FI20225657A1 - RFID tag arrangement with omni-radiating antenna features - Google Patents

Abstract

The RFID identification arrangement (1) comprises a first (20; 20'; 20"; 20"') and a second (30; 30'; 30"; 30"') antenna, each comprising an intermediate input 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 to the feed part and which extend in different directions. An RFID chip (24) is electrically connected to both of the input parts in between. The radiating dipole elements of the two antennas are arranged at a distance from each other and the parts in between are arranged to cross each other at least at one crossing point. A dielectric separation layer (4, 5) is arranged between the first and second intermediate parts at the mentioned crossing point or crossing points, so that the first antenna is galvanically separated from the second antenna. In this way, a versatile RFID tag arrangement with very good all-round radiation capability is obtained. In addition, a corresponding production method is provided.

Description

RFID TAG ARRANGEMENT WITH OMNIDIRECTIONAL ANTENNA

CHARACTERISTICS

Technical field of the invention

The present invention is related to a radio frequency identification (RFID) tag arrangement with omnidirectional antenna characteristics. The further relates to a manufacturing method for producing such an RFID tag arrangement.

Background

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

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

N Most commercially available RFID tags uses dipole, loop or slot types

O antennas. Such antennas are advantageous, due to their small size, simple

K structure and relatively low production costs. = However, a problem with most commercially available RFID tag > 25 antennas is that the radiation pattern is directional, such as donut shaped and

S the like, having angular positions with very poor radiation, such as deep null 3 points. This is generally not a great problem as long as the rotational position

N between the RFID tag and the reader can be easily controlled. However, in a many types of application, the rotational position between the reader and the

RFID 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. the situation for RFID tags used on stacked pulp bales. In such applications, the

RFID reader is typically located near the floor level, and should be able to identify e.g. a vertical tag which is located on a top of a bale. Pulp bales are challenging applications for RFID tags, due to the distance and height difference between the RFID reader and the RFID tag, and also since the tag may be oriented in a non-optimal vertical position. Such a vertical orientation may mean that the antenna radiation pattern exhibits a null point towards the reader, which makes the radio transmission very poor.

Similar problems are present also in many other applications, where the distance between the reader and the tag may, by necessity, be rather long, and/or where the rotational position between the tag and the reader may be difficult to control.

It has been proposed to provide RFID tag antennas with more omni- directional characteristics. Such an antenna is e.g. disclosed in US 2009/0303002, comprising an RFID chip with four ports, each connected to one antenna arm. However, the radiation and communication performance of this RFID tag is still inadequate for many applications, and the RFID tag is further complicated and costly to produce, e.g. requiring expensive multiport

RFID chips, and complicated and costly switching and feeding structures.

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

S produced cost-effectively.

N 25

S Summary = It is therefore an object of the present invention to provide an RFID tag

E arrangement and a manufacturing method for such RFID tag arrangements, p. which alleviates at least part of the above-discussed problems, and at least

LO 30 partially address one or more of the above-mentioned needs.

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

According to a first aspect of the invention there is provided an RFID tag arrangement comprising: a first antenna comprising a first intermediate feeding part and two first radiating dipole elements connected to the first intermediate feeding part and extending in different directions; a second antenna comprising a second intermediate feeding part and two second radiating dipole elements connected to the second intermediate feeding part and extending in different directions; a first RFID chip electrically coupled to the first intermediate feeding part; a second RFID chip electrically coupled to the second intermediate feeding part; wherein the first radiating dipole elements are arranged at a distance from the second radiating dipole elements, and the first and second intermediate parts are arranged to cross each other at at least one crossing point, wherein a dielectric separation layer is arranged between the first and second intermediate parts at said crossing point(s), thereby galvanically separating the first antenna from the second antenna.

The RFID tag arrangement of the present invention provides two separately operable antennas. Since the two antennas are arranged overlaying each other, the footprint of the RFID tag arrangement, i.e. the overall dimensions, can still be very limited, and not much greater than for an ordinary RFID tag. At the same time, since first radiating dipole elements are

N arranged at a distance form the second radiating dipole elements, the

N 25 radiation pattern of the two antennas are at least to some extent, and

S preferably essentially totally complementary to each other. Hereby, the weak = angular directions of the radiation pattern of the first antenna is

E complemented by a relatively stronger second antenna at the same angular p. directions, and vice versa. Thus, the overall radiation pattern of the RFID

LO 30 arrangement, including the said two antennas, is essentially omni-directional,

O with very good performance in all directions.

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

The RFID tag arrangement can also be produced very cost-efficiently, as will be discussed in more detail in the following. In particular, each of the antennas can be produced as relatively simple and easy-to-produce dipole antennas, and the RFID chips may each be of a common and conventional two-pole type. Hereby, contrary to what would normally be assumed, the production of an RFID tag arrangement with two such integrated RFID tags is infact much faster and more cost-efficient than production of other types of previously known omni-directional RFID tags, which generally require much more sophisticated and expensive multiport RFID chips, and complicated and expensive 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 to use two standard, and relatively simple, RFID tags, which, when brought together in a certain way, act as a much more complicated and versatile RFID tag arrangement, in which the RFID tags act more or less as one and the same RFID tag, but with a much improved radiation performance, etc. Thus, it hereby becomes possible to produce an RFID tag arrangement with e.g. an omni-directional radiation pattern, in a much easier and more cost-efficient way than has heretofore been possible.

