KR20090084267A - Structure of a circularl polarized antenna for uhf band rfid reader - Google Patents

Abstract

A structure of a circular polarized wave antenna is provided to accurately recognize a plurality of tags at a long distance by minimizing an error due to multipath signals. A signal generating part divides an original signal into two signals having a phase difference of 90 degree. A pair of strip lines is formed in a radiation patch(110), and performs a circular polarized wave after receiving the signals. A radiation plate(130) has two feeding points which are separated from the radiation patch in order to improve radiation efficiency. The radiation patch and the radiation plate have different sizes. A hybrid coupler is mounted in the radiation patch, and divides the original signal into the two signals having a phase difference of 90 degree.

Description

STRUCTURE OF A CIRCULARL POLARIZED ANTENNA FOR UHF BAND RFID READER}

The present invention relates to a circularly polarized antenna, and more particularly, to a structure of a circularly polarized antenna for a UHF band RFID reader which can simultaneously and accurately recognize a plurality of tags in the UHF band.

In general, radio frequency identification (RFID) uses radio frequency to contactlessly communicate with a tag having unique identification information to read information from or write information to the tag.

I say that. Such radio frequency identification (RFID) technology is used in various fields of recognizing tagged objects (eg, objects, animals, people, etc.), tracking objects, and managing objects.

The RFID system stores unique identification information, and is used to read or write information on a plurality of tags (electronic tags or transponders, hereinafter referred to as 'tags') attached to an object or animal, and information stored on the tags. It includes an RFID reader (Reader or Interrogator).

Currently, RFID systems use the HF frequency band (13.56 MHz), the UHF frequency band (800-960 MHz), and the ISM frequency band (2.4 GHz). Among them, the HF band has a disadvantage in that the antenna recognition region is very narrow by using the magnetic field coupling method. In addition, the ISM band is sensitive to the surrounding environment, so the performance of the entire RFID system is variable. On the other hand, the UHF band has the highest recognition rate and recognition distance of passive tags, and can simultaneously recognize multiple tags at a high speed using electromagnetic radiation. It is also known as the most popular band because it is very stable in the surrounding environment and low-cost production of tags and tag chips is possible.

Therefore, the RFID system is widely used in the UHF band, and the role of the antenna connecting the reader and the tag is important in the RFID system of the UHF band for smooth tag recognition.

Hereinafter, the tag recognition range will be described according to the conventional antenna type for the UHF band RFID reader.

The reader antenna is designed as a planar polarization antenna.

1A is an exemplary diagram illustrating a tag recognition range when using a planar polarization antenna in general.

Referring to FIG. 1A, the reader antenna 1 is configured as a planar polarization antenna. In this case, the reader antenna 1 emits electromagnetic waves in the form of linearly polarized wave (plane polarized wave). That is, the vibration direction of the electric field is radiated in a constant wave form. In this case, depending on the position of the tag 2 or the orientation of the tag antenna, the reader antenna 1 may have difficulty in recognizing several tags at the same time, and malfunction may occur due to multipath. In addition, since the position of the tag 2 must be in a straight line with the polarization plane of the linearly polarized wave radiated from the reader antenna 1, the position or the orientation of the tag antenna is not free.

Therefore, circular polarization is used instead of linear polarization in order to obtain a high recognition rate regardless of the direction of the tag antenna while minimizing the error due to the multipath signal. Circularly polarized waves are formed when two linearly polarized waves are out of phase, have the same amplitude, and are perpendicular to each other. The circularly polarized wave may radiate electromagnetic waves in a circular manner and simultaneously recognize a plurality of tags regardless of the position of the tag and the antenna direction. The antenna using the circular polarization is used in military radar systems or parabolic antennas for satellite communication because of its excellent ionospheric passage characteristics.

1B is an exemplary diagram illustrating a tag recognition range when using a circularly polarized antenna.

