A UHF band RFID near-field reader antenna

Abstract

The present invention belongs to the technical field of radio frequency identification reader / writer antennas and discloses a UHF band RFID near-field reader / writer antenna, comprising a dielectric plate, a metal ground, a microstrip circuit, and a radiating structure; the metal ground is disposed on the bottom surface of the dielectric plate; the microstrip circuit and radiating structure are disposed on the top surface of the dielectric plate; the microstrip circuit includes a first microstrip line, a second microstrip line, and a third microstrip line; and the radiating structure comprises N "reverse current pair" units, 4 (2N-1) capacitors, 5 (2N-1) transmission lines, and 2 (2N-1) inductors, where 1 ≤ N ≤ 8. The present invention not only achieves a strong and uniform magnetic field distribution within the read / write area but also adjusts the read / write area according to different application scenarios, making it widely applicable to UHF band near-field RFID systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of radio frequency identification reader-writer antennas, and in particular relates to a UHF frequency band RFID near-field reader-writer antenna. Background Art

[0002] Radio Frequency Identification (RFID) is a contactless automatic identification technology that uses radio frequency signals to automatically identify objects, enabling rapid item tracking and data exchange. RFID systems operate in four different frequency bands: low frequency (LF), high frequency (HF), ultrahigh frequency (UHF), and microwave (MW). The performance characteristics of systems operating in different frequency bands vary significantly. Compared to other frequency bands, UHF near-field RFID systems offer significant advantages for item-level identification, primarily including the ability to read multiple tags simultaneously, multiple read / write capabilities, large data capacity, and low tag cost. Currently, UHF near-field RFID systems are playing a significant role in supply chain management, modern logistics, pharmaceutical regulation, and retail. From a simple operating principle perspective, a basic RFID system consists of three main components: a reader / writer, a tag, and a PC. The reader / writer antenna, a key component of an RFID system, directly determines the system's recognition range, coverage area, and read / write stability.

[0003] Data and energy exchange between readers and tags can be achieved through electric or magnetic fields. However, UHF near-field RFID reader antennas based on magnetic field coupling maintain excellent performance in environments with metal and liquids, and have garnered widespread attention. The design of UHF near-field RFID reader antennas based on magnetic field coupling requires antennas with varying read / write areas depending on the application scenario. However, when the antenna has a large area, the magnetic field distribution becomes weak and uneven, resulting in read holes and affecting the performance of the reader antenna. Therefore, designing a reader antenna with a simple structure, an adjustable read / write area, and a strong and uniform magnetic field distribution has important research and application value. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a UHF band RFID near-field reader antenna that can obtain a read / write area with an adjustable, strong and uniform magnetic field distribution, thereby effectively improving the working performance of the reader antenna.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A UHF band RFID near-field reader antenna, characterized in that it comprises a dielectric plate, a metal ground, a microstrip circuit and a radiating structure; the metal ground is placed on the bottom surface of the dielectric plate; the microstrip circuit and the radiating structure are placed on the top surface of the dielectric plate; the microstrip circuit comprises a first microstrip line, a second microstrip line and a third microstrip line; the radiating structure comprises N "reverse current pair" units, 4 (2N-1) capacitors, 5 (2N-1) transmission lines and 2 (2N-1) inductors; the first "reverse current pair" unit is composed of a first meandering microstrip line and a second meandering microstrip line; the micro The strip circuit includes a first microstrip line starting from the antenna input port, a second microstrip line and a third microstrip line outputted in two upper and lower paths, the second microstrip line is connected to the input end of the first meandering microstrip line, the output end of the first meandering microstrip line is connected to the input end of the third meandering microstrip line via a first capacitor, a first transmission line, a first inductor, a second transmission line, a second capacitor, a third transmission line, a third capacitor, a fourth transmission line, a second inductor, a fifth transmission line, and a fourth capacitor; the third microstrip line is connected to the input end of the second meandering microstrip line, the output end of the second meandering microstrip line is connected to the input end of the third meandering microstrip line via a fifth capacitor, a sixth transmission line, a third inductor, and a seventh transmission line. , the sixth capacitor, the eighth transmission line, the seventh capacitor, the ninth transmission line, the fourth inductor, the tenth transmission line, the eighth capacitor are connected to the input end of the fourth meander microstrip line; and so on, the output end of the 2N-1 meander microstrip line is connected to the input end of the fourth meander microstrip line via the (8N-7)th capacitor, the (10N-9)th transmission line, the (4N-3)th inductor, the (10N-8)th transmission line, the (8N-6)th capacitor, the (10N-7)th transmission line, the (8N-5)th capacitor, the (10N-6)th transmission line, the (4N-2)th inductor, the (10N-5)th transmission line, the (8N-4)th capacitor and the The input end of the 2N+1 meander microstrip line is connected; the output end of the 2N meander microstrip line is connected to the input end of the 2N+2 meander microstrip line via the (8N-3)th capacitor, the (10N-4)th transmission line, the (2N+1)th inductor, the (10N-3)th transmission line, the (8N-2)th capacitor, the (10N-2)th transmission line, the (8N-1)th capacitor, the (10N-1)th transmission line, the (2N+2)th inductor, the (10N)th transmission line, and the (8N)th capacitor; the output ends of the 2N+1 meander microstrip line and the 2N+2 meander microstrip line are open-circuited.