N The omni-directional performance of the RFID tag arrangement is

N 25 provided by the arrangement of the first radiating dipole elements at a

S distance from the second radiating dipole elements, and by arranging the first = and second intermediate parts to cross each other at at least one crossing

E point, and with a dielectric separation layer arranged between the first and p. second intermediate parts at the crossing point(s). This essentially provides a

LO 30 combination of two antenna radiation patterns, which in combination provides

O a generally omni-directional radiation pattern, and with very limited electromagnetic coupling between the antennas.

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

Electromagnetic coupling between the first and second antenna leads to RF power from one antenna to a large extent coupling to the other, and 5 thereby not being properly radiated. It has been found that the main sources of such detrimental electromagnetic coupling are couplings that occur between matching loops of the antennas and between radiating dipole elements 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 intermediate parts, is an efficient measure to reduce electromagnetic coupling between the antennas.

Further, the arrangement of a dielectric separation layer between the antennas, at least in the areas of the crossing points, is also an efficient measure to reduce electromagnetic coupling between the antennas.

In addition, the parts of the antennas crossing each other at the one or more crossing points are further preferably arranged to extend non-parallel to each other in the vicinity of the crossing points, and preferably to extend essentially perpendicular to each other at the crossing points. This further limit the electromagnetic coupling between the antennas. It has been found that orthogonal crossings, or at least crossing at a relatively great angle, are of great benefit, both since it provides complementary differences in the radiation patterns, thereby providing a more omni-directional combined

N radiation pattern, and since it decreases electromagnetic coupling between

N 25 the antennas, which increases antenna gain.

S Preferably, the crossing paths of the antennas at or in the vicinity of the = crossing point/points, and thus the current directions, are directed with a

E relative angle in the range of 45-135 degrees, and preferably in the range of p. 60-120, and more preferably in the range of 75-105 degrees, and most

LO 30 preferably 85-95 degrees, such as about 90 degrees.

O Hereby, by this angular orientation, the antennas may be seen as being tilted in relation to each other. This is the case even if the radiating dipole elements may per se be arranged parallel to each other, since the intermediate parts also radiate, and form part of the radiating performance of the antennas. Thus, the intermediate parts form part of the dipoles, and the

RF currents are normally highest in the middle of the antennas, i.e. close to the RFID chips. Thus, by arranging the intermediate parts to cross each other, and to occur non-parallel over the crossing, a tilting of the two antennas in relation to each other is obtained, which is very beneficial to limit the electromagnetic coupling between the antennas. The tilted antennas are also beneficial to provide the omni-directional radiation pattern, since the tilted dipole antennas also produce different kinds of radiation patterns in respect of each other. This means that when the first antenna experiences null point at some direction, the second antenna performs much better in that direction.

Thus, by the tilted arrangement, any directions with no or limited radiation in the antenna pattern for one of the antennas will be compensated by the radiation pattern of the other antenna, since the radiation patterns are different and at least to some extent complementary to each other.

Put differently, the two antennas are effectively used and seen as one tag, 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 the same time, the dimensions of the two tags when combined are essentially the same as for one tag, and consequently, the footprint of the RFID tag arrangement is essentially the same as for a single RFID tag.

The RFID tag arrangement may be seen as two independent RFID tags, arranged to cooperate to generally appear to the reader, at least in

N certain situations, as a single, omni-directional tag. To this end, the two RFID

N 25 chips may also be programmed to have the same Electronic Production

S Code, EPC. This is the identification normally determined and programmed = by the tag manufacturer, and which is normally communicated to the reader.

E If the two chips are programmed with the same EPC, this enables the reader p. to identify the RFID tag arrangement by reception of signals from any of the

LO 30 two RFID chips, or from both simultaneously.

O The RFID chips are further preferably provided with a Tag

Identification, TID, which is normally an identity programmed into the chip by the chip manufacturer during the chip manufacturing process under defined conditions. The TID for the two RFID chips may be different, thereby enabling identification of the two RFID chips independently of each other, in situations where this is required.

The two tags, formed by the two antennas and the two RFID chips, are preferably integrated together, to form an integrated RFID tag arrangement.

The tags may e.g. be integrated together by being attached to the same substrate, such as being arranged on different sides of a dielectric substrate layer. Hereby, the dielectric separation layer may be provided by the dielectric substrate. Alternatively, the tags may be attached to different substrates, and the substrates may be attached together, e.g. by an adhesive. In this case, the dielectric separation layer may be provided by anyone, or both, of the substrates, and/or by the adhesive.

The crossing between the antennas may occur over a single line of each antenna, thereby forming a single crossing point. However, the crossing may also occur over a feeding or matching loop of each antenna, whereby four crossing points are formed. The feeding or matching loops may e.g. be shaped as essentially rectangular feeding/matching loops. However, other shapes are also feasible, such as circular, oval, hexagonal, and the like. The crossing may also occur between a single line and a loop, providing two crossing 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.

In one embodiment, the crossing of the first and second intermediates

S parts occurs in the first and second feeding loops.

