Miniaturized four-port MIMO antenna based on characteristic mode theory

Abstract

The invention discloses a miniaturized four-port MIMO (Multiple Input Multiple Output) antenna based on a characteristic mode theory. Comprising a dielectric substrate, a metal ground plane printed on the back surface of the dielectric substrate, a radiation unit printed on the front surface of the dielectric substrate, four feed units, an isolation circular hole etched in the metal ground plane and used for separating the feed units from the metal ground plane, and a metal short pin array inserted into the dielectric substrate and connected with the radiation unit and the metal ground plane. The radiation unit comprises a main radiation patch and an auxiliary radiation patch; the main radiation patch is a circular metal patch etched in the center of the front surface of the dielectric substrate; the auxiliary radiation patch comprises four auxiliary radiation patches arranged at four corners of the main radiation patch. The isolation degree of the MIMO antenna is optimized, the coupling problem caused by miniaturization of the MIMO antenna is avoided, meanwhile, the advantages of miniaturization and high isolation are achieved, and impedance matching of the antenna is also optimized on the side face.

Description

Technical Field

[0001] The invention belongs to the technical field of mobile phone communications, and relates to a miniaturized high-isolation mobile phone antenna, in particular to a miniaturized four-port MIMO antenna based on characteristic mode theory. Background Art

[0002] With the rapid development of communication technology, antennas need to meet more and wider frequency bands and also require greater data throughput. How to improve the channel capacity and coverage frequency band of antennas in mobile communication systems has become a challenging task. With the rapid development of wireless communication, traditional single antennas can no longer meet the growing channel capacity and performance requirements. Multiple-input Multiple-output (MIMO) technology, with its ability to realize parallel operation of multiple unit antennas, can provide more communication paths, greatly improve the channel capacity of antennas, and bring better stability and efficiency.

[0003] With the upgrade and optimization of mobile devices such as mobile phones, the smaller and smaller device footprint has become a major selling point, which also brings challenges to the application of MIMO antennas on mobile devices, and has higher requirements for the miniaturization of MIMO antennas. The reason why MIMO antennas have high requirements for size is that the integration of multiple antennas in a small space such as a mobile device will increase the coupling between each other. In the originally limited space, the increase in the number of antennas forces the distance between antennas to be reduced, and each port of the antenna will be interfered by the induced current generated by other ports, resulting in a negative impact on the diversity performance and impedance matching of the MIMO antenna. Therefore, it is necessary to add a decoupling structure to the MIMO antenna to offset the negative impact of the induced current.

[0004] In order to solve the above problems, many scholars have proposed many technologies related to antenna decoupling. At present, common decoupling technologies include decoupling stubs, electronic band gaps, parasitic branches, etc. Although these technologies improve the isolation of the antenna, they inevitably increase the size and complexity of the antenna and cannot meet the requirements of miniaturization. It can be seen that it is still a huge challenge to design an antenna with high isolation, good efficiency and gain, and miniaturization in a limited space.

[0005] In summary, the MIMO antenna needs to take into account the isolation between ports and the overall size during the design process, so a decoupling method that does not affect the size of the antenna is needed. The more commonly used and effective decoupling structure in the current research field needs to be added between the ports of the antenna to block the induced current, which increases the distance between the ports. Summary of the invention

[0006] The purpose of the present invention is to address the deficiencies in the prior art and propose a miniaturized four-port MIMO antenna based on characteristic mode theory. The overall design uses simple metal patches and FR-4 substrates. This design allows the antenna to be directly integrated with mobile devices such as mobile phones. It has a simple structure and excellent performance. The operating frequency band covers the N79 band of 5G, making it very suitable as an antenna for 5G communication mobile devices.

