KR101008798B1 - U-shaped broadband RFID tag antenna with a parasitic element - Google Patents

Abstract

A U-shaped wideband RFID tag antenna with parasitic elements is disclosed. Tag antennas of the RFID system according to the embodiment of the present invention, each having a first width and the first conductor portion and the second conductor having a second width and parallelly spaced apart from each other by a first distance connecting each of the first conductor portion A half-wave dipole antenna having a U-shape having two conductors; A feeding part connected to the second conductive part; And first parasitic conductors positioned inside the dipole antenna, each having an eleventh width and parallel to each other by an eleventh distance, and a second parasitic lead having a twelfth width and connecting the first parasitic lead portions. A parasitic element provided with a part is provided. Tag antenna according to the present invention has the advantage of ensuring a uniform recognition distance irrespective of frequency by minimizing the variation in the gain deviation characteristics according to the frequency change in the broadband.

Description

U-shaped broadband RFID tag antenna with a parasitic element

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna, and more particularly to an RFID tag antenna having a U-shaped dipole antenna and inserting a parasitic element inside a U-shaped dipole antenna, which has an even recognition distance performance regardless of frequency within a wide band. It is about.

RFID system, a contactless radio recognition technology, uses several frequency bands including LF band (125 KHz, 134KHz), HF band (13.56 MHz), UHF band (433.92 MHz, 860 ~ 960 MHz), microwave band (2.45 GHz). Among them, the UHF band has attracted great attention in the field of logistics and distribution as a next generation wireless recognition technology that will compensate for the shortcomings of the existing barcode due to the long recognition distance and fast transmission speed.

These UHF bands use different frequencies from country to country, such as Europe using 865 ~ 868 MHz band, North America using 902 ~ 928 MHz band, Japan using 950 ~ 956 MHz band, and Korea using 908.5 ~ 914 MHz band. Allocating Therefore, in order to provide interoperability between countries, a tag antenna having broadband characteristics is required.

In addition, since the attachment direction of the tag antenna used for the flexible object is not constant, there is a problem that the recognition rate rapidly drops in the vicinity of the null direction of the radiation characteristic. Therefore, it is preferable that the tag antenna has an isotropic radiation characteristic and has a recognition rate irrespective of position or direction.

In addition, it is good to secure the recognition distance regardless of the frequency by minimizing the variation of gain variation due to the frequency change. Furthermore, the tag antenna must deliver maximum power to the tag chip with high radiant efficiency and impedance conjugate matching between the antenna and the tag chip for remote recognition, and the tag antenna's input reactance has a very capacitive component. It should be designed to have inductive components.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide an RFID tag antenna having an even recognition distance performance regardless of frequency in a broadband.

The tag antenna of the RFID system according to the embodiment of the present invention for achieving the technical problem, each having a first width and the first conductor portion and a second width positioned in parallel spaced apart from each other by a first distance and the first antenna A dipole antenna having a U-shape having a second lead connecting the first leads; A feeding part connected to the second conductive part; And first parasitic conductors positioned inside the dipole antenna, each having an eleventh width and parallel to each other by an eleventh distance, and a second parasitic lead having a twelfth width and connecting the first parasitic lead portions. A parasitic element provided with a part is provided.

Preferably, the feeder, respectively, having a third width and are spaced apart from each other by a second distance, one end bent at a right angle is located facing each other, the other end is connected to the feed lead portion connected to the second lead portion It can be provided.

Preferably, a tag chip may be connected between one end of the feed lead portion. In this case, by adjusting the length of the feed lead portion, the impedance conjugate matching with the tag chip can be performed. Alternatively, by adjusting the second width, impedance conjugate matching with the tag chip may be performed.

Preferably, the U-shaped dipole antenna may be provided with a half-wave length of the received signal. In addition, the tag antenna may be printed in a single planar structure on a substrate.

Preferably, the direction of the current flowing through each of the first conductive parts may have a phase difference of 180 degrees.

