Ultrahigh-frequency RFID anti-serial-reading near-field antenna
By adopting a double-sided PCB structure and smooth trace design in the UHF RFID antenna, the multipath interference problem caused by the metal environment under high-density deployment is solved, realizing high-precision, short-distance tag reading, preventing tag cross-reading, and improving the reader's reading capability.
Patent Information
- Application Number
- CN202610027265.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-09
- Publication Date
- 2026-03-20
AI Technical Summary
Existing UHF near-field antennas are susceptible to the effects of metallic environments in high-density deployment scenarios, resulting in multipath interference, which reduces the reading capability of the reader and makes it easy for tag cross-reading or interference to occur.
The system employs a double-sided PCB structure, with the front side serving as the radiating surface for microstrip lines and the back side as the shielding ground. The grounding resistor and microstrip lines are connected via vias, and a smooth routing method is used to form a microstrip line layout with an arc radius larger than the line width. Impedance matching is achieved by combining an appropriate grounding resistor value.
It reduces clutter interference from the metallic environment on the antenna, achieves uniform magnetic field distribution, enhances the reader's reading capability, prevents tag misreading or cross-reading, and meets the application requirements of high-density deployment.
Smart Images
Figure CN121709925A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of microstrip antenna structure technology, and in particular to an ultra-high frequency RFID anti-cross-reading near-field antenna. Background Technology
[0002] Currently, the most common UHF near-field antennas on the market are circularly polarized near-field antennas and linearly polarized near-field antennas. Both types of antennas are based on the application method of etching microstrip lines on one side of the PCB board and removing copper on the other side, thereby generating a regional magnetic field in a limited area above / below the antenna plane. The tag is coupled through this magnetic field to receive antenna energy and signals, thereby realizing near-range tag reading. However, these two antenna forms are not suitable for application scenarios that require high-density antenna deployment.
[0003] In high-density antenna deployment applications, close antenna spacing is often required, such as 3cm. This necessitates an array deployment, such as 2... 2, 3 The third-order array configuration requires that neighboring tags not be read during tag reading, and that the tag corresponding to the antenna can be read reliably. For this application scenario, the commonly used circularly polarized near-field antenna has a PCB board with microstrip lines etched on one side and copper foil ground layer removed on the other. This configuration results in radio frequency radiation energy output from both sides of the antenna. When this antenna is assembled in a complex metallic environment, it is susceptible to the influence of the metallic environment, generating multipath interference. The superposition of multiple interference signals causes the radio frequency signal acquired by the antenna to contain strong clutter signals. Consequently, the radio frequency signal transmitted from the antenna to the reader also contains strong clutter signals, increasing the difficulty of radio frequency signal processing for the reader and reducing the reader's tag reading ability and sensitivity. Although appropriately increasing the radio frequency power can also achieve tag reading and writing, this card reading method will cause neighboring tags to be read or interfere with the reading of neighboring tags, and increases power consumption, which is not advisable.
[0004] For another type of linearly polarized near-field antenna, due to the linear polarization of the antenna, the radio frequency signal on the microstrip line will produce a vector synthesis effect, resulting in stronger radio frequency energy in the direction perpendicular to the microstrip line, which is not conducive to the deployment and application of the antenna in an equally spaced array.
[0005] Therefore, there is an urgent need for an ultra-high frequency RFID anti-cross-reading near-field antenna that can solve one or more of the above problems. Summary of the Invention
[0006] To address one or more problems existing in the prior art, this invention provides an ultra-high frequency RFID anti-crosstalk near-field antenna. The technical solution adopted by this invention to solve the above problems is: an ultra-high frequency RFID anti-crosstalk near-field antenna, comprising: a PCB, the front side of which is a radiating surface, on which a microstrip line formed by copper foil is laid; the back side of the PCB is a shielding ground, on which a copper foil layer is laid; and the PCB is provided with vias connecting the radiating surface and the shielding ground. The shield is provided with a grounding resistor, which is electrically connected to the copper foil layer. The grounding resistor is electrically connected to the terminal of the microstrip line through the via. The head of the microstrip line is electrically connected to the pin of the RF connector. The grounding resistor is used for impedance matching. The microstrip line is laid out using a smooth routing method, the radius of the arc formed by the smooth routing method is r, and the linewidth of the microstrip line is w, where r > 2w.
[0007] In some embodiments, the distance between the copper foil layer and the microstrip line is denoted as H. In the near field, the antenna readout distance is positively correlated with the value of H.
[0008] The technical effects achieved by this invention are as follows: The antenna structure reduces the influence of the metal environment on the shielding side of the PCB on the antenna to an extremely low level, thereby greatly reducing clutter interference. At the same time, it achieves impedance matching of the microstrip line on the other side, enabling the antenna to form a uniform and clearly defined magnetic field, thus enhancing the reader's ability to read tags. The layout of the microstrip line reduces interference from high-order harmonic components. By changing the H value, the antenna gain effect can be differentiated to meet practical needs.
