KR100652229B1 - Uhf band rfid tag antenna - Google Patents

Abstract

A UHF band RFID tag antenna is provided to control a resonance frequency and resonance length according thereto, by increasing or decreasing the number of stubs. According to a circular loop antenna, feed lines of a feeding part(110) are separated by a gap(D) in parallel with each other, and a top front of the first feed line(112) is extended to a top front of the second feed line(114) in a clockwise direction to form a diameter(R). A pair of side line parts(122,124) having a predetermined length(L2) along the center direction of the circular loop and N stubs(120) are formed on the circumference of the loop antenna.

Description

UHF band RF ID tag antenna {UHF BAND RFID TAG ANTENNA}

Figure 1a is a block diagram of the RF band RFID tag antenna in accordance with an embodiment of the present invention.

Figure 1b is a graph showing the return loss of the RF band RFID tag antenna according to an embodiment of the present invention.

Figure 1c is a graph showing a radiation pattern of the RF band RFID tag antenna according to an embodiment of the present invention.

Figure 2a is an exemplary view showing a circular loop antenna having an external feed structure.

2B is an exemplary view showing a circular loop antenna having an internal feeding structure.

2C is a graph showing a change in resonance frequency characteristics according to a power supply structure.

Figure 2d is a graph showing the change in the characteristics of the impedance according to the feeding structure.

2E is a graph showing a change in resonance frequency characteristics according to a feeding structure having different setting values.

2F is a graph showing a change in the characteristic of impedance according to a power supply structure having different setting values.

Figure 2g is a graph showing a radiation pattern according to the external power supply structure.

Figure 2h is a graph showing a radiation pattern according to the internal power supply structure.

3A shows an exemplary circular loop antenna prior to forming a stub.

3B is a graph showing return loss of a circular loop antenna prior to forming a stub.

3C is an exemplary diagram illustrating a circular loop antenna having stubs formed thereon.

3d is a graph showing return loss of a stub-shaped circular loop antenna;

3E is a graph showing a change in resonant frequency with increasing number of stubs.

3f is a graph showing a change in impedance with increasing number of stubs.

3G to 3J are graphs showing the radiation pattern according to the positional change of the stub.

<Description of Symbols for Main Parts of Drawings>

100: HS band RF ID tag antenna

110: feeder 112: first feeder

114: second feed line 120: side section

122: one side line portion 124: the other side line portion

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an RFID tag antenna, and more particularly, to a miniature HF band RFID tag antenna using a circular loop antenna.

Radio Frequency IDentification (RFID), which is expected as a next generation technology to replace the conventional bar code recognition system, is also called a smart tag due to its characteristic operation. Recently, such a RFID system is attracting attention as a major technology for realizing a ubiquitous world in combination with ubiquitous computing technology.

The RFID system is a system that identifies and processes an RFID tag of a thin flat form attached to an object in a non-contact manner through a radio signal of a predetermined radio frequency band, and performs an RFID reader (RF) reader that performs a reading and decoding function. Reader), a tag storing unique identification information, and providing the stored identification information to the reader, and predetermined operating software. In some cases, a separate wired / wireless communication system is further included.

For reference, the tag transmits a radio signal to a reader by itself and has a characteristic of receiving a power supply for all operations from its power supply unit, and simultaneously deforming and reflecting a radio signal received from the reader. It is divided into two types of passive tag, which is characterized by generating the power required for operation by using the induced current caused by the signal to the antenna.

The radio frequency bands used in the RFID system as described above are largely classified into LF (125KHz, 135KHz), HF (13.56MHz), and UHF (433.92MHz, 860MHz to 960MHz), and Microwave (2.45GHz). The UHF band (860MHz to 960MHz) has advantages over other bands in consideration of requirements such as identification distance, transmission speed, and manufacturing cost. It is expected to be widely used in fields such as distribution.