[0007] Characteristic mode theory is a hot topic in recent years for designing high-isolation antennas. It can reveal the radiation characteristics of antennas in frequency bands and is of great help in antenna design and optimization. Specifically, the surface of a metal conductor of any shape can define multiple mutually orthogonal characteristic modes. These modes are related to the shape of the metal conductor and have nothing to do with the excitation source. Characteristic mode theory can be used to design antennas because it obtains the current distribution in different modes through the structure of the antenna itself, and then chooses to add excitation sources at different positions to resonate different modes, so that the antenna can work in different modes. The orthogonality between different modes is the key to achieving excellent decoupling between antennas. In antenna design, the resonance behavior of the antenna can be analyzed through the characteristic mode theory, the inherent properties associated with the conductor structure can be calculated, and the current mode and corresponding far-field mode of the antenna can be analyzed by combining the changes in the antenna conductor and the selection of the feeding point. The advantage of this design is that, by analyzing the eigenvalues ​​of each mode, it is possible to quickly determine which modes contribute significantly to radiation within the target frequency band, thereby simplifying the design and optimization process; on the other hand, it can help design a structure with minimal inter-modal coupling in the early stages of MIMO antenna design, thereby improving the isolation between antenna ports, and by optimizing the excitation of different modes, it can improve the antenna's performance indicators, such as gain, bandwidth, and radiation pattern. The eigenmode theory can make the ports of the antenna itself work in different eigenmodes by designing the antenna's own working mode, thereby avoiding mutual interference and enabling the antenna to achieve excellent isolation.

[0008] A miniaturized four-port MIMO antenna based on characteristic mode theory, the structure includes the following key features: (1) 5G frequency band design: The antenna supports covering the 5th generation communication N79 frequency band (4.4-5GHz), and the present invention can achieve excellent isolation better than 19dB in this frequency band. (2) Low profile design: The antenna structure is simple and compact, using a single-layer PCB, and can be directly integrated on a mobile phone with a thickness of only 1.6mm. (3) Multiple-input multiple-output (MIMO) technology: Improve channel capacity and use multiple antennas. (4) Characteristic mode theory design: The characteristic mode theory is used to design the antenna structure and feeding position, so that adjacent ports can achieve excellent decoupling effect without using additional decoupling structure, avoiding the increase in size. (5) Decoupling short pin design: By adding a ground short pin to the main radiation patch, the isolation of the diagonal port can be improved without affecting the size of the antenna patch, helping the antenna to meet the requirements of miniaturization.

[0009] In order to achieve the object of the present invention, the present invention adopts the following scheme:

[0010] A miniaturized four-port MIMO antenna based on characteristic mode theory comprises: a dielectric substrate, a metal ground plane printed on the back of the dielectric substrate, a radiation unit printed on the front of the dielectric substrate, four feeding units, an isolation circular hole etched on the metal ground plane for separating the feeding unit and the metal ground plane, and a metal short needle array inserted into the dielectric substrate and connecting the radiation unit and the metal ground plane.

[0011] The upper layer of the dielectric substrate is printed with a radiation unit, and the lower layer is printed with a metal ground plane.

[0012] The radiation unit includes a main radiation patch and a secondary radiation patch. The main radiation patch is a circular metal patch etched on the front center of the dielectric substrate; the secondary radiation patch includes a first secondary radiation patch arranged at the upper left corner of the main radiation patch, a second secondary radiation patch arranged at the upper right corner of the main radiation patch, a third secondary radiation patch arranged at the lower left corner of the main radiation patch, and a fourth secondary radiation patch arranged at the lower right corner of the main radiation patch.

[0013] The four feeding units include a first feeding short pin, a second feeding short pin, a third feeding short pin and a fourth feeding short pin, and each feeding short pin passes through an isolation circular hole on the secondary radiation patch, the dielectric substrate and the metal ground plane.

[0014] The isolation circular holes include a first isolation circular hole, a second isolation circular hole, a third isolation circular hole, and a fourth isolation circular hole, which are respectively etched on the metal ground plane directly below the first feed short pin, the second feed short pin, the third feed short pin, and the fourth feed short pin.

[0015] The metal short pin array consists of 24 metal short pins arranged in a cross shape, with the intersection center located at the center of the main radiation patch, and passes through the main radiation patch, the dielectric substrate and the metal ground plane in sequence.

[0016] Preferably, the dielectric substrate has a dielectric constant of 4.4 and a size of 38×38×1.6 mm. 3 FR-4 substrate.

[0017] Preferably, the metal ground plane has a usable area of ​​38×38 mm 2 Square copper metal patch.

