A four-port high isolation MIMO antenna

Abstract

The present invention discloses a four-port high-isolation MIMO antenna, which belongs to the field of antennas. The antenna includes a rectangular dielectric substrate, four microstrip feeders arranged on the front of the dielectric substrate, and a ground plane arranged on the back of the dielectric substrate; a polygonal gap, two T-shaped gaps, and four convex-shaped gaps are arranged on the ground plane. The present invention feeds the antenna through four microstrip feeders, and electromagnetic waves are radiated through the convex-shaped gaps. The T-shaped gaps on the ground plane offset the microstrip line currents distributed up and down, thereby achieving high isolation between the upper and lower symmetrical unit antennas; at the same time, the polygonal gaps are introduced to change the distribution of the current on the defective floor, and the equivalent distance between each port is increased, so that the antenna isolation is greatly improved. The antenna has the advantages of wide bandwidth, low cost, miniaturization, high isolation, and wide radiation range.

Description

Technical Field

[0001] The invention belongs to the field of antennas, and in particular relates to a four-port high-isolation MIMO antenna. Background Art

[0002] MIMO antennas have the advantages of high signal transmission rate, high spectrum utilization, high spatial efficiency and low power consumption. They play a key role in the development of 5G and have very high practical value. Since the MIMO system was proposed by Bell Labs, the research on MIMO antennas has received widespread attention at home and abroad. At present, MIMO antennas are developing in the direction of miniaturization, ultra-wideband and high isolation. Usually, in order to meet the requirements of miniaturization of MIMO antennas, the coupling between antennas will increase as the distance between unit antennas decreases, which will deteriorate the performance of the MIMO antenna system. Therefore, improving the coupling between MIMO antenna units is of practical significance to the development of wireless communications.

[0003] At present, the methods of MIMO antenna decoupling in domestic and foreign papers can be roughly divided into three types. One of the methods of MIMO antenna decoupling is to change the current distribution on the antenna surface through metamaterials or EBG structures. Generally, metamaterials show negative dielectric constants or magnetic permeabilities, which have obvious advantages in suppressing surface wave coupling. EBG changes the current distribution through periodic planar structures. Another method to improve antenna isolation is to use antennas with complementary structures. Since the antenna itself has high isolation characteristics, high isolation can be achieved without any decoupling structure antenna. The third type of decoupling structure is to load parasitic patches or slots on the ground or load inductive or capacitive open ring resonators above the patches. For example, the two-port ultra-wideband MIMO antenna mentioned in the paper "Isolation Enhancement of a Very Compact UWB-MIMO Slot Antenna With Two Defected Ground Structures" in Volume 14 of "IEEE Antennas and Wireless Propagation Letters" in 2015 uses slots on the ground to improve the isolation between the two ports; however, the transmission rate of this antenna needs to be further improved to meet the needs of 5G technology. Summary of the invention

[0004] The present invention proposes a four-port high isolation MIMO antenna. To improve the data transmission rate of the antenna, the two-port MIMO antenna is first expanded into a four-port antenna. Then, without increasing the spacing between the unit antennas, the isolation of the antenna is improved by using the decoupling method of the defect ground. The antenna has the advantages of wide bandwidth, low cost, miniaturization, high isolation, and wide radiation range.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A four-port high-isolation MIMO antenna, characterized in that the antenna is both a left-right symmetrical structure and a top-bottom symmetrical structure, comprising a rectangular dielectric substrate, four microstrip feed lines arranged on the front of the dielectric substrate, and a ground plate arranged on the back of the dielectric substrate;

[0007] The microstrip feed line is a rectangular microstrip line, the long side of which is parallel to the long side of the dielectric substrate, and a short side of which coincides with the short side of the dielectric substrate, serving as a feeding port;

[0008] The grounding plate is provided with a polygonal gap, two T-shaped gaps, and four convex-shaped gaps;

[0009] The polygonal gap is arranged in the middle of the ground plate and divides the ground plate into two parts, left and right.

[0010] The longitudinal rectangular slot of the T-shaped slot is parallel to the short side of the dielectric substrate, the midline of the transverse rectangular slot coincides with the midline of the short side of the dielectric substrate, and one end of the transverse rectangular slot coincides with the short side of the dielectric substrate;

[0011] Two of the convex-shaped gaps are arranged in a forward direction, and two of the convex-shaped gaps are arranged in an inverted direction; the convex-shaped gaps are composed of a bottom rectangular portion and a raised rectangular portion; one side of the bottom rectangular portion coincides with the long side of the dielectric substrate, and the long side of the raised rectangular portion is parallel to the short side of the dielectric substrate.

[0012] Furthermore, the width of the middle portion of the polygonal gap is greater than the width of the two sides.

[0013] Furthermore, the polygonal gap is a dodecagonal gap, which is composed of a first rectangle, two isosceles trapezoids, and two second rectangles, wherein the middle part is the first rectangle, the two short sides of the first rectangle are respectively connected to the lower base of an isosceles trapezoid, and the upper base of the isosceles trapezoid is connected to the second rectangle.

