A terminal MIMO antenna unit based on LC symmetric structure and a design method thereof

Abstract

The present application relates to the technical field of communication antenna, in particular to a terminal MIMO antenna unit based on LC symmetric structure and a design method thereof, comprising a monopole antenna pair loaded with LC feed network, the monopole antenna pair is mirror-symmetrical about the decoupling structure center line of the lower surface of the dielectric substrate, and the LC feed network is grounded through the first metallized via; the monopole antenna pair has two paths through the second metallized via, one path on the upper surface of the dielectric substrate overlaps with the decoupling structure, and the other path is loaded on the lower surface through the second metallized via and directly connected with the decoupling structure. The present application realizes electrical decoupling and magnetic decoupling of the two resonant paths of the monopole antenna pair and the decoupling structure respectively, and meets the high-performance decoupling demand of a wider frequency band; loading the LC feed network on the monopole antenna pair can realize free adjustment of antenna resonance by changing the capacitance and inductance without changing the shape of the antenna itself, and is more feasible on a mobile phone terminal.

Description

Technical Field

[0001] This invention relates to the field of communication antenna technology, and more specifically, to a terminal MIMO antenna unit based on an LC symmetric structure and its design method. Background Technology

[0002] With the advent of 5G / 6G commercialization, users have increasingly higher demands for communication capacity and quality. Multiple-input multiple-output (MIMO) technology primarily utilizes multiple communication lines for independent communication, each line operating independently to achieve high-capacity communication. Specifically, in wireless communication, multiple antennas are placed at both the transmitting and receiving ends, with each antenna's transmission and reception independent of the others.

[0003] Currently, in mobile terminals, if two or more antennas are to form a MIMO antenna, the correlation between each antenna needs to be minimized (i.e., isolation needs to be increased). The most effective way to increase isolation is to increase the distance between the two antennas; the greater the distance, the higher the isolation. However, on the one hand, the limited space in a mobile terminal obviously makes it impossible to increase isolation by increasing the distance between antennas. On the other hand, when two antennas are very close together, and one antenna is operating, the radiator of the other antenna acts as a parasitic element, generating additional radiation. This distorts the antenna's radiation pattern, affecting radiation efficiency and pattern stability.

[0004] Chinese invention patent CN111370869A discloses a compact MIMO antenna system based on a suspended ring decoupling structure, and specifically discloses the following technical solution: including: a ground plane, a first antenna, a second antenna, and a suspended ring decoupling structure. The first antenna and the second antenna are configured on the ground plane and are arranged adjacent to each other or electrically connected. The suspended ring decoupling structure is a narrow closed-loop structure. Strong current distribution is generated on both sides of the long side with opposite current modes, and weak current distribution is generated in the middle area of ​​the long side. The first antenna and the second antenna are configured in the middle area of ​​the long side of the suspended ring decoupling structure. The invention claims that the suspended ring decoupling structure it provides has the characteristics of simple structure, high integration, and flexible installation, and can be compatible with multiple antenna types, thereby forming a highly compact MIMO antenna system with close unit spacing. However, the prior art still has the following defects: (1) it can only achieve resonant radiation by adjusting its own geometric size; (2) it can only achieve decoupling in a narrow frequency band.

[0005] Therefore, researching efficient decoupling techniques between antennas is currently a key research focus. Summary of the Invention

[0006] The purpose of this invention is to achieve electrical and magnetic decoupling through the two resonant paths of the monopole antenna pair and the decoupling structure, respectively, to meet the high-performance decoupling requirements of a wider frequency band. By loading an LC feed grid onto the monopole antenna pair, the antenna resonance can be freely adjusted by changing the capacitance and inductance without changing the shape of the antenna itself, which is more feasible in mobile terminals, thereby solving the problems pointed out in the background art.

[0007] The embodiments of the present invention are implemented through the following technical solutions: a terminal MIMO antenna unit based on an LC symmetric structure, comprising an upper surface metal layer, a dielectric substrate, and a lower surface metal layer arranged sequentially from top to bottom, and further comprising a first monopole antenna and a second monopole antenna loaded with an LC feed network. A ground layer and a symmetrical decoupling structure are disposed on the lower surface metal layer. The first monopole antenna and the second monopole antenna are mirror-symmetrical about the center line of the decoupling structure. The LC feed network is grounded through a configured first metallized via. The first monopole antenna and the second monopole antenna have a first resonant path and a second resonant path respectively through the configured second metallized via. The first resonant path configured on the upper surface metal layer has an overlapping area with the decoupling structure and is electrically decoupled from the decoupling structure through the overlapping area. The second resonant path is loaded on the lower surface metal layer through the second metallized via and is directly connected to the decoupling structure for magnetic decoupling.

