RFID reader array antenna

Abstract

The present application proposes an RFID reader array antenna, which includes a reflector placed on the bottom layer, a feed network placed on the middle layer, and multiple antenna units placed on the upper layer, wherein the multiple antenna units are respectively connected to the feed network, and the multiple antenna units and the feed network share the reflector. The present application loads an artificial transmission line structure on the antenna unit, and achieves miniaturization by changing the structure of the curved microstrip line and the interdigitated microstrip line; the antenna unit achieves circular polarization characteristics through a power division phase shift feed network; the antenna has miniaturization, low profile, long recognition distance, and acceptable recognition area.

Description

Technical Field

[0001] The present application relates to the field of wireless communication technology, and in particular to an RFID reader array antenna. Background Art

[0002] RFID (Radio Frequency Identification) technology is a contactless automatic identification technology. Its basic principle is to use the transmission characteristics of radio frequency signals and spatial coupling (inductive or electromagnetic coupling) to achieve automatic identification of the identified object. In recent years, scholars at home and abroad have devoted themselves to the research of near-field RFID antennas. The challenge of designing near-field reader antennas is to ensure that the magnetic field is uniform within the reading area and decays rapidly outside the reading area. Unlike far-field RFID antennas, near-field RFID reader antennas need to have low gain characteristics to avoid misreading tags outside the reading area and achieve a controllable reading range. According to the coupling mechanism, RFID systems can be divided into two types: capacitive coupling and magnetic coupling. Magnetic coupling systems can adapt to harsh environments, but there is a problem of short reading distance. Near-field reader antennas have the problems of low far-field gain and uneven electric field distribution outside the identification area.

[0003] In order to achieve a longer reading range, far-field reader antennas have been proposed. Modern wireless communication systems use a variety of technologies to continuously develop the far-field radiation direction of antenna arrays. Far-field reader antennas have the advantage of high gain. However, due to the narrow beam width of far-field antennas, tag misreading often occurs in far-field antennas.

[0004] For metal rack applications, current near-field RFID antennas and far-field RFID antennas are not suitable for use in metal rack environments because the read area of ​​metal racks is large and the read distance covering the rack is moderate. It is highly desirable to have a low-profile, miniaturized, low-misread rate RFID reader antenna. Summary of the invention

[0005] The technical problem to be solved by the present application is to design a miniaturized RFID reader array antenna with a large reading area and an acceptable reading distance for metal shelf applications.

[0006] The present application provides an RFID reader array antenna, including a reflector placed on the bottom layer, a feed network placed on the middle layer, and a plurality of antenna units placed on the upper layer arranged at preset angles, wherein the plurality of antenna units are respectively connected to the feed network, and the plurality of antenna units and the feed network share the reflector. Arrangement at a preset angle can be understood as taking one of the antenna units as a reference, and the remaining antenna units are rotated clockwise or counterclockwise in sequence to obtain a certain angle (such as 45°, 60°, 90°). With such a design, the antenna has miniaturization, low profile, long recognition distance, and acceptable recognition area.

[0007] Preferably, the RFID reader array antenna includes: four antenna units with the same structure, the four antenna units are configured to be obtained by rotating one of the antenna units counterclockwise or anti-clockwise by 90 degrees, 180 degrees and 270 degrees respectively, with one of the antenna units as a reference, and the four antenna units are respectively connected to the feeding network.

[0008] Preferably, the antenna unit further comprises: an artificial transmission line and a plurality of T-shaped branches, wherein the T-shaped branches are used to expand the bandwidth of the antenna, and the artificial transmission line comprises:

[0009] A curved microstrip line, an interdigitated microstrip line and an open microstrip line connected in sequence in a bow shape or multiple U shapes.

[0010] Preferably, the feeding network is a power division phase shift feeding network, and the surface of the power division phase shift feeding network is covered with a metal FR4 plate.

[0011] Preferably, the surface of the antenna unit is covered with a metal FR4 plate.

[0012] Preferably, a groove for increasing a current path is formed on the upper surface of the antenna unit.

[0013] Preferably, at least one supporting device for supporting the antenna unit is connected between the antenna unit and the reflector.

[0014] Preferably, at least one supporting device for supporting the antenna unit is connected between the antenna unit and the feeding network.

[0015] Preferably, the feeding network comprises four terminals, which are respectively connected to four terminals of four antenna units.

