Rf-id tag and rf-id communication system

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application claims the benefit of Japanese Patent Application JP 2011-081056, filed Mar. 31, 2011, the entire content of which is hereby incorporated by reference, the same as if set forth at length.

FIELD OF THE INVENTION

0002The present invention relates to an RF-ID (radio frequency identification) tag and an RF-ID communication system.

BACKGROUND OF THE INVENTION

0003In recent years, non-contact communication devices which receive information from the outside and send information to the outside using electromagnetic waves as a medium have come to be used commonly (refer to JP-A-2006-203852 and JP-A-2009-075687, for example). A non-contact IC label and a non-contact card which are example non-contact communication devices are equipped with an IC chip and a communication antenna that is electrically connected to the IC chip. When the communication antenna receives electromagnetic waves, electromotive force occurs in the communication antenna through resonance. The IC chip is activated by the electromotive force and information stored in the IC chip is converted into a signal. The signal representing the information is transmitted by the communication antenna and receivedby the antenna of a receiver. A controller of the receiver performs data processing such as signal identification.

0004JP-A-2006-203852 discloses a non-contact IC module which is free of risk the function of a booster antenna is impaired. In this non-contact IC module, an IC chip is disposed at a position (the center of an antenna) where the current density of a dipole structure is highest. JP-A-2009-075687 discloses an RF-ID tag which is increased in the accuracy of communication with an external circuit and the degree of freedom of sticking.

SUMMARY OF THE INVENTION

0005Non-contact communication devices as disclosed in JP-A-2006-203852 and JP-A-2009-075687 have a narrow resonance bandwidth because they are designed so as to perform a communication at a particular wavelength. However, since the frequency of transmitted electromagnetic waves depends on the country, it is necessary to prepare communication antennas that are specialized for frequencies used in individual countries. Because of the narrow resonance bandwidth, allowable variation ranges of performance items of components such as an IC chip and antenna members are narrow, which may increase the cost and affect the stability of product operation. Furthermore, the resonance frequency may shift depending on the use situation such as interference between the communication antennas of adjoining RF-ID tags, which may disable a stable communication.

0006In general, a one-turn loop antenna is connected to an IC chip and a booster antenna is disposed close to the coil of the 1-turn loop antenna in non-contact form. And the 1-turn loop antenna is disposed at the center of the booster antenna. Since the IC chip is disposed close to (for example, mounted on) the 1-turn loop antenna, the IC chip is located approximately at the center of the booster antenna. Therefore, in printing a label on an RF-ID tag, printing on a label central portion is avoided to prevent the IC chip (located in the label central portion) from being damaged. This restriction inevitably lowers the value of label expression.

0007The present invention has been made in the above circumstances, and a first object of the invention is to provide a configuration for increasing the bandwidth of a communication antenna of an RF-ID tag.

0008A second object of the invention is to increase the degree of freedom of disposition of an IC chip by making it possible to dispose the IC chip at a position other than the center of a communication antenna.

0009(1) An RF-ID tag according to the invention comprises an IC, a loop antenna to which the IC is connected, and a linear booster antenna which may be long and narrow as a whole, wherein:

0010the booster antenna has, as one end portion in its longitudinal direction, a fold-back portion which is wound; and

0011a portion, having a length that measures 73% or more of a one-turn overall length of a loop of the loop antenna, of the loop antenna extends along a portion, including the fold-back portion, of the booster antenna.

0012(2) An RF-ID communication system according to the invention comprises:

0013the RF-ID tag of item (1); and

0014a reader or a reader/writer which performs a wireless communication with the RF-ID tag.

0015The RF-ID tag and the RF-ID communication system according to the invention make it possible to provide a configuration for increasing the bandwidth of a communication antenna and thereby contribute to cost reduction and stabilization of product operation. Furthermore, disposing an IC chip at a position other than the center of a communication antenna prevents a disconnection from occurring in a connection portion of the IC chip and an antenna portion and eliminates restrictions relating to label printing to avoid lowering of the value of label expression.

BRIEF DESCRIPTION OF THE DRAWINGS

0016<figref idref="DRAWINGS">FIG. 1</figref> illustrates a dipole antenna and its current distribution.

0017<figref idref="DRAWINGS">FIG. 2</figref> shows the configuration of an RF-ID tag which is a combination of a loop antenna and a booster antenna.

0018<figref idref="DRAWINGS">FIG. 3A</figref> shows a configuration in which a booster antenna has meandering structures extending in its longitudinal direction, and <figref idref="DRAWINGS">FIG. 3B</figref> shows a configuration in which a booster antenna has meandering structures extending in the direction that is perpendicular to its longitudinal direction.

0019<figref idref="DRAWINGS">FIG. 4</figref> shows the configuration of an RF-ID tag according to an embodiment of the present invention.

0020<figref idref="DRAWINGS">FIG. 5</figref> is an exploded view of part of the RF-ID tag of <figref idref="DRAWINGS">FIG. 4</figref>.

0021<figref idref="DRAWINGS">FIG. 6</figref> shows a booster antenna model.

0022<figref idref="DRAWINGS">FIG. 7</figref> shows other forms of a fold-back portion of the booster antenna.

0023<figref idref="DRAWINGS">FIGS. 8A and 8B</figref> show models of booster antennas whose fold-back portions have different physical dimensions.

0024<figref idref="DRAWINGS">FIG. 9A</figref> is a sectional view schematically showing a state that bending stress is imposed on a smart card in which a loop antenna and an IC chip are disposed at the center, in the longitudinal direction, of a booster antenna, and <figref idref="DRAWINGS">FIG. 9B</figref> is a sectional view schematically showing a state that bending stress is imposed on a smart card incorporating the RF-ID tag shown in <figref idref="DRAWINGS">FIG. 4</figref>.

0025<figref idref="DRAWINGS">FIG. 10</figref> shows the configuration of an RF-ID tag according to another embodiment.

0026<figref idref="DRAWINGS">FIGS. 11A and 11B</figref> show the configurations of RF-ID tags according to other embodiments.

0027<figref idref="DRAWINGS">FIG. 12</figref> is a schematic wiring diagram of an RF-ID tag system in which one of the RF-ID tags according to the embodiments is used as an active tag.

0028<figref idref="DRAWINGS">FIG. 13</figref> shows an appearance of a recording tape cartridge and a label stuck to it.

0029<figref idref="DRAWINGS">FIG. 14</figref> is a schematic diagram showing plural tape cartridges and a library apparatus.