[0014] Furthermore, two straight-line gaps are provided on the ground plate, and the long sides of the straight-line gaps are parallel to the short sides of the dielectric substrate.

[0015] Furthermore, the spacing S between the two microstrip feed lines located on the left / right side is 7.6 mm, the length T2 of the longitudinal branch of the T-shaped slot is 8 mm, and the length T1 of the transverse branch is 7.5 mm; the center line of the two convex-shaped slots located on the left / right side is located at 0.25Ws from the long side of the dielectric substrate, and the total height of the bottom rectangular part and the raised rectangular part is 10.2 mm.

[0016] Furthermore, the distances between the I-shaped gap, the microstrip feed line and the longitudinal midline of the antenna are equal in length.

[0017] The present invention feeds the antenna through four microstrip feed lines, and the electromagnetic waves are radiated through the convex-shaped gaps. The T-shaped gaps on the ground plane offset the microstrip line currents distributed up and down on the left / right sides, thereby achieving high isolation between the upper and lower symmetrical unit antennas. However, due to the continuous distribution of current on the defective floor and the electromagnetic wave coupling between the ports, the coupling degree between the left / right ports is high. Therefore, a polygonal gap is introduced to change the distribution of current on the defective floor, which is equivalent to increasing the equivalent distance between the ports, thereby greatly improving the antenna isolation. Compared with the prior art, the advantages of the present invention are:

[0018] (1) The antenna has a small size and contains a large number of unit antennas, thereby increasing the data transmission rate.

[0019] (2) A reasonable defective ground structure is adopted to keep the distance between the unit antennas unchanged while reducing the coupling degree between the unit antennas.

[0020] (3) While meeting high isolation requirements, the relative bandwidth of the antenna can reach 97.3%. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a 3D perspective view of an embodiment of the present invention;

[0022] Figure 2 1 are top views and bottom views of an embodiment of the present invention, wherein (a) is a top view and (b) is a bottom view;

[0023] Figure 3 This is a schematic diagram of the structure of a polygonal gap in a defective ground according to an embodiment of the present invention;

[0024] Figure 4 is an S parameter diagram of an embodiment of the present invention;

[0025] Figure 5 The far-field radiation E-plane and H-plane diagrams of the antenna at three different frequencies according to the embodiment of the present invention, wherein (a) is the E-plane radiation diagram and (b) is the H-plane radiation diagram;

[0026] Figure 6 is a graph showing gain and antenna radiation efficiency according to an embodiment of the present invention;

[0027] Figure 7 Graph showing envelope correlation coefficients according to an embodiment of the present invention.

[0028] Figure numerals: 1 microstrip line, 2 dielectric substrate, 3 ground plane, 4 T-shaped gap, 5 convex-shaped gap, 6 polygonal gap, 7 straight-shaped gap. DETAILED DESCRIPTION

[0029] The following embodiments of the technical solution of the present invention are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and cannot be used to limit the scope of the present invention.

[0030] It should be noted that, unless otherwise specified, practical technical terms or scientific terms in this application should have the common meanings understood by technicians in the field to which the invention belongs.

[0031] like Figure 1 As shown, the embodiment of the present invention adopts a rectangular dielectric substrate 2, whose dielectric constant is 4.4 and thickness is 0.8mm. Four microstrip feed lines 1 are arranged on the upper layer of the dielectric substrate. The four microstrip feed lines are symmetrical about the middle line of the long side and the middle line of the short side of the dielectric substrate. The lower layer of the dielectric substrate is a ground plane 3. The antenna is fed by generating a voltage difference between the microstrip feed line 1 and the ground plane 3, and an SMA interface is usually used.

[0032] Figure 2 The figure shows the top view and bottom view of the embodiment of the present invention, and the grounding plate is provided with two T-shaped slots 4, four convex slots 5, two straight slots 7 and a polygonal slot 6. The two T-shaped slots are symmetrical about the midline of the long side of the dielectric substrate, the four convex slots are symmetrical about the midlines of the long side and the short side of the dielectric substrate respectively, and the straight slot is symmetrical about the midline of the long side of the dielectric substrate.

[0033] Combination Figure 1 , 2 In the embodiment of the present invention, the antenna is fed by a microstrip feeder, and the electromagnetic wave is radiated through the convex-shaped gap. The T-shaped gap on the ground plate offsets the microstrip feeder current distributed up and down on the left / right sides, thereby achieving high isolation between the upper-line symmetrical unit antennas. However, due to the continuous distribution of current on the defective floor and the electromagnetic wave coupling between the ports, the coupling degree between the left / right ports is high. Therefore, a polygonal gap is introduced to change the distribution of current on the defective floor, which is equivalent to increasing the equivalent distance between the ports, thereby greatly improving the antenna isolation.

[0034] Figure 3 It is a polygonal gap at the midline of the long side of the ground plate.

[0035] In order to further verify the performance of the above antenna structure, simulation is performed according to the specific parameter settings shown in Table 1. The simulation effect diagram is shown in the figure below. Figure 4-Figure 7 shown.