[0016] Preferably, the ratio of the length l4 of the curved microstrip line 11 in the width direction of the antenna unit to the width w1 of the open microstrip line is between 1.2 and 1.4. Such an antenna has a long recognition distance and an acceptable recognition area.

[0017] Compared with the solutions in the prior art, the advantages of the present application are as follows: the present application proposes an RFID reader array antenna, on which an artificial transmission line structure is loaded, and its miniaturization is achieved through a serpentine, bow-shaped or multiple U-shaped and sequentially connected curved microstrip line structure and an interdigitated structure microstrip line; through a power division phase-shifting feeding network, the four antenna units achieve circular polarization characteristics with the same amplitude and a phase difference of 90°; the antenna has miniaturization, low profile, long recognition distance, and acceptable recognition area. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present application is further described below in conjunction with the accompanying drawings and embodiments:

[0019] Figure 1A front view of an antenna unit of an RFID reader array antenna of the present application;

[0020] Figure 2 A top view of an antenna unit of an RFID reader array antenna of the present application;

[0021] Figure 3 This is a schematic diagram of the structure of the feeding network of the RFID reader array antenna of this application;

[0022] Figure 4 A top view of the RFID reader array antenna of this application;

[0023] Figure 5 A side view of the RFID reader array antenna of the present application;

[0024] Figure 6 The simulation and measured diagram of the RFID reader array antenna for this application;

[0025] Figure 7 The simulation and measured diagrams of the yz-plane and xz-plane of the RFID reader array antenna;

[0026] Figure 8 The axial ratio simulation and measured diagram of the RFID reader array antenna;

[0027] Fig. 9 The recognition rate of the RFID reader array antenna for this application. DETAILED DESCRIPTION

[0028] The above scheme is further described below in conjunction with specific examples. It should be understood that these examples are used to illustrate the present application and are not limited to the scope of the present application. The implementation conditions adopted in the examples can be further adjusted as the conditions of the specific manufacturer, and the unspecified implementation conditions are usually the conditions in conventional experiments.

[0029] The present application provides an RFID reader array antenna, including three layers, namely, an upper layer, a middle layer and a bottom layer from top to bottom. A reflector is placed on the bottom layer, a feed network is placed on the middle layer, and a plurality of antenna units are placed on the upper layer. The plurality of antenna units are respectively connected to the feed network, and the plurality of antenna units and the feed network share the reflector. Preferably, four antenna units are used, one of which is used as a reference during configuration, and then the other three antenna units are rotated counterclockwise by 90 degrees, 180 degrees and 270 degrees respectively.

[0030] Please refer to Figure 1-Figure 5 As shown, the upper layer of the RFID reader array antenna of the present application is 4 78*78*1mm3 antenna units 10, the middle layer is a 230*230*1mm3 feed network 20, and the bottom layer is a 300*300*2mm3 reflector 30.

[0031] The antenna unit 10 and the feed network 20 share a reflector 30, and the antenna unit 10 and the feed network 20 are isolated by air. The antenna unit 10 includes: 4 antenna units 10a / 10b / 10c / 10d. When configuring, one of the units (such as antenna unit 10a) is used as the reference, and then counterclockwise rotation is performed by 90 degrees, 180 degrees, and 270 degrees to obtain antenna unit 10b, antenna unit 10c, and antenna unit 10d. Antenna units 10a-10d have the same structure, and one of them is used as an example for description. Please refer to Figure 1 As shown,

[0032] The upper surface of the antenna unit 10a is provided with grooves for increasing the current path, thereby achieving a low profile, and the antenna mainly realizes the propagation of electromagnetic waves through the slot structure of the antenna unit. Specifically, the surface of the antenna unit is provided with multiple grooves, so that the antenna unit is in a plurality of U-shaped shapes.

[0033] In one embodiment of the present application, the antenna unit includes: an artificial transmission line and a plurality of T-shaped branches. Specifically, the antenna unit includes 4 T-shaped branches, and the T-shaped branches can be used to expand the antenna bandwidth. The artificial transmission line includes: a curved microstrip line 11 connected in sequence in a bow shape or multiple U shapes, an interdigitated open microstrip line, and the interdigitated open microstrip line includes: an interdigitated structure microstrip line 12 and an open microstrip line 13. The artificial transmission line is used to achieve the miniaturization of the RFID reader array antenna. Specifically, the artificial transmission line is composed of 3 sections of curved microstrip lines 11, 2 sections of interdigitated microstrip lines 12 and 4 sections of open microstrip lines 13. By adopting an RFID reader antenna based on an artificial transmission line, the miniaturization, low profile, longer recognition distance and acceptable recognition area of ​​the antenna can be achieved.