0030<figref idref="DRAWINGS">FIGS. 15A and 15B</figref> show analysis models having different positional relationships between a loop antenna and a booster antenna; <figref idref="DRAWINGS">FIG. 15A</figref> shows the configuration of a common antenna unit in which a loop antenna is disposed approximately at the center of a booster antenna, and <figref idref="DRAWINGS">FIG. 15B</figref> shows the configuration of an antenna unit in which a loop antenna is disposed at one end of a booster antenna.

0031<figref idref="DRAWINGS">FIG. 16</figref> is a graph showing simulation results of the S<b>11</b> parameter and the VSWR of each of the antenna units shown in <figref idref="DRAWINGS">FIGS. 15A and 15B</figref>.

0032<figref idref="DRAWINGS">FIG. 17</figref> shows an analysis model in which the position of a loop antenna is varied one end of a booster antenna to its center.

0033<figref idref="DRAWINGS">FIG. 18</figref> is a graph showing simulation results of the analysis model shown in <figref idref="DRAWINGS">FIG. 17</figref>.

0034<figref idref="DRAWINGS">FIGS. 19A</figref>, <b>19</b>B and <b>19</b>C show analysis models in which one end portion of a booster antenna coextends with two sides, three sides, and approximately four sides, respectively, of a loop antenna.

0035<figref idref="DRAWINGS">FIG. 20</figref> is a graph showing simulation results of the analysis model shown in <figref idref="DRAWINGS">FIGS. 19A</figref>, <b>19</b>B and <b>19</b>C.

0036<figref idref="DRAWINGS">FIG. 21</figref> shows an analysis model in which that portion of a loop antenna which coextends with one end portion of a booster antenna is varied between two sides and three sides.

0037<figref idref="DRAWINGS">FIG. 22</figref> is a graph showing simulation results of the analysis model shown in <figref idref="DRAWINGS">FIG. 21</figref>.

0038<figref idref="DRAWINGS">FIGS. 23A</figref>, <b>23</b>B and <b>23</b>C show analysis models in which a fold-back portion of a booster antenna has a spiral shape, a two-turn shape in which the inside loop and the outside loop are wound in opposite directions, and a shape in which a wide pad is formed inside a loop, respectively.

0039<figref idref="DRAWINGS">FIG. 24</figref> is a graph showing simulation results of the analysis model shown in <figref idref="DRAWINGS">FIGS. 23A</figref>, <b>23</b>B and <b>23</b>C.

0040<figref idref="DRAWINGS">FIG. 25</figref> shows an analysis model in which the length of a side including a projection, projecting from a loop antenna, of a fold-back portion of a booster antenna is varied.

0041<figref idref="DRAWINGS">FIG. 26</figref> is a graph showing simulation results of the analysis model shown in <figref idref="DRAWINGS">FIG. 25</figref>.

0042<figref idref="DRAWINGS">FIG. 27A</figref> shows simulation results with a condition X=0 mm, and <figref idref="DRAWINGS">FIG. 27B</figref> shows simulation results with a condition X=26 mm.

0043<figref idref="DRAWINGS">FIG. 28</figref> shows an analysis model in which the length of a projection, projecting from a loop antenna, of a fold-back portion of a booster antenna is varied.

0044<figref idref="DRAWINGS">FIG. 29</figref> is a graph showing simulation results of the analysis model shown in <figref idref="DRAWINGS">FIG. 28</figref>.

0045<figref idref="DRAWINGS">FIG. 30A</figref> shows simulation results with a condition X=0 mm, and <figref idref="DRAWINGS">FIG. 30B</figref> shows simulation results with a condition X=40 mm.

0046<figref idref="DRAWINGS">FIG. 31</figref> shows simulation results of the S<b>11</b> parameter and the VSWR of each of a one-turn loop antenna itself and a combination of a one-turn loop antenna and a booster antenna.

DESCRIPTION OF SYMBOLS

0000<ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0047"><b>13</b>: Antenna portion</li><li id="ul0001-0002" num="0048"><b>15</b>: IC chip</li><li id="ul0001-0003" num="0049"><b>17</b>: Loop antenna</li><li id="ul0001-0004" num="0050"><b>19</b>: Booster antenna</li><li id="ul0001-0005" num="0051"><b>21</b>: Pad</li><li id="ul0001-0006" num="0052"><b>23</b>: IC chip</li><li id="ul0001-0007" num="0053"><b>25</b>, <b>25</b>A: Loop antenna</li><li id="ul0001-0008" num="0054"><b>27</b>, <b>27</b>A: Booster antenna (linear booster antenna)</li><li id="ul0001-0009" num="0055"><b>27</b><i>a</i>: Side</li><li id="ul0001-0010" num="0056"><b>29</b>, <b>29</b>A: Fold-back portion</li><li id="ul0001-0011" num="0057"><b>31</b>, <b>32</b>, <b>33</b>: Side</li><li id="ul0001-0012" num="0058"><b>35</b>: Pad</li><li id="ul0001-0013" num="0059"><b>37</b>: Smart card</li><li id="ul0001-0014" num="0060"><b>41</b>: Receiving circuit</li><li id="ul0001-0015" num="0061"><b>43</b>: Transmitting circuit</li><li id="ul0001-0016" num="0062"><b>51</b>: Recording tape cartridge</li><li id="ul0001-0017" num="0063"><b>65</b>: Label</li><li id="ul0001-0018" num="0064"><b>67</b>: Tag</li><li id="ul0001-0019" num="0065"><b>100</b>, <b>200</b>, <b>300</b>, <b>400</b>: RF-ID tag</li><li id="ul0001-0020" num="0066"><b>600</b>: RF-ID tag system</li></ul>

DETAILED DESCRIPTION OF THE INVENTION

0067Embodiments of the present invention will be hereinafter described in detail with reference to the drawings.

0068First, a basic antenna configuration of an RF-ID tag and restrictions relating to antenna arrangement will be described briefly using a dipole antenna as an example.

0069<figref idref="DRAWINGS">FIG. 1</figref> illustrates a dipole antenna and its current distribution. The dipole antenna <b>11</b> has a linear antenna portion <b>13</b> and an IC chip <b>15</b> which is disposed at the center, in the longitudinal direction, of the antenna portion <b>13</b>. The dipole antenna <b>11</b> has a current density distribution that the current density is low at both ends and high at the center.

