11111111111111111111111111111111111111111111111111111111111111111111111111

(12) United States PatentFink et al.

(54) SYSTEMS, APPARATUSES AND METHODSFOR BEAMFORMING RFID TAGS

(71) Applicant: The United States of America asrepresented by the Administrator ofthe National Aeronautics and Space,Washington, DC (US)

(72) Inventors: Patrick W. Fink, Missouri City, TX(US); Gregory Y. Lin, Friendswood,TX (US); Phong H. Ngo, Friendswood,TX (US); Timothy F. Kennedy,Houston, TX (US)

(73) Assignee: The United States of America asrepresented by the Administrator ofthe National Aeronautics and SpaceAdministration, Washington, DC (US)

(*) Notice: Subject to any disclaimer, the term of thispatent is extended or adjusted under 35U.S.C. 154(b) by 349 days.

(21) Appl. No.: 14/201,402

Filed: Mar. 7, 2014

Related U.S. Application Data

Provisional application No. 61/775,871, filed on Mar.11, 2013.

Int. Cl.G06K 7/10 (2006.01)G06K 7/00 (2006.01)HOIQ 1/22 (2006.01)H04B 7/0408 (2017.01)U.S. Cl.CPC ....... G06K 7/10366 (2013.01); G06K 7/0008

(2013.01); HOIQ 1/2208 (2013.01); H04B7/0408 (2013.01)

,

(io) Patent No.: US 9,715,609 B1(45) Date of Patent: Jul. 25, 2017

(58) Field of Classification SearchNoneSee application file for complete search history.

(56) References Cited

U.S. PATENT DOCUMENTS

4,996,532 A * 2/1991 Kirimoto .................. GO IS 7/36342/17

7,183,922 B2 2/2007 Mendolia et al.7,187,288 B2 3/2007 Mendolia et al.7,456,726 B2 11/2008 Hansen et al.7,573,418 B2 8/2009 Kawai et al.7,667,652 B2 2/2010 Gevargiz et al.7,786,864 B1 8/2010 Shostak et al.7,873,326 B2 1/2011 Sadr7,911,324 B2 3/2011 Breed et al.8,072,311 B2 12/2011 Sadr et al.8,120,532 B2 2/2012 Rofougaran

2005/0148370 Al* 7/2005 Moldoveanu .......... HO IQ 1/246455/562.1

(Continued)

Primary Examiner Mohamed Barakat(74) Attorney, Agent, or Firm Kurt G. Hammerle

(57) ABSTRACT

A radio frequency identification (RFID) system includes anRFID interrogator and an RFID tag having a plurality ofinformation sources and a beamforming network. The tagreceives electromagnetic radiation from the interrogator.The beamforming network directs the received electromag-netic radiation to a subset of the plurality of informationsources. The RFID tag transmits a response to the receivedelectromagnetic radiation, based on the subset of the plu-rality of information sources to which the received electro-magnetic radiation was directed. Method and other embodi-ments are also disclosed.

22 Claims, 11 Drawing Sheets

D9

r,o8X

https://ntrs.nasa.gov/search.jsp?R=20170007250 2019-08-29T22:19:23+00:00Z

US 9,715,609 BIPage 2

(56) References Cited

U.S. PATENT DOCUMENTS

2005/0280504 Al * 12/2005 Pettus ................ G06K 19/0672340/10.1

2006/0055531 Al 3/2006 Cook et al.2007/0001811 Al* 1/2007 Kiyohara ............. HO IQ 1/2216

340/10.12007/0222610 Al* 9/2007 Tagato ............. G06K 19/07336

340/572.72010/0109903 Al* 5/2010 Carrick ..................... GO1S 5/14

340/8.12011/0160941 Al* 6/2011 Garrec .................. GO1S 13/913

701/17

* cited by examiner

U.S. Patent Jul. 25, 2017 Sheet 1 of 11 US 9,715,609 BI

?0

mw

FIG. 1

0

109

01107

108

U.S. Patent

FIG.

F1G, 4

Jul. 25, 2017

1 16

116

11

11

1100

Sheet 2 of 11

11n.4

US 9,715,609 B1

16

116

116

116

U.S. Patent

LNN

Jul. 25, 2017 Sheet 3 of 11 US 9,715,609 B1

N

C

c~: f

x

N---- ---------------------- ---- ----------------

U.S. Patent Jul. 25, 2017 Sheet 4 of 11

CN

N CON N

US 9,715,609 B1

M

U-

U.S. Patent

N

Jul. 25, 2017 Sheet 5 of 11

cv c

C --1-- R 1) i Y ~V.

CNI 0

US 9,715,609 B1

U.S. Patent Jul. 25, 2017 Sheet 6 of 11 US 9,715,609 B1

300— 303-315

302

304 306

301--- 305_. - ~1

30 `-304307

50;

500 525 , 520

5.30- pr/........~

U.S. Patent Jul. 25, 2017 Sheet 7 of 11 US 9,715,609 BI

86

80

805-

810--

833

81-32-

805-

830-

N.

?coo

101

85 7-'85

7 C~C14

563 ,- -864

820

--8t54.~

811

-812

--W--805

837

"-854853

',.) U 4

1005

80

FIG. 10

1012

FIG. 1

U.S. Patent

900

91

Jul. 25, 2017 Sheet 8 of 11 US 9,715,609 B1

FIG. 11

104 - 1,04

J3 ; 1 9~3

110

FIG. 13

I105

1100

i0ii

910

U.R. Patent Jul. 25, 2017 Sheet 9of11 US 9,713,609 GI

ƒ400

FIG. 14

FIG. 16

f/]Q

U.S. Patent Jul. 25, 2017 Sheet 10 of 11 US 9,715,609 B1

Q

1305c - J

!r.

1305c--

I

13000

0

!i

y ------------t\

~♦

M

1305b-'

303c`i

1,305a

FIG. 15

-->-- 1303b—ii

---1305b----- ~ 303b ---- i

1,302b

1305b

L

1300b

1000

Transmit electromagnetic radiation that is encoded 1625with identification codes identifying respective

information sources within Rl"lD tag

Receive encoded electromagnetic radiation ~----- 1030

Based on received encoded electromagneticradiation,

1--1X35

derive information pertaining to position or orientation

U.S. Patent Jul. 25, 2017 Sheet 11 of 11 US 9,715,609 B1

1500

Transmit electromagnetic radiation

Receive electromagnetic radiation

Direct received electromagnetic radiation to subset ofplurality of information sources within RFID to

Transmit encoded response to received electromagneticradiations, based on subset of plurality of information

sources to which received electromagnetic radiation wasdirected (response being encoded with identificationcodes of subset of plurality of information sources to

which received electromagnetic radiation was directed)

Receive response to received electromagnetic radiation

Based on received response to receivedelectromagnetic radiation, derive information

pertaining to position or orientation

FIG. 17

7505

1510

1515

1525

1530

1535

US 9,715,609 B1

SYSTEMS, APPARATUSES AND METHODSFOR BEAMFORMING RFID TAGS

CROSS-REFERENCE TO RELATEDAPPLICATIONS

This application claims priority to U.S. Provisional Appli-cation Ser. No. 61/775,871 titled "Systems and Methods forBeamforming RFID Tags," filed on Mar. 11, 2013, and isincorporated herein in its entirety by reference.

ORIGIN OF THE INVENTION

The invention described herein was made by employeesof the United States government and may be manufacturedand used by or for the government of the United States ofAmerica for governmental purposes without the payment ofany royalties thereon or therefor.

FIELD OF THE DISCLOSURE

The embodiments described herein relate generally to thefield of radio frequency identification ("RFID"). More par-ticularly, the disclosure relates to systems, apparatuses andmethods involving RFID tags that utilize beamforming.

BACKGROUND

RFID technology may be used, for example, to ascertainthe position of objects, to track assets, or to assist innavigation. In this technology, electromagnetic radiationmay be transmitted between an RFID tag and an RFIDinterrogator according to any of various arrangements, andthe RFID interrogator determines the presence or position ofthe RFID tag (or the object to which the RFID tag is axed)by decoding of information contained in the electromagneticsignal received from the RFID tag. With conventional RFIDtechnology, an RFID tag may use either a wide beamantenna or a narrow fixed beam antenna. Use of a wide beamantenna results in wide distribution of the electromagneticradiation transmitted by the RFID tag, or in other words, awide angular extent of coverage, but concomitantly theenergy is not focused and consequently the range of com-munication (linear extent or maximum distance withinwhich communication can be conducted) between tag andinterrogator is limited. Use of a narrow fixed beam antennaresults in a focused beam and hence a long range, butconcomitantly is restricted to a narrow angle of coveragesuch that communication between tag and interrogator islimited: the tag must be pointed in the direction of theinterrogator in order to communicate with the interrogator;if the interrogator is off to the side, beyond the angular extentof coverage, the tag and interrogator cannot communicate.Thus, there is a trade-off between linear extent and angularextent of coverage.

SUMMARY

Embodiments disclosed herein provide systems, methods,and apparatuses for beamforming RFID tags.

