RFID near-field antenna with uniform magnetic field over a wide range based on multi-unit coupling

Abstract

The present invention discloses a RFID near-field antenna with uniform magnetic field over a wide range based on multi-unit coupling, which is mainly composed of a rectangular dielectric substrate, two sections of bent microstrip lines and a 180° phase shifter close to its upper surface, a metal ground close to its lower surface, and two surface resistors close to its right side. The present invention increases the impedance bandwidth of the RFID antenna by adding matching resistors on the basis of the original RFID near-field antenna, and improves the uniformity of the magnetic field distribution of the RFID antenna by using a multi-unit coupling design that shifts and inserts the bent microstrip line units. While ensuring that the impedance bandwidth covers the entire UHF RFID frequency band, the antenna achieves uniform reading and writing functions for tags over a wide range.

Description

Technical Field

[0001] The invention relates to a large-range magnetic field uniform RFID near-field antenna based on multi-unit coupling, and belongs to the technical field of electromagnetic communication and microwave devices. Background Art

[0002] Radio frequency identification (RFID) technology refers to the use of radio frequency signals to achieve spatial coupling between the transmitting antenna and a specific target, and the receiving antenna transmits the coupled frequency signal carrying the target information to the reader for analysis, so as to achieve the purpose of contactless identification of specific targets. The operating frequency bands of RFID systems can be mainly divided into: low frequency band (LF: 125KHz ~ 134KHz), high frequency band (HF: 13.56MHz), ultra-high frequency band (UHF: 860MHz ~ 960MHz) and microwave band (2.45GHz and 5.8GHz). Traditional ultra-high frequency band RFID antennas basically transmit frequency signals through electric field coupling. This type of RFID system has the ability to identify tags at a long distance and has a fast tag identification speed. However, electric field coupling is easily affected by high dielectric constant materials such as liquids, which in turn affects the tag identification results; while magnetic field coupling has strong anti-interference ability and does not have strict requirements on the surrounding environment.

[0003] Judging from the current research status at home and abroad, most of the current research on RFID near-field antennas based on magnetic field coupling focuses on expanding the reading range of near-field antennas. There is little research on improving the uniformity of magnetic field distribution while expanding the reading range, which is a difficult point in research. Summary of the invention

[0004] The present invention relates to a RFID near-field antenna with a large-range uniform magnetic field based on multi-unit coupling. Specifically, a RFID near-field antenna with a large-range uniform magnetic field based on multi-unit coupling is provided. By performing a multi-unit coupling design with displacement and insertion on the basis of the original RFID near-field antenna, the uniformity of the antenna magnetic field distribution is improved, so as to solve the problem in the prior art that the reading distance and reading range of the near-field antenna cannot be well performed at the same time.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A multi-unit coupling-based RFID near-field antenna with uniform magnetic field over a wide range comprises a rectangular dielectric substrate, an antenna feeder, two bent metal microstrip lines, a 180° phase shifter, a rectangular metal ground, and two identical first and second resistors; the two bent metal microstrip lines comprise an upper bent microstrip line and a lower bent microstrip line, the 180° phase shifter is composed of metal microstrip lines of corresponding lengths, and the 180° phase shifter is connected between the antenna feeder and the upper bent microstrip line; the first resistor on the right side of the dielectric substrate is connected between a terminal of the upper bent microstrip line and the metal ground, and the second resistor on the right side of the dielectric substrate is connected between a terminal of the lower bent microstrip line and the metal ground.

[0007] Preferably, the upper section of the meander microstrip line and the lower section of the meander microstrip line are each composed of six bending units, and the total length of each bending unit is equal to the length of the operating wavelength.

[0008] Preferably, the antenna feed line, the 180° phase shifter and the two sections of bent metal microstrip lines have equal line widths.

[0009] Preferably, the two identical first and second resistors are both sheet resistors, the widths of the two sheet resistors are equal to the height of the rectangular dielectric substrate, and the size of the metal ground is the same as that of the dielectric substrate.