0070Therefore, when an RF-ID (radio frequency identification) tag is constructed by combining a loop antenna <b>17</b> and a booster antenna <b>19</b> in a manner shown in <figref idref="DRAWINGS">FIG. 2</figref>, maximum performance (maximum gain) is obtained by disposing the loop antenna <b>17</b> at the center of the booster antenna <b>19</b>. However, in this configuration, since the booster antenna <b>19</b> is long in its longitudinal direction, the position where the loop antenna <b>17</b> is disposed is restricted to the center of the booster antenna <b>19</b>.

0071Usually, if the loop antenna <b>17</b> is disposed at an end of the booster antenna <b>19</b>, the magnetic inductive coupling between the loop antenna <b>17</b> and the booster antenna <b>19</b> is insufficient and hence desired performance cannot be attained.

0072As shown in <figref idref="DRAWINGS">FIGS. 3A and 3B</figref>, the antenna length can be shortened by employing a meandering structure and the antenna length can be shortened further by adding wide pads <b>21</b> at both ends of an antenna.

0073Usually, a dipole antenna etc. are designed taking into consideration impedance matching in a frequency band used. However, in the case of UHF RF-ID tag antennas, it is desired that their bandwidth be made as wide as possible because it is expected that they will be used being stuck to things made of various materials such as paper, plastics, and wood and hence they need to be designed so as to accommodate variations of permittivity values of these materials.

0074The reflection coefficient S<b>11</b> parameter (reflection coefficient) and the VSWR (voltage standing wave ratio) are effective indices to be used for judging the level of bandwidth elongation. It is desirable that a dipole antenna or the like be designed so that the frequency range in which the S<b>11</b> parameter is smaller than or equal to −3 dB or the VSWR is smaller than or equal to 6 (in general, smaller than or equal to 2) is wide.

<First Example Configuration>

0075<figref idref="DRAWINGS">FIG. 4</figref> shows the configuration of an RF-ID tag according to an embodiment of the invention. The RF-ID tag <b>100</b> is equipped with an IC chip <b>23</b>, a loop antenna <b>25</b> to which the IC chip <b>23</b> is connected, and a linear booster antenna (hereinafter referred to as a booster antenna) <b>27</b> which is long and narrow over its entire length.

0076<figref idref="DRAWINGS">FIG. 5</figref> is an exploded view of part of the RF-ID tag <b>100</b>. As shown in <figref idref="DRAWINGS">FIG. 5</figref>, the loop antenna <b>25</b> and the booster antenna <b>27</b> are formed separately and placed close to each other in non-contact form with a dielectric layer (not shown) interposed in between. Examples of the dielectric layer are an air layer, an adhesive layer, a printed circuit board, a plastic member made of polycarbonate or the like, and a ceramic member. It is preferable that the interval, in the thickness direction, between the loop antenna <b>25</b> and the booster antenna <b>27</b> be shorter than or equal to 2 mm.

0077The loop antenna <b>25</b> is a rectangular-loop-shaped conductor, and the IC chip <b>23</b> is connected to (in electrical contact with) part of it. The loop antenna <b>25</b> is designed so as to have an optimum shape and size using its reflection coefficient S<b>11</b>, VSWR, and reverse transmission coefficient S<b>12</b> as indices so as to resonate in a UHF band around 900 MHz (850 MHz to 1 GHz). Alternatively, the loop antenna <b>25</b> may have a circular or polygonal shape.

0078In <figref idref="DRAWINGS">FIG. 5</figref>, the IC chip <b>23</b> is located at a corner of the loop antenna <b>25</b> over one end, in the longitudinal direction, of the booster antenna <b>27</b>. However, the IC chip <b>23</b> may be located at any position in the loop antenna <b>25</b> and hence may be located, for example, on a side or at a corner.

0079The booster antenna <b>27</b> has, as each end portion in its longitudinal direction, a fold-back portion <b>29</b>. Each fold-back portion <b>29</b> is wound in rectangular form and consists of a side <b>27</b><i>a </i>which extends in the same direction as the longitudinal direction of the booster antenna <b>27</b> to the end in the longitudinal direction and three sides <b>31</b>-<b>33</b> which are wound from the end of the side <b>27</b><i>a </i>(the side <b>31</b> is located at the end in the longitudinal direction of the booster antenna <b>27</b>). One fold-back portion <b>29</b> extends along the loop antenna <b>25</b>. In the embodiment, the sides of the loop antenna <b>25</b> coextend with at least three sides of the one fold-back portion <b>29</b> of the booster antenna <b>27</b>.

0080In the example configuration of <figref idref="DRAWINGS">FIG. 4</figref>, approximately the four wound sides <b>27</b><i>a </i>and <b>31</b>-<b>33</b> of the one fold-back portion <b>29</b> of the booster antenna <b>27</b> coextend with the sides of the loop antenna <b>25</b>. Alternatively, the sides <b>27</b><i>a </i>and <b>31</b>-<b>33</b> of one fold-back portion <b>29</b> of the booster antenna <b>27</b> may extend close to the sides of the loop antenna <b>25</b>. The fold-back portion <b>29</b> of the booster antenna <b>27</b> may be wound in circular or polygonal form so as to conform to the shape of the loop antenna <b>25</b>.

0081The overlap length should be greater than or equal to 73% (about ¾) of the entire one-turn length of the loop antenna <b>25</b>. Where the one-turn loop of the loop antenna <b>25</b> is circular, the overlap region is an arc region having a central angle 263°. Where the one-turn loop of the loop antenna <b>25</b> is square, the overlap region approximately corresponds to three sides.

0082The booster antenna <b>27</b> is line-symmetrical with respect to a line P which passes through its center in its longitudinal direction and perpendicular to it. A pad <b>35</b> which is part of the fold-back portion <b>29</b> of the booster antenna <b>27</b> is disposed inside the loop of the loop antenna <b>25</b>.

0083As shown in the bottom part of <figref idref="DRAWINGS">FIG. 7</figref>, where the fold-back portion <b>29</b> of a booster antenna <b>19</b> is of two turns, the booster antenna <b>19</b> exhibits somewhat different frequency characteristics when the fold-back portion <b>29</b> has a spiral form in which the inside loop is wound in the same direction as the outside loop and when the fold-back portion <b>29</b> has an oppositely wound form in which the winding direction of the inside loop is opposite to that of the outside loop. If the inside loop is replaced by a pad <b>35</b> having a pad surface, the booster antenna <b>19</b> is given a frequency characteristic that exhibits the frequency characteristics of both of the spiral form and the oppositely wound form. Whereas the fold-back portion <b>29</b> may be in either of the spiral form and the oppositely wound form, it is preferable that a loop-shaped pattern be formed around the outer circumference of a pad <b>35</b>.

