KR100751293B1 - Planar dipole antenna on the surface of conducting plane for rfid tag - Google Patents

Abstract

A planar dipole antenna for an RFID tag is provided to reduce the size of the RFID tag by reducing the height of the planar dipole antenna to 1mm at a frequency band of 900MHz. A planar dipole antenna for an RFID(Radio Frequency IDentification) tag includes a rectangular or square ground plate(G), a dielectric material(F), first to third patterns, and short-circuiting units(P1,P2). The dielectric material is mounted on the ground plate. The first pattern(110) is mounted on the dielectric material and has a T-like shape. The second pattern(120) is displaced from a left outer periphery of the first pattern. The third pattern(130) is arranged between the first and second patterns and has a predetermined elongation length from the left side peripheries of the first and second patterns. The short-circuiting units couple lower ends of the first and second patterns with the ground plate.

Description

Planar dipole antenna for metal surface mountable rafid tags {PLANAR DIPOLE ANTENNA ON THE SURFACE OF CONDUCTING PLANE FOR RFID TAG}

1 is a graph showing a change in gain according to the height of the ground plate and the radiating element in the conventional horizontal dipole antenna,

2 is a graph showing a change in impedance according to the height of the ground plate and the radiating element in the conventional horizontal dipole antenna,

3 is a schematic configuration diagram of a conventional low profile asymmetric dipole antenna,

4 is a schematic configuration diagram of an asymmetric dipole antenna implemented on a conventional ground plate;

5 is a graph showing the return loss according to FIG.

6 is a graph showing a radiation pattern according to FIG.

7 is a graph illustrating a dipole antenna according to the present invention;

8 is a configuration diagram for the first to third patterns according to the present invention,

9 is an exemplary view showing the size of a dipole antenna according to the present invention;

10 is a graph showing a frequency change according to the change of the parameter i of the present invention;

11 is a graph showing a change in impedance according to a change in parameter d of the present invention;

12 is a table showing parameters matched according to the height change between the first to third patterns and the ground plate of the present invention;

13 is a graph showing the reflection loss when the height between the first to third patterns and the ground plate of the present invention is 5mm,

14A and 14B are graphs showing radiation patterns for heights between the first to third patterns and the ground plate of the present invention.

15 and 16 are exemplary views showing a modified embodiment of the present invention.

** Description of symbols for the main parts of the drawing **

G: ground plate F: dielectric

110: first pattern 112: left side

114: Postal 120: Second Pattern

130: third pattern 132: protrusion length

P1, P2: Short circuit means

The present invention relates to a dipole antenna, and more particularly, to a planar dipole antenna for an RFID tag that can be easily mounted on a metal surface.

The RFID system refers to a system in which an IC chip including unique information of an object is attached to a small antenna so as to recognize the object, collect information, and track the corresponding object. Recently, the necessity of RFID is urgently required due to the frequent movement of logistics to domestic and foreign countries and the rapid increase of the movement. In particular, there is an increasing demand for antennas for metal surface-mounted RFID tags that can be easily attached to containers used for logistics movement by ship or aircraft.

However, as is well known, in the case of a metal surface-mounted antenna, a preferable radiation is not achieved due to a decrease in the impedance of the antenna due to an image effect, and furthermore, there is a disadvantage in that the bandwidth is narrow. In addition, antennas having a low profile among the antennas introduced to date are very large in volume and height, and thus are not suitable as antennas for RFID tags. For example, in the case of the asymmetric low-length dipole antenna as shown in the following [ Reference ] , the low-profile antenna radiating element is secured with a height of 0.03λ, but in order to increase the radiation gain, the 1 / 4λ ' As it adopts bazooka balun ', a' balun ( bal ance- un balance) 'space is required. Therefore, in terms of the overall size of the antenna it is somewhat insufficient to be miniaturized through a three-dimensional structure.

[ References ] -Takehiro Imura et al., "Excitation Dipole mode in Asymmetrical Ultra Low Profile Dipole Antenna", ISAP 2006.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a high gain flat dipole antenna for RFID tag, which can be mounted on a small surface using a CPW feeding structure.

