KR20080104592A - A folded inverted-f type antenna with conical radiation pattern for the container rfid tag applications - Google Patents

Abstract

A folded inverted-f type antenna with conical radiation pattern is provided to communicate with a RFID smoothly reader while making the size of the antenna small. A folded inverted-f type antenna with conical radiation pattern includes a ground plane(G), a dielectric(F) settled on the ground plane and a pair of horizontal rectangular or square elements(110, 120) symmetry of an extension lines(111a, 121a) settled on the top of the dielectric, Vertical device(V1, V2) extended from the extension line to the ground plane and A feeding line(FL) extended from the wire extend of the extension line of the horizontal element to the ground plane.

Description

FOLDED INVERTED-F TYPE ANTENNA WITH CONICAL RADIATION PATTERN FOR THE CONTAINER RFID TAG APPLICATIONS}

1 is an exemplary view showing a conical radiation pattern of the present invention,

2A is a configuration diagram of a monopole antenna and a folded monopole antenna;

Figure 2b is a graph showing the return loss of the monopole antenna and folded monopole antenna,

2C is a Smith chart of a monopole antenna and a folded monopole antenna;

2d is a radiation pattern diagram of a monopole antenna,

2E is a radiation pattern diagram of a folded monopole antenna;

3A is a configuration diagram of a folded inverted-L antenna and a folded inverted-F antenna;

3b is a graph showing return loss between a folded inverted L antenna and a folded inverted F antenna;

3C is a Smith chart of a folded inverted-L antenna and a folded inverted-F antenna;

3d is a radiation pattern diagram of a horizontal element of a folded inverted-F antenna;

3E is a radiation pattern diagram of a vertical element of a folded inverted-F antenna;

4A is a block diagram of a miniaturized folded inverted-F antenna;

4b is a detailed configuration diagram of a horizontal element of a miniaturized folded inverted-F antenna;

4C is an exemplary physical diagram of a miniaturized folded inverted-F antenna;

4d is a horizontal element radiation pattern diagram of a miniaturized folded inverted-F antenna;

4E is a vertical element radiation pattern diagram of a miniaturized folded inverted-F antenna;

5A is a block diagram of a miniaturized folded inverted-F antenna having a conical radiation pattern of the present invention;

5b is a detailed configuration diagram of a horizontal element of a miniaturized folded inverted-F antenna having a conical radiation pattern of the present invention;

5C is an exemplary physical figure for a miniaturized folded inverted-F antenna having a conical radiation pattern of the present invention;

5D is a radiation pattern diagram of a miniaturized folded inverted-F antenna having a conical radiation pattern of the present invention;

FIG. 5E is a characteristic comparison table for a 'folded inverted F-type antenna', 'a folded inverted F-type antenna miniaturized through a meander line structure', and a 'miniaturized folded inverted F-type antenna having a conical radiation pattern'

6A is a configuration diagram of an antenna according to a first modified embodiment of the present invention;

6b is a detailed configuration diagram of a horizontal element of an antenna according to a first modified embodiment of the present invention;

7A is a configuration diagram of an antenna according to a second modified embodiment of the present invention;

7b is a detailed configuration diagram of a horizontal element of an antenna according to a second modified embodiment of the present invention;

8A is a configuration diagram of an antenna according to a third modified embodiment of the present invention;

8B is a detailed configuration diagram of a horizontal element of an antenna according to a third modified embodiment of the present invention.

The present invention relates to an antenna for a container RFID tag, and more particularly, to a folded inverted-F antenna for forming a conical radiation pattern suitable for a container environment.

RFID (Radio Frequency IDentification) system attaches a tag with a unique ID to a thing, and is a system capable of collecting, processing, and tracking information of the thing [1]. Such RFID systems are largely classified into passive type and active type according to whether a tag battery is present. Passive RFID system uses the electromagnetic wave radiated from the reader to the power of the tag, and is widely used for distribution and logistics because of the production cost, but has a disadvantage of short recognition distance (1 to 3m). On the other hand, the active RFID system with its own power supply (battery) is applied to pallets, container management and factory parts management systems in airports and harbors because of its longer recognition distance (100m) [2].