[0034] Please refer to Figure 1 As shown, three curved microstrip lines 11 are arranged in the middle of the antenna unit. The three curved microstrip lines 11 are arranged along the length direction of the antenna unit. Each curved microstrip line 11 is the same and arranged in a plurality of U-shaped shapes. The length of the curved microstrip line 11 in the width direction of the antenna unit is l4.

[0035] Open microstrip lines 13 are respectively arranged at the upper, lower, left and right corners of the antenna unit, and each open microstrip line 13 corresponds to a T-shaped branch 14. The length of the open microstrip line 13 is along the length direction of the antenna unit, and the width of the open microstrip line 13 is along the width direction of the antenna unit. The T-shaped branch is aligned with the width direction of the open microstrip line 13. The curved microstrip line 11 is placed among the four open microstrip lines 13. The length of the open microstrip line 13 is l11, l13, and the width of the open microstrip line 13 is w1.

[0036] The antenna unit includes two interdigital microstrip lines 12, which are respectively placed in the length direction of the antenna unit. Specifically, the interdigital microstrip lines 12 are placed between two open - circuit microstrip lines 13. The width of the interdigital microstrip line 12 corresponds to the width of the open - circuit microstrip line 13. The length of the interdigital microstrip line 12 is along the length direction of the antenna unit, and the length of the interdigital microstrip line 12 is l12.

[0037] Specifically, the dimensions of each part of the antenna unit are as follows: w2 = 1mm, s2 = 1mm, l11 = 15mm, l12 = 15mm, l13 = 15mm, l15 = 6.5mm, l0 = 9mm, w1 = 10.5mm, w3 = 1.3mm, x2 = 1.5mm, l6 = 9mm, l7 = 10.5mm, l9 = 8mm, theta = 110deg, R0 = 19mm, dd = 70mm, y0 = 39mm, w = 1.59mm, l4 = 13.5mm, t = 0.15mm, w4 = 36.5mm, x1 = 0.8mm, y1 = 1.5mm, y2 = 5mm, h0 = 10mm, w6 = 1.5mm, w7 = 0.45mm.

[0038] In one embodiment of the present application, the back surface of the substrate of the antenna unit is composed of two microstrip lines with different lengths and widths and a top fan - shaped structure, which is used to achieve antenna impedance matching. The surface of the antenna unit is covered with a metal - coated epoxy glass cloth laminate (FR4), and the upper surface is coated with metals such as copper to meet the antenna characteristics, which is used to achieve the circular polarization of the reader antenna. The surface of the power - dividing and phase - shifting feeding network is also covered with a metal - coated FR4 flat plate. The FR4 flat plate uses an FR4 board with a dielectric constant of 4.4, a loss tangent of 0.02, and a thickness of 1mm.

[0039] In one embodiment of the present application, please refer to Figure 3 As shown, the feeding network includes four terminals a / b / c / d, which are respectively connected to four antenna units (10a - 10d). Among them, the terminals are circular - ring terminals, which are formed by three circles sleeved from the inside to the outside. The inner diameters of the three circles are r1, r2, and r3 respectively. There are multiple "zhong" characters formed in the feeding network. Specifically, please refer to Figure 3 As shown, the dimensions of the feeding network are: r1 = 3.75mm, r2 = 2.65mm, r3 = 1.5mm, L50 = 5mm, W50 = 1.8mm, W707 = 0.97mm, h1 = 5mm.

[0040] In one embodiment of the present application, the feeding network 20 is a power - dividing and phase - shifting feeding network, and the reflector is a reflective aluminum plate.

[0041] Please refer to 4, Figure 5As shown in the figure, the working principle of the RFID reader array antenna is as follows: by slotting the surface of the antenna unit, the effective current path is extended, the feeding network achieves equal amplitude, and the phases are 0°, 90°, 180° and 270° respectively, thereby realizing circular polarization of the array antenna. The RFID reader array antenna uses the input end of the power division phase shift feeding network as the feeding end, operates at 915MHz, and has a characteristic impedance of 50Ω. The antenna uses a gradient microstrip line with a fan-shaped top loading to achieve good impedance matching of the antenna.

