CN111276811A - MIMO antenna with compact mode diversity - Google Patents

Abstract

The invention provides a MIMO antenna with compact mode diversity, which is characterized in that four monopole antenna elements are orthogonally arranged at the corners of a substrate. A decoupling structure consisting of a circular patch and four L-shaped branches placed counterclockwise is printed on the upper surface of the substrate to reduce coupling between the antenna elements. The MIMO antenna exhibits omnidirectional radiation at low frequencies and directional radiation at high frequencies due to surface currents on a circular parasitic patch obtained by coupling with a monopole antenna, which has a size of 30 mm x 30 mm. The measurement results showed that the overlapping bandwidths (S) were in the range of 4.58 GHz to 6.12 GHz₁₁Less than or equal to-10 dB) is 28.8 percent, and the gain is more than 4.02 dBi. Furthermore, the measurement results of the mode diversity are substantially identical to the simulation results and the measured isolation is as high as 15.4 dB, which indicates that the proposed antenna can be applied to WLAN/5G/WiFi wirelessAnd (4) communication.

Description

MIMO antenna with compact mode diversity

Technical Field

The invention relates to the technical field of communication, in particular to a Multiple Input Multiple Output (MIMO) antenna with compact mode diversity.

Background

In the reality of limited bandwidth resources and increasing demand for high-speed data, a method of increasing transmit antennas is proposed to improve spatial freedom, system performance and frequency band utilization. A MIMO system implementing a weak diversity gain or spatial multiplexing scheme to eliminate the negative effects of multipath fading means to simultaneously use two or more antennas for transmission and reception through a wireless channel. IEEE 802.11n and IEEE 802.11ac Wireless Local Area Network (WLAN) standards [1] incorporate MIMO antenna technology. These WLAN standards may support up to two antenna elements and up to four antenna elements and four data streams at 2.4-2.5 GHz (802.11 n) for each user or mobile station at 4.9-5.725 GHz. Meanwhile, fifth generation (5G) communication technologies may provide many advantages such as higher transmission rates and smaller delays compared to current 4G systems. MIMO technology has been used to significantly increase the channel capacity of wireless communication systems. The more antenna elements that are provided in a MIMO array, the higher channel capacity will be achieved. Various types of MIMO antennas have been previously studied with various characteristics, such as dual-band, circular polarization, high isolation, compact size, to meet the requirements of WLAN, 5G and WiFi.

For small devices such as smartphones and tablet computers, one unique challenge of MIMO antenna design is to embed the antennas inside the device in a compact size while maintaining a sufficiently low degree of isolation or mutual coupling. Recently, in order to meet the demand for high rate and large data transmission capacity, various MIMO antenna arrays and decoupling structures have been proposed and studied. For example in x.m. Yang, X. G. Liu, X. The < mutual coupling between closely packed patch antennas using waveguide meta-material > published by y, Zhou and t.j. Cui introduces waveguide meta-material (WG-MTM) to obtain magnetic resonance characteristics and bandgap characteristics, and measurements show that mutual coupling of antennas is within 10 dB bandwidth, and isolation of antennas is reduced by at least 6 dB bandwidth. In a hybrid fractal plane monopole antenna published in IEEE Trans antenna transmission 3 month 2014, covering multiband wireless communication, implemented by MIMO, for handheld mobile devices, a T-shaped strip and a rectangular slot are inserted at the top of a ground plane to improve impedance matching and isolation between the antennas. In the "size reduction of self-isolation MIMO antenna system for 5G handset application" published in the IEEE antenna wireless propagation, an antenna element having self-isolation characteristics and compact size is proposed, in which a T-shaped feeding element, an inverted U-shaped radiating element and two additional vertical stubs are respectively designed to achieve isolation better than 19.1 db. Meanwhile, in the "compact 5GMIMO handset antenna with closely arranged orthogonal modes" published in IEEE Trans antenna propagation, an orthogonal mode method is also proposed to mitigate mutual coupling between closely arranged line pairs, and then, isolation performance (better than 20 dB) means that a 4 × 4 MIMO system can be a candidate for 5G applications. In an eight-element dual-polarization MIMO slot antenna system suitable for 5G smart phone application published by IEEE, a pair of circular ring/open parasitic structures and a polarization diversity technology are introduced to obtain the characteristics of high isolation and dual polarization.

