A decoupling structure of a dual-polarized MIMO antenna

Abstract

This invention discloses a decoupling structure for a dual-polarized MIMO antenna, applied to a four-element MIMO antenna. It includes six dielectric substrates: S1, S2, S3, S4, S5, and S6. Metal structure P4 is attached to substrate S1, metal structure P3 to substrate S2, metal structure P2 to substrate S4, and metal structure P1 to substrate S6. S7 is a cross dielectric substrate, vertically placed directly below the antenna element. A U-shaped feed line P5 is attached to the back of S7, and a rectangular metal sheet P6 is attached to the front. S8 is another cross dielectric substrate, vertically placed between adjacent isolation wall dielectric substrates S9, with a U-shaped metal ring P7 attached to its back. S9 is a metal isolation wall surrounding the cross dielectric substrate S7. M is a metal reflector. The advantages of this invention lie in its innovative decoupling structure and the achievement of high isolation within a wide bandwidth while maintaining a relatively small antenna element spacing.

Description

Technical Field

[0001] This invention belongs to the field of microwave antenna technology, specifically relating to a decoupling structure for a dual-polarized MIMO antenna. Background Technology

[0002] With the rapid development of mobile and wireless communication technologies, Multiple-Input Multiple-Output (MIMO) systems have become an important technology for improving system capacity and reliability. MIMO systems utilize multiple antennas at both the transmitting and receiving ends, transmitting data in parallel through multiple transmission channels, thereby improving data transmission rate and reliability. For MIMO systems, the isolation between antennas is crucial. Higher isolation results in less mutual interference between antennas, thus improving system performance. Therefore, achieving high isolation in MIMO antenna design is an important research direction. The ±45° compact high-isolation MIMO antenna is a novel MIMO antenna design method, possessing advantages such as compact size, low cost, and high isolation, and has broad application prospects in mobile communications, wireless LANs, and satellite communications.

[0003] In recent years, numerous studies have been conducted both domestically and internationally on how to improve the isolation of dual-polarized MIMO antennas. In 2017, K.-L. Wu et al. published an article entitled "Array-antenna decoupling surfaces for quasi-yagi antenna arrays" in IEEE Trans. Antenna Propag. (vol. 65, no. 12, pp. 6728-6738, Del. 2017), which first proposed antenna decoupling surfaces (ADS) to reduce the mutual coupling between antenna elements in large-scale array antennas. An ADS is a thin surface composed of multiple electrically small metal patches placed on top of the array antenna. Part of the diffracted wave from the ADS can be controlled to eliminate unwanted coupling waves. However, the decoupling method described in the article can only decouple the mutual coupling of ports with the same polarization; its decoupling effect on the orthogonal polarization ports of dual-polarized antennas is not significant.

[0004] In 2017, M.-C. Tang et al. published a paper entitled "Mutual Coupling Reduction Using Meta-Structures for Wideband Dual-Polarized and High-Density Patch Array" in IEEE Trans. Antennas Propag. (vol. 65, no. 8, pp. 3986-3998, Aug. 2017). The paper proposed a broadband dual-polarized patch antenna with a decoupling structure consisting of a capacitor-grounded load loop and a Π-type structure, improving the isolation between adjacent radiating elements in the E-plane and H-plane directions by 7.15 dB. However, the decoupling method described in the paper uses a half-wavelength spacing for MIMO antenna elements, which cannot meet the requirements of miniaturization and high isolation for base station antennas in communication systems. Furthermore, the method described in the paper is only applicable to decoupling 0° / 90° dual-polarized antennas.

[0005] In 2022, SJYang et al. published a paper titled "Self-Decoupled Dual-Band Dual-Polarized Aperture-Shared Antenna Array" in IEEE Trans. Antennas Propag. (vol. 70, no. 6, pp. 4890-4895, Jul. 2022). The paper proposed a compact, high-isolation 2×2 array with dual-frequency common aperture. The decoupling method employed is self-decoupling, which involves loading short-circuit patches on the low-frequency radiating patch to suppress scattering in the high-frequency range, and adding cross-shaped strips to the high-frequency antenna to reduce in-band coupling between high-frequency components. However, the proposed method is currently not suitable for the decoupling requirements of large-scale arrays, meaning it cannot meet the needs of practical base station antennas.