[0010] Preferably, the dielectric substrate is made of Rogers 5880.

[0011] Preferably, the size of the dielectric substrate is 500 mm*200 mm*1.6 mm.

[0012] Preferably, the line width of the 180° phase shifter and the metal microstrip line is 4.94 mm.

[0013] Preferably, the resistance value of the two identical surface resistors is 50Ω.

[0014] Preferably, the thickness of the metal ground is 0.035 mm, and the material is metallic copper.

[0015] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0016] The present invention is based on the design of a large-range magnetic field uniform RFID near-field antenna with multi-unit coupling. At the same time, matching resistance is added to the terminal to ensure that the impedance bandwidth of the antenna covers the entire UHF RFID frequency band. Through the multi-unit coupling design of shifting and plugging the bent microstrip line units, the antenna realizes the uniform reading and writing function of the tag in a large range. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the overall structure diagram of the RFID near-field antenna with a large-range magnetic field uniformity based on multi-unit coupling of the present invention, wherein (a) is a top view and (b) is a bottom view.

[0018] Figure 2 This is a simulation diagram of the reflection coefficient of the antenna structure.

[0019] Figure 3 This is the surface current distribution diagram of the antenna structure at the frequency of 880MHz.

[0020] Figure 4 It is the magnetic field intensity distribution diagram of the antenna structure at the frequency point of 880MHz and the horizontal plane at the height of z=10mm.

[0021] Among them, 1-antenna feed line, 2-180° phase shifter, 3-upper section bent microstrip line, 4-lower section bent microstrip line, 5-first surface resistor, 6-second surface resistor, 7-Rogers 5880 dielectric substrate, 8-metal ground. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0023] like Figure 1 As shown, the multi-unit coupled large-range magnetic field uniform RFID near-field antenna of the present invention is composed of an antenna feed line 1, a 180° phase shifter 2, an upper section meandering microstrip line 3, a lower section meandering microstrip line 4, surface resistors 5 and 6, a Rogers 5880 dielectric substrate 7, and a metal ground 8. The antenna feed line 1 is used to feed the 180° phase shifter, the upper section meandering microstrip line 3, the lower section meandering microstrip line 4, the first surface resistor 5, and the second surface resistor 6. The 180° phase shifter 2 close to the upper surface of the Rogers 5880 dielectric substrate 7 is connected between the antenna feed line 1 and the upper curved microstrip line 3. This design can make the surface currents on the upper curved microstrip line 3 and the lower curved microstrip line 4 have opposite phases; the surface resistor 5 close to the right side of the Rogers 5880 dielectric substrate 7 is connected between the terminal of the upper curved microstrip line 3 and the metal ground 8, and the surface resistor 6 close to the right side of the Rogers 5880 substrate 7 is connected between the terminal of the lower curved microstrip line 4 and the metal ground 8. This traveling wave structure design can increase the impedance bandwidth of the RFID near-field antenna.

[0024] in, Figure 1(a) is a top view, and 1(b) is a bottom view. The upper section of the meandering microstrip line 3 and the lower section of the meandering microstrip line 4 close to the upper surface of the Rogers 5880 substrate 7 are geometrically displaced and inserted. Such a multi-unit coupling design greatly improves the uniformity of the magnetic field intensity distribution of the RFID near-field antenna.