However, as the integration of handheld devices continues to increase, the space for mounting antennas also continues to shrink. Therefore, there is an urgent need to develop a unique decoupling structure having polarization diversity, pattern diversity, bandwidth extension, strong decoupling and dual-frequency characteristics. Then, a small antenna with higher isolation, pattern diversity, and broadband can satisfy the demand for wireless communication.

Disclosure of Invention

Therefore, in order to overcome the above problems, the present invention provides a MIMO antenna having compact mode diversity, comprising a MIMO antenna in which four monopole antenna elements are orthogonally disposed at the corners of a substrate, a decoupling structure consisting of a circular patch and four L-shaped branches is printed on the upper surface of the substrate to reduce coupling between the antenna elements, and a circular parasitic patch is disposed counterclockwise at the center of the MIMO antenna together with the four L-shaped branches.

Preferably, the printed circuit board is placed orthogonally on the upper surface of the substrate, the thickness of the printed circuit board is 0.8 mm, the dielectric constant is 4.4, the tangential loss is 0.02 of the four planar monopole antennas, and the four rectangular ground planes are placed orthogonally on the basic back surface.

Preferably, the MIMO antenna occupies a volume of only 30 × 30 × 0.8 mm³。

Preferably, the circular parasitic patch is provided with a parasitic element, and the surface current intensity of the parasitic element is slightly weaker than that of the planar monopole antenna when the planar monopole antenna operates at 5.0GHz and 5.5GHz, so that after the parasitic element is loaded, the coupling between the planar monopole antennas gradually increases at high frequency, but the coupling decreases a lot at low frequency, and when the planar monopole antenna operates at 6.0 GHz, the coupling current on the parasitic element is larger than that on the planar monopole antenna, thereby making up for the disadvantage of low isolation.

Preferably, the surface current on the parasitic element and the current distribution on the decoupling structure are the same and dependent on the surface current on the decoupling structure when operating at 5.0GHz, 5.5GHz and 6.0 GHz, respectively.

Preferably, the lengths of the current path lengths CPL1 and CPL 2, equal to half the circumference of the endless metal belt at 6.0 GHz, the following formula can be obtained according to the optimization parameters:

preferably, the MIMO antenna has excellent broadband, high isolation, and various modes, and maintains omni-directional radiation over the entire frequency band without a decoupling structure, exhibits quasi-omni characteristics at 5.0GHz, and obtains directional radiation with higher front-to-back ratios at 5.5GHz and 6.0 GHz.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a MIMO antenna with compact mode diversity, which is different from the decoupling structure in the prior art, and designs a novel decoupling structure, wherein the structure consists of a circular parasitic patch and four rotary L-shaped branches and aims to improve the isolation between antenna elements. Due to the decoupling structure obtained by coupling the surface currents to the planar monopole antenna. Not only enlarge the impedance bandwidth S₁₁Less than or equal to-10 dB, and diversity of directional diagrams is obtained. The measurement result shows that the antenna designed by the invention works in the range of 4.58 GHz to 6.12 GHz, the peak gain is 4.35 dBi, and the isolation is kept below-15.4 dB. The multi-mode radiation device has the advantages of small volume and high multi-mode radiation efficiency, the efficiency is over 75 percent, and the multi-mode radiation device is probably the most suitable choice for the WLAN (4.9-5.725 GHz)/5G (4.8-5.0 GHz)/WiFi (5.15-5.85 GHz).

Drawings

Fig. 1 is a proposed 4 x 4 MIMO antenna geometry of the present invention, (a) top view; (b) a bottom view; (c) a 3-D view;

fig. 2 shows three patterns obtained in the evolution process of the MIMO antenna of the present invention;

FIG. 3 shows the simulation results of the present invention comparing three different antennas (a) S₁₁；（b）S₂₁；

FIG. 4 is a graph of surface current distribution at 5.0GHz, 5.5GHz and 6.0 GHz for three antennas of the present invention;

FIG. 5 is a surface current path diagram of two antennas at 6.0 GHz according to the present invention (a) Ant2, (b) Ant 3;

FIG. 6 is a simulated 3-D radiation pattern of the present invention in 5.0GHz, 5.5GHz and 6.0 GHz (a) Ant 1, (b) Ant 2;

FIG. 7 is a plot of simulated | S' S for various pairs of G2, L2, W1, L5, L3 and W3 in accordance with the present invention₁₁Influence of | the number of proposed MIMO antennas (a) G2; (b) L2; (c) W1; (d) L5; (e) l3; (f) w3;

fig. 8 is a prototype of a MIMO antenna made in accordance with the present invention. (a) Top view (b) bottom view;