[0018] Preferably, the main radiation patch is a circular metal copper patch with a diameter of 18 mm, and the center of the circle is located at the center of the upper layer of the dielectric substrate.

[0019] Preferably, the structure of the secondary radiation patch is: based on four circular metal copper patches with a diameter of 17 mm, they are placed at the upper left corner, upper right corner, lower left corner and lower right corner of the dielectric substrate respectively, and the closest interval between the circumference of the four circular metal copper patches and the edge of the dielectric substrate is 0.5 mm; a circle with a diameter of 20 mm is drawn with the center of the upper layer of the dielectric substrate as the center, and the overlapping parts of the four circular metal copper patches and the circle are removed, so that a gap of 1 mm is maintained between the main radiation patch and the secondary radiation patch, thereby obtaining four secondary radiation patches.

[0020] Preferably, the feeding unit includes a first feeding short pin, a second feeding short pin, a third feeding short pin, and a fourth feeding short pin, all of which are cylindrical metal short pins with a diameter of 1.5 mm and a height of 1.6 mm; the first feeding short pin is 6.6 mm away from the left edge of the dielectric substrate and 1 mm away from the upper edge of the dielectric substrate; the second feeding short pin is 6.6 mm away from the upper edge of the dielectric substrate and 1 mm away from the right edge of the dielectric substrate; the third feeding short pin is 6.6 mm away from the lower edge of the dielectric substrate and 1 mm away from the left edge of the dielectric substrate; the fourth feeding short pin is 6.6 mm away from the right edge of the dielectric substrate and 1 mm away from the lower edge of the dielectric substrate.

[0021] Preferably, the isolation circular hole includes a first isolation circular hole, a second isolation circular hole, a third isolation circular hole, and a fourth isolation circular hole, which are placed on the metal ground plane directly below each feeding short pin, and have a diameter of 2.4 mm, which is larger than the diameter of the feeding short pin, and is used to prevent the feeding short pin from directly contacting the metal ground plane and causing a short circuit.

[0022] Preferably, the 24 metal short needles in the metal short needle array are all cylindrical metal short needles with a diameter of 0.5 mm and a height of 1.6 mm, and are arranged in a cross shape, that is, 12 metal short needles are arranged horizontally, and 12 metal short needles are arranged vertically, and the intervals between the short needles are 1.5 mm.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] The present invention, by exciting a specific mode with orthogonality and designing a ground short pin, does not change the original size of the antenna or add additional parasitic elements that affect the size of the antenna. It can optimize the isolation of the MIMO antenna to a great extent while making the antenna as compact as possible, avoiding the coupling problem caused by the miniaturization of the MIMO antenna, while achieving the advantages of miniaturization and high isolation. It also optimizes the impedance matching of the antenna on the side, making the antenna S parameter even better. The present invention adopts a relatively simple patch design in the design of the MIMO antenna, and the overall size is only 38×38×1.6mm 3 , suitable for use in mobile devices with limited internal space. The antenna itself has a compact structure and can achieve the effect of saving space. The simplicity of the overall antenna design also avoids the impact of complex processing on antenna performance, and can retain the best performance of the antenna itself to the greatest extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the top layer structure of the MIMO antenna;

[0026] Figure 2 This is a schematic diagram of the bottom layer structure of the MIMO antenna;

[0027] Figure 3 This is the left view of the MIMO antenna;

[0028] Figure 4 It is the current distribution diagram of each characteristic mode of the MIMO antenna;

[0029] Figure 5 is a pattern significance curve diagram corresponding to each characteristic mode of the MIMO antenna;

[0030] Figure 6 It is a curve diagram of the reflection coefficient S11 parameter simulation data of the MIMO antenna in the working frequency band;

[0031] Figure 7 It is a curve diagram of the simulation data of the isolation S12 between the antenna 1 and the adjacent unit antenna 2 of the MIMO antenna in the working frequency band;

[0032] Figure 8 It is a curve diagram of the simulation data of the isolation S14 between the antenna 1 and the diagonal unit antenna 4 of the MIMO antenna in the working frequency band;