0084The booster antenna <b>27</b> may be made of any material having high conductivity, and may be formed by any of various forming methods such as a method of sticking, to a subject item, a metal sheet that has been worked into an antenna shape, evaporation or sputtering onto a subject item, printing using a conductive ink, and direct formation by etching.

0085Although in the embodiment each of the loop antenna <b>25</b> and the booster antenna <b>27</b> is designed so as to resonate in a UHF band (850 MHz to 1 GHz), in the invention the resonance band is not limited to it.

0086<figref idref="DRAWINGS">FIG. 6</figref> shows a booster antenna model. As shown in <figref idref="DRAWINGS">FIG. 6</figref>, a linear booster antenna <b>19</b> has a length that is a half of a wavelength λ used. Therefore, in the embodiment, the above-described generally loop-shaped fold-back portion <b>29</b> to be electromagnetically coupled with the loop antenna <b>25</b> is disposed at one end, in the longitudinal direction, of the booster antenna <b>27</b>. It is appropriate to dispose the fold-back portion <b>29</b> in a λ/6 region (extending from the end) of the booster antenna <b>27</b>. In other words, a loop to be electromagnetically coupled with the loop antenna <b>25</b> is formed in either of the end regions excluding the central λ/6 region.

0087The term “wavelength λ” as used above is a wavelength as converted using a current distribution and is not a physical dimension. <figref idref="DRAWINGS">FIGS. 8A and 8B</figref> show models of the fold-back portion <b>29</b>. As shown in <figref idref="DRAWINGS">FIGS. 8A and 8B</figref>, although the two booster antennas <b>19</b> have different total physical antenna lengths, both of them measure λ/2 in terms of a current distribution. Current distribution differences occur only in the left-hand λ/6 region of the booster antennas <b>19</b>. Therefore, the two booster antenna <b>19</b> have approximately the same antenna center position in terms of a current distribution (i.e., the antenna center position is not affected by the loop length of the fold-back portion <b>29</b>).

0088In the RF-ID tag <b>100</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>, the loop antenna <b>25</b> is intentionally disposed at one end, in the longitudinal direction, of the booster antenna <b>27</b> where the current is small rather than at the center where the current is large and approximately the four sides of the loop antenna <b>25</b> are thereby coupled with the booster antenna <b>27</b> electromagnetically, whereby the communication-possible frequency band can be made wider while the communication sensitivity is kept sufficiently high. This makes it possible to use a single RF-ID tag to cover different frequencies used in individual countries. The increase in antenna bandwidth contributes to cost reduction and stabilization of product operation because allowable variation ranges of performance items of the IC chip <b>23</b>, antenna members, etc. are increased. Furthermore, the allowable range of resonance frequency variations that are caused by permittivity differences between goods havingRF-ID tags, interference between the antennas of many adjoining RF-ID tags, and environments (e.g., water contained in human bodies) of RF-ID tags.

0089The resonance frequency can be adjusted by forming meandering lines in portions of the booster antenna <b>27</b> excluding the portion that overlaps with the loop antenna <b>25</b>.

0090Since the IC chip <b>23</b> which is connected to the loop antenna <b>25</b> is disposed in the region that is not located at the center of the booster antenna <b>27</b>, occurrence of a disconnection in the connection portion of the IC chip <b>23</b> and the loop antenna <b>25</b> can be prevented when the RF-ID tag <b>100</b> is incorporated in a smart card. The disconnection preventing effect is enhanced by disposing the IC chip <b>23</b> at a position that is as close to the end, in the longitudinal direction, of the RF-ID tag <b>100</b> as possible.

0091The smart card is a card such as a battery-less (i.e., no power source (battery) is provided) IC card, magnetic card, optical card, or a combination thereof which complies with ISO 7810, as typified by a smart cart incorporating a microprocessor and a memory. The smart card may also be a plastic card for an identification purpose only and like ones.

0092<figref idref="DRAWINGS">FIG. 9A</figref> is a sectional view schematically showing a state that bending stress is imposed on a smart card <b>37</b> in which a loop antenna and an IC chip <b>15</b> are disposed at the center, in the longitudinal direction, of a booster antenna <b>19</b>. In this case, since the connection portion of the IC chip <b>15</b> and the loop antenna is located in a region M where the bending stress is concentrated, a disconnection tends to be induced in the connection portion.

0093<figref idref="DRAWINGS">FIG. 9B</figref> is a sectional view schematically showing a state that bending stress is imposed on a smart card <b>37</b> incorporating the RF-ID tag <b>100</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>. In this case, since the IC chip <b>23</b> is not located in a region M where the bending stress is concentrated, the risk of occurrence of a disconnection in the connection portion of the IC chip <b>23</b> and the loop antenna <b>25</b> can be lowered.

0094In the case of <figref idref="DRAWINGS">FIG. 9A</figref> in which the loop antenna and the IC chip <b>15</b> are disposed at the center of the booster antenna <b>19</b>, in forming a label using the RF-ID tag, printing etc. on a label central portion needs to be avoided to prevent the IC chip <b>15</b> which is located there from being damaged. This restriction inevitably lowers the value of label expression.

0095On the other hand, in the case of <figref idref="DRAWINGS">FIG. 9B</figref> in which the loop antenna <b>25</b> and the IC chip <b>23</b> are disposed at one end of the booster antenna <b>27</b>, the IC chip <b>23</b> can be disposed at a label corner portion, as a result of which no restriction is imposed on label printing and the value of label expression is not lowered.

0096In conventional, commonly employed antennas which are not designed so as to increase the bandwidth sufficiently, they are used in limited environments or countermeasures against influence of nearby objects (e.g., electronic components in general, water, a human body, and metal members) are taken such as addition of a radio wave absorbing sheet and formation of an ample internal space for reduction of influence. The RF-ID tag <b>100</b> shown in <figref idref="DRAWINGS">FIG. 4</figref> makes it possible to relax such restrictions relating to the design.

<Second Example Configuration>

0097Next, an RF-ID tag according to another embodiment will be described. <figref idref="DRAWINGS">FIG. 10</figref> shows the configuration of an RF-ID tag according to another embodiment. In this RF-ID tag <b>200</b>, as in the RF-ID tag <b>100</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>, a fold-back portion <b>29</b>A is formed at both ends, in the longitudinal direction, of a booster antenna <b>27</b>A and a loop antenna <b>25</b>A is laid on one fold-back portion <b>29</b>A so as to overlap with the latter. That is, a side <b>27</b><i>a</i>, a side <b>31</b>, and part of a side <b>32</b> of the booster antenna <b>27</b>A extend under (as viewed in <figref idref="DRAWINGS">FIG. 10</figref>) the loop antenna <b>25</b>A with a dielectric layer interposed in between.

