CN108429004A - Radio frequency identification (RFID) labels antenna and its implementation - Google Patents

Abstract

The present invention provides a radio frequency identification RFID tag antenna, comprising: a dielectric substrate, a dielectric bottom plate, and an antenna radiation plate, wherein the dielectric substrate, the dielectric bottom plate, and the antenna radiation plate form a rectangular microstrip patch structure, so as to concentrate the current and make the current flow to Uniform; a pair of T-shaped slots are symmetrically opened on the antenna radiation plate to increase the current path and inductive reactance; a feed point for matching antennas with different input impedances with RFID tag chips with different impedances is set between a pair of T-shaped slots . The antenna of the present invention has the characteristics of wide frequency band and miniaturization, and is suitable for UHF band RFID standards in different countries and regions. The tag antenna has certain stability when attached to the surface of a metal object, and can reach a communication distance of more than five meters. The purpose of saving production and labor costs can be achieved. In addition, the present invention also provides a method for realizing the RFID tag antenna.

Description

Radio frequency identification RFID tag antenna and its realization method

technical field

The invention belongs to the technical field of antennas, and relates to a radio frequency identification (RFID) tag antenna and a realization method thereof.

Background technique

Radio frequency identification (RFID, Radio Frequency Identification) technology is a kind of automatic identification technology. It is a technology for non-contact two-way data communication through radio frequency to identify targets and obtain relevant data. RFID technology can complete information input and processing without human intervention, direct contact, or optical visibility. It can work in various harsh environments, can identify high-speed moving objects, and can identify multiple objects at the same time.

When an ordinary tag antenna is directly placed on the surface of a metal object, its gain, input impedance and other performances will all change greatly. In response to this situation, most of the current methods are to place the label above a certain height from the surface of the metal object, but this will increase the cost, the performance of the label is very unstable, and its processing and installation are also inconvenient and other negative effects.

The performance design of the RFID antenna directly determines the performance of the entire RFID system, including the reading distance and cost of the system. At present, the research at this stage mainly focuses on antenna technology in the UHF and microwave frequency bands. Impedance matching between tag antenna and tag chip is one of the key issues, good impedance matching can achieve longer reading distance. From the point of view of manufacturing cost, it is required that the size of the tag antenna and the reader antenna be as small as possible while keeping the performance of the antenna unchanged. As we all know, the manufacture of RFID products must comply with the standards set by the user's country and regional standard organizations, so the differences in standards make the design and production of products more complicated and expensive. For example, in Europe, the ultra-high frequency (UHF, Ultra-high frequency) determined by RFID is 866-869MHz, and in Japan and some Asian countries, it is 952-955MHz. (Trial) The 800/900MHz frequency band is divided into two frequency bands 840-845MHz and 920-925MHz for RFID applications. Therefore, how to design a miniaturized tag antenna with broadband characteristics to be applicable to the standards of different countries and regions is a technical challenge.

Another problem is that the performance of RFID tag antennas based on free-space designs can become unstable on metal surfaces because electromagnetic waves are reflected by metals. Therefore, how to design a tag antenna that can be applied in a metal environment is also a technical problem.

Contents of the invention

The purpose of the present invention is to solve the defects in the above-mentioned prior art, and propose a radio frequency identification RFID tag antenna, which has the characteristics of wide frequency band and miniaturization, and is suitable for UHF band RFID standards in different countries and regions, and can be attached to the surface of metal objects. The time tag antenna has a certain stability and can reach a communication distance of more than five meters, which can achieve the purpose of saving production and labor costs. In addition, the present invention also provides a method for realizing the RFID tag antenna.

In order to achieve the above-mentioned purpose of the present invention, the present invention provides a kind of radio frequency identification RFID tag antenna on the one hand, comprising: dielectric substrate; The dielectric bottom plate that is arranged on the dielectric substrate lower layer, its lower surface is used to stick on the upper surface of metal object; Set The antenna radiating plate on the upper layer of the dielectric substrate; wherein, the dielectric substrate, the dielectric bottom plate and the antenna radiating plate form a rectangular microstrip patch structure; a pair of T-shaped slots are symmetrically opened on the antenna radiating plate; the pair of T A feed point for matching antennas with different input impedances with RFID tag chips with different impedances is arranged between the slots.