1B illustrates a case in which the reader antenna 3 is configured as a circularly polarized antenna. In this case, since the electromagnetic wave is radiated circularly from the reader antenna 3, multiple tags can be recognized simultaneously regardless of the position of the tag and the direction of the antenna. In other words, the tag can be recognized even if it is at an oblique position 4a, at a horizontal position 4b, or at a vertical position 4c.

2A and 2B show a circular polarization antenna for a conventional RFID reader capable of generating such circular polarization.

2A is a structure in which corners 5a and 5b of the radiation patch 5 having a predetermined area are cut off. In FIG. 2B, a slot 6a having a predetermined length and width is formed in the center of the radiation patch 6.

In other words, by modifying the shape of the radiation patches 5 and 6, a method of generating circular polarization by changing the current density of the radiation patches 5 and 6 is used.

In other words, FIGS. 2A and 2B have one feeding point at a predetermined portion of the radiation patch 5, 6, and the signal power supplied through the feeding point is supplied to the radiation patch 5, 6. In this case, a circular polarization is generated due to a change in current density at the corner cut surfaces 5a, 5b or slot 6a of the patch. In particular, the circularly polarized antenna is determined by the position of the feed point, the direction of the slot 6a, the shape of the slot 6a, and the first hand circularly polarized (RHCP) or the left hand circularly polarized (LHCP). .

However, such a conventional circular polarized antenna has a problem in that the manufacturing process is cumbersome because the radiation patch has to be modified, and the use of space is inefficient because the antenna size is largely manufactured.

An object of the present invention is to solve the above problems, to minimize errors due to the multi-path signal and to acquire a high recognition rate regardless of the direction of the tag antenna to accurately recognize multiple tags at the same time without errors at a distance To provide a circular polarized antenna structure for the UHF band RFID reader for.

Another object of the present invention is to maximize antenna radiation efficiency.

According to a feature of the present invention for achieving the above object, a signal generator for generating a signal separated by two signals having a 90 ° phase difference; In addition, there is provided a circular polarization antenna for an RFID reader of a radiation patch having a pair of strip lines configured to receive the generated signal and implement circular polarization.

In addition, in order to improve the radiation efficiency, the radiation patch and the radiation plate having two feed points which are provided at a predetermined distance from the configuration further comprises.

The circularly polarized antenna is used in the UHF band.

The signal generator further includes an impedance matched microstrip transmission line for compatibility with other RFID systems.

The signal generator is a hybrid coupler or Valium, the electrical characteristics are as follows. That is, in the 800 to 1000 MHz band, the insertion loss is 0.16 dB, the isolation is 23 dB, and the voltage standing wave ratio (VSWR) is 1.15.

The spin patch is' 11cm * 11cm 'size, the spin plate is '13 .4cm * 13.4cm' size.

The pair of strip lines have the same length and width from the spin patch to the feed point. The length L is '18cm', the width W is '2mm'.

The micro strip line has a length L of '4 cm' and a width W of '2 mm'.

The circularly polarized antenna for the RFID reader has an antenna gain of 5.09 to 6.19 dBi, a voltage standing wave ratio (VSWR) of 1.037, and a tag recognition distance of about 4M.

According to the structure of the circularly polarized antenna for the UHF band RFID reader of the present invention configured as described above has the following effects.

First, several tags can be recognized at the same time at a long time without errors.

In addition, a radiation plate with two feed points can be additionally designed to maximize antenna radiation efficiency.

According to the antenna performance measurement results, the return loss was very low at -914. 5dB at 914MHz frequency, and the antenna gain was at the commercialization level.

In addition, the microstrip line transmission line technique can be applied to all commercially available 900MHz band RFID system of about 50.48Ω, which is widely applicable.

In addition, the tag recognition distance provides approximately 4M of recognition distance, which provides the same level of electrical characteristics, even though the size is reduced to about half the size of the commercially available antenna products.

Hereinafter, a circular polarization antenna structure for a UHF band RFID reader according to the present invention will be described in detail with reference to a preferred embodiment shown in the accompanying drawings.

