KR100964117B1 - Antenna system and rfid terminal using the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna system having polarization diversity characteristics, and more particularly, to an RFID antenna system capable of effectively performing wireless access to various types of RFID tags using near field signals in an ultra high frequency (UHF) band, and the same. The present invention relates to an RFID terminal.

An antenna of the present invention comprises: an antenna having two patch surfaces and two feed points connecting thereto; And a power supply module including a power supply circuit for adjusting a phase of a predetermined signal and supplying the signal to the antenna and a timing controller for differently determining whether or not a signal is supplied to each power supply point according to a time interval. It features.

The antenna system according to the present invention has an advantage of selectively forming electromagnetic fields of various patterns, thereby ensuring higher reliability of a communication channel even in an environment in which polarization characteristics are severely changed.

Diversity, Polarization, RFID, Antenna, Tag

Description

ANTENNA SYSTEM AND RFID TERMINAL USING THE SAME

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antenna system having polarization diversity characteristics, and more particularly, to an RFID antenna system capable of effectively performing wireless access to various types of RFID tags using near field signals in an ultra high frequency (UHF) band, and the same. The present invention relates to an RFID terminal.

Recently, various transmission techniques have been introduced to increase communication transmission capacity or to secure higher reliability in mobile communication systems, and diversity technique is a method used to increase communication reliability. The present invention relates to an antenna having a polarization diversity characteristic among various diversity techniques.

In general, RFID (hereinafter, referred to as 'RFID') technology uses a radio frequency signal to read data stored in a tag, a label, a card, etc., in which a small semiconductor chip is embedded, without contact. Refers to a technique for identifying a subject.

Such RFID technology uses radio frequency signals to recognize the information of the article and its surroundings from the tags attached to the article, so that the information of each article can be collected, stored, processed and tracked, thereby locating and remotely identifying the article. It enables the provision of various services such as processing, management and information exchange between goods.

On the other hand, the recent RFID technology is gradually expanding the market to RFID applications using the ultra-high frequency (UHF) band (300MHz ~ 3GHz).

The RFID system of the UHF band is capable of tag recognition even at an effective recognition distance of 5 m or more, and also has an advantage of having a very high recognition speed and recognition rate compared to the HF band even at a short distance of less than 50 cm.

In such a UHF band RFID system, the farfield is mainly formed of an electric field, and thus tag recognition at a far distance is possible, but it is sensitive to the surrounding environment because it is operated by backscattering.

On the other hand, in the RFID system of the UHF band, the nearfield is mainly formed as a magnetic field and operated by a coupling, so that the tag recognition rate of the RFID reader is low because the influence of the material having high dielectric constant such as water or metal is hardly affected. It has the advantage of high recognition rate and high speed.

Currently used RFID tags can be classified into four types according to the type of electromagnetic field used, and RFID readers are also manufactured according to the tag types.

Vpol RFID tag using vertical polarized electromagnetic field, Hpol RFID tag using RFID polarized horizontal field, LHCP RFID tag using circular polarized electromagnetic field rotating to the left, RFID using circular polarized electromagnetic field rotating to the right As a tag, it can be classified as an RHCP RFID tag.

FIG. 1 illustrates a linear polarization RFID antenna according to the related art for performing wireless access to a linear polarization tag, a Vpol RFID tag and an Hpol RFID tag, and FIG. 2 illustrates a circular polarization tag, an LHCP RFID tag and an RHCP RFID tag. A circularly polarized RFID antenna according to the prior art for performing radio access to the antenna is shown.

The linearly polarized RFID antenna of FIG. 1 includes a cross strip line so as to correspond to both vertical and horizontal polarizations. The technique of FIG. 1 performs radio access to a Vpol RFID tag and an Hpol RFID tag by changing polarization characteristics by attaching and switching an element having an RF switch function to a slot antenna / dipole antenna and a patch antenna.

In the case of the circularly polarized RFID antenna shown in FIG. 2, the direction of the circularly polarized wave by the loop antenna 402 is determined using the switch 410 to perform radio access to the LHCP RFID tag or the RHCP RFID tag.