Wherein, the T-shaped slot is an open slot opened at the long side end of the antenna radiation plate.

Wherein, the long arm of the opening slot extends along the length direction of the antenna radiation plate.

Wherein, the short arm of the T-shaped slot is vertically connected to the long arm, and extends toward the short side along the width direction of the antenna radiation plate.

Wherein, the pair of short arms of the pair of T-shaped slots protrude from each other.

Wherein, the feed point is arranged between the pair of long arms of the pair of T-shaped slots.

Wherein, the feed point is located on the part between the long side end of the antenna radiation plate and the short arm of the T-shaped slot.

In addition, the present invention also provides a method for realizing the radio frequency identification RFID tag antenna, including:

setting a dielectric bottom plate on the lower surface of the dielectric substrate;

An antenna radiation plate is arranged on the upper surface of the dielectric substrate;

Wherein, the antenna radiating plate is made into a rectangle so as to concentrate the current and make the current flow uniform;

Wherein, a pair of T-shaped slots are symmetrically opened on the antenna radiation plate, so as to increase the current path and inductive reactance, and ensure that the microstrip patch structure can be well matched with the RFID tag chip when it is attached to the surface of the metal object;

Wherein, a feed point for matching antennas with different input impedances with RFID tag chips with different impedances is set between the pair of T-shaped slots.

Preferably, the input impedance of the antenna is adjusted by changing the length and width of the long arms of the pair of T-shaped slots.

Preferably, the input impedance of the antenna is adjusted by adjusting the position of the feed point between the pair of T-shaped slots.

Compared with the prior art, the RFID tag antenna of the present invention and its implementation method have the following advantages:

1. The radio frequency identification RFID tag antenna of the present invention adopts a rectangular microstrip patch structure, which can achieve the purpose of concentrating current, making the current flow uniform, and then achieving the purpose of increasing antenna gain.

2. The radio frequency identification RFID tag antenna of the present invention has symmetrical double T-shaped slots on the antenna radiation plate. On the one hand, it can concentrate the current flow direction, avoid the occurrence of circulating current as much as possible, and then improve the antenna gain and communication distance. On the other hand, it cuts off the original The surface current path on the radiation plate makes the current flow around the edge of the groove and the path becomes longer. In the equivalent circuit of the antenna, it is equivalent to introducing a cascaded inductance, so that the input impedance of the antenna presents a large inductive reactance, which can be compared with the impedance. The tag chip with a large capacitive reactance achieves a good match, that is, to ensure that the tag antenna can still achieve a good match with the tag chip when it is attached to the surface of a metal object, and the slot can extend the current path, thereby reducing the size of the antenna. Purpose.

3. When designing the radio frequency identification RFID tag antenna of the present invention, the feeding position between two symmetrical T-shaped slots can be changed, so that the input impedance of the tag antenna can change within a wide range, ensuring that it is attached to the surface of a metal object It can still be matched with more tag chips with different impedances to enhance the versatility of the antenna.

4. The implementation method of the radio frequency identification RFID tag antenna of the present invention can adjust the input impedance of the antenna by changing the length and width of the long arms of a pair of T-shaped slots, and adjust the position of the feed point between the pair of T-shaped slots. Adjust the input impedance of the antenna so that the antenna matches the tag chip with different impedances to achieve the purpose of wide bandwidth and anti-metal type, making it suitable for UHF frequency band RFID standards in different countries and regions, and meeting the requirements of different countries and regions Different requirements for RFID standards; and the antenna has a certain stability when attached to the surface of a metal object, and can achieve a communication distance of more than five meters, which can achieve the purpose of saving production and labor costs.

Description of drawings

FIG. 1 is a schematic structural diagram of the radio frequency identification RFID tag antenna of the present invention.

Fig. 2 is a schematic structural diagram of the antenna radiation plate of the radio frequency identification RFID tag antenna of the present invention.

Fig. 3 is a schematic diagram of the simulation structure of the radio frequency identification RFID tag antenna of the present invention.

Fig. 4a is a simulation graph of the real part RA of the input impedance of the radio frequency identification RFID tag antenna of the present invention changing with the length l1 of the long arm of the T-shaped slot.

