SE543837C2 - RFID tag arrangement with omnidirectional antenna characteristics - Google Patents

Abstract

An RFID tag arrangement (1) comprises a first (20; 20’; 20”; 20”’) and second (30; 30’; 30”; 30’”) antenna, each comprising an intermediate feeding part (23; 23’; 23”a, 23”b; 23”’a, 23”’b and 33; 33’; 33”a, 33”b; 33”’a, 33”’b) and two radiating dipole elements (21, 22; 21’, 22’; 21”, 22”; 21’”, 22’” and 31, 32; 31’, 32’; 31”, 32”; 31’”, 32’”) connected to the intermediate feeding part and extending in different directions. An RFID chip (24) is electrically coupled to each of the intermediate feeding parts. The radiating dipole elements of the two antennas are arranged at a distance from each other, and the intermediate parts are arranged to cross each other at least one crossing point. A dielectric separation layer (4, 5) is arranged between the first and second intermediate parts at said crossing point(s), thereby galvanically separating the first antenna from the second antenna. Hereby, a versatile RFID tag arrangement with very good omnidirectional performance is obtained. A corresponding production method is also provided.

Description

RFID TAG ARRANGEMENT WITH OMNIDIRECTIONAL ANTENNACHARACTERISTICS Technical field of the invention The present invention is related to a radio frequency identification(RFID) tag arrangement with omnidirectional antenna characteristics. Thefurther relates to a manufacturing method for producing such an RFID tagarrangement.

BackgroundRFID tags are nowadays used more and more frequently, and for a wide variety of applications, such as in smart labels/tags. The RFID tag isconventionally arranged as a flat configured transponder, e.g. arranged undera conventional print-coded label, and includes a chip and an antenna. Thelabels/tags are often made of paper, fabric or plastics, and are normallyprepared with the RFID inlays laminated between a carrier and a label media,e.g. for use in specially designed printer units. Smart labels offer advantagesover conventional barcode labels, such as higher data capacity, possibility toread and/or write outside a direct line of sight, and the ability to read multiplelabels or tags at one time.

It is also known to incorporate RFID labels directly in a packagingmaterial, to form so-called intelligent packaging products.

Most commercially available RFID tags uses dipole, loop or slot typesantennas. Such antennas are advantageous, due to their small size, simplestructure and relatively low production costs.

However, a problem with most commercially available RFID tagantennas is that the radiation pattern is directional, such as donut shaped andthe like, having angular positions with very poor radiation, such as deep nullpoints. This is generally not a great problem as long as the rotational positionbetween the RFID tag and the reader can be easily controlled. However, inmany types of application, the rotational position between the reader and theRFID tag cannot be controlled, and the reader need to be able to communicate with the RFID tag from many different positions. This is e.g. thesituation for RFID tags used on stacked pulp bales. ln such applications, theRFID reader is typically located near the floor level, and should be able toidentify e.g. a vertical tag which is located on a top of a bale. Pulp bales arechallenging applications for RFID tags, due to the distance and heightdifference between the RFID reader and the RFID tag, and also since the tagmay be oriented in a non-optimal vertical position. Such a vertical orientationmay mean that the antenna radiation pattern exhibits a null point towards thereader, which makes the radio transmission very poor.

Similar problems are present also in many other applications, wherethe distance between the reader and the tag may, by necessity, be ratherlong, and/or where the rotational position between the tag and the reader maybe difficult to control. lt has been proposed to provide RFID tag antennas with more omni-directional characteristics. Such an antenna is e.g. disclosed in US2009/0303002, comprising an RFID chip with four ports, each connected toone antenna arm. However, the radiation and communication performance ofthis RFID tag is still inadequate for many applications, and the RFID tag isfurther complicated and costly to produce, e.g. requiring expensive multiportRFID chips, and complicated and costly switching and feeding structures.

There is therefore still a need for an improved RFID tag arrangementwhich can be made more versatile, for use e.g. in pulp bale applications andthe like, which has good and improved RF performance, and/or which can beproduced cost-effectively.

SummaryIt is therefore an object of the present invention to provide an RFID tag arrangement and a manufacturing method for such RFID tag arrangements,which alleviates at least part of the above-discussed problems, and at leastpartially address one or more of the above-mentioned needs.

This object is obtained by means of an RFID tag arrangement and amanufacturing method in accordance with the appended claims.

According to a first aspect of the invention there is provided an RFIDtag arrangement comprising: a first antenna comprising a first intermediate feeding part and two firstradiating dipole elements connected to the first intermediate feeding part andextending in different directions; a second antenna comprising a second intermediate feeding part andtwo second radiating dipole elements connected to the second intermediatefeeding part and extending in different directions; a first RFID chip electrically coupled to the first intermediate feedingpart; a second RFID chip electrically coupled to the second intermediatefeeding part; wherein the first radiating dipole elements are arranged at a distancefrom the second radiating dipole elements, and the first and secondintermediate parts are arranged to cross each other at at least one crossingpoint, wherein a dielectric separation layer is arranged between the first andsecond intermediate parts at said crossing point(s), thereby galvanicallyseparating the first antenna from the second antenna.

The RFID tag arrangement of the present invention provides twoseparately operable antennas. Since the two antennas are arrangedoverlaying each other, the footprint of the RFID tag arrangement, i.e. theoverall dimensions, can still be very limited, and not much greater than for anordinary RFID tag. At the same time, since first radiating dipole elements arearranged at a distance form the second radiating dipole elements, theradiation pattern of the two antennas are at least to some extent, andpreferably essentially totally complementary to each other. Hereby, the weakangular directions of the radiation pattern of the first antenna iscomplemented by a relatively stronger second antenna at the same angulardirections, and vice versa. Thus, the overall radiation pattern of the RFIDarrangement, including the said two antennas, is essentially omni-directional,with very good performance in all directions.

Thus, the RFID tag arrangement of the present invention is highlysuitable for use in various types of applications where an omni-directional antenna pattern is of advantage, such as for applications where it is desirableor necessary to identify a tag regardless of its orientation in a package orproduct.