Specific features and advantages of the present invention will become more apparent from the following detailed description based on the accompanying drawings. In the meantime, when it is determined that the detailed description of the known functions and configurations related to the present invention may unnecessarily obscure the subject matter of the present invention, it should be noted that the detailed description is omitted.

Hereinafter, the characteristics of the conventional dipole antenna will be described in order to more clearly describe the technical idea of the present invention. The three items to look at are "characteristics of horizontal dipole antennas with ground plate height", "characteristics of low-profile asymmetric dipole antennas", and "characteristics of asymmetric dipole antennas on ground plates".

[Characteristics of Horizontal Dipole Antenna According to Ground Plate Height]

A general dipole antenna with a ground plate (or reflecting plate) is designed so that the height between the radiating element and the ground plate is 1/4 lambda to obtain maximum directivity in the broad side direction. The radiation gain at this time is 7dBi, and the maximum gain (9dBi) is obtained when the height is 1 / 10λ. 1 is a graph simulating the change of the gain according to the height change of the radiating element from the ground plate. As shown in the figure, the maximum gain is shown when 1 / 10λ, and the radiation efficiency is lower as it is smaller than 1 / 10λ.

In other words, when the radiating element is close to the ground plane, the antenna input impedance is lowered by the image effect, and the radiated electromagnetic waves are also canceled due to the reflected wave and the reversed phase (inverted phase), and as a result, the radiation efficiency is significantly reduced. Specifically, referring to FIG. 2, the impedance becomes very small as the distance between the radiating element and the ground plate gets closer, and eventually, the impedance converges to zero. Converging to zero implies that the antenna has lost radiation. From this characteristic, it is possible to increase the impedance of the antenna itself, suggesting that an antenna for increasing the impedance with the ground plane is required.

[Characteristics of Low Profile Asymmetric Dipole Antenna]

FIG. 3 is a schematic diagram of a dipole antenna matched by increasing the impedance of the antenna itself in order to satisfy low impedance in low profile. As shown in the figure, the impedance can be controlled by adjusting the length of the outer shell and the inner core of the coaxial cable (see reference). Here, the length of the parasitic element (a conductor or a copper wire extending to conduct with an external conductor in the drawing) greatly influences the change of frequency. In this structure, a balun having a 1 / 4λ length of the aforementioned bazooka structure is extended below the ground plate to increase impedance matching and radiation efficiency.

In these antennas, the radiating element achieves a high gain in the 7 to 9 dBi range with a low profile of wavelength 0.03λ. However, as pointed out above, there is a disadvantage in that a space for installing the balloon under the ground plate must be secured. Therefore, it is not suitable for RFID tag which is difficult to secure such space.

[ On ground plate  Asymmetric Dipole  Antenna characteristics]

4 shows an asymmetric dipole antenna implemented on a ground plane (reflective plate). 5 and 6 are graphs showing the reflection loss and the radiation pattern accordingly. When these antennas are placed on a metal plane (plane conductor), they exhibit a return loss of -20 dB and a gain of 6.14 dBi (4 dBd). However, it is not easy to manufacture below 0.01λ, and is not suitable for RFID tags requiring ultra low profile.

Preferred Embodiments of the Invention

The dipole antenna of the present invention shown in FIG. 7 includes a rectangular or square ground plate G, a dielectric material F having a predetermined permittivity to be seated on the ground plate, and a substantially 'T' shaped material seated on the dielectric. Between the first pattern 110 and the second '120' pattern '120' spaced apart from and disposed at a predetermined offset from the 'a' shaped left outer periphery of the first pattern, and between the patterns 110 and 120 The third pattern 130, which is spaced apart and disposed and has a feeding point (FP, Feeding Point) at the bottom, and has a predetermined protruding length with respect to the left end of the patterns, and a lower end of the first and second patterns The short circuit means P1 and P2 which conduct the vicinity and the ground plate are comprised.

Specifically, as described above, the ground plate G is also referred to as a reflecting plate, and the dielectric F is mounted on the ground plate to support the patterns 110, 120, and 130.

Referring to FIG. 8, the first pattern 110 forms the left side 112 and the post 114 to form a 'T' shape as a whole, and the post 114 has a predetermined step depth with respect to the left side 112. It is formed in the shifted state which has (10). The mail 114 may be understood to be a parasitic element.

