WO2022042817A1

WO2022042817A1 - Mimo antenna array decoupler

Info

Publication number: WO2022042817A1
Application number: PCT/EP2020/073623
Authority: WO
Inventors: Zhao XU; Peng MEI; Shuai ZHANG; Gert Frølund PEDERSEN
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2020-08-24
Filing date: 2020-08-24
Publication date: 2022-03-03

Abstract

An antenna assembly includes a substrate, an antenna element disposed in connection with the substrate and a dielectric stub member disposed over the antenna element. The dielectric stub member has an effective dielectric constant that is in a range of 2.0 to and including 6.0. Mutual couplings in dual-polarized, wideband and large-scale MIMO antenna arrays in the 5G millimeter-wave band are reduced by weakening the space wave couplings. Mutual coupling reduction in a wide band is realized due to the non-resonant properties of the dielectric stub members. The effective dielectric constant of the dielectric stub members determines the decoupling performance.

Description

MIMO ANTENNA ARRAY DECOUPLER

TECHNICAL FIELD

[0001] The aspects of the present disclosure relate generally to mobile communication devices and more particularly to a decoupler for a Multiple Input Multiple Output (MIMO) antenna array.

BACKGROUND

[0002] Massive multiple-input multiple-output (MIMO) is a technology for mobile terminal and base station communications that has significantly enhanced spectrum efficiency and channel capacity. However, mutual coupling between antenna elements is a concern since it is closely related to the performance of the entire MIMO wireless communication system.

[0003] Mutual couplings between antenna elements usually happen in three electromagnetic wave coupling paths, namely, space wave coupling in free space, surface wave coupling in the interface of the substrate and free space, and reflected wave coupling in the substrate. Weakening part or all of the coupling paths are strategies to achieve mutual coupling reductions.

[0004] Decoupling networks can introduce an extra coupling path to cancel the original couplings from part or all of the coupling paths to achieve mutual coupling reduction. However, the decoupling networks would be very complicated and lossy for large-scale and dual-polarized

MIMO antenna array decoupling. [0005] In closely spaced antenna arrays, there is limited space to deploy to electromagnetic bandgap (EBG) structures to block the surface wave coupling between antenna elements. Other approaches such as resonant structures, frequency selective surfaces, metasurface superstates and array-antenna decoupling surfaces (ADS) are generally not competent in dualpolarization, wideband, large-scale antenna arrays in the 5G millimetre-wave band.

[0006] Accordingly, it would be desirable to provide a decoupler for a MIMO antenna array that addresses at least some of the problems identified above.

SUMMARY

[0007] The aspects of the disclosed embodiments are directed to a decoupler to reduce mutual couplings in dual-polarized, wideband and large-scale MIMO antenna arrays in the 5G millimeter-wave band. This and other objectives are addressed by the subject matter of the independent claims. Further advantageous modifications can be found in the dependent claims.

[0008] According to a first aspect the above and further objectives and advantages are obtained by an antenna assembly. In one embodiment, the antenna assembly includes a substrate, an antenna element disposed in connection with the substrate and a dielectric stub member disposed over the antenna element. The dielectric stub member has an effective dielectric constant that is in a range of 2.0 to and including 6.0. The aspects of the disclosed embodiments are directed to reducing mutual couplings in dual-polarized, wideband and large-scale MIMO antenna arrays in the 5G millimeter-wave band by weakening the space wave couplings. Mutual coupling reduction in a wide band is realized due to the non-resonant properties of the dielectric stub members. The effective dielectric constant of the dielectric stub members determines decoupling performance. [0009] In a possible implementation form of the antenna assembly according to the first aspect, the dielectric stub member has a radius (Rl) that is in the range of 0.4X to and including 0.6X, where A is the wavelength of a centre frequency of the antenna element. The dimensions of the dielectric stub member are parameters used to control the decoupling performance of the antenna array. Mutual coupling reductions are realized when one or both of the radius and height of the dielectric stub member are in a range from 0.4X to 0.6X of the centre frequency of the antenna element in free space.

