CN101052775A

CN101052775A - RFID near field microstrip antenna

Info

Publication number: CN101052775A
Application number: CN200580037610.8A
Authority: CN
Inventors: 加里·马克·沙弗尔; 卡伦·贝鲁姆; 小乔治·A.·雷诺尔德斯; 克里斯托弗·马库斯; 约翰·福特; 连明仁; 爱德华·迪卡尔罗; 理查德·L·库普兰德
Original assignee: Sensormatic Electronics Corp
Current assignee: Adt Services LLC; Tyco Fire and Security GmbH; Sensormatic Electronics LLC
Priority date: 2004-11-02
Filing date: 2005-11-02
Publication date: 2007-10-10
Anticipated expiration: 2025-11-02
Also published as: CN101076644B; CN101084357A; CN101084602A; CN101076644A; CN101052775B; CN101103165A; CN101084602B; CN101103165B

Abstract

A near field antenna is disclosed which is configured to read an RFID label such that a localized electric E field emitted by the antenna at an operating wavelength resides substantially within a zone defined by the near field. The localized E field directs a current distribution along an effective length of the antenna corresponding to a half-wave to a full-wave structure.

Description

The RFID near field microstrip antenna

Background technology

[0002] be used to read that the existing scheme of RFID label adopts is traditional antenna, it can provide reading very on a large scale of RFID label.This scheme provides most antenna energy to arrive the far field.The definition in far-field region be apart from d＞＞λ/2 π, wherein λ is a wavelength.Under the UHF of 915MHz frequency, this numerical value is about 5cm.Therefore, the far-field region of 915MHz is basically outside 5cm, and similarly, the near field region is below 5cm basically.For example, most RFID reads antenna and is designed to read label on several meters distances of maximum, and certainly, this distance is in the far-field region.

[0003] in some applications, that is, a RFID label only be read and be write to RFID label applicator (Iabel applicator) and programmer need in one group of label of mutual close position.For example, on label applicator, a plurality of labels are wrapped on the reel, and it is convenient to handle on this machine.On reel, label be closely parallel arranged or end to end arranged cells.Yet, in traditional UHF antenna, be difficult on guiding energy to a label only once, this is because traditional UHF antenna has broad radiating pattern usually and can arrive the far field by guiding energy.Broad radiating pattern all the RFID labels in antenna range that can throw light on.If we attempt to write on a product code or series number to a label, then all illuminated labels are to utilize identical code or series number to be programmed.

[0004] traditional far field antenna of using in this RFID UHF uses is a paster antenna.Usually, the Chip Area of radiation is the connector feed by the excitation of RFID circuit.Be typically, conductive plate be installed in the back side and with the Chip Area very short distance of being separated by.

[0005] in these above-mentioned application, need read or write information to the very approaching RFID label of distance, for example, need once a label to be programmed, test and the label applicator of pasting, and traditional far field antenna can not be finished this task.Traditional radiating antenna requires to separate one section enough distance between tagged article, is read simultaneously or programmes in order that prevent a plurality of article, perhaps requires to use the metal window, is used to block the every other label that is programmed or reads beyond the label.

[0006] yet, this technology can not solve the above problems suitably, because if be separated by far between each label, can reduce the production capacity of label applicator, and limit the number of tags of given reel size.If use the technology of blocking, then need different shadow shields with the interval for every kind of different label shape.So, on the applicator line, to handle different labeling requirements and do various variations, this also reduces production capacity widely.

Summary of the invention

[0007] the present invention relates to a kind of near field antenna that is configured to read the RFID label.This antenna is configured to make it under operation wavelength local electric field E by this antenna emission and resides in basically in the zone that the near field limits.Local electric field E is along distributing corresponding to half-wave guide current to the effective antenna length of all-wave structure.In one embodiment, this antenna is configured to like this, and making it the near field region is to be limited by the distance that equals λ/2 π from antenna, and wherein λ is the operation wavelength of antenna.In another embodiment, near field antenna is operated under the frequency of about 915MHz, and therefore, the near field region distance is about 5cm.

[0008] the invention still further relates to a kind of method of the RFID of reading label, comprise step: provide a near field antenna device, this antenna assembly is configured to make it under operation wavelength to be resided in basically in the zone that is limited by the near field by the local electric field E of this antenna assembly emission, and wherein local electric field E is along corresponding to half-wave guide current distribution to the effective antenna length of all-wave structure.This method also comprises step: the local electric field E of coupling near field antenna device is to the RFID label that is arranged in the near field region.

[0009] in one embodiment, this method also comprises step: the configuration antenna assembly, and therefore, the near field region is to be limited by the distance that equals λ/2 π from antenna assembly, wherein λ is the operation wavelength of antenna assembly.In addition, this method can also comprise step: antenna assembly is operated under the frequency of about 915MHz, and therefore, the near field region distance is about 5cm.

[0010] the invention still further relates to a kind of near field antenna device that is used to read the RFID label, comprising: be configured to single and antenna continuous conductor.This antenna is to extend to the other end that forms termination point from an end that forms distributing point.Termination point is to be connected to ground plane by a resistor.Antenna assembly has relative dielectric constant, and the local electric field E that is configured to launch under operation wavelength resides in the zone of near field qualification basically.Local electric field E is along distributing corresponding to half-wave guide current on the effective antenna length of all-wave structure.

[0011] in one embodiment, the effective length of antenna assembly is such, the CURRENT DISTRIBUTION that is conducted through antenna produces the waveform that a wavelength is proportional to nv/f, wherein v is the velocity of wave of propagating, it equals the square root of the light velocity divided by the relative dielectric constant of antenna assembly, f be with Hz be the scope of the frequency of unit and n be from half-wavelength about 0.5 to all-wave long 1.0.In another embodiment, this antenna is a microstrip antenna, and the near field antenna device includes the substrate of first surface and second surface, its thickness is to be limited by the distance between them, wherein little band tracking antenna is arranged on the first surface of substrate, and ground plane is arranged on the second surface of substrate.

