Self-decoupling method of MIMO antenna array based on substructure eigenmode theory

Abstract

The present invention relates to a MIMO antenna array self-decoupling method based on substructure characteristic mode theory, including: establishing a dual-unit MIMO microstrip patch antenna array, obtaining modal significance and characteristic angle curves; taking the frequency point corresponding to the intersection of the modal significance curves of mode 1 and mode 2; making the difference of the characteristic angles of mode 1 and mode 2 at the frequency point close to 90°; calculating the low amplitude area and the zero amplitude area; taking the intersection area of ​​the low amplitude area and the zero amplitude area as the preferred area, placing the feeding port on the preferred area; taking all the coordinates of the preferred area as the coaxial feeding coordinates, simulating and comparing, and obtaining an axial ratio bandwidth of 1.66% and an excellent decoupling level of the lowest ‑42.9dB. The present invention reduces the number of modes, greatly reduces the analysis difficulty of multi-unit systems, more effectively and accurately determines the feeding position, can ensure circular polarization or linear polarization performance, and can achieve self-decoupling, providing a novel solution for solving such problems.

Description

Technical Field

[0001] The invention relates to the technical field of MIMO antennas, and in particular to a MIMO antenna array self-decoupling method based on substructure eigenmode theory. Background Art

[0002] Multiple-input multiple-output (MIMO) technology has become the core technology of the fifth generation (5G) mobile communications due to its high channel capacity and fast transmission speed. However, the overall system performance of the MIMO array is often degraded by the surface wave and space wave coupling effects between units. In order to cope with this problem, the mutual coupling problem between antenna elements has become a research focus.

[0003] With the in-depth research on decoupling technology, self-decoupling technology has received widespread attention in recent years. This technology does not require additional decoupling networks, but only relies on the characteristics of the antenna itself to achieve decoupling effects, and does not affect the radiation performance of the antenna. Characteristic mode theory has the natural advantage of solving the self-decoupling problem by virtue of its characteristics of analyzing the antenna's mode properties under passive conditions without the need for excitation. Among the many self-decoupling schemes based on characteristic mode theory, most use coupling to generate weak fields, odd and even mode cancellation, the natural isolation properties of orthogonal modes, energy transfer to higher-order modes, and cutting off coupling paths to achieve decoupling. However, most of these works focus on linear polarization radiation, and there are few attempts at self-decoupling of circularly polarized antennas. In addition, for the decoupling problem of multi-unit antennas, since the existing commercial software is an indiscriminate full-structure characteristic mode analysis, its mode structure is complex and the analysis is difficult. Summary of the invention

[0004] In order to solve the influence of additional decoupling structure on antenna performance and the problem of complex and difficult patterns when analyzing characteristic modes of multi-unit antennas in self-decoupling technology, the purpose of the present invention is to provide a MIMO antenna array self-decoupling method based on substructure characteristic mode theory for separate analysis of dual-unit antennas, which conforms to the actual operation of microstrip patch antenna pairs and reduces the number of significant modes, thereby simplifying and guiding the design of more complex self-decoupling MIMO antenna arrays.

[0005] To achieve the above object, the present invention adopts the following technical solution: a MIMO antenna array self-decoupling method based on substructure eigenmode theory, the method comprising the following steps in order:

[0006] (S1) Establish a dual-element MIMO microstrip patch antenna array consisting of one active element and one passive element, analyze the dual-element MIMO microstrip patch antenna array using substructure eigenmode theory, and obtain modal significance and eigenangle curves;

[0007] (S2) Determine the basic characteristic mode of the dual-element MIMO microstrip patch antenna array based on the resonance characteristics reflected by the modal significance and characteristic angle curves, determine a pair of orthogonal modes, namely mode 1 and mode 2, based on the mode current and mode electric field, and take the frequency point corresponding to the intersection of the modal significance curves of mode 1 and mode 2;

[0008] (S3) adjusting the size and spacing of the active unit and the passive unit so that the difference between the characteristic angles of mode 1 and mode 2 at the frequency point is close to 90°;

