A broadband circularly polarized pattern diversity antenna based on metasurface units

Abstract

The present invention discloses a broadband circularly polarized pattern diversity antenna based on a metasurface unit. The antenna comprises a top metal layer, an upper dielectric layer, an intermediate metal layer, a lower dielectric layer, and a bottom metal layer arranged from top to bottom. The top metal layer is provided with a metasurface radiating array; the intermediate metal layer is provided with five cross-shaped slots; and the bottom metal layer contains two feeding networks: the feeding network for the first port comprises a microstrip line sequentially coupled feeding structure, and the feeding network for the second port comprises three Wilkinson power dividers and four microstrip line sequentially coupled feeding structures. By utilizing the four characteristic modes of the metasurface array and the sequentially coupled feeding structure, the present invention enables the antenna to radiate circularly polarized waves while achieving pattern diversity. This not only solves the problem of multipath interference in wireless communication systems, but also reduces the antenna profile height and broadens the antenna's operating bandwidth.

Description

Technical Field

[0001] The present invention relates to the technical field of pattern diversity antennas, in particular to a broadband circularly polarized pattern diversity antenna based on a metasurface unit. Background Art

[0002] Improving antenna transmission and reception quality and enhancing spectrum efficiency have become important research areas in antenna design. Diversity technology not only leverages the incoherence of channels to compensate for individual signal fading and mitigate the effects of multipath fading, but also improves channel reliability and stability. Therefore, it is widely used in communication systems. Antenna diversity can be categorized into polarization diversity and pattern diversity. Polarization diversity exploits the mutual independence and non-interference of electromagnetic waves with different polarizations at the same location. Signals of different polarizations are received and combined at the receiving end to compensate for the effects of multipath fading, thereby achieving stable signal reception. Pattern diversity is more challenging than polarization diversity. This is because different operating modes require different radiation patterns, and these modes typically have different operating frequencies. Using multiple antennas inevitably complicates the overall structure and increases size. Pattern diversity antennas utilize pattern diversity to achieve uncorrelated channels, effectively addressing the problem in diversity systems where coupling between radiating elements can significantly increase signal correlation and reduce radiation efficiency.

[0003] Furthermore, circularly polarized antennas are very effective in combating multipath interference. Based on current reports, there are very few antennas that combine circular polarization performance with pattern diversity. Furthermore, they often have multi-layered, relatively complex structures and narrow operating bandwidths. Based on our research and understanding, the following existing technologies have been made public:

[0004] In 2014, Changjiang Deng, Zhenghe Feng, et al. published a paper titled "A Circularly Polarized Pattern Diversity Antenna for Hemispherical Coverage" in the journal IEEE Transactions on Antennas and Propagation. They proposed a two-part antenna that achieves circular polarization performance with pattern diversity. One component, a co-directionally fed bent monopole, provides an omnidirectional radiation pattern, while the other, through the excitation of an L-shaped monopole, achieves broadside circular polarization. Due to the curved microstrip and double-layer structure, the antenna is relatively complex and has a relatively narrow operating bandwidth of only 6.3%.

[0005] In 2018, Wei Lin, Hang Wong, et al. published a paper titled "Circularly Polarized Antenna With Reconfigurable Broadside and Conical Beams Facilitated by a Mode Switchable Feed Network" in the IEEE Transactions on Antennas and Propagation. They proposed a circularly polarized antenna with reconfigurable radiation patterns. The antenna utilizes a reconfigurable feed network and L-shaped probe coupling to excite the TM11 and TM21 modes of the upper radiating antenna, forming a circularly polarized antenna with reconfigurable broadside and conical radiation patterns. However, the antenna requires a reconfigurable DC bias circuit, making the overall structure relatively complex and resulting in a high profile. Furthermore, the antenna's operating bandwidth is only 7.8%, a relatively narrow one.

[0006] The difficulty of solving the above technical problems is: while achieving pattern diversity, the antenna cross-section can be kept smaller than 0.07λ0 and the antenna can obtain a wider operating bandwidth.