[0042] In one embodiment of the present application, please refer to Figure 5 As shown, at least one supporting device 40 for supporting the antenna unit is further connected between each antenna unit 10 and the feeding network 20, and at least one supporting device for supporting the antenna unit 10 is further connected between the antenna unit 10 and the reflecting plate 30. Specifically, the four antenna units 10a-10d are respectively connected to the feeding network 20 and the reflecting aluminum plate through copper pillars (e.g., with a height of 10 mm) to realize an RFID reader array antenna based on an artificial transmission line.

[0043] The present application loads an artificial transmission line structure on the antenna unit, and realizes its miniaturization by changing the structure of the curved microstrip line and the interdigitated microstrip line; through the power division phase shift feeding network, the four antenna units realize circular polarization characteristics with the same amplitude and a phase difference of 90°; the antenna has miniaturization, low profile, long recognition distance and acceptable recognition area.

[0044] The RFID reader array antenna described in this application can be used for warehouse shelves, please refer to Figure 6-Figure 9 As shown in the figure, the array antenna is below -10dB in the entire RFID frequency band |S11|, the far-field gain of the array antenna is about 1.4dBi at 0 degrees, and AR is below 3dB in the entire RFID frequency band. When the reader antenna based on the artificial transmission line is close to 50 dipole tag antennas, the actual measured reading distance can reach 40cm, and the identification area can reach 400×350×400mm3, which fully meets the application of warehouse shelf item detection.

[0045] The above embodiments are only for illustrating the technical concept and features of the present application, and their purpose is to enable people familiar with the technology to understand the content of the present application and implement it accordingly, and they cannot be used to limit the protection scope of the present application. Any equivalent transformation or modification made according to the spirit of the present application shall be included in the protection scope of the present application.

Claims

1. An RFID reader array antenna, characterized in that: include: A reflector is placed on the bottom layer, a feed network is placed on the middle layer, and a plurality of antenna units are placed on the upper layer and arranged at a preset angle. Among the plurality of antenna units, one antenna unit is used as a reference, and the remaining antenna units are arranged in a clockwise or counterclockwise rotation at a certain angle. The antenna unit also includes: an artificial transmission line and a plurality of T-shaped branches, wherein the T-shaped branches are used to expand the bandwidth of the antenna. The artificial transmission line includes: The curved microstrip line, interdigitated microstrip line and open microstrip line connected in sequence in a bow shape or multiple U shapes are used. The four corners of the antenna unit are respectively provided with open microstrip lines, each of which corresponds to a T-shaped branch. The length of the open microstrip line is along the length direction of the antenna unit, and the width of the open microstrip line is along the width direction of the antenna unit. The T-shaped branch is aligned with the width direction of the open microstrip line, and the curved microstrip line is placed in the four open microstrip lines. The interdigital microstrip line is placed between two open microstrip lines. The width of the interdigital microstrip line corresponds to the width of the open microstrip line. The length of the interdigital microstrip line is along the length direction of the antenna unit. The plurality of antenna units are respectively connected to a feeding network, A plurality of the antenna units and the feed network share the reflector.

2. The RFID reader array antenna according to claim 1, characterized in that: include: The four antenna units have the same structure. The four antenna units are configured to be obtained by rotating one of the antenna units clockwise or counterclockwise by 90 degrees, 180 degrees and 270 degrees respectively, with one of the antenna units as a reference. The four antenna units are respectively connected to a feeding network.

3. The RFID reader array antenna according to claim 1, characterized in that: The feeding network is a power division phase shifting feeding network, and the surface of the power division phase shifting feeding network is covered with a metal FR4 plate.

4. The RFID reader array antenna according to claim 1, characterized in that: The surface of the antenna unit is covered with a metal FR4 plate.

5. The RFID reader array antenna according to claim 1, characterized in that: The upper surface of the antenna unit is provided with a groove for increasing a current path.

6. The RFID reader array antenna according to claim 1, characterized in that: At least one supporting device for supporting the antenna unit is also connected between the antenna unit and the reflection plate.

7. The RFID reader array antenna according to claim 6, characterized in that: At least one supporting device for supporting the antenna unit is also connected between the antenna unit and the feeding network.

8. The RFID reader array antenna according to claim 1, characterized in that: The feeding network includes four terminals, which are respectively used to connect four terminals of four antenna units.

9. The RFID reader array antenna according to claim 1, characterized in that: The ratio of the length l4 of the bent microstrip line in the width direction of the antenna unit to the width w1 of the open microstrip line is between 1.2 and 1.4.

Images