The RFID tag arrangement can also be produced very cost-efficiently,as will be discussed in more detail in the following. ln particular, each of theantennas can be produced as relatively simple and easy-to-produce dipoleantennas, and the RFID chips may each be of a common and conventionaltwo-pole type. Hereby, contrary to what would normally be assumed, theproduction of an RFID tag arrangement with two such integrated RFID tags isin fact much faster and more cost-efficient than production of other types ofpreviously known omni-directional RFID tags, which generally require muchmore sophisticated and expensive multiport RFID chips, and complicated andexpensive antenna structures.

The RFID chips may e.g. be a high performance and low-cost IC chip,such as the commercially available NXP UCode 8.

The present invention is based on the realization that it is possible touse two standard, and relatively simple, RFID tags, which, when broughttogether in a certain way, act as a much more complicated and versatile RFIDtag arrangement, in which the RFID tags act more or less as one and thesame RFID tag, but with a much improved radiation performance, etc. Thus, ithereby becomes possible to produce an RFID tag arrangement with e.g. anomni-directional radiation pattern, in a much easier and more cost-efficientway than has heretofore been possible.

The omni-directional performance of the RFID tag arrangement isprovided by the arrangement of the first radiating dipole elements at adistance from the second radiating dipole elements, and by arranging the firstand second intermediate parts to cross each other at at least one crossingpoint, and with a dielectric separation layer arranged between the first andsecond intermediate parts at the crossing point(s). This essentially provides acombination of two antenna radiation patterns, which in combination providesa generally omni-directional radiation pattern, and with very limitedelectromagnetic coupling between the antennas.

Preferably, the first and second antennas are arranged to togetherprovide an omni-directional antenna characteristic.

Electromagnetic coupling between the first and second antenna leadsto RF power from one antenna to a large extent coupling to the other, andthereby not being properly radiated. lt has been found that the main sourcesof such detrimental electromagnetic coupling are couplings that occurbetween matching loops of the antennas and between radiating dipoleelements of the antennas.

The separation of the dipole antenna elements of the two antennas,and the arrangement of the crossing of the antennas only at the intermediateparts, is an efficient measure to reduce electromagnetic coupling between theantennas.

Further, the arrangement of a dielectric separation layer between theantennas, at least in the areas of the crossing points, is also an efficientmeasure to reduce electromagnetic coupling between the antennas. ln addition, the parts of the antennas crossing each other at the one ormore crossing points are further preferably arranged to extend non-parallel toeach other in the vicinity of the crossing points, and preferably to extendessentially perpendicular to each other at the crossing points. This furtherlimits the electromagnetic coupling between the antennas. lt has been foundthat orthogonal crossings, or at least crossing at a relatively great angle, areof great benefit, both since it provides complementary differences in theradiation patterns, thereby providing a more omni-directional combinedradiation pattern, and since it decreases electromagnetic coupling betweenthe antennas, which increases antenna gain.

Preferably, the crossing paths of the antennas at or in the vicinity of thecrossing point/points, and thus the current directions, are directed with arelative angle in the range of 45-135 degrees, and preferably in the range of60-120, and more preferably in the range of 75-105 degrees, and mostpreferably 85-95 degrees, such as about 90 degrees.

Hereby, by this angular orientation, the antennas may be seen asbeing tilted in relation to each other. This is the case even if the radiatingdipole elements may per se be arranged parallel to each other, since the intermediate parts also radiate, and form part of the radiating performance ofthe antennas. Thus, the intermediate parts form part of the dipoles, and theRF currents are normally highest in the middle of the antennas, i.e. close tothe RFID chips. Thus, by arranging the intermediate parts to cross eachother, and to occur non-parallel over the crossing, a tilting of the two antennasin relation to each other is obtained, which is very beneficial to limit theelectromagnetic coupling between the antennas. The tilted antennas are alsobeneficial to provide the omni-directional radiation pattern, since the tilteddipole antennas also produce different kinds of radiation patterns in respect ofeach other. This means that when the first antenna experiences null point atsome direction, the second antenna performs much better in that direction.Thus, by the tilted arrangement, any directions with no or limited radiation inthe antenna pattern for one of the antennas will be compensated by theradiation pattern of the other antenna, since the radiation patterns aredifferent and at least to some extent complementary to each other.

Put differently, the two antennas are effectively used and seen as onetag, and the tag antennas are designed such that the weak directions, e.g.null directions, in the radiation patterns are not in the same direction. At thesame time, the dimensions of the two tags when combined are essentially thesame as for one tag, and consequently, the foot print of the RFID tagarrangement is essentially the same as for a single RFID tag.

The RFID tag arrangement may be seen as two independent RFIDtags, arranged to cooperate to generally appear to the reader, at least incertain situations, as a single, omni-directional tag. To this end, the two RFIDchips may also be programmed to have the same Electronic ProductionCode, EPC. This is the identification normally determined and programmedby the tag manufacturer, and which is normally communicated to the reader.If the two chips are programmed with the same EPC, this enables the readerto identify the RFID tag arrangement by reception of signals from any of thetwo RFID chips, or from both simultaneously.

The RFID chips are further preferably provided with a TagIdentification, TID, which is normally an identity programmed into the chip bythe chip manufacturer during the chip manufacturing process under defined conditions. The TID for the two RFID chips may be different, thereby enablingidentification of the two RFID chips independently of each other, in situationswhere this is required.

The two tags, formed by the two antennas and the two RFID chips, arepreferably integrated together, to form an integrated RFID tag arrangement.The tags may e.g. be integrated together by being attached to the samesubstrate, such as being arranged on different sides of a dielectric substratelayer. Hereby, the dielectric separation layer may be provided by the dielectricsubstrate. Alternatively, the tags may be attached to different substrates, andthe substrates may be attached together, e.g. by an adhesive. ln this case,the dielectric separation layer may be provided by any one, or both, of thesubstrates, and/or by the adhesive.

The crossing between the antennas may occur over a single line ofeach antenna, thereby forming a single crossing point. However, the crossingmay also occur over a feeding or matching loop of each antenna, wherebyfour crossing points are formed. The feeding or matching loops may e.g. beshaped as essentially rectangular feeding/matching loops. However, othershapes are also feasible, such as circular, oval, hexagonal, and the like. Thecrossing may also occur between a single line and a loop, providing twocrossing points. Other numbers of crossing points may also be realized.

The first intermediate part preferably comprises a first feeding loop,and wherein the second intermediate part comprises a second feeding loop. ln one embodiment, the crossing of the first and second intermediatesparts occurs in the first and second feeding loops. ln another embodiment, the crossing of the first and secondintermediate parts occurs outside the first and second feeding loops.