[0007] Furthermore, the electrical length of the third microstrip line is greater than the electrical length of the second microstrip line by half a waveguide wavelength.

[0008] Furthermore, the electrical lengths of the first meandering microstrip line and the second meandering microstrip line of the first “reverse current pair” unit are both one waveguide wavelength.

[0009] Furthermore, the first capacitor is connected across the output end of the first meandering microstrip line and the input end of the first transmission line, the output end of the first transmission line is connected to the input end of the second capacitor, the two ends of the first inductor are respectively connected to the first transmission line and the second transmission line, and are connected to the first metal via through the second transmission line and then grounded; the output end of the second capacitor is connected to the input end of the third transmission line, the output end of the third transmission line is connected to the input end of the third capacitor, the output end of the third capacitor is connected to the input end of the fourth transmission line, the output end of the fourth transmission line is connected to the input end of the fourth capacitor, the output end of the fourth capacitor is connected to the input end of the third meandering microstrip line, the two ends of the second inductor are respectively connected to the fourth transmission line and the fifth transmission line, and are connected to the second metal via through the fifth transmission line and then grounded.

[0010] Furthermore, the N "reverse current pair" units in the radiation structure are composed of a microstrip line of half the waveguide wavelength, four capacitors, five transmission lines and two inductors connected in series, and 1≤N≤8.

[0011] From the above, it can be seen that the UHF band RFID near-field reader antenna provided by the present invention has the following advantages:

[0012] (1) The present invention strengthens the magnetic field strength in the read and write area through the "reverse current pair" unit, reduces the read and write voids, and reduces the misread rate.

[0013] (2) The present invention can further improve the magnetic field strength and uniformity and increase the reading distance of the reader antenna by controlling the number of capacitors and inductors and adjusting the spacing between the "reverse current pair" units.

[0014] (3) The present invention can adjust the read / write area of ​​the reader / writer antenna by increasing or decreasing the number of "reverse current pair" units, capacitors, and inductors according to actual application requirements, thereby obtaining an adjustable read / write area. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 1 is a schematic structural diagram of an antenna according to an optional embodiment of the present invention;

[0016] Figure 2 is a reflection coefficient curve diagram of an antenna according to an optional embodiment of the present invention;

[0017] Figure 3 Schematic diagram of the magnetic field distribution on the xoy plane at a distance of 10 mm from the antenna of an optional embodiment of the present invention;

[0018] Figure 4 This is an optional embodiment of the present invention. The magnetic field component 10 mm above the antenna |H z |Distribution plot along the y-axis.