[0009] (S4) calculating a low amplitude region of a mode current vector difference of an orthogonal mode of an active element of a dual-element MIMO microstrip patch antenna array and a zero amplitude region of a mode electric field sum of an orthogonal mode of a passive element;

[0010] (S5) taking the intersection area of ​​the low amplitude area and the zero amplitude area as the preferred area, placing the feeding port on the preferred area, that is, placing the port excitation on the active unit and matching the 50Ω impedance load on the passive unit;

[0011] (S6) All coordinates of the preferred area are used as coaxial feeding coordinates, and the MIMO microstrip patch antenna array is simulated and compared using HFSS simulation software, ultimately achieving an axial ratio bandwidth of 1.66% and an excellent decoupling level of -42.9 dB at the lowest.

[0012] The step (S1) specifically refers to: establishing a dual-unit MIMO microstrip patch antenna array, the array consists of two identical rectangular microstrip antennas, the two rectangular microstrip antennas are respectively used as an active unit and a passive unit, both of which are 15.0 mm long and 15.9 mm wide, and the distance between the two is 5.0 mm, and the two rectangular microstrip antennas are printed side by side on a single-layer dielectric substrate with a thickness of 1.50 mm and a dielectric constant of 2.65;

[0013] Based on the characteristic mode theory, for the dual-element MIMO microstrip patch antenna array, the hybrid potential integral equation MPIE is derived from the boundary conditions of the ideal electric conductor surface as follows:

[0014] ,

[0015] ,

[0016] in, is the induced surface current, is the incident electric field, is the reflected electric field, is the vector potential of the Green function, is the scalar potential of the Green function; n is the unit vector perpendicular to the conductor surface, is the angular momentum, is the magnetic permeability, is the relative dielectric constant;

[0017] Based on the substructure eigenmode theory, the mixed potential integral equations of active and passive units are adjusted to matrix equations:

[0018] ,

[0019] ,

[0020] in, Z is the impedance matrix, J are the RWG basis function coefficients, V is the excitation vector of the entire dual-element MIMO microstrip patch antenna array; and are the self-impedance matrices of active and passive units, respectively; and They are the mutual coupling matrices of active and passive units respectively; , Active unit J and V part of; , Passive units J and V part of;

[0021] Due to the existence of passive units, that is, , formula (4) is organized as follows:

[0022] ,

[0023] The weighted characteristic equation derived from the moment method and the electric field integral equation is shown below:

[0024] ,

[0025] in, , Represents the impedance matrix The real and imaginary parts of represents the characteristic current on the active unit, λ n yes The corresponding characteristic value, and the characteristic current on the passive unit Calculated as:

[0026] ,

[0027] After integration, the modal significance is defined as:

[0028] ,

[0029] Therefore, the modal significance MS and eigenvalue λ n When λ n <0, it is called capacitance mode; when λ n > 0, it is called inductive mode; when λ n =0, it is called the resonant mode; when the modal significance MS value is equal to 1, it means that this mode radiates most completely;

[0030] The characteristic angle is defined as:

[0031] ,

[0032] exist <180°, this mode can store magnetic energy; >180°, this mode can store electrical energy; =180°, the mode is in resonance.

[0033] The step (S3) specifically refers to: at the frequency point corresponding to the intersection of the modal significance curves of mode 1 and mode 2, the characteristic angles of mode 1 and mode 2 are differentiated, and the size and spacing of the active unit and the passive unit are adjusted so that the characteristic angle difference at the frequency point is close to 90°, indicating that the phase difference between mode 1 and mode 2 is 90° at this time.

[0034] The step (S4) specifically refers to: performing vector subtraction processing on the orthogonal mode current of the active unit, and there are low-amplitude areas near the four corners of the active unit; performing vector addition processing on the orthogonal mode electric field of the passive unit to generate a synthetic zero-amplitude area on the passive unit; when installing the feeding port on the active unit, the feeding port on the passive unit needs to be located in the zero-amplitude area at the same time.