According to a first aspect of the disclosure, a radiofrequency identification (RFID) system is provided, includ-ing an RFID tag. The RFID tag includes a plurality ofinformation sources and a beamforming network. The RFIDtag is configured to receive electromagnetic radiation, thebeamforming network is configured to direct the receivedelectromagnetic radiation to a subset of the plurality of

2information sources, and the RFID tag is configured totransmit a response to the received electromagnetic radia-tion, the response being based on the subset of the pluralityof information sources to which the received electromag-

5 netic radiation was directed.According to a second aspect of the disclosure, a radio

frequency identification (RFID) system is provided, includ-ing an RFID tag. The RFID tag includes a plurality ofinformation sources and a beamforming network. The RFID

10 tag is configured to transmit electromagnetic radiation viathe beamforming network, the electromagnetic radiationencoding one or more identification codes, each identifica-tion code identifying one of the plurality of information

15 sources, respectively.According to a third aspect of the disclosure, a radio

frequency identification (RFID) method is provided. TheRFID method includes receiving electromagnetic radiation,directing the received electromagnetic radiation to a subset

20 of a plurality of information sources within an RFID tag, andtransmitting a response to the received electromagneticradiation. The response is based on the subset of the pluralityof information sources to which the received electromag-netic radiation was directed.

25 According to a fourth aspect of the disclosure, a radiofrequency identification (RFID) method is provided. TheRFID method includes transmitting electromagnetic radia-tion, the electromagnetic radiation encoding one or moreidentification codes, each identification code identifying a

30 respective one of a plurality of information sources withinan RFID tag.

Other aspects and advantages of the embodimentsdescribed herein will become apparent from the followingdescription and the accompanying drawings, illustrating the

35 principles of the embodiments by way of example only.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures form part of the present specifica-40 tion and are included to further demonstrate certain aspects

of the present claimed subject matter, and should not be usedto limit or define the present claimed subject matter. Thepresent claimed subject matter may be better understood byreference to one or more of these drawings in combination

45 with the description of embodiments presented herein. Con-sequently, a more complete understanding of the presentembodiments and further features and advantages thereofmay be acquired by referring to the following descriptiontaken in conjunction with the accompanying drawings, in

50 which like reference numerals may identify like elements,wherein:FIG. 1 is a schematic diagram, in accordance with one or

more embodiments described herein, of a beamformingRFID tag.

55 FIG. 2 is a schematic diagram, in accordance with one ormore embodiments described herein, of a terminal portcircuit with a radio frequency (RF) distribution circuit andmultiple RFID information sources.FIG. 3 is a schematic diagram, in accordance with one or

60 more embodiments described herein, of a terminal portcircuit with an information source comprising an integratedcircuit and multiple sensors.FIG. 4 is a schematic diagram, in accordance with one or

more embodiments described herein, of a terminal port65 circuit with an RE distribution circuit and multiple RFID

information sources attached to a waveguide distributionnetwork.

US 9,715,609 B13

FIG. 5 is a schematic diagram, in accordance with one ormore embodiments described herein, of an RFID system,showing transmission of electromagnetic radiation from aninterrogator to an RFID beamforming tag.

FIG. 6 is a schematic diagram, in accordance with one ormore embodiments described herein, of an RFID system,showing transmission of electromagnetic radiation from anRFID beamforming tag to an interrogator.

FIG. 7 is a schematic diagram, in accordance with one ormore embodiments described herein, of an RFID systemsimilar to that of FIG. 5, but wherein the electromagneticradiation is transmitted to the RFID tag at a different anglecorresponding to two terminal ports of the RFID tag asopposed to a single port as in FIG. 5.

FIG. 8 is a schematic diagram, in accordance with one ormore embodiments described herein, of an RFID systemincluding multiple interrogators mounted on respectivemobile platforms and a multi-faceted structure containing anRFID beamforming tag on at least one facet thereof.

FIG. 9 is a schematic diagram, in accordance with one ormore embodiments described herein, of an RFID systemincluding interrogators mounted on mobile platforms and aconstellation of multiple RFID beamforming tags.

FIG. 10 is a schematic diagram, in accordance with one ormore embodiments described herein, of a beamformingnetwork that is a Butler matrix.

FIG. 11 is a schematic diagram, in accordance with one ormore embodiments described herein, of a beamformingnetwork that is a Rotman lens.

FIG. 12 is a schematic diagram, in accordance with one ormore embodiments described herein, of a multi-facetedbeamforming RFID tag, with a respective single-beam RFIDfacet-tag attached to each of three facets of the multi-facetedstructure, each of the single-beam RFID facet-tags includinga single antenna and terminal port.

FIG. 13 is a schematic diagram, in accordance with one ormore embodiments described herein, of a multi-facetedbeamforming RFID tag, with a respective beamformingRFID facet-tag attached to each of three faces of themulti-faceted structure, each of the beamforming RFIDfacet-tags including multiple antennas and multiple terminalports.

FIG. 14 is a schematic diagram, in accordance with one ormore embodiments described herein, illustrating an exem-plary spatial range of coverage of beamforming RFID tags.

FIG. 15 is a schematic diagram, in accordance with one ormore embodiments described herein, illustrating an exem-plary spatial range of coverage of a multi-faceted beam-forming RFID tag.

FIG. 16 is a schematic diagram, in accordance with one ormore embodiments described herein, illustrating a hybridRotman lens/van Arta retro-reflector.

FIG. 17 is a flow chart, in accordance with one or moreembodiments described herein, of a method of RFID usingone or more beamforming RFID tags.

FIG. 18 is a flow chart, in accordance with one or moreembodiments described herein, of a method of RFID usingone or more beamforming RFID tags.

NOTATION AND NOMENCLATURE

Certain terms are used throughout the following descrip-tion and claims to refer to particular system components andconfigurations. As one skilled in the art will appreciate, thesame component may be referred to by different names. Thisdocument does not intend to distinguish between compo-nents that differ in name but not function. In the following

_►,

discussion and in the claims, the terms "including" and"comprising" are used in an open-ended fashion, and thusshould be interpreted to mean "including, but not limitedto ...." The word "or" is used in the inclusive sense (i.e.,

5 "and/or") unless a specific use to the contrary is explicitlystated.

It should be noted that the terms "radio frequency" (RF)and "microwave" are used interchangeably herein. "Inter-rogator" and "reader" are likewise used interchangeably toconnote a transceiver that transmits electromagnetic radia-

10 tion to one or more RFID tags and receives responses fromthe one or more RFID tags. While the interrogator may beoperationally coupled to one or more processors, suchprocessors may be internal and/or external to the interroga-tor. For example, in some cases the interrogator may have an

15 internal or embedded processor that controls the function-ality of the interrogator and is also capable of decoding andutilizing information received from one or more tags. Inother cases, the interrogator might have an internal orembedded processor that controls the communication func-

20 tionality of the interrogator, and an interface to an externalprocessor enables the external processor to utilize informa-tion received from the one or more tags.In the case of surface acoustic wave (SAW) RFID tags,

the functionality of the SAW tag upon the acoustic wave

25 energy, which has been converted from electromagneticenergy by a transducer that imparts information to thatacoustic energy, is an encoding process that is also consid-ered a type of passive modulation. Hence, the terminology"encoding" and "modulation" of the signal with respect to

30 SAW devices is used interchangeably, and when used in ageneral sense, it is understood that "modulation" implies thepassive modulation or encoding characteristic of SAWdevices.

Although there is not unanimous concurrence regardingthe definition of'waveguides" and "transmission lines," the

35 consensus opinion is that transmission lines are a subset ofwaveguides that propagate, predominantly, transverse elec-tromagnetic (TEM) waves. Herein, the term "transmissionline" is used in a more general sense to denote an elongateddevice for transferring electromagnetic energy between two

40 pieces of equipment, a practice well known to those skilledin the art of electromagnetic engineering (having benefit ofthis disclosure), regardless of the specific propagationmodes established within the elongated device. Although theterm "waveguide" sometimes is construed to mean a hollow

45 elongated, usually conductive, tube, the intent in this docu-ment is the more general meaning relating to any structuredesigned to propagate an electromagnetic field in one ormore intended directions.The terms "pattern," "antenna pattern," "(antenna) radia-

50 tion distribution pattern" or the like used herein pertain tothe radiation distribution produced over a solid angularregion by injecting electromagnetic energy within a specificoperating frequency band or set of operating frequencybands into one of the terminal ports (described below). The

55 pattern may comprise one or more primary beams, wherein"beam" is used to denote a pattern of radiation density overan angular span that contains a peak radiation density, and"beam" can also be described as a major lobe. In someembodiments described herein, a pattern associated with a

60 terminal port might contain multiple lobes or beams, eachlobe or beam characterized by a local maximum of radiationdensity.

65

DETAILED DESCRIPTION

The foregoing description of the figures is provided forthe convenience of the reader. It should be understood,

US 9,715,609 B15

however, that the embodiments are not limited to the precisearrangements and configurations shown in the figures. Also,the figures are not necessarily drawn to scale, and certainfeatures may be shown exaggerated in scale or in general-ized or schematic form, in the interest of clarity and con-ciseness. Relatedly, certain features may be omitted incertain figures, and this omission may not be explicitly notedin all cases.

While various embodiments are described herein, itshould be appreciated that the present invention encom-passes many inventive concepts that may be embodied in awide variety of contexts. The following detailed descriptionof exemplary embodiments, read in conjunction with theaccompanying drawings, is merely illustrative and is not tobe taken as limiting the scope of the invention, as it wouldbe impractical to include all of the possible embodimentsand contexts of the invention in this disclosure. Uponreading this disclosure, many alternative embodiments willbe apparent to persons of ordinary skill in the art. The scopeof the invention is defined by the appended claims andequivalents thereof.

