Broadband circularly polarized metasurface antenna with low radar cross section

Abstract

The invention discloses a broadband circular polarization metasurface antenna with a low radar cross section. The broadband circular polarization metasurface antenna is composed of a top layer 4 * 4 antenna array, a middle layer metal ground, a bottom layer one-to-sixteen sequential rotation feed network and two dielectric plates among the three layers. The antenna array is composed of four subarrays which are arranged in a 2 * 2 period, and the four groups of subarrays are symmetrical up and down and left and right along the center of the antenna array and are arranged in a chessboard shape. Each antenna unit in the antenna array comprises a bow-tie-shaped metal patch, and the patch is connected with the output end of the feed network at the bottom layer through a first metalized through hole; the feed network is composed of three one-to-two second-order Wilkinson power dividers, four 90-degree phase shifters, twelve T-shaped power dividers and a plurality of sections of 50-ohm microstrip lines. Through fusion design of the antenna and the metasurface, the problem that in the design process of the metasurface antenna with the low radar cross section, the antenna aperture is increased due to the fact that the antenna and the metasurface are independently designed firstly and then integrated is solved, and the low radar cross section characteristic of the broadband and the high-performance circular polarization radiation characteristic are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of microwave antennas, and in particular to a broadband circularly polarized metasurface antenna with a low radar cross section. Background Art

[0002] Antennas are an important part of wireless communication equipment. Improving their performance has always been one of the important ways to improve the performance of communication systems. Therefore, high-performance antennas are constantly being designed and widely used. Metasurface antennas, as a new type of antenna, have received extensive attention and research in recent years. Metasurface antennas not only have the functions of transmitting and receiving electromagnetic waves of traditional antennas, but also can provide metasurface control functions such as polarization conversion, frequency selection, absorption and scattering of electromagnetic waves, and phase coding.

[0003] In addition, compared with linear polarization antennas, circular polarization antennas have the advantages of reducing multipath interference and multipath fading, overcoming polarization distortion caused by the Faraday rotation effect of the ionosphere, and reducing polarization mismatch loss. Therefore, broadband circularly polarized antennas with low radar cross-section can improve the communication quality while improving the electromagnetic stealth effect.

[0004] Traditional low radar cross-section circularly polarized metasurface antennas usually design the metasurface and antenna separately first, and then integrate the two. Under this design concept, the metasurface part plays an auxiliary role in improving the performance of the entire antenna. In the design process, the antenna and metasurface are not truly highly integrated and optimally achieved. In addition, the addition of the metasurface may also lead to problems such as an increase in the antenna aperture or an increase in the profile. Summary of the invention

[0005] Purpose of the invention: The purpose of the present invention is to provide a broadband circularly polarized metasurface antenna with a simple structure that can significantly reduce the radar scattering cross-section effect.

[0006] Technical solution: To achieve the above-mentioned purpose, a broadband circularly polarized metasurface antenna with a low radar scattering cross-section described in the present invention includes a 4×4 antenna array layer and a one-to-sixteen sequential rotating feed network layer. The 4×4 antenna array is divided into four groups of 2×2 periodically arranged antenna subarrays, and each antenna subarray includes an antenna unit composed of a bowtie-shaped metal patch, and the bowtie-shaped metal patch is connected to the sixteen output terminals of the feed network through a first metallized via.

[0007] Among them, the antenna array is located on the top layer, the feeding network is located on the bottom layer, the middle layer between the top layer and the bottom layer is a metal layer, a first dielectric plate is provided between the top layer and the middle layer, a second dielectric plate is provided between the middle layer and the bottom layer, and the first metallized via passes through the first dielectric plate, the metal layer, and the second dielectric plate to connect with the feeding network.

[0008] Wherein, a circular hole for passing the first metallized via hole is provided on the metal stratum, and the first metallized via hole is not in contact with the metal stratum.

[0009] The bow tie-shaped metal patch is composed of a circular structure and two fan-shaped structures, and an "L"-shaped groove is opened on the circular structure.

[0010] Wherein, the bowtie-shaped metal patch is placed along the diagonal line of the array unit.

[0011] Among them, when the four antenna sub-arrays in the 4×4 antenna array are symmetrical up and down and left and right relative to the horizontal center line of the antenna array layer and are arranged in a checkerboard shape, the bowtie-shaped metal patch serves as the radiation unit of the antenna. When a linearly polarized incident wave is incident, the antenna causes the reflected linearly polarized waves to cancel each other out due to a phase difference of 180°.