[0036] Table 1 Antenna size simulation data

[0037] A1 A2 B1 C1 C2 D1 D2 L 3.2mm 7mm 5mm 4mm 5mm 0.5mm 9mm 15mm L1 LS T1 T2 T3 W W W1 12mm 26mm 7.5mm 8mm 2mm 2mm 44mm 0.1mm W2 W3 W4 S 2mm 2mm 2mm 7.6mm

[0038] Combination Figure 1 , Figure 2, Figure 3 From the marked positions of the parameters, it can be seen that A1 and B1 represent the width and length of the bottom rectangular part of the convex-shaped gap, A2 and W4 represent the length and width of the raised rectangular part above the convex-shaped gap, C1 and D1 represent the length and width of the second rectangle in the polygonal gap, D2 represents the height of the isosceles trapezoid of the polygonal gap, C2 represents the width of the first rectangle of the polygonal gap, L and W represent the length and width of the microstrip feeder, W1 and L1 represent the width and length of the I-shaped gap, T1 and W3 represent the length and width of the transverse rectangular gap in the T-shaped gap, T2 and W2 represent the length and width of the longitudinal rectangular gap in the T-shaped gap, and Ws and Ls represent the length and width of the dielectric substrate.

[0039] Figure 4 The simulation results of the S parameters of the present invention are as follows: from 3.8 to 11 dB, S11<-10 dB, and within the working bandwidth, S21 is almost less than -20 dB, and S31 and S41 are less than -14 dB. These parameter ranges can meet the standards for engineering applications.

[0040] Figure 5 The radiation patterns of the antenna at 6, 8, and 10 GHz. It can be seen from the figure that when the antenna is working, it can achieve radiation coverage in a wide range.

[0041] Figure 6 Graphs 2 and 3 are the gain and radiation efficiency graphs of the antenna. It can be seen from the graph that within the operating frequency band of 3.8-11 GHz, the antenna gain is greater than 2 dB and the radiation efficiency is greater than 80%.

[0042] Figure 7 The antenna envelope correlation coefficient diagram is usually an important parameter to measure the coupling between antenna ports. Usually, if ECC is less than 0.5, it indicates that it has practical application value in engineering. Figure 7 It shows that the ports of the antenna of the present invention are all less than 0.15 within the working bandwidth, so the isolation between the ports is high.

[0043] In summary, it can be seen that the four-port high isolation MIMO antenna proposed by the present invention uses a defective ground method to decouple and achieve a high isolation effect. The antenna has the characteristics of small size, high isolation, ultra-wideband, wide radiation area, etc., and can be used in indoor mobile devices.

Claims

1. A four-port high-isolation MIMO antenna, characterized in that: The antenna is a left-right symmetrical structure as well as a top-bottom symmetrical structure, comprising a rectangular dielectric substrate, four microstrip feed lines arranged on the front of the dielectric substrate, and a grounding plate arranged on the back of the dielectric substrate; The microstrip feed line is a rectangular microstrip line, the long side of which is parallel to the long side of the dielectric substrate, and a short side of which coincides with the short side of the dielectric substrate, serving as a feeding port; The grounding plate is provided with a polygonal gap, two T-shaped gaps, and four convex-shaped gaps; The polygonal gap is arranged in the middle of the grounding plate and divides the grounding plate into two parts, the left and the right. The polygonal gap is a dodecagonal gap, which is composed of a first rectangle, two isosceles trapezoids, and two second rectangles, wherein the middle part is the first rectangle, the two short sides of the first rectangle are respectively connected to the lower base of an isosceles trapezoid, and the upper base of the isosceles trapezoid is connected to the second rectangle. The longitudinal rectangular slot of the T-shaped slot is parallel to the short side of the dielectric substrate, the midline of the transverse rectangular slot coincides with the midline of the short side of the dielectric substrate, and one end of the transverse rectangular slot coincides with the short side of the dielectric substrate; Two of the convex-shaped gaps are arranged in a forward direction, and two of the convex-shaped gaps are arranged in an inverted direction; the convex-shaped gaps are composed of a bottom rectangular portion and a raised rectangular portion; one side of the bottom rectangular portion coincides with the long side of the dielectric substrate, and the long side of the raised rectangular portion is parallel to the short side of the dielectric substrate.

2. A four-port high isolation MIMO antenna as claimed in claim 1, characterized in that: The ground plate is further provided with two straight-line gaps, and the long sides of the straight-line gaps are parallel to the short sides of the dielectric substrate.

3. A four-port high isolation MIMO antenna as claimed in claim 2, characterized in that: The distances between the I-shaped gap, the microstrip feeder and the longitudinal center line of the antenna are equal in length.

4. A four-port high isolation MIMO antenna as claimed in claim 3, characterized in that: The spacing S between the two microstrip feed lines on the left / right side is 7.6 mm, the length T2 of the longitudinal branch of the T-shaped slot is 8 mm, and the length T1 of the transverse branch is 7.5 mm; the midline of the two convex-shaped slots on the left / right side is located at 0.25Ws from the long side of the dielectric substrate, where Ws represents the length of the long side of the dielectric substrate; the total height of the bottom rectangular part and the raised rectangular part is 10.2 mm.

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