Accordingly, the U.S., Europe, and Japan are distributing frequencies in the UHF band according to their own countries, and according to the international trend, the UHF band is distributed in the UHF band of 908.5 MHz to 914 MHz (5.5 MHz bandwidth) in Korea. Pyo Chul-sik, Chae Jong-seok, "RFID Technology and Standardization Trends", TTA Journal No. 95, 2004).

Meanwhile, the tag of the RFID system using the UHF band is preferably miniaturized so that it can be easily attached to any article in order to be easily used in the fields of logistics and distribution. Currently, IC chips (transponders) used in tags are being miniaturized due to continuous research and development. On the other hand, the size of the antenna is determined according to the wavelength of the frequency to be used.

SUMMARY OF THE INVENTION An object of the present invention is to provide a compact UHF band RFID tag antenna, which is designed to solve the above problems.

The present invention for achieving the above object, the feed line 112, 114 of the feed portion 110 is formed in a printing plane of a conductive material having a predetermined thickness and width (W) extending to a predetermined length (L ₁ ) ) Are spaced apart at predetermined intervals D so as to be parallel to each other, and the upper end of the first feed line 112 extends to the upper end of the second feed line 114 in a clockwise direction CW so as to have a predetermined diameter as a whole. In the circular loop antenna having (R), a pair of side portions 122 and 124 having a predetermined length L _{2 in the} direction of the center point C of the circular loop on the circumferential line of the loop antenna and the center point ( N stubs 120 having the same shape as the yaw portion in which the front ends of the side portions 122 and 124 facing C) extend at predetermined intervals D ₂ are formed.

Preferably, the resonance frequency and the corresponding resonance length are adjusted by increasing or decreasing the number N of the stubs 120.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

Before describing the present invention in detail, it should be noted that the detailed description of known functions and configurations related to the present invention is omitted if it is determined that the gist of the present invention may unnecessarily obscure the subject matter of the present invention. . The RF band RFID tag antenna according to an embodiment of the present invention will be described with reference to FIGS. 1A to 1C as follows. FIG. 1A is a block diagram of a UE band RFID tag antenna according to an embodiment of the present invention, and FIG. 1B is a graph showing a reflection loss of a UE band RFID tag antenna according to an embodiment of the present invention. 1c is a graph showing a radiation pattern of the RF band RFID tag antenna according to an embodiment of the present invention.

As shown in FIG. 1A, the H.F.band RFID tag antenna 100 (hereinafter referred to as a "tag antenna") according to an embodiment of the present invention is a metal wire of a conductive material having a predetermined width (W). It is a planar (hereinafter referred to as "printing planar") wire formed through a printing method, and takes the shape of a circular loop as a whole. More specifically, the tag antenna 100 has a feed portion 110 that is connected or connected to the RFID chip inside the tag (RFID Tag) and the yaw portion shape formed extending from the feed portion 110 The stub 120 is included.

As shown in FIG. 1A, the feed unit 110 includes a first feed line 112 and a second feed line 114 having the same length L ₁ , each of which is at a predetermined interval D ₁ . Spaced apart and parallel to each other.

In the power supply unit 110 according to the characteristic aspect of the present invention, each upper end is positioned near the center point C of the circular loop, and extends by L ₁ length in the downward direction. This structure is referred to as a so-called internal feeding structure, whereas the upper end is located at a distance from the circumferential line of the circular loop to the outside by an L ₁ length, and the lower end thereof is located at the circular loop circumference. It is called a feeding structure. In the antenna having a circular loop shape as in the present embodiment, the internal feeding structure has a smaller volume and area than the external feeding structure, and thus may be referred to as a structure suitable for the tag antenna 100. Of course, the internal power supply structure and the external power supply structure as described above has a slight characteristic difference, and the description thereof will be described with reference to the following experimental examples.

The stub 120 is formed on a circular loop circumferential line as described above, and extends from the feed part 110 to be bent into a concave portion shape. In other words, the stub 110 may be said that the circumference of the circular loop is deformed (bended, extended).