[0006] To meet the requirements of 5G communication systems, the isolation requirements for base station MIMO antennas are becoming increasingly stringent, while the spacing between antenna elements is required to be as small as possible, so that more antenna elements can be placed in a limited space. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a decoupling structure for a dual-polarized MIMO antenna, applicable to the decoupling of a compact ±45° dual-polarized MIMO antenna. This invention adds a composite decoupling surface above the metal radiating patch and a U-shaped metal ring between the metal radiating patch and the ground plane. This ensures good matching over a wide frequency band while improving both the isolation of the same-polarization ports and the isolation of the opposite-polarization ports.

[0008] The technical problem addressed by this invention is solved as follows: A compact, high-isolation ±45° dual-polarized MIMO antenna is constructed. First, a ±45° dual-polarized metal radiating patch element is fed through a broadband balun structure. The ground plane distance to the antenna element is λ0 / 4, i.e., 1 / 4 of the air wavelength. The dual-polarized dipole elements are then assembled into a four-element MIMO antenna with an element spacing of 33.8 mm (0.4λ0@3.55GHz). After assembling the four-element MIMO antenna, due to the close spacing between the antenna elements, the isolation between the co-polarized and dissimilar polarized ports is very poor. Therefore, a U-shaped metal square ring P7 is added, primarily to improve the isolation of the dissimilar polarized ports. Composite decoupling structures S1, S2, S3, S4, S5, and P2, P3, P4 are added to primarily improve the isolation of both co-polarized and dissimilar polarized ports and improve matching. S9 can improve the isolation to a certain extent.

[0009] Three decoupling surfaces and metal radiating patches, P4, P3, P2, and P1, are attached to horizontal dielectric substrates S1, S2, S4, and S6, respectively. Two U-shaped feed lines P5 are attached to the back of the feed dielectric substrate S7. To prevent the two crossing feed lines from intersecting, the intersection of one feed line and the other is made into a bridge configuration. The front of the feed dielectric substrate S7 has two rectangular metal plates P6, which must contact both the metal radiating patch P1 and the ground plane M. The back of S8 has a U-shaped metal ring P7. Due to the crossing of the dielectric substrates, the intersection of the two U-shaped metal rings is removed. The surface of S9 is covered with metal, acting as an isolation wall. M is a metal reflector.

[0010] The MIMO antenna is a four-element MINO array with an antenna element spacing of 33.8mm (0.4λ0@3.55GHz). The coaxial inner core is attached to the Γ-shaped feed line for power supply, and the input impedance of the port is 50 ohms.

[0011] The beneficial effects of this invention are:

[0012] (1) The present invention adds 5 layers of composite decoupling surface above the radiating patch. Due to the presence of the 5 layers of composite decoupling surface, the electromagnetic waves pass through the 5 layers of composite decoupling surface and are reflected back in different paths. Therefore, part of the electromagnetic waves emitted by the fed antenna unit can be reflected back to the other 3 unfed antenna units with different phase differences. The reflected electromagnetic waves cancel out the phase of the electromagnetic waves directly coupled to the other three units. Since the polarization direction of the reflected wave is the same as that of the coupled wave, the mutual coupling of the same polarization port can be reduced in a wider frequency band.

[0013] (2) The present invention adds a cross dielectric plate and attaches a U-shaped metal square ring between the antenna radiating unit and the ground. Since the +45° arm of one unit and the -45° arm of the adjacent unit are very close and have opposite polarization directions, the added U-shaped metal square ring structure can reduce the mutual coupling of opposite polarization ports, including the mutual coupling of opposite polarization ports within the unit and the mutual coupling of opposite polarization ports of different units.

