CN110867640A

CN110867640A - Near field/far field reconfigurable RFID read-write antenna

Info

Publication number: CN110867640A
Application number: CN201911247520.1A
Authority: CN
Inventors: 刘强; 常宇佳; 李国林; 杜广星
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2019-12-09
Filing date: 2019-12-09
Publication date: 2020-03-06
Anticipated expiration: 2039-12-09
Also published as: CN110867640B

Abstract

The invention provides a near field/far field reconfigurable RFID read-write antenna, and belongs to the field of microwave technology and antennas. The structure of the device is sequentially a folded oscillator with a feed arm and a non-feed arm which are not of equal width, an upper substrate, eight vertical feed copper columns, a feed network with PIN diodes, a lower substrate and a metal floor from top to bottom. One ends of the eight feed copper columns are connected to the feed network, and the other ends of the eight feed copper columns feed the folded oscillator feed arm through eight identical through holes in the upper substrate; the feed network consists of a coupling line power divider, a delay line phase shifter and a PIN diode; the PIN diode is controlled to be switched on and off by loading forward and reverse voltages at the two ends of the PIN diode, so that the current distribution on the folded vibrator is reconstructed, and the flexible switching of the read-write working states of a near field and a far field is realized. The antenna has a near/far field reconfigurable function, the magnetic field distribution is uniform in a near field mode, the read-write range is large, and the far field radiation gain is very low; under the far field mode, the radiation circular polarization wave beam has the advantages of small axial ratio, large gain and high tag reading and writing accuracy.

Description

Near field/far field reconfigurable RFID read-write antenna

Technical Field

The invention relates to the field of microwave technology and antennas, in particular to a near field/far field reconfigurable RFID read-write antenna.

Background

The radio frequency identification technology is rapidly developed in the communication field by the advantages of non-contact automatic identification. Compared with automatic identification technologies such as bar codes, optical character identification and biological identification, the RFID can simultaneously process a plurality of electronic tags and identify the distance from a few millimeters of a near field to a few meters or even dozens of meters of a far field, and has the advantages of large amount of stored information, capability of working under severe conditions and the like. With the development of RFID technology, the need for a strong and uniform magnetic field distribution in the near field and a far field with a long read/write range is more and more urgent. The diversification of the requirements enables the RFID read-write antenna to work in a near-field mode and a far-field mode to have wide market application value.

The read-write antenna is an indispensable component of the RFID system and is vital to the performance of the RFID system; in recent years, in order to simultaneously realize the near-field and far-field read-write functions of the RFID read-write antenna, a near-field segmented loop technology is often combined with a patch antenna, and the properties of segmentation lines, slotting and current direction invariance in half-wavelength are used for designing the near-far-field antenna. However, the near/far field RFID reader antenna still has some non-negligible disadvantages: when the antenna works in the near field, the remote tag is easy to be misread due to the high gain of the far field; most of the existing structural designs can affect the magnetic field distribution uniformity of the antenna in the near field when working in the far field; and far-field radiation waves are mostly linearly polarized, and the flexibility of the label is small. However, for a near field/far field reconfigurable RFID read-write antenna, no report is yet made.

In view of the above application requirements, it is necessary to provide an antenna, which obtains a strong uniform magnetic field, a large read-write range and a low far-field gain when operating in the near field, thereby solving the problem of tag misreading; when the far field works, circularly polarized radiation with higher gain is realized, so that the labels placed in any direction can be accurately read.

Disclosure of Invention

The invention provides a near field/far field reconfigurable RFID read-write antenna, aiming at the defects that the existing RFID read-write antenna capable of working in the near field and the far field simultaneously is easy to misread a remote tag when the near field works, influences the uniform distribution of a magnetic field in the near area of the antenna when the far field works, has small tag configurable orientation flexibility and the like.

In order to achieve the purpose, the invention provides a near field/far field reconfigurable RFID read-write antenna. The structure of the folded vibrator is that a feed arm and a non-feed arm are different in width, an upper substrate, eight feed copper columns, a feed network with PIN diodes, a lower substrate and a metal floor are arranged from top to bottom in sequence. One ends of the eight feed copper columns are connected to the feed network, and the other ends of the eight feed copper columns feed the folded oscillator feed arm through eight identical through holes in the upper substrate; the feed network consists of 6 identical coupling line power dividers, 5 delay line phase shifters with the electrical length of 180 degrees, 2 delay line phase shifters with the electrical length of 90 degrees and 12 PIN diodes loaded simultaneously; the forward voltage and the reverse voltage are loaded at the two ends of the PIN diode, so that the connection and the disconnection of the PIN diode are controlled, the current distribution on the folded vibrator is configured, and the near field and the far field are switched finally.

