WO2004102735A2

WO2004102735A2 - Apparatus for and method of using a close-proximity antenna

Info

Publication number: WO2004102735A2
Application number: PCT/US2004/014396
Authority: WO
Inventors: Ronald A. Marino
Original assignee: Meadwestvaco Corporation
Priority date: 2003-05-09
Filing date: 2004-05-07
Publication date: 2004-11-25
Also published as: EP1668741A2; WO2004102735A3

Abstract

In accordance with an exemplary embodiment of the invention, an antenna structure (200) is provided having a “figure eight”-type geometry. Preferably, the “figure eight” antenna structure is a planar antenna having two center feed contacts (193A, 193B) which form a feed point for the antenna. The unique antenna structure has particular application in tag reader antenna systems for use in RFID (radio frequency identification) applications (13.56MHz) and the like. In accordance with an exemplary embodiment, multiple RF (radio frequency) antennae are utilized as part of an intelligent station to track items tagged with radio frequency identification (RFID) tags.

Description

APPARATUS FOR AND METHOD OF USING A CLOSE-PROXIMITY ANTENNA

[0001] This application claims the benefit of U.S. Provisional Application Nos. 60/469,024, filed May 9, 2003 ('024 application) and 60/479,846, filed June 20, 2003 ('846 application). This application is related to U.S. Patent Application No. 10/338,892 ('892 application), filed January 9, 2003, and U.S. Patent Application No. 10/348,941 ('941 application), where the '892 application claims the benefit of U.S. Provisional Application Nos. 60/346,388 ('388 application), filed January 9, 2002, and 60/350,023 ('023 application), filed January 23, 2002, where the '941 application is a continuation-in-part of the '892 application and claims the benefit of the '023 application. The disclosure of each of the '892, 941, '388, '023, '024 and '846 applications is expressly incorporated herein by reference in their respective entireties.

BACKGROUND

[0002] Radio frequency identification (RFID) systems typically use one or more reader antennae to send radio frequency (RF) signals to items tagged with RFID tags. The use of such RFID tags to identify an item or person is well known in the art. In response to the RF signals from a reader antenna, the RFID tags, when excited, produce a disturbance in the magnetic field (or electric field) that is detected by the reader antenna. Typically, such tags are passive tags that are excited or resonate in response to the RF signal from a reader antenna when the tags are within the detection range of the reader antenna.

[0003] The detection range of the RFID systems is typically limited by signal strength to short ranges, for example, frequently less than about one foot for

13.56 MHz systems. Therefore, portable reader units may be moved past a group of tagged items in order to detect all the tagged items, particularly where the tagged items are stored in a space significantly greater than the detection range of a stationary or fixed single reader antenna. Alternately, a large reader antenna with sufficient power and range to detect a larger number of tagged items may be used. However, such an antenna may be unwieldy and may increase the range of the radiated power beyond allowable limits. Furthermore, these reader antennae are often located in stores or other locations where space is at a premium and it is expensive and inconvenient to use such large reader antennae. In another possible solution, multiple small antennae may be used but such a configuration may be awkward to set up when space is at a premium and when wiring is preferred or required to be hidden.

[0004] Current RFID reader antennas are designed so that a maximum read range may be maintained between the antenna and associated tags, without running afoul of FCC limitations on radiated emissions. Often times, when tagged items are stacked, the read range of an antenna is impeded due to "masking" that occurs through the stacking. As a result, the masking limits the number of tags that an antenna may read through, and consequently affect the number of products that may be read. Furthermore, due to FCC limitations on radiated emissions, the reader antenna sizes cannot be adjusted to resolve such problems.

[0005] Resonant loop reader antenna systems are currently utilized in RFID applications, where numerous reader antennas are connected to a single reader. Each reader antenna may have its own tuning circuit that is used to match to the systems characteristic impedance. Use of multiple antennae (or components) has the drawback that multiple transmission cables are used to connect a reader unit to the multiple antennae and/or that the multiple antennae cannot be individually controlled when they are all connected by a single transmission cable to the reader unit.