[0035] The step (S6) specifically refers to: using all coordinates of the preferred area as coaxial feeding coordinates, simulating and comparing the MIMO microstrip patch antenna array using HFSS simulation software, the axial ratio bandwidth reaches 1.66%, and the optimal decoupling level reaches -42.9dB at 5.49GHz.

[0036] It can be seen from the above technical scheme that the beneficial effects of the present invention are as follows: the present invention separates the analysis objects in the multi-unit antenna, uses the substructure characteristic mode theory to analyze the multi-unit antenna, reduces the number of modes, and greatly reduces the analysis difficulty of the multi-unit system. It is more in line with the actual situation that one unit of the MIMO microstrip patch antenna pair radiates and the other unit is matched but not excited, and the feeding position is determined more effectively and accurately, which can not only ensure the circular polarization or linear polarization performance, but also realize self-decoupling, and provides a novel solution for solving such problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the method of the present invention;

[0038] Figure 2 It is a front view of the circularly polarized dual-unit MIMO microstrip patch antenna array in the present invention;

[0039] Figure 3 A top view of a circularly polarized dual-unit MIMO microstrip patch antenna array in the present invention;

[0040] Figure 4 is a modal significance curve diagram of the neutron structure characteristic mode theoretical analysis of the present invention;

[0041] Figure 5 It is a characteristic angle curve diagram of the theoretical analysis of the neutron structure characteristic mode of the present invention;

[0042] Figure 6 This is the basic mode electric field distribution diagram of the present invention;

[0043] Figure 7 is the basic mode current distribution diagram of the present invention;

[0044] Figure 8 is a diagram of the orthogonal mode current difference distribution of the active unit in the present invention;

[0045] Fig. 9 is the orthogonal mode electric field and distribution diagram of the passive unit in the present invention;

[0046] Fig.10 It is a diagram of the intersection area of ​​the orthogonal mode current difference low amplitude area and the orthogonal mode electric field and zero amplitude area of ​​the circularly polarized dual-unit MIMO microstrip patch antenna array of the present invention;

[0047] Fig.11 It is a schematic diagram of the axis ratio and S11 and S21 parameter curves of the present invention;

[0048] Fig.12 is the circular polarization pattern of the xoz plane at 5.44 GHz of the present invention;

[0049] Fig.13 is the circular polarization pattern of the yoz plane at 5.44 GHz of the present invention;

[0050] Fig.14 It is a histogram of modal weighting coefficients of the present invention at the lowest axial ratio and the lowest coupling level frequency point;

[0051] Fig.15 It is the front view of the linear polarization MIMO microstrip patch antenna array;

[0052] Fig.16It is a diagram of the intersection area of ​​the orthogonal mode current difference low amplitude region and the orthogonal mode electric field and zero amplitude region of the linear polarization dual-element MIMO microstrip patch antenna array;

[0053] Fig.17 It is a schematic diagram of the S11 and S21 parameter curves of the linearly polarized dual-element MIMO microstrip patch antenna array;

[0054] Fig.18 is the polarization pattern of the linearly polarized dual-element MIMO microstrip patch antenna array in the xoz plane at 5.36GHz;

[0055] Fig.19 This is the polarization pattern of the linearly polarized dual-element MIMO microstrip patch antenna array on the yoz plane at 5.36GHz. DETAILED DESCRIPTION

[0056] like Figure 1 As shown, a MIMO antenna array self-decoupling method based on substructure eigenmode theory includes the following steps in sequence:

[0057] (S1) establishing a dual-element MIMO microstrip patch antenna array including an active unit 1 and a passive unit 2, analyzing the dual-element MIMO microstrip patch antenna array using substructure eigenmode theory, and obtaining modal significance and characteristic angle curves;

