MIMO Antennas for Smart Grid Wireless Sensors

Abstract

The present invention discloses a MIMO antenna applied to a smart grid wireless sensor, comprising: four symmetrical IFA three-band antenna elements, a dielectric substrate and a floor defect structure; the dielectric substrate comprises a bottom dielectric substrate simulating a wireless sensor mainboard and a vertical dielectric substrate simulating a wireless sensor frame; a metal grounding plate is printed on the lower surface of the bottom dielectric substrate; the floor defect structure is etched on the metal grounding plate; four symmetrical IFA three-band antenna elements are printed on the vertical dielectric substrate, the feeder of the IFA three-band antenna element is printed on the bottom dielectric substrate, the IFA three-band antenna element adopts coupled feeding, and two horizontal radiation branches adopt a multi-branch bending structure, which reduces the antenna profile while realizing multi-band operation. Compared with the existing antennas applied to smart grid wireless sensors, the present invention can realize large-scale MIMO communication and reduce the antenna unit structure.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technology, and in particular to a MIMO antenna applied to a smart grid wireless sensor. Background Art

[0002] This section is intended to provide a background or context to the embodiments of the invention recited in the claims. No admission is made that the description herein is prior art by inclusion in this section.

[0003] MIMO antenna units are required to have high isolation to achieve high communication capacity and spectrum utilization. With the development of miniaturization, multi-band, and multi-antenna technologies for smart grid wireless sensors, existing MIMO antennas for smart grid wireless sensors are often configured in a small space. The close distance between antenna units will produce coupling effects, which will greatly affect the normal operation of MIMO antennas. Summary of the invention

[0004] The embodiment of the present invention provides a MIMO antenna applied to a smart grid wireless sensor, comprising: four symmetrical IFA tri-band antenna elements, a dielectric substrate and a floor defect structure; the dielectric substrate comprises a bottom dielectric substrate simulating a wireless sensor mainboard and a vertical dielectric substrate simulating a wireless sensor frame; a metal grounding plate is printed on the lower surface of the bottom dielectric substrate; and the floor defect structure is etched on the metal grounding plate;

[0005] Four symmetrical IFA tri-band antenna elements are printed on a vertical dielectric substrate, a feed line of the IFA tri-band antenna element is printed on a bottom dielectric substrate, and the IFA tri-band antenna element adopts coupled feeding.

[0006] The present invention designs a self-decoupling antenna element: four symmetrical IFA tri-band antenna elements, which are both radiating elements and decoupling elements. The antenna unit reduces the distance and fits tightly on both sides of the dielectric substrate, which can achieve good radiation performance and isolation performance at the same time, realize large-scale MIMO communication, and reduce the antenna unit structure at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0008] Figure 1 A schematic diagram of the structure of a MIMO antenna used in a smart grid wireless sensor according to an embodiment of the present invention;

[0009] Figure 2 Schematic diagram of the structure of a triple-band antenna element in an embodiment of the present invention;

[0010] Figure 3 is the simulation S of the triple-band antenna in the embodiment of the present invention 11 Schematic diagram;

[0011] Figure 4 Schematic diagram of current distribution of the working branches of the three-band antenna in an embodiment of the present invention, where (a) 2.4 GHz; (b) 3.5 GHz; (c) 5.0 GHz;

[0012] Figure 5 Schematic diagram of the dimensions of the T-slot in an embodiment of the present invention;

[0013] Figure 6 A schematic diagram of the ground plane current distribution before and after adding a gap in an embodiment of the present invention;

[0014] Figure 7 This is a comparison diagram of return loss under different GL lengths in an embodiment of the present invention;

[0015] Figure 8 This is a comparison diagram of isolation under different GL lengths in an embodiment of the present invention;

[0016] Fig. 9 A comparison diagram of return loss before and after etching the T-groove in an embodiment of the present invention;

[0017] Fig.10 This is a comparison diagram of the isolation before and after etching the T-groove in an embodiment of the present invention;

[0018] Fig.11 is the directional diagram of the MIMO antenna in the E plane (XOZ plane) in the embodiment of the present invention;

[0019] Fig.12 : is the directional diagram of the MIMO antenna in the H plane (YOZ plane) in the embodiment of the present invention. DETAILED DESCRIPTION