[0010] In a possible implementation form of the antenna assembly the dielectric stub member has a height (Hl) that is in the range of 0.4X to and including 0.6X. The dimensions of the dielectric stub member are parameters used to control the decoupling performance of the antenna array. Mutual coupling reductions are realized when one or both of the radius and height of the dielectric stub member equal the half-wavelength of the centre frequency of the antenna element in free space.

[0011] In a possible implementation form of the antenna assembly, the lateral surface dimension (LI) is greater than a lateral surface dimension of the antenna element. The size or cross-section of the dielectric stub member totally covers the radiating element to result in good decoupling performance.

[0012] In a possible implementation form of the antenna assembly, the dielectric stub member is disposed over the antenna element so that a lateral surface of the dielectric stub member is in contact with a surface of the antenna element. Good decoupling performance is realized when the dielectric stub member fully covers the antenna element. From an integrability viewpoint, the dielectric stub members are preferred to be positioned directly on the top of the antenna elements. [0013] In a possible implementation form of the antenna assembly, the dielectric stub member is disposed over the antenna element to define an air gap between the dielectric stub member and the antenna element. Good decoupling performance is realized when the dielectric stub member fully covers the antenna element. From an integrability viewpoint, the dielectric stub members are preferred to be positioned directly over the top of the antenna elements, even with a gap between the dielectric stub member and the antenna element.

[0014] In a possible implementation form of the antenna assembly, the antenna assembly includes a plurality of antenna elements forming an antenna array and a plurality of dielectric stub members forming a dielectric stub array. The aspects of the disclosed embodiments are directed to reducing mutual couplings in dual-polarized, wideband and large-scale MIMO antenna arrays in the 5G millimeter-wave band by weakening the space wave couplings.

[0015] In a possible implementation form of the antenna assembly a dielectric connecting member connects one dielectric stub member to another dielectric stub member. The dielectric stub members are highly symmetrical and homogenous, and applicable for large-scale antenna arrays with different element spacing in the horizontal and elevation planes.

[0016] In a possible implementation form of the antenna assembly a shape of the dielectric stub member comprises one of a cylindrical shape, a square shape, an elliptical shape, a conical shape or a hexagonal shape. The shape of the dielectric stub member is not restricted to any particular geometric shape. Any shape can be used as long as it covers the surface of the antenna element and both the radius and height around the half-wavelength at the centre frequency can be maintained. [0017] In a possible implementation form of the antenna assembly a shape of the lateral surface of the dielectric member over the antenna element is irregular. The shape of the dielectric stub member is not restricted to any particular geometric shape. Any shape can be used as long as the dielectric stub member covers the surface of the antenna element and both the radius and height around the half-wavelength at the centre frequency can be maintained.

[0018] In a possible implementation form of the antenna assembly the dielectric stub member comprises an air-perforated multilayer printed circuit board. The total cross-sectional area of the perforations cannot exceed approximately 20 percent of the entire cross section of the dielectric stub member. Good performance is realized even when the dielectric stub member is not a solid object.

[0019] In a possible implementation form of the antenna assembly, a radome member is connected to a second lateral surface of the dielectric stub member opposite to the lateral surface. The dielectric stub members can be integrated with a radome.

[0020] In a possible implementation form of the antenna assembly, the antenna assembly comprises a Multiple Input Multiple Output (MIMO) antenna assembly. The aspects of the disclosed embodiments are directed to reducing mutual couplings in dual-polarized, wideband and large-scale MIMO antenna arrays, particularly in the 5G millimeter-wave band.

[0021] In a possible implementation form of the antenna assembly, the antenna assembly comprises one of a slot antenna array, a patch antenna array, a dipole antenna array or a dualpolarized antenna array. The aspects of the disclosed embodiments are directed to reducing mutual couplings in dual-polarized, wideband and large-scale MIMO antenna arrays, particularly in the

5G millimeter-wave band. [0022] In a possible implementation form of the antenna assembly, a shape of one dielectric stub member is different from a shape of another dielectric stub member. The shape of a dielectric stub member can be any shape as long as the dielectric stub member covers the antenna element.