[0007] The significance of solving the above technical problems: Solving the above technical problems is conducive to achieving pattern diversity and integration in the communication system using the present invention as the antenna, and solves the requirement of wireless communication for higher circular polarization bandwidth due to the increase in frequency bands. Summary of the Invention

[0008] In order to solve the above technical problems, the present invention provides a broadband circularly polarized pattern diversity antenna based on a metasurface unit.

[0009] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0010] The present invention is a broadband circularly polarized pattern diversity antenna based on metasurface units, comprising a top metal layer, an upper dielectric layer, a middle metal layer, a lower dielectric layer, and a bottom metal layer arranged from top to bottom. A metasurface radiation array is disposed in the middle of the top metal layer. The array comprises a middle array composed of 3*3 square ring-shaped metal units and an outer array composed of four 3*3 square ring-shaped metal units, forming a cross-shape symmetrical about the central axis. The center of the metasurface radiation array coincides with the center of the upper dielectric layer.

[0011] A cross-shaped middle gap and four cross-shaped outer gaps are provided in the middle position of the middle metal layer, and the middle gap and the outer gaps coincide with the centers of the middle array and the outer array at corresponding positions on the top metal layer;

[0012] Two feeding networks are arranged on the bottom metal layer, wherein the feeding network fed by the first port feeds the metasurface radiation array through the middle microstrip line sequential coupling structure and the middle gap, so that the antenna radiates circularly polarized waves and a broadside radiation pattern; the feeding network fed by the second port feeds the metasurface radiation array through four outer microstrip line sequential coupling structures, three Wilkinson power dividers and four outer gaps, so that the antenna radiates circularly polarized waves and a conical radiation pattern.

[0013] A further improvement of the present invention is that the middle gap and the four outer gaps are formed by two rectangular gaps in the horizontal and vertical directions that are orthogonal to each other, wherein the two rectangular gaps in the middle gap have the same length and width, the width of one of the rectangular gaps of the outer gaps is smaller than the rectangular gap width of the middle gap, the width of the other rectangular gap is the same as the rectangular gap width of the middle gap, and the lengths of the two rectangular gaps of the outer gaps are the same as the length of the middle gap.

[0014] A further improvement of the present invention is that the middle microstrip line sequential coupling structure and the outer microstrip line sequential coupling structure both include a 90-degree phase delay structure, a feeding structure, and an impedance matching structure, wherein the 90-degree phase delay structure lengths of the middle microstrip line sequential coupling structure and the outer microstrip line sequential coupling structure are both 8.13 mm, the feeding structure lengths are both 1.5 mm, the impedance matching structure length of the middle microstrip line sequential coupling structure is 1.4 mm, and the impedance matching structure length of the outer microstrip line sequential coupling structure is 3.4 mm.

[0015] A further improvement of the present invention is that the impedances of the two feeding networks, the first port and the second port are all 50 ohms.

[0016] A further improvement of the present invention is that both the upper dielectric layer and the lower dielectric layer are made of Rogers 4003C high-frequency plate material, with a relative dielectric constant of 3.55 and a loss tangent of 0.0027.

[0017] A further improvement of the present invention is that the length of the upper dielectric layer and the width of the lower dielectric layer are both 115 mm and 100 mm, the thickness of the upper dielectric layer is 3.1 mm, and the thickness of the lower dielectric layer is 0.813 mm.

[0018] A further improvement of the present invention is that the spacing between the middle array and the outer arrays around it is 0.9 mm, the inner side length of the square ring-shaped metal unit in each array is 6.7 mm, the outer side length is 8.7 mm, and the spacing between two adjacent square ring-shaped metal units is 0.9 mm.

[0019] The beneficial effects of the present invention are: the present invention is the first to apply a cross-shaped metasurface radiation array to a circularly polarized pattern diversity antenna, which has the following effects: 1. Compared with the linear polarization pattern diversity antenna, the present invention uses a cross-shaped metasurface unit array composed of square ring-shaped metal units to realize that the antenna radiates circularly polarized waves while achieving pattern diversity, which has a very good effect in resisting multipath interference; 2. The present invention uses metasurface units to broaden the working bandwidth of the antenna, so that the circularly polarized pattern diversity antenna operates between 4.16GHz and 4.76GHz, with a relative bandwidth of 13.4%. Compared with the existing circularly polarized pattern diversity antenna mentioned in the background technology, the antenna working bandwidth of the present invention is increased by about 1 times; 3. The present invention maintains the low-profile characteristics of the antenna, and the cross-section of the antenna is 0.05λ0, which is conducive to the integration of the antenna. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention.