[0033] Fig. 9 This is the gain and efficiency simulation diagram of this MIMO antenna in the 5th generation N79 frequency band (4.4-5GHz);

[0034] Fig.10 This is a simulation diagram of the radiation pattern of the MIMO antenna at 5GHz;

[0035] Markings in the figure: 1-1, dielectric substrate; 1-2, metal ground plane; 2-1, main radiation patch; 2-2-1, first sub-radiation patch; 2-2-2, second sub-radiation patch; 2-2-3, third sub-radiation patch; 2-2-4, fourth sub-radiation patch; 3-1, first feed short pin; 3-2, second feed short pin; 3-3, third feed short pin; 3-4, fourth feed short pin; 4-1, first isolation circular hole; 4-2, second isolation circular hole; 4-3, third isolation circular hole; 4-4, fourth isolation circular hole; 5-1, metal short pin array. DETAILED DESCRIPTION

[0036] A miniaturized four-port MIMO antenna based on characteristic mode theory comprises: a dielectric substrate 1-1, a metal ground plane 1-2 printed on the back of the dielectric substrate, a radiation unit printed on the front of the dielectric substrate 1-1, four feeding units, an isolation circular hole etched on the metal ground plane for separating the feeding unit and the metal ground plane, and a metal short needle array 5-1 inserted into the dielectric substrate 1-1 and connecting the radiation unit and the metal ground plane 1-2.

[0037] in:

[0038] like Figure 1 In order to meet the application of antennas in mobile devices such as mobile phones, the dielectric substrate adopts a FR-4 substrate with a dielectric constant of 4.4 and a loss tangent value of 0.02; the dielectric substrate is 38 mm long, 38 mm wide and 1.6 mm high.

[0039] The radiation patch includes a main radiation patch 1-1 and a secondary radiation patch. The main radiation patch 1-1 is a circular metal patch etched at the center of the front side of the dielectric substrate. The secondary radiation patch includes a first secondary radiation patch 2-2-1, a second secondary radiation patch 2-2-2, a third secondary radiation patch 2-2-3, and a fourth secondary radiation patch 2-2-4, which are respectively located at the upper left corner, upper right corner, lower left corner, and lower right corner of the main radiation patch. The circumference of the secondary radiation patch is kept at a minimum distance of 0.5 mm from the edge of the dielectric substrate.

[0040] The feeding unit includes a first feeding short pin 3-1, a second feeding short pin 3-2, a third feeding short pin 3-3, and a fourth feeding short pin 3-4, which are respectively used as ports. Each feeding short pin passes through the isolation circular hole on the secondary radiation patch, the dielectric substrate and the metal ground plane, and is connected to the SMA connector for coaxial feeding.

[0041] The metal short needle array 5-1 consists of 24 metal short needles arranged in a cross shape, with the center of the intersection located at the center of the main radiation patch 2-1. It passes through the main radiation patch, the dielectric substrate and the metal ground plane in sequence to adjust the antenna resonance.

[0042] like Figure 2The isolation circular holes include a first isolation circular hole 4-1, a second isolation circular hole 4-2, a third isolation circular hole 4-3, and a fourth isolation circular hole 4-4, which are respectively etched on the metal ground plane directly below the first feed short pin 3-1, the second feed short pin 3-2, the third feed short pin 3-3, and the fourth feed short pin 3-4 to ensure that the feed short pin and the metal ground plane do not contact each other to cause a short circuit problem.

[0043] like Figure 3 The overall structure of the present invention is 38×38×1.6mm 3 The rectangular shape has a small and compact structure. This design is suitable for direct integration on the back substrate of a mobile phone. Compared with traditional mobile phone antennas, it has the advantages of miniaturization and integration flexibility.

[0044] like Figure 4 As shown in the characteristic mode current distribution diagram when the antenna is working, in the 7 characteristic modes of the antenna of the present invention, the current directions on the 4 sub-radiation patches are mutually orthogonal, that is, the direction difference is 90°. The purpose of this design is to avoid the currents on the sub-radiation patches from affecting each other. When the current directions are the same or opposite, there will be a coupling effect between the currents that enhances or cancels each other, and the coupling between the orthogonal currents is the lowest, which can successfully achieve the improvement of the isolation between adjacent ports without adding additional decoupling structure.