[0019] Reference numerals: 1 - metal ground, 2 - dielectric plate, 3 - first microstrip line, 4 - second microstrip line, 5 - third microstrip line, 6 - "reverse current pair" unit, 71 - capacitor, 72 - transmission line, 73 - inductor, 74 - metal via. DETAILED DESCRIPTION

[0020] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0021] As an optional specific embodiment, Figure 1 As shown, a UHF band RFID near-field reader antenna of the present invention comprises: a metal ground 1, a dielectric plate 2, a first microstrip line 3, a second microstrip line 4, a third microstrip line 5, four "reverse current pair" units 6, 28 capacitors 71, 35 transmission lines 72, 14 inductors 73, and 14 metal vias 74. In this embodiment, the dielectric constant ε of the dielectric plate 2 is r is 4.4 and has a thickness of 1.6 mm. The electrical length of the third microstrip line 5 is L0 longer than that of the second microstrip line 4. L0 is half the wavelength of the guided wave at the operating frequency of the reader antenna, satisfying Where c is the speed of light, f is the operating frequency of the reader antenna, and f=845MHz is selected, so L0=86mm; the electrical length L1 of the first curved microstrip line and the second curved microstrip line of the first "reverse current pair" unit are both one waveguide wavelength, so L1=185mm; the value of the capacitor 71 is 3.4pf, and the value of the inductor 73 is 5.25nh.

[0022] The RF signal is input from Port 1 and is divided into two paths, an upper path and an lower path, through the first microstrip line that starts feeding. The first path is connected to the input end of the first meandering microstrip line through the second microstrip line. The output end of the first meandering microstrip line is connected to the input end of the third meandering microstrip line through the first capacitor, the first transmission line, the first inductor, the second transmission line, the second capacitor, the third transmission line, the third capacitor, the fourth transmission line, the second inductor, the fifth transmission line, and the fourth capacitor. The output end of the third meandering microstrip line is connected to the input end of the third meandering microstrip line through the ninth capacitor, the eleventh transmission line, the fifth inductor, the twelfth transmission line, the tenth capacitor, the thirteenth transmission line, the eleventh capacitor, The fourteenth transmission line, the sixth inductor, the fifteenth transmission line, and the twelfth capacitor are connected to the input end of the fifth meander microstrip line. The output end of the fifth meander microstrip line is connected to the input end of the seventh meander microstrip line via the seventeenth capacitor, the twenty-first transmission line, the ninth inductor, the twenty-second transmission line, the eighteenth capacitor, the twenty-third transmission line, the nineteenth capacitor, the twenty-fourth transmission line, the tenth inductor, the twenty-fifth transmission line, and the twentieth capacitor. The output end of the seventh meander microstrip line is connected to the input end of the seventh meander microstrip line via the twenty-fifth capacitor, the thirty-first transmission line, the thirteenth inductor, the thirty-second transmission line, the twenty-sixth capacitor, The thirty-third transmission line, the twenty-seventh capacitor, the thirty-fourth transmission line, the fourteenth inductor, the thirty-fifth transmission line, and the twenty-eighth capacitor are connected at the rear terminal; the second path is connected to the input end of the second meandering microstrip line via the third microstrip line, the output end of the second meandering microstrip line is connected to the input end of the fourth meandering microstrip line via the fifth capacitor, the sixth transmission line, the third inductor, the seventh transmission line, the sixth capacitor, the eighth transmission line, the seventh capacitor, the ninth transmission line, the fourth inductor, the tenth transmission line, and the eighth capacitor; the output end of the fourth meandering microstrip line is connected to the input end of the fourth meandering microstrip line via the thirteenth capacitor, the sixteenth transmission line, the fifth The inductor, the seventeenth transmission line, the fourteenth capacitor, the eighteenth transmission line, the fifteenth capacitor, the nineteenth transmission line, the sixth inductor, the twentieth transmission line, and the sixteenth capacitor are connected to the input end of the sixth meandering microstrip line. The output end of the sixth meandering microstrip line is connected to the input end of the eighth meandering microstrip line via the twenty-first capacitor, the twenty-sixth transmission line, the seventh inductor, the twenty-seventh transmission line, the twenty-second capacitor, the twenty-eighth transmission line, the twenty-third capacitor, the twenty-ninth transmission line, the eighth inductor, the thirtieth transmission line, and the twenty-fourth capacitor. The output end of the eighth meandering microstrip line is open.