N 25 In another embodiment, the crossing of the first and second

S intermediate parts occurs outside the first and second feeding loops. = The first and second intermediate parts are preferably arranged to

E minimize electromagnetic coupling between them. p. In one embodiment, the loops are essentially shaped as rectangles,

LO 30 possibly with rounded corners, and the crossings occur between the relatively

O straight legs of the loops, thereby forming four crossing points. The loops preferably extend essentially orthogonally to each other, thereby forming four crossing points arranged in a diamond shape. This diamond shape is preferably provided essentially in the center of the antennas.

The antenna(s) may comprise two radiating dipole elements arranged essentially parallel to each other. In a preferred embodiment, the two radiating dipole elements of each antenna are arranged along lines separated from each other by a separation distance, and being connected by a slant intermediate element connecting the two radiating dipole elements. In a preferred embodiment, the extension direction of the intermediate element and each of the radiating dipole elements is about 135 degrees.

In embodiments where the intermediate parts comprise feeding or matching loops, the loops are preferably arranged to be partly displaced 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 of each loop, and preferably by less than 30%, and more preferably by 25% or less.

It has been found that by proper arrangement of the crossings and the isolation provided by the dielectric separation layer, a very low electromagnetic coupling can be obtained, resulting in good impedance matching 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 the antennas.

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

N The dielectric separation layer preferably extends over the entire extent

N 25 ofthefirst and second antennas, wherein the first antenna is arranged on a

S first side of the dielectric separation layer and the second antenna is arranged = on a second, opposite side of the dielectric separation layer.

E The first and second antennas are preferably identical and arranged p. mirrored in relation to each other. Thus, the antennas are essentially identical,

LO 30 butwith one flipped in orientation, either vertically or horizontally. This may

O correspond to one of the antennas being rotated by 180 degrees.

The dielectric separation layer may be realized in various ways. In one embodiment, 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 the

UHF freguency band.

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

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

The dielectric separation layer may have a thickness in the range of 20-300 um, and preferably in the range 50-200 um, and more preferably in the range 50-150 um, and most preferably in the range 70-130 um, such as 100 um. However, it is also possible to use even thicker dielectric substrates, suchasuptoimm, or up to 2 mm, or even thicker.

The RFID tag arrangement may be either passive, i.e. powered by a reader'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 is

N conductive. The antennas may be made by the same material, but may

N 25 alternatively be made of different materials. For example, the antenna may be

S formed by aluminum, but other metals, such as silver, and alloys may also be = used. Forming of the antenna on the substrate can be made in various ways,

E as is per se known in the art, such as by printing with conductive ink, such as p. silver ink, by first providing a conductive layer on the substrate and

LO 30 subsequently removing or forming this conductive layer into the desired

O shape, e.g. by means of grinding, cutting, etching or the like.

According to a second aspect of the invention there is provided a method for manufacturing an RFID tag arrangement, comprising the steps:

providing a first antenna on a first dielectric substrate portion, the first antenna comprising a first intermediate feeding part and two first radiating dipole elements connected to the first intermediate feeding part and extending in different directions; providing a second antenna on a second dielectric substrate portion, the second antenna comprising a second intermediate feeding part and two second radiating dipole elements connected to the second intermediate feeding part and extending in different directions; attaching a first RFID chip to the first antenna, electrically coupling it to the first intermediate feeding part; attaching a second RFID chip to the second antenna, electrically coupling it to the second intermediate feeding part; connecting the first and second dielectric substrate portions together so that the first radiating dipole elements are arranged at a distance from the second radiating dipole elements, and the first and second intermediate parts are arranged to cross each other at at least one crossing point; and providing a dielectric separation layer between the first and second intermediate parts at said crossing point(s), thereby galvanically separating the first antenna from the second antenna.

In accordance with this aspect, similar features and advantages as discussed in the foregoing, in relation to the first aspect, may be obtained.

In one embodiment, the first and second dielectric substrate portions are arranged on a single dielectric sheet, and wherein the step of connecting

N the first and second dielectric substrate portions together comprises folding a

N 25 part of the dielectric sheet comprising the first dielectric substrate portion over

S a part of the dielectric sheet comprising the second dielectric portion. Hereby, = the dielectric separation layer will be formed at least by the dielectric

E substrate portion, and possibly also by an adhesive connecting the portions p. together.

LO 30 In another embodiment, the first and second dielectric substrate

O portions are provided on separate dielectric sheets, wherein the step of connecting the first and second dielectric substrate portions together comprises laminating the separate dielectric sheets together. Hereby, the dielectric separation layer may be formed by one or both of the dielectric sheets, depending on whether they are arranged back-to-back or back-to- face. Additional dielectric separation may be provided by the adhesive connecting the sheets together. Alternatively, if the sheets are connected face-to-face, the dielectric separation layer may be formed only by the adhesive.

Thus, in one embodiment, the first and second dielectric portions may be connected so that the dielectric separation layer comprises at least one of said first and second dielectric portions.

It will be appreciated that the above-mentioned detailed structures and advantages of the first aspect of the present invention also apply to the further aspects of the present invention.