0098Each fold-back portion <b>29</b>A of the booster antenna <b>27</b>A is longer in the longitudinal direction than each fold-back portion <b>29</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>. More specifically, the side <b>32</b> and a pad <b>35</b>A of each fold-back portion <b>29</b>A is about two times as long as the side <b>32</b> and the pad <b>35</b> of each fold-back portion <b>29</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>. The portion other than the fold-back portions <b>29</b>A of the booster antenna <b>27</b>A is straight, and the entire booster antenna <b>27</b>A is line-symmetrical with respect to a center line P. By elongating each fold-back portion <b>29</b>A, the resonance frequency can be decreased without increasing the width of the entire booster antenna <b>27</b>A.

0099The loop antenna <b>25</b>A has the same size as the loop antenna <b>25</b> shown in <figref idref="DRAWINGS">FIG. 4</figref>, and an IC chip <b>23</b> is disposed on the loop antenna <b>25</b>A at a position that is right over the center of the side <b>31</b> (located at the end in the longitudinal direction) of the booster antenna <b>27</b>A.

0100According to the RF-ID tag <b>200</b> of this embodiment, the antenna characteristics are improved by disposing the loop antenna <b>25</b>A over the end-side half of the fold-back portion <b>29</b>A which is longer than the loop antenna <b>25</b>A.

<Third Example Configuration>

0101<figref idref="DRAWINGS">FIG. 11A</figref> shows an RF-ID tag according to still another embodiment. In the RF-ID tag <b>300</b> shown in <figref idref="DRAWINGS">FIG. 11A</figref>, three sides of a loop antenna <b>25</b>B are electromagnetically coupled with a side <b>27</b><i>a</i>, a side <b>31</b>, and part of a side <b>32</b> of a booster antenna <b>27</b>B and an IC chip <b>23</b> is disposed on the loop antenna <b>25</b>B at a position that is right over a corner of the side <b>31</b> (located at the end in the longitudinal direction) of the booster antenna <b>27</b>B.

0102According to the RF-ID tag <b>300</b> of this embodiment, the resonance frequency can be decreased without increasing the width of the entire booster antenna <b>27</b>B because a pad <b>35</b>B of the booster antenna <b>27</b>B is disposed at such a position as not to be surrounded by the sides <b>27</b><i>a</i>, <b>31</b>, and <b>32</b>.

<Fourth Example Configuration>

0103<figref idref="DRAWINGS">FIG. 11B</figref> shows an RF-ID tag according to yet another embodiment. In the RF-ID tag <b>400</b> shown in <figref idref="DRAWINGS">FIG. 11B</figref>, approximately four sides of a loop antenna <b>25</b>C are electromagnetically coupled with sides <b>27</b><i>a </i>and <b>31</b>-<b>33</b> of a booster antenna <b>27</b>C and an IC chip <b>23</b> is disposed on the loop antenna <b>25</b>C at a position that is right over a corner of the side <b>31</b> (located at the end in the longitudinal direction) of the booster antenna <b>27</b>C.

0104According to the RF-ID tag <b>400</b> of this embodiment, the resonance frequency can be decreased without increasing the width of the entire booster antenna <b>27</b>C because a pad <b>35</b>C of the booster antenna <b>27</b>C is disposed at such a position as not to be surrounded by the sides <b>27</b><i>a </i>and <b>31</b>-<b>33</b>.

<Fifth Example Configuration>

0105Each of the RF-ID tags <b>100</b>, <b>200</b>, <b>300</b>, and <b>400</b> according to the above embodiments can be used as not only a passive tag but also an active tag. The above-described advantages can also be obtained when each of the antenna configurations according to the above embodiments is applied to the antenna of a radio-type reader or a reader/writer.

0106<figref idref="DRAWINGS">FIG. 12</figref> shows the configuration of an RF-ID tag system in which one of the RF-ID tags <b>100</b>, <b>200</b>, <b>300</b>, and <b>400</b> according to the above embodiments is used as an active tag. <figref idref="DRAWINGS">FIG. 12</figref> is a schematic wiring diagram of the RF-ID tag system.

0107The RF-ID tag system <b>600</b> is equipped with an RF-ID tag antenna unit <b>500</b>, a receiving circuit <b>41</b> and a transmitting circuit <b>43</b> which are connected to the RF-ID tag antenna unit <b>500</b>, and a coupler <b>45</b> which splits a pair of signal lines coming from the RF-ID tag antenna unit <b>500</b> into two pairs of signal lines connected to the receiving circuit <b>41</b> and the transmitting circuit <b>43</b>, respectively.

0108The RF-ID tag antenna unit <b>500</b> has a loop antenna <b>25</b>D and a booster antenna <b>27</b>D, and the loop antenna <b>25</b>D is connected to the receiving circuit <b>41</b> and the transmitting circuit <b>43</b> via the coupler <b>45</b>. That is, in this embodiment, the IC chip is replaced by the active tag communication system.

0109As is understood from the above description, each of the RF-ID tags <b>100</b>, <b>200</b>, <b>300</b>, and <b>400</b> according to the embodiments can be applied to radio communication apparatus in general. More specifically, the following steps are taken. (1) A substrate with a loop antenna having a one-turn loop structure is manufactured and incorporated in an apparatus. (2) On the apparatus side, a booster antenna is disposed so as to have one of the above-describedpositional relationships with the one-turn loop antenna and to establish matching between them. In this case, the degree of freedom of the loop antenna position can be increased.

Example 1

0110In a multilayer substrate, two layers having an arbitrary interval is provided as a loop antenna forming layer and a booster antenna forming layer. Which layers a loop antenna and a booster antenna should be formed in is determined as appropriate taking into consideration the thickness of each layer of the substrate, the permittivity of the substrate, and the antenna shapes.

Example 2

0111A loop antenna is formed on a substrate which includes a power source for an active tag. A booster antenna is disposed on the inner surface or the outer surface of an apparatus case which houses the substrate, so as have a particular positional relationship with a loop antenna.

0112Where as in the above examples the loop antenna and the booster antenna are separate from and not in contact with each other and have no wiring line connecting them, the booster antenna can be attached and removed when necessary according to a use and whether to permit long-distance communication (security function) or a like item can be set. In these examples, the one-turn loop antenna alone functions as a magnetic induction type tag.