[0014] (3) The antenna radiation structure and feeding network described in this invention are simple and the decoupling method is novel. It achieves a significant improvement in isolation when the spacing between +45° dual-polarized antenna elements is small. Attached Figure Description

[0015] Figure 1 A three-dimensional diagram of the antenna;

[0016] Figure 2 A 3D view of dielectric substrate S6 and metal radiating patch P1;

[0017] Figure 3 Here is a structural diagram of the metal radiation patch P1;

[0018] Figure 4 A three-dimensional view of dielectric substrate S4 and first decoupling surface P2;

[0019] Figure 5 This is a structural diagram of the first decoupling surface P2;

[0020] Figure 6 A three-dimensional view of dielectric substrate S2 and second decoupling surface P3;

[0021] Figure 7 This is a three-dimensional view of the dielectric substrate S1 and the third decoupling surface P4.

[0022] Figure 8 The positional relationship of the composite decoupling structure;

[0023] Figure 9 The feed dielectric board S7, the Γ-type feed wire P5, and the rectangular metal sheet P6 are used.

[0024] Figure 10 This is a structural diagram of the P5 type Γ-type feeder cable;

[0025] Figure 11 This is a structural diagram of the rectangular metal sheet P6;

[0026] Figure 12 This is a structural diagram of the U-shaped metal square ring P7;

[0027] Figure 13 The reflection coefficient of the original four-element MIMO antenna;

[0028] Figure 14The original four-element MIMO antenna has its polarization ports mutually coupled.

[0029] Figure 15 The original four-element MIMO antenna has its polarization ports mutually coupled.

[0030] Figure 16 The reflection coefficient of the four-element MIMO antenna after adding the decoupling structure;

[0031] Figure 17 To achieve mutual coupling of the same polarization ports of the four-element antenna after adding the decoupling structure;

[0032] Figure 18 To achieve mutual coupling between the heteropolarized ports of the four-element antenna after adding the decoupling structure;

[0033] Figure 19 The radiation pattern of the four-element MIMO antenna at 0° / 90° when fed from one port at 3.55GHz after adding the decoupling structure;

[0034] Figure 20 The radiation pattern of the four-element MIMO antenna at 0° / 90° when fed by three ports at 3.55GHz after adding the decoupling structure. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0036] Example 1

[0037] This embodiment provides a decoupling structure for a dual-polarized MIMO antenna, such as Figure 1 As shown. A three-dimensional view of dielectric substrate S6 and antenna radiating structure P1 is shown below. Figure 2 As shown; the top view of the antenna radiating structure P1 is as follows. Figure 3 As shown; S5 is a separate dielectric substrate; the three-dimensional view of dielectric substrate S4 and the first decoupling surface P2 is shown below. Figure 4 As shown; the top view of the first decoupling surface P2 is as follows. Figure 5 As shown; S3 is a separate dielectric substrate; the three-dimensional view of dielectric substrate S2 and the second decoupling surface P3 is shown below. Figure 6 As shown; the side length of P3 is 0.8 times that of P2; the three-dimensional view of dielectric substrate S1 and the third decoupling surface P4 is shown below. Figure 7 As shown; the side length of P4 is 0.7 times that of P3; the positional relationship of the composite decoupling structure is as follows. Figure 8 As shown; cross-platform S7 Figure 9 As shown, a Γ-shaped feeder cable P5 is attached to the front surface, and a rectangular patch P6 is attached to the back surface. The Γ-shaped feeder cable P5 is as follows: Figure 10 As shown; the rectangular patch on the back, P6, is as follows. Figure 11 As shown; P7 is a U-shaped metal square ring structure, as shown. Figure 12As shown; the surface of S9 is a metal partition wall.