[0023] These and other aspects, implementation forms, and advantages of the exemplary embodiments will become apparent from the embodiments described herein considered in conjunction with the accompanying drawings. It is to be understood, however, that the description and drawings are designed solely for purposes of illustration and not as a definition of the limits of the disclosed invention, for which reference should be made to the appended claims. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In the following detailed portion of the present disclosure, the invention will be explained in more detail with reference to the example embodiments shown in the drawings, in which like numerals indicate like elements and:

[0025] Figure 1 illustrates a schematic block diagram of an exemplary antenna assembly incorporating aspects of the disclosed embodiments;

[0026] Figure 2 illustrates a side cross-sectional view of an exemplary antenna assembly incorporating aspects of the disclosed embodiments; [0027] Figure 3 illustrates a schematic block diagram of an exemplary antenna assembly that can be used with a dielectric stub array incorporating aspects of the disclosed embodiments;

[0028] Figure 4 illustrates a schematic block diagram of an exemplary antenna assembly incorporating aspects of the disclosed embodiments;

[0029] Figure 5 illustrates a side cross-sectional view of an exemplary antenna assembly incorporating aspects of the disclosed embodiments;

[0030] Figure 6 illustrates a side cross-sectional view of an exemplary antenna assembly incorporating aspects of the disclosed embodiments;

[0031] Figure 7 illustrates a side view of an exemplary antenna assembly incorporating aspects of the disclosed embodiments; and

[0032] Figure 8 illustrates an exemplary shape of a dielectric stub member incorporating aspects of the disclosed embodiments.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

[0033] Referring to Figure 1 , a schematic block diagram of an exemplary antenna assembly 100 incorporating aspects of the disclosed embodiments is illustrated. The aspects of the disclosed embodiments are directed to reducing mutual couplings in dual-polarized, wideband and large- scale MIMO antenna arrays by weakening the space wave couplings, particularly in the 5G millimeter-wave band. Mutual coupling reduction in a wide band is realized due to the non- resonant properties of the dielectric stub members 106. The effective dielectric constant of the dielectric stub members 106 determines the decoupling performance. [0034] As is illustrated in Figure 1, in one embodiment, the antenna assembly 100 includes a substrate 102. One or more antenna elements 104, examples of which are shown in Figures 2 and 3, are disposed in connection with the substrate 102. The antenna elements form an antenna array 114, an example of which is shown in Figure 3. One or more dielectric stub members 106 are disposed over respective ones of the antenna elements 104 and form a dielectric stub array 116. The dielectric stub members 106, with specific dimensions and effective dielectric constant, mounted on a surface of the antenna assembly 100, serve as a decoupling component.

[0035] The effects of the mutual coupling reduction of the aspects of the disclosed embodiments are highly related to the effective permittivity of the dielectric stub member 106, and the dimensions of the dielectric stub member 106. The effective permittivity or effective dielectric constant of the dielectric stub member 106 is used to determine the decoupling performance.

[0036] In one embodiment, the effective dielectric constant of the dielectric stub member is in a range of approximately of 2.0 to and including 6.0. Generally, the effective dielectric constant of the dielectric stub member 106 is around 3.0, which is higher than a relative permittivity of free space, which is 1.0. The dielectric stub members 106 of the disclosed embodiments serve as a perturbation to localize the electromagnetic fields in the near field of the antenna elements 104 and weaken the electromagnetic wave coupling in free space from one antenna element 104 to another antenna element 104. This results in low mutual couplings between antenna elements 104 in the antenna assembly 100.

[0037] When the effective dielectric constant of the dielectric stub member 106 reaches or exceeds a certain value, such as 6.0, the dielectric stub member 106 can be excited as a resonant element, where most of the electromagnetic fields would be confined in the dielectric stub members 106 to excite a specific mode. In such a situation, the dielectric stub member 106 cannot be considered a decoupling member, but rather a radiating antenna element. This would lead to high mutual couplings between antenna elements 104.