[0012] in another embodiment, the local electric field E that antenna assembly is configured to propagate is coupled on the RFID label, and this label machine-direction oriented is along on the effective length of antenna assembly.

Description of drawings

[0013] specifically notes theme of the present invention as embodiment, and provide clearly at the conclusion part of manual.Yet, when reading the following detailed description in conjunction with the accompanying drawings, can understand these embodiment better, they relate to tissue of the present invention and method of work, and purpose of the present invention, feature and advantage, wherein:

[0014] Fig. 1 represents according to the phantom drawing of the paster radiating antenna device of prior art the RFID label is arranged on a segment distance;

[0015] Fig. 2 represents the phantom drawing according to the linear monopole microstrip antenna assembly of one embodiment of the invention, and very big RFID label is arranged on it;

[0016] Fig. 3 is the plan view of linear antenna device shown in Figure 2;

[0007] Fig. 4 is the sectional drawing along Fig. 3 cathetus 4-4;

[0018] Fig. 5 is the curve map of electric current along linear little band tracking antenna of antenna assembly in Fig. 3 and 4;

[0019] Fig. 6 is the curve map of the half-wave electric field E on linear antenna device shown in Figure 4;

The curve map that all-wave electric field E distributed when [0020] Fig. 7 was 0 ° of phase place on linear antenna device shown in Figure 4;

The curve map that all-wave electric field E distributed when [0021] Fig. 8 was 90 ° of phase places on linear antenna device shown in Figure 4;

[0022] Fig. 9 is the plan view of linear antenna device shown in Figure 4, and wherein the orientation of RFID label is to be to be separated by a gap between the length of property antenna assembly along the line and each RFID label;

[0023] Figure 10 is the plan view that the linear monopole microstrip antenna assembly that extends ground plane is arranged according to one embodiment of the invention;

[0024] Figure 11 is the sectional drawing along Figure 10 cathetus 11-11;

[0025] Figure 12 is the end-view of antenna assembly among Figure 10, the distribution of its explanation electric field;

[0026] Figure 13 is the lateral view of antenna assembly among Figure 10, the distribution of its explanation electric field;

[0027] Figure 14 is the plan view that the linear monopole microstrip antenna assembly of external conductive casing is arranged according to one embodiment of the invention;

[0028] Figure 15 is the sectional drawing along Figure 14 cathetus 15-15;

[0029] Figure 16 is the phantom drawing according to the tortuous wire monopole microstrip antenna assembly of one embodiment of the invention;

[0030] Figure 17 is the plan view of tortuous wire antenna assembly among Figure 16;

[0031] Figure 18 is the sectional drawing along Figure 17 cathetus 18-18;

[0032] Figure 19 is the plan view of tortuous wire antenna assembly among Figure 17, and wherein the orientation of RFID label is to be to be separated by a gap between the length of tortuous wire antenna assembly and each RFID label;

[0033] Figure 20 is the plan view that the tortuous wire monopole microstrip antenna assembly that extends ground plane is arranged according to one embodiment of the invention;

[0034] Figure 21 is the sectional drawing along Figure 20 cathetus 21-21; Figure 22 is the plan view that the tortuous wire monopole microstrip antenna assembly of external conductive casing is arranged according to one embodiment of the invention; With

[0035] Figure 23 is the sectional drawing along Figure 22 cathetus 23-23.

The specific embodiment

[0036] detailed description that provides below the basis and the accompanying drawing of the specific embodiment of the invention can understand content of the present invention more fully, yet we should not be limited to specific embodiment to the present invention, and only with the explanation of doing content of the present invention.

[0037] can provide many concrete details herein, in order that understand the various possible embodiment of the present invention fully.Yet, those skilled in the art will understand that do not having also can to put into practice these embodiment under the condition of these details.Under other situation, do not describe the method for knowing in detail, process, parts and circuit become clear in order to make these embodiment.Should be appreciated that concrete structure disclosed herein and function detail are representational, rather than limit the scope of these embodiment.

[0038] some embodiment utilize term " coupling " and " connection " and their derivatives to describe.For example, some embodiment may utilize term " connection " to describe, and it is pointed out between two or more elements is direct physics contact or electrically contacts.In another example, some embodiment may utilize term " coupling " to describe, and it is pointed out between two or more elements is direct physics contact or electrically contacts.Yet term " coupling " also can mean not directly contact between two or more elements, but still can be to cooperate with each other or interact.Embodiment disclosed herein need not be confined to such linguistic context.

[0039] it should be noted that reference " embodiment " means in manual, in conjunction with the concrete feature that this embodiment describes, structure, or characteristic comprises in one embodiment at least.Occurring words " in one embodiment " needn't all be meant identical embodiment everywhere in manual.

[0040] describe details of the present invention now, Fig. 1 represents to comprise the paster radiating antenna device 10 of paster antenna 12, and this antenna has RFID label 20 on a segment distance of being separated by.Along the paster antenna electric field component excitation RFID label 20 of the dipole of RFID label 20 orientation, and allow equal Z1 apart from d on read information on the RFID label 20, Z1 is the distance with antenna assembly 10, wherein Z1 is far longer than λ/2 π and λ is a wavelength.