3 is a perspective view of a circular polarization antenna for a UHF band RFID reader according to a preferred embodiment of the present invention, FIG. 4 is a side view of FIG. 3, and FIG. 5 is a plan view of the radiation patch of FIG. 3. have. 6 shows a block diagram of a circularly polarized antenna for a UHF band RFID reader.

First, the antenna for the UHF band RFID reader should have little reflection loss in the operating frequency band and be designed to have good circular polarization. In addition, it should be designed to have a high radiation pattern for remote recognition and multi-tag recognition, and the size should be made small for efficient space utilization.

Therefore, this embodiment proposes a circular polarization antenna 100 for a UHF band RFID reader to satisfy such a condition.

The overall configuration will be described with reference to FIGS. 3 and 4.

3 is provided with a radiation patch 110 for implementing a circular polarization. And the radiation plate 130 for improving the radiation efficiency of the circular polarization is provided. The radiation patch 110 and the radiation plate 130 are installed spaced apart from a predetermined interval. The radiation patch 100 and the radiation plate 130 may be spaced apart by two feeding members 140a and 140b and one support member 150. Of course, the radiation patch 110 and the radiation plate 130 may be spaced apart only by the power supply members 140a and 140b.

The radiation patch 110 and the radiation plate 130 have different specifications from each other. The radiation patch 110 has a size of '11cm * 11cm', the radiation plate 130 has a size of '13 .4cm * 13.4cm '. Therefore, it can be seen that the radiation plate 130 is formed larger than the radiation patch 110 in the drawings.

Next, the configuration of the radiation patch 110 will be described in detail with reference to FIG. 5.

The radiation patch 110 is equipped with a hybrid coupler 112 for separating the original signal into two signals having a 90 ° phase difference. The hybrid coupler 112 has a 0.16 kHz insertion loss and a 90 ° phase difference. And the electrical characteristics of the hybrid coupler 112 is shown in Table 1 below.

TABLE 1

A pair of strip lines 114a and 114b are connected to the hybrid coupler 112. The other ends of the strip lines 114a and 114b are provided with feed points 116a and 116b to which the radiating plate 130 is connected. The feeding members 140a and 140b are installed at the feeding points 116a and 116b, so that feeding is possible even when the radiating plate 130 is spaced apart. The strip lines 114a and 114b should have the same length and width from the hybrid coupler 112 to the feed points 116a and 116b. In the present embodiment, the length L of the strip lines 114a and 114b is '18 cm ', and the width W has a' 2 mm 'standard. In addition, since the strip lines 114a and 114b having the above specification should be formed in the spinning patch 110 having a small size ('11cm * 11cm'), at least one or more places are formed to be bent, and the spinning patch 100 It is formed outward from the center of the back toward the center.

In addition, a microstrip line 118 having a substantially 'b' shape is connected to the hybrid coupler 112 at a lower portion of the radiation patch 100 in order to connect with another RFID system. That is, the impedance matching method is applied to transmit the data received by the circularly polarized antenna 100 to another RFID system. The microstrip line 118 has a length L of 4 cm and a width W of 2 mm.

Reference numeral 120 denotes a ground area.

6 shows a block configuration diagram of a circular polarization antenna for a UHF band RFID reader configured as described above as an equivalent circuit.

Referring to FIG. 6, a signal generator 112 for dividing an original signal into two signals having a 90 ° phase difference by 0.16 dB insertion loss and a 90 ° phase difference is provided. The signal generator 112 is a hybrid coupler or Valium is used.

The strip lines 114a and 114b, which receive signals separated into two signals by the signal generator 112 and implement circular polarization, are connected to the signal generator 112. The strip lines 114a and 114b may be formed in various ways such as 'λ / 2', '3λ / 4', and 'λ / 4', but the strip lines of the present embodiment may be 'λ / 2'. In addition, a radiation plate 130 having two feed points for implementing circular polarization using the signal having the 90 ° phase difference is provided to increase the power efficiency and radiation efficiency of the antenna.