[0009] The antenna structure described above meets the application requirements of multi-density antenna deployment scenarios, enabling short-range, high-precision, and controllable energy reading of tags, effectively preventing misreading or cross-reading of neighboring tags, and meeting the application scenario of "fixed-point reading". Attached Figure Description
[0010] Figure 1 This is a schematic diagram of the shielding ground side of the present invention; Figure 2 This is a schematic diagram of the radiating surface side of the present invention; Figure 3 This is a schematic diagram of the S11 parameters of the present invention; Figure 4 This is a three-dimensional electromagnetic field distribution diagram of the present invention at 915 MHz; Figure 5 This is the omnidirectional radiation pattern of the present invention.
[0011] In the diagram, 1 is the PCB; 10 is a via; 11 is a copper foil layer; 12 is a microstrip line; 2 is a grounding resistor; 3 is an RF connector; and 30 is a pin. Detailed Implementation
[0012] To make the above-mentioned objects, features, and advantages of the present invention more readily understood, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.
[0013] like Figure 1 , Figure 2 As shown, the present invention discloses an ultra-high frequency RFID anti-cross-reading near-field antenna, which includes: PCB1, the PCB1 is double-sided, the front side of the PCB1 is a radiating surface, the radiating surface is covered with a microstrip line 12 formed by copper foil, the back side of the PCB1 is a shielding ground, the shielding ground is covered with a copper foil layer 11, and the PCB1 is provided with a via 10 connecting the radiating surface and the shielding ground. The copper foil layer 11 is used to block the influence of the metallic environment on the microstrip line 12, so as to reduce noise interference; The shield is provided with a grounding resistor 2, which is electrically connected to the copper foil layer 11. The grounding resistor 2 is electrically connected to the terminal of the microstrip line 12 through the via 10. The head end of the microstrip line 12 is electrically connected to the pin 30 of the RF connector 3. The grounding resistor 2 is used for impedance matching. The microstrip line 12 is laid out in a smooth routing manner, the radius of the arc of the arc corner formed by the smooth routing manner is r, and the linewidth of the microstrip line 12 is w, where r > 2w; The antenna structure is electrically connected to the reader via the RF connector 3 and the RF feed line (the RF connector 3 is electrically connected to the RF feed line) to receive and transmit RF signals. The RF signals are transmitted and radiated on the microstrip line 12. The terminal of the microstrip line 12 is electrically connected to the grounding resistor 2 via the via 10 to implement RF link matching. The radio frequency connector 3 can be installed on the shielded side of the PCB1 or mounted on the side edge of the PCB1.
[0014] It should be noted that the impedance matching mentioned above is calculated through testing and engineering calculations to determine the optimal matching value or range between the grounding resistance and the antenna performance. The resistance value R of the grounding resistance 2 is selected in the range of approximately 100 ohms to 510 ohms (100 ohms ≤ R ≤ 510 ohms), and appropriate impedance matching is performed according to the length of the microstrip line 12.
[0015] The purpose of using a smooth trace and satisfying r > 2w is to eliminate or reduce parasitic capacitance effects, minimizing signal reflection and interference radiation. Specifically, parasitic capacitance effects occur when a microstrip line makes a right-angle turn, causing a higher current density on the inner side of the corner, essentially acting as a parallel capacitor. This introduces parasitic capacitance, which lowers the characteristic impedance at the corner. This impedance reduction creates a discontinuity at the corner, enhancing signal energy reflection and reducing energy radiation into space. Simultaneously, the abrupt change in current at the corner leads to charge accumulation, forming a monopole antenna at the corner, resulting in unnecessary electromagnetic radiation and electromagnetic interference.
[0016] The near-field antenna operates primarily by coupling energy between the antenna's magnetic field and the tag. Therefore, the tag's readability is directly related to the magnetic field strength distribution in the near-field region of the antenna. To obtain different magnetic field strengths and meet different reading distance requirements, the distance between the copper foil layer 11 and the microstrip line 12 is denoted as H. Within the near-field range, the antenna's reading distance is positively correlated with the value of H.
[0017] For example, in the near field, as the H value decreases, the magnetic field strength between the microstrip line and the shielding ground is weakened, resulting in a shorter reading distance; conversely, the reading distance increases. Specifically, when increasing the H value to improve the reading distance, it is necessary to ensure that the antenna radiation efficiency meets the requirements. If it does not, the H value cannot be increased further; that is, the H value cannot be too large, as an excessively large H value is also detrimental to impedance matching. In other words, the distance for reading the tag is changed by adjusting the dielectric thickness of the PCB1.
