurface units constitute a metasurface unit group, and the four metasurface unit groups are distributed in a 90-degree rotation to form a metasurface pattern that is generally symmetrical about left and right, up and down, and obliquely 45°, and the intermediate metal layer is located between the upper and lower dielectric layers and is closely attached to the upper and lower dielectric layers. The present invention introduces low RCS characteristics into a traditional polarization reconfigurable antenna, while improving the circular polarization bandwidth, etc., so that the availability of the low RCS polarization reconfigurable antenna is greatly increased.

Description

Technical Field

[0001] The invention belongs to the technical field of microwave antennas, and specifically relates to a three-polarization reconfigurable supersurface antenna with low RCS characteristics. Background Art

[0002] Wireless communication and military communication have increasing requirements for antenna performance. Antenna, as the terminal of the transmitter and the starting point of electromagnetic wave radiation, is the cornerstone of wireless communication development. After the introduction of the design of patch antenna on metasurface, great and rapid progress has been made.

[0003] Metasurface is an artificial sub-wavelength periodically arranged oscillator with negative refractive index. Its anomalous properties such as negative refractive index have attracted widespread attention for its application. In recent years, the research on metasurface antennas has made great progress: metasurfaces can be used as upper layer enhancement amplifiers of antennas, can be integrated with antennas, and used as radiation patches of the antennas themselves. To enhance the local performance of antennas. Metasurfaces, as a powerful tool in the new stage of antenna development, complement and influence each other with antennas. In addition, the limitations of antennas with single polarization performance in modern communication systems have spawned the development of polarization reconfigurable antennas. Multiple polarization reconfigurable antennas generally increase the complexity of the antenna feeding network and increase the number and thickness of the antenna substrate, which is not conducive to the design and processing of polarization reconfigurable antennas. In addition, the addition of too many PIN tubes and MEMS switches will weaken the radiation efficiency of polarization reconfigurable antennas and reduce the in-band gain stability.

[0004] Radar cross section (RCS) indicates the amount of scattering of a target object after it is illuminated by radar waves, and is also the equivalent reflection area reflected by the incident wave. Antennas with reduced out-of-band RCS are generally used as radomes of the original antenna, which increases the physical size of the antenna and is not conducive to commonality; and frequency selective surfaces will strongly reflect radar incident waves out-of-band.

[0005] There are many shortcomings in the existing polarization reconfigurable metasurface antennas: 1. The existing polarization reconfigurable antenna feeding network is relatively complex, and the feeding network with too many parameters makes the antenna design and parameter adjustment relatively time-consuming. 2. The performance of the existing polarization reconfigurable antenna is insufficient, and there is no similar low RCS three-polarization reconfigurable metasurface antenna available. 3. The introduction of too many PIN tubes and MEMS switches in common polarization reconfigurable antennas will change the original performance of the antenna. How to achieve more polarization types with fewer PIN tubes is the main direction and goal of the current reconfigurable antenna.

[0006] Therefore, there is an urgent need for a low-profile, multi-polarization integrated low RCS antenna with a simple feeding method. Summary of the invention

[0007] In order to solve the above technical problems, the present invention provides a three-level reconfigurable metasurface antenna with the third RCS characteristic, which aims to solve the above-mentioned shortcomings of the prior art and explore a new low RCS three-polarization reconfigurable metasurface antenna, simplify the feeding network design of the polarization reconfigurable metasurface antenna, integrate the metasurface antenna reflection layer and the radiation layer, introduce the low RCS characteristics into the traditional polarization reconfigurable antenna, and improve the circular polarization bandwidth, etc., so that the availability of the low RCS polarization reconfigurable antenna is greatly increased.

[0008] In order to achieve the above object, the present invention is achieved through the following technical solutions:

[0009] The present invention discloses a three-polarization reconfigurable metasurface antenna with low RCS characteristics. The three-polarization reconfigurable metasurface antenna comprises, from top to bottom, an upper metasurface metal layer with rotational phase slots, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer and a bottom feed network metal layer. The upper metasurface metal layer is composed of 4*4 periodically arranged metasurface units. Three congruent slots are arranged diagonally in the center of each metasurface unit. The slots are evenly distributed in the middle of each metasurface unit, and the three slots do not overlap with each other, and the spacing between two adjacent slots is equal. Four 2*2 metasurface units constitute a metasurface unit group. The four metasurface unit groups are distributed in a 90-degree rotation to form a metasurface pattern that is generally symmetrical about left and right, up and down, and diagonally 45 degrees. The intermediate metal layer is located between the upper dielectric layer and the lower dielectric layer and is tightly fitted with the upper dielectric layer and the lower dielectric layer. The geometric centers of the upper metasurface metal layer, the intermediate metal layer and the bottom feed network metal layer are all on the same straight line.