[0038] The dielectric substrates S1, S2, S4, and S6 are made of Rogers 4003 with a relative permittivity of 3.55, a loss tangent of 0.0027, and a thickness of 1.524 mm. Each dielectric substrate measures 147.6 mm × 50 mm. The dimensions of the first decoupling surface (L12 = 5, L13 = 6, L14 = 4, L15 = 2.8, L16 = 0.82 mm) are as follows: S3 and S5 are made of FR4 with a relative permittivity of 4.4, a loss tangent of 0.02, and a thickness of 2 mm. Each dielectric substrate... The dimensions of all boards are 167.6mm × 80mm; the dimensions of the unit antennas (L1 = 12, L2 = 9, L3 = 5, L4 = 2.5, L5 = 1.5, L6 = 3.5, S1 = 0.5, S2 = 0.5 (unit: mm); the heights of the six horizontal dielectric boards (h2 = 2, h3 = 9, h4 = 10, h5 = 22, h6 = 33 (unit: mm); the material of the cross dielectric board S7 is FR4 with a relative permittivity of 4.4 and a loss tangent of 0. 02. Thickness is 0.8mm, the size of each dielectric board is 16mm×16mm, the dimensions of the feed lines on the front surface of the cross dielectric board S7 (L7=6.9, L8=6.4, L9=7, L10=6, L11=1, W5=0.6, W6=0.6, W7=0.3, W8=0.8, W9=1.2, unit: mm), the dimensions of the rectangular metal plate on the back of S7 (W2=12, W3=3, W4=4.4, h1=16, unit: mm). The cross dielectric substrate S8 is made of FR4 with a relative permittivity of 4.4, a loss tangent of 0.02, and a thickness of 0.8 mm. Each dielectric substrate measures 12 mm × 12 mm. The dimensions of the U-shaped metal square ring P7 are (L17 = 4, L18 = 11, L19 = 1.5, L20 = 11 mm). The dimensions of a single antenna element are 24.9 mm × 24.9 mm (0.295λ0 × 0.295λ0 @ 3.55 GHz). Its operating frequency band is 3.3 GHz - 3.8 GHz (relative bandwidth 17%), the port reflection coefficient is less than -10 dB, and the half-power beamwidth of the XOZ (vertical to the array orientation) and YOZ (parallel to the array orientation) planes is approximately 60°. A four-element MIMO antenna is constructed horizontally, with an element spacing of 33.8 mm (0.4λ0 @ 3.55 GHz). Its operating frequency band is 3.3 GHz - 3.8 GHz (relative bandwidth 17%). Its reflection parameters are as follows: Figure 13 As shown, within the 3.3GHz-3.8GHz range, the reflection coefficient of all ports is below -10dB. Without any isolation structure, the isolation of the heteropolarized ports is only greater than 10dB, such as... Figure 14 As shown. The isolation of the same polarization ports is only greater than 12dB, such as... Figure 15 As shown. After adding a U-shaped metal square ring, a composite decoupling surface, and an isolation wall, the reflection coefficient of the new four-element MIMO antenna is as follows. Figure 16 As shown, the reflection coefficients of all ports are below -12dB between 3.3GHz and 3.8GHz. After adding a U-shaped metal ring, a composite decoupling surface, and an isolation wall, the mutual coupling coefficients of the same-polarization ports and the mutual coupling coefficients of the opposite-polarization ports of the four-element MIMO antenna are as follows: Figure 17 and 18 As shown, the isolation of the same polarization port has increased from 12dB to 21.5dB, an improvement of 9.5dB, and the isolation of the different polarization port has increased from 10dB to 22dB, an improvement of 12dB. Figure 19 To improve the directivity of the four-element MIMO antenna at 3.55 GHz with one-port feeding, after adding a U-shaped metal square ring, composite decoupling surface, and isolation wall, the half-power beamwidth of the XOZ plane (vertical to the array arrangement direction) is 58°, the half-power beamwidth of the YOZ plane (parallel to the array arrangement direction) is 141°, the highest directivity is 6.12 dBi, and the cross-polarization is 19 dB. Figure 20 To improve the directivity of the four-element MIMO antenna at 3.55 GHz with three-port feeding, after adding a U-shaped metal square ring, composite decoupling surface, and isolation wall, the half-power beamwidth of the XOZ plane (vertical to the array arrangement direction) is 48°, the half-power beamwidth of the YOZ plane (parallel to the array arrangement direction) is 123°, the highest directivity is 6.72 dBi, and the cross-polarization is 12 dB.