As described above, the signal generator 112 and the strip lines 114a and 114b are formed in the radiation patch 110, and the radiation patch 110 and the radiation plate 130 are two feeding members 140a. 140b and the support member 150 are spaced apart from each other by a predetermined interval.

The microstrip line 118 is connected to the signal generator 112 of the radiation patch 110. The microstrip line 118 is also formed in the radiation patch 110.

According to the circular polarization antenna 100 for a UHF band RFID reader configured as described above, reflection loss hardly occurs in the UHF frequency band, and a high quality circular polarization signal is generated. In addition, the radiation plate 130 provides a high radiation pattern due to the additional configuration, thereby enabling remote recognition and multi-tag recognition, thereby improving communication quality.

Thus, the operation characteristics of the circularly polarized antenna for the UHF band RFID reader will be described.

7 shows a configuration of a measuring device in the above-described measuring environment.

The measurement place in Fig. 7 is a radio wave anechoic chamber. The UHF band RFID reader circular polarization antenna 100 is set as a 'Target' antenna, and a standard antenna 200 as a reference for performance measurement is provided. The space between the two antennas 100 and 200 is 2.36m apart. A power supply device 150 is connected to the circularly polarized antenna 100, and a spectrum analyzer 160 is connected to the standard antenna 200.

The parameters of the standard antenna are shown in the following [Table 2].

TABLE 2

Under such a measurement environment, the standard antenna 200 is rotated in the horizontal and vertical directions to measure the accurate radiation pattern and the antenna gain according to the direction of the UHF band RFID reader circular polarization antenna 100, and the UHF band RFID reader circular polarization is The antenna 100 was measured while rotating in the 90 ° direction.

The antenna gain results for each of these measurement conditions are shown in Table 3 below.

TABLE 3

8 to 11 show radiation patterns according to the conditions shown in [Table 3].

FIG. 8 is a radiation pattern diagram of the first condition of the standard antenna horizontally and circularly polarized antenna in which the antenna gain is 5.59 dBi.

FIG. 9 is a radiation pattern diagram in a state in which the second condition, the standard antenna, the vertically polarized antenna is in front, and the antenna gain is 6.09 dBi.

FIG. 10 is a radiation pattern diagram in which the third condition, the standard antenna horizontal and circularly polarized antennas are rotated at 90 degrees, wherein the antenna gain is 6.19 dBi.

Fig. 11 is a radiation pattern diagram in a 90 ° rotation state of the standard antenna vertical and circular polarized antennas as the fourth condition, wherein the antenna gain is 5.09 dBi.

8 to 11, it can be seen that the antenna gain is provided with a value of 5.09 to 6.19 dBi, which is the current commercialization level.

Next, Figure 12 is a graph of the measurement results of the return loss of the UHF band RFID reader circular polarization antenna of the present embodiment.

12, the return loss is -33.355 dB at the 908.5 MHz frequency, the return loss is -38.168 dB at the 911.9 MHz frequency, and -45.529 dB at the 914 MHz frequency.

The return loss results are summarized in the following [Table 4].

TABLE 4

The reflection loss measurement results according to FIG. 12 and Table 4 show that the UHF band RFID reader circular polarization antenna of the present embodiment has greatly reduced reflection loss.

Next, FIG. 13 is a pattern diagram for measuring impedance matching parameters of the UHF band RFID reader circular polarization antenna of the present embodiment. In addition, the measured impedance value is shown in [Table 5].

TABLE 5

Referring to this, it can be seen that the impedance value is measured almost similarly, and thus is compatible with other RFID systems. Therefore, it is possible to connect an RFID system other than the RFID system first connected to the microstrip line, which is one of the configurations of the UHF band RFID reader circular polarization antenna.

Meanwhile, Table 6 compares the UHF band RFID reader circular polarization antenna of the present embodiment and a commercially available RFID antenna.