[0058] (S2) Determine the basic characteristic mode of the dual-element MIMO microstrip patch antenna array based on the resonance characteristics reflected by the modal significance and characteristic angle curves, determine a pair of orthogonal modes, namely mode 1 and mode 2, based on the mode current and mode electric field, and take the frequency point corresponding to the intersection of the modal significance curves of mode 1 and mode 2;

[0059] (S3) adjusting the size and spacing of the active unit 1 and the passive unit 2 so that the difference between the characteristic angles of mode 1 and mode 2 at the frequency point is close to 90°;

[0060] (S4) calculating a low amplitude region of a mode current vector difference of an orthogonal mode of an active unit 1 of a dual-unit MIMO microstrip patch antenna array and a zero amplitude region of a mode electric field sum of an orthogonal mode of a passive unit 2;

[0061] (S5) taking the intersection area of ​​the low amplitude area and the zero amplitude area as the preferred area 7, placing the feeding port 3 on the preferred area 7, that is, placing the port excitation on the active unit 1, and matching the 50Ω impedance load on the passive unit 2;

[0062] (S6) All coordinates of the preferred area 7 are used as coaxial feeding coordinates, and the MIMO microstrip patch antenna array is simulated and compared using HFSS simulation software, and finally an axial ratio bandwidth of 1.66% and an excellent decoupling level of the lowest -42.9dB are obtained.

[0063] The step (S1) specifically refers to: Figure 2 , Figure 3 As shown, a dual-unit MIMO microstrip patch antenna array is established, which consists of two identical rectangular microstrip antennas, the two rectangular microstrip antennas are used as active unit 1 and passive unit 2 respectively, both of which are 15.0 mm long and 15.9 mm wide, and the distance between them is 5.0 mm. The two rectangular microstrip antennas are printed side by side on a single-layer dielectric substrate 6 with a thickness of 1.50 mm and a dielectric constant of 2.65;

[0064] Characteristic mode theory is a mathematical method for analyzing and designing antenna systems. This theory is based on the vector potential theory of electromagnetic fields and can be used to predict the radiation and impedance characteristics of antenna systems, as well as to optimize antenna performance by adjusting the geometric shape. Since the antenna contains a dielectric substrate, for the microstrip patch antenna array structure, the integral singularity of the hybrid potential integral equation MPIE is weaker than the electric field integral equation EFIE; based on the characteristic mode theory, for the dual-element MIMO microstrip patch antenna array, the hybrid potential integral equation MPIE is derived from the boundary conditions of the ideal conductor surface as follows:

[0065] ,

[0066] ,

[0067] in, is the induced surface current, is the incident electric field, is the reflected electric field, is the vector potential of the Green function, is the scalar potential of the Green function; n is the unit vector perpendicular to the conductor surface, is the angular momentum, is the magnetic permeability, is the relative dielectric constant;

[0068] The substructure characteristic mode theory separates multiple analysis objects and only performs active analysis on a specific object. The other analysis objects are treated as passive objects and only parasitic effects are considered. Based on the substructure characteristic mode theory, the mixed potential integral equations of active unit 1 and passive unit 2 are adjusted to matrix equations:

[0069] ,

[0070] ,

[0071] in, Z is the impedance matrix, J are the RWG basis function coefficients, V is the excitation vector of the entire dual-element MIMO microstrip patch antenna array; and are the self-impedance matrices of active unit 1 and passive unit 2 respectively; and They are the mutual coupling matrices of active unit 1 and passive unit 2 respectively; , Active unit 1 J and V part of; , Passive unit 2 J and V part of;

[0072] Due to the existence of passive unit 2, that is, , formula (4) is organized as follows:

[0073] ,

[0074] The weighted characteristic equation derived from the moment method and the electric field integral equation is shown below:

[0075] ,

[0076] in, , Represents the impedance matrix The real and imaginary parts of represents the characteristic current on active unit 1, λ n yes The corresponding characteristic value, and the characteristic current on the passive unit 2 Calculated as:

[0077] ,

[0078] After integration, the modal significance is defined as:

[0079] ,

[0080] Therefore, the modal significance MS and eigenvalue λ n When λ n <0, it is called capacitance mode; when λ n > 0, it is called inductive mode; when λ n =0, it is called the resonant mode; when the modal significance MS value is equal to 1, it means that this mode radiates most completely;

[0081] The characteristic angle is defined as:

[0082] ,

[0083] exist <180°, this mode can store magnetic energy; >180°, this mode can store electrical energy; =180°, the mode is in resonance.

