Smart cabinet RFID reader and writer circular polarization array antenna and preparation method

Abstract

The application discloses an intelligent goods cabinet RFID reader-writer circular polarization array antenna and a preparation method thereof, and relates to the technical field of antennas.The circular polarization array antenna is composed of a plurality of unit antennas, the plurality of unit antennas are connected to form the circular polarization array antenna through a plurality of T-shaped power dividers, microstrip lines and impedance conversion microstrip lines, each unit antenna comprises a dielectric substrate, and the dielectric substrate is uniformly provided with a Wilkinson power division feeding network and four antennas.The application adopts a resonant four-arm spiral antenna structure, bends a copper sheet into an inverted F antenna form, reduces the size and improves impedance matching, feeds through a Wilkinson power division phase-shifting network, and realizes circular polarization of the antenna.The working frequency of the antenna can cover the most extensive 902MHz-928MHz frequency band standard.

Description

Technical Field

[0001] This invention relates to the field of non-contact automatic identification, specifically to a circularly polarized array antenna for an intelligent vending machine RFID reader and its fabrication method. Background Technology

[0002] RFID, as a non-contact automatic identification technology, has been widely used in recent years in fields such as retail, transportation and logistics, warehouse management, and access control. UHF RFID specifically refers to passive radio frequency identification technology in the 800 / 900MHz frequency band. Due to its advantages such as fast read / write speed, ability to identify high-speed moving objects, large number of targets that can be identified, long working distance, and low tag cost, it has gained attention from various countries and is developing rapidly. The reader antenna, as a key component of the RFID system, directly affects the system's performance. Reader antennas are typically required to be circularly polarized. The main purpose of using a planar array antenna is to improve antenna gain and compensate for the problem of missed tags or incomplete tag reading when there are many items in a container and multiple tags are stacked. Summary of the Invention

[0003] The technical problem to be solved by this invention is a circularly polarized array antenna for an intelligent vending RFID reader and its fabrication method. It adopts the principle of UHF RFID technology and can be applied to RFID planar array systems. In order to meet the requirements of intelligent vending tag reading and writing, the antenna adopts a resonant four-arm helical antenna structure, and the copper sheet is bent into an inverted F antenna shape to reduce the size and improve impedance matching. It is fed by a Wilkinson power divider phase shifter network to achieve circular polarization of the antenna.

[0004] The present invention is achieved through the following technical solution: a circularly polarized array antenna for an intelligent RFID reader / writer, comprising a circularly polarized array antenna composed of multiple unit antennas. The multiple unit antennas are connected to each other through multiple T-type power dividers, microstrip lines, and impedance transformation microstrip lines to form a circularly polarized array antenna. Each unit antenna includes a dielectric substrate, on which Wilkinson power divider feed networks and four antennas are arranged.

[0005] As a preferred technical solution, the Wilkinson power distribution network:

[0006] It includes Wilkinson power dividers, four antenna feed ports, one output port, and a phase extension line. Each Wilkinson power divider is connected in parallel with an ohmic resistor. The phase extension line connects each Wilkinson power divider. The four antennas are orthogonally arranged on the four antenna feed ports.

[0007] As a preferred technical solution, the phase extension line includes a 180° phase extension line and a 90° phase extension line, wherein two antenna feed ports are led out from the Wilkinson power divider through the 90° phase extension line, and the other two antenna feed ports are led out directly from the Wilkinson power divider.

[0008] As a preferred technical solution, each Wilkinson power divider carries a 70.7-ohm microstrip line.

[0009] As a preferred technical solution, the ohmic resistor is a 100-ohm resistor.

[0010] As a preferred technical solution, the impedance of the impedance transformation microstrip line is 35.3 ohms, and the microstrip line is a 50-ohm microstrip line.

[0011] As a preferred technical solution, the antenna is made of a copper sheet bent into an inverted F shape.

[0012] The method for fabricating the circularly polarized array antenna of the intelligent vending machine RFID reader of the present invention includes the following steps:

[0013] Step 1: First, design a single-unit antenna by bending a 1mm thick copper sheet into an inverted F shape. The length of the resonant arm is close to 1 / 4 wavelength of the frequency band. Adjust the antenna short-circuit branch, the height of the antenna from the dielectric substrate, and the length of the copper sheet.

