Broadband MIMO antenna array for enclosed space

Abstract

The invention discloses a broadband MIMO (Multiple Input Multiple Output) antenna array for a closed space, which comprises a plurality of antenna plate main bodies, and the antenna plate main bodies are arranged in an annular array along a side ridge; the antenna plate main body comprises a dielectric substrate and an antenna assembly, and the antenna assembly comprises a metamaterial assembly, a director, an excitation arm, a reflector and a balun module; in the direction from the upper end to the lower end of the dielectric substrate, the metamaterial assembly, the director, the excitation arm and the balun module are sequentially distributed in the middle on the front surface of the dielectric substrate, and the reflector is arranged on the back surface of the lower end part of the dielectric substrate; the metamaterial component, the director and the excitation arm are sequentially arranged at intervals, and the excitation arm is connected with the balun module through a microstrip line. The combination of the linear excitation arm and the bent excitation arm is designed, arc induction current is excited on the director to resonate with the rectangular split-ring resonator, and the Yagi antenna has the advantages of widening the bandwidth of the Yagi antenna and improving the gain of the antenna.

Description

Technical Field

[0001] The present invention relates to the technical field of antennas, and particularly to a broadband MIMO antenna array for a closed space. Background Art

[0002] The cumulative construction area of urban underground space in China is 2.7 billion square meters. Its development trend is significantly related to the urbanization process in China and can be applied to transportation facilities, commercial facilities, underground garages, municipal process pipeline facilities, urban comprehensive disaster prevention construction, military projects, storage facilities, and high-rise buildings. The wireless communication system in the underground space needs to have high-bandwidth and low-latency data transmission capabilities, which can not only meet the massive communication needs of the public but also ensure the safe operation of rail transit.

[0003] With the development of underground space, more and more antennas are put into use in the underground space, and the electromagnetic environment in the underground space becomes more and more complex. Especially in the underground space, electromagnetic waves often encounter strong reflection phenomena, resulting in an increase in field strength and more prone to electromagnetic interference. This complex electromagnetic environment may cause mutual interference between antennas and affect the communication quality. In addition, the reflection phenomenon may also have an adverse impact on other electronic devices, thus affecting the normal operation of various devices in the underground space. Traditional directional antennas have limitations in bandwidth and usually can only cover specific frequency bands. For the underground space that needs to support both dedicated rail transit communication (2.4 - 2.45 GHz) and civilian 4G and 5G communications (such as the frequency bands of 2.0 - 2.4 GHz and 3.4 - 3.6 GHz), traditional antennas cannot cover these multiple frequency bands alone, or the design volume will increase when covering multiple frequency bands. The most commonly used design method in the prior art is to use a Yagi antenna as a directional antenna. However, the Yagi antenna with high-gain improvement in the prior art often has too large a volume, and due to material limitations, the Yagi antenna cannot use an antenna size that is conformal to the carrier surface, and the working bandwidth of the traditional Yagi antenna is relatively narrow, with a relative bandwidth generally within 5%, making it difficult to meet the current requirements of multiple communication frequency bands. Summary of the Invention

[0004] The present invention provides a broadband MIMO antenna array for a closed space, which solves the problems that in the prior art, it is difficult for a Yagi antenna to maintain a high working bandwidth and expand a wide range of frequency bands while controlling the volume size.

[0005] The present invention is realized through the following technical solutions: A broadband MIMO antenna array for a closed space includes a plurality of antenna board bodies, and the antenna board bodies are arranged in a circular array along the side edge lines. The main body of the antenna board includes a dielectric substrate and an antenna assembly. The antenna assembly includes a metamaterial assembly, a director, an excitation arm, a reflector, and a balun module. Along the direction from the upper end to the lower end of the dielectric substrate, the metamaterial assembly, the director, the excitation arm, and the balun module are sequentially and centrally distributed on the front plane of the dielectric substrate, and the reflector is arranged on the back plane at the lower end of the dielectric substrate. The metamaterial assembly, the director, and the excitation arm are sequentially arranged at intervals, and the excitation arm is connected to the balun module through a microstrip line.