Preferably, the parasitic element may be provided in a shape in which the U-shape of the dipole antenna is rotated 180 degrees at the center of the upper end of the inside of the dipole antenna. In this case, the directions of the currents flowing through the first parasitic conductive wire parts may have a phase difference of 180 degrees, and may have the same phase as the directions of the currents flowing in the adjacent first conductive wire parts.

The first parasitic conductive parts are positioned parallel to the first conductive part positioned adjacent to each other by a twelfth distance, and one end thereof is spaced apart by the thirteenth distance from the second conductive part, and the second parasitic The lead may be positioned parallel to the second lead at the other end of the first parasitic lead.

The tag antenna according to the present invention has an advantage of ensuring a uniform recognition distance regardless of frequency by minimizing a change in gain variation due to a frequency change in a wide band.

DETAILED DESCRIPTION In order to fully understand the present invention, the operational advantages of the present invention, and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings which illustrate preferred embodiments of the present invention and the contents described in the drawings.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like reference numerals in the drawings denote like elements.

1 is a diagram illustrating a tag antenna according to a first embodiment of the present invention.

Referring to FIG. 1, the tag antenna 100 according to an exemplary embodiment of the present invention includes a dipole antenna 120, a power feeding unit 140, and a parasitic element PARA having a U shape. Preferably, the tag antenna 100 may be printed in a single planar structure on the RO 4003 substrate 200 having a relative dielectric constant of 3.38 and a thickness of 0.2032 mm.

The dipole antenna 120 having a U shape may be a half-wavelength (λ / 2) dipole antenna of a received signal. In particular, the U-shaped dipole antenna 120 according to the present invention may have a first width w1 and a first conductor portion 122 and a second width (parallel) spaced apart by a first distance g1. It is a dipole antenna having a U-shape having a second lead portion 124 having a w2) and connecting the first lead portions 122.

The U-shaped dipole antenna 100 has a phase difference of 180 degrees with respect to the directions of currents flowing along the equivalent surfaces of the two first conductive portions 122, and thus is null in the radiation pattern of the dipole antenna according to the prior art. null) can be offset. That is, the tag antenna according to the present invention may have a radiation pattern close to isotropic. 2 is an isotropic radiation pattern of a tag antenna according to an exemplary embodiment of the present invention. Fig. 2 shows the radiation pattern at 902 MHz, which is the minimum gain deviation point in the optimization conditions of tag antennas according to the embodiment of the present invention described below.

Due to the isotropic radiation pattern, the RFID system having the tag antenna 100 according to the present invention may have a recognition rate irrespective of the direction of the tag when receiving the unique information of the tag in the reader.

Referring back to FIG. 1, the feeder 140 is connected to the second lead 124. As shown in FIG. 1, each of the power feeding units 140 has a third width w3 and is spaced apart from each other by a second distance g2, and one end bent at a right angle is disposed to face each other, and the other end thereof is disposed. Feed conductors 142 connected to the second conductor part 124 may be provided.

In addition, the tag antenna 100 according to the present invention may be connected to the tag chip in the center of the lower end of the feeder (between the feed conductors 142) in order to facilitate impedance conjugate matching with the tag chip 300. Therefore, the feeder 140 according to the present invention may be provided in a square or similar shape having an empty space therein. In this case, the tag chip may be a Higgs chip of Alien.

By having the structure as described above, the power supply unit 140 according to the present invention has an inductive component of the antenna has an inductive component, and by canceling the capacitive component of the tag chip 300, the impedance conjugate matching Can be performed. In this case, the tag chip 300 may have an input impedance value of about 16-j131.