In addition, the second pattern 120 is disposed to have a predetermined offset from the left outer circumference ('-') of the first pattern, and the third pattern 130 is an offset region formed by the first and second patterns. Is placed on. Of course, the third pattern does not contact these 110 and 120. As shown in the drawing, the upper left front end of the third pattern 130 has a predetermined protrusion length 132 (hereinafter referred to as parameter i) compared to the left front end 116 of the first pattern and the left front end 122 of the second pattern. Referred to).

In contrast to the above-described configuration of the dipole antenna, the coaxial cable feeding has been replaced with a co-planar waveguide (CPW) feeding (50 ohm matching), and the balun has a short circuit (ground plate) below the first and second patterns. And conduction). In such a dipole antenna, the parameters c (left length) and d (post length or parasitic length) illustrated in FIG. 9 greatly influence the frequency change. In addition, the impedance matching is facilitated by adjusting the parameter i (protrusion length, 132).

The frequency for the parameter d change described above is illustrated in FIG. 10, and the impedance for the parameter i change (fixed at d: 85 mm and c: 65 mm) is illustrated in FIG. 11. Referring to FIG. 11, as the protrusion length i increases, the trajectory change characteristic of the clockwise direction CW is increased. When the protrusion length increases, the path between the feed point FP and the left end of the third pattern is increased. This is because it is expressed by the effect of increasing resistance (resistance) and increasing inductance. At this time, if the protrusion length is properly selected, impedance matching can be achieved.

FIG. 12 is a table showing the change of matched parameters (i, c, d) according to the height h between the patterns and the ground plate. In particular, as a result of experimenting with the return loss for the optimized dipole antenna when the height h is 5 mm, the -10 dB bandwidth was 6 MHz (0.6%) (see FIG. 13). On the other hand, the radiation pattern of the optimized dipole antenna at each height (h) is shown in Figure 14a (E-Plane) and 14b (H-Plane), the maximum gain is 9.14 when the height is 10mm (0.03λ). dBi (7 dBd), 7.2 dBi (6 dBd) at 3 mm (0.009 λ), 6.2 dBi (4.1 dBd) at 2 mm (0.006 λ), and 2.2 dBi (0.1 dBd) at 1 mm (0.003 λ). Showed characteristics. From this, it can be seen that the dipole antenna of the present invention can maintain high gain characteristics even on a metal surface, and can be used as an RFID tag antenna for metal surface mounting.

Modifiable Embodiments

FIG. 15 illustrates a possibility that the second pattern 120 may be omitted in the dipole antenna of the above-described preferred embodiment.

FIG. 16 illustrates a structure in which 'L'-shaped members 1 and 2 are added to each of the first pattern 110 and the second pattern 120. This is a planarization of the balun described in FIG. 4, which is a rough intermediate result of the inventors inventing the dipole antenna of the preferred embodiment. Here, it is apparent that the addition of the members 1 and 2 will slightly increase the complexity of the pattern, and will bring about a change in the radiation gain and the radiation pattern, but it is likely to be sufficiently applied.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

According to the present invention as described above, it is possible to provide a planar dipole antenna for RFID tag that can be mounted on a metal surface capable of securing a high gain.

In addition, since good radiation can be realized in low profile, miniaturization can be achieved, and impedance matching is easy. Furthermore, it can be applied to heights of 1mm (0.003λ) in the 900MHz band.

Claims (3)

Rectangular or square ground plate; A dielectric seated on the ground plate; An approximately 'T' shaped first pattern seated on the dielectric; A 'b' shaped second pattern spaced and disposed with an offset from the 'a' shaped left outer periphery of the first pattern; A third pattern spaced and disposed between the first pattern and the second pattern, the third pattern having a predetermined protruding length with respect to a left end of the first and second patterns; And Short circuiting means for conducting the lower ends of the first and second patterns with the ground plate; Planar dipole antenna for a metal surface mountable RFID tag comprising a. The method according to claim 1, The first pattern is, Forming a post with the left side, the post is a flat dipole antenna for a metal surface mountable RFID tag, characterized in that formed in a shifted state with a predetermined step depth with respect to the left side. The method according to claim 1, Flat surface dipole antenna for RFID tag mounting, characterized in that the input impedance matching is made by adjusting the length of the protrusion.

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