[0041] common, paster antenna 12 is radiating antennas, and it is designed to antenna impedance is true impedance basically, and mainly is that spoke constitutes by penetrating impedance.The numerical value of true impedance and the genertor impedance of feed system mate substantially, normally 50 ohm of the impedances of feed system.Antenna impedance mainly is a true impedance, and mainly is radiation resistance.The present invention relates to a kind of near field antenna device, this device reduces the radiation in far field consciously and strengthens local electric field E in the near field region.More particularly, this near field antenna device can limit energy in the zone near antenna, that is, and and the near field region, and prevent radiation in the far-field region.Therefore, can inquire about the RFID label actual approaching, rather than inquiry is positioned at the RFID label outside the near field region with near field antenna.Under the operating frequency of 915MHz, the distance of near field region and antenna is about 5cm.Label outside 5cm can not be read out or write.

[0042] though be referred to as antenna in the industry usually, as employed herein, antenna assembly is the combination of various parts, and wherein at least one parts comprises antenna, and this antenna is directly launched or received electromagnetic energy or signal.

[0043] in one embodiment of the invention, Fig. 2 represents to comprise the near field antenna device 110 of a linear tracer element microstrip antenna 112, and very big RFID label 120 is arranged on its close position.Shown in Fig. 3 and 4, near field antenna device 110 comprises the microstrip antenna 112 of thickness for " t ", and circuit is coupled to cable 114 on distributing point 116, cable 114 is coaxial cable normally, but be not limited to coaxial cable, with the terminating resistor " R1 " that is connected on end opposite or termination ends 118, it is normally 50 ohm.Cable 114 has first end or signal end 114a and second end or with reference to earth terminal 114b.Signal be from the distributing point terminal 116 of cable 114 by feed system 124 by feed-in.This signal is 50 ohm signal normally.

[0044] in one embodiment, electric capacity coupling paster 122 (Fig. 3) can be in 50 ohm of terminal 118 coupling of circuits that are used for impedance matching to linear antenna 112, normally for reflection loss is minimized.

[0045] shown in Fig. 3 and 4, linear microstrip devices 110 includes the basic rectangular microstrip tracking antenna 112 of substrate 140, and wherein substrate 140 has first surface 140a and opposing second surface 140b.Distance between first surface 142 and the second surface 144 is determined the thickness " H " of substrate 140.

[0046] microstrip devices 110 also comprises ground plane 150, and has such configuration, microstrip line 112 to be arranged on the first surface 140a of substrate 140, and ground plane 150 is arranged on the second surface 140b of substrate 140.In one embodiment, ground plane 150 is to separate with second surface 140b by dielectric barrier 164, and dielectric barrier 164 can be the air gap (suitable structure support does not draw).The first terminal 114a coupling of circuits of cable 114 is to microstrip antenna 112, and the second terminal 114b coupling of circuits is to ground plane 150.

[0047] in one embodiment, linear microstrip line 112 is rectangle basically, and width " W " is arranged.The length of antenna assembly 110 " L " is to extend to and comprise terminating resistor " R1 " from distributing point 116.For example, the conductor that linear microstrip line 112 is normally thin, but be not limited to copper.Under the frequency in the UHF scope, thickness " t " normally about 10 microns to about 30 microns scope.

[0048] substrate 140 is dielectric materials, and it can comprise pottery or FR-4 dielectric material usually, and its thickness is that " H " and total width are " W _s", ground plane 150 is set below substrate.Little with 112 termination point 118 in linearity, the termination point 118 of the linear microstrip line 112 of terminating resistor R1 coupling of circuits is to ground plane 150.

[0049] linear microband antenna 112 is designed to be substantially equal to the characteristic impedance of the cable 114 that electric feed signal is provided in the input impedance " Z " of distributing point 116, in order to make from the maximizes power of reader coupling.(reader is the part of feed system 124, and it is the electronic system of separating with cable 114 or transmission network.Antenna assembly 110 is coupled to reader system by cable 114.) ratio W/H is normally more than or equal to 1, concrete scope roughly is from 1 to 5.

[0050] in this case, be to provide with ohm input impedance " Z " of the linear microband antenna device of representing 110 by following formula:

Z = \frac{120 π}{\sqrt{ϵ_{re}}} {[\frac{W}{H} + 1.393 + 0.667 \ln (\frac{W}{H} + 1.444)]}^{- 1} - - - (1)

ϵ_{re} = (\frac{ϵ_{r} + 1}{2}) + (\frac{ϵ_{r} - 1}{2}) {(1 + \frac{12 H}{W})}^{- \frac{1}{2}} - - - (2)

" ε _r" be the relative dielectric constant of substrate 140.Therefore, the height H of the width W of little band and substrate is mainly determined impedance " Z ".

[0051] in one embodiment, the relative dielectric constant " ε of substrate _r" scope roughly be from 2 to 12.In another embodiment, the length of linear microstrip antenna device 110 " L " is corresponding to the effective length of half-wave to all-wave, and its suitable physical length is by formula approx

L = n \frac{c}{f \sqrt{ϵ_{re}}}

Determine that wherein " c " is that the light velocity (is about 3 * 10 ⁸M/s), " f " is to be the operating frequency and the " ε of unit with Hz _r" be the scope of the relative dielectric constant of substrate and " n " roughly be from suitable half-wave dipole antenna 0.5 to 1.0 of suitable full-wave doublet antenna.

[0052] in one embodiment, can adjust terminating resistor " R1 ", make it be substantially equal to the characteristic impedance of 50 ohm or feed cable 114 in the input impedance of distributing point 116.