FIG. 9 is a return loss of a 4-element MIMO antenna measured in four ports in accordance with the present invention;

FIG. 10 is a simulated and measured S-parameter amplitude for a 4-element MIMO antenna proposed by the present invention at frequency;

fig. 11 is a simulation and measurement of peak gain and radiation efficiency for a 4-element MIMO antenna as proposed by the present invention;

fig. 12 is a simulated and measured radiation pattern (a) of 5.0GHz for a 4-element MIMO antenna proposed in the xoz and yoz planes of the present invention; (b) 5.5 GHz; (c) 6.0 GHz;

figure 13 MIMO performance simulated and measured on the proposed 4-element MIMO antenna. (a) ECC; (b) DG.

Fig. 14. simulation and measurement of TARC for the proposed 4-element MIMO antenna.

Detailed Description

The following detailed description of the system principles of the present invention is provided in connection with the drawings and the examples.

As shown in fig. 1, in order to provide the geometry of the 4 × 4 MIMO antenna of the present invention, four planar monopole antennas are orthogonally disposed on the upper surface of the printed circuit board having a thickness of 0.8 mm, a dielectric constant of 4.4 and a tangential loss of 0.02FR-4, and four rectangular ground planes are orthogonally disposed on the back surface of the substrate; a decoupling structure consisting of a circular patch and four L-shaped branches is also printed on the upper surface of the FR-4 substrate; the circular parasitic patch and the four L-shaped branches are placed in the center of the MIMO antenna anticlockwise; the volume occupied by the antenna is only 30 multiplied by 0.8 mm³Smaller than the 4 x 4 MIMO antenna volume in the prior art.

Proposed size of MIMO antenna

As shown in fig. 2, three forms are obtained in the evolution process of the MIMO antenna of the present invention, and Ant 1 in fig. 2 is an MIMO antenna array composed of four planar monopoles without any decoupling branches; on the basis of the graph Ant 1, an Ant2 shows that a parasitic unit consisting of an annular band and four right-angled triangular patches is added in the center of the graph, so that the impedance bandwidth is improved; to further improve the isolation between planar monopole antenna elements, fig. Ant 3 is designed with a novel decoupling structure, unlike the parasitic elements in Ant 2. The four triangular patches are replaced by four L-shaped branches, which are rotated counterclockwise and located on the upper surface of Ant 2.

Further, the planar monopole antenna 1 (PMA 1) excited three antenna arrays by ANSYS HFSS for all antennas based on finite element method analysis to ensure a more stringent result.

As shown in FIG. 3, the simulation results of the present invention are compared for three different antennas (a) S₁₁；（b）S₂₁It can be seen that from 4.94 GHz to 6.0 GHz (S) is obtained in Ant 1₁₁≦ 10 dB) 19.4% impedance bandwidth, analog isolation (S) between PAM 1 and PAM 2₂₁) Also shown in fig. 3 (b).

Further, as shown in fig. 3 (b), the isolation of Ant 1 is at worst 14.5 dB, and the optimal isolation is 21.2 dB, so as to solve the defect that Ant2 has narrow bandwidth in the parasitic element, as can be seen from fig. 3 (a), the resonance bandwidth of Ant2 is 280 MHz wider than Ant 1 from 4.82 GHz to 6.16 GHz.

Further, Ant2 is subjected to analog isolation, the isolation of the antenna is deteriorated at a frequency of 5.18 GHz and is as high as 30.9 dB, and the isolation of the antenna at 5.25-6.18 GHz, so that the minimum isolation in the working bandwidth is only 12.2 dB, and in order to realize the isolation with higher broadband characteristics based on Ant2, a novel decoupling structure is designed to replace an Ant 3 parasitic unit. And Ant 3 corresponding to the simulation result.

Further, as also shown in fig. 3, by comparing the return loss curves of Ant2 and Ant 3 in port 1, it can be seen from fig. 3 (a) that the return loss of Ant 3 is similar to Ant2, and an attractive high isolation is also obtained. On the other hand, all signals within the isolated resonance bandwidth of graph Ant 3 are greater than 15dB, with the optimum isolation reaching 32.4 dB at 5.54 GHz.