The first and second intermediate parts are preferably arranged tominimize electromagnetic coupling between them. ln one embodiment, the loops are essentially shaped as rectangles,possibly with rounded corners, and the crossings occur between the relativelystraight legs of the loops, thereby forming four crossing points. The loopspreferably extend essentially orthogonally to each other, thereby forming four crossing points arranged in a diamond shape. This diamond shape ispreferably provided essentially in the center of the antennas.

The antenna(s) may comprise two radiating dipole elements arrangedessentially parallel to each other. ln a preferred embodiment, the tworadiating dipole elements of each antenna are arranged along lines separatedfrom each other by a separation distance, and being connected by a slantintermediate element connecting the two radiating dipole elements. ln apreferred embodiment, the extension direction of the intermediate elementand each of the radiating dipole elements is about 135 degrees. ln embodiments where the intermediate parts comprise feeding ormatching loops, the loops are preferably arranged to be partly displaced fromeach other, thereby to be only partly overlapping. Preferably, the areaencircled by the loops overlap by less than 50% of the total area of each loop,and preferably by less than 30%, and more preferably by 25% or less. lt has been found that by proper arrangement of the crossings and theisolation provided by the dielectric separation layer, a very lowelectromagnetic coupling can be obtained, resulting in good impedancematching and isolation between antennas as low as about -10dB or less,which means that only 1/10, or less, of the power is coupled between theantennas.

The first RFID chip may be arranged over an IC gap arranged in thefirst feeding loop, and the second RFID chip may be arranged over an IC gaparranged in the second feeding loop.

The dielectric separation layer preferably extends over the entire extentof the first and second antennas, wherein the first antenna is arranged on afirst side of the dielectric separation layer and the second antenna is arrangedon a second, opposite side of the dielectric separation layer.

The first and second antennas are preferably identical and arrangedmirrored in relation to each other. Thus, the antennas are essentially identical,but with one flipped in orientation, either vertically or horizontally. This maycorrespond to one of the antennas being rotated by 180 degrees.

The dielectric separation layer may be realized in various ways. ln oneembodiment, the dielectric separation layer is made of at least one of: paper,board, polymer film, textile and non-woven material.

The RFID tag arrangement is preferably configured for operation at theUHF frequency band.

The RFID arrangement is preferably configured for operation at afrequency within the range of 860-960 MHz.

The antenna and the antenna parts may have various shapes anddimensions, as is per se known in the art. For example, the dipole antennaparts may extend in a generally linear direction, or may extend in a non-linearway, such as in a meandering form or the like. The parts may also be foldedor curved, thereby extending in two or more directions. In one embodiment,dipole antenna parts may terminate, with end parts, which may have anenlarged width, at least at some positions. The end parts may e.g. have agenerally circular or a generally rectangular shape.

The dielectric separation layer may have a thickness in the range of20-300 um, and preferably in the range 50-200 um, and more preferably inthe range 50-150 um, and most preferably in the range 70-130 um, such as100 um. However, it is also possible to use even thicker dielectric substrates,such as up to 1 mm, or up to 2 mm, or even thicker.

The RFID tag arrangement may be either passive, i.e. powered by areader's electromagnetic field, or active, i.e. powered by an onboard battery.

The antennas may be made of any material, as long as the material isconductive. The antennas may be made by the same material, but mayalternatively be made of different materials. For example, the antenna may beformed by aluminum, but other metals, such as silver, and alloys may also beused. Forming of the antenna on the substrate can be made in various ways,as is per se known in the art, such as by printing with conductive ink, such assilver ink, by first providing a conductive layer on the substrate andsubsequently removing or forming this conductive layer into the desiredshape, e.g. by means ofgrinding, cutting, etching or the like.

According to a second aspect of the invention there is provided amethod for manufacturing an RFID tag arrangement, comprising the steps: providing a first antenna on a first dielectric substrate portion, the firstantenna comprising a first intermediate feeding part and two first radiatingdipole elements connected to the first intermediate feeding part and extendingin different directions; providing a second antenna on a second dielectric substrate portion,the second antenna comprising a second intermediate feeding part and twosecond radiating dipole elements connected to the second intermediatefeeding part and extending in different directions; attaching a first RFID chip to the first antenna, electrically coupiing it tothe first intermediate feeding part; attaching a second RFID chip to the second antenna, electricallycoupiing it to the second intermediate feeding part; connecting the first and second dielectric substrate portions togetherso that the first radiating dipole elements are arranged at a distance from thesecond radiating dipole elements, and the first and second intermediate partsare arranged to cross each other at at least one crossing point; and providing a dielectric separation layer between the first and secondintermediate parts at said crossing point(s), thereby galvanically separatingthe first antenna from the second antenna. ln accordance with this aspect, similar features and advantages asdiscussed in the foregoing, in relation to the first aspect, may be obtained. ln one embodiment, the first and second dielectric substrate portionsare arranged on a single dielectric sheet, and wherein the step of connectingthe first and second dielectric substrate portions together comprises folding apart of the dielectric sheet comprising the first dielectric substrate portion overa part of the dielectric sheet comprising the second dielectric portion. Hereby,the dielectric separation layer will be formed at least by the dielectricsubstrate portion, and possibly also by an adhesive connecting the portionstogether. ln another embodiment, the first and second dielectric substrateportions are provided on separate dielectric sheets, wherein the step ofconnecting the first and second dielectric substrate portions togethercomprises laminating the separate dielectric sheets together. Hereby, the 11 dielectric separation layer may be formed by one or both of the dielectricsheets, depending on whether they are arranged back-to-back or back-to-face. Additional dielectric separation may be provided by the adhesiveconnecting the sheets together. Alternatively, if the sheets are connectedface-to-face, the dielectric separation layer may be formed only by theadhesive.