[0053] in another embodiment, linear microband antenna 112 has the first longitudinal edge 112a and the second longitudinal edge 112B, and microstrip antenna 112 is the center at substrate 140 and ground plane 150 basically, therefore, the longitudinal edge 152a of the longitudinal edge 142a of

substrate

140 and 142b and ground plane 150 and distance that 152b extends separately are 2 times (" 2W ") of the width " W " of the first longitudinal edge 112a and the second longitudinal edge 112b at least.So, substrate 140 and ground plane 150 overall width " W separately _s" be 5 times (" 5W ") of width " W " at least.Substrate 140 also comprises the transverse edge 142c that distributing point 116 is set and the transverse edge 142d of terminating resistor R1 is set.Similarly, ground plane 150 also comprises transverse edge 152c that distributing point 116 is set and the transverse edge 152d that terminating resistor " R1 " is set.

[0054] near field antenna device 110 reduces the far field consciously and strengthens the near field region.More particularly, near field RFID antenna assembly 110 comprises element antenna 112, it is configured to like this, the local electric field E of antenna 112 emissions resides in the zone that is limited by the near field basically, and antenna 112 radiation emitted fields reside in the zone that is limited by the far field with respect to antenna 112 basically.Therefore, near field antenna device 110 is useful on many advantages of adjustment.It is this that not have the true impedance of the near field antenna device 110 of 50 ohm of terminating impedances be low-down.Therefore, radiation resistance also is very low.Add typical 50 ohm of terminating impedance R1, it makes input impedance equal 50 ohm approx, is used to mate the feed system 124 that power is provided by cable 114.This configuration and method of operating also cause low-down antenna " Q " factor, thereby make this antenna become broad-band antenna.

[0055] ideally, microstrip antenna 112 is half-wavelength " λ/2 " antennas, and its CURRENT DISTRIBUTION is along the length direction of following the tracks of microstrip antenna 112, as shown in Figure 5.

[0056] at distributing point 116, electric current reaches peak value, and basically with feed system 124 added voltage homophases.This electric current is reduced to zero at the mid point of microstrip antenna 112, continues then to reduce and be reduced to negative peak value in termination ends 118.

[0057] as shown in Figure 5, the linear microstrip antenna device 110 of this CURRENT DISTRIBUTION that is operated in the half-wave dipole configuration can be set up positive electric field E and set up negative electric field E in termination ends 118 at feed end 116.

[0058] Fig. 6 is illustrated in the coupling of the near field electric field E on the near field microstrip antenna 112.More particularly, Fig. 6 is the moment curve figure of the electric field E of the normalization time variation on the microstrip antenna under the half-wavelength situation 112.At distributing point 116, electric field E has maximum value.At the mid point of microstrip antenna 112, electric field E is decreased to zero.In termination ends 118, electric field E is decreased to negative peak value or minimum value.Because RFID label 120 just in time is placed on (see figure 2) on this antenna, the differential electric field E of microstrip antenna 112 is length direction driving or the guide current along RFID label 120, thereby excitation RFID label 120, therefore, it can be read or write by the RFID reader, that is, the near field antenna device 112.

[0059] therefore, be placed on the microstrip antenna 112 and along the RFID label 120 transmission information of length " L " orientation of microstrip antenna device 110 to microstrip antenna 112.Should be noted that the material that depends on substrate 140, substrate 140 is set up slow-wave structure effectively, thereby obtains total antenna length " L ", and it is

l = \frac{c}{2 f \sqrt{ϵ_{r}}},

Wherein " c " is light speed in a vacuum, and " f " is operating frequency and " ε _r" be the relative permitivity or the relative dielectric constant of substrate material in the half-wave dipole antenna configuration.Therefore, as the relative permitivity or the relative dielectric constant ε of substrate 140 _rDuring increase, the length of total antenna assembly " L " just reduces, so this antenna assembly can be used for less RFID label.For example, utilizing dielectric constant is 12.5 ceramic substrate, can realize that experimentally total Microstrip Length is 4.7cm, and theoretical length is 4.6cm.Less antenna assembly can be used for reading or detecting the RFID label of less article.

[0060] in one embodiment, linear microband antenna device 110 extends to the length corresponding to all-wave.Fig. 7 and 8 is illustrated in certain instantaneous time changing electric field E on the all-wave microstrip antenna device, for example, and the linear microband antenna device 110 when 0 degree and 90 is spent phase places respectively.

[0061] on distributing point 116, when the electric feed signal transmission that provides through cable 114 is spent phase places by complete 360, can observe two instantaneous specific figures of taking the photograph soon of differential electric field E.Two couples of differential electric field E are arranged when zero phase, and a pair of differential electric field E is only arranged when 90 phase places.The length " L " that to be coupled to the actual differential electric field E on the RFID label 120 be property microstrip antenna 112 along the line is inswept.This is favourable for aiming between linear microband antenna 112 and the RFID label 120.Increase dielectric strength (or the relative permitivity " ε of substrate 140 materials _r") can partly compensate the needs that increase total antenna length " L " at least.

[0062] with reference to Fig. 9, a series of RFID label 120a to 120e are placed to the clearance distance of being separated by and are " d ", and one of them RFID label 120c is on single linear microband antenna device 110.RFID label 120a to 120e has such orientation, and wherein the machine-direction oriented of the antenna dipoles of RFID label 120a to 120e is the length " L " of property microstrip antenna device 110 along the line.

[0063] in order to prevent that near field linear microband antenna device 110 from reading or writing near label 120b or the 120d the label 120c that is addressed, can correspondingly adjust little bandwidth " W ", length " L " and total substrate width " W _s".Gap " d " between RFID label 120a to 120e is when reducing, total substrate width " W that must reduce little bandwidth " W " and be about " 5W " _s".The size in gap " d " can make

adjacent label

120a, 120b, 120d, 120e is considerably beyond the transverse edge 142a and the 142b of the substrate 140 of linear microband antenna 112, and therefore, microstrip antenna device 110 can not detect adjacent

R FID label

120a, 120b, 120d, the existence of 120e.Can adjust the tracking width W, the parameter W/H of length L and substrate and ε _rThereby, realize effectively corresponding to the CURRENT DISTRIBUTION of half-wave to the all-wave structure.

