CN107221739B

CN107221739B - RFID reader antenna based on orthogonal slot technology

Info

Publication number: CN107221739B
Application number: CN201710439409.7A
Authority: CN
Inventors: 黄惠芬; 王彬
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2017-06-12
Filing date: 2017-06-12
Publication date: 2023-02-14
Anticipated expiration: 2037-06-12
Also published as: CN107221739A

Abstract

The invention discloses an RFID reader antenna based on an orthogonal slot technology, which comprises a dielectric substrate, wherein a Z-shaped feeder line is printed on the back surface of the dielectric substrate, a first slot, a second slot, a third slot, a fourth slot and a fifth slot are printed on the front surface of the dielectric substrate, the first slot, the second slot and the fifth slot are symmetrical relative to the diagonal line of the dielectric substrate, and the third slot and the fourth slot are symmetrical relative to the diagonal line of the dielectric substrate; the three PIN diodes are respectively arranged at the initial section, the middle section and the end section of the second gap, and the working states of the three PIN diodes are the same. The circularly polarized reader antenna disclosed by the invention covers a universal UHF frequency band and a WLAN frequency band, and has the excellent characteristics of small size, wide bandwidth, insensitivity to polarization and reconfigurable working frequency band.

Description

RFID reader antenna based on orthogonal slot technology

Technical Field

The invention relates to a reconfigurable dual-frequency circularly polarized antenna, in particular to an RFID reader antenna based on an orthogonal slot technology.

Background

In recent years, the development of RFID technology has been accelerated, and the RFID technology is gradually applied to warehouse management, retail systems, and the like. UHF (ultra high frequency 0.9 GHz) and WLAN (wireless metropolitan area network 2.45 GHz) frequency band RFID (radio frequency identification) systems have the advantages of long detection distance, high reading speed, high data transmission rate and the like, so that the RFID systems have the advantages in many practical applications. UHF frequency bands allocated by various countries are not uniform, so that the antenna needs to cover a universal UHF frequency band of 0.84-0.96 GHz. A typical RFID system consists of a reader antenna and a tag antenna, wherein the tag antenna is usually linearly polarized. Since the polarization of the tag antenna is random, the reader antenna is required to have a circular polarization characteristic so as to avoid a serious polarization mismatch between the reader antenna and the tag antenna.

The challenge in designing RFID circular polarization reader antennas today is to cover both the general UHF band (0.84-0.96 GHz) and the WLAN band (2.4-2.48 GHz) while maintaining a small size. The following are common circular polarization techniques: for the corner cut of the radiation patch, a perturbation unit, a cross dipole antenna, a feed network with 90-degree phase difference and the like are introduced into the square slot. However, these methods have disadvantages of large size and narrow bandwidth. The slot antenna has the advantages of simple structure, low profile, easy impedance matching, wide bandwidth and high radiation efficiency. Therefore, the circularly polarized antenna can be designed by using the slot, and the size can be kept small while the broadband is achieved.

Disclosure of Invention

In order to overcome the defects and shortcomings in the prior art, the invention provides the RFID reader antenna based on the orthogonal slot technology, and the reader antenna has the advantages of wide frequency band, small size, easiness in manufacturing, reconfigurable working frequency band and the like.

The invention adopts the following technical scheme:

an RFID reader antenna based on an orthogonal slot technology comprises a dielectric substrate, wherein a Z-shaped feeder line is printed on the back surface of the dielectric substrate, a first slot, a second slot, a third slot, a fourth slot and a fifth slot are printed on the front surface of the dielectric substrate, the first slot, the second slot and the fifth slot are symmetrical relative to a diagonal of the dielectric substrate, and the third slot and the fourth slot are symmetrical relative to the diagonal of the dielectric substrate;

the three PIN diodes are respectively arranged at the initial section, the middle section and the end section of the second gap, and the working states of the three PIN diodes are the same.

The first gap is formed by two L-shaped branches, the long sides of the two L-shaped branches are connected in an orthogonal mode and are symmetrical about the diagonal of the medium substrate, and openings are formed in the short sides of the two L-shaped branches.