[0010] A further improvement of the present invention is that there is a cross-shaped opening at the geometric center of the square of the middle metal layer, and the feeding energy of the three polarization modes is coupled to the upper super-surface metal layer through the cross-shaped opening to generate radiation, and the long side of the cross-shaped opening is parallel to the length of the outer contour of the antenna.

[0011] The bottom metal layer of the feeding network includes three independently working ports, three microstrip lines extending to the center and an open ring. The cross-shaped openings and the open ring of the middle metal layer overlap to facilitate magnetic coupling. The port energy is introduced into the microstrip line by the impedance matching line and finally transmitted to the central 270-degree open ring through the PIN tube. The outer side of the open ring is connected to three independently working PIN tubes. Power is fed in at 0 degrees, 135 degrees and 270 degrees of the open ring, forming different electric field propagation modes.

[0012] The equivalent resistance of the three PIN tubes in the on state is 5.2 ohms, and the equivalent capacitance in the off state is 0.025 pF.

[0013] When a port is fed, a DC bias is applied to the corresponding PIN tube on the microstrip of the port to switch it to the on state. The equivalent resistance of the PIN tube in the on state should not be too high. Port 1 and port 2 are mirror-symmetric about a plane parallel to the z-axis at a 45-degree angle, so port 1 and port 2 have the same performance indicators and work in polarization modes with opposite circular polarization directions. When port 1 is fed alone, the antenna radiates left-handed circularly polarized waves; when port 2 is fed alone, the antenna radiates right-handed circularly polarized waves. This greatly simplifies the complex feeding network design process of the traditional polarization reconfigurable antenna.

[0014] When one port is working, the insertion loss of the other ports is completely controlled by the disconnection of the PIN tube, which is less than -20dB. When port three is fed, the antenna works in linear polarization mode. At this time, the open ring is symmetrical with respect to the feeding position of port three, similar to the Wilkinson power divider structure. The electric field strength and phase of the arcs on both sides of the open ring are consistent, so a linear polarization wave is formed.

[0015] The three reconfigurable polarization modes are:

[0016] When PIN tube No. 1 is turned on and PIN tubes No. 2 and 3 are turned off, power is fed to port 1 to generate a left-hand circularly polarized wave;

[0017] When PIN tube No. 2 is turned on and PIN tubes No. 1 and 3 are turned off, power is fed to port 2 to generate a right-hand circularly polarized wave;

[0018] When PIN tube No. 3 is turned on and PIN tubes No. 1 and 2 are turned off, power is fed to port 3 to generate a linearly polarized wave.

[0019] The gap width between the microstrip and the open ring where each PIN tube is located is consistent. At the gap, the microstrip and open ring feeding structures are completely separated, and only the PIN tube controls the on-off.

[0020] The beneficial effects of the present invention are:

[0021] The present invention has a low RCS three-polarization reconfigurable metasurface antenna, which fills the gap in the field of polarization reconfigurable metasurface antennas in radar stealth.

[0022] Compared with traditional polarization reconfigurable antennas, the feed network design process is simplified, and a reusable feed network is used to achieve a circular polarization bandwidth that exceeds that of traditional polarization reconfigurable antennas. The simple structure of the feed network reduces the use of PIN tubes and micro-nano devices, which is very beneficial for reducing cross-polarization during antenna radiation, has lower interference with the main polarization, and improves the main polarization radiation efficiency.

[0023] The present invention innovatively combines the radiation layer and the reflection layer of the low RCS antenna, and introduces three incident wave resonance points at the out-of-band high frequency by opening 3*16 slots on the metasurface metal layer, thereby achieving a significant 6dB single-station RCS reduction with minimal sacrifice of the antenna's in-band radiation gain.

[0024] Compared with traditional low RCS antennas, the profile height and radiation surface area are saved, so that the present invention has a lower profile and smaller size, which is easy to conform to targets such as aircraft and tanks. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the decomposed structure of the reconfigurable metasurface antenna of the present invention.