0113Specific apparatus corresponding to the above Example 1 will be described below with reference to <figref idref="DRAWINGS">FIGS. 13 and 14</figref>.

0114<figref idref="DRAWINGS">FIG. 13</figref> shows a recording tape cartridge <b>51</b> in which a magnetic tape T as an information recording medium is wound on a single reel <b>55</b> which is housed rotatably in a flat case <b>53</b>. When the recording tape cartridge <b>51</b> is loaded into a drive apparatus (not shown) in the direction indicated by arrow A, a window <b>57</b> which is located in a headportion in the loading direction is opened and a leader member <b>59</b> which is provided at the head of the magnetic tape T is drawn out through the window <b>57</b> by the drive apparatus. The magnetic tape T is guided along a prescribed tape path in the drive apparatus and information is written to or read from the magnetic tape T.

0115A label <b>65</b> is stuck to a label area in a recess of a back surface <b>61</b> (located on the origin side of arrow A) of the flat case <b>53</b> of the recording tape cartridge <b>51</b>. While not in use, the recording tape cartridge <b>51</b> is stored in a library apparatus with such orientation that the label <b>65</b> which is stuck to the label area <b>63</b> can be seen. Information represented by characters, symbols, etc. that can be seen by a user is printed or hand-written on the label <b>65</b>.

0116An active or passive tag <b>67</b> including the receiving circuit <b>41</b>, the transmitting circuit <b>43</b>, the coupler <b>45</b>, and the loop antenna <b>25</b>D which are shown in <figref idref="DRAWINGS">FIG. 12</figref> is provided in the recording tape cartridge <b>51</b> at a position that is close to the label area <b>63</b>. On the other hand, the booster antenna <b>27</b>D shown in <figref idref="DRAWINGS">FIG. 12</figref> is formed in the label <b>65</b>. When the label <b>65</b> is stuck to the label area <b>63</b>, as described above the prescribed portion of the booster antenna <b>27</b>D overlaps with the loop antenna <b>25</b>D with the wall of the case of the recording tape cartridge <b>51</b> interposed in between.

0117Information that was represented before by a bar code in the case of a bar code label, for example, information for unified management of the individual cartridge <b>51</b> while it is stored or is being conveyedby an autoloader, and other information are stored in the receiving circuit <b>41</b> and the transmitting circuit <b>43</b> of the tag <b>67</b> or a storage unit (not shown) connected to them.

0118To use many recording tape cartridges <b>51</b> as backup cartridges or the like, a library apparatus is used which includes a holder for storing many recording tape cartridges <b>51</b> and an autoloader for automatically loading and removing a recording tape cartridge <b>51</b> into and from a drive apparatus. As shown in <figref idref="DRAWINGS">FIG. 14</figref>, plural recording tape cartridges <b>51</b> are arranged at regular intervals in their thickness direction in a holder of a library apparatus <b>70</b> with such orientation that their labels <b>65</b> can be seen.

0119A movable head <b>69</b> having a reader or a reader/writer is provided in the library apparatus <b>70</b> so as to be moved by a transport mechanism facing the labels <b>65</b> of the respective recording tape cartridges <b>51</b> which are arranged in the holder. In the library apparatus <b>70</b>, while being moved in the arrangement direction of the recording tape cartridges <b>51</b>, the movable head <b>69</b> reads or writes information by performing a short-distance wireless (non-contact) communication with the booster antenna <b>27</b>D and the loop antenna <b>25</b>D of each recording tape cartridge <b>51</b> through a reader antenna or a reader/writer antenna as a communication antenna.

0120According to the RF-ID tag system <b>600</b> shown in <figref idref="DRAWINGS">FIG. 12</figref>, the tag <b>67</b> can be disposed in a corner portion of the recording tape cartridge <b>51</b>, whereby a dead space can be utilized effectively and hence the efficiency of space utilization of the recording tape cartridge <b>51</b> can be made high.

0121Since the tag <b>67</b> does not require printing, it is not necessary to provide, for example, a structure for preventing the IC chip from being damaged at the time of printing. Since the label <b>65</b> is provided with only the booster antenna <b>27</b>D, there are no restrictions relating to label printing and hence the value of label expression is not lowered. Since the dielectric layer which is the wall, interposed between the loop antenna <b>25</b>D and the booster antenna <b>27</b>D, of the case of the recording tape cartridge <b>51</b> can be as thick as about several millimeters, the degree of freedom of disposition of the loop antenna <b>25</b>D and the booster antenna <b>27</b>D is increased in the case where the loop antenna <b>25</b>D is disposed inside the recording tape cartridge <b>51</b>.

0122According to this embodiment, since no wiring line exists between the loop antenna <b>25</b>D and the booster antenna <b>27</b>D, no such failure as a disconnection or a contact failure is induced. In disassembling work of the recording tape cartridge <b>51</b>, it is not necessary to conduct such appurtenant work as removal of screws or connector wires between the antennas.

0123Therefore, according to this embodiment, whereas the advantages of bandwidth increase are obtained, the risk of failure is lowered and the number of components and the cost of working can be decreased. The increase of a bandwidth used makes it possible to greatly relax the restrictions relating to the use conditions/environment of an RF-ID tag. For example, margins against influence of the permittivity of water contained in a sticking subject item (made of metal or plastics), a human body, or the like, interference between adjoining RF-ID tags, and other phenomena, whereby the quality of communication is made less prone to disturbances of a human body etc. Furthermore, this embodiment is advantageous when applied to tags with a wideband specification (worldwide specification).

<Simulation Results>

0124Next, a description will be made of simulation results of the antenna characteristics of the RF-ID tags according to the embodiments.

(Analysis 1: Dependence on Arrangement of Loop Antenna and Booster Antenna)

0125<figref idref="DRAWINGS">FIGS. 15A and 15B</figref> show analysis models having different positional relationships between a loop antenna <b>25</b> and a booster antenna <b>27</b>. More specifically, <figref idref="DRAWINGS">FIG. 15A</figref> shows the configuration of a common antenna unit in which a loop antenna <b>25</b> is disposed approximately at the center of a booster antenna <b>27</b>. <figref idref="DRAWINGS">FIG. 15B</figref> shows the configuration of an antenna unit in which a loop antenna <b>25</b> is disposed at one end of a booster antenna <b>27</b>.