Illustrative embodiments of the invention are describedbelow. In the interest of clarity, not all features of an actualimplementation are described or illustrated in this specifi-cation. In the development of any such actual embodiment,numerous implementation-specific decisions may need to bemade to achieve the design-specific goals, which may varyfrom one implementation to another. It will be appreciatedthat such a development effort, while possibly complex andtime-consuming, would nevertheless be a routine undertak-ing for persons of ordinary skill in the art having the benefitof this disclosure.Embodiments disclosed herein may provide certain

advantages and benefits, such as described as follows. Thebeamforming RFID tags described herein may permit links(communication) between interrogators and tags over longerdistances at a fixed interrogator transmission power, or overthe same distance at a lesser interrogator transmissionpower, than is typically feasible in conventional RFIDcommunication links. Thus, the beamforming RFID tagsmay permit tracking of assets over greater distances. Navi-gation or localization applications are also possible due tothe multiple, angle-dependent beams associated with thebeamforming RFID tags. Long range wireless sensor inter-rogation applications are also possible when the tag incor-porates one or more sensing mechanisms.More specifically, the beamforming RFID tags described

herein may provide antenna directivity that far surpassestypical values associated with RFID tag antennas. Thebeamforming RFID tags described herein may also provideretro-directive functionality, which simulates automatedpassive steering, such that the signal received from theinterrogator is focused on a specific RFID tag and retrans-mitted back in the direction of the interrogator. Accordingly,the beamforming RFID tags described herein may bereferred to as beamformer RFID retro-reflector tags. Inaddition to the range information associated with typicalRFID links, bearing information may also be provided to theinterrogator, based on the identification information in thesignal that is reflected back to the interrogator. That is, thebeamforming RFID tag may have the ability to associate aunique identification code to each beam port, so that theidentification code contained in the response signal trans-mitted by the tag indicates the angle of transmission. Thisprovision of bearing information permits enhanced naviga-tion functionality; e.g., road signs that return bearing esti-mation in addition to the typically provided range and

Tpossibly range-rate. Further, the beamformer (or beamform-ing network) in the beamforming RFID tags describedherein may spatially condense the power of the incomingelectromagnetic radiation (signal) to essentially a point that

5 may be referred to as a beam port (or terminal port). Thecondensing of power at the beam port makes this RFIDretro-reflector technology suitable for use not only withsurface acoustic wave circuits but also with integratedcircuit-based RFID tags, which require a minimum thresh-

io old voltage at the integrated circuit because the integratedcircuit is powered by the rectified field. The increased powerpermits longer communication links.A general description of some embodiments disclosed

herein is given immediately below, followed by a descrip-15 tion of embodiments with reference to the figures herein.

Methods, apparatuses, and systems for long-range RFID-enabled communication, tracking and other functions, usingbeamforming RFID tags, are disclosed, including an RFIDsystem comprising (i) an interrogator operationally con-

20 nected to a processor and (ii) one or more beamformingRFID tags. Each of the beamforming RFID tags comprisesone or more antennas (e.g., an antenna array), one or moreterminal port circuits, and a beamforming network. Thebeam forming network comprises one or more antenna ports

25 connecting to the one or more antennas and one or moreterminal ports connecting to the one or more terminal portcircuits. Each of the terminal port circuits comprises one ormore RFID information sources. In some embodiments, theinformation sources are RFID integrated circuits that are

so powered by rectifying incident electromagnetic energy. Insome embodiments, the information sources are surfaceacoustic wave (SAW) circuits that receive RE energy andtransmit encoded RE pulses that are received by the inter-rogator and decoded by the processor to derive the identi-

35 fication of the one or more information sources responding.The responding terminal port circuits, and the informationsources associated with the responding terminal port cir-cuits, are determined by (i) the angle of incidence of theelectromagnetic wave impinging on the antennas, relative to

4o a coordinate reference system defined in terms of the anten-nas' positions and orientations, and (ii) the design of thebeamforming network. The beamforming RFID tags arecharacterized by a fixed characteristic set of antenna radia-tion distribution patterns (e.g., beams), each such radiation

45 distribution pattern being associated with one or more of theterminal ports of the beamforming network, and each radia-tion distribution pattern determined by the location of theantennas connected to the beamforming network and by thedesign of the beamforming network. In some embodiments,

50 the beamforming RFID tags are able to receive more powerby using multiple antennas to achieve a higher effectivedirectivity.In an embodiment, the terminal port circuits include

sensors attached to one or more of the RFID information55 sources so that the processor of the RFID system receives

sensor telemetry in addition to the identification informationassociated with the information source. In another embodi-ment, the RFID information sources are inherently inte-grated with a sensor modality, such as SAW circuits for

60 which temperature telemetry, in addition to the identificationcode, is derived by the processor of the RFID system.In some embodiments, the beamforming network is a

Rotman lens. In some embodiments the beamforming net-work is a Ghent lens. In some embodiments, the beamform-

65 ing network comprises RE dividers and combiners. In someembodiments, the beamforming network is a matrix oftransmission lines and hybrid couplers. In some embodi-

US 9,715,609 B17

ments, the matrix of transmission lines and couplers is aButler matrix. In some embodiments, a matrix of transmis-sion lines and directional couplers forms a Blass beamform-ing network.

In some embodiments, a multi-faceted structure supportsa beamforming RFID tag on each face, and the beamformingRFID tag on each face provides antenna coverage over apredetermined angular span such that the collective beam-forming RFID tags over the multi-faceted structure providecoverage over a predetermined angular span that exceeds thespan of the composite of the single antenna beams associ-ated with a single face.

In some embodiments, a beamforming RFID tag isformed from a multi-faceted structure in which each facesupports a fixed beam antenna with an associated antennabeam, each fixed beam antenna being connected to an RFIDinformation source such that the multiple antenna beamsassociated with multiple faces provide coverage over apredetermined angular span that exceeds the span of any ofthe single antenna beams associated with a single face.

In some embodiments, the processor operationally con-nected to the interrogator is configured to estimate the angleof the RFID tag antenna array relative to the direction inwhich the interrogator is transmitting based on the identifi-cation of the responding information sources. In someembodiments, a constellation of one or more beamformingRFID tags are arranged and surveyed so that the position andorientation of each is known. A mobile platform with anRFID system radiates RF signals to the one or more beam-forming RFID tags and the processor operationally con-nected to the interrogator is configured to estimate theposition and/or orientation of the mobile platform based onthe identification of the information sources respondingfrom the constellation of one or more beamforming RFIDtags.

In some embodiments of the beamforming RFID tag, theinformation sources attached to the terminal ports of thebeamforming network are battery powered transmitters thatsend out RF pulses, and each information source is trans-mitted through one or more beams, each beam covering aspecified angular region according to the beamformerdesign. In some embodiments, the battery powered trans-mitters are ultra-wideband (UWB) transmitters. In someembodiments, sensors are attached to one or more of theinformation sources so that the transmitted information overthe multitude of beams contains sensor telemetry in additionto the identification associated with the information source.FIG.1 depicts one or more embodiments described herein

as a beamforming RFID tag 100 comprising multiple anten-nas 101 (four shown), a beamforming network 102 withmultiple antenna ports 107 (four shown) and multiple ter-minal ports 103 (five shown), and multiple terminal portcircuits 110, 111, 112, 113 and 114. Antenna ports 107couple antennas 101 to beamforming network 102, andterminal ports 103 couple terminal port circuits 110, 111,112,113 and 114 to beamforming network 102. The numbersof antennas 101, antenna ports 107, terminal ports 103 andterminal port circuits 110-114 may vary from the numbersillustrated in FIG. 1, the numbers of each of these elementsmay be two or more, the number of antennas 101 may matchthe number of antenna ports 107, and the number of terminalports 103 may match the number of terminal port circuits110-114.The beamforming RFID tag 100 may be said to have a

(fixed) characteristic set of antenna radiation distributionpatterns, illustrated in FIG. 1 in a simplified manner in theform of single beams or major lobes 120, 121, 122, 123 and

8124. In some embodiments, RFID tag 100 may have antennaradiation distribution patterns of types different from thoseillustrated in FIG. 1. The antennas 101 may receive elec-tromagnetic radiation, e.g., an RF signal 130 that has been

5 transmitted by an RFID interrogator (not shown) at a givenangle of incidence 109 relative to a fixed coordinate systemor frame of reference defined by the position and orientationof the antennas 101, such as Cartesian coordinate system108 defined by an x-axis and a y-axis intersecting at origin

io O (0,0). The antennas 101 may transfer the received signal130 via the multiple antenna ports 107 to beamformingnetwork 102. Beamforming network 102 may focus thepower (direct the received electromagnetic radiation) to aselected one or more of the terminal ports 103 (and hence to

15 a selected one or more of the corresponding terminal portcircuits 110-114 and corresponding information sourcescontained therein, described below), in accordance with theangle of incidence 109 of the signal 130 relative to the arrayof antennas 101. While the selected one or more of the

20 terminal ports 103/terminal port circuits 110-114/informa-tion sources may be referred to as a "subset' of the terminalports 103/terminal port circuits 110-114/informationsources, it is to be understood that such subset may be eithera proper subset, or an improper subset including the entire