[0026] Figure 2 It is a top view of the reconfigurable metasurface antenna of the present invention.

[0027] Figure 3 This is a left-hand circularly polarized S-parameter diagram of a one-port-fed reconfigurable metasurface antenna of the present invention.

[0028] Figure 4 It is a two-port fed right-hand circularly polarized S-parameter diagram of the reconfigurable metasurface antenna of the present invention.

[0029] Figure 5 It is the S parameter diagram of the three-port fed 45-degree linear polarization of the reconfigurable metasurface antenna of the present invention.

[0030] Figure 6 It is the RCS diagram of the working bandwidth of the reconfigurable metasurface antenna of the present invention and the reference slot antenna.

[0031] Figure 7 It is an axial ratio curve diagram of left-handed and right-handed circular polarization of the reconfigurable metasurface antenna of the present invention.

[0032] Figure 8 It is a curve diagram of gain versus frequency variation of three polarization modes of the reconfigurable metasurface antenna of the present invention.

[0033] Fig. 9 It is a left-handed circularly polarized radiation pattern of a single-port feeding of the reconfigurable metasurface antenna of the present invention.

[0034] Fig.10 It is the two-port fed right-hand circular polarization pattern of the reconfigurable metasurface antenna of the present invention.

[0035] Fig.11 It is the three-port feeding 45-degree linear polarization pattern of the reconfigurable metasurface antenna of the present invention.

[0036] Fig.12 It is a bottom view of the reconfigurable metasurface antenna of the present invention. DETAILED DESCRIPTION

[0037] The following will disclose the embodiments of the present invention with drawings. For the purpose of clear description, many practical details will be described together in the following description. However, it should be understood that these practical details should not be used to limit the present invention. That is to say, in some embodiments of the present invention, these practical details are not necessary.

[0038] like Figure 1 As shown, the present invention is a three-polarization reconfigurable metasurface antenna with low RCS characteristics, which is mainly composed of three metal layers and two dielectric layers of different materials: from top to bottom, it includes an upper metasurface metal layer with a rotating phase slot, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer and a bottom feed network metal layer.

[0039] The upper dielectric layer preferably adopts a 3.5mm thick FR-4 substrate with a dielectric constant of 4.3 and a loss tangent of 0.025. The lower dielectric layer preferably adopts a 0.813mm thick RO4003C substrate with a dielectric constant of 3.55 and a loss tangent of 0.0027. There is a cross-shaped opening at the geometric center of the square of the intermediate metal layer, which facilitates the coupling of the feeding energy of the three polarization modes to the upper super-surface metal layer through the cross hole to generate radiation. The intermediate metal layer is tightly fitted between the upper dielectric layer and the lower dielectric layer, and has no contact with the upper super-surface metal layer and the lower feeding network metal layer, so that the distance between the upper metal layer and the lower metal layer is always the thickness of the upper dielectric layer, and the distance between the lower metal feeding network layer and the upper metal layer is always the thickness of the lower dielectric layer.

[0040] The slot length of the cross-shaped opening is less than half the side length of the square, and the slot width of the cross-shaped opening is not greater than the outer diameter of the central opening ring of the bottom feed network metal layer. The length of the cross-shaped opening is 22 mm and the width is 4.5 mm. The upper dielectric layer, the middle metal layer and the lower dielectric layer are provided with cut corners, and the antenna is a pentagon with a low-profile structure, and the cut corners are consistent with the outer contours of the upper and lower dielectric plates.

[0041] like Figure 2 As shown, the upper metasurface metal layer is composed of 4*4 periodically arranged metasurface units. Each of the metasurface units is composed of a cut-corner square with a side length of 16.5mm and a cut-corner width of 9.9mm. The gap between each of the metasurface units is 0.9mm. The side length of the square where the outer contour of the three-polarized reconfigurable metasurface antenna is located is not less than 75mm. There is a 45° oblique cut corner in the upper right corner of the top view, and the width of the cut corner is no more than 10mm, which does not overlap with the metasurface unit patch.