The second slit is formed by two orthogonal L-shaped branches, and the second slit is positioned in an area surrounded by the two L-shaped branches of the first slit.

The third and fourth slits are both rectangular.

The fifth slot is formed by two mutually orthogonal rectangular branches.

And the PIN diode positioned in the middle section of the second slot is specifically arranged at the position of the front surface of the dielectric substrate corresponding to the top end branch in the Z-shaped feeder line.

The invention has the beneficial effects that:

(1) Compared with the existing antenna design applying the RFID circularly polarized reader, the bending, opening and orthogonal gaps provided by the invention can effectively reduce the size of the antenna;

(2) In the invention, the circular polarization bandwidth is effectively increased by etching the slots which are symmetrical about the diagonal line of the antenna, so that the universal UHF frequency band (0.84-0.96 GHz) and the WLAN frequency band (2.4-2.48 GHz) can be covered;

(3) The two working frequency bands can be independently adjusted, and cannot influence each other;

(4) The working frequency band can be switched by controlling the states of the 3 PIN diodes.

Drawings

FIG. 1 is a schematic structural view of the present invention;

FIG. 2 is a dimensional schematic of an embodiment of the invention;

FIG. 3 is a return loss plot of a simulation of an embodiment of the antenna of FIG. 1 after installation;

fig. 4 is an axial ratio diagram of a simulation of the implementation example of fig. 1 after the antenna is installed.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the embodiments of the present invention are not limited thereto.

Examples

As shown in fig. 1 and fig. 2, an RFID reader antenna based on orthogonal slot technology includes a dielectric substrate, the back of the dielectric substrate is printed with a Z-shaped feeder 6, the front of the dielectric substrate 8 is printed with a first, a second, a third, a fourth and a

fifth slots

1, 2, 3, 4, 5, the first slot 1, the second slot 2 and the fifth slot 5 are symmetrical with respect to the diagonal of the dielectric substrate, the third slot 3 and the fourth slot 4 are symmetrical with respect to the diagonal of the dielectric substrate, the diagonal of the dielectric substrate is the same, the diagonal of the dielectric substrate in this embodiment is the diagonal of the dielectric substrate which is obtuse angle with the positive direction of the horizontal plane, and the circular polarization bandwidth of the antenna is effectively increased.

The three PIN diodes are arranged at the initial section 7a, the middle section 7b and the final section 7c of the second gap respectively, are in the same working state, are closed or simultaneously open, and correspond to working modes of a UHF frequency band and a WLAN frequency band respectively, so that the reconstruction of the working frequency band is realized.

First gap 1 comprises two L type branches, the long limit quadrature of two L type branches is connected, and is symmetrical about the diagonal of medium base plate, the minor face of two L type branches all is equipped with the opening.

Second gap 2 comprises two orthogonal L type branches, the second gap is located the region that two L type branches of first gap enclose, two limits of two L type branches of second gap are connected perpendicularly and are formed similar M shape structure, adjacent limit contained angle is 90 degrees in the M shape structure, three PIN diodes are located initial section, interlude and the end section in second gap respectively, initial section is the horizontal direction, the end section is vertical direction, and the second gap is symmetrical about medium base plate diagonal.

The third gap 4 and the fourth gap 3 are both rectangular, the two gaps are symmetrical with respect to the diagonal line of the medium substrate, the third gap is arranged in the horizontal direction and is connected with the left side edge of the medium substrate, and the fourth gap is arranged in the vertical direction and is connected with the upper side edge of the medium substrate.

The fifth gap is formed by two mutually orthogonal rectangular branches, and the fifth gap is positioned at the tail part of a diagonal line of the medium substrate.

The Z-shaped feed line 6 is composed of three sequentially vertical branches, and a PIN diode is arranged at a position where the front surface of the dielectric substrate corresponding to the top branch of the Z-shaped feed line coincides with the middle section of the second slot, so that a broadband circularly polarized bandwidth and an impedance bandwidth are generated.