[0045] Figure 5 is the mode significance (MS) of the 7 characteristic modes of the antenna. The higher the mode significance of the characteristic mode at a certain frequency point, the higher the possibility that the mode is excited at the frequency point. When MS=1, it means that the mode is successfully excited. The frequency band where the MS curve of the antenna of the present invention is densely distributed is the frequency band in which the antenna works.

[0046] like Figure 6 The simulation data of antenna S11 shows that the two frequency bands with better performance of S11 correspond to Figure 5 The two frequency bands with relatively dense MS curves together constitute the working frequency band of the antenna. The -6dB working frequency band of the antenna of the present invention under simulation is 4.25-5.47GHz, which can cover the N79 frequency band (4.4-5GHz) used for 5G mobile phone communication.

[0047] Figure 7The simulation data of antenna S12, S12 is the isolation between antenna port 1 and port 2, i.e., the adjacent ports of the antenna. Due to the symmetry of the antenna, the isolation between port 1 and port 2 is equivalent to the isolation between port 1 and port 3, so only the data of S12 is shown. The simulated S12 of the antenna of the present invention at the operating frequency is better than -19dB. The simulation data shows that the MIMO antenna of the present invention has high isolation between adjacent ports. This is because the current directions between adjacent ports of the antenna designed based on the characteristic mode theory are orthogonal, and the current directions are distributed at 90°, which will not interfere with each other and cause coupling.

[0048] Figure 8 The simulation data of antenna S14, S14 is the isolation between antenna port 1 and port 4, i.e., the diagonal port of the antenna. The simulation S14 of the antenna of the present invention at the operating frequency is better than -19dB. The simulation data shows that the diagonal ports of the MIMO antenna of the present invention have high isolation, because the metal short pin array has the function of isolating the induced current of the diagonal port, and optimizes the mutual coupling between the diagonal ports.

[0049] like Fig. 9 The gain of the MIMO antenna in the N79 frequency band (4.4-5GHz) reaches 3.4-3.8dBi, and the efficiency is 54%-72%, which can ensure the stability of signal strength.

[0050] Fig.10 The figure below is a simulation of the radiation pattern of the MIMO antenna at 5GHz, where the left and right figures are the radiation patterns of Phi=0° and Phi=90° respectively. It can be seen that the designed antenna has good simulation directivity, and the overall pattern shows omnidirectional characteristics, which meets the requirements of mobile phone antennas and can achieve radiation in all directions.

[0051] Through characteristic mode theory analysis, the present invention designs a novel miniaturized four-port MIMO antenna. By designing the antenna patch through the characteristic mode theory and adding a ground short pin, the antenna can achieve high isolation without adding a decoupling structure that affects the size of the antenna. The above simulation results verify that the antenna can achieve the advantages of miniaturization, simple structure and high isolation. Various performance indicators are good, which is in line with the current development trend of antennas. It has the advantages of miniaturization, simple design, easy processing and excellent performance, and is very suitable for application in 5G communications and other related fields of mobile devices.

[0052] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It is obvious to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is defined by the attached claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved.

Claims

1. A miniaturized four-port MIMO antenna based on characteristic mode theory, characterized in that: It comprises a dielectric substrate, a metal ground plane (1-2) printed on the back of the dielectric substrate (1-1), a radiation unit printed on the front of the dielectric substrate, four feeding units, an isolation circular hole etched on the metal ground plane (1-1) for separating the feeding unit and the metal ground plane, and a metal short needle array (5-1) inserted into the dielectric substrate (1-1) to connect the radiation unit and the metal ground plane (1-1); The dielectric substrate (1-1) has a radiation unit printed on the upper layer and a metal ground plane (1-2) printed on the lower layer.