[0014] Step 2: To achieve circular polarization of the antenna, two conditions must be met: 1. Adjacent antenna ends must be orthogonal to each other; 2. The phase difference between adjacent antenna feed ports must be 90°. The antennas are placed orthogonally, with a total of four antenna feed ports. The phase of each antenna feed port is either delayed or led by 90° in sequence.

[0015] Step 3: After the individual array elements are designed, the array elements are assembled into a planar array. A uniform planar array is used, characterized by the same amplitude of each element and a phase difference of 0°. Seven T-type power dividers are used to connect the antennas of each element. The T-type power divider needs to consider the 1 / 4 wavelength impedance transformation. Using the T-type section microstrip line impedance formula, the impedance of the microstrip line with the 1 / 4 wavelength impedance transformation of the T-type power divider is calculated to be 35.3Ω.

[0016] Step 4: Select an FR4 dielectric substrate. The substrate has a dielectric constant εr = 4.4, a loss tangent tan δ = 0.02, a dielectric thickness of 1.6 mm, and a copper foil thickness of 0.035 mm. Use the LineCacl tool in ADS electromagnetic simulation software to calculate the required microstrip line width. The results show that the width of the 50Ω microstrip line is 3 mm, the width of the 70.7Ω microstrip line is 1.58 mm, and the width of the 35.3Ω impedance transformation microstrip line is 5.24 mm.

[0017] The beneficial effects of this invention are: 1. This invention

[0018] The antenna can cover the 902-928MHz frequency band. The S11 meets the basic requirements of antennas with a phase difference of less than -10dB. The Wilkinson power divider has a phase difference of 90°. It adopts a four-wall spiral inverted F antenna. Adjacent antennas are orthogonal to each other, thus realizing the circular polarization of the antenna array elements. It is a right-hand circularly polarized antenna with an antenna axial ratio AR of less than 3dB and a 3dB beamwidth (half-power beam) of more than 100°.

[0019] 2. After the antenna array is assembled, the simulation results show that the maximum gain at the center frequency of 915MHz is 8.01dbi, while the actual measurement in the microwave anechoic chamber is 7.3dbi.

[0020] III. The antenna of the present invention

[0021] It can be used on RFID readers in smart vending machines, and its applications can be expanded to include retail, transportation, logistics, warehouse management, access control, and other fields. Actual testing shows that when multiple tags are stacked on a vending machine, the communication distance can exceed 5 meters, and the communication distance for a single tag can reach 12 meters. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a layout diagram of the Wilkinson power divider network of the present invention on a dielectric substrate;

[0024] Figure 2 For the present invention Figure 1 A three-dimensional image;

[0025] Figure 3 This is a design diagram of the antenna array element for this invention;

[0026] Figure 4 This is a plan view of the antenna array elements after being assembled according to the present invention;

[0027] Figure 5 For the present invention Figure 4 A schematic diagram of the three-dimensional structure in the diagram;

[0028] Figure 6 This is a schematic diagram of the design principle of the Wilkinson power divider used in this invention;

[0029] Figure 7 A simulation model diagram of a Wilkinson power divider;

[0030] Figure 8 The simulation results of insertion loss for each port are shown in the figure;

[0031] Figure 9 The simulation results for the phase of each port are shown in the figure;

[0032] Figure 10 The diagram shows the simulation model of the array elements;

[0033] Figure 11 Simulation results for antenna S11 Figure 1 ;

[0034] Figure 12 Simulation results of antenna half-power beamwidth Figure 1 ;

[0035] Figure 13 The 2d direction of the antenna's E-plane and H-plane. Figure 1 ;

[0036] Figure 14 The 2d direction of the antenna's E-plane and H-plane. Figure 2 ;

[0037] Figure 15 3D direction of the antenna Figure 1 ;

[0038] Figure 16 3D direction of the antenna Figure 2 ;

[0039] Figure 17 The antenna pattern is a left-handed LHCP3d radiation pattern.