[0064] in an embodiment shown in Figure 10 and 11, linear microband antenna device 110 ' comprises a ground plane that extends or reel.More particularly, linear microband antenna device 110 ' be with linearity little be with 110 identical, different is to replace ground plane 150, microstrip line 112 is arranged on the first surface 140a of substrate 140 and ground plane 150 ' is arranged in the substrate 140 to the first surface 140a of small part, but it does not contact with microstrip line 112.Ground plane 150 ' also is separately positioned on the first edge 142a and the second edge 142b of substrate 140, and on the second surface 140b of substrate 140.Ground plane 150 ' can also separate with second surface 140b by dielectric barrier 164.

[0065] ground plane 150 ' can also comprise tablet or

end

180a and 180b, the overlapping and distance " W that extends internally respectively of they and first surface 140a _G" arrive

edge

112a and 112b, but be not with 112 to contact with tracking is little.

[0066] as shown in figure 11, RFID label 120a to 120e can closely be arranged on the antenna assembly 110 ', therefore, in the time of on a label 120c rests on linear tracking microstrip antenna 112,

adjacent label

120b and 120d roughly rest on the tablet or

end

180a and 180b of ground plane 150 '.As shown in figure 12, the position of antenna assembly 110 ' control RF energy, wherein by propagating near-field energy and ground plane 150 ' coiling tablet or

end

180a and 180b, these two ends distance W that extends internally _GArrive

edge

112a and 112b respectively, but do not contact with tracking microstrip antenna 112.So electric field E only extends to tablet or

end

180a and 180b from following the tracks of microstrip antenna 112 basically, thereby stops electric field E effectively, and prevents that antenna assembly 110 ' is coupled to

adjacent label

120b and 120d.

[0067] time of Figure 13 explanation on the near field microstrip antenna 112 of antenna assembly 110 ' changes the instantaneous coupling figure of near field electric field E, and it is watched from a side, for example, and the side 152b of the ground plane 150 ' of antenna assembly 110 '.More particularly, Figure 13 is the curve map of the normalization electric field E under the half-wave length situation.According to the similar fashion of Fig. 6, at distributing point 116, electric field E has maximum value.At the mid point along the microstrip antenna 112 of length " L ", electric field E is reduced to zero.At termination point 118, electric field E is reduced to negative peak value or maximum value.

[0068] when RFID label 120 just in time is placed on the antenna assembly 110 ', as shown in figure 12, the differential electric field E of microstrip antenna 112 is along driving on the length of RFID label antenna 112 or guide current, thereby excitation RFID label 120, so, it can be read or write by the RFID reader, that is, and and near field antenna device 112.Therefore, be placed on the microstrip antenna 112 and also be coupled to microstrip antenna 112 along the RFID label 120c of the length L orientation of microstrip antenna device 110 '.Similarly, can adjust the tracking width W, length L, and the parameter W/H of substrate and ε _rThereby, realize effectively distributing corresponding to the effective current of half-wave to the all-wave structure.

[0069] in one embodiment, with reference to Figure 14 and 15, linear microband antenna device 110 (or 110 ') can be installed in the external conductive casing 160 or on the external conductive casing 160.External conductive casing 160 comprises base 162 and two longitudinal side wall 162a and 162b, and two lateral sidewalls 162c that are connected with its quadrature usually and 162d.The bottom surface 154 of ground plane 150 is arranged on the base 162, in order that coupling of circuits external conductive casing 160 is to ground plane 150.So external conductive casing 160 is by ground plane 150 ground connection.

[0070] sidewall 162a to 162d can open with edge 142a to the 142d branch of substrate 140.Edge 142a to 142d can contact external conductive casing 160, and still, it may need a spatial content, thereby antenna assembly 110 (or 110 ') is encased in the external conductive casing 160.Sidewall 162a to 162d can also separate with linear microband antenna 112 by dielectric barrier material 170, and therefore, external conductive casing 160 is and linear microband antenna 112 that capacity load 122 and terminating resistor R1 circuit are isolated.The dielectric barrier material can comprise the air gap.The material of external conductive casing 160 can comprise aluminium, red copper, brass, stainless steel, or similar metallics.Can imagine, increase the external conductive casing 160 that extends the side is arranged, it be utilize with microstrip antenna device 110 in the adjacent sidewall 162a to 162d of the side 142a to 142d of substrate 140 realize, can further reduce the unnecessary coupling of adjacent RFID label 120 and linear microband antenna device 110.

[0071] in the one embodiment of the invention shown in Figure 16-18, under given overall antenna size, the microstrip antenna device 210 of tortuous line unit can make apparent antenna length " L " become longer, for example, can be used for reading very little RFID label.Tortuous wire antenna assembly 210 is similar to the microstrip antenna device 110 of linear unit in many aspects, and therefore, content described herein is in order to discern their difference in structure and operation.

[0072] more particularly, Figure 16-18 expression comprises the near field antenna device 210 of tortuous line unit microstrip antenna 212.When tortuous wire antenna 212 when " L " proceeds to the terminating resistor R1 of termination ends 118 from distributing point 116 along length, it is the width " W at substrate 140 _s" go up " going in a zigzag ".The thickness of the little band tracking antenna 212 of tortuous wire is that " t " and coupling of circuits arrive the cable 114 at distributing point 116, and terminates on the terminating resistor R1 of termination ends 118, and the resistance value of resistor R 1 is generally 50 ohm.