[0021] Figure 2 It is a structural schematic diagram of the metasurface radiation unit of the present invention.

[0022] Figure 3 It is a schematic structural diagram of the intermediate metal layer of the present invention.

[0023] Figure 4 It is a structural diagram of the feeding network of the present invention.

[0024] Figure 5 It is a detailed schematic diagram of the sequential coupling structure of microstrip lines in the feeding network of the present invention.

[0025] Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 and Figure 11 It is a simulation curve diagram of the axial ratio when the microstrip line sequential coupling structure in the feed network of the present invention is designed with different sizes.

[0026] Figure 12 4 is a curve diagram of S-parameter simulation results of an embodiment of the present invention.

[0027] Figure 13 It is a simulation curve diagram of the axial ratio when the broadside radiation pattern (first port feeding) is excited according to an embodiment of the present invention.

[0028] Figure 14 It is a simulation curve diagram of the axial ratio at 4.4 GHz phi=0° and phi=45° when the broadside radiation pattern (first port feeding) is excited according to an embodiment of the present invention.

[0029] Figure 15This is the radiation pattern of phi=0° and phi=45° at 4.4 GHz when the broadside radiation pattern (first port feeding) is excited according to the embodiment of the present invention.

[0030] Figure 16 It is a simulation curve diagram of the axial ratio when the conical radiation pattern (second port feeding) is excited according to an embodiment of the present invention.

[0031] Figure 17 It is a simulation curve diagram of the axial ratio at 4.4 GHz phi=0° and phi=45° when the conical radiation pattern (second port feeding) is excited according to an embodiment of the present invention.

[0032] Figure 18 This is the radiation pattern at 4.4 GHz with phi=0° and phi=45° when the conical radiation pattern is excited (second port feeding) according to the embodiment of the present invention.

[0033] Among them, 1-top metal layer, 2-upper dielectric layer, 3-middle metal layer, 4-lower dielectric layer, 5-first port, 6-bottom metal layer, 7-outer microstrip line sequential coupling structure, 8-outer array, 9-middle array, 10-square ring metal unit, 11-outer gap, 12-second port, 13-Wilkinson power divider, 14-middle gap, 15-middle microstrip line sequential coupling structure. DETAILED DESCRIPTION

[0034] In order to more clearly illustrate the technical solution of the present invention, the technical solution of the present invention is further described in detail below with reference to the accompanying drawings:

[0035] This antenna is a broadband circularly polarized pattern diversity antenna based on a metasurface unit. It comprises three metal layers and two dielectric layers: from top to bottom: top metal layer 1, upper dielectric layer 2, middle metal layer 3, lower dielectric layer 4, and bottom metal layer 6. Both upper dielectric layer 2 and lower dielectric layer 4 are made of Rogers 4003C high-frequency sheet material, with a relative dielectric constant of 3.55 and a loss tangent of 0.0027. Both upper dielectric layer 2 and lower dielectric layer 4 are 115 mm long and 100 mm wide, but upper dielectric layer 2 is 3.1 mm thick, while lower dielectric layer 4 is 0.813 mm thick.

[0036] A central array 9 is formed by nine square ring-shaped metal units arranged in a 3x3 pattern in the center of the top metal layer 1 on the upper surface of the upper dielectric layer 2. Each outer array 8 is formed by nine square ring-shaped metal units arranged in a 3x3 pattern at 0.9mm intervals on each of the four edges of the central array. The inner side of each square ring-shaped metal unit 10 is 6.7mm long, and the outer side is 8.7mm long. The spacing between two adjacent square ring-shaped metal units 10 is 0.9mm.