[0008] According to a preferred embodiment, the LC feed network includes an inductor connected in series along the feed port direction and a capacitor connected in parallel along the direction perpendicular to the feed port, wherein the first metallized via is loaded in the direction away from the feed port of the capacitor.

[0009] According to a preferred embodiment, the first resonant path of the first monopole antenna is inverted "L" shape, and the second resonant path of the first monopole antenna is inverted "L" shape.

[0010] According to a preferred embodiment, the decoupling structure and the second resonant path are loaded on the front of the lower surface metal layer, and the ground layer is loaded on the rear of the lower surface metal layer.

[0011] According to a preferred embodiment, the decoupling structure is mushroom-shaped, the grounding layer is rectangular, and the corner of the grounding layer is parallel to the side adjacent to the decoupling structure.

[0012] According to a preferred embodiment, the short side of the inverted "L"-shaped first resonant path and the corner of the "mushroom"-shaped decoupling structure near the ground layer have the overlapping area.

[0013] The present invention also provides a method for designing a terminal MIMO antenna element based on an LC-symmetric structure as described above, comprising: By loading an inductor at the front end of the feed port, loading a capacitor in the direction perpendicular to the feed port, and loading a metallized via next to the capacitor in the direction away from the feed port, the antenna-to-ground capacitance can be adjusted, thus completing the LC feed network design. according to as well as For the first resonant path respectively Second resonant path The design aims to achieve electromagnetic decoupling between the first and second monopole antennas. Specifically, during magnetic decoupling, the total current of the first monopole antenna is directly coupled to the coupling current of the second monopole antenna. , Indicates the second resonant path The current on the circuit, when electro-decoupling is performed. , Indicates the first resonant path The current aI1 is coupled to the decoupling structure and continues to be coupled from the decoupling structure to the current on the second monopole antenna; Based on engineering requirements, a suitable microwave dielectric material is selected as the dielectric substrate for the antenna unit. Electromagnetic simulation software is used for simulation modeling, and the antenna unit parameters are optimized. When the simulation output results meet the design requirements, including isolation, the antenna unit design is completed.

[0014] The technical solution of the terminal MIMO antenna unit based on LC symmetry structure and its design method according to the embodiments of the present invention has at least the following advantages and beneficial effects: The present invention performs electrical decoupling and magnetic decoupling respectively through the two resonant paths of the monopole antenna pair and the decoupling structure, which meets the high-performance decoupling requirements of a wider frequency band; and by loading an LC feed grid on the monopole antenna pair, the antenna resonance can be freely adjusted by changing the capacitance and inductance without changing the shape of the antenna itself, which is more feasible in mobile terminals. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the upper surface of the MIMO antenna unit provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the structure of the lower surface of the MIMO antenna unit provided in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the overall structure of the MIMO antenna unit provided in Embodiment 1 of the present invention; Figure 4 The LC feed network structure and its corresponding equivalent model provided in Embodiment 1 of the present invention; Figure 5 This is the equivalent electrical decoupling model between the first resonant path and the decoupling structure provided in Embodiment 1 of the present invention; Figure 6 This is the equivalent magnetic decoupling model between the second resonant path and the decoupling structure provided in Embodiment 1 of the present invention; Figure 7 The reflection coefficient provided in Embodiment 1 of the present invention The curve showing how the inductance value L changes; Figure 8 The reflection coefficient provided in Embodiment 1 of the present invention The curve showing the change in capacitance value C; Figure 9 A comparison of S-parameters with and without decoupling structure provided in Embodiment 1 of the present invention; Figure 10 The curve showing the maximum true gain versus frequency provided in Embodiment 1 of the present invention; Icons: 1-Feed port, 2-Surface mount inductor, 3-Surface mount capacitor, 4-First metallized via, 5-Second metallized via, 6-First resonant path, 7-LC feed network, 8-Monopole antenna, 9-First monopole antenna, 10-Second monopole antenna, 11-Dielectric substrate, 12-Second resonant path, 13-Decoupling structure, 14-Ground layer. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0017] Example 1 This invention provides a terminal MIMO antenna unit based on an LC-symmetric structure. (See also...) Figure 3 As shown, Figure 3 This is a schematic diagram of the overall structure of the MIMO antenna unit.