[0018] The above antenna structure was tested and verified using actual equipment: Test environment: 1. Room temperature 25 degrees Celsius, humidity less than 90%; 2. RF output power set to 20 dBm; 3. Antenna assembly space interval 3 cm, forming 2 2. Array, 4PCS antennas polling tags; 4. UHF tags using 28 The antenna is 10mm in diameter and the chip is Impinj M4QT.
[0019] Test results: Data was read 100,000 times, and there were 3 instances of cross-referencing. The probability of cross-referencing was less than 1 / 10,000, demonstrating excellent practical performance. The test results were also far better than the cross-referencing rate of hundreds of tags currently used by the customer.
[0020] Combination Figure 3 As shown, Figure 3 The S11 parameter diagram of the antenna structure in this application is shown. To verify the impedance matching status of the antenna structure at different frequencies (characteristic impedance is 50 ohms), the Mark point frequencies are selected as 866MHz, 915MHz, and 922MHz, respectively. In S11, 1 corresponds to 915MHz, 2 corresponds to 866MHz, and 3 corresponds to 922MHz. Figure 3 As shown on the Smith chart on the right, their impedance matching is 49.179 ohms, 55.125 ohms, and 47.948 ohms, respectively; as Figure 3 As shown in the top left figure, their return losses are -17.883dB, -19.998dB, and -17.751dB, respectively, demonstrating excellent matching of the antenna structure within the aforementioned operating frequency bands; Figure 3 As shown in the lower left figure, their VSWRs are 1.2925, 1.2223, and 1.2977, respectively, demonstrating excellent antenna structure matching within the aforementioned operating frequency bands. Combined with... Figure 3 The return loss, VSWR, and Smith chart waveforms show that the impedance matching of the antenna is close to the characteristic impedance of 50 ohms, achieving good impedance matching within the product's application frequency band.
[0021] Combination Figure 4 As shown, Figure 4 This is a three-dimensional electromagnetic field distribution diagram of the antenna structure of this application at 915MHz. In the diagram, red indicates a larger electric field strength and blue indicates a weaker electric field strength. The diagram shows that the electric field strength is stronger in the direction perpendicular to the radiating surface of the antenna plate and weaker in the direction along the antenna plate (and the side of the antenna). That is, a uniform and clearly defined magnetic field can be formed in the direction perpendicular to the radiating surface of the antenna plate, which enhances the reader's ability to read tags.
[0022] Combination Figure 5 As shown in the figure, this figure is the radiation pattern of the electric field E of the antenna structure. It can be seen from the figure that in the direction of maximum radiation of the main lobe of the circularly polarized antenna, the amplitude of the LHCP component is larger than that of the RHCP component. Therefore, the antenna can be identified as a left-hand circularly polarized antenna. The antenna gain is approximately -4.8 dB.
[0023] In summary, the antenna structure described above minimizes the impact of the metallic environment on the shielding side of the PCB, significantly reducing clutter interference. Simultaneously, it achieves impedance matching of the microstrip lines on the other side, enabling the antenna to generate a uniform and clearly defined magnetic field, enhancing the reader's tag recognition capability. The microstrip line layout reduces interference from higher harmonic components. Furthermore, by varying the H value, the antenna gain effect can be differentiated to meet practical requirements.
[0024] The antenna structure described above meets the application requirements of multi-density antenna deployment scenarios, enabling short-range, high-precision, and controllable energy reading of tags, effectively preventing misreading or cross-reading of neighboring tags, and meeting the application scenario of "fixed-point reading".
[0025] The embodiments described above are merely illustrative of one or more implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.
Claims
1. A near-field antenna for preventing cross-reading of ultra-high frequency RFID, characterized in that, The PCB has a radiating surface on its front side, on which a microstrip line formed by copper foil is laid. The back side of the PCB is a shielding ground, on which a copper foil layer is laid. The PCB is provided with vias connecting the radiating surface and the shielding ground. The shield is provided with a grounding resistor, which is electrically connected to the copper foil layer. The grounding resistor is electrically connected to the terminal of the microstrip line through the via. The head of the microstrip line is electrically connected to the pin of the RF connector. The grounding resistor is used for impedance matching.
2. The UHF RFID anti-crosstalk near-field antenna according to claim 1, characterized in that, The distance between the copper foil layer and the microstrip line is denoted as H. In the near field, the antenna's readout distance is positively correlated with the value of H.
3. The UHF RFID anti-crosstalk near-field antenna according to claim 1, characterized in that, The grounding resistor has a resistance value of 100 ohms to 510 ohms.
4. The UHF RFID anti-crosstalk near-field antenna according to claim 1, characterized in that, The microstrip line is laid out using a smooth routing method, the radius of the arc formed by the smooth routing method is r, and the linewidth of the microstrip line is w, where r > 2w.