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

Brief description of the drawings

For exemplifying purposes, the invention will be described in closer detail in the following with reference to embodiments thereof illustrated in the attached drawings, wherein:

Fig. 1a is a top plan view of an RFID tag arrangement in accordance with a first embodiment;

Fig. 1b is a cross-sectional view of the RFID tag arrangement of Fig. 1a;

S Fig. 2 is a top plan view of an RFID tag arrangement in accordance

N 25 with a second embodiment;

S Fig. 3 is a top plan view of an RFID tag arrangement in accordance = with a third embodiment;

E Fig. 4 is a top plan view of an RFID tag arrangement in accordance p. with a fourth embodiment;

LO 30 Figs. 5 and 6 schematically illustrate two manufacturing processes for

O production of RFID tag arrangement in accordance with embodiments of the invention;

Figs. 7-9 schematically illustrate the layer construction of various embodiments of RFID tag arrangements in accordance with embodiments of the present invention;

Figs. 10a-10e are diagrams illustrating simulation results for the RFID tag arrangement of Fig. 2;

Figs. 11a-110 are diagrams illustrating measurements on the RFID tag arrangement of Fig. 3; and

Figs. 12a-12d are diagrams illustrating simulation results for the RFID tag arrangement of Fig. 4.

Detailed description of preferred embodiments

In the following detailed description preferred embodiments of the invention will be described. However, it is to be understood that features of the different embodiments are exchangeable between the embodiments and may be combined in different ways, unless anything else is specifically indicated. It may also be noted that, for the sake of clarity, the dimensions of certain components, parts and elements illustrated in the drawings may differ from the corresponding dimensions in real-life implementations of the invention, such as the thickness of various layers, the relative dimensions of the different antenna parts, etc.

Fig 1a and 1b illustrate an RFID tag arrangement 1 in accordance with an embodiment of the present invention. The RFID tag arrangement comprises a first RFID tag 2 and a second RFID tag 3, arranged on one or

N more substrates 4.

N 25 The first RFID tag 2 comprises a first antenna 20, comprising two first

S radiating dipole elements 21 and 22, interconnected by a first interconnecting = intermediate feeding part 23. The feeding part 23 comprises an IC gap (not

E shown), and an RFID chip 24 arranged over said IC gap, to transmit and p. receive RF power from the two sides of the antenna.

LO 30 The two radiating dipole elements 21, 22 are preferably arranged at

O opposite end areas of the antenna. The dipole elements are at one of their ends, the ends being closest to each other, connected to the intermediate feeding part 23. Thus, the intermediate feeding part 23 forms a bridge between the radiating dipole elements. Two power feeding areas (not shown) separated by the IC gap are provided, the first power feeding area connected to the first dipole element 21, whereas the second power feeding area is connected to the second dipole element 22. The power feeding areas are connected to connectors of an integrated circuit, the RFID chip 24, which will consequently be arranged overlying and bridging the gap.

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

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

In the illustrative example, the longitudinal axes of the dipole elements extend along two parallel lines, the two lines being separated from each other by a separation distance.

The longitudinal directions of the radiating dipole elements 21, 22 and the longitudinal direction of the intermediate feeding part 23 forms angles a1 and a2, respectively. The angles are preferably of equal size. The angles are preferably obtuse angles, and preferably in the range of 115-155 degrees, and more preferably 125-145 degrees, and most preferably about 135 degrees.

The dipole elements 21, 22 are, in this illustrated embodiment, shaped as elongate conductive lines. However, other shapes are also feasible. For example, the part may, at least over a part, extend in a meandering shape.

N The parts may also have an overall folded or curved shape. Many other

N 25 shapes are also feasible, as is per se well-known. Some examples of other

S shapes of the dipole elements will be discussed in relation to the other = embodiments.

E The antenna is a dipole antenna arranged to be used in an RFID tag, 5 and is preferably arranged to operate in the UHF band, and in particular at a

LO 30 frequency within the range of 860-960 MHz.

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

The longitudinal directions of the radiating dipole elements 31, 32 and the longitudinal direction of the intermediate feeding part 33 forms angles 31 and B2, respectively. As in the first antenna, the angles are preferably of equal size. The angles are preferably obtuse angles, and preferably in the range of 115-155 degrees, and more preferably 125-145 degrees, and most preferably about 135 degrees.

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

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 20 are arranged at a distance from the second radiating dipole elements 31 and 32 of the second antenna 30. Preferably, one of the first dipole elements and one of the second dipole elements, such as dipole elements 21 and 32, have longitudinal directions extending along the same first line, and the other two first and second dipole elements, such as dipole elements 22 and 31, have longitudinal directions extending along the same second line, the first and second lines being separated from each other.

The first and second intermediate parts 23, 33 are arranged to cross each other at at least one crossing point. In the here illustrated embodiment, the crossing occurs at a single crossing point. Further, the longitudinal

S directions of the intermediate parts form crossing angles y1 and y2 in relation

N 25 toeach other. These angles are preferably in the range of 45-135 degrees,

S 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.

E A dielectric separation layer 5 is arranged between the first and second p. intermediate parts at said crossing point, thereby galvanically separating the

LO 30 first antenna from the second antenna. In this example, the dielectric

O separation layer 5 is formed by the substrate 4. To this end, the first antenna 20 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 on the 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 to together provide an omni-directional antenna characteristic. Further, the crossing arrangement of the first and second intermediate parts, together with the dielectric separation layer, minimizes electromagnetic coupling between the antennas.