0126<figref idref="DRAWINGS">FIG. 16</figref> is a graph showing simulation results of the S<b>11</b> parameter and the VSWR of each of the antenna units shown in <figref idref="DRAWINGS">FIGS. 15A and 15B</figref>. In <figref idref="DRAWINGS">FIG. 16</figref>, the left-hand vertical axis represents the S<b>11</b> parameter, the right-hand vertical axis represents the VSWR, and the horizontal axis represents the frequency.

0127In the models used in the simulation being discussed and simulations to be described later, a one-turn loop antenna <b>25</b> and a booster antenna <b>27</b> are formed on the respective surfaces of a 1-mm-thick dielectric layer made of a material having a permittivity 2.6. The loop antenna <b>25</b> has external dimensions 7.5 mm×14 mm and a pattern width 1 mm. The booster antenna <b>27</b> has a basic pattern width 1 mm and its overall length is adjusted so that it has a resonance frequency 960 MHz.

0128As seen from <figref idref="DRAWINGS">FIG. 16</figref>, the minimum value of the S<b>11</b> parameter of the antenna unit of <figref idref="DRAWINGS">FIG. 15B</figref> in which a spiral fold-back portion is formed at one end of the booster antenna and the loop antenna <b>25</b> is laid on the fold-back portion is smaller than that of the antenna unit of <figref idref="DRAWINGS">FIG. 15A</figref>. And the resonance bandwidths of the S<b>11</b> parameter and the VSWR of the antenna unit of <figref idref="DRAWINGS">FIG. 15B</figref> are wider than those of the antenna unit of <figref idref="DRAWINGS">FIG. 15A</figref>.

(Analysis 2: Dependence on Position of One-Turn Loop Antenna in Linear Booster Antenna)

0129<figref idref="DRAWINGS">FIG. 17</figref> shows an analysis model in which the position of a loop antenna <b>25</b> is varied one end of a booster antenna <b>27</b> to its center.

0130<figref idref="DRAWINGS">FIG. 18</figref> shows analysis results. As the distance X decreases, that is, as the loop antenna <b>25</b> is moved from the center of the booster antenna <b>27</b> to its end, the minimum value of the S<b>11</b> parameter is increased and the resonance bandwidths of the S<b>11</b> parameter and the VSWR are reduced. The bandwidth reduction of each of the S<b>11</b> parameter and the VSWR is remarkable on the high frequency side. These analysis results coincide with descriptions that are made in JP-A-2006-203852 and JP-A-2009-075687 as conditions for minimizing the S<b>11</b> parameter.

(Analysis 3: Dependence on Shape of Overlap Between One-Turn Loop Antenna and End Portion of Booster Antenna)

0131<figref idref="DRAWINGS">FIGS. 19A-19C</figref> show analysis models in which one end portion of a booster antenna <b>27</b> coextends with two sides, three sides, and four sides, respectively, of a loop antenna <b>25</b>.

0132<figref idref="DRAWINGS">FIG. 20</figref> shows analysis results. As the area of overlap between the one end portion of the booster antenna <b>27</b> and the loop antenna <b>25</b> increases, the minimum value of the S<b>11</b> parameter is made smaller and the resonance bandwidths of the S<b>11</b> parameter and the VSWR are increased.

0133<figref idref="DRAWINGS">FIG. 21</figref> shows an analysis model in which that portion of a loop antenna <b>25</b> which coextends with one end portion of a booster antenna <b>27</b> is varied between two sides and three sides. The entire overlap length is equal to the overlap length of the two sides plus a distance X.

0134<figref idref="DRAWINGS">FIG. 22</figref> shows simulation results. In <figref idref="DRAWINGS">FIG. 22</figref>, proportions of overlaps with the one end portion of the booster antenna <b>27</b> are also shown in percentage with respect to the overall length C (100%) of the one-turn loop antenna <b>25</b>. It is seen from <figref idref="DRAWINGS">FIG. 22</figref> that it is preferable that the overlap length be greater than or equal to 73% of the overall length C of the one-turn loop antenna <b>25</b> (X=10 mm) because in that range the S<b>11</b> parameter is smaller than −3 dB and the VSWR is smaller than 6.

(Analysis 4: Dependence on Shape of Fold-Back Portion of Booster Antenna)

0135<figref idref="DRAWINGS">FIGS. 23A-23C</figref> show analysis models in which a fold-back portion <b>29</b> of a booster antenna <b>27</b> has a spiral shape of approximately two turns, a loop shape of approximately two turns in which the inside loop and the outside loop are wound in opposite directions, and a shape in which a wide pad <b>35</b> is formed inside a loop, respectively.

0136<figref idref="DRAWINGS">FIG. 24</figref> shows analysis results. The minimum value of the S<b>11</b> parameter is decreased and the resonance bandwidth of the S<b>11</b> parameter is increased in order of the oppositely wound shape, the spiral shape, and the pad-inclusive shape (the shape of the fold-back portion <b>29</b>). The resonance bandwidth of the VSWR is also increased in the same order.

0000(Analysis 5: Dependence on Shape of End Portion, Coextending with Three Sides of One-Turn Loop Antenna, of Booster Antenna)

0137<figref idref="DRAWINGS">FIG. 25</figref> shows an analysis model in which the length of a side including a projection <b>71</b>, projecting from a loop antenna <b>25</b>, of a fold-back portion <b>29</b> of a booster antenna <b>27</b> is varied. In this analysis, the overall length L, in the longitudinal direction, of the booster antenna <b>27</b> was set in a range of 105 mm to 108 mm and the length X of the projection <b>71</b> was set at 0 mm, 6 mm, 26 mm, and 36 mm.

0138<figref idref="DRAWINGS">FIG. 26</figref> shows analysis results. The minimum value of the S<b>11</b> parameter is decreased as the length X varies from 0 mm to 6 mm, and is increased as the length X varies from 6 mm to 26 mm and then to 36 mm. The resonance bandwidth of the S<b>11</b> parameter is increased as the length X increases. The resonance bandwidth of the VSWR is increased as the length X increases. The resonance bandwidth is increased particularly on the high frequency side as the length X varies from 6 mm to 26 mm and then to 36 mm.

0139To analyze the performance of communication between the antenna unit of the above analysis model and a reader/writer, values of the S<b>12</b> parameter, the S<b>12</b> parameter, and the VSWR were calculated under a condition that the antenna unit of the above analysis model and a wideband antenna (not shown) were opposed to each other with a distance 120 mm. <figref idref="DRAWINGS">FIGS. 27A and 27B</figref> show calculation results. It is seen that the resonance bandwidths of the S<b>11</b> parameter, the S<b>12</b> parameter, and the VSWR obtained when the length X is equal to 26 mm are greater than those obtained when length X is equal to 0 mm. It is concluded from the above analysis results that an optimum range of the length X is 26 mm to 36 mm.