Fig. 4b is a simulation graph showing the imaginary part XA of the input impedance of the radio frequency identification RFID tag antenna of the present invention changing with the length l1 of the long arm of the T-shaped slot.

Fig. 5a is a simulation graph showing the real part RA of the input impedance of the radio frequency identification RFID tag antenna of the present invention changing with the width w1 of the long arm of the T-shaped slot.

Fig. 5b is a simulation graph showing the imaginary part XA of the input impedance of the radio frequency identification RFID tag antenna of the present invention changing with the width w1 of the long arm of the T-shaped slot.

FIG. 6 is a curve diagram of input impedance of the radio frequency identification RFID tag antenna designed for the ALN-9338-R tag chip of Alien Company according to the present invention.

FIG. 7 is a graph of the return loss of the radio frequency identification RFID tag antenna designed for the ALN-9338-R tag chip of Alien Company according to the present invention.

Fig. 8 is the radiation pattern of the RFID tag antenna designed by the present invention for the ALN-9338-R tag chip of Alien Company.

Accompanying drawing 9 a is the graph that the input impedance real part RA of the radio frequency identification RFID tag antenna designed for Alien's ALN-9338-R tag chip varies with the surface size of the metal object.

Fig. 9b is a graph showing the imaginary part XA of the input impedance of the radio frequency identification RFID tag antenna designed for the ALN-9338-R tag chip of Alien Company as a function of the surface size of the metal object.

Detailed ways

The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described below are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

As shown in Figure 1, it is the structural representation of the radio frequency identification RFID tag antenna of the present invention, as can be seen from the figure, the tag antenna of the present invention comprises: dielectric substrate 2; The dielectric substrate 3 that is arranged on the dielectric substrate 2 lower floors, its lower surface It is pasted on the upper surface of the metal object; the antenna radiation plate 1 is arranged on the upper layer of the dielectric substrate 2 .

Wherein, the dielectric substrate 2, the dielectric bottom plate 3 and the antenna radiation plate 1 of the present invention all adopt rectangular plates, so that the dielectric substrate 2, the dielectric bottom plate 3 and the antenna radiation plate 1 form a rectangular microstrip patch structure when assembled together , so as to concentrate the current and make the current flow uniform, thereby achieving the purpose of increasing the antenna gain.

Wherein, as shown in FIG. 2 , a pair of T-shaped slots, ie, a first T-shaped slot 5 and a second T-shaped slot 6 , are provided symmetrically on the antenna radiation plate 1 in the present invention. Preferably, the T-shaped slot is an open slot whose opening is opened on the long side end of the antenna radiation plate 1, the long arm of the open slot extends along the length direction of the antenna radiation plate 1, and the short arm of the T-shaped slot is vertically connected to the long arm. Extending toward the short side end of the antenna radiation plate 1 along the width direction of the antenna radiation plate 1, a pair of short arms of a pair of T-shaped slots protrude from each other, and a pair of T-shaped slots are symmetrical about the center line of the antenna radiation plate 1 . During design, by changing the length and width of the long arms of the first and second T-shaped slots, the input impedance ZA of the tag antenna can be easily adjusted, which is conducive to good matching between the tag antenna and tag chips with different impedances, and is also convenient Suitable for metal object surfaces of different sizes.

The present invention can achieve the following three purposes by opening a pair of symmetrical T-shaped slots on the antenna radiation plate 1: 1. It can concentrate the current flow direction, avoid the occurrence of circulating current as much as possible, and then improve the antenna gain and communication distance; 2. Cut off the The surface current path on the antenna radiating plate makes the current flow around the edge of the groove and the path becomes longer. In the equivalent circuit of the antenna, it is equivalent to introducing a cascaded inductance, so that the input impedance of the antenna presents a large inductive reactance, which can be compared with the impedance The tag chip with a large capacitive reactance can achieve a good match, that is, to ensure that the tag antenna can still achieve a good match with the tag chip when it is attached to the surface of a metal object; 3. Opening a T-shaped slot on the antenna radiation plate can extend the current path. Furthermore, the purpose of reducing the size of the antenna is achieved.