The first and second RFID chips 24, 34 are preferably programmed with identical Electronic Product Codes (EPCs), but may be provided with different Tag Identifications (TIDs).

With reference to Fig. 2, another embodiment of the RFID tag arrangement 1 also comprises two RFID tags 2 and 3, having a first antenna 20" and a second antenna 30’. In this embodiment, the antennas and the arrangement of the antennas in the RFID tag arrangement are similar to the first embodiment discussed above, with reference to Figs. 1a and 1b. Thus, apart from the differences discussed in the following, the features and advantages discussed above in relation to the first embodiment are applicable also for this second embodiment.

In this second embodiment, the first dipole elements 21’ and 22’ and the second dipole elements 31’ and 32’ are arranged in the same way as in the first discussed embodiment, with their longitudinal directions arrange along two parallel but separated lines. However, in this embodiment, the dipole elements are provided with a meandering shape, thereby increasing

S the radiating length of the dipole elements in a compact, short length.

N 25 Further, the intermediate parts 23' and 33' are here provided in the

S form of first and second feeding loops, for impedance matching. The feeding = loops in this embodiment are arranged essentially in the form of rectangular

E loops. However, other loop forms are also feasible, as will be discussed in p. more detail in the following.

LO 30 In this embodiment, the crossing between the intermediate parts 23’

O and 33' is a crossing of the two feeding loops, providing four crossing points.

However, the intermediate parts crossing each other are still crossing each other essentially orthogonally. Thus, the crossing paths of the antennas at or in the vicinity of all the crossing points, and thus the current directions, are preferably directed with a relative angle 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.

With reference to Fig. 3, another embodiment of the RFID tag arrangement 1 also comprises two RFID tags 2 and 3, having a first antenna 20” and a second antenna 30”. In this embodiment, the antennas and the arrangement of the antennas in the RFID tag arrangement are similar to the first and second embodiments discussed above, with reference to Figs. 1a, 1b and 2. Thus, apart from the differences discussed in the following, the features and advantages discussed above in relation to the first and second embodiments are applicable also for this second embodiment.

In this third embodiment, the first dipole elements 21” and 22” and the second dipole elements 31” and 32” are arranged in the same way as in the first discussed embodiment, with their longitudinal directions arrange along two parallel but separated lines. However, in this embodiment, the dipole elements are provided partly with a meandering shape, similar to the second embodiment, and partly with a straight configuration, as in the first embodiment. In this embodiment, the straight part is arranged closest to the free end, and the meandering part arranged closest to the connection to the intermediate part.

Further, the intermediate parts here comprises both first and second feeding loops 23*b and 33”b, for impedance matching, and straight parts

N 23'a, and 33”a. The feeding loops in this embodiment are arranged

N 25 essentially in the form of rectangular loops. However, other loop forms are

S also feasible, as will be discussed in more detail in the following. The feeding = loops in this example are provided displaced towards one of the dipole

E elements. Thus, some of the dipole elements in this embodiment are p. shortened, to make room for the feeding loops — in this example, the dipole

LO 30 elements 31” and 22” — whereby the two dipole elements of each antenna are

O different. However, in the shortened dipole elements, the meandering parts are made more compact, and the overall length of the antennas remain the same.

In this embodiment, the crossing between the intermediate parts is provided as a crossing of the two straight parts 23”a and 33”a, providing one crossing point. The intermediate parts are crossing each other essentially orthogonally, similar to the first discussed embodiment.

With reference to Fig. 4, another embodiment of the RFID tag arrangement 1 also comprises two RFID tags 2 and 3, having a first antenna 20” and a second antenna 30”. In this embodiment, the antennas and the arrangement of the antennas in the RFID tag arrangement are similar to the first, 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 and second embodiments are applicable also for this second embodiment.

In this fourth embodiment, the first dipole elements 21” and 22” and the second dipole elements 31” and 32” are arranged in the same way as in the first discussed embodiment, with their longitudinal directions arrange along two parallel but separated lines, and essentially occurring through straight line.

Further, similar to the third embodiment, the intermediate parts here comprises both first and second feeding loops 23”b and 33”*b, for impedance matching, and straight parts 23”a, and 33” a. In this embodiment, the crossing of the intermediate parts occurs both in the straight parts 23” a and 33”a and the feeding loop parts 23”b and 33”b. Hereby, three crossing points are provided.

S The feed loops 23”b and 33”b are preferably arranged to be partly

N 25 displaced from each other, thereby to be only partly overlapping. Preferably,

S the area encircled 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

E less. In this embodiment, the crossing between the intermediate parts in the p. feed loops 23” and 33” is a crossing such that the crossing paths in the

LO 30 vicinity of all the crossing points, and thus the current directions, are

O preferably directed with a relative angle 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.

Further, the crossing between the straight parts 23”a and 33”'a of the intermediate parts are preferably arranged to cross each other essentially orthogonally. The 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.