[0084] The step (S3) specifically refers to: at the frequency point corresponding to the intersection of the modal significance curves of mode 1 and mode 2, the characteristic angles of mode 1 and mode 2 are differentiated, and the size and spacing of the active unit 1 and the passive unit 2 are adjusted so that the characteristic angle difference at the frequency point is close to 90°, indicating that the phase difference between mode 1 and mode 2 is 90° at this time.

[0085] It can be seen that for the dual-element MIMO microstrip patch antenna array, the substructure characteristic mode analysis is performed and the following is obtained: Figure 4 The modal significance curves shown in Figure 5 The characteristic angle curve is shown.

[0086] According to the definition of modal significance, the closer the amplitude is to 1, the greater the potential for the mode to be excited. Figure 4 It can be seen from the modal significance curve shown that in the 5.3 to 5.8 GHz band, the values ​​at frequencies of 5.47 GHz and 5.70 GHz are close to 1, so the two modes determine the basic modes, and they are named the first basic characteristic mode and the second basic characteristic mode, namely mode 1 and mode 2. According to the characteristic current and electric field distribution, it can be seen that the directions of the two modes are orthogonal. If circularly polarized radiation of the antenna is to be achieved, modes with a phase difference of 90° and the same amplitude are required as orthogonal modes to synthesize the radiation field. At nearly 5.57 GHz, the modal significance of mode 1 and mode 2 is the same, indicating that at this frequency point, mode 1 and mode 2 can produce radiation effects with similar amplitudes under appropriate excitation. The mode electric field and mode current of mode 1 and mode 2 are shown as follows: Figure 6 , Figure 7 shown.

[0087] The step (S4) specifically refers to: performing vector subtraction processing on the orthogonal mode current of the active unit 1, and there are low amplitude areas near the four corners of the active unit 1; performing vector addition processing on the orthogonal mode electric field of the passive unit 2, and generating a synthetic zero amplitude area on the passive unit 2; when the feeding port 3 is installed on the active unit 1, the feeding port 3 on the passive unit 2 needs to be located in the zero amplitude area at the same time. Figure 8As shown, the amplitudes of the four corner regions on the active unit 1 are relatively low, and these regions are selected as the locations where the feeding ports 3 of the active unit 1 are placed; Fig. 9 As shown, the amplitude of the diagonal area on the passive unit 2 is 0, and this area is selected as the placement location of the feeding port 3 of the passive unit 2; Fig.10 It is the intersection of the above two areas and is the area where the final feeding port is placed.

[0088] The step (S6) specifically refers to: taking all coordinates of the preferred area 7 as coaxial feeding coordinates, simulating and comparing the MIMO microstrip patch antenna array using HFSS simulation software, the axial ratio bandwidth reaches 1.66%, and the optimal decoupling level reaches -42.9dB at 5.49GHz.

[0089] All the coordinates of the desired preferred area 7 are used as coaxial feed coordinates to simulate the MIMO microstrip patch antenna array using HFSS simulation software. After comparison, the position with the best impedance matching, circular polarization and decoupling effect is selected. After simulation, by observing Fig.11 S11, S21, axis ratio and Fig.12 , Fig.13 The circular polarization radiation pattern shows that its impedance bandwidth (S11<-10dB) reaches 5.94% (5.39-5.72GHz), the circular polarization bandwidth (AR<3dB) reaches 1.66% (5.39-5.48GHz), and the best decoupling effect can reach -42.9dB at 5.49GHz, so it has good circular polarization and self-decoupling performance.

