CN108767429A - Micro-strip leaky wave antenna towards the application of ultra-high-frequency passive RFID Distributed coverages - Google Patents

Abstract

The invention discloses a microstrip leakage antenna oriented to the application of UHF passive RFID distributed coverage. Slot combination, the slot combination based on the periodic figure-eight slot unit can make energy radiation along the microstrip line, so as to effectively read the passive tags in the long strip area. Finally, the reading uniformity of the tags along the antenna is improved by adjusting the resistance of the terminal load. As an RFID reader antenna, the present invention has the advantages of low cost, light weight, easy conformation, strong concealment, etc., and can be effectively applied to the fields of the Internet of Things such as libraries, storage shelves, smart homes, and security fences.

Description

Microstrip Leaky Antenna for UHF Passive RFID Distributed Coverage Applications

technical field

The invention relates to the technical field of antennas, in particular to a microstrip leaky antenna oriented to the application of UHF passive RFID distributed coverage.

Background technique

Radio Frequency Identification (RFID) technology, as a key technology for building the Internet of Things, has received more and more attention. In recent years, some new requirements have appeared in its application field, mainly in how to achieve distributed coverage for a specified area, especially when the area is a long and narrow area, such as long rows of layered bookshelves in libraries, industrial Assembly lines in production, areas monitored by security electronic fences, irregular coverage areas in smart homes, etc. Conventional directional radiating antennas are not up to the task due to their inflexible beam coverage area. In order to solve this RFID distributed coverage application requirement, the currently adopted solution generally uses multiple antennas to work simultaneously to cover a designated area, which usually increases the cost of the entire system, and the system layout complexity is relatively high.

Considering the above-mentioned characteristics of the application requirements of the Internet of Things, the specially designed periodic gap etched on the metal floor layer of the traditional microstrip line can realize energy transmission and radiation at the same time, and the formed microstrip leakage antenna is expected to provide effective RFID reader antenna. A solution to achieve distributed coverage of designated areas. Based on this, the present invention designs a microstrip leaky antenna for UHF passive RFID distributed coverage applications. The RFID antenna has a planar structure that is conducive to conformal installation and has better concealment. At the same time, it adopts physical foaming As the dielectric substrate of the microstrip line, the medium can further reduce the cost and weight, so that it can be effectively applied to the Internet of Things fields such as libraries, storage shelves, smart homes, and security fences to solve some new requirements.

Contents of the invention

The purpose of the present invention is to provide a strip-shaped microstrip leakage antenna, which can be applied as an UHF passive RFID reader antenna to realize distributed coverage of a specific narrow and long area, and then effectively identify tags in this area.

The present invention is achieved through the following technical solutions:

The microstrip leaky antenna oriented to UHF passive RFID distributed coverage application of the present invention includes a metal microstrip layer, a dielectric substrate and a metal floor layer arranged in sequence from top to bottom, and the metal floor layer is provided with periodic-based The gap combination of the character-eight gap unit.

The microstrip leaky antenna oriented to UHF passive RFID distributed coverage application of the present invention, the dielectric substrate covers FR4, F ₄ B, physical foamed dielectric board and other dielectric substrates.

In the microstrip leakage antenna oriented to the application of UHF passive RFID distributed coverage, the slot combination based on the periodic figure-of-eight slot unit is a horizontal or vertical periodic arrangement of multiple figure-of-eight slot units.

In the microstrip leakage antenna oriented to the application of UHF passive RFID distributed coverage, when the eight-character slot units based on the periodic eight-character slot unit are arranged vertically, the number of eight-character slot units is 3 or more The length and width of the slits are equal or different, and the spacing can be equal or non-equal.

In the microstrip leakage antenna oriented to the application of UHF passive RFID distributed coverage, when the slot units based on the slot combination of periodic slot units are arranged horizontally, the number of slot units is 4 or more The length and width of the slits are equal or different, and the spacing can be equal or non-equal.

In order to improve the uniformity of label reading along the line when the antenna works, the microstrip leakage antenna oriented to UHF passive RFID distributed coverage application can be appropriately changed according to the actual antenna.

From the technical solution provided by the above invention, it can be seen that the long-strip microstrip leaky antenna for UHF passive RFID near-field reading provided by the embodiment of the present invention has the characteristics of high energy leakage and long-distance transmission, and can be used as a reading The transmitter antenna realizes the distributed coverage of a specific long and narrow area.

Description of drawings

Figure 1 is a schematic diagram of the distributed coverage of a microstrip leaky antenna as a passive RFID system reader antenna.

FIG. 2 is a schematic structural diagram of a microstrip leaky antenna in an embodiment of the present invention.

Fig. 3 is a structural diagram of a vertical slot in the floor of the microstrip leakage antenna in an embodiment of the present invention.

Fig. 4 is a structural diagram of a transverse gap in the floor of the microstrip leakage antenna in an embodiment of the present invention.

FIG. 5 is a distribution curve of electric field intensity at different distances along the line of the microstrip leaky antenna in an embodiment of the present invention.

Fig. 6 is a distribution curve of electric field intensity at 30 cm under different loads of the microstrip leaky antenna in the embodiment of the present invention.