In the above-discussed embodiment, dielectric separation layer extends over the entire extent of the first and second antennas, wherein the first antenna is arranged on a first side of the dielectric separation layer and the second antenna is arranged on a second, opposite side of the dielectric separation layer. However, other arrangements of the dielectric separation layer are also feasible. For example, the dielectric separation layer may be provided locally, only at, or at an area surrounding the connection points, or at an area covering the connection points, preferably with a margin, but not covering the entire antennas.

The dielectric separation layer can essentially be of any non- conductive material, such as paper, board, polymer film, textile non-woven material and non-conductive adhesive. In particular, the layer can be made of paper.

The antenna may be made of any material, as long as the material is conductive. The antennas may be made of the same material, but different materials may also be used. For example, the antenna may be formed by aluminum, but other metals, such as silver, and alloys may also be used. For example, it is feasible to use an alloy having a relatively low melting

S temperature, such as an alloy comprising tin and bismuth. Forming of the

N 25 antenna on the substrate can be made in various ways, as is per se known in

S the art, such as by printing with conductive ink, such as silver ink, by first = providing a conductive layer on the substrate and subsequently removing or

E forming this conductive layer into the desired antenna shape, e.g. by means p. of grinding, cutting, etching or the like.

LO 30 The RFID chip may take any of a number of forms (including those of

O the type commonly referred to as a "chip" or a "strap" by one of ordinary skill in the art), including any of a number of possible components and being configured to perform any of a number of possible functions. Preferably, the

RFID chip includes an integrated circuit for controlling RF communication and other functions of the RFID tag.

The RFID tag arrangement may be manufactured in various ways. For example, the two antennas or RFID tags may be provided on separate substrates, as is per se known, and be laminated together to form the RFID tag 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 dielectric substrate portion, the first antenna comprising a first intermediate feeding part and two first radiating dipole elements connected to the first intermediate feeding part and extending in different directions; providing a second antenna on a second dielectric substrate portion, the second antenna comprising a second intermediate feeding part and two second radiating dipole elements connected to the second intermediate feeding part and extending in different directions; attaching a first RFID chip to the first antenna, electrically coupling it to the first intermediate feeding part; attaching a second RFID chip to the second antenna, electrically coupling it to the second intermediate feeding part; connecting the first and second dielectric substrate portions together so that the first radiating dipole elements are arranged at a distance from the second radiating dipole elements, and the first and second intermediate parts

N are arranged to cross each other at at least one crossing point; and

N 25 providing a dielectric separation layer between the first and second

S intermediate parts at said crossing point(s), thereby galvanically separating = the first antenna from the second antenna.

E The the first and second dielectric substrate portions may be arranged p. on a single dielectric sheet, and wherein the step of connecting the first and

LO 30 second dielectric substrate portions together comprises folding a part of the

O dielectric sheet comprising the first dielectric substrate portion over a part of the dielectric sheet comprising the second dielectric portion. Such an embodiment is illustrated in Fig. 5. Hereby, the RFID tags may be identically provided on the substrate portions, and then be folded over each other to form the RFID tag arrangement.

In another manufacturing method, the first and second dielectric substrate portions are provided on separate dielectric sheets, wherein the step of connecting the first and second dielectric substrate portions together comprises laminating the separate dielectric sheets together. Such an embodiment is illustrated in Fig. 6. Here, the RFID tags may be identically provided on the substrate portions, and one of the sheet being 180 degrees twisted during manufacturing, or one of the RFID tags may be provided in a mirrored state, as illustrated in Fig. 6, thereby requiring no twisting of the sheets.

The dielectric separation layer 5 may be provided in various ways, as will be explained further in the following.

In one embodiment, as illustrated in Fig. 7, the antennas and RFID tags 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 side of the substrate portions together by an adhesive 6. Hereby, the antennas are separated by both the substrate layers 4, and also by the adhesive layer 6. In such embodiments, the galvanic separation provided by the substrate layers 4 may suffice, and the adhesive layer 6 may be either conductive or non- conductive. Such an embodiment is easily achievable by laminating separate sheets together.

In another embodiment, as illustrated in Fig. 8, the antennas and

N RFID tags are provided in layers 20, 30 on afirst side of the substrate

N 25 portions 4, and the substrate portions are connected together by attaching the

S these sides, carrying the antenna layers, together by an adhesive 6. Hereby, = the antennas are separated only by the adhesive layer. However, by using a

E non-conductive adhesive, the galvanic separation between the antennas may 5 still be sufficient. Such an embodiment is easily achievable by laminating

LO 30 separate sheets together.

O In yet another embodiment, as illustrated in Fig. 9, the antennas and

RFID tags are provided in layers 20, 30 on afirst side of the substrate portions 4, and the substrate portions are connected together by attaching 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. In such embodiments, the galvanic separation provided by the substrate layer 4 may suffice, and the adhesive layer 6 may be either conductive or non-conductive. However, preferably the adhesive layer is non-conductive, thereby increasing the galvanic separation between the antennas. Such an embodiment is easily achievable by folding a single sheet to form the RFID tag arrangement.