[0038] As is illustrated in Figure 1, a dielectric member 106 will have lateral dimensions of LI and a radius of Rl. Figure 2 illustrates the height Hl of an exemplary dielectric member 106. The dimensions of the dielectric stub member 106 are used to control the decoupling performance. In one embodiment, the radius Rl and height Hl will be approximately a half- wavelength of the centre frequency of the antenna element 104, in free space. Preferably, the dimensions of the radius Rl and height Hl are in the range of 0.4X to and including 0.6X.

[0039] Referring to Figure 4, in one embodiment, the lateral surface dimension LI of the dielectric stub member 106 is greater than a lateral surface dimension of the surface 124 of the respective antenna element 104. According to the aspects of the disclosed embodiments, a size or cross-section of the dielectric stub member 106, referred to herein as the lateral surface dimension LI, is configured to totally cover the surface or surface area 124 of the antenna element 104. This results in good decoupling performance. The center-to-center spacing between dielectric stub members 106 should be the same as the center-to-center spacing between antenna elements 104.

[0040] In one embodiment, as is shown in Figures 1 and 2, a shape of a dielectric stub member 106 is cylindrical. However, the aspects of the disclosed embodiments are not so limited. In alternate embodiments, the shape of dielectric stub member 106 can be any suitable geometric shape other than including cylindrical. For example, other shapes of the dielectric stub member 106, can include, but are not limited to square, elliptical, conical and hexagonal. The lateral surface area LI of the particular shape must cover the surface area 124 of the antenna element 104. [0041] In the example of Figure 4, the dielectric stub member 106 has an irregular shape 402. The surface area dimensions LI of the irregular shape 402 encompass the surface area 124 of the antenna element 104. In one embodiment, referring to Figure 8, the dielectric stub member 106 can be implemented with air-perforated multi-layer printed circuit boards (PCB). In this example, the total cross-sectional area of the perforations 802 cannot exceed approximately 20 percent of the entire cross-sectional area of the dielectric stub member 806. The dielectric stub members 106 can be printed using 3-D printing technology and then fixed within the antenna array 114.

[0042] The shapes of the individual dielectric stub members 106 do not all need to be the same. For example, different ones of the dielectric stub members that form the dielectric stub array 116 can have different shapes, where the shape cover the surface area 124 of the respective antenna element 104.

[0043] In one embodiment, the dielectric stub members 106 are solid structures that do not include magnetic material. A material of the dielectric stub member 106 can include, but is not limited to, Acrylonitrile Butadiene Styrene (ABS) or Polylactic Acid (PLA), for example.

[0044] Referring to Figure 2, in one embodiment, the dielectric stub member 106 can include a hollowed portion or cavity 118. The hollowed portion or cavity 118 is configured to accommodate the respective antenna element 104, when the dielectric stub member 106 is disposed over and around the antenna element 104. In one embodiment, the hollowed portion or cavity 118 can be larger than the surface area of the respective antenna element 104. As will be described further below, the dielectric stub member 106 can be in contact with the antenna element 104 or there can be a gap between the dielectric stub member 106 and the respective surface, or surfaces of the antenna element 104.

[0045] When the dielectric stub members 106 includes a hollowed portion or cavity 118, the total cross-sectional area of the hollowed portion 118 cannot exceed approximately 20 percent of the entire cross-sectional of the dielectric stub member 106. If the dimensions of the hollowed portion 118 are too large, the dielectric stub members 106 will not offer good decoupling performance.

[0046] In the example of Figure 1, dielectric connecting members 108 are used to connect one dielectric stub member 106 to another dielectric stub member 106 and form the dielectric stub array 116. In the example of Figure 1, the position of the dielectric connecting members 108 is at or near a bottom portion of the respective dielectric stub members 106, closer to the antenna element array 114. In alternate embodiments, the dielectric connecting members 108 can be located at any suitable position along the respective dielectric stub members 106 to make the required connection. The additions of the dielectric connecting members 108 should not influence the decoupling performance of the dielectric stub members 106.

[0047] In one embodiment, the dielectric stub member array 116 can be configured without the connecting dielectric members 108. The dielectric stub members 106 of the dielectric stub array 116 can be connected to the antenna element array 114 in any suitable manner. The addition of the dielectric connecting members 108 is configured so that the decoupling performance of the dielectric stub members 106 is not degraded.