[0018] Specifically, the MIMO unit includes an upper surface metal layer, a dielectric substrate 11, and a lower surface metal layer arranged sequentially from top to bottom. In one embodiment of this example, the dielectric substrate 11 is selected from FR-4 substrates with a relative permittivity of 4.4, a dielectric loss tangent of 0.02, and a thickness of 0.8 mm. Both the upper and lower surface metal layers are made of copper and have a thickness of 0.035 mm.

[0019] Further, see Figure 1As shown, the upper surface metal layer is configured with a portion of the first monopole antenna 9 and the second monopole antenna 10 loaded with the LC feed network 7, and the remaining portions of the first monopole antenna 9 and the second monopole antenna 10 are loaded on the lower surface metal layer. The specific features will be described in detail later.

[0020] See Figure 2 and Figure 4 As shown ( Figure 4 , 5 In 6 and 9, the decoupling structure 13 is represented by a symmetrical structure (the upper surface metal layer is represented by the upper copper sheet of the dielectric substrate 11, and the lower surface metal layer is represented by the lower copper sheet of the dielectric substrate 11). The lower surface metal layer is also provided with a ground layer 14 and a symmetrical decoupling structure 13. The decoupling structure 13 is located between the first monopole antenna 9 and the second monopole antenna 10, and the first monopole antenna 9 and the second monopole antenna 10 are mirror images of each other about the center line of the decoupling structure 13. In addition, the LC feed network 7 is connected to the ground layer 14 and grounded through the first metallized via 4 located at the grounding point A.

[0021] Through power supply port 1 ( Figure 4 In this embodiment, the LC feed network 7 for the first monopole antenna 9 is denoted as port 1 (LC feed network 7 feed port 1 for the second monopole antenna 10 is denoted as port 2). An inductor is loaded at the front end, a capacitor is loaded in the direction perpendicular to the feed port 1, and a metallized via is loaded next to the capacitor in the direction away from the feed port 1, thereby achieving adjustable antenna capacitance to ground and completing the design of the LC feed network 7. In one embodiment, the LC feed network 7 includes an inductor connected in series along the direction of the feed port 1 and a capacitor connected in parallel in the direction perpendicular to the feed port 1. The first metallized via 4 is loaded in the direction away from the feed port 1. The loaded capacitor and the first metallized via 4 configured at ground point A effectively achieve adjustable antenna capacitance to ground. The loaded inductor effectively changes the distributed inductance of the antenna itself. The loaded capacitor and inductor can be equivalent to an LC resonant circuit. By changing the capacitance and inductance values, better impedance matching with the monopole antenna 8 can be achieved.

[0022] Specifically, in this embodiment, the inductor is a surface-mount inductor 2, and the capacitor is a surface-mount capacitor 3; except Figure 1 In addition to the location at grounding point A, the first metallized via 4 can also be located at other locations close to the center of the LC feed network 7 to ensure that the reference point for signal transmission is stable and has low noise. No specific restrictions are imposed here.

[0023] Furthermore, the first monopole antenna 9 and the second monopole antenna 10 each have a first resonant path 6 via the second metallized via 5 located at the path inflection point B. Second resonant path 12 The path turning point B is below the LC feed network 7, which, after the first metallized via 4 is loaded, connects to the second resonant path 12. Connected, with the first resonant path 6 Electrically decoupled from decoupling structure 13, second resonant path 12 After being directly connected to the decoupling structure 13, magnetic decoupling is performed, thereby realizing a MIMO antenna pair with wideband decoupling.

[0024] Specifically, the first monopole antenna 9 and the second monopole antenna 10 are designed as follows: the first resonant path 6 is disposed on the upper surface metal layer. The first resonant path 6 has an overlapping region with the decoupling structure 13 and is electrically decoupled from the decoupling structure 13 through the overlapping region. It is inverted "L" shape; the second resonant path 12 Magnetic decoupling is achieved by loading the second metallized through-hole 5 onto the lower surface metal layer and directly connecting it to the decoupling structure 13, resulting in the second resonant path 12. It has an inverted "L" shape.