SUMMARY

[0006] In accordance with an exemplary embodiment of the invention, an antenna structure is provided having a "figure eight"-type geometry. Preferably, the "figure eight" antenna structure is a planar antenna having two center feed contacts which form a feed point for the antenna. The unique antenna structure has particular application in tag reader antenna systems for use in RFID (radio frequency identification) applications (13.56 MHz) and the like. In accordance with an exemplary embodiment, multiple RF (radio frequency) antennae are utilized as part of an intelligent station to track items tagged with radio frequency identification (RFID) tags.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 illustrates an antenna structure having a "figure eight" geometry in accordance with an exemplary embodiment of the invention;

[0008] FIG. 2 illustrates a "backplane" antenna system in accordance with an exemplary embodiment of the invention for reading product tags;

[0009] FIG. 3A illustrates a first "shelf" configuration antenna system in accordance with an exemplary embodiment of the invention for reading product tags;

[0010] FIG. 3B illustrates a second "shelf" configuration antenna system in accordance with an exemplary embodiment of the invention for reading product tags; [0011] FIG. t ts a DIOCK αiagram illustrating an exemplary antenna system incorporating a lumped element impedance matching circuit in accordance with an exemplary embodiment of the invention;

[0012] FIG. 5 is a block diagram illustrating another exemplary antenna system incorporating coaxial cable impedance matching components in accordance with an exemplary embodiment of the invention;

[0013] FIG. 6 is a block diagram illustrating another exemplary antenna system incorporating primary and secondary controllers to select antenna in accordance with an exemplary embodiment of the invention;

[0014] FIG. 7 illustrates an electrical circuit for switching an RF signal into a group of antennae controlled by a secondary controller in accordance with an exemplary embodiment of the invention;

[0015] FIG. 8 illustrates an electrical circuit for switching an RF signal for an individual antenna in accordance with an exemplary embodiment of the invention;

[0016] FIG. 9 illustrates an electrical circuit for tuning an individual antenna in accordance with an exemplary embodiment of the invention;

[0017] FIG. 10 illustrates antenna loop assemblies for the antenna of FIG. 1, wherein the assemblies are incorporated into a housing in accordance with an exemplary embodiment of the invention;

[0018] FIG. 11 illustrates the back side of a display fixture showing certain circuitry components in accordance with an exemplary embodiment of the invention; [0019] FIG. 12 illustrates the front side of a display fixture in accordance with an exemplary embodiment of the invention;

[0020] FIG. 13 illustrates the wiring between circuit components of a backplane in accordance with an exemplary embodiment of the invention; and

[0021] FIGS. 14-17 illustrate block diagrams showing exemplary implementations of the RF connections between display fixtures in accordance with embodiments of the invention.

DETAILED DESCRIPTION

[0022] Preferred embodiments and applications of the invention will now be described. Other embodiments may be realized and changes may be made to the disclosed embodiments without departing from the spirit or scope of the invention. Although the preferred embodiments disclosed herein have been particularly described as applied to the field of RFID systems, it should be readily apparent that the invention may be embodied in any technology having the same or similar problems.

[0023] FIG. 1 illustrates an antenna structure 200 having a "figure eight"-type geometry in accordance with an embodiment of the invention. The antenna 200 has width and height (or length) portions (190, 191, respectively) that together form two adjacent loops separated (and defined on one side by) two center feed contacts 193 A, 193B, which create a feed point 202, as shown in FIG. 1. Feed point 202 is adapted to connect the antenna to a receiver or transmitter (not shown in FIG. 1) through a feed line (not shown in FIG. 1). Alternating current can then be transmitted to/from the antenna along such a feed line. In an exemplary embodiment, the antenna 200 is planar and may be etched from a single side circuit board, where the trace has a predetermined width 192. The antenna, however, may be made from one or more pieces, using one or more materials or mediums, in any manner known in the art.