[0048] In one embodiment, the height of a dielectric connecting member 108 should be less than 0.25k and a width of a dielectric connecting member 108 should be less than 0.2k. The additions of the dielectric connecting members 108 should not influence the decoupling performance of the dielectric stub members 106.

[0049] In the example of Figure 1, the connections of the dielectric stub members 106 and dielectric connecting members 108 form a generally cross-shaped pattern. In alternate embodiments, the connection of the dielectric stub members 106 and dielectric connecting members 108 can form any suitable pattern, other than including a cross-shaped pattern.

[0050] The dielectric stub members 106 of the dielectric stub array 116 are disposed over respective ones of the antenna elements 104 of the antenna array 114. In one embodiment, dielectric stub member 106 is in contact with, or touching a surface of the respective antenna element 104. In another embodiment, as illustrated in Figure 6, the dielectric stub member 106 is disposed over the respective antenna element 104 such that there is a gap 602 between the dielectric stub member 106 and the antenna element 104. Good decoupling performance is realized when the dielectric stub member 106 fully covers the antenna element 104. From an integrability viewpoint, the dielectric stub members 106 are preferred to be positioned directly on the top of the respective antenna elements 104.

[0051] In the example of Figure 5, in one embodiment, the dielectric stub member 106 is disposed in contact with a radiating surface of the antenna element 104. As shown in Figure 5, a surface 126 of the dielectric stub member 106 is in contact with the surface 124 of the antenna element 104. In this example, there is no air gap between the surface 126 of the dielectric stub member 106.

[0052] Figure 6 illustrates an example of an air gap 602 between a surface 126 of the dielectric stub member 106 and the respective surface 124 of the antenna element 104. In one embodiment, the maximum air gap cannot exceed a gap that is in the range of 0.06X to and including 0.1X. In alternate embodiments, the size of the gap 602 is any suitable dimension that does not degrade the decoupling performance of the dielectric stub members 106. The lateral dimension LI of the surface 126 of dielectric stub member 106 needs to cover or encompass the lateral dimension of the surface 124 of the respective antenna element 104.

[0053] Referring to Figures 1 and 3, the antenna assembly 100 includes a 4 x 4 dual polarized patch antenna array 114 and a corresponding dielectric stub array 116. Although the example of Figure 1 is directed to a 4 x 4 antenna assembly, the aspects of the disclosed embodiments are not so limited. In alternate embodiment, the antenna assembly 100 and be any suitably sized N x N antenna assembly, such as 4x4, 8x8, 16x16, 32x32. . .N x N, for example.

[0054] To accommodate the requirements of practical massive MIMO base station applications in the 5G millimetre- wave frequency band, the 4 x 4 antenna array 114 of Figure 3 is +/- 45-degree polarization, and the spacing of antenna elements 104 in the azimuth plane is smaller than the spacing in the elevation plane. The decoupling frequency demonstrated in this example is from 26.5 to 29.5 GHz, where the mutual couplings between all ports are required to be below -25 dB.

[0055] The dielectric stub members 106 of the disclosed embodiments are symmetrical and homogenous. The electromagnetic energy in one polarization is not converted to the orthogonal polarization to increase the cross -polarized mutual coupling of the antenna element 104. In this manner, the aspects of the disclosed embodiments are suitable of dual-polarized applications. [0056] The dielectric stub array 116 of the disclosed embodiments has been demonstrated to reduce the mutual coupling of a 4 x 4 dual-polarized patch antenna array below -25 dB from 26.5 to 29.5 GHz. This can significantly improve the performance of the corresponding MIMO base station in the 5G millimetre-wave band, (the improvement on PAs). The dielectric stub array 116 can also be implemented on much larger scale N x N dual-polarized antenna arrays. The aspects of the disclosed embodiments can also be implemented in large-scale antenna arrays with different element spacing in the horizontal and elevation planes.