However, in the related art, the polarization characteristic may be degraded between transceivers in an environment in which a fading effect in a multi path and a polarization characteristic change due to various tag antenna structures vary depending on the RFID application.

In addition, even if one antenna can be stably used for either a set of circular polarization or a linear polarization, at least two RFID antennas or RFID readers are required to detect all four types of RFID tags. Remaining.

An object of the present invention for solving the above problems is to provide an RFID antenna system and an RFID terminal that can effectively wirelessly access various types of RFID tags.

Another object of the present invention is to provide an antenna system capable of securing reliability in an environment where polarization characteristics change frequently.

The present invention proposes an antenna having polarization diversity characteristics that are time-divisionally variable so that the polarization characteristics can be used in a large environment.

An antenna of the present invention for achieving the above object, the antenna having two patch surfaces and two feed points connecting it; And a power supply module including a power supply circuit for adjusting a phase of a predetermined signal and supplying the signal to the antenna and a timing controller for differently determining whether or not a signal is supplied to each power supply point according to a time interval. It features.

Preferably, the two patch surfaces overlap each other in parallel, and the two feed points may be in the form of a line connecting the two patch surfaces vertically.

delete

Preferably, the two feed points may be positioned such that the center line and the two line segments forming each of the feed points are orthogonal to each other on the smaller patch surface of the two patch surfaces.

Preferably, the power supply module may be configured to repeatedly supply a power supply signal to only one selected from the two power supply points or supply the power supply signal with a phase difference of 90 ° to the power supply points according to the time interval. .

delete

Preferably, the antenna may be an RFID antenna for performing radio access with an RFID tag.

An RFID terminal of the present invention for achieving the above object, RFID antenna having two feed points; A power supply module including a power supply circuit for adjusting a phase of a predetermined signal and supplying the signal to the RFID antenna and a timing controller for differently determining whether or not a signal is supplied to each power supply point according to a time interval; And a reading unit which transmits the predetermined signal to the power supply module to perform data communication with the RFID tag.

When implementing the RFID antenna system according to the present invention, an antenna having a polarization diversity effect has the advantage of implementing both a circular polarization (RHCP, LHCP), linear polarization (Vpol, Hpol) by changing the phase in the double feeder have. That is, while having a single RFID antenna, there is an advantage that can effectively wirelessly access various types of RFID tags.

In addition, the antenna system according to the present invention has the advantage of selectively forming a variety of electromagnetic fields of various patterns, to ensure a higher reliability for the communication channel even in an environment where the polarization characteristics change severely.

An RFID antenna system according to an embodiment of the present invention includes a power supply circuit including an RFID antenna and a switching circuit as two features embodying the spirit of the present invention.

More specifically, the RFID antenna system according to an embodiment of the present invention, an antenna for an RFID terminal having a polarization diversity effect, may have a structure of a double feed antenna, and change a phase at two feed points to change a circular polarization ( RHCP, LHCP) and linearly polarized switching (Vpol, Hpol) can be implemented to include a switching circuit.

3A, 3B and 4 illustrate one embodiment of an RFID antenna of the present invention. Preferably, the illustrated RFID antenna has a polarization diversity effect and has a dual feed antenna structure.

The illustrated RFID antenna has two planar conductor shaped patch faces 120, 140 overlapping in parallel with each other. That is, when looking down in the vertical direction of the plane, it is preferable to implement so that one patch surface 140 of the two patch surface is completely included in the other patch surface 120.

In addition, two feed points in the form of a line connecting the two patch surfaces (120, 140) are provided. In this case, the two feed points 162 and 164 are located at a point spaced apart from the center point of the smaller one of the two patch surfaces 120 and 140, and the two line segments connecting the feed point and the center point are perpendicular to each other. It is desirable to implement. In addition, the two feed points 162 and 164 are preferably spaced apart from the center point by the same distance.

For convenience of installation of the RFID antenna, one of the two patch surfaces 120 and 140 may have a rectangular shape, and the small one may have a rectangular or circular shape.