0000(Analysis 6: Dependence on Shape of End Portion, Coextending with Approximately Four Sides of One-Turn Loop Antenna, of Booster Antenna)

0140<figref idref="DRAWINGS">FIG. 28</figref> shows an analysis model in which the length of a projection <b>73</b>, projecting from a loop antenna <b>25</b>, of a fold-back portion <b>29</b> of a booster antenna <b>27</b> is varied. In this analysis, the overall length L, in the longitudinal direction, of the booster antenna <b>27</b> was set in a range of 110 mm to 114 mm and the length X of the projection <b>73</b> was set at 0 mm, 10 mm, 30 mm, and 40 mm.

0141<figref idref="DRAWINGS">FIG. 29</figref> shows analysis results. The minimum value of the S<b>11</b> parameter is decreased as the length X varies from 0 mm to 10 mm, and is increased as the length X becomes 10 mm, 20 mm, 30 mm, and 40 mm in this order. The resonance bandwidth of the S<b>11</b> parameter is increased as the length X increases. The resonance bandwidth of the VSWR is increased as the length X increases. The resonance bandwidth is increased particularly on the high frequency side as the length X becomes 10 mm, 20 mm, 30 mm, and 40 mm in this order.

0142The performance of communication between the antenna unit of the above analysis model and a reader/writer was analyzed.

0143<figref idref="DRAWINGS">FIGS. 30A and 30B</figref> show analysis results. It is seen that the resonance bandwidths of the S<b>11</b> parameter, the S<b>12</b> parameter, and the VSWR obtained when the length X is equal to 40 mm are greater than those obtained when length X is equal to 0 mm. The bandwidth increase of each parameter is remarkable on the high frequency side. It is concluded from the above analysis results that an optimum range of the length X is 30 mm to 40 mm.

(Analysis 7: Differences in Performance Between One-Turn Loop Antenna Itself and Combination of One-Turn Loop Antenna and Booster Antenna)

0144Because of its simplest configuration, it is difficult to attain matching between a one-turn loop antenna and an IC chip on the market. The resonance frequency of a one-turn loop antenna is determined by a combination of a capacitance component (C) of the IC chip and an inductance component (L) of the one-turn loop antenna. The inductance component the one-turn loop antenna mainly depends on the loop size, and a loop size is determined by an inductance component that conforms to a resonance frequency. However, in this state, the resistance component of the one-turn loop antenna is smaller than that of the IC chip and the VSWR is larger than 100, as a result of which matching is not attained.

0145On the other hand, if a one-turn loop antenna and a booster antenna are arranged so as to satisfy proper conditions, the booster antenna serves as a resistance component of the one-turn loop antenna. As a result, a combination of an IC chip and the unit consisting of the one-turn loop antenna and the booster antenna satisfies an impedance matching condition.

0146<figref idref="DRAWINGS">FIG. 31</figref> shows calculation results of the S<b>11</b> parameter and the VSWR of each of a one-turn loop antenna itself and a combination of a one-turn loop antenna and a booster antenna. Whereas the VSWR of the one-turn loop antenna itself is equal to about 140, the VSWR of the combination of the one-turn loop antenna and the booster antenna is smaller than 2 (see <figref idref="DRAWINGS">FIG. 18</figref> (X=54 mm).

0147The invention is not limited to the individual embodiments, and elements of different embodiments can be combined together. A person skilled in the art may be able to make modifications or applications on the basis of the disclosure of the specification and known techniques, and such modifications and applications should be covered by the scope to be protected.

0148As described above, the following features are disclosed in the specification:

0149(1) An RF-ID tag comprising an IC, a loop antenna to which the IC is connected, and a linear booster antenna which may be long and narrow as a whole, wherein:

0150the booster antenna has, as one end portion in its longitudinal direction, a fold-back portion which is wound; and

0151a portion, having a length that measures 73% or more of a one-turn overall length of a loop of the loop antenna, of the loop antenna extends along a portion, including the fold-back portion, of the booster antenna.

0152(2) The RF-ID tag of item (1), wherein the loop antenna is laid on the fold-back portion of the booster antenna with a dielectric layer interposed in between.

0153(3) The RF-ID tag of item (1) or (2), wherein the loop of the loop antenna has a circular or polygonal shape.

0154(4) The RF-ID tag of item (3), wherein the fold-back portion of the booster antenna is wound in circular or polygonal form.

0155(5) The RF-ID tag of any one of items (1) to (4), wherein the fold-back portion of the booster antenna is wound in rectangular form and at least three of four wound sides of the fold-back portion extend along sides of the loop antenna.

0156(6) The RF-ID tag of any one of items (1) to (5), wherein the IC is disposed on the loop antenna at one end, in the longitudinal direction, of the booster antenna.

0157(7) The RF-ID tag of any one of items (1) to (6), wherein the booster antenna is symmetrical with respect to a line that passes through a center, in the longitudinal direction, of the booster antenna and is perpendicular to the longitudinal direction.

0158(8) The RF-ID tag of any one of items (1) to (7), wherein at least part of the fold-back portion of the booster antenna coextends with an inside portion that is located inside the loop of the loop antenna.

0159(9) The RF-ID tag of any one of items (1) to (8), wherein the fold-back portion of the booster antenna is disposed in a region between one end, in the longitudinal direction, of the booster antenna and a position that is distant from the one end by ⅙ of a wavelength used.

0160(10) The RF-ID tag of any one of items (1) to (9), wherein an insertion loss represented by an S<b>11</b> parameter is smaller than or equal to −3 dB and a voltage standing wave ratio (VSWR) is smaller than or equal to 6.

0161(11) The RF-ID tag of item (10), wherein each of the loop antenna and the booster antenna has a resonance frequency in a range of 850 MHz to 1 GHz.

0162(12) The RF-ID tag of any one of items (1) to (11), wherein a portion, excluding the one end portion in the longitudinal direction, of the booster antenna has a meandering shape.

0163(13) An RF-ID communication system comprising:

0164the RF-ID tag of any one of items (1) to (12); and

0165a reader or a reader/writer which performs a wireless communication with the RF-ID tag.

0166Although the invention has been described above in relation to preferred embodiments and modifications thereof, it will be understood by those skilled in the art that other variations and modifications can be effected in these preferred embodiments without departing from the scope and spirit of the invention.