[0037] The size of the middle metal layer 3 is consistent with the lower surface of the upper dielectric layer 2, with a length of 115 mm and a width of 100 mm. Figure 3 As shown, five cross-shaped slots are provided in the middle dielectric layer 3 for achieving coupling feeding of the middle array 9 and the outer array 8, namely a middle slot located in the middle of the middle dielectric layer 3 and four outer slots located outside the middle slot. Each slot is composed of two mutually orthogonal rectangular slots, wherein the two rectangular slots of the middle slot have the same length and width, the width of one of the rectangular slots of the outer slots is smaller than the width of the rectangular slot of the middle slot, the width of the other rectangular slot is the same as the width of the rectangular slot of the middle slot, and the length of the two rectangular slots of the outer slots is the same as the length of the middle slot. Preferably, the length of the two rectangular slots of the middle slot is 15 mm and the width is 1 mm. The width of one of the rectangular slots of each outer slot is 0.4 mm, the width of the other rectangular slot is 1 mm, and the length is 15.5 mm.

[0038] like Figure 4 As shown, the bottom metal layer 6 includes two feeding networks, wherein the feeding network fed by the first port 5 feeds the metasurface radiation array through the middle microstrip line sequential coupling structure 15 and the middle slot 14, so that the antenna radiates circularly polarized waves and a wide-sided radiation pattern; the feeding network fed by the second port 12 feeds the metasurface radiation array through four outer microstrip line sequential coupling structures 7, three Wilkinson power dividers 13 and four outer slots 11, so that the antenna radiates circularly polarized waves and a conical radiation pattern. The width of the two feeding networks is 1.77mm, and the branch line width of the Wilkinson power divider 13 is 0.9mm and the length is 10.23mm. Figure 5 As shown, the length of the 90-degree phase delay structure 151 of the middle microstrip line sequential coupling structure 15 is L1 = 8.13 mm, the length of the feeding structure 152 is L2 = 1.5 mm, and the length of the impedance matching structure 153 is L3 = 1.4 mm. The length of the 90-degree phase delay structure 71 of the outer microstrip line sequential coupling structure 7 is L4 = 8.13 mm, the length of the feeding structure 72 is L5 = 1.5 mm, and the length of the impedance matching structure 73 is L6 = 3.4 mm. Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 and Figure 11 It is known that the middle microstrip line sequential coupling structure 15 and the outer microstrip line sequential coupling structure 7 designed according to this size provide the metasurface radiation array with two electric field components with equal amplitudes and a phase difference of 90 degrees, which can optimize the axial ratio performance of the antenna.

[0039] The S parameter simulation results of the preferred embodiment of the present invention in CST simulation software are as follows: Figure 12 As shown in the figure, the first port 5 corresponds to port 1 in the simulation software, and port 12 corresponds to port 2. In the figure, |S11| is the curve of the broadside pattern excited by the first port 5, |S22| is the curve of the conical pattern excited by the second port 12, and |S21| is the isolation between the first port 5 and the second port 12. As can be seen from the figure, the common frequency range in which the values ​​of |S11| and |S22| are less than -10dB is 4.12GHz to 4.82GHz. Within the operating frequency range, the isolation band between the two ports is less than -21dB.

[0040] The simulation diagram of the axial ratio variation with frequency when stimulating the broadside radiation pattern of the preferred embodiment of the present invention is as follows: Figure 13 As shown in the figure, it can be seen that the axial ratio of the antenna is less than 3dB at 4.14GHz to 4.76GHz, achieving circular polarization radiation characteristics. The axial ratio diagram and radiation pattern of the antenna at 4.4GHz with phi = 0° and phi = 45° are shown as follows: Figure 14 and Figure 15 As shown, the antenna radiates a broadside radiation pattern with a maximum gain of 4.66dBi and a cross-polarization greater than 19dB.