[0006] Traditional directional antennas have limitations in bandwidth and usually can only cover specific frequency bands. For underground spaces that need to support both dedicated rail transit communication and civilian communication simultaneously, traditional antennas cannot cover these multiple frequency bands singly, or the design volume will increase when covering multiple frequency bands. In the prior art, the most commonly used design method is to use a Yagi antenna as a directional antenna. However, the Yagi antennas with high-gain improvements in the prior art are often too large in size, and due to material limitations, the antenna size of the Yagi antenna cannot be conformal with the carrier surface. Moreover, the working bandwidth of traditional Yagi antennas is relatively narrow, and the relative bandwidth is generally within 5%, making it difficult to meet the current requirements of multiple communication frequency bands. Based on this, the present invention provides a broadband MIMO antenna array for enclosed spaces to solve the problems that in the prior art, it is difficult for a Yagi antenna to maintain a high working bandwidth and expand a wide range of frequency bands while controlling the size.

[0007] Further, the metamaterial assembly includes two I-shaped metamaterial units and a number of circular metamaterial units. The I-shaped metamaterial units and the circular metamaterial units are sequentially and centrally arranged on the front plane of the dielectric substrate along the direction from the upper end to the lower end of the dielectric substrate. The two I-shaped metamaterial units are horizontally arranged side by side with their ends facing the side of the dielectric substrate, and the circular metamaterial units are arranged in a rectangular array on the front plane of the dielectric substrate.

[0008] Further, the rectangular array is a rectangular array with the long side parallel to the end of the dielectric substrate. The rectangular array form includes two rows of circular metamaterial units, and the number of circular metamaterial units in each row is 4.

[0009] Further, the director includes a number of curved directors. Each curved director is sequentially and centrally arranged on the front plane of the dielectric substrate along the direction from the upper end to the lower end of the dielectric substrate. The outer arc side of each curved director faces the upper end of the dielectric substrate.

[0010] Further, the metamaterial assembly includes a rectangular split-ring resonator, and the rectangular split-ring resonator is arranged between the last two curved directors along the direction from the upper end to the lower end of the dielectric substrate.

[0011] Further, the excitation arms include two curved excitation arms and two linear excitation arms, both the curved excitation arms and the linear excitation arms are horizontally arranged side by side with their ends facing the side of the dielectric substrate, and the curved excitation arm and the linear excitation arm on the same side on the front plane of the dielectric substrate are connected; the outer arc side of the curved excitation arm faces the upper end of the dielectric substrate.

[0012] Further, the connection manner between the curved excitation arm and the linear excitation arm on the same side on the front plane of the dielectric substrate is set as: the end of the curved excitation arm far from the side of the dielectric substrate is connected to the end of the linear excitation arm far from the side of the dielectric substrate.

[0013] Further, the two linear excitation arms are connected to the balanced end of the balun module through microstrip lines, and the unbalanced end of the balun module extends and is connected to the lower end of the dielectric substrate.

[0014] Further, the relative dielectric constant of the dielectric substrate is denoted as ξ r , and the relative dielectric constant ξ r = 3.48.

[0015] Further, the number of antenna board bodies in the broadband MIMO antenna array is set to 4.

[0016] Compared with the prior art, in the present invention, a combination of a linear stub excitation arm and a curved excitation arm that can reduce the mutual coupling effect and generate multiple frequencies is designed for each element, an arc-shaped induced current is excited on the director and resonates with the rectangular open resonator ring, and a metamaterial unit based on the open resonator ring and the I-shaped structure is printed in the director direction, which has the advantages of broadening the bandwidth of the quasi-Yagi antenna and improving the antenna gain. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, form a part of this application, and do not limit the embodiments of the present invention. In the drawings: Figure 1 is a schematic front view structure diagram of the antenna board body of the present invention; Figure 2 is a schematic back view structure diagram of the antenna board body of the present invention; Figure 3 is a schematic three-dimensional structure diagram of the broadband MIMO antenna array in the side view direction of the present invention; Figure 4 is a schematic three-dimensional structure diagram of the broadband MIMO antenna array in the top view direction of the present invention; Figure 5 is a simulation diagram of the element reflection coefficient of a single antenna board body of the present invention; Figure 6It is the simulation diagram of the element reflection coefficient of the MIMO antenna array of the present invention; Figure 7 It is the simulation diagram of the S parameter of the circular metamaterial unit of the present invention; Figure 8 It is the three-dimensional diagram of the unit model of the rectangular split-ring resonator and the I-shaped metamaterial unit of the present invention; Figure 9 It is the electromagnetic characteristic diagram of the S parameter of the rectangular split-ring resonator of the present invention; Figure 10 It is the electromagnetic characteristic diagram of the refractive index and equivalent permeability of the rectangular split-ring resonator of the present invention; Figure 11 It is the electromagnetic characteristic diagram of the S parameter of the I-shaped metamaterial unit of the present invention; Figure 12 It is the electromagnetic characteristic diagram of the refractive index and equivalent permeability of the I-shaped metamaterial unit of the present invention; Figure 13 It is the three-dimensional diagram of the unit model of the circular metamaterial unit of the present invention.