[0090] The modal weighting coefficient is used in the characteristic mode theory to describe the weight of different modes in forming the total field. This coefficient indicates the contribution of each mode to the overall electromagnetic field distribution and the relative importance of each mode in the overall electromagnetic field. After determining the final feeding position, its modal weighting coefficient is as follows: Fig.14 As shown, both Mode 1 and Mode 2 occupy the largest proportion of all modes, which means that Mode 1 and Mode 2 are effectively stimulated and play a leading role, thus verifying that the above method is correct.

[0091] A long narrow linear polarization dual-unit MIMO microstrip patch antenna array is established. The array consists of two identical first rectangular microstrip antennas. The two first rectangular microstrip antennas serve as the first active unit 4 and the first passive unit 5, respectively. The length of the first active unit 4 and the first passive unit 5 are both 14.0 mm, the width is both 36 mm, and the spacing is 6.0 mm. The two first rectangular microstrip antennas are printed side by side on a first single-layer dielectric substrate 9 with a thickness of 2.0 mm and a dielectric constant of 2.65. A first feeding port 8 is placed on a first preferred area 10, as shown in FIG. Fig.15According to the present invention, the first preferred region 10 of the structure is obtained after the substructure characteristic mode analysis, as shown in FIG. Fig.16 As shown, all coordinates of the first preferred area 10 are used as coaxial feed coordinates to simulate the linear polarization dual-unit MIMO microstrip patch antenna array using HFSS simulation software. After simulation, by observing Fig.17 S11, S21 and Fig.18 , Fig.19 The polarization radiation pattern shows that its impedance bandwidth (S11<-10dB) reaches 10.74% (5.20-5.79GHz), the decoupling bandwidth (S21<-20dB) reaches 2.97% (5.30-5.46GHz), and the overlapping bandwidth (S11<-10dB, S21<-20dB) reaches 2.97% (5.30-5.46GHz). The best decoupling effect can reach -67.23dB at 5.36GHz.

[0092] In summary, the present invention separates the analysis objects in the multi-unit antenna, uses the substructure eigenmode theory to analyze the multi-unit antenna, reduces the number of modes, and greatly reduces the analysis difficulty of the multi-unit system. It is more in line with the actual situation that one unit of the MIMO microstrip patch antenna pair radiates and the other unit is matched but not excited. It can determine the feeding position more effectively and accurately, and can not only ensure the circular polarization or linear polarization performance, but also achieve self-decoupling, providing a novel solution to this type of problem.

Claims

1. A MIMO antenna array self-decoupling method based on substructure eigenmode theory, characterized by: The method comprises the following steps in order: (S1) Establish a dual-element MIMO microstrip patch antenna array consisting of one active element and one passive element, analyze the dual-element MIMO microstrip patch antenna array using substructure eigenmode theory, and obtain modal significance and eigenangle curves; The substructure characteristic mode theory is to perform active analysis on a specific object only, and treat other analysis objects as passive objects, only consider parasitic effects, and adjust the mixed potential integral equations of active units and passive units to calculate the modal parameters; (S2) Determine the basic characteristic mode of the dual-element MIMO microstrip patch antenna array based on the resonance characteristics reflected by the modal significance and characteristic angle curves, determine a pair of orthogonal modes, namely mode 1 and mode 2, based on the mode current and mode electric field, and take the frequency point corresponding to the intersection of the modal significance curves of mode 1 and mode 2; (S3) adjusting the size and spacing of the active unit and the passive unit so that the difference between the characteristic angles of mode 1 and mode 2 at the frequency point is close to 90°; (S4) calculating the low amplitude region of the mode current vector difference of the orthogonal mode of the active element of the dual-element MIMO microstrip patch antenna array, and the mode electric field and zero amplitude region of the orthogonal mode of the passive element; (S5) taking the intersection area of ​​the low amplitude area and the zero amplitude area as the preferred area, placing the feeding port on the preferred area, that is, placing the port excitation on the active unit and matching the 50Ω impedance load on the passive unit; (S6) All coordinates of the preferred area are used as coaxial feeding coordinates, and the MIMO microstrip patch antenna array is simulated and compared using HFSS simulation software, ultimately achieving an axial ratio bandwidth of 1.66% and an excellent decoupling level of -42.9 dB at the lowest.