[0041] The simulation diagram of the axial ratio variation with frequency when the conical radiation pattern is excited in the preferred embodiment of the present invention is as follows: Figure 16 As shown in Figure 1, the antenna has an axial ratio of less than 3dB at 4.16GHz to 4.76GHz, achieving circularly polarized radiation characteristics. The axial ratio diagram and radiation pattern of the antenna at 4.4GHz with phi = 0° and phi = 45° are shown in Figure 1. Figure 17 and Figure 18 As shown, the antenna radiates a conical radiation pattern with a maximum gain of 5.95dBi and a cross-polarization greater than 20dB. Ultimately, the antenna operates in a frequency range of 4.16GHz to 4.76GHz, with a relative bandwidth of 13.4%. The above embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications made to the technical solution in accordance with the technical principles of the present invention fall within the scope of protection of the present invention.

Claims

1. A broadband circularly polarized pattern diversity antenna based on a metasurface unit, comprising a top metal layer, an upper dielectric layer, a middle metal layer, a lower dielectric layer, and a bottom metal layer arranged from top to bottom, characterized in that: A metasurface radiation array is provided in the middle of the top metal layer. The array includes a middle array composed of 3*3 square ring-shaped metal units and an outer array composed of four 3*3 square ring-shaped metal units, forming a cross-shaped symmetric shape about the central axis. The center of the metasurface radiation array coincides with the center of the upper dielectric layer. A cross-shaped middle gap and four cross-shaped outer gaps are provided in the middle position of the middle metal layer, and the middle gap and the outer gaps coincide with the centers of the middle array and the outer array at corresponding positions on the top metal layer; The middle gap and the four outer gaps are formed by two rectangular gaps in the horizontal and vertical directions orthogonal to each other, wherein the two rectangular gaps in the middle gap have the same length and width, the width of one of the rectangular gaps in the outer gaps is smaller than the width of the rectangular gap in the middle gap, and the width of the other rectangular gap is the same as the width of the rectangular gap in the middle gap, and the lengths of the two rectangular gaps in the outer gaps are the same as the length of the middle gap; Two feeding networks are provided on the bottom metal layer, wherein the feeding network fed by the first port feeds the metasurface radiation array through the intermediate microstrip line sequential coupling structure and the intermediate gap, so that the antenna radiates circularly polarized waves and a broadside pattern; The feeding network fed by the second port feeds the metasurface radiation array through four outer microstrip line sequential coupling structures, three Wilkinson power dividers and four outer slots, so that the antenna radiates circularly polarized waves and a conical radiation pattern; The middle microstrip line sequential coupling structure and the outer microstrip line sequential coupling structure both include a 90-degree phase delay structure, a feeding structure, and an impedance matching structure.

2. The broadband circularly polarized pattern diversity antenna based on a metasurface unit according to claim 1, characterized in that: The 90-degree phase delay structure lengths of the middle microstrip line sequential coupling structure and the outer microstrip line sequential coupling structure are both 8.13 mm, the feeding structure lengths are both 1.5 mm, the impedance matching structure length of the middle microstrip line sequential coupling structure is 1.4 mm, and the impedance matching structure length of the outer microstrip line sequential coupling structure is 3.4 mm.

3. The broadband circularly polarized pattern diversity antenna based on a metasurface unit according to claim 1, characterized in that: The impedances of the two feeding networks, the first port and the second port are both 50 ohms.

4. The broadband circularly polarized pattern diversity antenna based on a metasurface unit according to claim 1, characterized in that: The upper dielectric layer and the lower dielectric layer are both made of Rogers 4003C high-frequency plate material, with a relative dielectric constant of 3.55 and a loss tangent value of 0.0027.

5. The broadband circularly polarized pattern diversity antenna based on a metasurface unit according to claim 4, characterized in that: The length of the upper dielectric layer and the width of the lower dielectric layer are both 115 mm and 100 mm, the thickness of the upper dielectric layer is 3.1 mm, and the thickness of the lower dielectric layer is 0.813 mm.

6. The broadband circularly polarized pattern diversity antenna based on a metasurface unit according to claim 1, characterized in that: The spacing between the middle array and the outer arrays around it is 0.9 mm. The inner side length of the square ring-shaped metal unit in each array is 6.7 mm, the outer side length is 8.7 mm, and the spacing between two adjacent square ring-shaped metal units is 0.9 mm.

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