25 set of the terminal ports 103/terminal port circuits 110-114/information sources. If the angle of incidence 109 is alignedwell with a single one of the characteristic antenna radiationdistribution patterns, or beams, 120-124 of the beamformingRFID tag 100, then according to at least one embodiment the

30 signal 130 power is directed predominantly to the one of theterminal port circuits 110-114 that corresponds to the single(aligned) one of the beams 120-124. If the angle of incidence109 of the signal 130 is within two or more of the beams120-124 of the beamforming RFID tag 100, then according

35 to at least one embodiment, the signal 130 power is distrib-uted between the two or more of terminal port circuits110-114 that correspond to the two or more of the beams120-124. It is noted there is not necessarily a fixed mappingbetween a given one of the beams 120-124 of the charac-

40 teristic antenna radiation distribution set and a given one ofthe terminal port circuits 110-114, or a unique mappingbetween the beams 120-124 and the terminal port circuits110-114. However, in many embodiments, the beamformingnetwork 102 is designed such that each of the major beams

45 120-124 of the characteristic antenna radiation distributionset is associated with only one of the terminal port circuits110-114 (and hence with the corresponding informationsource contained therein), where "associated" means thatenergy received over that beam is predominantly directed to

50 the one associated port, and by reciprocity of the beamform-ing network 102 and the array of antennas 101, electromag-netic energy transmitted into that port is radiated predomi-nantly through only the one associated beam of thecharacteristic set of antenna radiation distribution patterns. It

55 is further noted that, while beamforming network 102 mayfocus or direct the received electromagnetic radiation to aselected one or more terminal ports 103/terminal port cir-cuits 110-114/information sources, it may occur that (someof) the non-selected, or non-preferred, one(s) of the terminal

60 ports 103/terminal port circuits 110-114/information sourcesalso receive sufficient signal power to permit response to theinterrogator due to the well-known fact that the directivity orfocusing quality of beamforming networks is finite, as wellas to unintended scattering that occurs in beamforming

65 networks. The likelihood of occurrences of non-selected, ornon-preferred, terminal ports 103/terminal port circuits 110-114/information sources receiving sufficient signal power to

US 9,715,609 B19

permit response to the interrogator is likely to increase insituations in which the RE link is exceptionally strong, suchas when the range between the interrogator and tag is veryclose or when the interrogator is transmitting a much higherlevel of power than is needed to permit communication withonly the selected, or preferred, terminal ports 103/terminalport circuits 110-114/information sources.Each one of the terminal port circuits 110-114 includes an

information source (illustrated in FIGS. 2-4) that, afterreceiving an incident signal (i.e., a signal directed thereto bythe beamforming network 102), transmits a modulated orencoded form of the incident signal back into the beam-forming network 102, the modulated or encoded signalcontaining information. Due to reciprocity, the beamformingnetwork 102 redistributes the encoded or modulated signalpower back to the antennas 101 with relative time delayssuch that the signal is transmitted back at the angle ofincidence (at which the signal was initially received) and inthe direction opposite the direction from which the signalinitially arrived at the RFID tag 100, that is, in the approxi-mate direction of the interrogator that initially sent the signalto the RFID tag 100. (The "direction from which the signalinitially arrived at the RFID tag 100" may be thought of interms of a vector oriented at the angle of incidence anddirected away from the interrogator and toward the tag(compare signal 235 in FIG. 5, discussed below) and "thedirection opposite the direction from which the signal ini-tially arrived at the RFID tag 100" may be thought of interms of a vector oriented at the same angle and directedaway from the tag and toward the interrogator (comparesignal 236 in FIG. 6, discussed below). In this regard, theresponse from each one of the terminal port circuits 110-114is radiated back to the interrogator according to the fixedantenna radiation distribution pattern associated with therespective one of the terminal port circuits 110-114. Theinterrogator may then receive this response signal (electro-magnetic radiation) that has been transmitted back to theinterrogator by the RFID tag 100. Each information sourcemay include an identification code. In at least one embodi-ment, each information source is an RFID integrated circuitcapable of responding with such identification code identi-fying the particular information source (i.e., capable ofencoding the response signal with such identification code).In at least one embodiment, each information sourceincludes an RFID integrated circuit and a sensor and iscapable of responding (i.e., encoding the response signal)with such an identification code and sensor telemetry. In atleast one embodiment, each information source includes aSAW RFID tag (inherently integrated with a sensor modal-ity) that encodes the response signal with such an identifi-cation code and, optionally, sensor telemetry. The interro-gator may be associated with a mapping between theidentification codes of the information sources and angles atwhich the responses are transmitted by the RFID tag. Theinterrogator may also be associated with logic for deriving,from the response signal, information pertaining to a posi-tion and/or an orientation of the interrogator and/or tag, asdescribed in fuller detail below.As will be understood from the above, the particular

information sources (or particular terminal port circuits110-114) to which a given incoming signal 130 (signal 130arriving at the tag 100) is directed by the beamformingnetwork 102 may be determined by (selected in accordancewith) the angle of incidence 109 of the incoming signal 130.Also, the information sources to which a given incomingsignal 130 is directed may be the information sources thatrespond to the incoming signal, sending a response to the

10incoming signal 130 back to the interrogator. Thus, theparticular information sources that respond to the incomingsignal 130 may also be determined by (selected in accor-dance with) the angle of incidence 109 of the incoming

5 signal 130. Thus, the response signal received by the inter-rogator from the RFID tag may include (i.e., be encodedwith) one or more identification codes identifying the par-ticular information source(s) to which the initial signal(transmitted by the interrogator to the RFID tag 100) was

io directed and from which the response (from tag 100 tointerrogator) was transmitted. In this sense the responsesignal may be based on the particular information sources towhich the received signal was directed by the beamformingnetwork 102. As will be understood, the response signal may

15 depend on the angle of incidence 109 of the incoming signaland on the design of the beamforming network 102.The design of beamforming networks will now be

described. Typically, a beamforming network is designed toimplement, in conjunction with attached antennas, a fixed

20 set of characteristic beams such as beams 120, 121,122, 123and 124, which in FIG. 1 are shown superimposed uponCartesian coordinate system 108. The set of characteristicbeams, or radiation distribution pattern, is determined by thedesign of the antennas, the locations of the antennas 101, and

25 the design of the beamforming network 102. As noted, FIG.1 is schematic, and those skilled in the art now havingbenefit of this disclosure will understand that in reality beampatterns may have additional side lobes, for example. More-over, in at least one embodiment, the beamformer 102 and

30 the spacing between antennas 101 are designed such that theantenna radiation distribution pattern associated with one ormore of the terminal ports 103/terminal port circuits 110-114exhibits multiple main lobes or beams, such as are com-monly referred to as grating lobes in the art of antenna

35 arrays. In at least one embodiment, the antennas 101 arecollinear, although this need not (but may) be the case inother embodiments. Each of the terminal ports 103 (andcorresponding terminal port circuit and information source)may be associated with one or more of the characteristic

4o beams 120-124. In this disclosure, the association of termi-nal ports 103 and beams 120-124 is intended to imply thatan RE excitation at a specific terminal port 103 producesradiation predominantly through the one or more associatedones of the characteristic beams 120-124. For example, in

45 one embodiment consistent with FIG. 1, terminal port circuit110 (and corresponding information source) may be asso-ciated uniquely with characteristic beam 120, terminal portcircuit 111 (and corresponding information source) may beassociated uniquely with beam 121, terminal port circuit 112

50 (and corresponding information source) may be associateduniquely with beam 122, terminal port circuit 113 (andcorresponding information source) may be associateduniquely with beam 123, and terminal port circuit 114 (andcorresponding information source) may be associated

55 uniquely with beam 124. (It is noted that in such one-to-oneassociation of characteristic beams with terminal port cir-cuits, the pairing of the characteristic beams and the terminalport circuits need not accord with their left-to-right orright-to-left ordering, e.g., beam 120 could be associated

60 with a terminal port circuit other than 110, etc.) Sincereciprocity applies to this passive beamforming network 102and the attached antennas 101, radiation received in aspecific direction will result in the beamforming network102 directing the received power toward the particular ones

65 of the terminal ports 103 that are associated with the one ormore of the beams 120-124 that are directed in that specificdirection. The design of the characteristic beam set of the

US 9,715,609 B111

beamforming network 102 permits infinite degrees of free-dom with respect to the primary direction and spacing of thebeams 120-124, in addition to infinite degrees of freedomwith respect to the coupling of the beams 120-124 to specificones of the terminal ports 103/terminal port circuits 110-114,and with respect to the number of beams and antenna ports.Such functionality of beamforming networks is well knownto those skilled in the art now having benefit of thisdisclosure.As also seen in FIG. 1, beam overlap can vary. For

example, beam 122 is depicted as having less overlap withbeams 121 and 123 as compared to the overlap betweenbeams 120 and 121 and to the overlap between beams 123and 124. In at least one embodiment, the beamformingnetwork 102 is designed such that the beams overlap sufli-ciently that the beamforming RFID tag 100 is capable ofcommunicating with an interrogator over the entire range ofangles covered by the characteristic beam set. In FIG. 1, thisrange would include the entire span from the beam center ofbeam 120 to the beam center of beam 124, through all thebeams between beams 120 and 124, in addition to the spansfrom the beam centers of beams 120 and 124 to the respec-tive limiting angles on the outside of beams 120 and 124,where "limiting angle" is defined as the angle at which theminimum antenna gain required to permit the communica-tion link between the interrogator and the beamformingRFID tag 100 is obtained. (The term "limiting angle" neednot be restricted in use to beams at the extremes of a set ofbeams, but may be applied to other beams, for example, inthe case of beams that do not sufficiently overlap to providefor continuous coverage.) It is noted that the "limiting angle"is dependent upon several parameters of the link between theinterrogator and the tag 100, including but not limited to thetransmit power of the interrogator and the propagationenvironment surrounding the interrogator and the tag 100.When an incident signal arrives at an angle at which twobeams intersect, within (inside) the limiting angles of bothbeams, the terminal ports 103 associated with both beamsmay receive the incoming power, and likewise the signalreturned from both terminal ports 103 may be reradiated atsubstantially the same angle on the same two beams. Itshould be noted that the overlap of beams and the distribu-tion of incoming power to more than one terminal port, andhence to more than one information source, does not nec-essarily lead to simultaneous transmission from each of thereceiving terminal ports and information sources. In fact, inat least one embodiment, the information sources compriseRFID integrated circuits that avoid tag collisions (interfer-ence between simultaneous tag transmissions) through tim-ing of tag responses dictated by a communication protocolsuch as the EPCglobal Class 1 Generation 2 UHF protocol.In such a protocol, the RFID integrated circuits may besingulated through a protocol known as an "Aloha" proce-dure in which only one tag responds at a time.