[0018] Marks in the attached drawings and corresponding component names: 1 - dielectric substrate, 2 - I-shaped metamaterial unit, 21 - circular metamaterial unit, 22 - rectangular split-ring resonator, 3 - curved director, 4 - curved excitation arm, 41 - straight excitation arm, 5 - balun module, 6 - reflector. Detailed implementation manners

[0019] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in combination with embodiments and the attached drawings. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and do not limit the present invention. Embodiment

[0020] As Figure 1 shown, this embodiment is a broadband MIMO antenna array for a closed space, including a plurality of antenna board bodies, and the antenna board bodies are arranged in a circular array along the side edges; The antenna board body includes a dielectric substrate and an antenna assembly. The antenna assembly includes a metamaterial assembly, a director, an excitation arm, a reflector and a balun module; along the direction from the upper end to the lower end of the dielectric substrate, the metamaterial assembly, the director, the excitation arm and the balun module are sequentially centered and distributed on the front plane of the dielectric substrate, and the reflector is arranged on the back plane at the lower end of the dielectric substrate; the metamaterial assembly, the director and the excitation arm are sequentially arranged at intervals, and the excitation arm and the balun module are connected by a microstrip line.

[0021] Among them, the metamaterial component includes two I-shaped metamaterial units and a number of circular metamaterial units. The I-shaped metamaterial units and the circular metamaterial units are sequentially arranged in the middle along the upper end to the lower end direction of the dielectric substrate on the front plane of the dielectric substrate; the two I-shaped metamaterial units are horizontally arranged side by side with their ends facing the side of the dielectric substrate, and the circular metamaterial units are arranged in a rectangular array on the front plane of the dielectric substrate; The excitation arms include two curved excitation arms and two straight excitation arms, and the curved excitation arms and the straight excitation arms are both horizontally arranged side by side with their ends facing the side of the dielectric substrate, and the curved excitation arm and the straight excitation arm on the same side on the front plane of the dielectric substrate are connected; the outer arc side of the curved excitation arm faces the upper end of the dielectric substrate.

[0022] Further, the connection mode between the curved excitation arm and the straight excitation arm on the same side on the front plane of the dielectric substrate is set as: the end of the curved excitation arm far from the side of the dielectric substrate is connected to the end of the straight excitation arm far from the side of the dielectric substrate; the two straight excitation arms are connected to the balanced end of the balun module through microstrip lines, and the unbalanced end of the balun module extends and is connected to the lower end of the dielectric substrate; the number of antenna board bodies in the broadband MIMO antenna array is set to 4.

[0023] The Yagi antenna is the most classic directional antenna, but the high-gain Yagi antenna is often too large in size, and limited by materials, the Yagi antenna cannot use the antenna size to be conformal with the carrier surface, and the traditional Yagi antenna has a narrow working bandwidth, and the relative bandwidth is generally within 5%, which is difficult to meet the current requirements of multiple communication frequency bands. Based on the design principle of the quasi-Yagi antenna, this embodiment designs a 6-element dual-band quasi-Yagi antenna with working frequency bands of 2.315 ~ 2.493 GHz, as Figure 1 shown. By arranging multiple antenna board bodies in a circular arrangement along the side edge lines, this layout can make full use of space and improve the space utilization rate of the antenna array. The metamaterial component is used to utilize the special electromagnetic properties of the metamaterial to improve the working bandwidth and gain of the antenna. The director is mainly used to improve the radiation directivity of the antenna, reduce signal scattering, and improve the signal focusing ability. The excitation arm is the main radiation element of the antenna and is used to radiate electromagnetic waves to the antenna. The optimization of its structure can further improve the gain and working bandwidth of the antenna. The reflector is arranged on the back of the lower end of the dielectric substrate, which can effectively reflect electromagnetic waves to the required direction, enhance the radiation efficiency of the signal, and reduce signal loss.