[0020] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0021] Existing MIMO antennas are often configured in a small space, which easily produces the above-mentioned two coupling effects. In order to achieve large-scale MIMO communication, the antenna unit is required to have a high degree of isolation. The present invention aims to comprehensively realize the miniaturization and high isolation design of the MIMO antenna, and at the same time, a sufficient number of antenna elements should be arranged as much as possible in the smart grid wireless sensor. Therefore, the present invention loads a defective ground structure between the MIMO antenna units integrated inside the wireless sensor for smart grid applications, so that the surface waves with the same amplitude and opposite phase introduced by the antenna units on both sides of the defective ground can cancel each other, thereby achieving a high isolation design.

[0022] The present invention proposes a MIMO antenna for smart grid wireless sensors, such as Figure 1 As shown, the structure includes: four symmetrical IFA (Inverted-F Antenna, with two arms of grounding and feeding, and a structure shaped like an inverted F) three-band antenna elements, a dielectric substrate and a floor defect structure. Among them, the dielectric substrate includes a bottom dielectric substrate simulating a wireless sensor mainboard and a vertical dielectric substrate simulating a wireless sensor frame, and a metal grounding plate is printed on the lower surface of the bottom dielectric substrate; the floor defect structure is etched on the metal grounding plate. Four symmetrical IFA three-band antenna elements are printed on the vertical dielectric substrate, and the feed line of the IFA three-band antenna element is printed on the bottom dielectric substrate. The IFA three-band antenna element adopts coupled feeding.

[0023] Specifically, Figure 1 As shown in the figure, the dielectric substrate uses FR4 material and has a size of 146mm×71.5mm×5mm, simulating the metal frame of the wireless sensor (size 146.7mm×71.5mm×7.4mm). The four antenna elements are printed equidistantly on the vertical dielectric substrate, where equidistant means that the distance between the two antenna elements on one side is equal to the distance between the two antenna elements on the other side (i.e. D2). Equidistant also means that the distance between each antenna element and the non-side is equal (i.e. D1). There is only a 0.8mm gap between the end of the radiating branch (bottom dielectric substrate) and the ground (Ground), and the length of the ground branch is only 0.2mm. The symmetrically arranged MIMO system is very compact and has a small profile. The dielectric substrate also leaves a lot of clear space for adding antennas working in the 2G / 3G / 4G / GPS bands. The distance D2 between adjacent antenna elements on the same side is 23.2mm, which is about λ / 4 at 3.5GHz. Generally speaking, when the distance between antenna elements is less than λ / 2, the floor current and space surface waves will obviously cause coupling in the system, reducing the isolation. Therefore, placing a suitable decoupling structure is the design direction of the MIMO antenna for miniaturized wireless terminals, and this method will be applied later.

[0024] Specifically, the antenna element proposed in the present invention is derived from the IFA antenna and has the same structure, such as Figure 2 As shown. Different from the traditional IFA antenna, the IFA tri-band antenna designed in the present invention adopts coupling feeding, and the horizontally placed coupling branch is directly connected to the feed line; above the horizontally placed coupling branch are two horizontally placed radiation branches on the left and right; the left end of the left radiation branch is open-circuited, the middle is connected to the metal ground plate through a bent microstrip line, and the right end is the coupling feeding end; the left end of the right radiation branch is the coupling feeding point end, and the right end is connected to the metal ground plate through a bent microstrip line.

[0025] Specifically, Figure 2 As shown in the figure, the left radiating branch is grounded through the middle point E, the left end is an open circuit end, and the right end is a feeding end. Different electrical lengths (L data in the figure) can produce different resonant frequencies. The right radiating branch is grounded through point J and adopts a multi-branch bending structure to achieve miniaturization and reduce the profile.

[0026] Table 1 shows the specific dimensions.

[0027] Table 1 Specific dimensions of IFA tri-band antenna elements (unit: mm)

[0028]

[0029]

[0030] The ABDE, GHIJ, and BCF branches of the antenna excite three resonant frequencies of 2.4 GHz, 3.5 GHz, and 5.0 GHz, respectively. Figure 3 As shown in the figure, the operating frequency band covers Wi-Fi 6 (IEEE 802.11.ax) and 5G (Sub-6), achieving multi-band characteristics based on compact size.