The stub 120 according to the characteristic aspect of the present invention is composed of one side portion 122 and the other side portion 124 corresponding to the inner side of the yaw portion, and corresponds to the inlet of the yaw portion. lateral line portion each of the front end is a predetermined distance (D ₁₎ to be spaced apart. in addition, each of the other front end has a predetermined distance the lateral line portion (122, 124) facing the central point (C) of 122,124 to (D ₂ ) spaced apart. Here, the length L ₂ of the side portions 122 and 124 is smaller than the length L ₁ of the feed portion 110, which facilitates the bonding or connection with the RFID chip to be arranged in the circular loop and the impedance matching. To do this. Therefore, this length difference L ₁ -L ₂ can be adjusted appropriately. As shown in FIG. 1A, a plurality of yaw-shaped stubs 120 having such a structural feature are formed on the circumference of the circular loop, each of which is formed at a predetermined interval h. In the present embodiment, L ₂ is set to be smaller than L ₁ , but the present invention is not limited thereto.

In the tag antenna 100 having the characteristic structure as described above, the number N of the stubs 120, the distance from the center point C of the circular loop antenna to the circumference thereof (radius r), L Setting ₁ , L ₂ , W, D ₁ , and D ₂ to 15, 27 mm, 25 mm, 17 mm, 1 mm, and 1 mm, respectively, optimizes the resonant frequency of 911.25 MHz. In addition, as shown in FIG. 1B, the tag antenna 100 configured as described above has a characteristic that a return loss is about -9.942 dB (Decibel) and a -3 dB bandwidth is 84.35 MHz. In addition, the radiation pattern of the tag antenna 100 has a non-directional characteristic on a horizontal plane as shown in Figure 1c, the gain of the zx plane (approximately -0.37dBd, HPBW 88 °), yx plane (yx plane) ) Shows a gain of about -1.52 dBd due to the phase difference in the diameter R of the circular loop.

This can be seen that the area reduction (miniaturization) of about 69.6% is achieved compared to the circular loop antenna according to the following experimental example, the radius formed to have the same resonance frequency is 49mm (diameter 98mm), through the stub 120 It can be seen that the resonance frequency and thus the resonance length can be easily adjusted.

More specific characteristic advantages of the tag antenna 100 according to the embodiment of the present invention described above will be described with reference to the following experimental examples and the accompanying drawings.

[First Experimental Example]

As described above, the feeding structure of the circular loop antenna is largely divided into an internal feeding structure and an external feeding structure. Each of these characteristics will be described with reference to FIGS. 2A through 2H. 2A is an exemplary view illustrating a circular loop antenna having an external feeding structure, FIG. 2B is an exemplary view illustrating a circular loop antenna having an internal feeding structure, and FIG. 2C is a graph illustrating a change in resonance frequency characteristics according to the feeding structure. FIG. 2D is a graph showing a change in impedance characteristics according to a feeding structure, FIG. 2E is a graph showing a change in resonance frequency characteristics according to a feeding structure having different setting values, and FIG. 2F is a characteristic of impedance according to a feeding structure having different setting values. 2G is a graph illustrating a radiation pattern according to an external power supply structure, and FIG. 2H is a graph illustrating a radiation pattern according to an internal power supply structure.

2A and 2B, the diameter R of the circular loop is set to 98 mm, the planar wire width W is set to 2 mm, and D ₁ and D ₂ are set to 3 mm. When the lengths L ₁ and L ₂ are changed in 5 mm intervals from 0 mm to 80 mm, respectively, as shown in FIG. 2C, the resonant frequency is changed to about 1051 MHz to 710 MHz for L ₁ , and about 1056 MHz to L ₂ . The linear degradation characteristic changes to 730MHz. In addition, as shown in FIG. 2D, each impedance trajectory according to the change as described above exhibits a clockwise (CW) trajectory characteristic. This is a phenomenon that appears when the length (L ₁ , L ₂ ) of the feed section 110 is longer because the current distribution on the feed section 110 affects the entire length of the circular loop antenna. In addition, considering the impedance of the antenna itself as the load impedance, it can be estimated that the impedance rotation trajectory from the load in the clockwise direction CW appears according to the change in the position of the input point.