[0024] The outer arc side of the curved excitation arm faces the upper end of the dielectric substrate to reduce the reflection and noise of electromagnetic waves and improve the directivity of the antenna. The excitation arms are arranged horizontally side by side, and the ends face the side of the dielectric substrate to guide the signal through different parts of the antenna array to ensure the effective propagation of the signal, which helps to increase the stability of the radiation direction, reduce signal offset and phase error. The curved excitation arm and the linear excitation arm on the same side are connected by their ends away from the side of the dielectric substrate, which can ensure the mutual complement of the signals of the two excitation arms and enhance the frequency bandwidth and operating bandwidth of the antenna. The connection of the curved excitation arm and the linear excitation arm can adjust the phase relationship of the signal to ensure the maximization of the signal radiation performance of the antenna in different frequency bands. The balun module is used to mutually convert balanced signals and unbalanced signals according to signal requirements. Extending the unbalanced end of the balun module to the lower end of the dielectric substrate can optimize the input impedance of the antenna, making the matching between the antenna and the external circuit more precise and reducing signal reflection and power loss. The antenna array includes 4 antenna board bodies, and the system can support the 4×4 MIMO mode through the 4 antenna board bodies, which can effectively improve the capacity and quality of signal transmission. In a complex underground space environment, MIMO technology can optimize signal coverage through means such as multipath propagation and space-time division multiplexing. As a specific application, in this embodiment, the curvature of the curved excitation arm is set to K 0 , and the curvature of the director closest to the curved excitation arm is set to K 2 , and the curvature of the remaining directors is set to K 1 . The y-axis is set along the end direction of the dielectric substrate, and the x-axis is set along the side direction of the dielectric substrate. Then the calculation formula of the curvature K 0 is set as: ; The calculation formula of the curvature K 1 is set as: ; The calculation formula of the curvature K 2 is set as: ; The above calculation formulas are obtained through simulation calculation, and setting them in this way can make the antenna bandwidth and frequency band gain reach the best state.

[0025] Furthermore, as a feasible embodiment, the rectangular array is a rectangular array with the long side parallel to the end of the dielectric substrate; the rectangular array form includes two rows of circular metamaterial units, and the number of circular metamaterial units in each row is 4; the director includes a number of curved directors, and each of the curved directors is sequentially centered on the front plane of the dielectric substrate along the direction from the upper end to the lower end of the dielectric substrate; the outer arc side of each of the curved directors faces the upper end of the dielectric substrate.

[0026] The type-I metamaterial unit regulates the phase, frequency, and wavelength of electromagnetic waves. The circular metamaterial unit is used to provide uniform radiation characteristics and a stable beam width, and is suitable for broadband antenna designs in multiple frequency bands. Two type-I metamaterial units are arranged horizontally side by side with their ends facing the side of the dielectric substrate, which can increase the gain of the antenna and optimize the radiation pattern of the antenna at the same time. Through this side-by-side arrangement, the type-I units can interact in the antenna array, contributing to the formation of a stronger directional radiation. The circular metamaterial units are arranged in a rectangular array, which can improve the space utilization rate and enhance the overall radiation characteristics of the antenna, ensuring that the electromagnetic wave phases and directions of each unit are effectively coordinated, thereby enhancing the radiation efficiency and gain of the antenna, and increasing the effective radiation area of the antenna. The curved director is used to guide the propagation direction of electromagnetic waves and optimize the radiation pattern of the antenna. The curved director usually controls the radiation direction by changing the propagation path of electromagnetic waves, improving the directivity and gain of the antenna array. The outer arc side of the curved director faces the upper end of the dielectric substrate to ensure that the electromagnetic waves propagate along the desired direction during antenna radiation. By optimizing the direction of the director, the propagation path of the signal can be more precisely controlled, reducing the interference caused by multipath effects and reflections.

[0027] Furthermore, as a feasible implementation, the metamaterial assembly includes a rectangular split-ring resonator, and the rectangular split-ring resonator is disposed between the last two curved directors along the direction from the upper end to the lower end of the dielectric substrate.