The meanings of reference numerals in the figure are: 1 is a metal microstrip line, 2 is a dielectric substrate, 3 is a metal floor layer, and 4 is a slot combination of periodic figure-eight slot units.

Detailed ways

The technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The microstrip leakage antenna applied to UHF passive RFID of the present invention, its preferred embodiment is:

It includes a metal microstrip line, a dielectric substrate layer, and a metal floor layer arranged in sequence from top to bottom, and the metal floor layer is provided with a slot combination based on a periodic figure-eight slot unit.

The slot combination based on the periodic figure-eight slot unit is a combination of multiple slots arranged horizontally or vertically

When the slot combination based on the periodic figure-eight slot unit is a multi-slot combination arranged vertically, a three-slot combination structure is adopted.

When the slot combination based on the periodic figure-eight slot unit is a multi-slot combination arranged horizontally, a four-slot combination structure is adopted.

The microstrip leakage antenna oriented to UHF passive RFID application of the present invention is used as a passive RFID reader antenna, and has the characteristic of electromagnetic signal radiation while transmitting. As an UHF passive RFID reader antenna, the microstrip leaky antenna can effectively identify tags along the antenna in a specific long and narrow area.

In the present invention, the microstrip leaky antenna adopts a long-distance design, and the length can be reasonably designed according to the requirements of the application occasion. The metal floor layer adopts a slot pattern based on a slot combination of periodic figure-eight slot units.

The slot combination based on the periodic figure-eight slot unit is in the form of multi-slot combination, and multiple slots can be arranged vertically or horizontally.

Preferably, the dielectric substrate adopts a physically foamed medium, which can effectively reduce the design cost and reduce the weight of the antenna.

Preferably, the slot combination based on the periodic figure-of-eight slot unit adopts a vertical three-slot arrangement, which can increase the energy radiation along the line when the microstrip leakage antenna is designed at a shorter distance, which is conducive to strengthening the protection against wireless antennas under the short-distance antenna structure. The reading distance of the source tag.

Preferably, the slot combination based on the periodic eight-character slot unit adopts a horizontal four-slot arrangement, which can make the microstrip leaky antenna have a relatively uniform energy distribution along the line during long-distance design, which is conducive to increasing the passiveness of the microstrip leaky antenna along the line. label recognition rate.

Preferably, when the microstrip leaky antenna is working, the terminal load can be adjusted according to the actual application to improve the label reading uniformity along the antenna.

Beneficial effects of the present invention:

The microstrip leaky antenna proposed by the present invention and applied to the UHF passive RFID system brings a brand new application mode and design mode to the microstrip leaky antenna.

1. The slit design adopted in the present invention on the microstrip floor can improve the two-way electromagnetic energy leakage, and has good application value in some application occasions.

2. The slot design of the figure-of-eight structure with longitudinal multi-slot arrangement is adopted, and the energy radiation along the line can be changed by changing the inclination angle of the slot, which ultimately makes the microstrip leakage antenna have a longer reading distance in applications with a shorter length.

3. The slot design of the eight-character structure with horizontal multi-slot arrangement is suitable for the design of long-distance microstrip leakage antennas. The horizontal arrangement structure can make the energy distribution along the line relatively uniform and improve the recognition rate of passive tags under the coverage of the antenna.

4. Compared with the traditional near-field UHF RFID reader antenna, this microstrip leaky antenna can achieve distributed coverage of a specific narrow and long area, thus effectively solving some new requirements in the field of Internet of Things.

Specific examples:

In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Referring to Fig. 2, the present invention provides a structural diagram of a microstrip leaky antenna embodiment 1 with uniform energy leakage along the line, specifically including a microstrip metal layer 1, a dielectric substrate layer 2, a metal floor layer 3, and a metal floor layer 3 based on The slot combination 4 of the periodic figure-eight slot unit.

This structure is based on the microstrip line, designed as a UHF passive RFID antenna, the working center frequency is 915MHz, the characteristic impedance of the microstrip line is 50 ohms, and the metal microstrip width w ₁ of the microstrip line layer can be determined by the microstrip The line characteristic impedance formula is obtained:

Among them, h represents the thickness of the dielectric substrate, ε _r is the relative permittivity of the dielectric substrate, and t represents the thickness of the metal layer of the microstrip line.

The period of the figure-eight slot structure adopting horizontal or vertical multi-slot arrangement can be determined by the following formula:

Where λ ₀ is the wavelength at the center operating frequency of the antenna, c is the propagation speed of electromagnetic waves in vacuum, f ₀ is the central operating frequency of the microstrip leaky antenna in the RFID system, _εr is the relative permittivity of the dielectric substrate of the microstrip leaky antenna, and P is the period length of the figure-eight slot unit.

The values of length and width of each gap are:

20mm≤L _i ≤40mm

2mm≤w _i ≤4mm

A figure-eight slit unit is formed by combining longitudinal multiple slits, as shown in Figure 3. The spacing of each slit is 10mm≤m≤20mm. Adjusting the length, width and spacing of each slit can control the energy coupling between the slit units. degree, thereby changing the overall radiation performance.