Thus, in one embodiment, the first and second dielectric portions maybe connected so that the dielectric separation layer comprises at least one ofsaid first and second dielectric portions. lt will be appreciated that the above-mentioned detailed structures andadvantages of the first aspect of the present invention also apply to the furtheraspects of the present invention.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

Brief description of the drawinqs For exemplifying purposes, the invention will be described in closerdetail in the following with reference to embodiments thereof illustrated in theattached drawings, wherein: Fig. 1a is a top plan view of an RFID tag arrangement in accordancewith a first embodiment; Fig. 1b is a cross-sectional view of the RFID tag arrangement of Fig.1a; Fig. 2 is a top plan view of an RFID tag arrangement in accordancewith a second embodiment; Fig. 3 is a top plan view of an RFID tag arrangement in accordancewith a third embodiment; Fig. 4 is a top plan view of an RFID tag arrangement in accordancewith a fourth embodiment; Figs. 5 and 6 schematically illustrate two manufacturing processes forproduction of RFID tag arrangement in accordance with embodiments of the invention; 12 Figs. 7-9 schematically illustrate the layer construction of variousembodiments of RFID tag arrangements in accordance with embodiments ofthe present invention; Figs. 10a-10e are diagrams illustrating simulation results for the RFIDtag arrangement of Fig. 2; Figs. 11a-11o are diagrams illustrating measurements on the RFID tagarrangement of Fig. 3; and Figs. 12a-12d are diagrams illustrating simulation results for the RFIDtag arrangement of Fig. 4.

Detailed description of preferred embodiments ln the following detailed description preferred embodiments of theinvention will be described. However, it is to be understood that features ofthe different embodiments are exchangeable between the embodiments andmay be combined in different ways, unless anything else is specificallyindicated. lt may also be noted that, for the sake of clarity, the dimensions ofcertain components, parts and elements illustrated in the drawings may differfrom the corresponding dimensions in real-life implementations of theinvention, such as the thickness of various layers, the relative dimensions ofthe different antenna parts, etc.

Fig 1a and 1b illustrate an RFID tag arrangement 1 in accordance withan embodiment of the present invention. The RFID tag arrangementcomprises a first RFID tag 2 and a second RFID tag 3, arranged on one ormore substrates 4.

The first RFID tag 2 comprises a first antenna 20, comprising two firstradiating dipole elements 21 and 22, interconnected by a first interconnectingintermediate feeding part 23. The feeding part 23 comprises an IC gap (notshown), and an RFID chip 24 arranged over said IC gap, to transmit andreceive RF power from the two sides of the antenna.

The two radiating dipole elements 21, 22 are preferably arranged atopposite end areas of the antenna. The dipole elements are at one of theirends, the ends being closest to each other, connected to the intermediatefeeding part 23. Thus, the intermediate feeding part 23 forms a bridge 13 between the radiating dipole elements. Two power feeding areas (not shown)separated by the IC gap are provided, the first power feeding area connectedto the first dipole element 21, whereas the second power feeding area isconnected to the second dipole element 22. The power feeding areas areconnected to connectors of an integrated circuit, the RFID chip 24, which willconsequently be arranged overlying and bridging the gap.

At the other ends of the radiating dipole elements, not being connectedto the power feeding areas, end parts may be provided. The end parts arepreferably provided with smooth, rounded corners.

The two dipole elements 21, 22 are preferably about equal in size andshape, and are preferably symmetrical with each other.

In the illustrative example, the longitudinal axes of the dipole elementsextend along two parallel lines, the two lines being separated from each otherby a separation distance.

The longitudinal directions of the radiating dipole elements 21, 22 andthe longitudinal direction of the intermediate feeding part 23 forms angles oi1and oi2, respectively. The angles are preferably of equal size. The angles arepreferably obtuse angles, and preferably in the range of 115-155 degrees,and more preferably 125-145 degrees, and most preferably about 135degrees.

The dipole elements 21, 22 are, in this illustrated embodiment, shapedas elongate conductive lines. However, other shapes are also feasible. Forexample, the part may, at least over a part, extend in a meandering shape.The parts may also have an overall folded or curved shape. Many othershapes are also feasible, as is per se well-known. Some examples of othershapes of the dipole elements will be discussed in relation to the otherembodiments.

The antenna is a dipole antenna arranged to be used in an RFID tag,and is preferably arranged to operate in the UHF band, and in particular at afrequency within the range of 860-960 MHz.

The second RFID tag 3 comprises a first antenna 30, comprising twosecond radiating dipole elements 31 and 32, interconnected by a firstinterconnecting intermediate feeding part 33. The feeding part 33 comprises 14 an IC gap (not shown), and an RFID chip 34 arranged over said IC gap, totransmit and receive RF power from the two sides of the antenna.

The longitudinal directions of the radiating dipole elements 31, 32 andthe longitudinal direction of the intermediate feeding part 33 forms angles ß1and ß2, respectively. As in the first antenna, the angles are preferably ofequal size. The angles are preferably obtuse angles, and preferably in therange of 115-155 degrees, and more preferably 125-145 degrees, and mostpreferably about 135 degrees.

The second antenna 30 is preferably essentially identical to the firstantenna 20, but mirrored or folded, so that it is in a 180 degrees flippedorientation.

The two RFID tags 2 and 3 are arranged overlaying each other.Hereby, the first radiating dipole elements 21 and 22 of the first antenna 20are arranged at a distance from the second radiating dipole elements 31 and32 of the second antenna 30. Preferably, one of the first dipole elements andone of the second dipole elements, such as dipole elements 21 and 32, havelongitudinal directions extending along the same first line, and the other twofirst and second dipole elements, such as dipole elements 22 and 31, havelongitudinal directions extending along the same second line, the first andsecond lines being separated from each other.

The first and second intermediate parts 23, 33 are arranged to crosseach other at at least one crossing point. ln the here illustrated embodiment,the crossing occurs at a single crossing point. Further, the longitudinaldirections of the intermediate parts form crossing angles V1 and V2 in relationto each other. These angles are preferably in the range of 45-135 degrees,and preferably in the range of 60-120, and more preferably in the range of 75-105 degrees, and most preferably 85-95 degrees, such as about 90 degrees.

A dielectric separation layer 5 is arranged between the first and secondintermediate parts at said crossing point, thereby galvanically separating thefirst antenna from the second antenna. ln this example, the dielectricseparation layer 5 is formed by the substrate 4. To this end, the first antenna20 is arranged in a first layer, arranged on one side of the substrate 4, whereas the second antenna 30 is arranged in a second layer, arranged onthe opposite side of the substrate 4, as best seen in cross-section of Fig. 1b.

By this arrangement, the first and second antennas are arranged totogether provide an omni-directional antenna characteristic. Further, thecrossing arrangement of the first and second intermediate parts, together withthe die|ectric separation layer, minimizes electromagnetic coupling betweenthe antennas.

