CN107221739B - RFID reader antenna based on orthogonal slot technology - Google Patents

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

An 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 orthogonal slot technology.

Background technique

In recent years, RFID technology has developed faster and faster, and is gradually applied to warehouse management and retail systems. RFID (Radio Frequency Identification) systems in the UHF (Ultra High Frequency 0.9GHz) and WLAN (Wireless Metropolitan Area Network 2.45GHz) bands have shown advantages in many practical applications due to their advantages such as long detection distance, fast reading speed and high data transmission rate. The UHF frequency band allocated by each country is not uniform, so the antenna needs to cover the general UHF frequency band of 0.84-0.96GHz. A typical RFID system consists of a reader antenna and a tag antenna, where the tag antenna is usually linearly polarized. Since the polarization of the tag antenna is random, the reader antenna is required to have circular polarization characteristics so as to avoid serious polarization mismatch between the reader antenna and the tag antenna.

The current challenge in designing circularly polarized reader antennas for RFID is to cover the common UHF frequency band (0.84-0.96GHz) and WLAN frequency band (2.4-2.48GHz) while maintaining a small size. Common circular polarization techniques include the following: cutting the corners of the radiation patch, introducing perturbation units into square slots, crossed dipole antennas, and feed networks with 90° phase difference. However, these methods have the disadvantages of large size and narrow bandwidth. The slot antenna has simple structure, low profile, easy impedance matching, wide bandwidth and high radiation efficiency. Therefore, designing circularly polarized antennas with slots can achieve broadband while maintaining a small size.

Contents of the invention

In order to overcome the shortcomings and deficiencies of the prior art, the present invention provides an RFID reader antenna based on orthogonal slot technology. The reader antenna has the advantages of wide frequency band, small size, easy manufacture, and reconfigurable working frequency band.

The present invention adopts following technical scheme:

An RFID reader antenna based on orthogonal slot technology, including a dielectric substrate, a Z-shaped feeder is printed on the back of the dielectric substrate, and the first, second, third, fourth and fifth slots are printed on the front of the dielectric substrate, The first slit, the second slit, and the fifth slit are all symmetrical to the diagonal of the dielectric substrate, and the third and fourth slits are symmetrical to the diagonal of the dielectric substrate;

It also includes three PIN diodes, which are respectively arranged at the initial section, the middle section and the end section of the second slit, and the working states of the three PIN diodes are the same.

The first slit is composed of two L-shaped branches, the long sides of the two L-shaped branches are connected orthogonally, and are symmetrical about the diagonal of the dielectric substrate, and the short sides of the two L-shaped branches are provided with Open your mouth.

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

The third and fourth slits are both rectangular.

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

The PIN diode located in the middle section of the second slit is specifically arranged on the front side of the dielectric substrate corresponding to the top branch of the Z-shaped feeder.

Beneficial effects of the present invention:

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

(2) In the present invention, the circular polarization bandwidth is effectively increased by etching symmetrical slits about the antenna diagonal, so as to cover the general UHF frequency band (0.84-0.96GHz) and the WLAN frequency band (2.4-2.48GHz);

(3) In the present invention, the two operating frequency bands can be adjusted independently without mutual influence;

(4) In the present invention, the working frequency band can be switched by controlling the states of the three PIN diodes.

Description of drawings

Fig. 1 is a structural representation of the present invention;

Fig. 2 is the size schematic diagram of the embodiment of the present invention;

Fig. 3 is the return loss diagram of implementing the example simulation after the antenna is installed in Fig. 1;

Fig. 4 is an axial ratio diagram of the example simulation after the antenna in Fig. 1 is installed.

Detailed ways

The present invention will be described in further detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

Example

As shown in Figure 1 and Figure 2, an RFID reader antenna based on orthogonal slot technology includes a dielectric substrate, the Z-shaped feeder 6 is printed on the back of the dielectric substrate, and the first and second , the third, fourth and fifth slits 1, 2, 3, 4, 5, the first slit 1, the second slit 2 and the fifth slit 5 are all symmetrical about the dielectric substrate diagonal, the third slit 3 and the fourth gap 4 are symmetrical about the diagonal of the dielectric substrate, and the diagonal of the dielectric substrate is the same. In this embodiment, the diagonal of the dielectric substrate is the diagonal of the dielectric substrate that forms an obtuse angle with the positive direction of the horizontal plane , effectively increasing the circular polarization bandwidth of the antenna.

It also includes three PIN diodes, which are respectively arranged in the initial section 7a, the middle section 7b and the end section 7c of the second gap. The working states of the three PIN diodes are the same, and they are closed or open at the same time, respectively corresponding to the UHF frequency band and WLAN frequency band working mode, so that the working frequency band can be reconfigured.

The first gap 1 is composed of two L-shaped branches, the long sides of the two L-shaped branches are connected orthogonally, and are symmetrical about the diagonal line of the dielectric substrate, and the short sides of the two L-shaped branches are set There are openings.

