KR20090092967A - U-shaped RFID TAG antenna with near-isotropic radiation characteristic - Google Patents

Abstract

A U-shaped RFID tag antenna is provided to obtain a low gain deviation characteristic by forming a slit in the lower center of a dipole body. A U-shaped RFID tag antenna includes a dipole body(120) and a feeder(140). The dipole body has a U shape. The dipole body includes first conductive lines and second conductive lines. The first conductive line has the first width. The first conductive line is separated with a first distance and is positioned in parallel. The second conductive line has the second width. The second conductive line connects the first conducive lines. The feeder is connected to the second conductive line. The feeder has feeding conductive lines(142). The feeding conducive lines have the third width. A tag chip(300) is connected between one ends of the conducive lines.

Description

U-shaped RFID TAG antenna with near-isotropic radiation characteristic

The present invention relates to an antenna, in particular, having a U-shaped dipole body, which has a radiation gain of low gain deviation close to isotropy, and easily connects a tag chip to a center of a lower end of a feeder, thereby easily matching an impedance conjugate with a tag chip. The present invention relates to an RFID tag antenna having a lower gain deviation characteristic by having a slit at the bottom center of a dipole body.

RFID, a contactless wireless recognition technology, can transmit long- and long-distance signals and simultaneously recognize multiple tags in a short time. In addition, a large amount of unique information can be stored in a tag and semi-permanent use is possible. Due to these characteristics, it has been spotlighted as one of the next-generation core technologies that can complement the shortcomings of existing barcodes and magnetic cards and improve the ease of use in logistics and distribution fields. Furthermore, RFID systems are being recognized as an essential element for establishing a ubiquitous environment in the future due to the rapid development of IT technology, miniaturization, low cost, and high functionalization.

RFID is largely divided into reader and tag. When the reader copies radio waves to the tag, the unique information stored in the tag chip is returned from the tag antenna through the backscattering method. The tag has a structure in which an antenna and a tag chip are combined.

Since the tag is used attached to a moving object, the antenna of the reader should have a recognition rate independent of the direction of the tag. Thus, readers often use antennas with circular polarization. On the other hand, since the tag must be miniaturized due to the characteristics of the tag, a linear polarized antenna is often used. Furthermore, the antenna of the tag is printed in a single planar structure, and it is required to have a structure that facilitates impedance conjugate matching between the antenna and the tag chip.

The antenna of the dipole structure satisfies the above requirements and is widely used as a tag antenna. However, since the dipole antenna has a donut-shaped radiation pattern characteristic, there is an area that is not radiated. This may cause a problem in that the recognition rate decreases and the recognition distance in the reader decreases according to the direction in which the tag is placed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a tag antenna having low gain deviation radiation characteristics close to isotropy irrespective of the direction of the tag and easily matching the conjugate with the tag chip.

The tag antenna of the RIFD system according to an embodiment of the present invention for achieving the technical problem is the first conductor having a first width and the first conductor portion and a second width positioned in parallel spaced apart by a first distance, respectively And a dipole body having a U-shape having a second lead portion connecting the portions, and a power feeding portion connected to the second lead portion.

Preferably, each of the feeder portions has a third width and is spaced apart from each other by a second distance, one end bent at right angles to face each other, and the feeder conductor portions are connected to the second lead portion. can do. In this case, a tag chip may be connected to the center of the feed lead portions.

Preferably, the impedance conjugate matching between the tag antenna and the tag chip may be performed by adjusting the length of the feed lead portions. Alternatively, by adjusting the second width, impedance conjugate matching between the tag antenna and the tag chip may be performed.

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

Preferably, a slit formed in the second conductive portion may be further provided.

The tag antenna of the RFID system according to the embodiment of the present invention for achieving the technical problem is the first conductor having a first width and the first conductor and a second width positioned in parallel spaced apart by a first distance, respectively A dipole body having a U-shape having a second lead portion connecting the portions, and a slit formed in the second lead portion.

Preferably, the tag antenna further includes a feed part connected to the second lead part, wherein the feed parts each have a third width and are spaced apart from the outside of the slit, and have one end bent at a right angle. The other end may be provided with feed lead portions connected to the second lead portion.

The tag antenna according to the present invention has a U-shaped dipole main body, which has a radiation gain with a low gain deviation close to isotropic, and easily connects the tag chip to the center of the lower part of the feeder, thereby easily matching impedance conjugate with the tag chip. There is an advantage.

Furthermore, the tag antenna according to the present invention has an advantage of having a lower gain deviation characteristic by having a slit in the center of the lower end of the dipole body.

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 tag antenna according to a first embodiment of the present invention.

2 (a), 2 (b) and 2 (c) show the radiation pattern characteristics of the tag antenna of FIG. 1 as viewed in xy-plane, xz-plane, and yz-plane at 911 MHz, which is the center frequency of the domestic UHF band. Drawing.