[0012] Among them, when the antenna units are arranged in a two-dimensional periodic manner to form an infinitely large metasurface, the bowtie-shaped metal patch serves as the metasurface unit of the antenna, converting the x- or y-polarized incident wave into a cross-polarized wave within a specific frequency band.

[0013] The feeding network is composed of three second-order Wilkinson power dividers, four 90° phase shifters, twelve T-shaped power dividers and several 50-ohm microstrip lines, including a signal input end and four signal output ends. The output phases of the four signal output ends differ by 90° respectively, and each signal output end is connected to two power distribution networks composed of T-shaped power dividers. The four power distribution networks are respectively used for feeding 4×4 antenna arrays.

[0014] The phases of the output signals of the four signal output terminals satisfy the counterclockwise rotation relationship of 0°, -90°, -180°, and -270°.

[0015] The output signal of each signal output terminal is equally distributed to four antenna units of an antenna subarray through three T-shaped power dividers.

[0016] Beneficial effects: The present invention has the following advantages: 1. The broadband circularly polarized radiation metasurface antenna with low radar scattering cross-section proposed in the present invention integrates the design of the antenna and the metasurface unit into the same structure, and the antenna profile is relatively low; 2. Due to the polarization conversion capability of the bowtie-shaped periodic array and the checkerboard arrangement design of the bowtie-shaped units on the top layer of the metasurface antenna, the radar scattering cross-section inside and outside the band is significantly reduced; 3. By reasonably designing a sequential rotating feeding network with a simple structure and broadband working characteristics, the circularly polarized radiation axis of the antenna is wider than the bandwidth, and the in-band directivity pattern is stable. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the decomposition of the metasurface antenna structure in an embodiment of the present invention;

[0018] Figure 2 A top view of a bowtie-shaped antenna unit according to an embodiment of the present invention;

[0019] Figure 3 Schematic diagram of a polarization conversion metasurface in an embodiment of the present invention;

[0020] Figure 4 A top view of a metasurface antenna in an embodiment of the present invention;

[0021] Figure 5 This is a bottom view of a metasurface antenna in an embodiment of the present invention;

[0022] Figure 6 : is the reflection coefficient and gain diagram of the bowtie-shaped antenna unit in an embodiment of the present invention and its normalized 2D radiation pattern at the resonant frequency;

[0023] Figure 7 This is a graph of the polarization conversion performance of the metasurface in an embodiment of the present invention;

[0024] Figure 8 A working performance diagram of a sequentially rotating feeder network in an embodiment of the present invention;

[0025] Fig. 9 is a reflection coefficient diagram of a metasurface antenna in an embodiment of the present invention;

[0026] Fig.10 is an axial ratio diagram of a metasurface antenna in an embodiment of the present invention;

[0027] Fig.11 is a gain diagram of a metasurface antenna in an embodiment of the present invention;

[0028] Fig.12 is the normalized radiation pattern of the metasurface antenna at different frequencies in the embodiment of the present invention;

[0029] Fig.13 This is a single-station radar cross-section performance diagram of the metasurface antenna in an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described in detail below in conjunction with the embodiments and drawings.

[0031] like Figure 1 As shown, a broadband circularly polarized metasurface antenna with a low radar scattering cross section described in the present invention includes a top layer, a middle layer, a bottom layer, a first dielectric plate 3 located between the top layer and the middle layer, and a second dielectric plate 6 located between the middle layer and the bottom layer, wherein the top layer includes a 4×4 antenna array composed of sixteen bowtie-shaped metal patches 1, the middle layer is a metal ground 4, and the bottom layer is a one-to-sixteen sequential rotating feeding network 7.