It will readily be recognized by those skilled in the art ofbeamforming networks, now having benefit of this disclo-sure, that there are a number of types of beamformingnetworks that could be used to implement a beamformingnetwork 102 for application as described herein for a beam-forming RFID tag 100. For example, in at least one embodi-ment, the beamforming network 102 could be a microwavelens. The design of the microwave lens could be any of anumber of well known microwave lens designs. Forexample, in at least one embodiment the microwave lenscould be a Rotman lens, as described, for example, in "WideAngle Microwave Lens for Line Source Applications" by W.Rotman and R. Turner (IEEE Transactions on Antennas and

12Propagation, vol. 11, issue 6, 1963, pp. 623-632) or inPhased Array Antennas by A. K. Bhattacharyya (Wiley-Interscience, ISBN-13: 978-0-471-72757-6, 2006, pp. 379-415), or any of the microwave lens designs derivative of the

5 Rotman lens, as described, for example, in the aforemen-tioned Phased Array Antennas (pp. 379-415), in "Procedurefor correct refocusing of the Rotman lens according toSnell's law" by D. R. Gagnon (IEEE Transactions onAntennas and Propagation, vol. 37, March 1989, pp. 390-

io 392), or in "Comparison of the Performance of the RotmanType Lenses Obtained by Different Design Approaches" byP. K. Singhal and R. D. Gupta (TENCON 99, Proceedingsof the IEEE Region 10 Conference, vol. 1, 1999, pp.738-741). In at least one embodiment, the microwave lens

15 could be a lens following design procedures outlined in theaforementioned Phased Array Antennas (pp. 379-415) or theaforementioned "Procedure for correct refocusing of theRotman lens according to Snell's law" (pp. 390-392). In atleast one embodiment, the lens could be a derivative of the

20 Rotman lens such that the antenna ports and beam ports areinterspersed around a circular region to create a beamform-ing network capable of providing coverage over 360degrees, as described in the aforementioned "Comparison ofthe Performance of the Rotman Type Lenses Obtained by

25 Different Design Approaches" (pp. 738-741). In at least oneembodiment, the microwave lens could be a Luneberg lens,or a derivative thereof, as described in "Fan-Beam Milli-meter-Wave Antenna Design Based on the CylindricalLuneberg Lens" by X. Wu and J. Lauren (IEEE Transactions

30 on Antennas and Propagation, vol. 55, no. 8, August 2007,pp. 2147-2156). In at least one embodiment, the beamform-ing network could be formed from power dividers/combin-ers, waveguides, and phase shifters, or the beamformingnetwork could be a derivative of such a beamforming

35 network. In at least one embodiment the beamformingnetwork could be formed from hybrid couplers, waveguides,and phase shifters, or the beamforming network could be aderivative of such a beamforming network. In at least oneembodiment, the beamforming network could be a Butler

40 matrix, as described in the aforementioned Phased ArrayAntennas (pp. 379-415), or a derivative thereof. In at leastone embodiment, the beamforming network could be a Blassmatrix, as described in the aforementioned Phased ArrayAntennas (pp. 379-415), or a derivative thereof. In at least

45 one embodiment, the beamforming network could be aGhent lens, or a derivative thereof, as described in BritishProvisional Patent Specification No. 25926/56 ("Improve-ments in or Relating to Electromagnetic-Wave Lens andMirror Systems," S. S. D. Jones, H. Ghent, and A. A. L.

5o Browne, August, 1956). All of the documents cited in thisparagraph are hereby incorporated herein by reference.

It is further recognized by and familiar to those skilled inthe art, now having benefit of this disclosure, that theselection of the beamforming network might impose certain

55 constraints. For example, a Butler matrix is more easilyimplemented if the number of antenna ports is 2 to the powerm, where m is a positive integer. The Butler matrix can alsobe designed such that the beams are orthogonal, as is wellknown in the art, as described in the aforementioned Phased

60 Array Antennas (pp. 379-415). It should be noted that theexample shown in FIG. 1 is one of many possible beam-forming RFID tag implementations, and that certain selec-tions of beamforming networks might impose constraintsthat might not be consistent with the operation or number or

65 placement of beams and ports as shown in FIG. 1. Forexample, beamforming networks created as a Butler matrix,as described in the aforementioned Phased Array Antennas

US 9,715,609 B113

(pp. 379-415), are readily implemented with an even numberof antenna ports and terminal ports, although other configu-rations are possible.

Terminal port circuits 110-114 may be of varying types,some of which are illustrated in FIGS. 2-4, description ofwhich is provided after the general description immediatelyfollowing. Each one of terminal port circuits 110-114 mayinclude an RE interface (terminal port circuit interface) tothe corresponding terminal port, and an RE distributioncircuit connected to the RE interface and also connected toone or more information sources. The RE distribution circuitmay be, for example, an RE power divider or a distributedwaveguide. The information sources may include RFIDintegrated circuits or SAW circuits and may include one ormore sensors of one or more types. The RFID integratedcircuit may be attached to the RE interface and include anon-board memory. The RFID integrated circuit may beattached to a data acquisition unit, with one or more sensorsattached to a data acquisition unit. In this case, the dataacquisition unit may sample one or more of the attachedsensors and provide the sensor sample and unique sensorsource identification to the RFID integrated circuit, and theRFID integrated circuit may store each sensor sample andunique sensor source identification on the on-board memory,and the RFID integrated circuit may communicate with theinterrogator to provide each sensor sample and associatedsensor identification number to a processor connected to theinterrogator. The RFID integrated circuit may be powered byrectifying the RE signal transmitted by the interrogator. TheRFID integrated circuit may be compliant with one or moreof the EPCglobal RFID standards. In some embodiments, allthe terminal port circuits 110-114 may be the same such thatthe signal transmitted by the tag is characterized by a singleidentification code.

In some embodiments the information sources includeRFID integrated circuits. In other embodiments, the infor-mation sources include SAW circuits. In still other embodi-ments, some information sources include RFID integratedcircuits and others include SAW circuits. The informationsources may also include one or more sensors of one or moretypes (e.g., modalities). The information sources may bepowered by a battery and capable of responding to aninterrogation signal. The information sources may periodi-cally transmit a signal containing a unique identification.Such signal may include sensor telemetry. Such periodictransmission may occur in the absence of any signal trans-mitted by an interrogator to the tag.One type of the terminal port circuits 110-114 is shown in

FIG. 2 according to at least one embodiment. Although theterminal port circuit illustrated in FIG. 2 is assigned refer-ence numeral 110a, it may be thought of as representative ofany or all of the terminal port circuits 110-114 in RFID tag100, as all of the terminal port circuits 110-114 may (butneed not) be of the same type. Terminal port circuit 110a isa parallel RE terminal port circuit. Terminal port circuit 110ais connected to a terminal port 103 (shown in FIG. 1) ofbeamforming network 102 (shown in FIG. 1) via terminalport circuit interface 104. Terminal port circuit 110aincludes element 115a, which may be an RE power divider(or divider/combiner) or a hybrid coupler, and multipleinformation sources 116. A signal (referred to herein also asan "incident signal') received by terminal port circuit 110afrom beamforming network 102 via terminal port circuitinterface 104 is distributed through RE power divider orhybrid coupler 115a to information sources 116. Each infor-mation source 116 includes at least one RFID source (notshown), such as an RFID integrated circuit or a SAW circuit,

14and, in some embodiments, one or more sensors (notshown). According to at least one embodiment, each infor-mation source 116 directs an encoded or modulated form ofthe incident signal back to the terminal port circuit interface

5 104 for transmission into the beamforming network 102 andback to the interrogator through the antennas 101 (shown inFIG. 1) attached to the beamforming network 102. In someembodiments, only one information source 116 responds atany given time, and the sequence of responses may be

io governed by the interrogator. For example, as mentionedabove, in the EPCglobal Class 1 Generation 2 protocol,compliant tag RFID integrated circuits only respond in turnas governed by the protocol. The encoded or modulatedsignal is encoded or modulated with information that

15 includes the identification code or information associatedwith the information source 116, and, in some embodiments,also sensor telemetry. Although terminal port circuit 110a isshown in FIG. 2 with an RE power divider/combiner or REcoupler 115a that distributes power four ways, in other

20 embodiments the coupling factor could be two or three or itcould be more than four.