Further, to explain the principle of high isolation and wide band on Ant 3 intuitively. The surface current distribution at frequencies of 5.0GHz, 5.5GHz, and 6.0 GHz by observing Ant 1 and Ant2 is shown in fig. 4. When Ant 1 and Ant2 operate at 5.0GHz and 5.5GHz, respectively, it can be seen from fig. 4 that the surface current intensity of the parasitic element is slightly weaker than that of PMA 1. At 5.0GHz and 5.5GHz, the operating mode of the MIMO array is mainly affected by the surface current on PMA 1. At 6.0 GHz, the coupling current on the parasitic element is larger than the surface current on PMA 1 both in amplitude and density. Therefore, in the operating mode, it can be seen from Ant2 that the current is determined by the distributed current on the parasitic element. In summary, it can be seen from Ant2 that the broadband characteristic can be attributed to a new resonance point generated by surface current coupling on the parasitic element.

Further, by comparing the surface current distributions on Ant 1 and Ant2, it can also be concluded that the coupling between the planar monopole antennas gradually increases at high frequencies, but the coupling frequency drops much at low frequencies, after loading the parasitic elements.

Further, it can be seen in fig. Ant 3 that the disadvantage of low isolation is compensated for, and a corresponding current distribution diagram is also given in fig. 4.

Further, it can be seen from Ant 3 in fig. 4 that the surface current on the parasitic cell and the current distribution on the decoupling structure are substantially the same when operating at 5.0GHz, 5.5GHz and 6.0 GHz, respectively, depending on the surface current on the decoupling structure.

As shown in FIG. 5, the surface current path diagrams of two antennas at 6.0 GHz of the present invention are (a) Ant2, (b) Ant 3; in fig. 5, which shows two surface schematics in the current paths of Ant2 and Ant 3 in 6.0 GHz, the Current Path Length (CPL) of Ant2 can be regarded as the length of CPL1, which is approximately equal to half the circumference of the annular metal band. Similarly, the current path length in graph Ant 3 is the length of CPL 2 in fig. 5 (b). From the optimized parameters in the table, the following formula can be obtained:

when λ takes a wavelength of 6.0 GHz, it can be found by combining fig. 4 and the above formula that the return loss curve is substantially consistent with the graph Ant2 in the graph Ant 3, as shown in fig. 3.

Further, by further analyzing the distribution of the coupling current on Ant 3, it can be found that the coupling current on the planar monopole antenna is significantly weaker than that on Ant 2. On the other hand, the location of coupling current concentration is also shifted from the circular metal strip to the L-shaped branch, thereby improving isolation in graph Ant 3.

As shown in FIG. 6, the simulated 3-D radiation patterns of the present invention at 5.0GHz, 5.5GHz and 6.0 GHz are (a) Ant 1 and (b) Ant 2. As shown in fig. 6 (a), the MIMO antenna without the decoupling structure maintains omnidirectional radiation over the entire frequency band. While the radiation pattern of Ant 3 exhibits quasi-omni characteristics at 5.0 GHz.

Further, for the case of 5.5GHz and 6.0 GHz, directional radiation with a higher front-to-back ratio can be obtained, and an attractive front-to-back ratio is favored by wireless communication systems. Therefore, it has excellent wideband, high isolation and multiple modes as the optimal MIMO antenna array in fig. Ant 3.

As shown in fig. 7, different pairs of MIMO antennas | S of G2, L2, W1, L5, L3 and W3 of the present invention₁₁The simulation was performed. (a) G2; (b) l2; (c) w1; (d) l5; (e) l3; (f) w3; analysis G2 as a first parameter, the corresponding simulated reflection coefficient is also shown in fig. 7 (a).

Further, as G2 increases, the center frequency of the MIMO antenna gradually shifts to a low frequency. Meanwhile, the influence of the impedance transformation microstrip lines (e.g., L2 and W1) on the simulation results was also analyzed, and the results are shown in fig. 7 (b) and 7 (c). With the increasing L2, the resonant frequency of the MIMO antenna shows only a slight shift, but the impedance matching at 6.0 GHz gradually deteriorates, eventually mismatching. With respect to W1, as can be seen from fig. 7 (c), the change in W1 not only affects the impedance matching, but also has a great effect on the shift of the resonance frequency. Next, the parameter analysis was performed on L5, and the corresponding simulation result is shown in fig. 7 (d). When L5 is increased from 8mm to 10 mm, the impedance bandwidth of the MIMO antenna remains substantially unchanged, but the amplitude of S11 fluctuates greatly at low frequencies and little at high frequencies.