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

First, an antenna corresponding to the one discussed above in relation to Fig. 2 was evaluated. Fig. 10a is a diagram illustrating simulation results of the S-parameters in dB over a range of frequencies, from 0.7 GHz to 1.5

GHz. From these results, it may be deduced that there is good impedance matching and a very good isolation between the antennas. The electrical coupling at the UHF band is only about -10 dB, which means that only 1/10 of the RF power is coupled between the antennas. Fig. 10b is a diagram illustrating simulation results for free air read range, in meter, for the two antennas, over the same frequency range of 0.7-1.5 GHz. As can be seen from the diagram, the read range at the UHF band is about 13 meters, which is very good, and more than sufficient for most applications. Figs. 10c and 10d illustrate simulated 3D radiation patterns for the first and second antenna.

The radiation patterns show that each antenna has distinct radiation patterns,

N and that wherever the first antenna has weak radiation, a null direction, the

N 25 secondantenna performs well in this direction, and vice versa. Thus, in

S combination, the two antennas have omni-directional characteristics. Finally, = Fig. 10e illustrates a polar plot of the radiation patterns of the two antennas,

E with the gain in dBi for different Phi directions in the range 0-360 degrees, p. where the omni-directional characteristics of the combined antennas is also

LO 30 clearly deducible. For example, the realized gain of the second antenna

O (“ant2”) in the direction Theta=90 and Phi=240 is >20 dB higher than the realized gain of the first antenna (“ant1”) in the same direction.

Secondly, an antenna corresponding to the one discussed above in relation to Fig. 3, and with a NXP UCODES used as the RFID chip, was evaluated. Fig. 11a is a diagram illustrating measured results for the power in dBm and the read range in meter for the antennas when measured separately, over a frequency range of 800-1000 MHz. As can be seen, the tuning and performance of the antennas are essentially identical. Fig. 11b a diagram illustrating measured results for the power in dBm and the read range in meter for the antennas when measured in combination, over a frequency range of 800-1000 MHz. The measured antennas have been combined in accordance with Fig. 7 (“SE132_3ab opt1”), Fig. 8 ('SE132 3ab opt2”), and Fig. 9 ('SE132 3ac”), respectively. As can be seen, the tuning and performance of the different antenna combinations are essentially identical. 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 the tuning and performance.

Further, measurements were made by measuring with four different antennas in different angular positions, as illustrated in Fig. 11c, where the antennas (“ant1”-“ant4”) are separated by 30 degrees. This set-up was used to measure at 0-90 degrees, 120-210 degrees and 240-330 degrees. For comparison, the same measurements were also made on a commercially available RFID tag, the "ECO Bumper”, produced by Stora Enso, which is adapted for UHF frequency range, and which uses an NXP UCODES as the

RFID chip. Measurements were made on two different RFID tag

N arrangements of the inventive example and two different comparative RFID

N 25 tags. The measured results are the power in dBm and the read range in

S meter for the antennas when measured separately, over a freguency range of = 800-1000 MHz.

E Figs. 11d-110 shows the measurement results of these measurements, p. where Fig. 11d shows the measurements made at O degrees, Fig. 11e at 30

LO 30 degrees, Fig. 11f at 60 degrees, Fig. 11g at 90 degrees, Fig. 11h at 120

O degrees, Fig. 11i at 150 degrees, Fig. 11j at 180 degrees, Fig. 11k at 210 degrees, Fig. 111 at 240 degrees, Fig. 11m at 270 degrees, Fig. 11n at 300 degrees, and Fig. 110 at 330 degrees.

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), 240 degrees (Fig. 11d), 300 degrees (Fig. 11n) and 330 degrees (Fig. 110).

However, at many angular positions, the inventive example performs much better than the comparative examples, such as at O 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 Inv. Ex. Com. Ex. Inv. Ex. Comp. Ex. = i EE (m) (m) o Jar lo Jo Js 60 ooo fa = ja ls 9 Jas se f2 120 [48 qe 0

N a 2 s0 18 fs 00 [10 ls ” = 5 Thus, the measured power in dBm for the different measurements, and a 15 in the frequency range of most interest, i.e. in the range 860-960 MHz, varies

N in the following ranges: - For the inventive examples between -15 and -18

- For the comparative examples between -2.5 and -22

The measured read range in m for the different measurements, and in the frequency range of most interest, in the range 860-960 MHz, varies in the following 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 ECO

Bumper, 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 in relation to Fig. 4 was evaluated. Fig. 12a is a diagram illustrating simulation results of the S-parameters in dB over a range of frequencies, from 0.7 GHz to 1.5 GHz. From these results, it may be deduced that there is good impedance matching and a very good isolation between the antennas. Fig. 12b is a diagram illustrating simulation results for free air read range, in meter, for the two antennas, over the same frequency range of 0.7-1.5 GHz.

As can be seen from the diagram, the read range at the UHF band is about 18 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 the two antennas, with the gain in dBi for different Phi directions in the range O- 360 degrees, where the omni-directional characteristics of the combined

N antennas is also clearly deducible.

N 25 The person skilled in the art realizes that the present invention is not

S limited to the above-described embodiments. For example, the general = antenna design may be varied in many ways, as is per se well-known in the

E art. For example, the dipole elements may be shaped differently than in the p. above-discussed embodiments, and the feeding loop, etc, may also have

LO 30 other shapes. The antenna may further be adapted for different operational

O freguencies.