The second slit 2 is composed of two orthogonal L-shaped branches, the second slit is located in the area surrounded by the two L-shaped branches of the first slit, and the two L-shaped branches of the second slit The two sides are vertically connected to form a similar M-shaped structure, the angle between adjacent sides in the M-shaped structure is 90 degrees, and the three PIN diodes are respectively located at the beginning section, the middle section and the end section of the second slit. The initial section is in the horizontal direction, the ending section is in the vertical direction, and the second slit is symmetrical with respect to the diagonal of the dielectric substrate.

Both the third slit 4 and the fourth slit 3 are rectangular, and the two slits are symmetrical to the diagonal of the dielectric substrate, the third slit is arranged in the horizontal direction and is connected to the left edge of the dielectric substrate, and the fourth slit is vertical The direction is set and connected with the upper side edge of the dielectric substrate.

The fifth slit is formed by two mutually orthogonal rectangular branches, and the fifth slit is located at the end of the diagonal line of the dielectric substrate.

The Z-shaped feeder 6 is composed of three successively vertical branches, and a PIN diode is arranged at the overlap between the front position of the dielectric substrate corresponding to the top branch and the middle section of the second slit, thereby generating a broadband circular polarization bandwidth and impedance bandwidth, In this embodiment, the top branches are arranged in the horizontal direction.

Technical scheme realization process of the present invention is as follows:

The first is to realize the circular polarization characteristic covering the common UHF frequency band. Print an open, bent, and orthogonal first slit on the front of the dielectric substrate to form the main body of circularly polarized radiation in the UHF frequency band, and print a Z-shaped feeder on the back of the dielectric substrate. The current on the two arms of the intersection forms a 90° phase difference, thereby realizing circular polarization. Then, the third slot, the fourth slot, and the fifth slot that are symmetrical and orthogonal to the antenna diagonal are printed on the front of the dielectric substrate, so that the circular polarization bandwidth covers the general UHF frequency band.

The second is to realize the circular polarization characteristics of the WLAN frequency band. Print an open, bent, and orthogonal second slot to form the main body of the circularly polarized radiation in the WLAN frequency band. Achieve circular polarization characteristics.

Finally, the reconfigurability of the working frequency band is realized. The three PIN diodes on the front of the dielectric substrate are respectively located at the two ends of the second gap and above the microstrip line. The states of the three PIN diodes are closed or open at the same time, corresponding to the UHF frequency band and WLAN frequency band working modes, so as to achieve the working mode Band reconfigurable.

In order to verify the effectiveness of this scheme, a specific example is given below to illustrate.

In this example, an FR4 dielectric substrate with a relative permittivity of 4.4, a loss tangent of 0.02, and a thickness of 0.8 mm is selected. The plane size of the dielectric substrate is L×L, where L=98 mm. The distance from the apex of the first slit to the left side 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 widest width of the first slit is W1=11mm, and the widths of the second, third and fourth slits are respectively W2=5mm, W3=8mm, W4=10mm. In actual implementation, a 50-ohm coaxial line is used for direct feeding, the inner conductor of the coaxial line is connected to the microstrip feeder line, and the outer conductor is connected to the radiation patch.

The simulated return loss and axial ratio results of the RFID reader antenna manufactured with the size shown in Figure 2 above are shown in Figure 3 and Figure 4, respectively. It can be seen from the figure that the RFID reader antenna has a return loss of less than -10dB and an axial ratio of less than 3dB within 0.75-1.1GHz and 2.36-2.7GHz, covering the general UHF frequency band (0.84-0.96GHz) and the WLAN frequency band (2.4- 2.48GHz).

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the embodiment, and any other changes, modifications, substitutions and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (3)

1. An RFID reader antenna based on orthogonal slot technology, characterized in that it comprises a dielectric substrate, the Z-shaped feeder is printed on the back side of the dielectric substrate, and the first, second, third, and third are printed on the front side of the dielectric substrate Fourth and fifth slits, the first slit, the second slit, and the fifth slit are all symmetrical to a diagonal of the dielectric substrate, and the third and fourth slits are symmetrical to the diagonal of the dielectric substrate; It also includes three PIN diodes, which are respectively arranged at the initial section, the middle section and the end section of the second slit, and the working states of the three PIN diodes are the same; The first slit is composed of two L-shaped branches, the long sides of the two L-shaped branches are connected orthogonally, and are symmetrical with respect to the diagonal line of the dielectric substrate, and the short sides of the two L-shaped branches are both has an opening; The second slit is composed of two orthogonal L-shaped branches, and the second slit is located in the area surrounded by the two L-shaped branches of the first slit; The PIN diode located in the middle section of the second slit is arranged on the front side of the dielectric substrate corresponding to the top branch in the Z-shaped feeder; The Z-shaped feeder passes near the center of the first slot, and the currents on the two orthogonal arms of the first slot form a 90 ^° phase difference, thereby realizing circular polarization. 2. The RFID reader antenna according to claim 1, wherein the third and fourth slots are both rectangular. 3. The RFID reader antenna according to claim 1, characterized in that, the fifth slot is composed of two mutually orthogonal rectangular branches.

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