Further, a parametric analysis of the decoupling structure was performed. Corresponding simulation results as shown in fig. 7 (e) and 7 (f), when L3 was increased from 6.2mm to 7.8mm, it can be seen from fig. 7 (e) that the high frequency resonance point was gradually shifted to the low frequency, and the change of L3 had little effect on the low frequency resonance point, while, as W3 was increased from 0.6mm to 1.4mm, it can be found that the effect of W3 on the return loss was negligible, as shown in fig. 7 (f).

Fig. 8 shows a prototype of a MIMO antenna made by the present invention. (a) Top view (b) bottom view; a prototype MIMO antenna array was shown, using an Agilent E5080A network analyzer and a saimo Starlab near field measurement system to measure the electrical parameters of the antenna, including return loss, antenna gain, radiation efficiency and radiation pattern.

As shown in fig. 9, the simulated and measured return loss of four planar monopole antenna elements is shown. Simulation results show that return loss of the four ports is basically the same, and impedance bandwidth is kept in a range of 4.78-6.23 GHz. Meanwhile, the measurement results show that the bandwidth of the designed antenna has a relative bandwidth of 28.8% (4.58-6.12 GHz). The measurement results showed a smaller range frequency deviation compared to the simulation results, mainly due to deviations in the manufacturing process and variations in the dielectric constant of the FR4 substrate.

As shown in fig. 10, is the simulated and measured S-parameter amplitude at frequency for a 4-element MIMO antenna as proposed by the present invention; in connection with FIG. 9, it can be concluded that the prototype fabricated operates at a frequency of 5.35 GHz with an inter-element isolation of ≧ 15dB, even though the spacing between the antenna elements is small (G1 ≈ 0.5 λ 0). Wherein λ 0 represents a wavelength of 5.0 GHz.

As shown in fig. 11, the peak gain and radiation efficiency are simulated and measured for the MIMO antenna of the present invention; from the simulation results, it can be found that the maximum gain is 4.31 dBi at 6.12 GHz. Meanwhile, the measurement results show that the maximum gain is 4.02 dBi at 5.95 GHz.

Further, fig. 11 also plots the simulated radiation efficiency of the 4-element MIMO antenna. The average simulated efficiency of 4.58-6.12 GHz was 95.6%. For comparison, the measured radiation efficiency of the MIMO antenna is also given in fig. 11, where the average efficiency is 76.6%. It can be seen that the peak gain and radiation efficiency measurements are slightly reduced compared to the simulation results. This is mainly due to tolerances in the antenna test and the influence of the SMA connector.

As shown in fig. 12, the simulated and measured radiation patterns for the present invention at xoz and the yoz plane 4-element MIMO antenna (a) 5.0 GHz; (b) 5.5 GHz; (c) 6.0 GHz;

in the measurement, one element is excited, while the other element is terminated by a 50 Ω load. As can be seen from fig. 12 (a), the measurement patterns of the xoz plane and the yoz plane both show quasi-omnidirectional radiation at 5.0 GHz. And simultaneously obtaining a 5.5GHz radiation pattern with the maximum radiation direction of 280 phi (phi) on the yoz plane.

Further, as shown in fig. 12 (c), the pattern of 6.0 GHz measured on two planes is an orientation pattern with an attractive front-to-back ratio. This is due to the fact that surface currents on the novel decoupling structure cause additional radiation at high frequencies. Through comparison, the measurement result of the radiation pattern is basically consistent with the simulation result, and the characteristic of pattern diversity is obtained.

As shown in fig. 13, simulated and measured MIMO performance on proposed 4-element MIMO antennas (a) ECC; (b) DG. For attractive MIMO systems, the values of the envelope correlation coefficient ECC and the total active reflection coefficient TARC should be less than 0.5 and 0 dB, respectively. The ECC of the neighboring element and the opposite element may use the following formula:

i and j represent the serial numbers of the antenna elements, respectively. The corresponding results are plotted in fig. 13 (a), and it can be concluded that the ECC values for both the adjacent element and the opposite element are below 0.15. The ECC between the opposite ports is low, indicating that the proposed antenna can provide good pattern diversity for all operating frequencies.