In 2005, the US Customs Service issued a mandatory policy to attach RFID tags to containers. RFID tags will be attached to all containers entering and leaving the United States [2]. Port logistics applications using active RFID systems will be used in a variety of areas, including cargo tracking management, cargo entry and exit management at terminal gates, shipping automation, and container security management, to implement automation of port logistics systems.

The active frequency of the active RFID system attached to the container is 433.67 ~ 434.17MHz (500 kHz bandwidth), and the wavelength (693mm) is long, so that the RFID tag antenna can be miniaturized and easily attached to the container. In addition, the tag must be able to be attached to the metal (considering the material of the container). Such antennas are currently in use with an externally attached microstrip patch antenna and a loop antenna embedded in the tag [3]. The microstrip patch antenna can be miniaturized using a high dielectric constant, but the antenna loss due to the dielectric constant is large and weighs a lot. On the other hand, the closer the loop antenna is to the metal, the smaller the input impedance, leading to a decrease in antenna efficiency. Therefore, the antenna attached to the container must be compact, low profile, embedded in the tag and attached to the surface of the container, ie metal.

[One]. Klaus Finkenzeller, RFID Handbook, Wiley, 2003

[2]. Lee, Eun-Ju, Sung Nak-Sun, Young-Gil Choi, Cheol-Sik, "Active RFID Technology for Port Logistics", Korea Electromagnetic Engineering Society, Vol. 16, No. 3, pp 26-32, 2005.7

[3]. http://www.savi.com

The present invention has been made in view of the above problems, it can be mounted on the metal surface while making a compact through a low profile, so as to achieve a smooth communication with the RFID reader in a harsh environment in which the container is dense and stacked as shown in FIG. Provided is a folded inverted-F antenna for a container RFID tag that forms a conical radiation pattern.

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, experimental examples for understanding the antenna of the present invention will be described. The following experimental examples may be understood as a series of design processes which the present inventors went through to establish a "folded inverted-F antenna for a container RFID tag" of a preferred structure.

[Compared to monopole antenna and folded monopole antenna]

In general, the closer the antenna is to a metal conductor, the smaller the input impedance, which leads to a decrease in efficiency as well as to a smooth emission. Therefore, it is desirable to design a low profile antenna having a high input impedance as an antenna for an RFID tag of a container made of a metal conductor as a whole.

In FIG. 2A, reference numeral [A] denotes a strip line type monopole antenna fabricated at a frequency of 433 MHz in a container RFID system, and reference numeral [B] denotes a folded monopole antenna in a strip line type. Both constitute a finite ground plane (400 mm x 400 mm), the radiating element length of the monopole antenna is 0.24 lambda (165 mm), and the radiating element length of the folded monopole antenna is 0.22 lambda (155 mm). In addition, the width of a quantum antenna is 2 mm, and the space | interval of a folded monopole antenna is 2 mm.

As shown in FIGS. 2B and 2C, the input impedance of the monopole antenna has 25.6 + j9.4 Ω, and the folded monopole antenna has a higher impedance than the monopole antenna of 87-j29 Ω. The high impedance of the folded monopole antenna is due to mutual coupling according to the spacing of the radiating elements.

2D is a radiation pattern diagram of a monopole antenna, and FIG. 2E is a radiation pattern diagram of a folded monopole antenna. The radiation pattern of the quantum antenna is conical, and the maximum gain is -0.25dBd (zx plane) for monopole antenna and 1.12dBd (zx plane) for folded monopole antenna, which is 1.37dB higher than monopole antenna. Able to know. This is due to the phenomenon that the radiation resistance is increased and the efficiency of the folded monopole antenna is good.

[Folded Inverted-F Type Antenna ]

The inventors of the present invention attempted to design an antenna that maintains the posture and the conical radiation pattern by deforming the folded monopole antenna to an inverted L shape in view of the characteristics of the foregoing embodiment.