[0025] Further, the decoupling structure 13 and the second resonant path 12 are applied to the front part of the lower surface metal layer. Preferably, the decoupling structure 13 is applied to the very front of the lower surface metal layer, and the ground layer 14 is applied to the rear part of the lower surface metal layer. A gap is left between the decoupling structure 13 and the ground layer 14. The second resonant path 12... Loaded at the gap. In a preferred embodiment of this example, the decoupling structure 13 is mushroom-shaped, the grounding layer is rectangular, and the corner of the grounding layer adjacent to the decoupling structure 13 is parallel; the short side of the inverted "L"-shaped first resonant path 6 overlaps with the corner of the mushroom-shaped decoupling structure 13 near the grounding layer.

[0026] In summary, this invention achieves electrical and magnetic decoupling between the two antenna paths of the monopole pair and the decoupling structure 13, respectively, to meet the high-performance decoupling requirements of a wider frequency band. Furthermore, by loading an LC feed network 7 onto the antenna pair, the antenna resonance can be freely adjusted by changing the capacitance and inductance without altering the antenna structure itself, making it more feasible in the limited space of a mobile phone.

[0027] In this embodiment, the MIMO antenna unit achieves electromagnetic decoupling between the first monopole antenna 9 and the second monopole antenna 10 based on the designed decoupling structure. The specific theoretical principle is as follows: See Figure 5 As shown, Figure 5 This is the equivalent model of electrical decoupling between the first resonant path 6 and the decoupling structure.

[0028] The first resonant path 6 of the first monopole antenna 9 When excited, considering the first resonant path 6 Current on , The current is weak and can be ignored. Since the decoupling structure 13 is positioned between the first monopole antenna 9 and the second monopole antenna 10, and is connected to the first resonant path 6... Not directly connected, therefore the current The current coupled to the decoupling structure 13 is First resonant path 6 The current aI1 is coupled to the decoupling structure 13, and the current that continues to be coupled from the decoupling structure 13 to the second monopole antenna 10 is During electrical decoupling, the total current of the first monopole antenna 9 is directly coupled to the coupling current of the second monopole antenna 10. Therefore, when At this time, electrical decoupling is achieved between the first monopole antenna 9 and the second monopole antenna 10 through the decoupling structure 13. It should be noted that when the first resonant path 6... At resonance, This is the direct decoupling coefficient between the first monopole antenna 9 and the second monopole antenna 10. It is the decoupling coefficient between the first monopole antenna 9 and the decoupling structure 13, and between the decoupling structure 13 and the second monopole antenna 10.

[0029] See Figure 6 As shown, Figure 6 For the second resonant path 12 Equivalent model of magnetic decoupling between decoupling structure 13 and decoupling structure 13.

[0030] The second resonant path 12 of the first monopole antenna 9 When excited, considering the second resonant path 12 Current on , The current is weak and can be ignored. Since the decoupling structure 13 is configured between the first monopole antenna 9 and the second monopole antenna 10, and in the second resonant path 12 Directly connected, therefore the current The current can be directly connected to the second monopole antenna 10 through the decoupling structure 13. However, during magnetic decoupling, the total current of the first monopole antenna 9 is directly coupled to the coupling current of the second monopole antenna 10. Therefore, when At this time, magnetic decoupling is achieved between the first monopole antenna 9 and the second monopole antenna 10 through the decoupling structure 13. It should be noted that when the second resonant path 12... At resonance, This is the direct decoupling coefficient between the first monopole antenna 9 and the second monopole antenna 10. It is the decoupling coefficient between the first monopole antenna 9 and the decoupling structure 13, and between the decoupling structure 13 and the second monopole antenna 10.

[0031] Furthermore, based on engineering requirements, a suitable microwave dielectric material was selected as the dielectric substrate 11 of the antenna element. Electromagnetic simulation software was used for simulation modeling, and the antenna element parameters were optimized. When the simulation output met the design requirements, including isolation, the antenna element design was completed. Specifically, to verify the performance of the MIMO antenna element after loading an LC feed network, Figure 7 The reflection coefficient is given. The curve showing the change in inductance value L. Figure 8 The reflection coefficient is given. The curve showing the change in capacitance C reveals that wideband antenna resonance can be achieved relatively easily by changing the capacitance and inductance.