The value range of the inclination angle θ is 55°≤θ≤65°. The larger the angle θ is, the greater the longitudinal cutting current of the slit will be, the electromagnetic energy leaked along the line will increase, and the transmission loss will increase.

The principle of selecting the values of the above parameters is: the gap period P should be selected according to the design microstrip leakage antenna length and the leaky wave antenna period formula; the value range of the gap width is within the above range; the value of the gap length L is based on the floor width It is determined by the design length of the microstrip leakage antenna. When L increases, the transmission loss increases, the energy transmission distance becomes shorter, and the actual working distance of the antenna becomes shorter.

The arrangement of the eight-character gap units in the above embodiment can also be adjusted as follows:

The figure-of-eight slot unit based on the slot combination 4 of the periodic figure-of-eight slot unit is changed from a vertical multi-slot arrangement to a horizontal multi-slot parallel arrangement, as shown in Figure 4. At this time, the radiation along the line of the microstrip leakage antenna is strengthened, and the working length of the antenna is shortened.

A figure-eight slit unit is formed by combining multiple horizontal slits, and the value range of the spacing m of each horizontal slit is changed to 5mm≤m≤10mm.

Generally, when the multi-slot periodic figure-of-eight unit is used as shown in Figure 2, when the leaky microstrip line is working, the terminal load mode can choose different load forms according to the designed length and size to increase the uniformity of label reading along the antenna.

The floor slot pattern shown in Figure 3 is used as an example of numerical calculation: the example here is just to demonstrate that the above-mentioned implementation method is applied to a specific microstrip leakage antenna design, and does not mean that the above-mentioned implementation solution is only applicable to the data listed below.

The dielectric substrate is selected as a physically foamed dielectric substrate with a relative permittivity of 1.26, a dielectric substrate with a thickness of 2 mm and a width of 40 mm, a metal copper layer with a width of 40 mm and a thickness of 0.035 mm for the upper metal microstrip line. Select slot period P=243.5mm; equal length of slot L=21.3mm; equal width of slot w=4mm; equal distance between parallel slots m=16.8mm; slot inclination angle θ=59°, total length of antenna is 6 periods, long It is 1461mm.

The model simulation is carried out in the HFSS full-wave 3D electromagnetic simulation software. The input power of the microstrip leaky antenna is 1W, and the terminal is connected with a matching load. Figure 5 shows the distribution curve of the electric field intensity in the polarization direction at different distances along the microstrip leaky antenna . Calculate the electric field intensity at 30cm directly above the microstrip leakage antenna, and the electric field intensity value in more than 90% of the areas is greater than 0.8V/m. For common UHF passive tags, taking Alien 9662 as an example, its minimum activation power is generally -15dBm, and the calculated minimum electric field strength value of the corresponding activatable tag is 0.478V/m. Figure 6 shows the electric field intensity distribution curves at 30cm along the line of the microstrip leakage antenna under three special termination load modes. It can be seen from the figure that changing the matching load can improve the electric field distribution along the line and increase the tag recognition rate along the line. Therefore, the microstrip leaky antenna is used as an UHF passive RFID reader antenna. Under 1W power input, the recognition rate of the passive tag at 30cm along the microstrip line leakage antenna can reach more than 90%.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person familiar with the technical field can easily conceive of changes or modifications within the technical scope disclosed in the present invention. Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (6)

1. A microstrip leakage antenna facing UHF passive RFID distributed coverage application, characterized in that it comprises a metal microstrip line (1), a dielectric substrate (2), and a metal floor layer arranged sequentially from top to bottom (3), the metal floor layer (3) is provided with a slot combination (4) based on periodic figure-eight slot units. 2. the microstrip leakage antenna facing UHF passive RFID distributed coverage application according to claim 1, is characterized in that, described dielectric substrate (2) covers FR4, F ₄ B, physical foaming dielectric board etc. Various dielectric substrates. 3. the microstrip leakage antenna facing the UHF passive RFID distributed coverage application according to claim 1, characterized in that, the slot combination (4) based on the periodic figure-of-eight slot unit is a plurality of figure-of-eight slot units Horizontal parallel arrangement or vertical parallel arrangement. 4. according to claim 1 and 2, face the microstrip leakage antenna of UHF passive RFID distributed coverage application, it is characterized in that, when the slit combination (4) of the slit combination (4) based on the periodical slit unit The units are arranged in parallel in the longitudinal direction, the number of slit units is 3 or more, the length and width of the slits are equal or different, and the spacing can be equal or unequal. 5. according to claim 1 and 2, face the microstrip leakage antenna of UHF passive RFID distributed coverage application, it is characterized in that, when the slit combination (4) of the slit combination (4) based on the periodical slit unit The units are arranged in parallel in the horizontal direction, the number of slit units is 4 or more, the length and width of the slits are equal or different, and the spacing can be equal or unequal. 6. According to claim 1 or 2, the microstrip leakage antenna facing UHF passive RFID distributed coverage application is characterized in that, in order to improve the uniformity of label reading along the line when the antenna is working, the terminal can be appropriately changed according to the actual antenna. connected to the load form.