The illustrated RFID antenna can selectively express polarization characteristics of RHCP, LHCP, Vpol, and Hpol according to the phase adjustment of the feed signal applied to the two feed points 162 and 164 by the method according to the spirit of the present invention. . That is, the two feed points 162 and 164 are applied with two signals in which the same feed signal is shifted only in phase, thereby operating the RFID antenna.

5A, 5B to 8A and 8B illustrate the forms of the near electromagnetic field radiated on the two patch surfaces according to the phases of the feed signals applied to the second feed point of the RFID antenna according to the embodiment of the present invention.

For convenience of description, when the patch surface is viewed vertically in the area where the RFID tag to perform wireless access is located vertically, the feed point that passes first when rotated clockwise about the center point is referred to as a first feed point. The feeding point passing after the next 90 ° rotation will be referred to as the second feeding point.

In the case of circular polarization, LHCP or RHCP can be efficiently implemented by applying a feed signal having a different phase to two feed points spaced apart from each other at right angles at a center point of an RFID antenna having two patch surfaces.

5A and 5B, a feed signal which is 90 ° out of phase with a feed signal supplied to the second feed point is supplied to the first feed point among the two feed points positioned at the ends of the line segments orthogonal to each other at the center point, thereby providing an LHCP type proximity. The radiation pattern and surface current when the electromagnetic field is formed are shown.

6A and 6B show a radiation pattern and a surface current when a feed signal that is 90 degrees out of phase with the feed signal supplied to the second feed point is supplied to the first feed point to form a proximity electromagnetic field in the form of RHCP. .

As shown in Fig. 5A, the highest gains in the Ex and Ey directions are 5.87 dBi and 4.73 dBi, respectively, and satisfy the CP antenna characteristics with an axial ratio of 3 dB or less. In FIG. 5B, it can be seen that the surface current distribution rotates clockwise as time changes. 6A and 6B can be analyzed as well.

In the case of horizontal / vertical polarization, a vertical polarization or horizontal polarization is generated by supplying a feed signal to only one of the two feed points located at the ends of the line segments perpendicular to each other at the center point, which can form a vertical or horizontal line with the center point. Can be implemented.

On the other hand, in this case, the feed point to which the feed signal is not supplied is opened by the inductor and diode cathode terminals connected to the feed point.

7A and 7B show a radiation pattern and a surface current when a feed signal is supplied only to a first feed point that can form a vertical line at the center point and the reference point of view of the figure, thereby forming a proximity electromagnetic field in the form of a vertical polarization. have.

8A and 8B illustrate a radiation pattern and a surface current when a feed signal is supplied only to a second feed point that may form a horizontal line segment at the center point and the reference point of view of the drawing, thereby forming a proximity electromagnetic field in the form of a horizontal polarization. have.

As shown in Fig. 7A, the highest gains in the Ex and Ey directions are 8.32 dBi and -13.74 dBi, respectively, and satisfy the LP antenna characteristics in the X direction. In FIG. 7B, it can be seen that surface current is distributed in the X direction with time. 8A and 8B can be analyzed as well.

FIG. 9 illustrates an embodiment of an RFID antenna system for using a dual-feed RFID antenna according to the spirit of the present invention, and for differently driving the phase and whether the feed signal is supplied to each of the two feed points in time division. The physically illustrated structure may take the form of an RFID terminal for reading an RFID tag together with the RFID reading unit 700.

An RFID antenna system according to the illustrated embodiment includes: an RFID antenna 100 of the structure of FIG. 4 including two feed points having dual polarization diversity characteristics; A feeding circuit 200 for adjusting a phase of a feeding signal input from an external RFID reading unit 700 and supplying the adjusted feeding signal to the RFID antenna; And a timing controller 600 for differently determining a phase adjusted by the power supply circuit 200 and whether power is supplied according to a time interval.

The timing controller 600 controls the operation of the power supply circuit 200 according to a time interval. When using this, the power supply is supplied to feed points 162 and 164 of the RFID antenna 100 time-divisionally. The phase of the signal can be controlled.