[0032] Among them, the 4×4 antenna array is divided into four groups of 2×2 periodically arranged sub-arrays, and the four sub-arrays are symmetrical up and down and left and right relative to the horizontal center line of the top layer, and are arranged in a chessboard shape as a whole and attached to the upper side of the first dielectric plate 3 with a thickness of h1. The radiation part of each antenna unit in the antenna array is a bow tie-shaped metal patch 1, and an "L"-shaped gap is opened inside the metal patch 1, and the center of the metal patch 1 is connected to the first metallized via 2, and the metallized via 2 passes through the first dielectric plate 3, the metal ground 4, and the second dielectric plate 6 respectively, and finally connected to the bottom feeding network 7; the middle metal ground layer 4 has sixteen circular holes, and the first metallized via 2 passes through the center of the circular hole opened on the metal ground layer 4 but does not contact the metal ground 4. The one-to-sixteen sequential rotation feeding network 7 consists of three second-order Wilkinson power dividers, four 90° phase shifters, twelve T-shaped power dividers and a number of 50 ohm microstrip lines, and is attached to the lower side of the second dielectric plate 6 with a thickness of h2. Each of the 90° phase shifters is connected to the metal ground 4 via a group of second metallized vias 5. The relative dielectric constant of the first dielectric plate 3 and the second dielectric plate 6 is 2.2, and the loss tangent is 0.002.

[0033] like Figure 2 As shown, the side length of the antenna unit is p, and its radiating part is a bowtie patch, which is composed of a circular structure with a diameter of d_inn and two fan-shaped structures with an angle θ (the size of the angle θ needs to be optimized according to the radiation and scattering performance requirements) and a radius of d_out / 2. An "L"-shaped groove with a width of w is opened on the circular structure, and the distance between the inner edge of the "L"-shaped groove and the center of the unit is d. The bowtie patch is placed along the diagonal of the unit, and the center of the patch is connected to the first metallized via 2 with a diameter of d_coax.

[0034] The bow-tie-shaped metal patch 1 is both a radiation unit of the antenna and a polarization conversion metasurface unit; as an antenna unit, it radiates linearly polarized electromagnetic waves; as a metasurface unit, it can convert x- or y-polarized incident waves into cross-polarized waves, i.e., y- or x-polarized reflected waves, within the required frequency band. Therefore, this design can achieve joint regulation of electromagnetic wave radiation and scattering by arranging the bow-tie-shaped metal patches in a two-dimensional plane according to certain rules to form a metasurface antenna, so as to simultaneously obtain good radiation and scattering characteristics.

[0035] Figure 3 The figure shows a schematic diagram of 4×4 units selected from an infinitely large metasurface formed by a two-dimensional periodic arrangement of antenna units. The metasurface can convert x- or y-polarized incident waves into cross-polarized waves, i.e., y- or x-polarized reflected waves, within the required working frequency band.

[0036] like Figure 4As shown in the figure, the 4×4 antenna array is composed of 2×2 periodically arranged sub-arrays, and the four groups of sub-arrays are symmetrical in both vertical and horizontal directions to form a chessboard layout. In order to achieve a better radar cross-section reduction effect, a cross-shaped gap with a width of dm is left between the four groups of sub-arrays. According to the principle of phase cancellation, when a single linearly polarized wave is incident on the antenna surface, the chessboard arrangement of the array can make the linearly polarized waves reflected by adjacent sub-arrays cancel each other due to a phase difference of 180°, thereby reducing the radar cross-section of the target.

[0037] like Figure 5 As shown, the one-to-sixteen sequential rotation feeding network is composed of three second-order Wilkinson power dividers 701, four 90° phase shifters 704, twelve T-shaped power dividers 705 and several 50 ohm microstrip lines. Resistor 702 (R1) and resistor 703 (R2) are connected between the two transmission lines of each second-order Wilkinson power divider. If only the transmission characteristics of the five ports of port 706, port 707, port 708, port 709 and port 710 are considered, the signal input from port 706 will be output to the other four ports with equal amplitude, and the output phases of these four ports are 90° different in sequence. Each of ports 707, port 708, port 709 and port 710 is connected to two power distribution networks composed of T-shaped power dividers, thereby forming the above-mentioned one-to-sixteen sequential rotation feeding network. By optimizing and selecting appropriate structural parameters, the broadband circularly polarized metasurface antenna with low radar scattering cross section can achieve right-hand circularly polarized radiation in a wider frequency band, while significantly reducing the radar scattering cross section inside and outside the structural band. The structural parameters selected in the embodiment of the present invention are: h1=3mm, h2=0.5mm, p=15mm, d_inn=4mm, θ=55°, d_out=15mm, w=0.3mm, d=1.3mm, d_coax=0.6mm, dm=3mm, R1=65Ω, R2=505Ω.