[0042] Three congruent slots are arranged obliquely in the center of each metasurface unit. The slots can decompose the incident wave into scattered waves in each reflection direction, thereby realizing a low RCS design. The length of the three slots is 10.5 mm, the width is 1.3 mm, the spacing between two adjacent slots is 3.5 mm, the slots are evenly distributed in the middle of each metasurface unit, the three slots do not overlap with each other, and the spacing between two adjacent slots is equal. Four metasurface units of 2*2 constitute a metasurface unit group. The four metasurface unit groups are distributed in a 90-degree rotation to form an overall metasurface pattern that is symmetrical about left and right, up and down, and obliquely 45°. The intermediate metal layer is located between the upper dielectric layer and the lower dielectric layer and is tightly fitted with the upper dielectric layer and the lower dielectric layer. The geometric centers of the upper metasurface metal layer, the intermediate metal layer, and the bottom feed network metal layer are all on the same straight line.

[0043] like Fig.12 As shown, the bottom feeding network metal layer includes three independently working ports, three microstrip lines extending to the center and an open ring. When the three ports are fed separately, three polarization modes are formed, and different polarization modes are suitable for different communication scenarios. The cross-shaped openings of the intermediate metal layer and the open ring are overlapped in the top view, which is convenient for magnetic coupling. The port energy is introduced into the microstrip line by the impedance matching line and finally the excitation is transmitted to the 270-degree open ring in the center through the PIN tube. The outer side of the open ring is connected to the three independently working PIN tubes, and the feed is respectively given at 0 degrees, 135 degrees and 270 degrees of the open ring, forming different electric field propagation modes. The feeding energy of the three polarization modes is coupled to the upper super-surface metal layer through the cross hole to generate radiation, and the long side of the cross-shaped opening is parallel to the length of the outer contour of the antenna.

[0044] Figure 3 and Figure 4 Feeding port 1 and port 2, the S parameter curve of circular polarization working mode. Because port 1 and port 2 are mirror images in the geometric structure, the performance is exactly the same. Figure 3 Conduct analysis, Figure 4 Same reason. Figure 3 The matching bandwidth of medium return loss reaches 20% (2.2GHz-3.35GHz). Due to the isolation effect of the disconnected PIN tube in the feeder, S21 and S31 are both lower than -20dB within the working bandwidth, and the three-port feeder has excellent port isolation.

[0045] Figure 5 This is the S parameter diagram when the three-port feed works as linear polarization. The matching bandwidth of the return loss reaches 10%.

[0046] (2.42GHz-2.99GHz) At the same time, the maximum values ​​of S23 and S13 do not exceed -25dB, which fully meets the feeder network isolation requirements.

[0047] Figure 6 For comparison of the RCS curves of the reference antenna (slot antenna) and the present invention, according to Figure 6 The -6dB bandwidth of RCS reduction reaches 12% (9.35GHz-11.9GHz), and three resonance points are introduced outside the band to achieve broadband low RCS characteristics.

[0048] Figure 7 The axial ratio bandwidth is shown for left-hand and right-hand circular polarization. When port one is fed, the axial ratio bandwidth for left-hand circular polarization is 8%. When port two is fed, the axial ratio bandwidth for right-hand circular polarization is 10.1%. They are all included in the matching bandwidth of the corresponding port return loss, so the left-hand circular polarization working bandwidth of this embodiment is 8%, and the right-hand circular polarization working bandwidth is 10%.

[0049] according to Figure 8 When the antenna works in circular polarization mode, the maximum gain is about 7dBi, and when the antenna works in linear polarization mode, the maximum gain is 5.8dBi. The gain flatness is good within the working bandwidth.

[0050] Fig. 9 , Fig.10 , Fig.11 The 2.8GHz radiation pattern when port three is fed separately includes the main polarization, i.e. left-hand, right-hand and linear polarization, and cross polarization. It can be seen that the cross polarization is always less than -20dB in the main polarization direction. The polarization purity of the antenna is good in each working mode, and the main directions of the three polarization gains are all radiated forward along the wide side.

[0051] The present invention uses a multiplexed 270-degree open annular coupling feeding method, and feeds three ports at different positions separately to achieve different antenna polarization modes. Good port isolation is generated by controlling the on-off of the PIN tube in the feed network layer. When port one and port two are fed separately, two circularly polarized radiation modes with opposite rotation directions are generated. When port three is fed separately, the antenna radiates a 45-degree linearly polarized wave. Above the antenna feed network, the metasurface unit adopts a 4*4 low RCS three-slot structure with a rotating phase, which integrates the scattering layer of the traditional low RCS structure with the metasurface radiation layer of the antenna, achieving a low-profile structure while ensuring the antenna radiation performance.