Wherein, as shown in Figure 2, the present invention is provided between a pair of T-shaped grooves and is used for making the antenna of different input impedances and the RFID tag chip of different impedance match the feed point, and this feed point is arranged in a pair of T-shaped grooves Between a pair of long arms, preferably, the feed point is located on the part between the long side end of the antenna radiation plate and the short arm of the T-shaped slot. During the design, by changing the position of the feed point between two symmetrical T-shaped slots, the input impedance of the tag antenna can be changed in a wide range, so that it can still be connected with more tag chips with different impedances when it is attached to the surface of a metal object. Matching to enhance the versatility of the antenna.

As shown in FIG. 3 , it is a schematic diagram of the structure when the radio frequency identification RFID tag antenna of the present invention is used for simulation. The total size of the tag antenna used in the simulation is only L×W=30mm×110mm. The material of the dielectric substrate 2 is FR-4, which is the most commonly used material in tag antenna design. The thickness of the substrate is 1.6mm, and its relative permittivity is ε _r = 4.4, the loss tangent is tanδ=0.02, which ensures the miniaturization and low cost of the antenna. In Fig. 3, what l1 represents is the length of the long arms of the first and second T-shaped slots provided on the antenna radiation plate, and what w1 represents is the width of the long arms of the first and second T-shaped slots opened, by changing the first and second T-shaped slots long arms The length and width of the long arm of the T-shaped slot can easily adjust the input impedance ZA of the tag antenna, which is conducive to a good match between the tag antenna and tag chips with different impedances, and is also convenient to apply to the surface of metal objects of different sizes .

Accompanying drawing 4 a is the simulation graph that the input impedance real part RA of the radio frequency identification RFID tag antenna designed by the present invention changes with the length l1 of the T-shaped groove long arm, and accompanying drawing 4 b is the radio frequency identification RFID tag antenna designed by the present invention The simulation graph of the imaginary part XA of the input impedance changing with the length l1 of the long arm of the T-shaped slot.

It can be seen from Figures 4a and 4b that when the length l1 of the long arm of the T-shaped slot is 82mm, 83mm, and 84mm respectively, the real and imaginary parts of the input impedance of the antenna are between 840-960MHz in the entire UHF frequency band Both change, with the increase of the length l1 of the long arm of the T-shaped slot, the real part and imaginary part of the input impedance of the antenna both increase, and the increase range is relatively large. It can be seen that by changing the length l1 of the long arm of the T-shaped slot, the input impedance of the anti-metal tag antenna can be adjusted in a large range, so that it can obtain good conjugate matching with tag chips with different impedances state.

Accompanying drawing 5 a is the simulation graph that the input impedance real part RA of the radio frequency identification RFID tag antenna of the present invention changes with the width w1 of the T-shaped groove long arm, and accompanying drawing 5 b is the input impedance imaginary part of the radio frequency identification RFID tag antenna of the present invention The simulation graph of XA changing with the width w1 of the long arm of the T-shaped slot.

It can be seen from Figures 5a and 5b that when the width w1 of the long arm of the T-shaped slot is 0.5mm, 1.0mm, and 1.5mm respectively, the real part of the antenna input impedance and Both the imaginary part changes, and with the increase of the long arm width w1 of the T-shaped slot, both the real part and the imaginary part of the input impedance of the antenna show an increasing trend. It can also be seen from this figure that when the long arm width w1 of the T-shaped slot is increased to 1 mm, increasing it has little effect on the real part of the antenna input impedance; however, the imaginary part of the antenna input impedance has a relatively small impact on w1 Sensitive, increasing with the increase of w1. Therefore, by changing the long arm width w1 of the T-shaped slot, the real part and imaginary part of the input impedance of the anti-metal tag antenna can also be changed within a certain range, and then conjugate matching can be achieved with some tag chips with different impedances.

For the ALN-9338-R tag chip of Alien Company (the performance impedance of this tag chip at 915MHz is 11-j422 ohms), it can be obtained by optimizing the design of simulation software, when l1=85mm, w1=1mm, the designed of the present invention A good matching state can be achieved between the radio frequency identification RFID tag antenna and the tag chip, and the antenna performance is the best.