[0038] Figure 6 The figure shows the radiation performance diagram of the bow tie antenna unit, where Figure (a) is the reflection coefficient and gain diagram of the antenna unit, and Figure (b) is the normalized radiation diagram of the bow tie antenna unit at the resonant frequency. As shown in Figure (a), the resonant frequency of the antenna unit in this embodiment is 8.45 GHz, and the maximum gain of 6.88 dBi is obtained at the frequency of 8.05 GHz. The normalized radiation diagram shown in Figure (b) shows that the antenna radiates well, and the main radiation lobe is in the +z direction.

[0039] Figure 7 for Figure 3 The polarization conversion performance diagram of the two-dimensional infinite period structure shown in . Figure 7 (a) is the co-polarization reflection coefficient R obtained when the x (or y) polarized wave is incident on the metasurface xx (or R yy) and the cross-polarization reflection coefficient R yx (or R xy ); Figure (b) shows the polarization conversion rate when the corresponding x (or y) polarized wave is incident. It should be noted that when the x-polarized electromagnetic wave When incident vertically onto the metasurface, the reflected wave contains an x-polarization component. and the y-polarization component Defining the co-polarization reflection coefficient and the cross-polarization reflection coefficient They are used to measure the degree of co-polarization reflection and cross-polarization reflection of the metasurface. Similarly, for the y-polarized incident electromagnetic wave, the corresponding co-polarization reflection coefficient and cross-polarization reflection coefficient are defined as and On this basis, the polarization conversion rate is defined (x-polarized incident) and (y-polarized incident) is used to measure the polarization conversion capability. Generally speaking, if PCR is greater than 0.9 within a certain frequency range, it indicates that the tested structure has good polarization conversion capability within the frequency range. Figure 7 (a) It can be seen that in the frequency band of 8.06-16.43 GHz, the co-polarization reflection coefficient of the metasurface is below -10 dB, and the cross-polarization reflection coefficient is close to 0 dB. Figure 7 (b) shows that the polarization conversion rate of the periodic structure is above 0.9 in the frequency band of 8.12-16.36 GHz, indicating that the periodic structure has good polarization conversion performance in the range of 8.12-16.36 GHz. The two-dimensional infinite periodic structure composed of bowtie-shaped units constitutes a linearly polarized polarization conversion metasurface.

[0040] Figure 8 is the performance diagram of the bottom feeding network; here we only consider the S parameters when the signal is input from port 706 and output from ports 707, 708, 709 and 710 after distribution. Figure 8 (a) is the amplitude of each S parameter, Figure 8 (b) is the phase difference of the S parameters of adjacent output ports. The subscript numbers 1, 2, 3, 4, and 5 of the S parameters represent ports 706, 707, 708, 709, and 710, respectively. Figure 8 (a) It can be seen that in the frequency range of 5.2-12.0 GHz, |S 11 |Always remain below -10dB, which means that port 706 has a good match; |S 21 |、|S 31 |、|S 41 | and |S 51|All remain near -6dB, which means that the signal power output from ports 707, 708, 709 and 710 accounts for about 1 / 4 of the input signal power of port 706. Figure 8 (b) The phase difference of adjacent output ports is kept within 90°±25° in the 5.2-12.0 GHz frequency band, indicating that the network has the characteristics of sequential rotation feeding. The above results show that the designed feeding network has good broadband sequential rotation feeding characteristics.

[0041] Fig. 9 The figure shows the reflection coefficient of the metasurface antenna at port 706 in the embodiment of the present invention. It can be concluded from the figure that the impedance bandwidth with a reflection coefficient less than -10 dB is 5.0-14.1 GHz.

[0042] Fig.10 This is a trend graph of the axial ratio of the main radiation direction (+z direction) of the metasurface antenna changing with frequency. From the graph, it can be read that the frequency band in which the axial ratio of the metasurface antenna is less than 3dB is 4.8-13.4GHz.

[0043] Fig.11 The gain of the metasurface antenna in the main radiation direction varies with frequency. As can be seen from the figure, the metasurface antenna has a maximum gain of 12.8dBic at a frequency of 8.4GHz, and a 3dB gain bandwidth of 7.3-12.1GHz.

[0044] Fig.12 (a) to (f) are the normalized radiation patterns of the metasurface antenna at 7 GHz, 8 GHz, 9 GHz, 10 GHz, 11 GHz and 12 GHz, respectively. As can be seen from the figure, as the frequency increases, the main lobe of the antenna always remains in the +z direction but its beam width gradually narrows. At the same time, the side lobes of the antenna begin to increase, and the side lobe amplitude gradually becomes stronger. Fig.12 The results show that the radiation pattern of the metasurface antenna in the embodiment of the present invention still has stable radiation characteristics within a wider frequency band.