What [0073] tortuous wire microstrip antenna 212 and linear microband antenna 112 were different is that tortuous wire microstrip antenna 212 is guide current on two-dimensional directional.More particularly, in one embodiment, tortuous wire microstrip devices 210 comprises a plurality of alternately contact

conductive segments

214 and 216 of quadrature, and they are configured to the square wave figure of the little band tracking antenna 212 of tortuous wire.Conductive segment 214 is and length " L _M" aim at point-blank, and be arranged essentially parallel at least one

vertical side

142a and 142b in the substrate 140.Conductive segment 216 is to contact with conductive segment 214 lateral alignment and with the conductive segment 214 of adjusting to a line to form the square wave figure.The orientation of each conductive segment 216 is along centerline axis C-C, and centerline axis C-C is the length L along conductive segment _sExtend and its width of halving.The

conductive segment

214 and 216 of contact can integrally form single little band tracking antenna.Tortuous wire antenna 212 can form and inconsistent other figures of square wave figure, and wherein alternately the

conductive segment

214 and 216 of contact is not a quadrature.Under this linguistic context, these embodiment are unrestricted.

Conductive segment

214 and 216 configuration can make local electric field E drive or guide current along two-dimensional directional.

[0074] at least one edge 142a in the substrate 140, the length of 142b is " L _M", and the

conductive segment

214 and 216 of quadrature contact is with respect to this at least one

edge

142a, 142b is arranged to horizontal and vertical orientation alternately.

[0075] as shown in figure 17, conductive segment 214 is arranged to longitudinally be orientated, and they lump together the total length " L that determines the little band tracking antenna 212 of tortuous wire _M", tracking antenna 212 is to extend to and be included in terminating resistor R1 on the termination point 118 from distributing point.Width " the W of tortuous wire tracking antenna 212 _M" be defined as the width that a conductive segment 214 longitudinally is orientated.

[0076] is similar to linear microband antenna device 110, the length " L of tortuous wire microstrip antenna device 210 _M" such overall size, its scope are arranged is length from the length that equals suitable half-wave dipole antenna substantially to suitable full-wave doublet antenna.It is identical with the Electric Field Distribution of the linear antenna device 110 shown in Fig. 6-8 that the electric field (electric field E) that forms distributes.

[0077] in one embodiment, " the W of tortuous wire microstrip antenna device 210 _M/ H " ratio can be more than or equal to 1, specifically, roughly can be to about 5 scope about 1.The relative dielectric constant of substrate 140 roughly can be about 2 to about 12 scope.At least one edge 142a in the substrate 140,142b can be configured to like this, and it is from conductive segment 214 horizontal expansions one segment distance of being arranged to longitudinally be orientated, and this distance is substantially equal to or greater than the width " W of the little band tracking antenna 212 of tortuous wire _M" twice " 2W _M" or many times.In another embodiment, at least one edge 152a of ground plane 150,152b are that this distance is equal to or greater than the width " W of tortuous wire tracking antenna 212 from conductive segment 214 horizontal expansions one segment distance of being arranged to longitudinally be orientated _M".Can also imagine that tortuous wire antenna assembly 210 can comprise the capacity load 122 of coupling of circuits to the little band tracking antenna 212 of tortuous wire, it is normally adjacent with terminating resistor R1.

[0078] shown in Figure 17-19, (and describe according to the mode that is similar to linear antenna device 110 shown in Figure 9), be to be separated by clearance distance (d) between a series of RFID label 120a to 120e, the position of one of them RFID label 120c is on single tortuous wire microstrip antenna device 210.Tortuous wire microstrip antenna device 210 is configured to like this, and the local electric field E of tortuous wire antenna 212 is coupled to a RFID label 120, and it machine-direction oriented is the length direction along tortuous wire microstrip antenna device 210.Local electric field E is two-dimensional directional driving or the guide current along antenna 212.

[0079] contiguous label 120b or the 120d of label 120c in order to prevent that near field tortuous wire microstrip antenna device 210 from reading or writing and being addressed can correspondingly adjust little bandwidth " W _M", length " L _M" and total substrate width " W _s".When the reducing of the gap " d " between the RFID label 120a to 120e, little bandwidth " W _M" and total substrate width " W _s" also reduce.The size in gap " d " makes

adjacent label

120a, 120b, 120d, the position of 120e exceeds the transverse sides 142a and the 142b of tortuous wire microstrip antenna 212, and therefore, microstrip antenna device 210 can not detect

adjacent label

120a, 120b, the existence of 120d and 120e.Under the situation of tortuous wire microstrip antenna, adjust and follow the tracks of width W _M, total effective length L _MAnd the substrate parameter, can realize distributing corresponding to the effective current of half-wave to the all-wave structure.This can be at given regular length L _MDown by increasing the period L of tortuous wire tracking antenna ' _MNumber is realized.

[0080] in one embodiment, for example, the embodiment shown in Figure 20 and 21, tortuous wire microstrip antenna device 210 ' comprise the ground plane that extends or reel.More particularly, tortuous wire microstrip antenna device 210 ' is identical with tortuous wire microstrip antenna 210, different is, replace ground plane 150, microstrip line 212 is arranged on the first surface 140a of substrate 140, and ground plane 150 ' is arranged in the substrate 140 to the first surface 140a of small part, but do not contact with microstrip line 212.According to the mode that is similar to linear microband antenna 110 ', ground plane 150 ' is arranged on the first edge 142a of substrate 140 and the second edge 142b and on the second surface 140b of substrate 140.Ground plane 150 ' can separate with substrate by one or more dielectric barrier 164.

[0081] ground plane 150 ' can comprise tablet or

end

180a and 180b, the overlapping and distance " W that extends internally of they and first surface 140a _G" after arrive edge 212a and 212b respectively, but not with follow the tracks of microstrip antenna 212 and contact.