Continuing to refer to FIG. 2, as discussed above, in someembodiments the information sources 116 include RFIDintegrated circuits, in other embodiments the information

25 sources 116 include SAW circuits, and in still other embodi-ments some information sources 116 include RFID inte-grated circuits and others include SAW circuits. Informationsources 116 may also include one or more sensors of varioustypes (e.g., modalities).

30 Terminal port circuit 110a shown in FIG. 2 represents oneexemplary type of terminal port circuits 110-114 of FIG. 1.FIG. 3 depicts terminal port circuit 110b, which representsan alternative exemplary type of terminal port circuits110-114 of FIG. 1, according to at least one embodiment. As

35 with terminal port circuit 110a, terminal port circuit 110b isconsidered representative of any or all of the terminal portcircuits 110-114 in RFID tag 100. Terminal port circuit 110bis connected to a terminal port 103 (shown in FIG. 1) ofbeamforming network 102 (shown in FIG. 1) via terminal

40 port circuit interface 104. Terminal port circuit 110bincludes an RFID integrated circuit communications section117 coupled to a data acquisition section 118, which in turnis coupled to one or more information sources 116. Eachinformation source 116 may include an RFID integrated

45 circuit and a sensor. According to at least one embodiment,the RFID integrated circuit communicates with the interro-gator (not shown) by alternately backscattering and receiv-ing the incident signal in order to return a modulated signal,as is well established in many forms of passive RFID tag

50 interrogation. In some embodiments, the RFID integratedcircuit communications section 117 is powered by rectifyingall or a portion of the incident RE signal, and the samerectified RE power is also used to power the data acquisitionsection 118 and the sensors. In some embodiments, the

55 rectified power is used to sustain only the function of theintegrated circuit communications section 117, and the dataacquisition 118 and sensors are powered independently by abattery or other power source. In some embodiments, ter-minal port circuit 110b may be implemented as a single

60 system on a chip (SoC) and deemed an RFID IC. In someembodiments, RFID communications section 117 may con-stitute an RFID IC and information source 116 may containa sensor.

Further to terminal port circuits 110a and 100b of FIGS.65 2 and 3, respectively, FIG. 4 depicts terminal port circuit

110c, which represents another alternative exemplary typeof terminal port circuits 110-114 of FIG. 1, according to at

US 9,715,609 B115

least one embodiment. As with terminal port circuits 110aand 110b, terminal port circuit 110c is representative of anyor all of the terminal port circuits 110-114 in RFID tag 100.Terminal port circuit 110c is connected to a terminal port103 (shown in FIG. 1) of beamforming network 102 (shownin FIG. 1) via terminal port circuit interface 104. Terminalport circuit 110c includes a waveguide circuit 115c andinformation sources 116 coupled to the waveguide circuit115c. For example, waveguide circuit 115c may be amicrostrip line with couple lines feeding the one or moreinformation sources 116. Alternatively, waveguide circuit115c might be a microstrip or stripline power divider thatcouples power to information sources 116. Other variants ofwaveguide circuit 115c are possible.FIGS. 5 and 6 are schematic illustrations depicting an

RFID system including an interrogator and at least oneRFID beamforming tag, according to some embodiments.The figures will be described in detail following a prelimi-nary background explanation. FIG. 5 depicts an act orprocess of receiving or reception, in which the interrogatortransmits electromagnetic radiation to the tag, the tag anten-nas receive the transmitted electromagnetic radiation, andthe tag beamformer directs the received radiation toward oneor more terminal port circuits/information sources. In thisregard, the information source may be receiving instructionsor commands from the interrogator, it may be writing datato memory on-board the integrated circuit, or it may berectifying the received electromagnetic energy to power theintegrated circuit of the information source. Alternatively,the on-board integrated circuit might be in a state that willreflect the received power upon arrival at the on-boardintegrated circuit. FIG. 6 depicts an act or process oftransmission, in which a modulated or encoded form of theelectromagnetic radiation received from the interrogator istransmitted back to the interrogator by the tag, as describedbelow. In the case of a system using RFID tags havingintegrated circuits, the signals sent by the interrogator maybe continuous wave (CW) signals for a duration of time. Thetypical response of an RFID tag having an integrated circuit,when such a CW signal impinges on the RFID tag, will nowbe described. Specifically, RFID tags with integrated circuitstypically respond by modulating the CW signal transmittedby the interrogator, where the modulation is achieved byalternating periods of (1) reflecting the CW signal back tothe interrogator and (2) absorbing the energy of the CWsignal. Modulation of the received signal may involvemodification not only of its amplitude but also of its phase.During the periods of absorption, less than 100% of theenergy may be absorbed; accordingly, some of the electro-magnetic radiation, ordinarily a small portion, may bereflected to the interrogator during the periods of absorption.In addition, during the periods of absorption, rectification ofthe absorbed energy may occur, the rectified energy beingused to power and sustain the integrated circuit. In someRFID protocols, it is also possible that, during the periods ofreflection, a small amount of power is absorbed to continuesupporting the integrated circuit. FIG. 6 depicts an exampleof a period (1) during which the received signal is beingreflected back toward the interrogator (in theory FIG. 6could also represent period (2) during which the energy ofthe signal is absorbed, assuming the absorption is not 100%,so that a portion of the signal is reflected to the interrogator).In sum, during periods (1), namely, reflection, most or all ofthe power received by the tag from the interrogator istransmitted back to the interrogator, while during periods(2), namely, absorption, little or none of the power receivedby the tag from the interrogator is transmitted back to the

16interrogator. It should be noted that reception (shown in FIG.5) may, and often does, occur simultaneously with trans-mission (namely, alternating periods of reflection, shown inFIG. 6, and absorption). The process of transmission/modu-

5 lation varies across different RFID protocols. The sequenceaccording to which the tag is alternately absorbing andreflecting power, and the durations of these alternatingprocesses, determine the information with which the signalis modulated or encoded. In contrast to RFID integrated

io circuits, other types of RFID information sources, such asSAW circuits, respond by passively modulating or encodingthe received electromagnetic signal without rectification. InSAW-based RFID, signals transmitted by the interrogatorare typically not CW signals, and are often modulated RE

15 pulses. Regardless, the beamforming RFID tag is compatiblewith the wide range of modulation schemes in practice withboth SAW and IC-based systems. In the context of aSAW-based RFID system, FIG. 5 represents the reception ofan RE pulse by the beamforming tag, and FIG. 6 represents

20 one of a plurality of RE pulses being reflected from the SAWdevice in response to the received pulse. Thus, althoughFIGS. 5 and 6 illustrate distinct processes of receiving andtransmitting electromagnetic power, those of ordinary skillin the art, now having benefit of this disclosure, will recog-

25 nize that the beamforming RFID tag beamformers andantennas, as passive linear devices, support simultaneousreception and transmission of electromagnetic radiation. Tobe sure, the information sources may be capable of exclusivereception and exclusive transmission.

30 Turning now to FIG. 5 more closely, RFID interrogator225 is coupled to a processor 230 and to an antenna 220.RFID interrogator 225 radiates an RFID signal 235, viaantenna 220, in the direction of beamforming RFID tag 202.Tag 202 includes a beamforming network 240, antennas 201

35 coupled to antenna ports 207 of beamforming network 240,and terminal port circuits 231, 232, 233 and 234 coupledrespectively to terminal ports 203 of beamforming network240. Each of terminal port circuits 231, 232, 233 and 234includes at least one information source. Each information

40 source includes an RFID source, such as an RFID integratedcircuit or a SAW circuit, and optionally one or more sensors.As described with respect to FIG. 1, the numbers of antennas201, antenna ports 207, terminal ports 203, and terminal portcircuits 231-234 may vary from that shown in FIGS. 5 and

45 6.With continued reference to FIG. 5, RFID signal 235 is

received by antennas 201 of tag 202 at an angle 210a definedrelative to Cartesian coordinate system or frame of reference214. The RFID signal received by the antennas 201 is

50 transmitted to the beamforming network 240, and the beam-forming network 240 directs the inputs from the antennas201 so that they add at least substantially in phase at theterminal port(s) 203 that correspond(s) to the incident angle210a. Thus, the incident RFID signal is effectively distrib-

55 uted to a selected one or more of the terminal ports 203,specifically the terminal port(s) 203 corresponding to inci-dent angle 210a. At each selected terminal port 203, acorresponding one of the terminal port circuits 231-234receives the power of the incident signal. (As discussed

6o above with reference to FIG. 1, non-selected ones of termi-nal port(s) 203/terminal port circuits 231-234/informationsources may receive some signal power, due to the finitedirectivity or focusing quality of beamforming networksand/or to unintended scattering, although FIG. 5 does not

65 illustrate signal power being received by non-selected ter-minal port(s) 203/terminal port circuits 231-234/informationsources.)