[0023] The first capacitor is connected across the output end of the first meandering microstrip line and the input end of the first transmission line, the output end of the first transmission line is connected to the input end of the second capacitor, the two ends of the first inductor are connected to the first transmission line and the second transmission line, and are connected to the first metal via through the second transmission line and then grounded; the output end of the second capacitor is connected to the input end of the third transmission line, the third capacitor is connected across the output end of the third transmission line and the input end of the fourth transmission line, the output end of the fourth transmission line is connected to the input end of the fourth capacitor, the output end of the fourth capacitor is connected to the third meandering microstrip line, the two ends of the second inductor are connected to the fourth transmission line and the fifth transmission line, and are connected to the second metal via through the fifth transmission line and then grounded; the fifth capacitor is connected across the output end of the second meandering microstrip line and the input end of the sixth transmission line. The output end of the sixth transmission line is connected to the input end of the sixth capacitor, the two ends of the third inductor are respectively connected to the sixth transmission line and the seventh transmission line, and are connected to the third metal via through the seventh transmission line and then grounded; the output end of the sixth capacitor is connected to the input end of the eighth transmission line, the seventh capacitor is connected across the output end of the eighth transmission line and the input end of the ninth transmission line, the output end of the ninth transmission line is connected to the input end of the eighth capacitor, the output end of the eighth capacitor is connected to the fourth meandering microstrip line, the two ends of the fourth inductor are respectively connected to the ninth transmission line and the tenth transmission line, and are connected to the fourth metal via through the tenth transmission line and then grounded; the above is the connection method of the first and second "reverse current pair" units. By analogy, the second, third and fourth "reverse current pair" units are all connected in the same way, which will not be repeated here.

[0024] The present invention can increase the number of "reverse current pair" units to expand the read and write range, and at the same time, can further expand the read and write range by increasing or decreasing the number of capacitors and inductors.

[0025] Figure 2 This is a reflection coefficient curve for an antenna according to an optional embodiment of the present invention. As can be seen from the figure, within the 830-850MHz and 860-870MHz frequency bands, the reflection coefficient is less than -10dB, meeting the UHF RFID frequency bands of 840-845MHz in China and 865-868MHz specified by the European Telecommunications Standards Institute (ESTI).

[0026] Figure 3 This is a schematic diagram of the magnetic field distribution on the xoy plane at a distance of 10 mm from the antenna of an optional embodiment of the present invention. As can be seen from the figure, the reader / writer antenna of this embodiment can generate a strong and relatively uniform magnetic field distribution over a large area in the near field, which is conducive to identifying tags placed at any position.

[0027] Figure 4 This is an optional embodiment of the present invention, the magnetic field component 10 mm above the antenna |H z |Distribution graph along the y-axis. If the label threshold -20dBA / m is used as the boundary, |Hz |In the range of 0mm≤y≤483mm, it is stronger than this value; this further proves that the reader / writer antenna of an optional embodiment of the present invention can provide a strong and uniform magnetic field.

[0028] In summary, the near-field reader / writer antenna proposed in the embodiment of the present invention can have a strong and uniform magnetic field distribution within the read / write area to avoid identification blind spots. In addition, the proposed antenna can also adjust the read / write area according to different application scenarios, so that it can be widely used in near-field RFID systems in the UHF frequency band.

[0029] The present invention provides a UHF band RFID near-field reader / writer antenna. There are many methods and approaches to implement this technical solution. The above embodiments are merely exemplary. It should be noted that a person skilled in the art can make several improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also fall within the scope of protection of the present invention.