[0057] Referring to Figure 7, the antenna assembly 100 of the disclosed embodiments can be implemented with a radome 702. In the example of Figure 7, a surface 136 of the dielectric stub member 106 opposite the surface 126, is shown in connection with the radome 702. In this manner, the radome 702 can be integrated with the dielectric stub members 106. In this example, the dielectric stub members 106 forming the dielectric stub array 116 can be mounted directly on a large-scale antenna array 114 with or without an air gap.

[0058] The dielectric stub members and dielectric stub array reduce mutual couplings of dual-polarized, wideband, and large-scale MIMO antenna arrays in the 5G millimetre-wave band. The dielectric stub members with specific dimensions and effective dielectric constant, are mounted on or over the surface of an antenna array, serving as a decoupling component. The dielectric stub members of the disclosed embodiments serve as perturbations to localize the electromagnetic fields in the near field of antenna elements to weaken the electromagnetic wave coupling in free space from one antenna element to others, resulting in low mutual couplings between antenna elements. Due to the non-resonant properties of the dielectric stub members, the aspects of the disclosed embodiments can achieve mutual coupling reduction in a wide band, including low frequencies and high frequencies.

Claims

1. An antenna assembly (100), comprising: a substrate (102); an antenna element (104) disposed in connection with the substrate (102); and a dielectric stub member (106) disposed over the antenna element (104), wherein the dielectric stub member (106) has an effective dielectric constant that is in a range of 2.0 to and including 6.0.

2. The antenna as sembly ( 100) according to claim 1 , wherein the dielectric stub member (106) has a radius (Rl) that is in the range of 0.4X to and including 0.6X, where X is the wavelength of a centre frequency of the antenna element.

3. The antenna assembly (100) according to any one of the preceding claims, wherein the dielectric stub member (106) has a height (Hl) that is that is in the range of 0.4X to and including 0.6

4. The antenna assembly (100) according to any one of the preceding claims, wherein a lateral surface dimension (LI) of the dielectric stub member (106) is greater than a lateral surface dimension of the antenna element (104).

5. The antenna assembly (100) according to any one of the preceding claims wherein the dielectric stub member (106) is disposed over the antenna element (104) so that a lateral surface (126) of the dielectric stub member (106) is in contact with a surface (124) of the antenna element (104).

6. The antenna assembly (100) according to any one of claims 1 to 4, wherein the dielectric stub member (106) is disposed over the antenna element (104) to define an air gap (602) between the dielectric stub member (106) and the antenna element (104).

7. The antenna assembly (100) according to any one of the preceding claims, wherein the antenna assembly (100) comprises a plurality (114) of antenna elements (104) forming an N x N antenna array (114) and a plurality (116) of dielectric stub members (106) forming an N x N dielectric stub array (116).

8. The antenna assembly (100) according to any one of the preceding claims further comprising a dielectric connecting member (108) connecting one dielectric stub member (106) to another dielectric stub member (106).

9. The antenna assembly (100) according to any one of the preceding claims, wherein a shape of the dielectric stub member (106) comprises one of a cylindrical shape, a square shape, an elliptical shape, a conical shape or a hexagonal shape.

10. The antenna assembly (100) according to any one of the preceding claims, wherein a shape of the lateral surface (126) of the dielectric stub member (106) is irregular.

11. The antenna assembly (100) according to any one of the preceding claims, wherein the dielectric stub member (106) comprises an air-perforated multilayer printed circuit board (PCB).

12. The antenna assembly (100) according to any one of the preceding claims, further comprising a radome member (702) connected to a second lateral surface (136) of the dielectric stub member (106) opposite to the lateral surface (126).

13. The antenna assembly (100) according to any one of the preceding claims, wherein the antenna assembly (100) comprises a Multiple Input Multiple Output (MIMO) antenna array.

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14. The antenna assembly (100) according to any one of the preceding claims, wherein the antenna assembly (100) comprises one of a slot antenna array, a patch antenna array, a dipole antenna array or a dual-polarized antenna array.

15. The antenna assembly (100) according to any one of the preceding claims wherein a shape of one dielectric stub member (106) is different from a shape of another dielectric stub member (106).

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