US 9,715,609 B117

In the case illustrated in FIG. 5, the angle 210a isassociated with a peak 211 of the characteristic beam 212 ofthe beamforming RFID tag. In this case, the inputs from theantennas 201 arrive predominantly in-phase at only oneterminal port 203 of the beamforming network 240; as 5shown in FIG. 5, this terminal port 203 is associated withterminal port circuit 234 having information code ID4.Although only one characteristic beam 212 (and hence onepeak 211) is shown in FIG. 5, tag 202 may have more thanone characteristic beam 212, each having a peak 211. l0

FIG. 6 depicts the system (components) of FIG. 5 in aprocess of transmission. As mentioned, in the process ofreception (FIG. 5), the RE power added in phase predomi-nantly at one terminal port 203 and entered the correspond- 15ing terminal port circuit 234. In FIG. 6, terminal port circuit234 directs a modulated or encoded form of the received REenergy back into the beamforming network 240. As dis-cussed above, the process of encoding and/or modulating thereceived signal may result in a substantially reduced or 20insignificant amount of energy being transmitted back to theinterrogator during certain finite periods of time. For infor-mation sources comprising RFID integrated circuits, duringthose periods of time in which a substantially reduced orinsignificant amount of energy is transmitted back to the 25interrogator, the energy that is not transmitted back butrather absorbed may be rectified and used to power theintegrated circuit. Due to reciprocity of the beamformingnetwork 240, the antennas 201, and any interconnectingwaveguides (not shown in FIG. 6), the beamforming net- 30work 240 distributes the modulated or encoded signal to thearray of antennas 201 with relative time delays between therespective portions of the signal reaching successive ones ofthe antennas 201 such that the resulting transmitted radiation236 is focused approximately in the direction of the inter- 35rogator 225 (that is, along angle 210a at which the powerarrived) or, expressed more simply, such that the signal 236is transmitted back approximately in the direction of theinterrogator 225.

Although the beamforming RFID tag system is depicted 40in FIGS. 5 and 6 with only a single beam and is describedas performing two distinct processes for convenience ofdescription, typically the beamforming RFID tag 202 oper-ates continuously with multiple beams and may perform theprocesses of FIGS. 5 and 6 (reception and transmission) 45simultaneously. In one or more embodiments, the informa-tion sources each comprise a distinct integrated circuit RFIDsource, such as an RFID integrated circuit or a SAW circuit,with a unique identification such that each RFID source iscapable of responding to a different interrogator such as 50prescribed by an RFID protocol standard known as theEPCglobal Class 1 Generation 2 UHF standard. Forexample, an RFID integrated circuit within terminal portcircuit 234 with identification ID4 is able to communicatewith an interrogator 225 while simultaneously an RFID 55integrated circuit within terminal port circuit 231 withidentification IDI is able to communicate with a differentinterrogator (not shown).

In this regard, it should be noted that the orientation ofbeam 212 is a characteristic of the device. While in FIGS. 5 60and 6, beam 212 is aligned with interrogator 225, if inter-rogator 225 moves the orientation of beam 212 will notchange. Thus, as stated, beamforming RFID tag 202 typi-cally operates with multiple beams, as better illustrated, e.g.,in FIG. 1. Multiple beams thus permit coverage over a larger 65continuous angular range than would a single beam, per-mitting communication between tag and interrogator while

18interrogator is within this larger range (discussed also withreference to FIGS. 8 and 9 below).

With continued reference to FIGS. 5 and 6, the shape ofthe beamforming network depicted therein has the generalcharacteristic outline of a Rotman lens with five antennaports and four terminal ports. However, the choice of fiveantenna ports and four terminal ports is merely for the sakeof illustration, and as noted, a different number and/orplacement of antenna ports or terminal ports is possible. Forexample, a terminal port along the center axis of the Rotmanlens, as well as two off-axis points, is often associated withminimal aberration, although such a central axis terminalport is not shown at this location in FIGS. 5 and 6. Thenumber of antenna ports may but is not required to match thenumber of terminal ports. Generally speaking, the Rotmanlens has M antenna elements (antennas) along a linear axisknown as an outer contour (not shown in FIGS. 5 and 6)connected to a two-dimensional propagation medium, suchas parallel plates, by M waveguides that are each of aspecified electrical length. The M waveguides feed thetwo-dimensional propagation medium at antenna ports thatlie on a so-called inner contour (not shown in FIGS. 5 and6) (the M waveguides connect the antennas to the antennaports). The opposing boundary (shown as the "left" side inFIGS. 5 and 6) of the propagation medium is a so-calledfocal arc, along which N input ports (terminal ports) lie.Each input port is a focal point for radiation traversing thepropagation medium. There are only three optimal points onthe focal arc at which the theoretical aberration is zero, butthe aberration can be made acceptably low for many appli-cations. The electrical length of the M waveguides, the x-ycoordinates of each antenna port on the inner contour, andthe x-y coordinates of each input port on the focal arc areselected such that the radiation arriving from an incidentangle (e.g., 210a in FIG. 5) adds in phase, predominantly, inone region of the focal arc and is received by one or moreinput ports in that region. As shown in FIG. 5, the Rotmanlens is configured as an RFID retro-reflector tag with radia-tion along the direction associated with ID4. As shown, thisdevice constitutes an RFID tag device that issues fouridentification codes, possibly unique, associated with fourdifferent beam positions. If the beams are sufficientlyspaced, then it is possible that the device returns only onebeam and one associated identification. If two or morebeams overlap (e.g., as in FIG. 7, described below), it ispossible that multiple beams are reflected along with themultiple associated identifications. Signal strengths associ-ated with each of the beam positions can be used to refine thebearing estimate. In the event that multiple informationsources respond to the interrogator, anti-collision mecha-nisms that prevent interference are provided by the RFIDprotocol medium access control. For example, in manySAW RFID systems, anti-collision is obtained by usingorthogonal codes for the SAW RFID tags. In many IC-basedRFID systems, the tags respond in a so-called "aloha"protocol in which only one integrated circuit responds at anytime.

Notwithstanding the general characteristics of the Rotmanlens, the intent of FIGS. 5 and 6 is to illustrate a generalfunctionality of the beamforming RFID tag that is notlimited to the selection of any particular beamformingnetwork. As stated previously, the selection of a givenbeamforming network bestows certain characteristics thatmight not be achievable with a different beamformingnetwork. For example, the beam orthogonality readilyachieved with a Butler matrix beamforming network might

US 9,715,609 B119

not be as easily achieved with some Rotman lens beam-forming network implementations.

FIG. 7 is a schematic illustration depicting the system ofFIG. 5 but a different scenario, in accordance with at leastone embodiment. For the sake of convenience in describing 5this example, FIG. 7 shows two characteristic beams 212and 215, which overlap one another to a small degree, ratherthan the single beam 212 illustrated in FIG. 5. As notedabove, in practice, both the systems shown in FIGS. 5 and7 would typically operate with multiple beams, which may iocollectively span a larger continuous angular range. In FIG.7, the incoming electromagnetic radiation or incident signal236 (also denoted by dashed line 217) arrives at an angle ofincidence 210b (defined with respect to Cartesian coordinatesystem 214), which falls within the edges of the two beams 15212, 215, in contrast to angle of incidence 210a that falls ator near the peak 211 of a single beam 212 as shown in FIG.5. At this angle of incidence 210b, the focal point of thebeamforming network 240 is nearest to and in between thetwo terminal ports 203 corresponding to terminal port cir- 20cuits 233 and 234 and as a result the received power from theantennas 201 adds predominantly in phase at those twoterminal ports 203. The two terminal port circuits 233 and234 are thus associated with characteristic beams 212 and215, respectively. It will be understood that although FIG. 7 25(like FIG. 5) illustrates a process of reception, a process oftransmission (like FIG. 6) also occurs in the system of FIG.7, that is, the information source in each of the two terminalports 233, 234 transmits a modulated or encoded form of thereceived signal back into the beamforming network 240 30such that the respective modulated or encoded signal isreradiated through the respective one of the characteristicbeams 212, 215 associated with the respective terminal port.For example, if (as indicated) characteristic beam 212 isassociated with terminal port circuit 233, a modulated or 35encoded form of the signal reaching the terminal port circuit233 information source would be reradiated in the directionof beam 212 such that power would be returned predomi-nantly in the direction of the interrogator 225 at an effectiveantenna gain level as established by the angle 210b relative 40to the peak 211 of beam 212. Similarly, where characteristicbeam 215 is associated with terminal port circuit 234, amodulated or encoded form of the signal reaching theterminal port circuit 234 information source would be rera-diated in the direction of beam 215 such that power would 45be returned predominantly in the direction of the interroga-tor 225 at an effective antenna gain level as established bythe angle 210b relative to the peak 216 of beam 215. Themodulated or encoded signal would be modulated orencoded with the information of the one or more RFID 50sources (such as RFID integrated circuits or SAW circuits)of the respective terminal port circuit (233 or 234) and, inone or more embodiments, with sensor telemetry. The signalreturned to the interrogator 225 by the beamforming tag 202is generally not in the direction of the peak of the beam 55unless the angle 210b happens to align with the angle of thebeam peak. In general, it is possible that more than twobeams will overlap such that an interrogator will address andcommunicate with more than two terminal port circuits. Asdescribed above, the process of modulating or encoding may 60result in a substantially negligible level of power beingdirected back into the beamforming network over certaindelimited periods of time.FIG. 8 is a schematic illustration of an RFID system 300

including an RFID beamforming tag 307 attached to one 65facet 304 of a multi-faceted structure 301, and multipleinterrogators (not illustrated in FIG. 8) mounted on respec-