3 is a diagram illustrating a tag antenna according to a second embodiment of the present invention.

4 and 5 are graphs showing return loss and gain deviation characteristics of the optimized tag antenna, respectively.

6 is a graph showing the radiation efficiency characteristics of the tag antenna optimized as described above.

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 main body 120 and a power feeding unit 140. 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 main body 120 may be a half-wavelength (λ / 2) dipole antenna of the received signal. The main body 120 of the tag antenna 100 according to the present invention has, in particular, first conductor parts 122 and a second width (W) having a first width w1 and positioned parallel to each other 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.

2 (a), 2 (b) and 2 (c) show the radiation pattern characteristics of the tag antenna of FIG. 1 as viewed in xy-plane, xz-plane, and yz-plane at 911 MHz, which is the center frequency of the domestic UHF band. Drawing. Referring to FIG. 2, the isotropic radiation pattern characteristic of the tag antenna 100 according to the present invention may be confirmed.

The U-shaped dipole antenna 100 has a phase difference of 180 Hz in the direction of the current flowing along the equivalent surface of the main body 120, thereby canceling a portion where nulls are generated in the radiation pattern of the conventional dipole antenna. can do. Therefore, the tag antenna according to the present invention may have an isotropic radiation pattern as shown in FIG. 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, tag chips (ALL-9238, 9250) 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 Can be connected. Therefore, the feeder 140 according to the present invention may be provided in a square or similar shape having an empty space therein.

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 13-j133 at 914 MHz.

The optimized antenna design parameters of the tag antenna as shown in FIG. 1 are L ₁ = 32 mm, L ₂ = 76 mm, L ₃ = 14.5 mm, L ₄ = 14.6 mm, w ₁ = 4 mm, w ₂ = 8 mm, w ₃ = 2.3 mm, w ₄ = 2.0 mm, g ₁ = 24 mm, g ₂ = 10 mm.

As described above, the tag antenna 100 according to the present invention may be easily conjugated with the tag chip 300. That is, according to the present invention, impedance conjugate matching between the tag antenna 100 and the tag chip 300 may be performed by adjusting the length of the first side or the second side of the power feeding unit 140.

Through the design parameters of the optimized tag antenna as described above, the change in the impedance characteristics of the tag antenna 100 according to the present invention will be described in detail. First, the dipole body 120 is fixed, and the vertical length L3 of the power feeding unit 140 is changed. When L ₃ is increased from 12.5 mm to 18.5 mm by 2 mm intervals, the input resistance and input reactance are constantly increased. Similarly, changing the left and right length L ₄ of the feed section 140, similarly to the result of the L3 length change, the input resistance and the input reactance are constantly increased.

In addition, impedance conjugate matching between the tag antenna 100 and the tag chip 300 may be performed by adjusting the second width w2 of the dipole body 120.

The impedance characteristic change will be described in detail through the design variables of the optimized tag antenna as described above. When the bottom width w ₂ of the dipole body 120 is increased in 6 mm to 12 mm intervals by 2 mm, the input resistance and the input reactance decrease.

As described above, the tag antenna according to the present invention can easily adjust the input resistance and the input reactance by adjusting the vertical length of the feeder, the left and right lengths, or the width of the lower end of the main body. Therefore, it is possible to easily design a tag in which the tag antenna and the tag chip are conjugate conjugate matched.

4 and 5 are graphs showing return loss and gain deviation characteristics of the tag antenna optimized as described above. In particular, the dotted lines represent return loss and gain deviation characteristics for the tag antenna of FIG. On the other hand, the solid line represents return loss and gain deviation characteristics of the tag antenna of FIG. 3 to be described later, which will be described later.

4 and 5, when the tag antenna 100 according to the present invention is matched to the tag chip 300, the bandwidth of the antenna is a voltage standing wave ratio (hereinafter referred to as VSWR) indicating an impedance matching degree VSWR < Based on 2, it has a bandwidth of about 1.76% (1.7) from 901 to 917 MHz to accommodate the domestically allocated UHF frequencies. In addition, the gain deviation of the tag antenna 100 representing the difference between the maximum gain and the minimum gain in all directions of 360 degrees may have a gain deviation characteristic of 1.63 dB or less within a given bandwidth. In addition, the bandwidth based on VSWR <5.8 has a bandwidth of about 6.1% from 875 to 930 MHz, and gain deviation of less than 3.8 dB.

6 is a graph showing the radiation efficiency characteristics of the tag antenna optimized as described above. 6 and 4, the radiation efficiency characteristic of the tag antenna of FIG. 1, which will be described later by dotted lines, is shown by a solid line.