[0040] Figure 18 The right-handed LHCP3d radiation pattern of the antenna;

[0041] Figure 19 Antenna axial ratio AR simulation results;

[0042] Figure 20 Modeling and simulation of the antenna array;

[0043] Figure 21 Simulation results for antenna S11 Figure 2 ;

[0044] Figure 22 The 2d direction of the antenna's E-plane and H-plane. Figure 3 ;

[0045] Figure 23 The 2d direction of the antenna's E-plane and H-plane. Figure 4 ;

[0046] Figure 24 3D direction of the antenna Figure 3 ;

[0047] Figure 25 3D direction of the antenna Figure 4 ;

[0048] Figure 26 Here is a picture of the actual antenna.

[0049] Figure 27 Antenna direction for testing in microwave anechoic chamber Figure 1 ;

[0050] Figure 28 Antenna direction for testing in microwave anechoic chamber Figure 2 ;

[0051] Figure 29 Antenna direction for testing in microwave anechoic chamber Figure 3 ;

[0052] Figure 30 Antenna direction for testing in microwave anechoic chamber Figure 4 . Detailed Implementation

[0053] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0054] like Figures 1-5 As shown, a circularly polarized array antenna for an intelligent vending RFID reader of the present invention includes a circularly polarized array antenna composed of multiple unit antennas. The multiple unit antennas are connected to each other through multiple T-type power dividers, microstrip lines 29, and impedance transformation microstrip lines. Each unit antenna includes a dielectric substrate 15, on which a Wilkinson power divider feed network 100 and four antennas are arranged. The four antennas include a first antenna 16, a second antenna 17, a third antenna 18, and a fourth antenna 19. The multiple T-type power dividers are a first T-type power divider 20, a second T-type power divider 21, a third T-type power divider 22, a fourth T-type power divider 23, a fifth T-type power divider 24, a sixth T-type power divider 25, and a seventh T-type power divider 26. The impedance transformation microstrip lines include a first impedance transformation microstrip line 27 and a second impedance transformation microstrip line 28.

[0055] like Figure 1 , Figure 2 as well as Figure 6 As shown, the Wilkinson power divider feed network includes Wilkinson power dividers, four antenna feed ports, one output port 5, and a phase extension line. Each Wilkinson power divider is connected in parallel with an ohmic resistor. The phase extension line connects each Wilkinson power divider. The four antennas are orthogonally arranged on the four antenna feed ports.

[0056] In this embodiment, the four antenna feed ports are the first antenna feed port 1, the second antenna feed port 2, the third antenna feed port 3, and the fourth antenna feed port 4, which are respectively located at the four pins of the dielectric substrate 15.

[0057] like Figure 1 and Figure 2 As shown, the phase extension lines include a 180° phase extension line 10 and a 90° phase extension line. The second antenna feed port 2, the fourth antenna feed port 4, and the Wilkinson power divider are led out through the 90° phase extension line. In addition, the first antenna feed port 1 and the third antenna feed port 3 are directly led out from the Wilkinson power divider. There are two 90° phase extension lines, namely the first 90° phase extension line 9 and the second 90° phase extension line 11.

[0058] In this embodiment, each Wilkinson power divider carries a 70.7-ohm microstrip line. Three 70.7-ohm microstrip lines are used in this embodiment: a first microstrip line 12, a second microstrip line 13, and a third microstrip line 14. Each line has a 100-ohm resistor. Connecting 100-ohm resistors in parallel between the power dividers primarily aims to improve antenna isolation. The impedance of the impedance transformation microstrip line is 35.3 ohms. A 50-ohm microstrip line is used. In this embodiment, there are three 100-ohm resistors: a first ohm resistor 6, a second ohm resistor 7, and a third ohm resistor 8.

[0059] The antenna is made by bending a copper sheet into an inverted F shape. Specifically, a 1mm thick copper sheet is bent into an inverted F shape. Figure 3 As shown, the length of the resonant arm is close to 1 / 4 wavelength of the frequency band. By adjusting the antenna short-circuit branch, the height of the antenna from the dielectric substrate, and the length of the copper sheet, the antenna can have good impedance characteristics in the 902-928MHz frequency band.