[0031] In order to deeply understand the proposed antenna model, the working mechanism of the coupled feeding and floor defect structure is analyzed based on the surface current distribution and S parameters of the radiation patch.

[0032] (1) Coupled feed

[0033] In order to better explain the working mode of each branch, Figure 4 (a) Figure 4 (b) Figure 4(c) shows the current distribution of the antenna at 2.4GHz, 3.5GHz and 5.0GHz. At 2.4GHz, the ABDE part, as the main radiation patch, produces the first resonant frequency with a length of 23.1mm, which is approximately 0.18λ at 2.4GHz. According to the transmission line theory, the ABDE part can be equivalent to a parallel circuit with a short-circuited terminal. At 3.5GHz, another radiation patch, GHIJ, produces the second resonant frequency with a length of 19.1mm, which is approximately 0.20λ at ​​3.5GHz. It is also equivalent to a parallel circuit with a short-circuited terminal. At 5.0GHz, BCF, as the remaining part of the main radiation patch, and the coupled feed source (the middle patch structure) jointly produce the third resonant frequency with a length of 9.9mm, which is approximately 0.17λ at 5GHz. Normally, the resonant mode of an IFA antenna is λ / 4. However, under the excitation of a coupled feed source, the radiating patch is not directly connected to the feeding port, which can excite a resonant mode with a smaller electrical length, thus achieving the purpose of miniaturization of the MIMO antenna.

[0034] The following formulas (1) to (4) can determine the electrical length of the IFA antenna operating at three frequency points, where L ABDE , L GHIJ and L BCF They represent the approximate electrical lengths at 2.4 GHz, 3.5 GHz, and 5.0 GHz, respectively. c is the speed of light in free space, L is the electrical length of the antenna, and ε r is the relative dielectric constant.

[0035]

[0036] L ABDE =L AB +W2+L5+H s (2)

[0037] L GHIJ =L7+2L 10 +H s (3)

[0038] L BCF =L BC +L2+W2+L4 (4)

[0039] (2) T-slot (floor defect structure)

[0040] The floor defect structure is to eliminate the original coupling of the floor by etching a slot on the floor. The working principle is that the groove will change the distribution of the floor current, thereby playing a band blocking role on the coupled current. It can also be understood that the slot is equivalent to the bending and meandering technology of the antenna. Without changing the total area of ​​the floor and taking up extra space, the equivalent current path is extended, and the high floor impedance also limits the transmission induction current.

[0041] For the antenna inside the smart grid wireless sensor, the ground plane is part of the system radiator. The ground plane size of this model is 146mm×71.1mm. The size of the ground plane will be closely related to the impedance matching and isolation of the antenna, because the floor current and near field will cause mutual coupling between the two antenna elements. In order to achieve high isolation of the system, T-slots are etched between adjacent antennas during the design process as floor defect structures. Its structure and system model are shown in Figure 2. Figure 5 , Figure 1 shown.

[0042] Figure 6 The current distribution comparison before and after the MIMO antenna is added with a T-slot (i.e., the left figure shows a structure without a floor defect, and the right figure shows a structure with a floor defect) is shown, explaining the working principle of the floor defect structure in the system. Before the T-slot is added in the left figure, when the antenna's feed port 1 (port 1) is excited, a large amount of coupling current is generated in the floor near antenna element 1, flowing to other ports. This is the original coupling current of the MIMO system. After the T-slots (Slot 1 and Slot 2) are added, the floor currents between adjacent antennas converge around the antenna gap. This is because the T-slots create an additional current path for the coupling current, thereby effectively suppressing the transmission of the floor current between the elements and offsetting most of the coupling current from the excitation port to the non-excitation port. It is an effective decoupling structure.

[0043] The following is a parameter analysis and antenna performance description.

[0044] Figure 7 and Figure 8 The influence of the change of the length GL of the T-slot on the impedance matching and isolation of the antenna is given respectively. From the simulation results, it can be seen that with the increase of GL, mainly in the low frequency band, the impedance matching of the antenna gradually improves, and the decoupling performance also improves, but the decoupling frequency band also moves to the left. After comprehensive consideration, GL is selected as 18.8mm.