The timing controller 600 may be implemented as a circuit that sequentially repeats two or more types of output signals at predetermined time intervals. Since such circuits are disclosed in various forms in the general electronics industry, detailed descriptions thereof will be omitted.

10 illustrates an embodiment of the power supply circuit. The power supply circuit implements a path switching function using a pin diode having a relatively low cost and sufficient performance.

The illustrated power feeding circuit includes a first feed path module for supplying a feed signal to a first feed point and a second feed path module for supplying a feed signal to a second feed point.

Each of the feed path modules includes two internal paths different in phase change when the feed signal passes, in order to adjust the phase of the feed signal to two types. The two internal paths include a first internal path through which the feed signal passes without phase change and a second internal path through which the feed signal passes through the phase shift by λg / 4.

The first feed path module may include a first pin diode (D1) intermittent with the first internal path; A second pin diode (D2) which intercepts the second internal path; A first inductor L1 having one end connected to an anode of the first pin diode D1 and the other end connected to a driving voltage terminal V1 for the first pin diode; A second inductor L2 having one end connected to the cathode of the first pin diode D1 and the other end connected to ground; A first phase adjusting element P1 having one end connected to an anode of the second pin diode D2; A third inductor L3 having one end connected to the other end of the first phase adjusting element and the other end connected to a driving voltage terminal V2 for the second pin diode; A second phase adjusting element P2 having one end connected to the cathode of the second pin diode D2; One end is connected to the other end of the second phase adjusting element P2 and the other end is formed of a fourth inductor L4 connected to ground.

Also, a feed signal input from an external RFID reading unit is input to the first / second pin diode via a coupling capacitor, and a feed signal output from the first / second pin diode is connected to a coupling capacitor. Is preferably output to the RFID antenna.

To this end, in the illustrated structure, a first capacitor C1 is provided as a coupling capacitor for the anode of the first pin diode, and a second capacitor C2 is provided as a coupling capacitor for the cathode of the first pin diode. And a first capacitor C1 and a third capacitor C3 as a coupling capacitor for the anode input of the second pin diode, and a second capacitor C2 as a coupling capacitor for the cathode input of the second pin diode. And a fourth capacitor C4.

The power supply circuit gives a predetermined phase to the input power supply signal, and outputs it to one end of an internal conductor of the RFID antenna. That is, when the first path is selected, the power supply circuit transfers the input feed signal to the RFID antenna without phase change, and when the second path is selected, transfers the input feed signal by 90 ° to the RFID antenna. .

To this end, the first phase adjustment element P1 and the second phase adjustment element P2 may be implemented in a structure having a phase of 0 ° and 90 ° by changing the electrical length of the micro strip line. In the drawing, λg means wavelength according to the effective dielectric constant in the micro strip line.

On the other hand, the switching to the pin diode may be performed by applying the voltage to the two driving voltage terminals (V1, V2).

Since the second feed path module has a symmetrical structure composed of the same components as the first feed path module, a detailed description thereof will be omitted.

FIG. 11A illustrates a current flow diagram and a signal path when the power supply circuit shown in FIG. 10 is switched to a mode for generating RHCP, and FIG. 11B illustrates a current flow diagram and signal path when a mode for the LHCP generation is switched. 12A shows a current flow diagram and a signal path when switching to a mode for generating a vertical polarization, and FIG. 12B shows a current flow diagram and a signal path when switching to a mode for generating a horizontal polarization. In the figure, the shaded line shows the flow of the RF signal, and the solid line shows the flow of current turning on the pin diode.

The operation of the RFID antenna system according to an embodiment of the present invention is as follows.

First, in order to form the RHCP, as shown in FIG. 11A, when a voltage equal to or higher than a threshold voltage at which the pin diode can operate is applied to the voltage terminals V2 and V3 of the power supply circuit, the first pin diode D2 and the third pin diode (D3) is turned on. Accordingly, the signal applied from the reading part is converted into a signal having a phase of Port 1 (-90 °) and Port 2 (0 °) to obtain an antenna gain having CP characteristics as shown in FIGS. 5A and 5B. Can be.