In FIG. 3A, reference numeral [A] denotes a folded inverted L antenna, and [B] denotes a folded inverted F antenna. The folded inverted L-type antenna manufactured as shown in the drawing has a length of 20 vertical elements at a design frequency of 433 MHz. Mm (0.03 lambda), the length of the horizontal element is 152 mm (0.2 lambda), and the width and the distance of the conducting wire are 2 mm. At this time, the return loss is -2.4dB (7.6 + j16.6) as shown in FIG. 3B and 50 ohm impedance matching was not performed. This is because the force impedance decreases as the ground plane and the horizontal element of the folded inverted L antenna are closer to each other as shown in the Smith chart of FIG. 3C.

Therefore, for impedance matching, the modified inverted F-type antenna as shown in [B] of FIG. 3A. The folded inverted-F antenna of the figure may achieve impedance matching according to the distance g between the vertical element and the feeding line. The return loss of the folded inverted F-type antenna thus produced showed -20.8dB, -10dB bandwidth of 5.8MHz (1.3%) at resonant frequency, and showed better impedance matching than the folded inverted L-type antenna.

FIG. 3D is a radiation pattern diagram of a horizontal element of a folded inverted-F antenna, and FIG. 3E is a radiation pattern diagram of a vertical element. The maximum gain of the horizontal device was 1.6dBd, the HPBW (z-y plane) was 122 °, the maximum gain of the vertical device was -1.3dBd, and the HPBW (z-x plane) was 81 °. The ground plane of the fabricated folded inverted-F antenna has a finite size (400 mm x 400 mm), and it can be considered that the ground plane is electrically small and there is much back radiation. Since the basic folded F-type antenna is large in size to be used as an antenna for a container RFID tag, it needs to be further miniaturized. Therefore, the 'meander line' structure is combined as follows.

[ Miniaturized folded inverted-F antenna with meander line structure ]

4A is a view showing the configuration of a miniaturized folded inverted-F antenna, a square ground plane (G), a dielectric (F, foam) seated on the ground plane, and seated on the dielectric The horizontal element 10, the vertical elements V1 and V2 vertically extending from the ends of the open extension lines 11a and 12a of the horizontal element to the ground plane and shorted to the ground plane, and grounded from one open extension line 12a. It constitutes a feeding line (FL, extending in the plane direction).

Referring to FIG. 4B, the horizontal element 10 includes a first meander line portion 11 and a second meander line portion 12 that are symmetrically arranged left and right with respect to the vertical gap S in the center. However, the entire outline forms a rectangle. Here, the term "meander" refers to a plurality of pulse-like lines (PL) that are continuous as shown in the figure, which is similar to the 'squiggly' shape. The first meander line portion 11 and the second meander line portion 12 are continuous lines, the first meander line portion is the first open extension line 11a, and the second meander line portion is the first line. 2 to form an open extension line (12a).

The folded inverted-F antenna having such a configuration was optimized (miniaturized) to a size of 42 mm (width) x 40 mm (length) x 20 mm (height) as shown in Fig. 4C. Specifically, the length reduction rate of the horizontal element is 74% (111mm) based on the basic folded F-type antenna described above, and the return loss at the design frequency is -18.4dB, -10dB bandwidth of 4.7MHz (1%). Showed. This sufficiently accommodates the frequency band (500 kHz) of the container RFID system.

4D is a horizontal element radiation pattern diagram of a miniaturized folded inverted-F antenna, and FIG. 4E is a vertical element radiation pattern diagram. In the case of the horizontal element radiation pattern, the gain is reduced compared to the basic type due to the miniaturization, and the maximum gain is -2.2dBd and HPBW (z-y plane) 79 °. The radiation pattern of the horizontal element z-y surface can be seen that the vertical element is strongly radiated due to the miniaturization of the horizontal element. The radiation pattern of the vertical device also decreased due to the miniaturization, but the overall radiation pattern is maintained. However, such a miniaturized antenna does not form a conical radiation pattern to be implemented in the present invention, it is not suitable for a yard on which containers are stacked. Therefore, in order to form a conical radiation pattern, an antenna in which a horizontal element is symmetric about the x-axis is designed as in the following preferred embodiment.