On the other hand, if the flat wire width (W) is fixed to 2mm, and the length (L ₁ , L ₂ ) of the feed section 110 to 45mm, D ₁ , D ₂ is changed to 5mm intervals from 3mm to 28mm each 2e, it can be seen that the resonant frequency when D ₁ and D ₂ is 3mm is 911.25MHz, and when the resonant frequency when D ₁ and D ₂ is 28mm, the characteristics decrease to 776MHz and 786MHz, respectively. have. In addition, as the impedance D ₁ and D ₂ increase, it can be seen that the capacitance component increases in the clockwise direction CW as shown in FIG. 2F. This series of characteristic changes is because the feeding unit 110 plays a part as an independent antenna rather than the line role as D ₁ , D ₂ increases.

As described above, the circular loop antennas causing the characteristic change are fixed at a resonant frequency of 911.25 MHz, a length L ₁ , L ₂ of the feeder 110 at 45 mm, and D ₁ , D ₂ at 3 mm. When the impedance is matched, the return loss in the external feed structure is -22.95dB, -10dB bandwidth is 109.6MHz, and in the internal feed structure, the reflection loss is -25.61dB, -10dB bandwidth is 104MHz. Through this, it can be seen that the characteristics of the external feeding structure and the internal feeding structure are almost the same. In addition, as shown in FIGS. 2G and 2H, the radiation pattern measurement results of each of the feed structures show a non-directional pattern characteristic in the horizontal plane of the xy plane, and the gains are 2.09 dBd and 2.05 dB, respectively. Magnetic dipole radiation pattern characteristics.

As a result of the first experimental example as described above, when the feed unit 110 is positioned outside the circular loop as shown in FIG. 2A, or when the feed unit 110 is positioned inside as shown in FIG. 2B. It can be seen that each characteristic change has a negligible difference. Therefore, in order to achieve the characteristic object of the present invention of miniaturization of the antenna, it is efficient to adopt the internal feeding structure.

[Example 2 Experiment]

Hereinafter, the characteristics of the stub 120 having a yaw portion shape applied in an embodiment of the present invention will be described with reference to FIGS. 3A to 3J. FIG. 3A is an exemplary view showing a circular loop antenna before the stub is formed, FIG. 3B is a graph showing the return loss of the circular loop antenna before the stub is formed, and FIG. 3C is an example showing the circular loop antenna with the stub formed thereon. FIG. 3D is a graph showing return loss of a stub-shaped circular loop antenna, FIG. 3E is a graph showing a change in resonant frequency with increasing number of stubs, and FIG. 3F is a change in impedance with increasing number of stubs. 3G to 3J are graphs illustrating a radiation pattern according to a change in position of the stub.

A planar structure formed by a printing method to be easily attached to an article based on the first experimental example described above, and as shown in FIG. 3A, a foam having a relative dielectric constant? _R of about 1.06. Internal feed structure fabricated using copper with a thickness of 0.05mm and a width of 2mm on the top, with reference numerals D ₁ , L ₁ , and R set to 2 mm, 39 mm, and 98 mm, respectively, so that the resonance frequency is 911.25 MHz. Return loss characteristics of the circular loop antenna having a, as shown in Figure 3b, the return loss is -22.5dB at the frequency 911.25MHz, -10dB bandwidth is 77.46MHz. In addition, when the width W is changed from 1 mm to 10 mm based on the center point of the copper wire having a width W of 2 mm, the resonance frequency is increased, and the bandwidth is increased. This can be estimated that as the width W of the conductive wire becomes wider, the area formed inside the circular loop becomes smaller, so that the frequency is increased and the bandwidth is increased because the current path is formed in various ways.