2. The miniaturized four-port MIMO antenna based on characteristic mode theory according to claim 1, characterized in that: The radiation unit comprises a main radiation patch (2-1) and a secondary radiation patch, wherein the main radiation patch (2-1) is a circular metal patch etched at the center of the front face of a dielectric substrate; the secondary radiation patch comprises a first secondary radiation patch (2-2-1) arranged at the upper left corner of the main radiation patch (2-1), a second secondary radiation patch (2-2-2) arranged at the upper right corner of the main radiation patch (2-1), a third secondary radiation patch (2-2-3) arranged at the lower left corner of the main radiation patch (2-1), and a fourth secondary radiation patch (2-2-4) arranged at the lower right corner of the main radiation patch (2-1); The four feeding units include a first feeding short pin (3-1), a second feeding short pin (3-2), a third feeding short pin (3-3), and a fourth feeding short pin (3-4), and each feeding short pin passes through an isolation circular hole on the secondary radiation patch, a dielectric substrate, and a metal ground plane; The isolation circular holes include a first isolation circular hole (4-1), a second isolation circular hole (4-2), a third isolation circular hole (4-3), and a fourth isolation circular hole (4-4), which are respectively etched on a metal ground plane (1-2) directly below the first feed short pin (3-1), the second feed short pin (3-2), the third feed short pin (3-3), and the fourth feed short pin (3-4); The metal short needle array (5-1) consists of 24 metal short needles arranged in a cross shape, with the center of the intersection located at the center of the main radiation patch (2-1), and passes through the main radiation patch, the dielectric substrate and is connected to the metal ground plane in sequence.

3. The miniaturized four-port MIMO antenna based on characteristic mode theory according to claim 2, characterized in that: The dielectric substrate (1-1) has a dielectric constant of 4.4 and a size of 38×38×1.6 mm. 3 FR-4 substrate; The metal ground plane (1-2) has a use area of ​​38×38 mm 2 Square copper metal patch.

4. The miniaturized four-port MIMO antenna based on characteristic mode theory according to claim 3, characterized in that: The main radiation patch (2-1) is a circular metal copper patch with a diameter of 18 mm; The structure of the secondary radiation patch is as follows: based on four circular metal copper patches with a diameter of 17 mm, they are placed at the upper left corner, upper right corner, lower left corner and lower right corner of the dielectric substrate respectively, and the closest interval between the circumference of the four circular metal copper patches and the edge of the dielectric substrate is 0.5 mm; a circle with a diameter of 20 mm is drawn with the center of the upper layer of the dielectric substrate as the center, and the overlapping parts of the four circular metal copper patches and the circle are removed, so that a gap of 1 mm is maintained between the main radiation patch and the secondary radiation patch, thereby obtaining four secondary radiation patches.

5. The miniaturized four-port MIMO antenna based on characteristic mode theory according to claim 4, characterized in that: The feeding unit comprises a first feeding short pin (3-1), a second feeding short pin (3-2), a third feeding short pin (3-3) and a fourth feeding short pin (3-4), all of which are cylindrical metal short pins with a diameter of 1.5 mm and a height of 1.6 mm; the first feeding short pin (1-3-1) is 6.6 mm away from the left edge of the dielectric substrate and 1 mm away from the upper edge of the dielectric substrate; the second feeding short pin (1-3-2) is 6.6 mm away from the upper edge of the dielectric substrate and 1 mm away from the right edge of the dielectric substrate; the third feeding short pin (1-3-3) is 6.6 mm away from the lower edge of the dielectric substrate and 1 mm away from the left edge of the dielectric substrate; the fourth feeding short pin (1-3-4) is 6.6 mm away from the right edge of the dielectric substrate and 1 mm away from the lower edge of the dielectric substrate.

6. The miniaturized four-port MIMO antenna based on characteristic mode theory according to claim 5, characterized in that: The isolation circular holes include a first isolation circular hole (4-1), a second isolation circular hole (4-2), a third isolation circular hole (4-3), and a fourth isolation circular hole (4-4), which are placed on the metal ground plane (1-2) directly below each feeding short pin and have a diameter of 2.4 mm.

7. The miniaturized four-port MIMO antenna based on characteristic mode theory according to claim 6, characterized in that: The 24 metal short needles in the metal short needle array (5-1) are all cylindrical metal short needles with a diameter of 0.5 mm and a height of 1.6 mm. 12 metal short needles are arranged horizontally, and 12 metal short needles are arranged vertically. The intervals between the short needles are 1.5 mm.

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