Miniaturized Folded Inverted-F Antenna with Conical Radiation Pattern

5A and 5B, an antenna according to a preferred embodiment of the present invention includes a ground plane (G), a dielectric material (F) seated on the ground plane, and one open facing the dielectric material. A pair of square or rectangular horizontal elements 110 and 120 which are symmetrical about the extension lines 111a and 121a (symmetric about the x-axis), and extend vertically in the direction of the ground plane from the one open extension line A feed line FL extending in the direction of the ground plane from the vertical elements V1 and V2 shorted to the surface, and the extension lines BL of the other open extension lines 112a and 122a of the horizontal elements 110 and 120, and An extension vertical element (V) extending vertically from the extension line in the direction of the ground plane and shorted to the ground plane. Here, the other open extension line, that is, the open extension line 112a of the left horizontal element 110 and the open extension line 122a of the right horizontal element 120 in FIG. 5B form an integrated extension line as shown by a member symbol 'BL'. . In addition, each of the horizontal elements 110 and 120 constitutes a first meander line portion and a second meander line portion that are symmetrical (y-axis symmetry in the drawing) with respect to the vertical gap as described above. 5C is a diagram showing physical values (dimensions) of such an antenna.

In the antenna of the above-described configuration, the current raised through the vertical element is reversed in the direction of the current about the x-axis so that the radiation component of the horizontal element is cancelled. Therefore, the horizontal element affects the resonance length, and the 'conical radiation pattern' is formed by the vertical element. The return loss of the designed antenna is -13.4dB and -10dB bandwidth is 4.7MHz (1%).

5D is a radiation pattern diagram of a miniaturized folded inverted-F antenna having a conical radiation pattern. The radiation pattern was measured in the θ direction at intervals of 45 ° from Φ = 0 ° to Φ = 135 °. As a result, a uniform radiation pattern was formed in each direction, so that the conical radiation pattern to be implemented in the present invention appeared.

FIG. 5E illustrates the above-described 'folded inverted F-type antenna', 'folded inverted F-type antenna' through a meander line structure, and 'miniaturized folded inverted F-type antenna having conical radiation pattern'. Table of characteristics comparison.

Hereinafter, the modified examples of the horizontal device will be described based on the above-described preferred embodiment. In the description of the variations, references to dielectrics, including configurations common to preferred embodiments, such as ground planes, are omitted.

First Modified Example

6A and 6B, three rectangular horizontal elements 210, 220, and 230 are disposed at an angle of 120 °, not shown from one open extension line 211a, 221a, and 231a of each horizontal element. It includes a vertical element extending vertically in the direction of the ground plane and the ground plane and short. In addition, the other open extension lines 212a, 222a, and 232a of each horizontal element form an extension line BL integrally formed at the conformal center point, and the feed line and the ground line from the extension line are not shown. Extending vertically extending in the direction and shorted to the ground plane (V; only a part of which is shown in the figure).

As shown in FIG. 6B, the horizontal elements 210, 220, and 230 each have a first meander line portion and a second meander line portion that are symmetrical with respect to the vertical gap S, as described above. The lower part (corner) forms a triangular incision.

Second Modified Example

Referring to FIGS. 7A and 7B according to the second modified embodiment, four triangular horizontal elements 310, 320, and 330 disposed in a rectangular shape and having vertices (virtual vertices) positioned at the center thereof And a vertical element 340 which extends vertically from the one open extension line 311a, 321a, 331a, and 341a of each horizontal element 310, 320, 330, 340 in the direction of the ground plane, and is shorted to the ground plane. Not shown). The other open extension lines 312a, 322a, 332a, and 342a of each horizontal element form an extension line BL formed integrally, and a feed line (not shown) extending from the extension line in the direction of the ground plane and from the extension line in the direction of the ground plane. Extends vertically to form an extended vertical element (V) shorted to the ground plane.

In addition, each horizontal element (310, 320, 330, 340) is composed of a first meander line portion and a second meander line portion symmetrical with respect to the vertical gap (S), and has a triangular shape having a vertex Take it.

Third Modified Example

8A and 8B according to the third modified embodiment, the left, right, top, bottom four fan-shaped horizontal elements 410, 420, 430, and 440 which are disposed in a garden shape as a whole and whose vertices are located at the center are shown. And vertically extending from the one open extension line 411a, 421a, 431a, 441a of each horizontal element 410, 420a, 430, 440 in the direction of the ground plane and shorting the ground plane. do. In addition, similar to the first and second modified embodiments, the other open extension lines 412a, 422a, 432a, and 442a of each horizontal element form an extension line BL formed integrally, and extend from the extension line toward the ground plane. Configure the feed line shown.