20tive mobile platforms 310, 315, in accordance with at leastone embodiment. A first characteristic beam 302 of the tag307 oriented at an upper angle provides a first identificationcode to a first mobile platform 310 located at an upper anglerelative to the facet 304 having the tag 307, and a secondcharacteristic beam 305 of the tag 307 oriented at a lowerangle provides a second identification code to a secondmobile platform 315 located at a lower angle relative to thefacet 304 having the tag 307. As with FIGS. 5-7, so too inFIG. 8, to simplify description of the example, two charac-teristic beams are shown whereas in practice multiplebeams, which may collectively span a larger continuousangular range, would typically be used. In this way, mobileplatforms at any angular location relative to the tag withinthe range may conduct RFID communication with the tag.Also, in some embodiments, multi-faceted structure 301may have multiple tags 307 associated respectively withmultiple facets 304. This type of structure may serve, forexample, to further increase the continuous angular range ofcoverage.FIG. 8 shows the tag transmitting a modulated or encoded

signal back to the interrogator. The reception of the elec-tromagnetic power (sent from the interrogator) by the tag isassumed although not shown in FIG. 8. Thus, the modulatedsignals 303 and 306 shown in FIG. 8 are assumed to be fullymodulated or encoded signals that may be characterized byhaving substantially little or no power over one or more timeperiods for certain types of amplitude modulation. Thus, asseen in FIG. 8, beamforming RFID tag 307 returns twosignals 303 and 306 along two different angles associatedwith characteristic beams 302 and 305, respectively, inresponse to two interrogation signals (not shown) that werepreviously broadcast by interrogators (not shown) located onthe two aircrafts (mobile platforms) 310 and 315, respec-tively, and received by the tag 307. The signal 303 withmodulated identification broadcast through beam 302 isidentified by a processor (not shown) coupled to the inter-rogator on aircraft 310 as being associated with the specificbeam 302 belonging to beamforming RFID tag 307. Simi-larly, a processor (not shown) connected to the interrogatoron aircraft 315 receives returned signal 306 with modulatedidentification that was broadcast through beam 305 andidentifies signal 306 as being associated with beam 305. Itis assumed that the position and orientation of beamformingRFID tag 307, as well as the angles associated with each ofthe beams comprising the characteristic beam set of beam-forming RFID tag 307, all constitute information establisheda priori and available to each of the processors coupled to theinterrogators on the aircraft 310, 315, respectively, in orderthat each of the processors can use the respective receivedmodulated identification to determine the approach angle ofthe respective aircraft. It is also possible that the aircraft 310,315 receive through wireless communications (not shown)the location and orientation of the constellation of one ormore beamforming tags 307 (only one shown) from adatabase or repository (not shown). Thus, based on one ormore signals returned from the constellation of one or morebeamforming tags 307 and on information established andmade available a priori to the software program running onthe processors, or information received real-time or near-realtime through wireless communication, the processor is ableto determine the approach angle. When the beams within thefixed characteristic antenna radiation distribution pattern setof a beamforming RFID tag 307 overlap such that theinterrogator in the aircraft receives information from morethan one information source (as described with reference toFIG. 7 above), the received signal strength indication (RSSI)

US 9,715,609 B121

associated with each information source can be used toestimate the angle of incident radiation with greater accu-racy and finer resolution. Of course, the processor may alsodetermine range (distance) and range-rate (speed) informa-tion, based on the information contained in the returnedsignal 306 together with the aforementioned informationknown a priori. In addition, it will be understood that just asinformation pertaining to position and orientation of theinterrogator (or its platform, aircraft) relative to the tag maybe determined by the processor, so too information pertain-ing to position and orientation of the tag (or object bearingthe tag) relative to the interrogator may be determined by theprocessor, based likewise on the returned signal 306 and theaforementioned information known a priori, since the infor-mation pertaining to position and orientation of the tag isequivalent to (for example, obtainable by simple transfor-mation from) the information pertaining to position andorientation of the interrogator. (The tag may be referred toas an entity that transmits a response to electromagneticradiation it receives, e.g., from the interrogator, and theinterrogator may be referred to as an entity that receives theresponse to the electromagnetic radiation received by thetag, the response, e.g., being transmitted by the tag.)Although FIG. 8 depicts the RFID system 300 utilizingbeamforming RFID tag 307 as a navigation aid to aircraft310, 315, the concept is directly applicable to navigationaids for other mobile platforms such as automobiles, pedes-trians, bicycle riders, etc. equipped with RFID interrogatorshaving connectivity to one or more processors.

FIG. 9 is a schematic illustration of an RFID system 500including a constellation of (multiple) beamforming RFIDtags 501 and one or more mobile platforms, in accordancewith at least one embodiment. Each tag 501 has a charac-teristic beam set 510. Mobile platforms) may include avehicle 520 or person 530, as illustrated for the sake of thisexample, or another type of platform, as described abovewith reference to FIG. 8. Each mobile platform is equippedwith an interrogator 525 (interrogator not shown for person530). The constellation of tags 501 may be used to assist innavigation and/or localization of the mobile platforms. Theterm "localization" refers to the determination of positionand/or orientation of the mobile platform. In some embodi-ments, the interrogators of mobile platforms 520, 530 are ofa type that uses broad-beam antennas such that signals maybe received from multiple (or all) beamforming RFID tags501 of the constellation. Processors (not shown) coupled tothe interrogators use the received signals together withinformation established a priori such as the position andorientation of each of the beamforming RFID tags 501 todetermine the angle of the mobile platform relative to eachof the beamforming RFID tags 501 and, using the deter-mined angles to each of the beamforming RFID tags 501, todetermine the position of the mobile platform relative to theconstellation of beamforming RFID tags 501. As part of thisprocess, as described above, the identification informationencoded in the received signal is used to identify theinformation source and associated beam from which thesignal was received.

With continued reference to FIG. 9, according to a first setof embodiments the interrogators initiate communicationwith the beamforming RFID tags by transmitting an REsignal to the tags, and in response the tags transmit returnsignals to the interrogators. In a second set of embodiments,the tags are active tags and send signals to the interrogators(which may be simply receivers) without such prior prompt-ing by the interrogators. In the second set of embodiments,each of the beamforming RFID tags may include a power

OWsource. For example, the terminal port circuit informationsources attached to the terminal ports of the beamformingRFID tags may be active radios (e.g., ultra-wideband radios)powered by batteries, the radios transmitting periodic pulses

5 containing identification information, and the interrogatorsmay be or include receivers that demodulate and decode theperiodic pulses. In some embodiments of the second set, theradios are attached to sensors and the periodic pulses containsensor telemetry in addition to identification information,

io such that the interrogator receivers decode the identificationand the sensor telemetry. While the embodiments describedin this disclosure with reference to figures other than FIG. 9are for the most part described as operating according to thefirst set of embodiments (i.e., two-way communication: tag

15 responds to signal transmitted by interrogator), it is ingeneral possible to adapt such embodiments to operateaccording to the second set of embodiments just described(i.e., one-way communication: tag sends signal to receiver;receiver does not send signal to tag).

20 Embodiments operating according to the second set ofembodiments (i.e., one-way communication: tag sends sig-nal to receiver; receiver does not send signal to tag) may befurther characterized as follows. As described heretofore, thesignal (electromagnetic radiation) sent from tag to receiver

25 may encode one or more identification codes, each identi-fication code identifying one of the plurality of informationsources, respectively. The one or more identification codesencoded in the signal may correspond to angular informationindicating an angle at which the signal is transmitted. The

30 transmitted signal may, due to the action of the beamformingnetwork, be distributed to the antennas with the relative timedelay of the signal to each antenna such that the combinedradiation power from the antennas is concentrated within anantenna beam directed over a predetermined angular range

35 according to the terminal port from which the transmittedsignal originated. The receiver may be associated with logicconfigured to derive, from the transmitted signal (e.g., fromthe identification codes encoded therein), information per-taining to a position of the receiver and/or an orientation of

40 the receiver. In this regard, a mapping between the identi-fication codes of the plurality of information sources andangles at which the responses are transmitted by the RFIDtag may be used. The RSSI may also be used.

FIG. 10 is a schematic illustration of a beamforming45 RFID tag 800, wherein the beamforming network 820 is a

Butler matrix, in accordance with at least one embodiment.(As mentioned above, a Butler matrix is described in PhasedArray Antennas by A. K. Bhattacharyya (pp. 379-415).)beamforming RFID tag 800 includes a Butler matrix beam-

50 forming network 820, antennas 861, 862, 863, and 864, eachattached to a corresponding antenna port 802 of the beam-forming network 820, and terminal port circuits 851, 852,853, and 854, each attached to a corresponding terminal port803 of the beam forming network 820. Each terminal port

55 circuit 851, 852, 853, and 854 includes at least one infor-mation source; in some embodiments, each terminal portcircuit also includes one or more sensors. In some embodi-ments, as further illustrated in FIG. 10, the Butler matrixbeamforming network 820 includes hybrid couplers 805

60 connected to antenna ports 802 on one side and connected tophase shifters 810 and 811 on the other side, and additionalhybrid couplers 805 connected to phase shifters 810 and 811on one side and to terminal ports 803 on the other side. Theformer hybrid couplers 805 (the pair closest to the antennas

65 ports 802) serve the function of power division for incomingsignals (signals received by the tag) and power combiningfor outgoing signals (signals being transmitted from the tag),

US 9,715,609 B123

while the latte