The folded dipoles are four same dipoles which are rotationally symmetrical about the center of the upper substrate, the feed arms and the non-feed arms of the folded dipoles are not equal in width, the total length of each folded dipole is lambda/2, and lambda is the wave guide wavelength.

The upper substrate and the lower substrate are both electronic device substrates; the thickness of the upper substrate and the lower substrate is 1mm, and the distance from the bottom surface of the upper substrate to the top surface of the lower substrate is 30 mm; the diameters of the eight copper columns between the substrates are all 0.5 mm.

The feed network is composed of 6 identical coupling line power dividers, 5 delay line phase shifters with the electrical length of 180 degrees, 2 delay line phase shifters with the electrical length of 90 degrees and 12 PIN diodes loaded at the same time.

The near field and far field working mode switching of the antenna is realized by controlling the connection and the disconnection of the PIN diode in the feed network. When the magnetic-field-based remote reading device works in a near field, the magnetic field is uniformly distributed, the reading and writing range is large, and the far field gain is low, so that the problem of misreading a tag positioned in a remote range is solved; when the antenna works in a far field, circularly polarized radiation is generated, the maximum gain in a UHF frequency band is 6.9dBi, and tags placed in any direction can be read.

Drawings

Fig. 1 is a 3D schematic of the present invention.

Fig. 2 is a schematic front view of the present invention.

Fig. 3 is a schematic top view of the present invention.

Fig. 4 is a schematic diagram of the feed network of the present invention.

FIG. 5 is a graph showing the reflection coefficient S of the present invention in near field or far field operation₁₁Figure (a).

Fig. 6 is a graph of magnetic field strength in the vertical direction varying along the X-axis or Y-axis 30mm above the antenna for near field operation of the present invention.

Fig. 7 is a gain plot for near field or far field operation of the present invention.

Fig. 8 is an axial ratio plot for the far field operating condition of the present invention.

Fig. 9 is a graph of magnetic field strength distribution parallel to the in-plane vertical direction of the antenna at 10mm above the antenna under near field operation of the present invention.

Fig. 10 is a graph of magnetic field strength distribution parallel to the in-plane vertical direction of the antenna at 50mm above the antenna under near field operation of the present invention.

In the figure: the antenna comprises a 1-folded oscillator, a 2-upper substrate, A3-feeding copper column, a 4-feeding network, 5-16-PIN diodes, a 17-lower substrate, a 18-metal floor, a 19-excitation port, and ports fed by the feeding network to the upper substrate, wherein the ports are A1, B1, C1, D1, A2, B2, C2 and D2.

Detailed Description

The technology of the present invention will be described in further detail with reference to the accompanying drawings, but the scope of the present invention is not limited to the description.

As shown in fig. 1 to 4, the present invention provides a near field/far field reconfigurable RFID read/write antenna, in this embodiment, the reconfigurable antenna has a side length of 200mm, an FR-4 epoxy board (dielectric constant 4.4, loss tangent 0.02) is used as an upper substrate and a lower substrate, the thicknesses are both 1mm, and the distance between the two is 30 mm. The structure of the folded dipole comprises a folded dipole 1 with a feed arm and a non-feed arm which are not of equal width, an upper substrate 2, eight feed copper columns 3, a feed network 4 with PIN diodes (5-16), a lower substrate 17 and a metal floor 18 from top to bottom. The total length of the folded dipole is 135mm, the widths of the feeding arm and the non-feeding arm are respectively 8mm and 2mm, and the distance is 1 mm. One end of each of eight feeding copper columns with the diameter of 0.5mm is connected to the feeding network, and the other end of each feeding copper column feeds power to the folded oscillator feeding arm through eight same through holes of the upper substrate.