Each of the horizontal elements 410, 420, 430, and 440 includes a first meander line portion and a second meander line portion that have left and right symmetry with respect to the vertical gap S, and have a vertex shape having a vertex. Is formed.

According to the present invention described above, as well as providing a miniaturized folded inverted-F antenna to form a conical radiation pattern, as well as to achieve a smooth communication with the RFID reader in an environment where the container is dense, stacked as An antenna for an RFID tag can be provided.

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 right of invention.

Claims (9)

A ground plane, a dielectric seated on the ground plane, a pair of rectangular or square horizontal elements symmetrical with respect to one open extension line facing and facing the dielectric surface, from the one open extension line toward the ground plane A vertical element extending and shorted to the ground plane, a feeding line extending from the extension line of the other open extension line of the horizontal element to the ground plane, and an extension vertical element extending from the extension line to the ground plane and shorted to the ground plane Including; The horizontal device is a folded inverted F type for a container RFID tag having a conical radiation pattern, comprising a first meander line portion and a second meander line portion which are left-right symmetrical with respect to the center vertical gap. antenna. The method according to claim 1, The extension line is, A folded inverted-F antenna for a container RFID tag having a conical radiation pattern, wherein the other open extension lines of each of the horizontal elements are integrally formed. A ground plane, a dielectric seated on the ground plane, three rectangular or square horizontal elements disposed at an angle of 120 ° above the dielectric, and extending from one open extension line of the horizontal element in the direction of the ground plane to short-circuit the ground plane. A vertical element, a feeding line extending in the direction of the ground plane from an extension line of the other open extension line of the horizontal element, and an extension vertical element extending from the extension line in the direction of the ground plane and shorted to the ground plane, The horizontal device is a folded inverted F type for a container RFID tag having a conical radiation pattern, comprising a first meander line portion and a second meander line portion which are left-right symmetrical with respect to the center vertical gap. antenna. The method according to claim 3, The extension line is, The folded inverted-F antenna for the container RFID tag having a conical radiation pattern, wherein the other open extension lines of each of the horizontal elements are formed integrally with the conformal center point. The method according to claim 3, A folded inverted-F antenna for a container RFID tag having a conical radiation pattern, wherein the outer lower portion of the first meander line portion and the second meander line portion form a triangular cutout. A ground plane, a dielectric seated on the ground plane, four triangular horizontal elements positioned at the top of the dielectric and having a vertex at the center thereof, and a ground plane from one open extension line of the horizontal element; Vertical element extending in the direction and shorted to the ground plane, a feeding line extending from the extension line of the other open extension line of the horizontal element in the direction of the ground plane, and an extension extending from the extension line in the direction of the ground plane to the ground plane Including vertical elements, The horizontal device is a folded inverted F type for a container RFID tag having a conical radiation pattern, comprising a first meander line portion and a second meander line portion which are left-right symmetrical with respect to the center vertical gap. antenna. The method according to claim 6, The extension line is, A folded inverted-F antenna for a container RFID tag having a conical radiation pattern, wherein the other open extension lines of each of the horizontal elements are integrally formed. A ground plane, a dielectric seated on the ground plane, four flat fan-shaped horizontal elements seated on top of the dielectric and having vertices at the center, and one open extension line of the horizontal element A vertical element extending in the plane direction and shorted to the ground plane, a feeding line extending in the direction of the ground plane from an extension line of the other open extension line of the horizontal element, and extending from the extension line in the direction of the ground plane to short the ground plane; Including an extension vertical element, The horizontal device is a folded inverted F type for a container RFID tag having a conical radiation pattern, comprising a first meander line portion and a second meander line portion which are left-right symmetrical with respect to the center vertical gap. antenna. The method according to claim 8, The extension line is, A folded inverted-F antenna for a container RFID tag having a conical radiation pattern, wherein the other open extension lines of each of the horizontal elements are integrally formed.

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