[0025] On the lower surface of the Rogers 5880 substrate 7, there is a metal ground 8 of the same size. The metal ground 8 is directly connected to the first and second surface resistors 5 and 6. The thickness of the metal ground 8 is 0.035 mm, and the material is metal copper. Its function is to provide a floor for the microstrip antenna. The reason why the size of the metal ground 8 is the same as that of the Rogers 5880 substrate 7 is that it can provide the best floor reflection effect within the maximum area allowed. The metal ground 8 is used in conjunction with the upper bending microstrip line 3 and the lower bending microstrip line 4 to improve the uniformity of the antenna magnetic field distribution. The metal ground 8 is used in conjunction with the surface resistors 5 and 6 to improve the impedance bandwidth of the antenna. The line widths of the antenna feed line 1, the 180° phase shifter 2, the upper bending microstrip line 3 and the lower bending microstrip line 4 affect the input port impedance of the antenna. The spacing between the upper bending microstrip line 3 and the lower bending microstrip line 4 affects the uniformity of the magnetic field intensity distribution of the RFID near-field antenna. The resistance values ​​of the surface resistors 5 and 6 affect the reflection coefficient of the antenna and the uniformity of the magnetic field intensity distribution.

[0026] like Figure 2 As shown, it is a reflection coefficient simulation diagram of the antenna structure. The -10dB impedance bandwidth of the antenna reaches 820~980MHz, which can cover the internationally used UHF RFID frequency band range (860~960MHz).

[0027] like Figure 3 As shown, it is the surface current distribution diagram of the antenna structure at the frequency point of 880MHz. The currents on the upper meander microstrip line 3 and the lower meander microstrip line 4 are both distributed in traveling waves with a phase difference of 180°.

[0028] like Figure 4 As shown, it is the magnetic field strength distribution diagram of the antenna structure at the frequency point of 880MHz and the horizontal plane at a height of z=10mm. The average magnetic field strength above the upper curved microstrip line 3 and the lower curved microstrip line 4 reaches -12.3dBA / m and -14.8dBA / m respectively. The magnetic field distribution has good uniformity within the range of 500*140mm and can meet the threshold requirement (-24dBA / m) of RFID system tag reading.

[0029] Finally, those skilled in the art should know that the choice of dielectric substrate material does not necessarily require Rogers 5880, as long as the relative dielectric constant and thickness meet the resonance requirements.

[0030] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A RFID near-field antenna with uniform magnetic field over a wide range based on multi-unit coupling, characterized in that: The invention comprises a rectangular dielectric substrate, an antenna feed line, two bent metal microstrip lines, a 180° phase shifter, a rectangular metal ground, and two identical first resistors and second resistors; the two bent metal microstrip lines comprise an upper bent microstrip line and a lower bent microstrip line, the 180° phase shifter is composed of metal microstrip lines of corresponding lengths, and the 180° phase shifter is connected between the antenna feed line and the upper bent microstrip line; The first resistor on the right side of the dielectric substrate is connected between the terminal of the upper bent microstrip line and the metal ground, the second resistor on the right side of the dielectric substrate is connected between the terminal of the lower bent microstrip line and the metal ground, the upper bent microstrip line and the lower bent microstrip line are both composed of six bending units, the total length of each bending unit is equal to the length of the working wavelength, the antenna feed line, the 180° phase shifter and the two bent metal microstrip lines have the same line width, the two identical first and second resistors are both surface resistors, the widths of the two surface resistors are equal to the height of the rectangular dielectric substrate, and the size of the metal ground is the same as the size of the dielectric substrate.

2. The large-range magnetic field uniform RFID near-field antenna based on multi-unit coupling according to claim 1 is characterized in that: The material of the dielectric substrate is Rogers5880.

3. The large-range magnetic field uniform RFID near-field antenna based on multi-unit coupling according to claim 1, characterized in that: The size of the dielectric substrate is 500 mm*200 mm*1.6 mm.

4. The large-range magnetic field uniform RFID near-field antenna based on multi-unit coupling according to claim 1, characterized in that: The line width of the 180° phase shifter and the metal microstrip line is 4.94 mm.

5. The large-range magnetic field uniform RFID near-field antenna based on multi-unit coupling according to claim 4, characterized in that: The resistance value of the two identical sheet resistors is 50Ω.

6. The large-range magnetic field uniform RFID near-field antenna based on multi-unit coupling according to claim 1, characterized in that: The thickness of the metal ground is 0.035 mm, and the material is metal copper.

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