Further, the diversity gain is related to the ECC value of the MIMO antenna system given in (4):

as shown in fig. 13 (b), DG >9.85 dB can be seen. For MIMO systems, multiple antennas can interact when actively engaged in transmission or reception, and thus they can change the overall operating bandwidth and efficiency. TARC, a new indicator, has been used to integrate the overall combined effect of all antennas in a MIMO system. In particular, for the case where the 4 th antenna is excited at the ith port and the other ports are connected to matched loads, TARC as a function of frequency can be calculated according to the following equation:

sp and [ a ] represent the relationship between the excitation port and a given excitation, respectively:

thus, the scattering matrix can be described as

When will be

Excitation set to (use)

Time appointment), can be directly used

The TARC of the linear polarization was calculated.

At this time, it can be found that:

when:

further solving the following steps:

as shown in fig. 14, for the simulation and measurement of TARC for the proposed 4-element MIMO antenna of the invention, it can be concluded from the figure that the TARC value of the proposed antenna is less than-5 dB over the entire frequency band.

Further, proposed MIMO systems are designed entirely for various wireless applications. Compared with several MIMO antennas of the prior art, the proposed design is very competitive with the reported design in terms of impedance bandwidth, isolation, size/profile and pattern diversity. The following table and proposed MIMO show that the antenna system not only has a compact size but also has efficient performance compared to the full extent of the state of the art. In contrast, moreover, the proposed design has ideal ECC, DG and TARC values.

The MIMO antenna with compact mode diversity introduces a novel decoupling structure, thereby obtaining good isolation, wider bandwidth and mode diversity. The measurement results show that the overlap bandwidth is 28.8% (4.58-6.12 GHz) and the gain exceeds 4.8 dBi. For the proposed 4 x 4 MIMO system, the measured isolation is better than 15.4 dB despite the close distance between elements. Furthermore, the radiation efficiency of the proposed 4 x 4 MIMO system is 70% -80%, and the proposed 4 x 4 ECC is better than 0.15 over the whole band. Furthermore, the measured radiation patterns show that the proposed MIMO system provides a new solution for compact 5G MIMO mobile phone antennas with diversity performance.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and are not limited. Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (7)

1. A MIMO antenna having compact mode diversity, characterized in that it is orthogonally placed at the corners of a substrate by four monopole antenna elements, the upper surface of which is printed with a decoupling structure consisting of a circular patch and four L-shaped branches to reduce coupling between the antenna elements, the circular parasitic patch being placed counterclockwise in the center of the MIMO antenna together with the four L-shaped branches.

2. The MIMO antenna of claim 1, wherein the upper surface of the substrate has a printed circuit board thickness of 0.8 mm placed orthogonally, a dielectric constant of 4.4, a tangential loss of 0.02 four planar monopole antennas, and the substantially back surface has four rectangular ground planes placed orthogonally.

3. The MIMO antenna with compact mode diversity according to claim 1, wherein the circular parasitic patch has a parasitic element thereon, and the surface current intensity of the parasitic element is slightly weaker than that of the planar monopole antenna when operating at 5.0GHz and 5.5GHz, so that after the parasitic element is loaded, the coupling between the planar monopole antennas gradually increases at high frequency, but the coupling frequency decreases a lot at low frequency, and the coupling current on the parasitic element is larger than that on the planar monopole antenna when operating at 6.0 GHz, thereby making up for the disadvantage of low isolation.

4. A MIMO antenna with compact mode diversity according to claims 1 and 3, characterized in that the surface currents on the parasitic elements and the currents on the decoupling structure are equally distributed and dependent on the surface currents on the decoupling structure when operating at 5.0GHz, 5.5GHz and 6.0 GHz.

5. The MIMO antenna with compact mode diversity according to claim 4, wherein the lengths of the current path lengths CPL1 and CPL 2 at 6.0 GHz, equal to half the circumference of the annular metal strip, are such that the following formula can be obtained according to the optimized parameters:

。

6. having a compact structure as claimed in claim 1MIMO antenna with mode diversity, characterized in that the volume occupied by the MIMO antenna is only 30 × 30 × 0.8 mm³。

7. The MIMO antenna with compact mode diversity according to claim 1, wherein the MIMO antenna has excellent wideband, high isolation and diverse modes, and the MIMO antenna without the decoupling structure maintains omni-directional radiation over the entire frequency band, exhibits quasi-omni characteristics at 5.0GHz, and obtains directional radiation with higher front-to-back ratio at 5.5GHz and 6.0 GHz.

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