The first and second RFID chips 24, 34 are preferably programmedwith identical Electronic Product Codes (EPCs), but may be provided withdifferent Tag ldentifications (TlDs).

With reference to Fig. 2, another embodiment of the RFID tagarrangement 1 also comprises two RFID tags 2 and 3, having a first antenna20' and a second antenna 30'. ln this embodiment, the antennas and thearrangement of the antennas in the RFID tag arrangement are similar to thefirst embodiment discussed above, with reference to Figs. 1a and 1b. Thus,apart from the differences discussed in the following, the features andadvantages discussed above in relation to the first embodiment are applicablealso for this second embodiment. ln this second embodiment, the first dipole elements 21' and 22' andthe second dipole elements 31' and 32' are arranged in the same way as inthe first discussed embodiment, with their longitudinal directions arrangealong two parallel but separated lines. However, in this embodiment, thedipole elements are provided with a meandering shape, thereby increasingthe radiating length of the dipole elements in a compact, short length.

Further, the intermediate parts 23' and 33' are here provided in theform of first and second feeding loops, for impedance matching. The feedingloops in this embodiment are arranged essentially in the form of rectangularloops. However, other loop forms are also feasible, as will be discussed inmore detail in the following. ln this embodiment, the crossing between the intermediate parts 23'and 33' is a crossing of the two feeding loops, providing four crossing points.However, the intermediate parts crossing each other are still crossing eachother essentially orthogonally. Thus, the crossing paths of the antennas at or 16 in the vicinity of all the crossing points, and thus the current directions, arepreferably directed with a relative angle in the range of 45-135 degrees, andpreferably in the range of 60-120, and more preferably in the range of 75-105degrees, and most preferably 85-95 degrees, such as about 90 degrees.

With reference to Fig. 3, another embodiment of the RFID tagarrangement 1 also comprises two RFID tags 2 and 3, having a first antenna20” and a second antenna 30”. ln this embodiment, the antennas and thearrangement of the antennas in the RFID tag arrangement are similar to thefirst and second embodiments discussed above, with reference to Figs. 1a,1b and 2. Thus, apart from the differences discussed in the following, thefeatures and advantages discussed above in relation to the first and secondembodiments are applicable also for this second embodiment.

In this third embodiment, the first dipole elements 21” and 22” and thesecond dipole elements 31” and 32” are arranged in the same way as in thefirst discussed embodiment, with their longitudinal directions arrange alongtwo parallel but separated lines. However, in this embodiment, the dipoleelements are provided partly with a meandering shape, similar to the secondembodiment, and partly with a straight configuration, as in the firstembodiment. In this embodiment, the straight part is arranged closest to thefree end, and the meandering part arranged closest to the connection to theintermediate part.

Further, the intermediate parts here comprises both first and secondfeeding loops 23”b and 33”b, for impedance matching, and straight parts23”a, and 33”a. The feeding loops in this embodiment are arrangedessentially in the form of rectangular loops. However, other loop forms arealso feasible, as will be discussed in more detail in the following. The feedingloops in this example are provided displaced towards one of the dipoleelements. Thus, some of the dipole elements in this embodiment areshortened, to make room for the feeding loops - in this example, the dipoleelements 31” and 22” - whereby the two dipole elements of each antenna aredifferent. However, in the shortened dipole elements, the meandering partsare made more compact, and the overall length of the antennas remain thesame. 17 In this embodiment, the crossing between the intermediate parts isprovided as a crossing of the two straight parts 23”a and 33”a, providing onecrossing point. The intermediate parts are crossing each other essentiallyorthogonally, similar to the first discussed embodiment.

With reference to Fig. 4, another embodiment of the RFID tagarrangement 1 also comprises two RFID tags 2 and 3, having a first antenna20”' and a second antenna 30”'. ln this embodiment, the antennas and thearrangement of the antennas in the RFID tag arrangement are similar to thefirst, second and third embodiments discussed above, with reference to Figs.1a, 1b, 2 and 3. Thus, apart from the differences discussed in the following,the features and advantages discussed above in relation to the first andsecond embodiments are applicable also for this second embodiment.

In this fourth embodiment, the first dipole elements 21”' and 22”' andthe second dipole elements 31”' and 32"' are arranged in the same way as inthe first discussed embodiment, with their longitudinal directions arrangealong two parallel but separated lines, and essentially occurring throughstraight line.

Further, similar to the third embodiment, the intermediate parts herecomprises both first and second feeding loops 23'”b and 33”*b, for impedancematching, and straight parts 23”'a, and 33'”a. In this embodiment, thecrossing of the intermediate parts occurs both in the straight parts 23”'a and33”'a and the feeding loop parts 23'”b and 33”'b. Hereby, three crossingpoints are provided.

The feed loops 23”'b and 33'”b are preferably arranged to be partlydisplaced from each other, thereby to be only partly overlapping. Preferably,the area encircled by the loops overlap by less than 50% of the total area ofeach loop, and preferably by less than 30%, and more preferably by 25% orless. In this embodiment, the crossing between the intermediate parts in thefeed loops 23”' and 33"' is a crossing such that the crossing paths in thevicinity of all the crossing points, and thus the current directions, arepreferably directed with a relative angle in the range of 45-135 degrees, andpreferably in the range of 60-120, and more preferably in the range of 75-105degrees, and most preferably 85-95 degrees, such as about 90 degrees. 18 Further, the crossing between the straight parts 23”'a and 33”'a of theintermediate parts are preferably arranged to cross each other essentiallyorthogonally. The angles are preferably in the range of 45-135 degrees, andpreferably in the range of 60-120, and more preferably in the range of 75-105degrees, and most preferably 85-95 degrees, such as about 90 degrees. ln the above-discussed embodiment, dielectric separation layerextends over the entire extent of the first and second antennas, wherein thefirst antenna is arranged on a first side of the dielectric separation layer andthe second antenna is arranged on a second, opposite side of the dielectricseparation layer. However, other arrangements of the dielectric separationlayer are also feasible. For example, the dielectric separation layer may beprovided locally, only at, or at an area surrounding the connection points, or atan area covering the connection points, preferably with a margin, but notcovering the entire antennas.