On the other hand, a stub 120 as in the embodiment of the present invention is formed in the same circular loop antenna as shown in Figure 3a vertically in the lower direction of the feed unit 110 as shown in Figure 3c, the stub 120 The circular loop antenna made of the length (L ₂ ) of the side portions 122, 124 of 20) and the spacing D ₂ of the side portions 122, 124 of ₂ mm equal to D ₁ As shown in FIG. 3D, the resonance frequency is lowered by approximately 30 MHz from 911.25 MHz to 881.25 MHz. Here, currents having various paths are distributed in the stub 120 formed as shown in FIG. 3C. In addition, about 12% is increased compared to the total length of the circular loop antenna as shown in FIG. 3A, and the resonance frequency is lowered due to the capacitance component.

Therefore, if the resonance at the same frequency (911.25MHz) as described above, the overall diameter of the circular loop antenna is reduced, as a result it can be seen that the small circular loop antenna can be implemented by the stub 120. In addition, with the same setting as shown in FIG. 3C, if the number of stubs 120 is increased, the resonance frequency decreases substantially linearly as shown in FIG. 3E, and the impedance is as shown in FIG. 3F. It can be seen that the inductance component is increased again after the capacitance component due to the increase effect of the current path is increased.

On the other hand, looking at the radiation pattern after changing the position (Φ) of the stub 120 shown in Figure 3c at an interval of 45 ° from 270 ° to 45 °, as shown in Figure 3g to 3j and Table 1 below, The antenna gain is shown as 1.69dBd on average in the zx plane and 0.07dBd on average in the yx plane. This means that the gain and the HPBW change according to the position Φ change of the stub 120 are hardly changed.

Stub position (Φ) [Deg.] z-x Plane Gain [dBd] y-x plane gain [dBd] HPBW [Deg.] 270 1.7 0.17 86 315 1.78 0.42 91 0 1.7 0 86 45 1.51 -0.32 91 Average 1.69 0.07 88.5

Thus, in increasing the stub 120 for miniaturization of the circular loop antenna, it can be said that the stub 120 is not affected by its respective position Φ.

Tag antenna 100 having the above-described characteristic configuration through the first experimental example and the second experimental example described above, that is, the miniaturization of the RFID tag antenna that can be used in the above-described object of the present invention, UHF band Characteristic purposes can be achieved. In addition, by providing a flat antenna of the printing method so that it can be easily attached to the article, by adjusting the number (N) of the stub (120) provides a characteristic advantage that the resonant frequency and the corresponding resonant length can be easily adjusted can do.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited to the drawing.

According to the present invention as described above, there is an effect that can be miniaturized the RFID tag antenna that can be used in the UHF band.

In addition, according to the present invention as described above, the effect of providing a planar antenna of the printing method that can be easily attached to the article, and by adjusting the number of stubs (N) of the yaw portion resonant frequency and the There is also an effect that can be easily adjusted according to the resonance length.

Claims (4)

It is formed in a printing plane of a conductive material having a predetermined thickness and width (W), the feed line 112, 114 of the feed section 110 extending to a predetermined length (L ₁ ) is spaced at a predetermined interval (D) The upper end of the first feed line 112, which is upright in parallel to each other, extends to the upper end of the second feed line 114 in a clockwise direction CW, so as to have a circular loop antenna having a predetermined diameter R as a whole. In A pair of side portions 122 and 124 having a predetermined length L ₂ on the circumferential line of the loop antenna in the direction of the center point C of the circular loop and the side portions 122 and 124 facing the center point C. UHF band RFID tag antenna, characterized in that N stubs (120) are formed in the shape of a yaw that extends at predetermined intervals (D ₂ ). The method of claim 1, HHF RFID tag antenna, characterized in that for controlling the resonant frequency and the corresponding resonant length through the increase and decrease of the number (N) of the stub (120). The method of claim 1, The predetermined length L ₁ is larger than L ₂ RF band RFID tag antenna. The method of claim 1, W, L ₁ , L ₂ , R, D ₁ , D ₂ , and N are, UHF band RFID tag antenna which is 1mm, 25mm, 17mm, 54mm, 1mm, 1mm, 15, respectively.

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