[0045] Fig.13 This is a single-station radar cross-section performance diagram of a metasurface antenna and an equal-sized metal plate. By comparing the single-station radar cross-section scattering performance diagrams of a metasurface antenna and an equal-sized metal plate, it can be seen that the metasurface antenna can achieve radar cross-section reduction in a wider frequency band, among which the 10dB reduction range can cover the 9.4-22.2GHz frequency band.

[0046] In summary, the broadband circularly polarized metasurface antenna with low radar cross section proposed in the present invention integrates the design of the antenna and the metasurface unit into the same structure, that is, the bowtie-shaped metal patch is both the radiator of the antenna unit and the metasurface unit, which can reduce the radar cross section of the antenna without increasing the size of the antenna and does not affect the radiation performance of the antenna. Through reasonable design, the right-handed circular polarization axis of the antenna is wider than the bandwidth, and the in-band radiation pattern is stable, so it can be used in communication systems that require broadband electromagnetic stealth.

Claims

1. A broadband circularly polarized metasurface antenna with low radar cross section, characterized in that: It includes a 4×4 antenna array layer and a one-to-sixteen sequential rotating feed network layer. The 4×4 antenna array is divided into four groups of 2×2 periodically arranged antenna subarrays. Each antenna subarray includes an antenna unit composed of a bowtie-shaped metal patch. The bowtie-shaped metal patch is connected to the sixteen output ends of the feed network through a first metallized via.

2. The broadband circularly polarized metasurface antenna with low radar cross section according to claim 1, characterized in that: The antenna array is located on the top layer, the feeding network is located on the bottom layer, a metal ground layer is provided on the middle layer between the top layer and the bottom layer, a first dielectric plate is provided between the top layer and the middle layer, a second dielectric plate is provided between the middle layer and the bottom layer, and the first metallized via passes through the first dielectric plate, the metal ground layer, and the second dielectric plate to be connected to the feeding network.

3. The broadband circularly polarized metasurface antenna with low radar cross section according to claim 2, characterized in that: The metal stratum is provided with a circular hole for passing the first metallized via hole, and the first metallized via hole is not in contact with the metal stratum.

4. The broadband circularly polarized metasurface antenna with low radar cross section according to claim 1, characterized in that: The bow tie-shaped metal patch is composed of a circular structure and two fan-shaped structures, and an "L"-shaped groove is opened on the circular structure.

5. The broadband circularly polarized metasurface antenna with low radar cross section according to claim 4, characterized in that: The bow-tie-shaped metal patch is placed along the diagonal line of the array unit.

6. The broadband circularly polarized metasurface antenna with low radar cross section according to claim 5, characterized in that: When the four antenna sub-arrays in the 4×4 antenna array are arranged vertically and horizontally symmetrically with respect to the horizontal center line of the antenna array layer and in a chessboard shape, the bowtie-shaped metal patch serves as a radiation unit of the antenna.

7. The broadband circularly polarized metasurface antenna with low radar cross section according to claim 5, characterized in that: When the antenna units are arranged two-dimensionally and periodically to form an infinitely large metasurface, the bowtie-shaped metal patch serves as the metasurface unit of the antenna.

8. The broadband circularly polarized metasurface antenna with low radar cross section according to claim 1, characterized in that: The feeding network is composed of three second-order Wilkinson power dividers, four 90° phase shifters, twelve T-shaped power dividers and a number of 50-ohm microstrip lines, including a signal input end and four signal output ends. The output phases of the four signal output ends differ by 90° respectively, and each signal output end is connected to two power distribution networks composed of T-shaped power dividers. The four power distribution networks feed the 4×4 antenna array respectively.

9. The broadband circularly polarized metasurface antenna with low radar cross section according to claim 8, characterized in that: The phases of the output signals of the four signal output terminals satisfy the counterclockwise rotation relationship of 0°, -90°, -180°, and -270°.

10. The broadband circularly polarized metasurface antenna with low radar cross section according to claim 8, characterized in that: The output signal of each signal output terminal is equally distributed to the four antenna elements of an antenna subarray through three T-shaped power dividers.

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