Claims

1. A UHF band RFID near-field reader antenna, characterized by: The invention comprises a dielectric plate, a metal ground, a microstrip circuit and a radiating structure; the metal ground is arranged on the bottom surface of the dielectric plate; the microstrip circuit and the radiating structure are arranged on the top surface of the dielectric plate; the microstrip circuit comprises a first microstrip line, a second microstrip line and a third microstrip line; the radiating structure comprises N "reverse current pair" units, 4 (2N-1) capacitors, 5 (2N-1) transmission lines and 2 (2N-1) inductors; the first "reverse current pair" unit is composed of a first meandering microstrip line and a second meandering microstrip line; the microstrip circuit comprises a first microstrip line starting from an antenna input port, and second and third microstrip lines are output in two upper and lower paths; the second microstrip line is connected to the input end of the first meandering microstrip line, and the output end of the first meandering microstrip line is connected to the input end of the third meandering microstrip line via a first capacitor, a first transmission line, a first inductor, a second transmission line, a second capacitor, a third transmission line, a third capacitor, a fourth transmission line, a second inductor, a fifth transmission line and a fourth capacitor; The third microstrip line is connected to the input end of the second meandering microstrip line, and the output end of the second meandering microstrip line is connected to the input end of the fourth meandering microstrip line via the fifth capacitor, the sixth transmission line, the third inductor, the seventh transmission line, the sixth capacitor, the eighth transmission line, the seventh capacitor, the ninth transmission line, the fourth inductor, the tenth transmission line, and the eighth capacitor; and so on, the output end of the 2N-1 meandering microstrip line is connected via the (8N-7)th capacitor, the (10N-9)th transmission line, the (4N-3)th inductor, the (10N-8)th transmission line, the (8N-6)th capacitor, the (10N-7)th transmission line, the (8N-5)th capacitor, the (10N-6)th transmission line, the (4N-2)th The inductor, the (10N-5)th transmission line, the (8N-4)th capacitor are connected to the input end of the 2N+1 meander microstrip line; the output end of the 2N meander microstrip line is connected to the input end of the 2N+2 meander microstrip line via the (8N-3)th capacitor, the (10N-4)th transmission line, the (2N+1)th inductor, the (10N-3)th transmission line, the (8N-2)th capacitor, the (10N-2)th transmission line, the (8N-1)th capacitor, the (10N-1)th transmission line, the (2N+2)th inductor, the (10N)th transmission line, and the (8N)th capacitor; the output ends of the 2N+1 meander microstrip line and the 2N+2 meander microstrip line are open-circuited.

2. The UHF band RFID near-field reader antenna according to claim 1, characterized in that: The electrical length of the third microstrip line is greater than the electrical length of the second microstrip line by half a waveguide wavelength.

3. The UHF band RFID near-field reader antenna according to claim 1, characterized in that: The electrical lengths of the first meandering microstrip line and the second meandering microstrip line of the first “reverse current pair” are both one waveguide wavelength.

4. The UHF band RFID near-field reader antenna according to claim 1, characterized in that: The first capacitor is connected across the output end of the first meandering microstrip line and the input end of the first transmission line, the output end of the first transmission line is connected to the input end of the second capacitor, the two ends of the first inductor are respectively connected to the first transmission line and the second transmission line, and are connected to the first metal via through the second transmission line and then grounded; the output end of the second capacitor is connected to the input end of the third transmission line, the output end of the third transmission line is connected to the input end of the third capacitor, the output end of the third capacitor is connected to the input end of the fourth transmission line, the output end of the fourth transmission line is connected to the input end of the fourth capacitor, the output end of the fourth capacitor is connected to the input end of the third meandering microstrip line, the two ends of the second inductor are respectively connected to the fourth transmission line and the fifth transmission line, and are connected to the second metal via through the fifth transmission line and then grounded.

5. The UHF band RFID near-field reader antenna according to claim 1, characterized in that: The N "reverse current pair" units in the radiation structure are composed of a microstrip line of half a waveguide wavelength, four capacitors, five transmission lines and two inductors connected in series, and 1≤N≤8.

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