[0028] The rectangular split-ring resonator is a metamaterial unit for regulating the frequency response of electromagnetic waves, and is used to work in cooperation with the director and the excitation arm to improve the bandwidth, gain, and radiation characteristics of the antenna. The design of the rectangular split-ring resonator can usually provide a relatively wide bandwidth and a high gain. The rectangular split-ring resonator is placed between the last two curved directors along the direction from the upper end to the lower end of the dielectric substrate, which can enhance the resonance effect of electromagnetic waves on the basis of the curved director and further optimize the radiation pattern of the antenna. Regarding the improvement of the antenna performance gain of the type-I metamaterial unit by the rectangular split-ring resonator, as shown in Figure 8 the spatial coordinate axis model of Figure 8 where figure a represents the model diagram of the rectangular split-ring resonator, and figure b represents the model diagram of the type-I metamaterial unit. Since the incident electromagnetic wave is x-polarized and propagates along the y-axis, the two surfaces parallel to the x-o-z plane are set as port 1 and port 2, the surface parallel to the x-o-y plane is set as a perfect electric conductor, and the surface parallel to the y-o-z plane is set as a perfect magnetic conductor. The electromagnetic characteristics of the rectangular split-ring resonator are as Figures 9 - 10As shown, the rectangular split-ring resonator resonates near 3.5 GHz and exhibits negative permeability characteristics in the range of 3.38 - 3.53 GHz, with its refractive index approaching 0. Therefore, when electromagnetic waves pass through the rectangular split-ring resonator, it exhibits the behavior of coupled current, thereby enhancing the antenna gain at 3.4 GHz. The electromagnetic characteristics of the type-I metamaterial unit are as Figures 11 - 12 shown. The type-I metamaterial unit exhibits negative permeability characteristics in the range of 2.42 - 3.53 GHz, with its refractive index approaching 0. Therefore, placing it in front of the conductor can promote current coupling, thereby enhancing the antenna gain throughout the operating frequency band. As a specific implementation, as Figure 13 shown, the circular metamaterial unit in this embodiment is composed of concentric rings with an outer radius R and an opening gap g, the width of the ring is w, the material of the circular metamaterial unit is a copper sheet with a thickness of 0.035 mm, and the period of the unit cell is 21 mm. When the polarized incident wave (the magnetic field direction is along the z-axis direction) propagates along the z-axis and passes through the SRR unit, the SRR will resonate at a certain frequency point. At this resonance frequency, the SRR unit cell will exhibit single-negative magnetic characteristics and can suppress the propagation of the polarized incident wave. The scattering parameters and equivalent electromagnetic parameters of the SRR are as Figure 7 shown. The circular metamaterial unit resonates at 2.45 GHz, thereby increasing the induced current in the antenna director and achieving the purpose of increasing the antenna gain.

[0029] The curved excitation arm, director, and balun unit are printed on the front side of the dielectric substrate, and a metal patch is provided on the back side of the dielectric substrate as the reflector of the antenna. When the active oscillator is used as the excitation arm and is fed, electromagnetic waves are generated in space. Through the coupling effect, an induced current is generated on the director, and the electromagnetic field of the active oscillator is canceled by the reflector, so that the electromagnetic waves radiate outward along the director direction (the main radiation direction). To increase the operating frequency band of the antenna, two types of stubs are added to the excitation arm of the traditional single-frequency quasi-Yagi antenna in this embodiment. The longer stub excites the low-frequency point to work, and the shorter stub excites the high-frequency point to work, thereby realizing the dual-frequency operation of the trackside antenna. Third, design the type-I structure electromagnetic metamaterial unit, split-ring resonator structure, and rectangular split-ring resonator unit. Add a rectangular split-ring resonator between the excitation arm and the first director to broaden the bandwidth of the antenna array, and add a type-I metamaterial unit at the front end of the director to increase current coupling to improve the gain. In specific applications, the length of the dielectric substrate can be set to 160 mm, the width is 60 mm, and the thickness is 1 mm, making the board surface of the antenna system relatively compact, suitable for deployment in a closed environment with limited space, and the smaller area is convenient for integrating the antenna array in the limited space of the underground space. In this embodiment, the relative dielectric constant of the dielectric substrate is represented as ξ r , and the relative dielectric constant ξ r= 3.48; The materials of the dielectric substrates are all copper, and side-feed ports are used for feeding. Materials with relatively large relative dielectric constants will cause the signal propagation speed in the dielectric substrate to slow down, and the relative dielectric parameter ξ r being set to 3.48 means that the signal propagation speed is approximately in free space. At this time, the signal propagation speed is slower, which helps to adjust the resonant frequency of the antenna. In this embodiment, the simulation results of the reflection coefficient of the elements of a single antenna board body are as Figure 5 shown, Figure 5 and the S 11 curves shown above in the frequency band below -10 dB are respectively: 2.315 GHz to 2.493 GHz, 3.34 GHz to 3.453 GHz. Therefore, the normal operating bandwidth of this antenna element is: 178 MHz, 113 MHz. From Figure 5 it can be seen that the maximum gain of this antenna element is 8.82 dBi. And in this embodiment, the simulation results of the reflection coefficient of the elements of the MIMO antenna array are as Figure 6 shown, Figure 6 and the S 11 curves shown above in the frequency band below -10 dB are respectively: 2.082 GHz to 2.467 GHz, 3.288 GHz to 3.563 GHz. Therefore, the normal operating bandwidth of this antenna array is: 385 MHz, 275 MHz. From Figure 8 it can be seen that the maximum gain of this antenna array is 10.03 dBi.