[0082] as shown in figure 21, RFID label 120a to 120e can closely be arranged on the antenna assembly 210 ', therefore, in the time of on a label 120c rests on tortuous wire tracking microstrip antenna 212,

adjacent label

120b and 120d roughly rest on the tablet or

end

180a and 180b of ground plane 150 ' respectively.

[0083] in addition, shown in Figure 22 and 23, and according to the mode that is similar to Figure 14 and 15 illustrated embodiments, the ground plane 150 of tortuous 210 (or 210 ') of wire microstrip antenna device can coupling of circuits arrive external conductive casing 160.Sidewall 162a to 162d can open with edge 142a to the 142d branch of substrate 140.Edge 142a to 142d can contact external conductive casing 160, but may need a spatial content, and antenna assembly 110 (or 110 ') is encased in the external conductive casing 160.Sidewall 162a to 162d can also separate with tortuous wire microstrip antenna 212 by dielectric barrier material 170, and therefore, external conductive casing 160 is and tortuous wire microstrip antenna 212 that capacity load 122 and terminating resistor R1 circuit are isolated.The material of external conductive casing 160 can comprise aluminium, red copper, brass, stainless steel, or similar metallics.

[0084] as discussed above, adjust and follow the tracks of width W _M, total effective length L _MAnd the parameter of substrate, can realize distributing corresponding to the effective current of half-wave to the all-wave structure.This can be at given regular length L _MDown by increasing the period L of tortuous wire tracking antenna ' _MNumber is realized.

[0085] our above embodiment of near field antenna device 110,110 ', 210,210 ' openly, it is that unit configuration by cable 114 and terminating resistor R1 provides power.The professional can know, near field antenna device 110,110 ', 210, and 210 ' can also provide power by the dipole arrangement that comprises transformer.Under this linguistic context, these embodiment are unrestricted.

[0086] in view of above description, embodiments of the invention relate to the near field antenna device 110,110 ', 210 that is used to read the RFID label, 210 ', wherein antenna assembly 110, and 110 ', 210,210 ' has such configuration, antenna assembly 110,110 ', 210,210 ' the local electric field E that launches down in operation wavelength " λ " resides in the zone that is limited by the near field basically, and antenna assembly 110,110 ', 210,210 ' operation wavelength " λ " down the radiation field of emission reside in basically by with respect to antenna assembly 110, in the zone that 110 ', 210,210 ' far field limits.

[0087] various embodiment disclosed herein are designed to like this, can increase the amplitude of local electric field E with respect to the radiation field amplitude, and have only when RFID label 120c be in the near field region time, it can be by antenna or antenna assembly 110,110 ', 210,210 ' read (and when RFID label 120c be in the far-field region time, it can not be by antenna assembly 110,110 ', 210,210 ' reads).In addition, can reduce the amplitude of radiation field with respect to local electric field E amplitude, therefore, have only when RFID label 120c be in the near field region time, it can be by antenna or antenna assembly 110,110 ', 210,210 ' read (and when RFID label 120c be in the far-field region time, it can not be by antenna assembly 110,110 ', 210,210 ' reads).Antenna assembly 110,110 ', 210,210 ' relative dielectric constant is " ε _r".

[0088] antenna or antenna assembly 110,110 ', 210,210 ' is configured to like this, the near field region is to be limited by the distance that equals " λ/2 π " from antenna or antenna assembly 110,110 ', 210,210 ', wherein " λ " is antenna or antenna assembly 110,110 ', 210,210 ' operation wavelength.In one embodiment, antenna or antenna assembly 110,110 ', 210,210 ' roughly are operated under the frequency of about 915MHz, and therefore, the near field region distance is about 5cm.

[0089] we also disclose a kind of method that is used to read or write RFID label 120c, may further comprise the steps: near field antenna device 110 is provided, 110 ', 210,210 ', it has such configuration, antenna or antenna assembly 110,110 ', 210,210 ' the local electric field E that launches down in operation wavelength " λ " resides in the zone that is limited by the near field basically, and antenna or antenna assembly 110,110 ', 210,210 ' operation wavelength " λ " down the radiation field of emission reside in basically by with respect to antenna assembly 110,110 ', in the zone that 210,210 ' far field limits; With the local electric field E of coupling near field antenna device 110,110 ', 210,210 ' to the RFID label 120c that in the near field region, is provided with.

[0090] antenna assembly 110,110 ', 210,210 ' effective length L or L _MCan be like this, the CURRENT DISTRIBUTION that is conducted through antenna produces the waveform that wavelength is directly proportional with nv/f, wherein v is a velocity of wave propagation, it equals the light velocity divided by antenna assembly 110, the root of redressing of 110 ', 210,210 ' relative dielectric constant, f is to be the frequency of unit with Hz, and the scope of n be from half-wavelength about 0.5 to all-wave long about 1.0.

[0091] this method can also comprise step: increase the amplitude of local electric field E with respect to the radiation field amplitude, therefore, have only when RFID label 120c be in the near field region time, it can be by antenna assembly 110,110 ', 210,210 ' reads, and when RFID label 120c be in the far-field region time, it can not be by antenna assembly 110,110 ', 210,210 ' reads.

[0092] this method can also comprise step: the amplitude that reduces radiation field with respect to local electric field E amplitude, therefore, have only when RFID label 120c be in the near field region time, it can be by antenna assembly 110,110 ', 210,210 ' reads, and when RFID label 120c be in the far-field region time, it can not be by antenna assembly 110,110 ', 210,210 ' reads.This method can also comprise step: configuration antenna assembly 110,110 ', 210,210 ', and making the near field region is by from antenna assembly 110, and 110 ', 210, the 210 ' distance that equals " λ/2 π " limits, and wherein " λ " is the operation wavelength of antenna.This method can also comprise step: near field antenna is to work under the frequency of about 915MHz, and therefore, the near field region distance is about 5cm.Antenna assembly 110,110 ', 210,210 ' effective length L or L _MCan be like this, the CURRENT DISTRIBUTION that is conducted through antenna produces the waveform that wavelength is directly proportional with nv/f, wherein v is a velocity of wave propagation, it equals the light velocity divided by antenna assembly 110, the root of redressing of 110 ', 210,210 ' relative dielectric constant, f be with Hz be the scope of the frequency of unit and n be from half-wavelength about 0.5 to all-wave long about 1.0.