The technical scheme of the invention is realized as follows:

firstly, the circular polarization characteristic covering the general UHF frequency band is realized. The front surface of the dielectric substrate is printed with a first slot which is opened, bent and orthogonal to form a main body of UHF frequency band circular polarization radiation, the back surface of the dielectric substrate is printed with a Z-shaped feeder line, the feeder line passes through the vicinity of the center of the first slot, and the current on two orthogonal arms of the first slot forms a phase difference of 90 degrees, so that circular polarization is realized. And then, printing a third gap, a fourth gap and a fifth gap which are symmetrical and orthogonal with respect to the diagonal line of the antenna on the front surface of the dielectric substrate, so that the circularly polarized bandwidth covers the universal UHF frequency band.

Secondly, the circularly polarized characteristic of the WLAN frequency band is realized, a second gap with an opening, a bend and an orthogonal is printed to form a main body of the circularly polarized radiation of the WLAN frequency band, and the Z-shaped feeder passes through the vicinity of the center of the second gap, so that the circularly polarized characteristic of the WLAN frequency band is realized.

And finally, realizing the reconfiguration of the working frequency band. And the three PIN diodes on the front surface of the dielectric substrate are respectively positioned at two ends of the second gap and above the microstrip line, and the three PIN diodes are in a closed state or an open state at the same time and respectively correspond to working modes of a UHF frequency band and a WLAN frequency band, so that the reconstruction of the working frequency band is realized.

In order to verify the effectiveness of the present solution, specific examples are given below for explanation.

In this example, an FR4 dielectric substrate having a relative dielectric constant of 4.4, a loss tangent of 0.02 and a thickness of 0.8mm was selected, and the planar dimensions of the dielectric substrate were L × L, where L =98mm. The distance from the apex of the first slit to the left of the substrate is L1=59mm, the length of the third and fourth slits is L2=43.5mm, and the length of one side of the fifth slit is L3=42mm. The first slit has a maximum width W1=11mm, and the second, third and fourth slits have widths W2=5mm, W3=8mm, and W4=10mm, respectively. In practical implementation, a coaxial line of 50 ohms is used for direct feeding, the inner conductor of the coaxial line is connected with the microstrip feed line, and the outer conductor is connected with the radiation patch.

The simulated return loss and axial ratio results for the RFID reader antenna fabricated with the dimensions shown in fig. 2 above are shown in fig. 3 and 4, respectively. As can be seen from the figure, the RFID reader antenna has the return loss of less than-10 dB and the axial ratio of less than 3dB within 0.75-1.1GHz and 2.36-2.7GHz, and covers the common UHF frequency band (0.84-0.96 GHz) and the WLAN frequency band (2.4-2.48 GHz).

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. An RFID reader antenna based on an orthogonal slot technology is characterized by comprising a dielectric substrate, wherein a Z-shaped feeder line is printed on the back surface of the dielectric substrate, a first slot, a second slot, a third slot, a fourth slot and a fifth slot are printed on the front surface of the dielectric substrate, the first slot, the second slot and the fifth slot are symmetrical about a diagonal of the dielectric substrate, and the third slot and the fourth slot are symmetrical about the diagonal of the dielectric substrate;

the three PIN diodes are respectively arranged at the initial section, the middle section and the end section of the second gap, and the working states of the three PIN diodes are the same;

the first gap is formed by two L-shaped branches, long sides of the two L-shaped branches are connected in an orthogonal mode and are symmetrical about the diagonal line of the medium substrate, and openings are formed in the short sides of the two L-shaped branches;

the second gap is formed by two orthogonal L-shaped branches and is positioned in an area surrounded by the two L-shaped branches of the first gap;

the PIN diode is positioned in the middle section of the second gap and arranged on the position, corresponding to the front surface of the dielectric substrate, of the top end branch in the Z-shaped feeder line;

the Z-shaped feed line passes near the center of the first slot and current formation 90 occurs on the two orthogonal arms of the first slot ⁰ Phase difference, thereby realizing circular polarization.

2. The RFID reader antenna of claim 1, wherein the third and fourth slots are each rectangular.

3. The RFID reader antenna of claim 1, wherein the fifth slot is formed by two mutually orthogonal rectangular branches.