The feed network consists of 6 identical coupled line power dividers, 5 delay line phase shifters with the electrical length of 180 degrees, 2 delay line phase shifters with the electrical length of 90 degrees and 12 PIN diodes loaded. The forward voltage and the reverse voltage are loaded at the two ends of the PIN diode, so that the connection and the disconnection of the PIN diode are controlled, the current distribution on the folded vibrator is configured, and the near field and the far field are switched finally. When the

PIN diodes

5 and 8 are conducted and the

PIN diodes

6 and 7 are cut off, the 90-degree delay line phase shifter is connected into the feed network; when the

PIN diodes

9 and 12 are conducted and 10 and 11 are cut off, the 180-degree delay line phase shifter is connected into the feed network; when the

PIN diodes

13, 16 are on and 14, 15 are off, the 90 ° delay line phase shifter is switched into the feed network.

Therefore, when the antenna works in a far-field state, the

PIN diodes

5, 8, 9, 12, 13 and 16 are conducted, the

PIN diodes

6, 7, 10, 11, 14 and 15 are cut off, the ports A1, B1, C1 and D1 sequentially form constant-amplitude signals with phase differences of 0 degrees, 180 degrees, 270 degrees and 90 degrees, and the ports A2, B2, C2 and D2 sequentially form constant-amplitude signals with phase differences of 180 degrees, 0 degrees, 90 degrees and 270 degrees; when the antenna works in a near-field state, the

PIN diodes

5, 8, 9, 12, 13 and 16 are turned off, the

PIN diodes

6, 7, 10, 11, 14 and 15 are turned on, the ports A1, B1, C1 and D1 sequentially form constant amplitude signals with phase differences of 0 degrees, 180 degrees and 0 degrees, and the ports A2, B2, C2 and D2 sequentially form constant amplitude signals with phase differences of 0 degrees, 180 degrees and 0 degrees.

The results of the specific examples are shown in FIGS. 5-10. The central frequency of the antenna near field is 915MHz, and the gain in the antenna aperture direction is lower than-15 dBi, so that the misreading of a long-distance tag is avoided. It can be seen from fig. 6, 9 and 10 that the magnetic fields above the antenna are uniformly distributed in the square region with different distances from the upper surface of the antenna and the side length of 120mm, and the magnetic field intensity is distributed in the square region with the distance of 30mm from the upper surface of the antenna at about-6.4 dB. As can be seen from fig. 5, 7 and 8, when the antenna operates in the far field, circularly polarized radiation is generated, the maximum value of the far field gain is 6.9dBic, and the axial ratio of the antenna in the frequency band of 0.77-1GHz is less than 3 dB. Therefore, the near-field far field can switch to work in the same working frequency band (902-928MHz), and has the advantages of uniform near-field magnetic field distribution, large reading and writing range, capability of avoiding misreading of a label at a long distance, wide far-field working frequency band, capability of accurately identifying the label placed in any direction and the like.

The above embodiments are only used to illustrate the technical solutions of the present invention, but the present invention is not limited thereto. Any person skilled in the art can easily conceive of variations or equivalent substitutions within the technical scope of the present disclosure, and all the variations or equivalent substitutions are included in the scope of the present disclosure, which is included in the claims of the present disclosure.

Claims

1. A near field/far field reconfigurable RFID read-write antenna is characterized in that: the structure of the device is sequentially a folded oscillator with a feed arm and a non-feed arm which are not of equal width, an upper substrate, eight vertical feed copper columns, a feed network with PIN diodes, a lower substrate and a metal floor from top to bottom.

2. The near field/far field reconfigurable RFID read-write antenna of claim 1, characterized in that: one end of each of the eight feed copper columns is connected with the feed network, and the other end of each of the eight feed copper columns feeds the folded oscillator feed arm through eight identical through holes in the upper substrate.

3. The near field/far field reconfigurable RFID read-write antenna of claim 1, characterized in that: the feed network consists of 6 identical coupled line power dividers, 5 delay line phase shifters with the electrical length of 180 degrees, 2 delay line phase shifters with the electrical length of 90 degrees and 12 PIN diodes.

4. The near field/far field reconfigurable RFID read-write antenna of claim 1, characterized in that: the PIN diode is controlled to be switched on and off by loading forward and reverse voltages at the two ends of the PIN diode, so that the current distribution on the folded vibrator is reconstructed, and the flexible switching of the read-write working states of a near field and a far field is realized.

5. The near field/far field reconfigurable RFID read-write antenna of claim 1, characterized in that: the folded vibrators are four same vibrators which are rotationally symmetrical about the center of the upper substrate, the feed arms and the non-feed arms of the folded vibrators are not equal in width, the total length of each folded vibrator is lambda/2, and lambda is the guided wave wavelength.