Accompanying drawing 6 is the input impedance curve of the anti-metal tag antenna designed for Alien's ALN-9338-R tag chip. At 915MHz, the input impedance ZA of the anti-metal tag antenna is 8.30+j122.56 ohms, which is close to the conjugate impedance of Alien's ALN-9338-R tag chip at 915MHz, which is 6.2-j127 ohms. The anti-metal tag antenna can achieve a good match with the tag chip. And it can also be seen from the figure that in the entire UHF frequency band 840-960MHz in the world, the real part of the input impedance of the antenna varies from about 3.05 to 20.33 ohms, and the imaginary part varies from about 73.84 to 187.11 ohms. Meet the matching requirements of most UHF frequency band tag chips.

Accompanying drawing 7 is the return loss curve of the anti-metal tag antenna designed for the ALN-9338-R tag chip of Alien Company. It can be seen from this figure that in the entire UHF frequency band 840-960MHz in the world, the S11 is less than -10dB, and the S11 corresponding to the lowest point of 920MHz is -38.92dB. It can be seen that the anti-metal tag antenna is the same as Alien's ALN-9338-R The tag chip has reached a good conjugate matching state. If other tag chips with different impedances are selected to match with the anti-metal tag antenna, a good matching state can also be obtained in this frequency band.

Accompanying drawing 8 is the radiation pattern of the anti-metal tag antenna designed for the ALN-9338-R tag chip of Alien Company. Usually, in order to make the tag have good readability and reduce the dependence on the special placement direction, it is generally required that the radiation pattern of the tag antenna has good omnidirectionality. It can be seen from this figure that in the direction of phi=0deg, the tag antenna has good omnidirectionality, which meets the application requirements of the tag antenna. The maximum theoretical reading distance of the tag antenna can be calculated by using the distance calculation formula of the RFID tag antenna:

In the above formula, λ is the free-space wavelength, P _t is the transmit power of the reader, G _t is the gain of the reader antenna, G _r is the gain of the tag antenna, P _th is the threshold activation power of the tag chip, and χ is the read/write The polarization matching coefficient between the device antenna and the tag antenna, τ is the power transfer coefficient. It can also be seen from the figure that the maximum radiation gain G _r of the tag antenna is about -1.96dBi. According to the above formula, it can be calculated that the maximum theoretical reading distance of the tag antenna can reach 6.6m.

As can be seen from Figures 6, 7, and 8, the new UHF frequency band radio frequency identification anti-metal tag antenna designed by the present invention has a S11 of less than -10dB in the entire UHF frequency band 840-960MHz in the world, and the radiation pattern has a good omnidirectional The maximum theoretical reading distance can be as long as 6.6m, and the input impedance of the tag antenna can be adjusted in a wide range by adjusting the length l1 and width w1 of the T-shaped slot.

Accompanying drawing 9 a is the graph that the input impedance real part RA of the anti-metal tag antenna designed for Alien's ALN-9338-R tag chip changes with the surface size of a metal object, and accompanying drawing 9 b is for Alien's ALN- The curve graph of the imaginary part XA of the input impedance of the anti-metal tag antenna designed by the 9338-R tag chip varies with the surface size of the metal object.

It can be seen from Figs. 9a and 9b that, with the increase of the surface area of the metal object, the curves of the real part and the imaginary part of the input impedance of the antenna are in the same direction, and there are only slight changes. It can be seen that when the anti-metal tag antenna is attached to the surface of metal objects of different sizes, it can still achieve good impedance matching with the tag chip. It is proved that the antenna still has a certain stability when working on the surface of metal objects, and can reach a communication distance of more than five meters.

It should be noted that for RFID in the present invention, its full English is Radio Frequency Identification, and its Chinese is radio frequency identification; UHF in this invention, its full English is Ultra-high frequency, and its Chinese is ultra-high frequency band.

In addition, the present invention also provides a method for realizing the radio frequency identification RFID tag antenna, including:

A dielectric bottom plate 3 is arranged on the lower surface of the dielectric substrate 2;

An antenna radiation plate 1 is arranged on the upper surface of the dielectric substrate 2;

Wherein, the antenna radiation plate 1 is made into a rectangle so as to concentrate the current and make the current flow uniform;

Among them, a pair of T-shaped slots are symmetrically opened on the antenna radiation plate 1, so as to increase the current path and inductive reactance, and ensure that the microstrip patch structure can be well matched with the RFID tag chip when it is attached to the surface of a metal object;

Wherein, a feed point 4 for matching antennas with different input impedances with RFID tag chips with different impedances is set between a pair of T-shaped slots.