In order to form the LHCP, as shown in FIG. 11B, when a voltage equal to or higher than a threshold voltage at which the pin diode can operate is applied to the voltage terminals V1 and V4 of the power supply circuit, the first pin diode D1 and the fourth pin diode ( D4) is turned on. Accordingly, the signal applied from the reading part is converted into a signal having a phase of Port 1 (0 °) and Port 2 (-90 °) to obtain an antenna gain having CP characteristics as shown in FIGS. 6A and 6B. Can be.

In order to form a vertical polarization, as shown in FIG. 12A, when a voltage equal to or greater than a threshold voltage at which the pin diode can operate is applied only to the voltage terminal V1, only the first pin diode D1 is turned on. Accordingly, only the signal Port 1 for the first feed point is applied, so that an antenna gain having vertical polarization characteristics as shown in FIGS. 7A and 7B can be obtained.

In order to form a horizontal polarization, as shown in FIG. 12B, when a voltage equal to or higher than a threshold voltage at which the pin diode can operate is applied to only the V3 voltage terminal, only the second pin diode D2 is turned on. Accordingly, only the signal Port 2 for the second feed point is applied, so that an antenna gain having vertical polarization characteristics as shown in FIGS. 8A and 8B can be obtained.

Four combinations of whether a signal is supplied to each feed point and its phase are implemented to be repeated at a time interval sufficient to recognize an RFID tag. Accordingly, one RFID terminal having an RFID antenna system according to the spirit of the present invention can recognize four types of RFID tags.

An example of constructing the four combinations and converting them time-divisionally is shown in Table 1 below. The time intervals in the following table are exemplified, and different time intervals may be applied according to the actual environment, and different time intervals may be applied according to each radiation mode.

In the table, one cycle consisting of 0 to 40 ms is continuously circulated, attempting wireless access to the RFID tag. In the table, 10ms, the length of each time interval, is sufficient time for the RFID terminal to recognize the RFID tag, and 40ms, the length of one cycle, is short enough for the RFID tag to stay in the radio accessible area of the RFID antenna.

FIG. 13 shows the antenna reflection coefficient of the UHF RFID band when the RFID antenna system for the terminal of the UHF RFID band is implemented as the RFID antenna system according to an embodiment of the present invention, and has characteristics of -20 dB or less at the center frequency of 915 MHz. Shows.

Although the technical spirit of the present invention has been described in detail according to the above-described preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

For example, in the above description, the present invention has been specifically described as an RFID antenna system for performing wireless access with various types of RFID tags. However, if the antenna system is used in a wireless communication environment where polarization characteristics are severely changed, the inventive concept may be easily applied. It will be apparent that this also belongs to the scope of the invention.

For example, in the above description, the embodiment is described in detail with an RFID antenna system having two feeding points, but an RFID antenna including an RFID antenna having three or more feeding points and a feeding circuit for switching feed signals for the three or more feeding points, respectively. The idea of the present invention can be applied to the system, which also belongs to the scope of the present invention. In the case of vertical / horizontal polarization, it is possible to pursue better characteristics by controlling two or more feed points to which a feed signal is supplied. In the case of circular polarization, three or more provided on a circular line rotating about a center point By providing sequential phase differences to the feed points, it is possible to pursue better characteristics.

1 is a circuit diagram showing a conventional RFID antenna that can be applied to vertical and horizontal polarization.

Figure 2 is a circuit diagram showing a conventional RFID antenna that can be applied to LHCP and RHCP.

Figure 3a is a top view showing an embodiment of an RFID antenna for the idea of the present invention.

Figure 3b is a top view showing another embodiment of the RFID antenna for the idea of the present invention.

Figure 4 is a side view showing an embodiment of an RFID antenna for the idea of the present invention.

5A and 5B are graphs showing a radiation pattern and surface current when generating LHCP in the RFID antenna system of FIG.

6A and 6B are graphs showing radiation patterns and surface currents when generating RHCP in the RFID antenna system of FIG.

7A and 7B are graphs showing a radiation pattern and surface current when generating vertical polarization in the RFID antenna system of FIG.