[0032] To verify the wideband decoupling performance of the MIMO antenna element, Figure 9 A comparison of S-parameters is presented for a traditional monopole antenna pair with an LC-fed network (without the decoupling structure provided in this invention) (hereinafter referred to as Structure 1) and the scheme of this invention (hereinafter referred to as Structure 2); both structures are based on By comparing the frequency bands, it can be seen that structure 1 achieves a narrower frequency band ( Isolation (within 3.45GHz-4.05GHz) with a bandwidth of 0.6GHz. Structure 2 provides a wider frequency band (); while the structure provided by structure 2 achieves a wider frequency band ( High isolation (achieved within 3.42GHz-4.18GHz) with a bandwidth of 0.76GHz. ).

[0033] Therefore, the structure of the MIMO antenna unit provided in this embodiment can meet the high-performance decoupling requirements of a wider frequency band, and is more feasible in mobile terminals.

[0034] Figure 10 The curves showing the maximum true gain versus frequency are presented, indicating that the MIMO antenna element achieves a good gain of more than 3.3 dBi in the range of 3.42 GHz to 4.18 GHz.

[0035] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A terminal MIMO antenna unit based on an LC-symmetric structure, comprising an upper surface metal layer, a dielectric substrate (11), and a lower surface metal layer arranged sequentially from top to bottom, characterized in that, It also includes a first monopole antenna (9) and a second monopole antenna (10) loaded with an LC feed network (7). A ground layer (14) and a symmetrical decoupling structure (13) are disposed on the lower surface metal layer. The first monopole antenna (9) and the second monopole antenna (10) are mirror-symmetrical about the center line of the decoupling structure (13). The LC feed network (7) is grounded through a first metallized via (4). The first monopole antenna (9) and the second monopole antenna (10) have a first resonant path (6) and a second resonant path (12) respectively through the configured second metallized via (5). The first resonant path (6) configured on the upper surface metal layer has an overlapping area with the decoupling structure (13) and is electrically decoupled from the decoupling structure (13) through the overlapping area. The second resonant path (12) is loaded on the lower surface metal layer through the second metallized via (5) and is directly connected to the decoupling structure for magnetic decoupling. The LC feed network (7) includes an inductor connected in series along the direction of the feed port (1) and a capacitor connected in parallel along the direction perpendicular to the feed port (1). The first metallized via (4) is loaded in the direction away from the feed port (1) of the capacitor.

2. The terminal MIMO antenna unit based on LC symmetry structure as described in claim 1, characterized in that, The first resonant path (6) of the first monopole antenna (9) is inverted "L" shape, and the second resonant path (12) of the first monopole antenna (9) is inverted "L" shape.

3. The terminal MIMO antenna unit based on LC symmetry structure as described in claim 2, characterized in that, The decoupling structure (13) and the second resonant path (12) are loaded on the front part of the lower surface metal layer, and the ground layer (14) is loaded on the rear part of the lower surface metal layer.

4. The terminal MIMO antenna unit based on LC symmetry structure as described in claim 3, characterized in that, The decoupling structure (13) is mushroom-shaped, the grounding layer (14) is rectangular, and the corner of the grounding layer (14) is parallel to the side of the decoupling structure (13).

5. The terminal MIMO antenna unit based on LC symmetry structure as described in claim 4, characterized in that, The short side of the inverted "L"-shaped first resonant path (6) and the corner of the "mushroom"-shaped decoupling structure (13) near the ground layer (14) have the overlapping area.

6. A method for designing a terminal MIMO antenna unit based on an LC-symmetric structure as described in any one of claims 1-5, characterized in that, include: By loading an inductor at the front end of the feed port (1), loading a capacitor in the direction perpendicular to the feed port (1), and loading a metallized via next to the capacitor in the direction away from the feed port (1), the antenna-to-ground capacitance can be adjusted, and the LC feed network (7) design is completed. according to as well as For the first resonant path (6) respectively The second resonant path (12) The design aims to achieve electromagnetic decoupling between the first monopole antenna (9) and the second monopole antenna (10). Specifically, during magnetic decoupling, the total current of the first monopole antenna (9) is directly coupled to the coupling current of the second monopole antenna (10). , Indicates the second resonant path (12) When electrical decoupling is performed, the total current of the first monopole antenna (9) is directly coupled to the coupling current of the second monopole antenna (10). , Indicates the first resonant path (6) The current aI1 is coupled to the decoupling structure (13) and continues to be coupled from the decoupling structure (13) to the current on the second monopole antenna (10); According to the engineering requirements, a suitable microwave dielectric material is selected as the dielectric substrate of the antenna unit (11); The antenna element parameters were optimized using electromagnetic simulation software. The antenna element design was completed when the simulation output met the design requirements, including isolation.

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