[0060] In the fabrication of the circularly polarized array antenna for the smart vending RFID reader of the present invention, a single unit antenna is first designed by bending a 1mm thick copper sheet into an inverted F shape, with the resonant arm length close to 1 / 4 wavelength of the frequency band. The antenna short-circuit branch, the height of the antenna from the dielectric substrate, and the length of the copper sheet are adjusted.

[0061] To achieve circular polarization, an antenna must meet two conditions: 1. Adjacent antenna ends must be orthogonal to each other; 2. The phase difference between adjacent antenna feed ports must be 90°. The antennas are placed orthogonally, with a total of four antenna feed ports. The phase of each antenna feed port is either delayed or led by 90° (0°, 90°, 180°, 270° or 0°, -90°, -180°, -270°).

[0062] After the individual array elements are designed, they are assembled into a planar array using a uniform planar array. The characteristic of this array is that the amplitude of each element is the same and the phase difference is 0°. Seven T-type power dividers are used to connect the antennas of each element. The T-type power dividers need to consider the 1 / 4 wavelength impedance transformation. Using the T-type section microstrip line impedance formula, the impedance of the microstrip line with the 1 / 4 wavelength impedance transformation of the T-type power divider is calculated to be 35.3Ω.

[0063] FR4 dielectric substrate was selected, with a dielectric constant εr = 4.4, loss tangent tanδ = 0.02, dielectric thickness 1.6 mm, and copper foil thickness 0.035 mm. The required microstrip line width was calculated using the LineCacl tool in ADS electromagnetic simulation software. The results showed that the width of the 50Ω microstrip line was 3 mm, the width of the 70.7Ω microstrip line was 1.58 mm, and the width of the 35.3Ω impedance transformation microstrip line was 5.24 mm.

[0064] Figure 7 A simulation model diagram of a Wilkinson power divider; Figure 8 The simulation results for insertion loss at each port are shown in the figure. Figure 8 Simulation results show that the insertion loss of the port is between -6.4 and -7.3 dB, which is very close to the theoretical calculated value of -6 dB.

[0065] Figure 9 The simulation results for the phase of each port are shown in the figure. The simulation results show that the phase difference between the ports is close to 90°. Figure 10 The diagram shows the simulation model of the array elements; Figure 11 The simulation results for antenna S11 are shown in the figure. Figure 11 Simulation results show that the center frequency S11 is -15.8dB. Note: In the 902-928MHz frequency band, the basic requirement that S11 is less than -10dB is met.

[0066] Figure 12 The figure shows the simulation results of the antenna half-power beamwidth. The simulation results show that the included angle of -3dB is -54° to 56°, or 110°, which meets the design requirement of greater than 100°.

[0067] Figure 13 and Figure 14 The 2d radiation patterns are shown in the E-plane and H-plane directions of the antenna. Figure 15 and Figure 16 The image shows the 3D radiation pattern of the antenna, from which the maximum gain Gian = 3.9 dBi can be observed.

[0068] Figure 15 and Figure 16 This is the 3D radiation pattern of the antenna; Figure 17 The 3d radiation pattern of the left-handed LHCP antenna; Figure 18 The figure shows the 3d radiation pattern of the right-hand circularly polarized (LHCP) antenna. The simulation results in the figure show that the antenna is a right-hand circularly polarized antenna.

[0069] Figure 19 The image shows the AR simulation results for the antenna axial ratio. Figure 19 In the simulation, the antenna axial ratio AR is calculated to be 2.59 dB.

[0070] Figure 20 To create a model and simulation model for the antenna array; Figure 21 The simulation results for antenna S11 are shown in the figure. Figure 21 The simulation results show that the center frequency S11 is -16.7dB, and the 902-928MHz range satisfies s11 < -10dB.

[0071] Figure 22 and Figure 23 Both are 2d radiation patterns in the E-plane and H-plane directions of the antenna.

[0072] Figure 24 and Figure 25 All are 3D antenna radiation patterns, with the maximum gain Gian = 8.01 dBi.

[0073] Figure 26 Here is a picture of the actual antenna. Figures 27-30 This is the antenna pattern for testing in a microwave anechoic chamber.