[0045] Fig. 9 and Fig.10The comparison of MIMO antenna return loss and isolation before and after adding T-slots is shown. The simulation results show that in the low, medium and high frequency bands, |S11| is improved by 8dB, 2.5dB and 11dB respectively (|S11| represents the return loss of the antenna input), while |S21| is improved by at least 26dB, 3dB and 5dB respectively (|S21| represents the isolation between antennas on the same side plane, and |S23| represents the isolation of the opposite side antenna). In the working frequency band, the reflection coefficient of each antenna element is less than -10dB, and the system isolation is greater than 20dB, and the best can be close to 50dB. At the same time, the antenna distance is only λ / 4 (at 3.5GHz), which has higher performance among the same type of MIMO antennas.

[0046] At the same time, in the antenna design of smart grid wireless sensors, the radiation pattern is also an indicator that deserves special attention. Fig.11 and Fig.12 The directional patterns of the MIMO antenna in the E plane (XOZ plane) and H plane (YOZ plane) at three center frequencies are given, and the ordinate is the radiation gain. From the radiation pattern, the antenna has no electric field zero points on both planes and has omnidirectional radiation performance, proving that the MIMO antenna can receive signals from all directions of wireless communication.

[0047] In summary, the present invention proposes a MIMO antenna for use in smart grid wireless sensors, which can achieve the following beneficial effects:

[0048] (1) The bending meander technology is used to adjust and deform the structure of the IFA antenna, which is suitable for the metal frame of the conventional wireless sensor terminal device, thereby achieving the miniaturization advantage of the present invention.

[0049] (2) The present invention uses a coupled feeding structure, which is different from a contact feeding structure and can further reduce the size of the antenna while having good impedance matching.

[0050] (3) The present invention achieves the advantage of spatial omnidirectional radiation through symmetrical layout and reasonable antenna distance configuration, and is suitable for the working application of wireless sensors for smart grids.

[0051] (4) The present invention etches a floor defect structure on the MIMO antenna model, reduces the floor coupling current, achieves the decoupling effect, and has the advantage of high system isolation.

[0052] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0053] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0054] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0055] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0056] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A MIMO antenna for a smart grid wireless sensor, characterized in that: include: Four symmetrical IFA tri-band antenna elements, dielectric substrate and floor defect structure; The dielectric substrate includes a bottom dielectric substrate simulating a wireless sensor mainboard and a vertical dielectric substrate of a wireless sensor frame; A metal ground plate is printed on the lower surface of the bottom dielectric substrate; The floor defect structure is etched into the metal ground plane; Four symmetrical IFA tri-band antenna elements are printed on a vertical dielectric substrate, the feed lines of the IFA tri-band antenna elements are printed on the bottom dielectric substrate, and the IFA tri-band antenna elements use coupled feeding; The defective structure of the floor is a T-slot; The transverse groove spacing of the T-slot is 18.8 mm; Four symmetrical IFA tri-band antenna elements are printed equidistantly on a vertical dielectric substrate; Two IFA tri-band antenna elements are printed on a vertical dielectric substrate on one side, and two IFA tri-band antenna elements are printed on a vertical dielectric substrate on the other side; Equidistant means that the distance between two antenna elements on one side is equidistant from the distance between two antenna elements on the other side, and each antenna element is equidistant from the side not on which it is located; The IFA triple-band antenna adopts coupled feeding, and the horizontally placed coupling branch is directly connected to the feed line; above the horizontally placed coupling branch are two horizontal radiating branches placed on the left and right; the left end of the left radiating branch is open, and the middle is connected to the metal ground plate through a bent microstrip line, and the right end is the coupled feeding end; the left end of the right radiating branch is the coupled feeding point end, and the right end is connected to the metal ground plate by a bent microstrip line; the open part of the left end of the left radiating branch is an inverted L shape.

2. The MIMO antenna for smart grid wireless sensors according to claim 1, characterized in that: The distance between the two IFA tri-band antenna elements on the same side is 23.2mm.

3. The MIMO antenna for smart grid wireless sensors according to claim 1, characterized in that: The floor defect structure is replaced by an H-shaped groove, a C-shaped groove or a U-shaped groove.

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