1, the tag antenna according to an exemplary embodiment of the present invention increases the separation distance (first distance g1) between the first conductive parts 122 to increase the frequency band that the tag antenna can receive. Can be increased. That is, the tag antenna according to the embodiment of the present invention may operate in a wide band. However, when only a dipole antenna having a U-shape and no parasitic elements is provided, the gain deviation characteristic of the tag antenna may increase the minimum gain deviation characteristic at a high frequency outside the frequency band that can be received as the first distance increases. You can have

However, as shown in FIG. 1, the tag antenna 100 according to an exemplary embodiment of the present invention includes a parasitic element PARA inside a U-shaped lead portion, so that the minimum gain deviation characteristic of the tag antenna 100 is wider at a center frequency in the broadband. By doing so, it is possible to reduce the difference in recognition distance performance according to the frequency.

As described above, the parasitic element PARA has a U shape at the center of an upper end of the dipole antenna 120 having a U shape surrounded by the first conductive parts 122 and the second conductive parts 124. It is provided in the shape rotated 180 degrees. In this case, since the parasitic element PARA is printed on the same substrate 200 as the dipole antenna 120, the parasitic element PARA may be formed of the same material as the dipole antenna 120 having a U shape.

In particular, as shown in FIG. 1, the parasitic element PARA has a width pw1 and a width pw2 connecting the first parasitic lead portions p122 and the first parasitic lead portions p122 that are spaced apart by a distance pg1. It may be implemented as a second parasitic lead portion (p124). The first parasitic lead portions p122 may also be spaced apart from the corresponding first lead portions 122 by a distance pg2. In addition, the first parasitic conductive parts p122 may be spaced apart from the second conductive part 124 by a distance pg3.

In this case, the direction of the current flowing through each of the first parasitic lead portions p122 of the parasitic element PARA may correspond to the first lead portions 122 corresponding to each of the first parasitic lead portions p122, that is, the first parasitic lead. It may coincide with the direction of the current flowing in the first lead portions 122 positioned adjacent to each of the portions p122. Accordingly, currents flowing at both ends of the dipole antenna 120 flow with a phase difference of 180 degrees, respectively.

As such, the tag antenna according to the embodiment of the present invention includes a parasitic element, and thus, even if the first distance g1 is increased so that the tag antenna has a wideband characteristic, the tag antenna has a phase difference in the direction of the current flowing through each of the first lead portions. The null area of the radiation pattern can be canceled out. That is, the tag antenna according to the embodiment of the present invention minimizes the variation of the gain variation according to the frequency change in the wideband as shown in FIG. 3, and thus the recognition distance evenly selected regardless of the frequency as shown in FIG. Can be secured.

Hereinafter, with reference to FIGS. 3 and 4, the characteristics of the tag antenna according to an embodiment of the present invention as described above.

3 and 4 are graphs showing reflection loss, gain deviation characteristics, and radiation efficiency characteristics of the tag antenna of FIG. 1 optimized, respectively. The optimized antenna design parameters of the tag antenna of FIG. 1 are L1 = 48 mm, L2 = 61.9 mm, L3 = 6.2 mm, L4 = 16.4 mm, w1 = 4 mm, w2 = 10 mm, w3 = 1 mm, w4 = 1 Mm, pw1 = 4 mm, pw2 = 1 mm, g1 = 40 mm, g2 = 14.4 mm, pg1 = 17 mm, pg2 = 7.5 mm, pg3 = 8 mm. The antenna was optimized using Zeland's EM simulator, IE3D.

Referring to FIG. 3, the simulation result of the impedance matching of the antenna of the tag antenna and the impedance of the tag chip optimized as described above shows that the bandwidth of the antenna is a voltage standing wave ratio (hereinafter referred to as VSWR) indicating an impedance matching degree. The gain deviation of the tag antenna, which has a bandwidth of about 4.41% from 888 to 928 MHz and shows the difference between the maximum gain and the minimum gain in all directions of 360 방향, has a gain deviation of less than 3.16 dB in the bandwidth. Able to know. In the bandwidth based on VSWR <5.8, it can be seen that it has a bandwidth of about 11.05% from 859.5 to 960 MHz and a gain deviation characteristic of less than 5.00 dB.