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

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Claims (19)

1. An RFID tag arrangement (1) comprising: a first antenna (20; 20’; 20”; 20”) comprising a first intermediate feeding part (23; 23’; 23a, 23”b; 23”a, 23”b) and two first radiating dipole elements (21, 22; 21°, 22; 217, 22”; 21”, 22”) connected to the first intermediate feeding part (23; 23’; 23a, 23”b; 23”a, 23”b) and extending in different directions; a second antenna (30; 30’; 30”; 30”) comprising a second intermediate feeding part (33; 33’; 33”a, 33”b; 33”a, 33”b) and two second radiating dipole elements (31, 32; 31°, 32’; 31”, 32”; 31”, 32”) connected to the second intermediate feeding part (33; 33’; 33”a, 33”b; 33”a, 33”b) and extending in different directions; a first RFID chip (24) electrically coupled to the first intermediate feeding part (23; 23’; 23”a, 23’b; 23”a, 23”b); a second RFID chip (34) electrically coupled to the second intermediate 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 dipole elements (31, 32; 31', 32’; 31”, 32”; 31”, 32”), and the first and second intermediate parts are arranged to cross each other at at least one crossing point, wherein a dielectric separation layer (4, 5) is arranged between the first and second intermediate parts at said crossing point(s), thereby galvanically N separating the first antenna (20; 20’; 20”; 20”) from the second antenna (30; N 25 30' 30”; 30”).

S 2. The RFID tag arrangement of claim 1, wherein the first and = second antennas are arranged to together provide an omni-directional E antenna characteristic.

p. 3. The RFID tag arrangement of claim 1 or 2, wherein the first and LO 30 second intermediate parts are arranged to minimize electromagnetic coupling O between them.

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

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

8. The RFID tag arrangement of any one of the claims 5-7, wherein the first RFID chip (24) is arranged over an IC gap arranged in the first feeding loop, and the second RFID chip (34) is arranged over an IC gap arranged 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 the first and second antennas, wherein the first antenna (20; 20’; 20”; 20”) is arranged on a first side of the dielectric separation layer and the second antenna (30; 30’; 30”; 30”) is arranged on a second, opposite side of the dielectric separation layer (4, 5). S

10. The RFID tag arrangement of any one of the preceding claims, N 25 wherein the first and second RFID chips (24, 34) are programmed with S identical Electronic Product Codes (EPCs). =

11. The RFID tag arrangement of any one of the preceding claims, E wherein the first and second RFID chips (24, 34) are provided with different p. Tag Identifications (TIDs). LO 30

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

13. The RFID tag arrangement of any one of the preceding claims, wherein each of the first and second antennas are arranged on a first and second dielectric substrate (4), wherein the dielectric separation layer (5) comprises at least one of said first and second dielectric substrates (4).

14. The RFID tag arrangement of any one of the preceding claims, wherein the tag arrangement is configured for operation at a frequency within the range of 860-960 MHz.

15. The RFID tag arrangement of any one of the preceding claims, wherein the dielectric separation layer (4, 5) is made of at least one of: paper, board, polymer film, textile and non-woven material.

16. A method for manufacturing an RFID tag arrangement (1), comprising the steps: providing a first antenna (20; 20’; 20”; 20”) on a first dielectric substrate portion, the first antenna comprising a first intermediate feeding part (23; 23; 237a, 23”b; 23”a, 23”b) and two first radiating dipole elements (21, 22; 21', 22°; 217, 22”; 21”, 22”) connected to the first intermediate feeding part and extending in different directions; providing a second antenna (30; 30'; 30”; 30”) on a second dielectric substrate portion, the second antenna comprising a second intermediate feeding part (33; 33'; 33”a, 33”b; 33”a, 33”b) and two second radiating dipole elements (31, 32; 31°, 32’; 317, 32”; 31”, 32”) connected to the second intermediate feeding part and extending in different directions; attaching a first RFID chip (24) to the first antenna, electrically coupling N it to the first intermediate feeding part (23; 23’; 23”a, 23”b; 23”a, 23”b); N 25 attaching a second RFID chip (34) to the second antenna, electrically S coupling it to the second intermediate feeding part (33; 33'; 33”a, 33”b; 33”'a, - 33”b); E connecting the first and second dielectric substrate portions together p. so that the first radiating dipole elements are arranged at a distance from the LO 30 secondradiating dipole elements, and the first and second intermediate parts O are arranged to cross each other at at least one crossing point; and providing a dielectric separation layer (4, 5) between the first and second intermediate parts at said crossing point(s), thereby galvanically separating the first antenna from the second antenna.

17. The method of claim 16, wherein the first and second dielectric substrate portions are arranged on a single dielectric sheet (4), and wherein the step of connecting the first and second dielectric substrate portions together comprises folding a part of the dielectric sheet comprising the first dielectric substrate portion over a part of the dielectric sheet comprising the second dielectric portion.

18. The method of claim 16, wherein the first and second dielectric substrate portions are provided on separate dielectric sheets (4), wherein the step of connecting the first and second dielectric substrate portions together comprises laminating the separate dielectric sheets together.

19. The method of any one of the claims 16-18, wherein the first and second dielectric portions are connected so that the dielectric separation layer comprises at least one of said first and second dielectric portions. N QA O N K <Q N I a a NN LO O LO N N O N