8A and 8B are graphs showing radiation patterns and surface currents when generating horizontal polarization in the RFID antenna system of FIG.

9 is a block diagram illustrating one embodiment of an RFID antenna system in accordance with the present invention.

FIG. 10 is a circuit diagram illustrating an embodiment of a power supply circuit constituting the RFID antenna system of FIG. 9. FIG.

11A and 11B are circuit diagrams showing the paths of RF signals activated according to the phase relationship of the two feed signals applied in the feed circuit of FIG. 9 for application to LHCP and RHCP.

12A and 12B are circuit diagrams showing the path of an RF signal activated according to a feed signal selectively applied in the feed circuit of FIG. 9 for application to vertical polarization and horizontal polarization.

13 is a graph showing the reflection coefficient of the RFID antenna of the UHF band implemented in accordance with the spirit of the present invention.

<Explanation of symbols for the main parts of the drawings>

100: RFID antenna 120: first patch surface

140: second patch surface 162: first feed point

164: second feed point 200: feed circuit

600: timing controller 700: reading unit

Claims (17)

An antenna having two patch faces and two feed points connecting them; And A power supply module including a power supply circuit for adjusting a phase of a predetermined signal and supplying the signal to the antenna and a timing controller for differently determining whether or not a signal is supplied to each power supply point according to a time interval An antenna system comprising a. delete The method of claim 1, The two patch surfaces, An antenna system, characterized in that overlapped in parallel with each other. The method of claim 3, The two feed points are in the form of a line connecting the two patch surfaces vertically. The method of claim 4, wherein The two feed points, And two line segments forming a center point and each of the feed points on a smaller patch surface of the two patch surfaces are positioned to be orthogonal to each other. delete The method of claim 1, The power supply module, According to the time interval, the antenna system, characterized in that repeatedly supplying a feed signal to only one selected from the two feed points, or a feed signal with a phase difference of 90 ° to the feed points. The method of claim 1, The power supply circuit, And two feed path modules connected to the two feed points, respectively, for imparting a selective phase to the signal and delivering them to each feed point. The method of claim 8, Each of the power supply route module, A first pin diode and a second pin diode; A first inductor having one end connected to an anode of the first pin diode and the other end connected to a driving voltage terminal for the first pin diode; A second inductor having one end connected to a cathode of the first pin diode and the other end connected to ground; A first phase adjustment element, one end of which is connected to an anode of the second pin diode; A third inductor having one end connected to the other end of the first phase adjusting element and the other end connected to a driving voltage terminal for the second pin diode; A second phase adjusting element, one end of which is connected to the cathode of the second pin diode; A fourth inductor having one end connected to the other end of the second phase adjusting element and the other end connected to ground; An input coupling capacitor that transfers the signal to the first pin diode or the second pin diode; And An output coupling capacitor transferring a signal output from the first pin diode or the second pin diode to the feed point An antenna system comprising a. The method of claim 1, The antenna is an antenna system, characterized in that the RFID antenna for performing radio access with the RFID tag. An RFID antenna having two feed points; A power supply module including a power supply circuit for adjusting a phase of a predetermined signal and supplying the signal to the RFID antenna and a timing controller for differently determining whether or not a signal is supplied to each power supply point according to a time interval; And A reading unit which transmits the predetermined signal to the power supply module to perform data communication with an RFID tag RFID terminal comprising a. delete The method of claim 11, The RFID antenna, RFID terminal comprising two patch surfaces overlapping in parallel with each other. The method of claim 13, The RFID antenna, And two feed points connecting the two patch surfaces. The method of claim 14, Two feed points connecting the patch surfaces, And two line segments forming the center point and each of the feed points on the smaller patch surface of the two patch surfaces are arranged to be orthogonal to each other. delete The method of claim 14, The power supply module, According to the time interval, a feed signal is supplied only to one selected from two feed points connecting the patch surfaces repeatedly, or a feed signal with a phase difference of 90 ° is supplied to the two feed points connecting the patch surfaces. RFID terminal, characterized in that.

Images