The dielectric separation layer can essentially be of any non-conductive material, such as paper, board, polymer film, textile non-wovenmaterial and non-conductive adhesive. ln particular, the layer can be made ofpapen The antenna may be made of any material, as long as the material isconductive. The antennas may be made of the same material, but differentmaterials may also be used. For example, the antenna may be formed byaluminum, but other metals, such as silver, and alloys may also be used. Forexample, it is feasible to use an alloy having a relatively low meltingtemperature, such as an alloy comprising tin and bismuth. Forming of theantenna on the substrate can be made in various ways, as is per se known inthe art, such as by printing with conductive ink, such as silver ink, by firstproviding a conductive layer on the substrate and subsequently removing orforming this conductive layer into the desired antenna shape, e.g. by meansofgrinding, cutting, etching or the like.

The RFID chip may take any of a number of forms (including those ofthe type commonly referred to as a "chip" or a "strap" by one of ordinary skillin the art), including any of a number of possible components and beingconfigured to perform any of a number of possible functions. Preferably, the 19 RFID chip includes an integrated circuit for controlling RF communication andother functions of the RFID tag.

The RFID tag arrangement may be manufactured in various ways. Forexample, the two antennas or RFID tags may be provided on separatesubstrates, as is per se known, and be Iaminated together to form the RFIDtag arrangement. Alternatively, the antennas or RFID tags may be provided Generally, a method for manufacturing an RFID tag arrangement,comprising the steps: providing a first antenna on a first die|ectric substrate portion, the firstantenna comprising a first intermediate feeding part and two first radiatingdipole elements connected to the first intermediate feeding part and extendingin different directions; providing a second antenna on a second die|ectric substrate portion,the second antenna comprising a second intermediate feeding part and twosecond radiating dipole elements connected to the second intermediatefeeding part and extending in different directions; attaching a first RFID chip to the first antenna, electrically coupling it tothe first intermediate feeding part; attaching a second RFID chip to the second antenna, electricallycoupling it to the second intermediate feeding part; connecting the first and second die|ectric substrate portions togetherso that the first radiating dipole elements are arranged at a distance from thesecond radiating dipole elements, and the first and second intermediate partsare arranged to cross each other at at least one crossing point; and providing a die|ectric separation layer between the first and secondintermediate parts at said crossing point(s), thereby galvanically separatingthe first antenna from the second antenna.

The the first and second die|ectric substrate portions may be arrangedon a single die|ectric sheet, and wherein the step of connecting the first andsecond die|ectric substrate portions together comprises folding a part of thedie|ectric sheet comprising the first die|ectric substrate portion over a part ofthe die|ectric sheet comprising the second die|ectric portion. Such anembodiment is illustrated in Fig. 5. Hereby, the RFID tags may be identically provided on the substrate portions, and then be folded over each other toform the RFID tag arrangement.ln another manufacturing method, the first and second dielectricsubstrate portions are provided on separate dielectric sheets, wherein thestep of connecting the first and second dielectric substrate portions togethercomprises Iaminating the separate dielectric sheets together. Such anembodiment is i||ustrated in Fig. 6. Here, the RFID tags may be identicallyprovided on the substrate portions, and one of the sheet being 180 degreestwisted during manufacturing, or one of the RFID tags may be provided in amirrored state, as i||ustrated in Fig. 6, thereby requiring no twisting of thesheets.The dielectric separation layer 5 may be provided in various ways, aswill be explained further in the following.In one embodiment, as i||ustrated in Fig. 7, the antennas and RFIDtags are provided in layers 20, 30 on a first side of the substrate portions 4,and the substrate portions are connected together by attaching the other sideof the substrate portions together by an adhesive 6. Hereby, the antennas areseparated by both the substrate layers 4, and also by the adhesive layer 6. lnsuch embodiments, the galvanic separation provided by the substrate layers4 may suffice, and the adhesive layer 6 may be either conductive or non-conductive. Such an embodiment is easily achievable by Iaminating separatesheets together.In another embodiment, as i||ustrated in Fig. 8, the antennas andRFID tags are provided in layers 20, 30 on a first side of the substrateportions 4, and the substrate portions are connected together by attaching thethese sides, carrying the antenna layers, together by an adhesive 6. Hereby,the antennas are separated only by the adhesive layer. However, by using anon-conductive adhesive, the galvanic separation between the antennas maystill be sufficient. Such an embodiment is easily achievable by Iaminatingseparate sheets together.In yet another embodiment, as i||ustrated in Fig. 9, the antennas and RFID tags are provided in layers 20, 30 on a first side of the substrateportions 4, and the substrate portions are connected together by attaching 21 one antenna side and one non-antenna side together by an adhesive 6.Hereby, the antennas are separated by both one of the substrate layers 4,and also by the adhesive layer 6. ln such embodiments, the galvanicseparation provided by the substrate layer 4 may suffice, and the adhesivelayer 6 may be either conductive or non-conductive. However, preferably theadhesive layer is non-conductive, thereby increasing the galvanic separationbetween the antennas. Such an embodiment is easily achievable by folding asingle sheet to form the RFID tag arrangement.

To evaluate the new concept a number of experimental tests andsimulations have been performed.

First, an antenna corresponding to the one discussed above in relationto Fig. 2 was evaluated. Fig. 10a is a diagram illustrating simulation results ofthe S-parameters in dB over a range of frequencies, from 0.7 GHz to 1.5GHz. From these results, it may be deduced that there is good impedancematching and a very good isolation between the antennas. The electricalcoupling at the UHF band is only about -10 dB, which means that only 1/10 ofthe RF power is coupled between the antennas. Fig. 10b is a diagramillustrating simulation results for free air read range, in meter, for the twoantennas, over the same frequency range of 0.7-1 .5 GHz. As can be seenfrom the diagram, the read range at the UHF band is about 13 meters, whichis very good, and more than sufficient for most applications. Figs. 10c and10d illustrate simulated 3D radiation patterns for the first and second antenna.The radiation patterns show that each antenna has distinct radiation patterns,and that wherever the first antenna has weak radiation, a null direction, thesecond antenna performs well in this direction, and vice versa. Thus, incombination, the two antennas have omni-directional characteristics. Finally,Fig. 10e illustrates a polar plot of the radiation patterns of the two antennas,with the gain in dBi for different Phi directions in the range 0-360 degrees,where the omni-directional characteristics of the combined antennas is alsoclearly deducible. For example, the realized gain of the second antenna(“ant2”) in the direction Theta=90 and Phi=240 is >20 dB higher than therealized gain of the first antenna (“ant1”) in the same direction. 22 Secondly, an antenna corresponding to the one discussed above inrelation to Fig. 3, and with a NXP UCODE8 used as the RFID chip, wasevaluated. Fig. 11a is a diagram illustrating measured results for the power indBm and the read range in meter for the antennas when measuredseparately, over a frequency range of 800-1000 MHz. As can be seen, thetuning and performance of the antennas are essentially identical. Fig. 11b adiagram illustrating measured results for the power in dBm and the readrange in meter for the antennas when measured in combination, over afrequency range of 800-1000 MHz. The measured antennas have beencombined in accordance with Fig. 7 (“SE132_3ab opt1”), Fig. 8 (“SE132_3abopt2”), and Fig. 9 (“SE132_3ac”), respectively. As can be seen, the tuningand performance of the different antenna combinations are essentiallyidentical. Thus, it may be deuced that the way the tags are attached together,and how the dielectric separation layer is formed, has little impact on thetuning and performance.