TABLE 6

Referring to [Table 6], it can be seen that the antenna size is reduced overall. That is, the commercial antenna size is about 21 cm 3 or more, but the antenna of this embodiment is about 13.4 cm 3, which is about 1/2 smaller in size.

In addition, the antenna gain is 5.09 ~ 6.19dBi depending on the antenna direction, despite the smaller antenna size, which has an antenna gain similar to that of commercial antennas.

In addition, the voltage standing wave ratio (VSWR) value is 1.037, which is superior to that of commercial antennas, and in the tag recognition distance, the embodiment antenna provides a recognition distance of approximately 4M, but the commercial antenna is about 3M or less, which provides excellent characteristics at the recognition distance. can do.

Although described with reference to the illustrated embodiment of the present invention as described above, this is merely exemplary, those skilled in the art to which the present invention pertains various modifications without departing from the spirit and scope of the present invention. It will be apparent that other embodiments may be modified and equivalent. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1A is an exemplary diagram illustrating a tag recognition range in general when using a plane polarized antenna.

Figure 1b is an exemplary view showing a tag recognition range when using a circularly polarized antenna.

Figure 2a and 2b is a configuration diagram of a circular polarization antenna for a conventional RFID reader that can generate circular polarization.

3 is a perspective view of a circularly polarized antenna for a UHF band RFID reader according to an embodiment of the present invention.

4 is a side view of FIG. 3;

5 is a plan view of the radiation patch of FIG.

6 is a block diagram of a circularly polarized antenna for a UHF band RFID reader.

7 is a block diagram of a measuring device for measuring the performance of a circularly polarized antenna for the UHF band RFID reader according to an embodiment of the present invention.

8 to 11 are each radiation pattern in the direction of the standard antenna and the circularly polarized antenna under the measuring device conditions of FIG.

12 is a graph showing measurement results of return loss of the UHF band RFID reader circular polarization antenna of the present embodiment.

FIG. 13 is a pattern diagram for measuring an impedance matching parameter of a UHF band RFID reader circular polarization antenna of the present embodiment. FIG.

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

110: radiation patch 112: hybrid coupler

114a, 114b: strip line 116a, 116b: feed point

118: microstrip line 130: radiation plate

140: power supply member 150: support member

Claims (8)

A signal generator for separating the original signal into two signals having a 90 ° phase difference; And, Circular polarized antenna structure for a UHF band RFID reader, characterized in that it comprises a radiation patch formed with a pair of strip lines for receiving the generated signal to implement a circular polarization. The method of claim 1, Circular polarization antenna structure for UHF band RFID reader, characterized in that further comprising a radiation plate having two feed points which are installed spaced apart from the radiation patch to improve radiation efficiency. The method of claim 2, The radiation patch and the radiation plate are composed of different sizes, The radiation patch is '11cm * 11cm' size, The radiation plate is a circular polarized antenna structure for a UHF band RFID reader, characterized in that the size of '13 .4cm * 13.4cm '. The method according to claim 1 or 2, The signal generator is a circular polarized antenna structure for UHF band RFID reader, characterized in that the impedance-matched microstrip transmission line is further configured for compatibility with other RFID systems. The method of claim 4, wherein The signal generator, Hybrid coupler or Valium, Circularly polarized antenna structure for UHF band RFID reader, characterized by providing the following electrical characteristics.

The method of claim 4, wherein The micro strip transmission line has a length (L) of '4cm', the width (W) is a circular polarized antenna structure for a UHF band RFID reader, characterized in that. The method according to claim 1 or 2, The pair of strip lines have the same length (L) and width (W) from the radiation patch to the feed point, The length (L) is '18cm', the width (W) is a circular polarized antenna structure for a UHF band RFID reader, characterized in that '2mm'. The method according to claim 1 or 2, The circular polarization antenna for the UHF band RFID reader, Circularly polarized antenna structure for UHF band RFID reader, characterized in that the antenna gain is 5.09 ~ 6.19dBi, the voltage standing wave ratio (VSWR) is 1.037, and the tag recognition distance is about 4M.

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