[0030] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A broadband MIMO antenna array for a closed space, comprising a plurality of antenna panel bodies, characterized in that: The antenna panel bodies are arranged in a circular array along the side ridges; The antenna board body includes a dielectric substrate and an antenna component, and the antenna component includes a metamaterial component, a director, an excitation arm, a reflector and a balun module; along the direction from the upper end to the lower end of the dielectric substrate, the metamaterial component, the director, the excitation arm and the balun module are sequentially distributed centrally on the front plane of the dielectric substrate, and the reflector is arranged on the back plane of the lower end of the dielectric substrate; the metamaterial component, the director and the excitation arm are sequentially spaced, and the excitation arm and the balun module are connected through a microstrip line.

2. A broadband MIMO antenna array for a closed space according to claim 1, characterized in that: The metamaterial component includes two type I metamaterial units and a number of circular metamaterial units, and the type I metamaterial units and the circular metamaterial units are sequentially arranged in the center of the front plane of the dielectric substrate from the upper end to the lower end of the dielectric substrate; the two type I metamaterial units are horizontally arranged side by side with their ends facing the side of the dielectric substrate, and the circular metamaterial units are arranged in a rectangular array on the front plane of the dielectric substrate.

3. A broadband MIMO antenna array for a closed space according to claim 2, characterized in that: The rectangular array is a rectangular array with a long side parallel to the end of the dielectric substrate; the rectangular array includes two rows of circular metamaterial units, and the number of circular metamaterial units in each row is 4.

4. The broadband MIMO antenna array for a closed space according to claim 1, characterized in that: The director comprises a plurality of curved directors, each of which is centrally arranged on the front plane of the dielectric substrate in sequence from the upper end to the lower end of the dielectric substrate; the outer arc side of each curved director faces the upper end of the dielectric substrate.

5. The broadband MIMO antenna array for a closed space according to claim 4, characterized in that: The metamaterial component comprises a rectangular open resonant ring, and the rectangular open resonant ring is arranged between the last two curved directors in the direction from the upper end to the lower end of the dielectric substrate.

6. The broadband MIMO antenna array for a closed space according to claim 1, characterized in that: The excitation arm includes two curved excitation arms and two linear excitation arms, and the curved excitation arms and the linear excitation arms are arranged horizontally side by side with their ends facing the side of the dielectric substrate, and the curved excitation arm and the linear excitation arm located on the same side on the front plane of the dielectric substrate are connected; the outer arc side of the curved excitation arm faces the upper end of the dielectric substrate.

7. The broadband MIMO antenna array for a closed space according to claim 6, characterized in that: The connection between the curved excitation arm and the linear excitation arm located on the same side of the front plane of the dielectric substrate is set as follows: one end of the curved excitation arm away from the side of the dielectric substrate is connected to one end of the linear excitation arm away from the side of the dielectric substrate.

8. The broadband MIMO antenna array for a closed space according to claim 6, characterized in that: The two linear excitation arms are connected to the balanced end of the balun module through a microstrip line, and the unbalanced end of the balun module is extended and connected to the lower end of the dielectric substrate.

9. The broadband MIMO antenna array for a closed space according to claim 1, characterized in that: The relative dielectric parameter of the dielectric substrate is expressed as ξ r , the relative dielectric parameter ξ r =3.

48.

10. The broadband MIMO antenna array for a closed space according to claim 1, characterized in that: The number of antenna board bodies in the broadband MIMO antenna array is set to 4.

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