Claims

1. A decoupling structure for a dual-polarized MIMO antenna, comprising a four-element MIMO antenna composed of antenna elements, characterized in that, The MIMO antenna includes, from top to bottom, dielectric substrates S1, S2, S3, S4, S5, and S6; four sets of cross-shaped feed dielectric substrates; four isolation wall dielectric substrates positioned directly below the feed dielectric substrates; dielectric substrate groups positioned between adjacent isolation wall dielectric substrates; and a reflector at the bottom. The lower surface of dielectric substrate S6 has four metal radiating patches. The upper surface of dielectric substrate S4 has a first decoupling surface. The upper surface of dielectric substrate S2 has a second decoupling surface, which has the same shape as the first decoupling surface but is 0.8 times larger in size. The upper surface of dielectric substrate S1 has a third decoupling surface, which has the same shape as the second decoupling surface but is 0.7 times larger in size. The back sides of the two cross-shaped feed dielectric substrates have... The feeder cable has rectangular metal sheets on its front side; the dielectric substrate assembly includes two pairs of cross-shaped dielectric substrates, each with a U-shaped metal ring on its back; the insulating wall dielectric substrate is covered with metal to form a metal insulating wall; the reflector is a metal reflector, with rectangular metal sheets on the front and back surfaces of the feeder dielectric substrates, respectively. A rectangular metal sheet is used as the feed line, with its upper edge in contact with a metal radiating patch and its lower edge in contact with a reflector, forming a broadband balun feed structure. This structure can be adjusted... The length and width of the feed line, as well as the distance between the two rectangular metal plates, change the antenna matching.

2. The decoupling structure of a dual-polarized MIMO antenna according to claim 1, characterized in that, The first decoupling surface reflects a portion of the incident wave from the antenna element, which cancels out the phase of the coupled wave that is directly coupled to another antenna element. By adjusting the height of the dielectric substrate S4 and the size of the first decoupling surface, the matching and isolation of the same polarization port are changed.

3. The decoupling structure of a dual-polarized MIMO antenna according to claim 1, characterized in that, The incident electromagnetic wave is refracted and partially reflected after passing through the dielectric substrate S5. By adjusting the height of the dielectric substrate S5, the mismatch caused by adding the decoupling surface can be compensated, and the isolation of the low-frequency co-polarized port can be improved.

4. The decoupling structure of a dual-polarized MIMO antenna according to claim 1, characterized in that, The incident electromagnetic wave is refracted and partially reflected after passing through the dielectric substrate S3. By adjusting the height of the dielectric substrate S3, the mismatch caused by adding the decoupling surface can be compensated, and the isolation of the low-frequency co-polarized port can be improved.

5. The decoupling structure of a dual-polarized MIMO antenna according to claim 1, characterized in that, By adjusting the height and size of the second-layer decoupling surface, the matching, isolation of co-polarized ports, and isolation of dissimilar ports can be improved.

6. The decoupling structure of a dual-polarized MIMO antenna according to claim 1, characterized in that, By adjusting the height and size of the third-layer decoupling surface, the matching, isolation of co-polarized ports, and isolation of dissimilar ports can be improved.

7. The decoupling structure of a dual-polarized MIMO antenna according to claim 1, characterized in that, The isolation of the antenna's polarization ports can be changed by adjusting the distance between the dielectric substrate group and the center of the line connecting the two antenna elements, as well as the height of the U-shaped metal square ring.

8. The decoupling structure of a dual-polarized MIMO antenna according to claim 1, characterized in that, The distance between the reflector and the metal radiation patch is less than 16mm.

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