Can imagine that [0093] favorable characteristics of near field antenna device disclosed herein comprises:

The scope of (1) reading/writing the RFID label be subjected to distance of near field d＜＜restriction of λ/2 π;

(2) near

field antenna

112 or 212 very big part electric field energy loss are on terminating load resistor R 1;

(3) the far field antenna device with radiation compares, and the near field antenna device has the low Q factor;

(4) lead the broad band uhf application that the wide bandwidth of operation that obtains can be used for the whole world from the low Q factor;

(5) the wide bandwidth of operation and the low Q factor can make the RFID reader circuitry of simplification not need to be used to the frequency hopping that prevents that reader from interfering with each other;

(6) antenna assembly with radiation compares, and the near field antenna device has low radiation resistance and radiation efficiency.So, can reduce far-field radiation greatly;

(7) the near field antenna device disposes the tracking size, the microstrip type antenna of substrate properties and ground plane, and it is designed to be operated in the scope from the half-wave antenna to the all-wave antenna;

(8) compare with other differential fed arrangement that may need transformer, the unit fed arrangement provides a kind of simple and more effective fed arrangement, wherein electrical input or cable directly are connected to the starting end of microstrip antenna, and the ground of connector directly is connected to the ground plane of substrate bottom;

(9) external conductive casing has the open side of placing the near field antenna device, and external conductive casing is grounding to the ground plane of antenna assembly.This external conductive casing helps to reduce to attempt to be coupled to the stray electric field of adjacent R FID label, and these labels are adjacent with the RFID label that is set directly on the microstrip antenna;

(10) launch the electric field localization is convenient to defer to regulation in the near field region requirement.

[0094] in view of above description, the RFID label that embodiments of the invention allow to be close to mutually is programmed.For example, the feature of the RFID label on the reel is that very little spacing distance is arranged between each label.Embodiments of the invention do not require be separated by very big distance and can prevent that a plurality of labels from being read together or programme of these labels.In addition, embodiments of the invention are convenient to discern the defectiveness label adjacent with the normal function label.

[0095], should not be construed to limitation of the scope of the invention to these details, and only be illustration as the preferred embodiment of the present invention though above description comprises many concrete details.In spirit and scope of the invention, the professional it is contemplated that out many other possible schemes.

Claims

1. near field antenna, be configured to read the RFID label, the local electric field E that this antenna is configured to make it this antenna emission under operation wavelength resides in the zone that is limited by the near field basically, and local electric field E is along corresponding to half-wave guide current distribution to the effective antenna length of all-wave structure.

2. according to the near field antenna of claim 1, wherein this antenna is configured to like this, and making the near field region is to be limited by the distance that equals λ/2 π from antenna, and wherein λ is the operation wavelength of antenna.

3. according to the near field antenna of claim 2, wherein near field antenna is to work under the frequency of about 915MHz, and therefore, the near field region distance is about 5cm.

4. method that is used to read the RFID label may further comprise the steps:

A near field antenna device is provided, the local electric field E that this antenna assembly is configured to make it this antenna emission under operation wavelength resides in the zone that is limited by the near field basically, and wherein local electric field E is along corresponding to half-wave guide current distribution to the effective antenna length of all-wave structure; With

The local electric field E of coupling near field antenna device is to the RFID label that is arranged in the near field region.

5. according to the method for reading the RFID label of claim 4, also comprise step: the configuration antenna assembly, therefore, the near field region is to be limited by the distance that equals λ/2 π from antenna assembly, wherein λ is the operation wavelength of antenna assembly.

6. according to the method for reading the RFID label of claim 5, also comprise step: antenna assembly is operated under the frequency of about 915MHz, and therefore, the near field region distance is about 5cm.

7. near field antenna device that is used to read the RFID label comprises:

Be configured to single and antenna continuous conductor, this antenna is to extend to the other end that forms termination point from an end that forms distributing point;

Termination point is connected to ground plane by a resistor, and antenna assembly has relative dielectric constant;

The local electric field E that this antenna is configured to make it this antenna emission under operation wavelength resides in the zone that the near field limits basically, and local electric field E is along distributing corresponding to half-wave guide current on the effective antenna length of all-wave structure.

8. according to the near field antenna device of claim 7, wherein the effective length of antenna assembly is such, the CURRENT DISTRIBUTION that makes it to be conducted through antenna produces the waveform that a wavelength is proportional to nv/f, wherein v is the velocity of wave of propagating, it equals the square root of the light velocity divided by the relative dielectric constant of antenna assembly, f is to be the frequency of unit with Hz, and the scope of n be from half-wavelength about 0.5 to all-wave long 1.0.

9. according to the near field antenna device of claim 7, wherein this antenna is little band tracking antenna, and this near field antenna device comprises:

The substrate that first surface and second surface are arranged, its thickness are to be limited by the distance between them;

Wherein little band tracking antenna is arranged on the first surface of substrate, and ground plane is arranged on the second surface of substrate.

10. according to the near field antenna device of claim 7, wherein the antenna assembly local electric field E that is configured to make it by this antenna assembly is propagated is coupled to the RFID label, and this label machine-direction oriented is the effective length along antenna assembly.