Referring to FIG. 6, the radiation efficiency characteristics of the tag antenna 100 of FIG. 1 are 90% or more at 901 to 917 MHz (VSWR <2), and at least 86.4% at 875 to 930 MHz (VSWR <5.8). It can be seen that the radiation efficiency characteristics are shown.

As described above with reference to FIGS. 4 to 6, the tag antenna according to the present invention has a low gain deviation characteristic, thereby ensuring a uniform recognition distance regardless of the position or orientation of the tag when receiving the unique information of the tag in the reader. . In addition, since it has a low return loss and high radiation efficiency, the RFID system having the tag antenna according to the present invention can accurately transmit information between the reader and the tag even with low power.

3 is a diagram illustrating a tag antenna according to another embodiment of the present invention.

Referring to FIG. 3, unlike the tag antenna 100 of FIG. 1, the tag antenna 400 of FIG. 3 includes a slit 460 inserted into a lower end of the dipole body 420 (the second conductive part 424). Equipped. At this time, the feeder 440 of the tag antenna 400 of FIG. 3 is spaced apart by a width g2 or more of the slit 460, one end bent at a right angle to face each other, the other end is a second conductor The feed conductors may be connected to the unit 424. Since the structure and operation of the tag antenna of FIG. 3 are the same as those of the tag antenna of FIG. 1, a detailed description thereof will be omitted.

The optimized design parameters of the U-shaped RFID tag antenna with slit as shown in FIG. 3 are L ₁ = 32 mm, L ₂ = 76.5 mm, L ₃ = 13 mm, L ₄ = 14 mm, w ₁ = 4 mm, w ₂ = 1 mm, w ₃ = 8 mm, w ₄ = 2 mm, g ₁ = 24 mm, g ₂ = 6 mm, g ₃ = 10 mm.

Hereinafter, with reference to FIGS. 4 to 6, the improved characteristics of the tag antenna having the slits shown in FIG. 3 will be described. As described above, the dotted lines of FIGS. 4 to 6 represent the characteristics of the tag antenna of FIG. 1, and the characteristics of the tag antenna of FIG. 3 of the solid line.

Referring to FIG. 4, tag antennas with slits based on VSWR <2 have a bandwidth of about 1.53% at 906 to 920 MHz, and tag antennas without slits have a bandwidth of about 1.76% at 901 to 917 MHz. Slits have a slightly narrower bandwidth than slits, but both structures can accommodate domestically allocated UHF frequencies.

In addition, the U-type tag antenna with slit has a bandwidth of about 4.65% with 891 to 933.5 MHz at the bandwidth based on VSWR <5.8, and the U-type tag antenna without slit is about 6.1 with 875 to 930 MHz. Has% bandwidth. With slit, it can have a bandwidth of about 1.45% narrower than without slit.

As described above, the U-type tag antenna with the slit has a high impedance characteristic in the low frequency band, and thus has a relatively small return loss than without the slit.

Referring to FIG. 5, it can be seen that within the VSWR <2 bandwidth, the gain deviation characteristic of the slit having a gain deviation of 0.74 dB or less is 0.89 dB lower than that of a tag antenna without a slit having a gain deviation of 1.63 dB or less. Can be. In addition, within the VSWR <5.8 bandwidth, the tag antenna with a slit has a gain deviation characteristic of less than 1.27 dB, which is lower than that of a tag antenna without a slit having a gain deviation of 3.8 dB or less.

Accordingly, the tag antenna of FIG. 3 having a slit can secure a more even recognition distance by reducing the ratio of the maximum recognition distance and the minimum recognition distance when the reader system receives the unique information of the tag.

Referring to FIG. 6, it can be seen that, based on VSWR <5.8, a slit has a radiation efficiency of 90% or more, and a slit has a radiation efficiency of 86.4% or more.

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. 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.

Claims (12)

In the tag antenna of the RFID system, A dipole body 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 a second conductor portion having a second width and a second conductor portion connecting the first conductor portions; And And a feed part connected to the second lead part. The method of claim 1, wherein the power supply unit, Each tag antenna has a third width and is spaced apart from each other by a second distance, one end bent at right angles to face each other, and the other end is provided with 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 body, 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 further comprises a slit formed in the second lead portion. A tag comprising the tag antenna of claim 1. In the tag antenna of the RFID system, A dipole body having a U-shape having first conductor portions each having a first width and spaced apart by a first distance and parallelly spaced, and a second conductor portion having a second width and connecting the first conductor portions; And And a slit formed in said second lead portion. The method of claim 10, The tag antenna, And a feeder connected to the second conductive part. The feed section, Each tag antenna having a third width and spaced apart from the outside of the slit, the one end bent at a right angle is located facing each other, the other end is provided with a feed lead portion connected to the second lead portion . The method of claim 11, The tag antenna, characterized in that the tag chip is connected between one end of the feed lead portion.