Wherein, the method of arranging the dielectric bottom plate 3 on the lower surface of the dielectric substrate 2 and the antenna radiation plate 1 on the upper surface can adopt the manufacturing method of the prior art, and will not be repeated here.

Preferably, when making the tag antenna of the present invention, the input impedance of the antenna is adjusted by changing the length and width of the long arms of a pair of T-shaped slots, and the antenna is adjusted by adjusting the position of the feed point 4 between the pair of T-shaped slots. input impedance.

Using the method of the present invention, making a rectangular microstrip patch structure, opening symmetrical double T-shaped slots on the antenna radiation plate 1 and feeding power between two symmetrical T-shaped slots, the tag antenna broadband can be realized. With the characteristics of uniqueness, miniaturization, and anti-metal type, it can meet the different requirements of RFID UHF frequency bands in different countries and regions and the requirements of normal operation of the antenna attached to the surface of metal objects.

In summary, the anti-metal tag antenna proposed in the present invention adopts a rectangular microstrip patch structure, and opens symmetrical double T-shaped slots on the antenna radiation plate and feeds power between two symmetrical T-shaped slots. The way to design a miniaturized anti-metal tag antenna with broadband characteristics makes it suitable for UHF frequency band RFID standards in different countries and regions, and the antenna has a certain stability when attached to the surface of a metal object, and can reach Communication distance of more than five meters. Therefore, from another point of view, the purpose of saving production and labor costs can also be achieved.

The above are the preferred embodiments of the present invention. It should be pointed out that those skilled in the art can make some improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered as the present invention. protection scope of the invention.

Claims (10)

1. A radio frequency identification RFID tag antenna, comprising: Dielectric substrate; The dielectric bottom plate arranged on the lower layer of the dielectric substrate, the lower surface of which is used to stick to the upper surface of the metal object; An antenna radiation plate arranged on the upper layer of the dielectric substrate; It is characterized by: The dielectric substrate, dielectric bottom plate and antenna radiation plate form a rectangular microstrip patch structure; A pair of T-shaped slots are symmetrically opened on the antenna radiation plate; A feed point for matching antennas with different input impedances with RFID tag chips with different impedances is set between the pair of T-shaped slots. 2 . The tag antenna according to claim 1 , wherein the T-shaped slot is an open slot opened at the long side end of the antenna radiation plate. 3 . 3. The tag antenna according to claim 2, wherein the long arm of the opening slot extends along the length direction of the antenna radiation plate. 4 . The tag antenna according to claim 3 , wherein the short arm of the T-shaped slot is vertically connected to the long arm, and extends toward the short side along the width direction of the antenna radiation plate. 5. The tag antenna according to claim 4, wherein the pair of short arms of the pair of T-shaped slots protrude from each other. 6 . The tag antenna according to claim 2 , wherein the feed point is disposed between a pair of long arms of the pair of T-shaped slots. 7 . The tag antenna according to claim 6 , wherein the feed point is located on the portion between the long side end of the antenna radiation plate and the short arm of the T-shaped slot. 8. A method for realizing a radio frequency identification RFID tag antenna, comprising: setting a dielectric bottom plate on the lower surface of the dielectric substrate; An antenna radiation plate is arranged on the upper surface of the dielectric substrate; Wherein, the antenna radiating plate is made into a rectangle so as to concentrate the current and make the current flow uniform; Wherein, a pair of T-shaped slots are symmetrically opened on the antenna radiation plate, so as to increase the current path and inductive reactance, and ensure that the microstrip patch structure can be well matched with the RFID tag chip when it is attached to the surface of a metal object; Wherein, a feed point for matching antennas with different input impedances with RFID tag chips with different impedances is set between the pair of T-shaped slots. 9. The method according to claim 8, wherein the input impedance of the antenna is adjusted by changing the length and width of the long arms of the pair of T-shaped slots. 10. The method according to claim 8 or 9, wherein the input impedance of the antenna is adjusted by adjusting the position of the feed point between the pair of T-shaped slots.