[0052] The present invention combines polarization reconfiguration with a low RCS structure, simplifying the complex feed network of common polarization reconfigurable antennas. The characteristics of multiple polarization reconfigurations and low RCS make the present invention have important application prospects in airborne radar stealth antennas.

[0053] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A three-polarized reconfigurable metasurface antenna with low RCS characteristics, characterized in that: The three-polarization reconfigurable metasurface antenna includes, from top to bottom, an upper metasurface metal layer with rotating phase slots, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer and a bottom feed network metal layer. The upper metasurface metal layer is composed of 4*4 periodically arranged metasurface units. Three congruent slots are arranged diagonally in the center of each metasurface unit. The slots are evenly distributed in the middle of each metasurface unit, and the three slots do not overlap with each other, and the spacing between two adjacent slots is equal. Four 2*2 metasurface units constitute a metasurface unit group. The four metasurface unit groups are rotated 90 degrees to form an overall metasurface pattern that is symmetrical about left and right, up and down, and diagonally 45°. The intermediate The metal layer is located between the upper dielectric layer and the lower dielectric layer and is tightly attached to the upper dielectric layer and the lower dielectric layer. The geometric centers of the upper metasurface metal layer, the intermediate metal layer and the bottom feed network metal layer are all on the same straight line. There is a cross-shaped opening at the geometric center of the square of the intermediate metal layer. The bottom feed network metal layer includes three independently working ports, three microstrip lines extending toward the center and an open ring. Each microstrip line is connected to the open ring through a PIN tube. The cross-shaped opening of the intermediate metal layer and the open ring are in an overlapping relationship. Each of the metasurface units is composed of a cut-corner square, the number of cut corners is 2 and they are respectively located at two diagonal corners of the square.

2. The three-polarization reconfigurable metasurface antenna with low RCS characteristics according to claim 1, characterized in that: The feeding energy of the three polarization modes is coupled to the upper metasurface metal layer through the cross hole to generate radiation, and the long side of the cross hole is parallel to the side length of the outer contour of the antenna.

3. The three-polarization reconfigurable metasurface antenna with low RCS characteristics according to claim 1, characterized in that: The port energy is introduced into the microstrip line by the impedance matching line and finally transmitted to the central 270-degree open ring through the PIN tube. The outer side of the open ring is connected to three independently working PIN tubes. Power is fed into the open ring at 0 degrees, 135 degrees and 270 degrees, respectively, forming different electric field propagation modes.

4. The three-polarization reconfigurable metasurface antenna with low RCS characteristics according to claim 3, characterized in that: The equivalent resistance of the three PIN tubes in the on state is 5.2Ω, and the equivalent capacitance in the off state is 0.025pF.

5. The three-polarization reconfigurable metasurface antenna with low RCS characteristics according to claim 3, characterized in that: When one of the ports is working, a DC bias is added to the PIN tube on the microstrip line where the port is located to make it conductive, and the other two PIN tubes remain disconnected, so that the energy is confined to the open ring in the center, magnetically coupled to the upper metasurface metal layer to generate polarized waves, thereby forming a polarized reconfigurable antenna.

6. The three-polarization reconfigurable metasurface antenna with low RCS characteristics according to claim 1, characterized in that: The unit area of ​​the remaining super surface unit after the slot hole is opened should not be less than two-thirds of the area of ​​the square in which it is located.

7. The three-polarization reconfigurable metasurface antenna with low RCS characteristics according to claim 6, characterized in that: The side length of the square is 16.5 mm, the corner width is 9.9 mm, and the gap between each metasurface unit is 0.9 mm.

8. The three-polarization reconfigurable metasurface antenna with low RCS characteristics according to claim 7, characterized in that: The three slots have a length of 10.5 mm and a width of 1.3 mm, and a spacing between two adjacent slots is 3.5 mm.

9. A three-polarization reconfigurable metasurface antenna with low RCS characteristics according to any one of claims 1 to 8, characterized in that: The upper dielectric layer, the middle metal layer and the lower dielectric layer are provided with cut corners, and the antenna is in the shape of a pentagon with a low-profile structure.

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