According to the simulation results as described above, the tag antenna according to an embodiment of the present invention is provided with a parasitic element inside the U-shape, to provide an RFID tag antenna having a uniform recognition distance performance regardless of the frequency in the broadband have.

4, the radiation efficiency of the optimized tag antenna has a radiation efficiency of 89.0% or more within VSWR <2 bandwidth, and a radiation efficiency of 74.0% or more within VSWR <5.8 bandwidth.

Referring back to FIG. 1, the tag antenna 100 according to the present invention adjusts the length L3 of the first side or the length L4 of the second side of the feeder 140 or has a U-shape. By adjusting the lower width W2 of the dipole antenna 120, impedance conjugate matching between the tag antenna 100 and the tag chip 300 may be performed.

As described above, optimal embodiments have been disclosed in the drawings and the specification. Although specific terms have been used herein, these terms are only used for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. For example, FIG. 1 and the like show a parasitic element having a shape of rotating a dipole antenna 180 degrees, but is not limited thereto. A parasitic element having a shape and an in-phase shape of the dipole antenna may be provided. It may be.

Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS In order to better understand the drawings cited in the detailed description of the invention, a brief description of each drawing is provided.

1 is a diagram illustrating a U-shaped broadband tag antenna having parasitic elements according to an embodiment of the present invention.

FIG. 2 is a graph illustrating radiation pattern characteristics of the tag antenna of FIG. 1.

FIG. 3 is a graph illustrating return loss and gain deviation characteristics of the tag antenna of FIG. 1.

4 is a graph illustrating radiation efficiency characteristics of the tag antenna of FIG. 1.

Claims (12)

In the tag antenna of the RFID system, A dipole antenna having a U-shape having first conductor portions each having a first width and spaced apart from each other by a first distance, and having second conductor portions having a second width and connecting the first conductor portions; A feeding part connected to the second conductive part; And First parasitic lead portions located inside the dipole antenna, each having an eleventh width and spaced apart from each other by an eleventh distance, and a second parasitic lead portion having a twelfth width and connecting the first parasitic lead portions. And a parasitic element provided. The method of claim 1, wherein the power supply unit, Each of the tag antennas having a third width and spaced apart from each other by a second distance, one end bent at a right angle to face each other, the other end having a feed lead portion connected to the second lead portion . The method of claim 2, The tag antenna, characterized in that the tag chip is connected between one end of the feed lead portion. The method of claim 3, wherein The tag antenna, characterized in that the impedance conjugate matching with the tag chip is performed by adjusting the length of the feed lead portion. The method of claim 3, wherein And adjusting the second width to perform impedance conjugate matching with the tag chip. The method of claim 1, wherein the dipole antenna, Tag antenna, characterized in that provided with a half-wave length of the received signal. The method of claim 1, wherein the tag antenna, Tag antenna, characterized in that printed on a substrate in a single plane structure. The method of claim 1, The tag antenna, characterized in that the direction of the current flowing through each of the first conductive wire portion has a phase difference of 180 degrees. The method of claim 1, wherein the parasitic element, The tag antenna, characterized in that in the center of the upper end of the inside of the dipole antenna, the U-shape of the dipole antenna is rotated 180 degrees. The method of claim 9, The direction of the current flowing in each of the first parasitic lead portion has a phase difference of 180 degrees with each other, and the tag antenna, characterized in that the same phase as the direction of the current flowing in the adjacent first lead portion. The method of claim 1, Each of the first parasitic lead portions, Spaced apart in parallel with the twelfth distance from the first conductive part positioned adjacent to each other, and one end thereof is spaced apart from the second conductive part by a thirteenth distance, The second parasitic lead portion, The tag antenna, characterized in that located in parallel with the second lead portion at the other end of the first parasitic lead portion. A tag comprising the tag antenna of claim 1.

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