Further, measurements were made by measuring with four differentantennas in different angular positions, as illustrated in Fig. 11c, where theantennas (“ant1”-“ant4”) are separated by 30 degrees. This set-up was usedto measure at 0-90 degrees, 120-210 degrees and 240-330 degrees. Forcomparison, the same measurements were also made on a commerciallyavailable RFID tag, the “ECO Bumper”, produced by Stora Enso, which isadapted for UHF frequency range, and which uses an NXP UCODE8 as theRFID chip. Measurements were made on two different RFID tagarrangements of the inventive example and tvvo different comparative RFIDtags. The measured results are the power in dBm and the read range inmeter for the antennas when measured separately, over a frequency range of800-1000 MHz.

Figs. 11d-11o shows the measurement results of these measurements,where Fig. 11d shows the measurements made at 0 degrees, Fig. 11e at 30degrees, Fig. 11fat 60 degrees, Fig. 11g at 90 degrees, Fig. 11h at 120degrees, Fig. 11i at 150 degrees, Fig. 11j at 180 degrees, Fig. 11k at 210degrees, Fig. 11l at 240 degrees, Fig. 11m at 270 degrees, Fig. 11n at 300degrees, and Fig. 11o at 330 degrees. 23 From these measurements, it can be deduced that the inventive examples perform about as well as the comparative example for many of the angular positions, such as at 30 degrees (Fig. 11e), 60 degrees (Fig. 11f),120 degrees (Fig. 11h), 150 degrees (Fig. 11i), 210 degrees (Fig. 11k), 2405 degrees (Fig. 11d), 300 degrees (Fig. 11n) and 330 degrees (Fig. 11o).However, at many angular positions, the inventive example performs much better than the comparative examples, such as at 0 degrees (Fig. 11d),90 degrees (Fig. 11g), 180 degrees (Fig. 11j) and 270 degrees (Fig. 11m).The poorest values of the measured power in dBm and the read range in m for the different angular positions, and in the frequency range of most interest (i.e. 860-960 MHz) are summarized in the following table: Angular lnv. Ex. Com. Ex. lnv. Ex. Comp. Ex.position Power (dBm) Power (dBm) Read range Read range(m) (m)0 -17 -22 10 1530 -18 -20 12 1460 -18 -16 990 -15 -5 6120 -18 -16 10150 -18 -20 12 14180 -18 -22 10 16210 -18 -20 12 13240 -18 -16 10 7270 -15 -2.5 7 1.5300 -18 -16 10 8330 -18 -20 12 14 Thus, the measured power in dBm for the different measurements, and in the frequency range of most interest, i.e. in the range 860-960 MHz, varies in the following ranges: For the inventive examples between -15 and -18 24 - For the comparative examples between -2.5 and -22 The measured read range in m for the different measurements, and inthe frequency range of most interest, in the range 860-960 MHz, varies in thefollowing ranges: - For the inventive examples between 6 and 12 - For the comparative examples between 1.5 and 16 Thus, it can be concluded that the comparative example, the ECOBumper, performs very well in certain directions, but poorly in other directions,and the performance varies greatly in dependence on the angle. However,the inventive example has extremely low variation, and performs at a good,adequate level for all the measured angular positions.

Thirdly, an antenna corresponding to the one discussed above inrelation to Fig. 4 was evaluated. Fig. 12a is a diagram illustrating simulationresults of the S-parameters in dB over a range of frequencies, from 0.7 GHzto 1.5 GHz. From these results, it may be deduced that there is goodimpedance matching and a very good isolation between the antennas. Fig.12b is a diagram illustrating simulation results for free air read range, inmeter, for the two antennas, over the same frequency range of 0.7-f .5 GHz.As can be seen from the diagram, the read range at the UHF band is about18 meters, which is very good, and more than sufficient for most applications.Figs. 12c and 12d illustrate simulated polar plot of the radiation patterns of thetwo antennas, with the gain in dBi for different Phi directions in the range 0-360 degrees, where the omni-directional characteristics of the combinedantennas is also clearly deducible.

The person skilled in the art realizes that the present invention is notlimited to the above-described embodiments. For example, the generalantenna design may be varied in many ways, as is per se well-known in theart. For example, the dipole elements may be shaped differently than in theabove-discussed embodiments, and the feeding loop, etc, may also haveother shapes. The antenna may further be adapted for different operationalfrequencies.

Such and other obvious modifications must be considered to be withinthe scope of the present invention, as it is defined by the appended claims. lt should be noted that the above-described embodiments illustrate rather thanlimit the invention, and that those skilled in the art will be able to design manyalternative embodiments without departing from the scope of the appendedclaims. ln the claims, any reference signs placed between parentheses shallnot be construed as limiting to the claim. The word ”“comprising”” does notexclude the presence of other elements or steps than those listed in theclaim. The word “a” or “an” preceding an element does not exclude thepresence of a plurality of such elements.