2. The MIMO antenna array self-decoupling method based on substructure eigenmode theory according to claim 1, characterized in that: The step (S1) specifically refers to: establishing a dual-unit MIMO microstrip patch antenna array, the array consists of two identical rectangular microstrip antennas, the two rectangular microstrip antennas are respectively used as an active unit and a passive unit, both of which are 15.0 mm long and 15.9 mm wide, and the distance between the two is 5.0 mm, and the two rectangular microstrip antennas are printed side by side on a single-layer dielectric substrate with a thickness of 1.50 mm and a dielectric constant of 2.65; Based on the characteristic mode theory, for the dual-element MIMO microstrip patch antenna array, the hybrid potential integral equation MPIE is derived from the boundary conditions of the ideal electric conductor surface as follows: ， ， in, is the induced surface current, is the incident electric field, is the reflected electric field, is the vector potential of the Green function, is the scalar potential of the Green's function; n is the unit vector perpendicular to the conductor surface, is the angular momentum, is the magnetic permeability, is the relative dielectric constant; Based on the substructure eigenmode theory, the mixed potential integral equations of active and passive units are adjusted to matrix equations: ， ， in, Z is the impedance matrix, J are the RWG basis function coefficients, V is the excitation vector of the entire dual-element MIMO microstrip patch antenna array; and are the self-impedance matrices of active and passive units, respectively; and They are the mutual coupling matrices of active and passive units respectively; , Active unit J and V part of; , Passive units J and V part of; Due to the existence of passive units, that is, , formula (4) is organized as follows: ， The weighted characteristic equation derived from the moment method and the electric field integral equation is shown below: ， in, , Represents the impedance matrix The real and imaginary parts of represents the characteristic current on the active unit, λ n yes The corresponding characteristic value, and the characteristic current on the passive unit Calculated as: ， After integration, the modal significance is defined as: ， Therefore, the modal significance MS and eigenvalue λ n When λ n <0, it is called capacitance mode; when λ n > 0, it is called inductive mode; when λ n =0, it is called the resonant mode; when the modal significance MS value is equal to 1, it means that this mode radiates most completely; The characteristic angle is defined as: ， exist <180°, this mode can store magnetic energy; >180°, this mode can store electrical energy; =180°, the mode is in resonance.

3. The MIMO antenna array self-decoupling method based on substructure eigenmode theory according to claim 1, characterized in that: The step (S3) specifically refers to: at the frequency point corresponding to the intersection of the modal significance curves of mode 1 and mode 2, the characteristic angles of mode 1 and mode 2 are differentiated, and the size and spacing of the active unit and the passive unit are adjusted so that the characteristic angle difference at the frequency point is close to 90°, indicating that the phase difference between mode 1 and mode 2 is 90° at this time.

4. The MIMO antenna array self-decoupling method based on substructure eigenmode theory according to claim 1, characterized in that: The step (S4) specifically refers to: performing vector subtraction processing on the orthogonal mode current of the active unit, and there are low-amplitude areas near the four corners of the active unit; performing vector addition processing on the orthogonal mode electric field of the passive unit to generate a synthetic zero-amplitude area on the passive unit; when installing the feeding port on the active unit, the feeding port on the passive unit needs to be located in the zero-amplitude area at the same time.

5. The MIMO antenna array self-decoupling method based on substructure eigenmode theory according to claim 1, characterized in that: The step (S6) specifically refers to: using all coordinates of the preferred area as coaxial feeding coordinates, simulating and comparing the MIMO microstrip patch antenna array using HFSS simulation software, the axial ratio bandwidth reaches 1.66%, and the optimal decoupling level reaches -42.9dB at 5.49GHz.

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