[0074] The measured data of the antenna in the microwave anechoic chamber are shown in Table 1 below:

[0075]

[0076] Table 1

[0077] The simulation results show that the antenna of this invention can cover the 902-928MHz frequency band, s11 meets the basic requirements of antennas less than -10dB, the phase difference of the Wilkinson power divider is 90°, and a four-walled spiral inverted F antenna is adopted. The adjacent antennas are orthogonal to each other, thus realizing the circular polarization of the antenna array elements. It is a right-hand circularly polarized antenna with an antenna axial ratio AR of less than 3dB and a 3dB beamwidth (half-power beam) greater than 100°.

[0078] After the antenna array was assembled, the simulation results showed that the maximum gain at the center frequency of 915MHz was 8.01dbi, while the actual measurement in the microwave anechoic chamber was 7.3dbi.

[0079] The antenna of this invention can be used on RFID readers in smart vending machines. Of course, it can also be extended to applications in retail, transportation, logistics, warehouse management, access control and other fields. Through actual testing, when multiple tags are read and stacked on the vending machine, the communication distance can reach more than 5 meters, and the communication distance for a single tag can reach 12 meters.

[0080] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions conceived without inventive effort should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. An intelligent locker RFID reader-writer circular polarization array antenna, characterized in that: The application relates to a circular polarization array antenna composed of multiple unit antennas, wherein the multiple unit antennas are connected by multiple T-type power dividers, microstrip lines and impedance conversion microstrip lines to form the circular polarization array antenna; each unit antenna comprises a dielectric substrate, a Wilkinson power division feeding network and four antennas which are uniformly arranged on the dielectric substrate. The Wilkinson power division feeding network comprises Wilkinson power dividers, four antenna feeding ports, an output port and phase extension lines; an ohmic resistor is connected in parallel to each Wilkinson power divider; the Wilkinson power dividers are connected by the phase extension lines; and the four antennas are orthogonally arranged on the four antenna feeding ports. The phase extension lines comprise 180-degree phase extension lines and 90-degree phase extension lines; two antenna feeding ports are connected to the Wilkinson power dividers by the 90-degree phase extension lines; and the other two antenna feeding ports are directly connected to the Wilkinson power dividers. Each Wilkinson power divider is provided with a 70.7-ohm microstrip line. The ohmic resistor is a 100-ohm resistor. The impedance conversion microstrip line has an impedance of 35.3 ohms; and the microstrip line is a 50-ohm microstrip line. The antenna is a copper sheet which is bent into an inverted F shape.

2. A preparation method of the intelligent cabinet RFID reader circular polarization array antenna according to claim 1, which is prepared by the following steps: Step one: a unit antenna is designed; a copper sheet with a thickness of 1 mm is bent into an inverted F shape; the resonant arm length is close to 1 / 4 wavelength of the frequency band; the antenna height to the dielectric substrate and the copper sheet length are adjusted; Step two: the antenna needs to satisfy two conditions to realize circular polarization:

1. adjacent antenna ends are orthogonal to each other; and 2. the phase difference between adjacent antenna feeding ports is 90 degrees; the antennas are orthogonally arranged; there are four antenna feeding ports; and the antenna feeding port phase is sequentially delayed or advanced by 90 degrees; The amplitudes of the unit antennas are the same, and the phase difference is 0 degrees; seven T-type power dividers are used to connect the unit antennas; the T-type power divider needs to consider 1 / 4 wavelength impedance conversion; the impedance of the 1 / 4 wavelength impedance conversion microstrip line of the T-type power divider is calculated to be 35.3 ohms by using a T-type section microstrip line impedance formula; Step three, after the design of a single array element, the array element group surface array, using a uniform plane array, the characteristic is Step four: an FR4 material dielectric substrate is selected; the dielectric constant of the substrate is epsilon r=4.4; the loss tangent is tan delta=0.02; the dielectric thickness is 1.6 mm; the copper foil thickness is 0.035 mm; the width of the required microstrip line is calculated by using a LineCacl tool in ADS electromagnetic simulation software; the width of the 50-ohm microstrip line is 3 mm; the width of the 70.7-ohm microstrip line is 1.58 mm; and the width of the 35.3-ohm impedance conversion microstrip line is 5.24 mm. ​

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