Claims (19)

1. An RFID tag arrangement (1) comprising: a first antenna (20; 20”; 20"; 20"') comprising a first intermediatefeeding part (23; 23'; 23"a, 23”b; 23"'a, 23"'b) and two first radiating dipoleelements (21, 22; 21', 22'; 21", 22"; 21"', 22"') connected to the firstintermediate feeding part (23; 23'; 23"a, 23”b; 23"'a, 23"'b) and extending indifferent directions; a second antenna (30; 30'; 30"; 30"') comprising a second intermediatefeeding part (33; 33'; 33”a, 33”b; 33"'a, 33"'b) and two second radiating dipoleelements (31, 32; 31 ', 32'; 31", 32"; 31"', 32"') connected to the secondintermediate feeding part (33; 33'; 33"a, 33”b; 33"'a, 33"'b) and extending indifferent directions; a first RFID chip (24) electrically coupled to the first intermediatefeeding part (23; 23'; 23"a, 23”b; 23"'a, 23"'b); a second RFID chip (34) electrically coupled to the secondintermediate feeding part (33; 33'; 33”a, 33”b; 33"'a, 33"'b); wherein the first radiating dipole elements (21, 22; 21', 22'; 21", 22";21"', 22"') are arranged at a distance from the second radiating dipoleelements (31, 32; 31 ', 32'; 31", 32"; 31"', 32"'), and the first and secondintermediate parts are arranged to cross each other at at least one crossingpoint, wherein a dielectric separation layer (4, 5) is arranged between the firstand second intermediate parts at said crossing point(s), thereby galvanicallyseparating the first antenna (20; 20”; 20"; 20"') from the second antenna (30;30'; 30"; 30"').

2. The RFID tag arrangement of claim 1, wherein the first andsecond antennas are arranged to together provide an omni-directionalantenna characteristic.

3. The RFID tag arrangement of claim 1 or 2, wherein the first andsecond intermediate parts are arranged to minimize electromagnetic couplingbetween them. 27

4. The RFID tag arrangement of any one of the preceding claims,wherein, at said crossing points, the first and second intermediate partsextend in essentially orthogonal directions.

5. The RFID tag arrangement of any one of the preceding claims,wherein the first intermediate part (23'; 23”a, 23”b; 23”a, 23”'b) comprises afirst feeding loop, and wherein the second intermediate part (33'; 33”a, 33”b;33”a, 33”b) comprises a second feeding loop.

6. The RFID tag arrangement of claim 5, wherein the crossing ofthe first and second intermediates parts (23'; 23”a, 23”b; 33'; 33”a, 33”b)occurs in the first and second feeding loops.

7. The RFID tag arrangement of claim 5, wherein the crossing ofthe first and second intermediate parts (23”a, 23”b; 33”a, 33”b) occurs outsidethe first and second feeding loops.

8. The RFID tag arrangement of any one of the claims 5-7, whereinthe first RFID chip (24) is arranged over an IC gap arranged in the firstfeeding loop, and the second RFID chip (34) is arranged over an IC gaparranged in the second feeding loop.

9. The RFID tag arrangement of any one of the preceding claims,wherein dielectric separation layer (4, 5) extends over the entire extent of thefirst and second antennas, wherein the first antenna (20; 20'; 20"; 20”') isarranged on a first side of the dielectric separation layer and the secondantenna (30; 30'; 30"; 30”') is arranged on a second, opposite side of thedielectric separation layer (4, 5).

10.wherein the first and second RFID chips (24, 34) are programmed withidentical Electronic Product Codes (EPCs).

11.wherein the first and second RFID chips (24, 34) are provided with differentTag ldentifications (TlDs).

12. wherein the first and second antennas are identical and arranged mirrored in The RFID tag arrangement of any one of the preceding claims, The RFID tag arrangement of any one of the preceding claims, The RFID tag arrangement of any one of the preceding claims, relation to each other. 28

13.wherein each of the first and second antennas are arranged on a first and The RFID tag arrangement of any one of the preceding claims, second dielectric substrate (4), wherein the dielectric separation layer (5)comprises at least one of said first and second dielectric substrates (4).14.wherein the tag arrangement is configured for operation at a frequency withinthe range of 860-960 MHz.15.wherein the dielectric separation layer (4, 5) is made of at least one of: paper, The RFID tag arrangement of any one of the preceding claims, The RFID tag arrangement of any one of the preceding claims, board, polymer film, textile and non-woven material. 16.comprising the steps: providing a first antenna (20; 20'; 20”; 20”') on a first dielectricsubstrate portion, the first antenna comprising a first intermediate feeding part(23; 23'; 23”a, 23”b; 23”'a, 23”'b) and two first radiating dipole elements (21,22; 21', 22'; 21”, 22”; 21”', 22”') connected to the first intermediate feedingpart and extending in different directions; A method for manufacturing an RFID tag arrangement (1), providing a second antenna (30; 30'; 30”; 30'”) on a second dielectricsubstrate portion, the second antenna comprising a second intermediatefeeding part (33; 33'; 33”a, 33”b; 33'”a, 33'”b) and two second radiating dipoleelements (31, 32; 31 ', 32'; 31”, 32"; 31”', 32”') connected to the secondintermediate feeding part and extending in different directions; attaching a first RFID chip (24) to the first antenna, electrically couplingit to the first intermediate feeding part (23; 23'; 23”a, 23”b; 23”'a, 23'”b); attaching a second RFID chip (34) to the second antenna, electricallycoupling it to the second intermediate feeding part (33; 33'; 33”a, 33”b; 33'”a,33”'b); connecting the first and second dielectric substrate portions togetherso that the first radiating dipole elements are arranged at a distance from thesecond radiating dipole elements, and the first and second intermediate partsare arranged to cross each other at at least one crossing point; and providing a dielectric separation layer (4, 5) between the first and 29 second intermediate parts at said Crossing point(s), thereby galvanicallyseparating the first antenna from the second antenna. 17.substrate portions are arranged on a single dielectric sheet (4), and wherein The method of claim 16, wherein the first and second dielectric the step of connecting the first and second dielectric substrate portionstogether comprises fo|ding a part of the dielectric sheet comprising the firstdielectric substrate portion over a part of the dielectric sheet comprising thesecond dielectric portion. 18.substrate portions are provided on separate dielectric sheets (4), wherein the The method of claim 16, wherein the first and second dielectric step of connecting the first and second dielectric substrate portions togethercomprises Iaminating the separate dielectric sheets together. 19.second dielectric portions are connected so that the dielectric separation layer The method of any one of the c|aims 16-18, wherein the first and comprises at least one of said first and second dielectric portions.