[0024] As illustrated in FIG. 2, one or more "figure eight" antenna structures may be arranged in a "backplane" (i.e., where the antenna structure(s) are located behind items or products of interest). As shown, the antennas may be separately mounted in the backplane and subsequently coupled together, may be made as an integral unit, or from any unitary or composite materials. The backplane 290 may subsequently be mounted in a variety of positions depending on the application. As shown in FIG. 2, for example, backplane 290 may be positioned in an upright configuration set approximately perpendicular to shelf 293. Shelf 293 may hold one or more items or products 292 (e.g., DND products) each containing RFID tags 291 affixed to, incorporated on, embedded in, or otherwise associated with products 292. To obtain optimum readings from antennas 200, products 292 are positioned on shelf 293 such that tags 291 are substantially parallel to the surface (or plane) of backplane 290. Although only a single backplane 290 has been illustrated, it should be readily apparent that multiple backplanes may be utilized, for example, coupled together to track items on multiple shelves, as will be explained in further detail below.

[0025] In accordance with an embodiment of the invention, a single "figure eight" antenna structure may be utilized to track items or products on one or more shelves. As shown in FIG. 3A, for example, a single "figure eight" antenna structure 200 may be incorporated into (or alternatively, on or under) a storage or other display structure (e.g., shelf, etc.) used to support items or products 292.

For optimum readings by antenna 200, products 292 may be positioned over antenna 200 in a "face forward" orientation such that tags 291 (or the plane of tags 291) are substantially perpendicular to the surface (or plane) of antenna 200, as well as substantially parallel to the length (or height) of the "figure eight" antenna structure 200. Preferably the tags are located in proximity to the antenna structure as shown for example along an edge of the product.

[0026] Alternatively, as shown in FIG. 3B, optimum readings may also be achieved from antenna 200 by positioning products 292 in a "bookshelf" orientation. In this orientation, products 292 are tilted (relative to the plane of antenna 200) such that the tags 291 are within a given angle (e.g., an acute angle such as 45 degrees) relative to the plane of antenna 200, and such that the plane of the tag 291 is skewed (or otherwise not parallel) relative to the plane of the antenna structure 200. Preferably, the tags are located in proximity to the antenna structure as shown, for example along an edge of the product. (One or more antenna structures (or structures incorporating such antenna structures) may be coupled together to track items over multiple structures.)

[0027] In accordance with an exemplary embodiment of the invention, a multiple RFID antenna system is illustrated in FIG. 4. The exemplary antenna system includes reader antennae 10, with associated antenna tuning boards 20, secondary controllers 30, a lumped element impedance matching circuit 40, and an RFID reader 50. (Although not shown, it should be apparent that antenna tuning boards 20 may include a selector switch, tuning components, a switch to tune or detune the associated antenna on demand, and other necessary components, and that secondary controllers 30 may include logic and switching controls as necessary to perform the operations described herein.)

[0028] Each secondary controller 30 of the exemplary system is connected to one or more of the antenna tuning boards 20 by a connection 60 such as a coaxial cable for transmission of RF signals and control cables for digital signals. In FIG. 4, for each secondary controller 30 there are shown eight antennae 10 and eight tuning boards 20 (although there may be more or less than eight of such elements in reducing the exemplary system to practice). Preferably, if groups of tuning boards 20 are at different distances from their respective secondary controllers 30, the respective lengths of connections 60 are kept approximately equal. For example, if group 23 of multiple tuning boards is closer to its secondary controller 30 than groups 21 and 22 are to their controllers, then some slack (shown as connection 65) may be provided in its connection so that all lengths of the connections are approximately constant.

[0029] The RFID feed system shown in FIG. 4 incorporates an RFID reader 50 and a matching circuit 40. In accordance with an exemplary embodiment, the matching circuit 40, for a nominally 50 Ω system, may be determined as follows: A resonant antenna tuning board 20 is used to rune the antenna 10 to the characteristic 50 Ω impedance of the system. A 50 Ω shunt resistor 41 is used for protection of the system components. When an antenna 10 is activated, its 50 Ω impedance is in parallel with a 50 Ω shunt resistor 41, giving a resulting impedance of 25 Ω going into the matching circuit 40. The matching circuit 40 is designed as an impedance transformer (e.g., an LC network) that will step up the 25 Ω impedance at point "a" to a 50 Ω impedance at point "b" such that the reader 50 will always see a perfect match at its design frequency. The matching circuit 40 is preferably equivalent to a quarter wavelength section of 35 Ω line.

[0030] Parts or all of the system described so far may be contained within a structure such as a store display fixture or gondola 70. When additional gondolas are used, each additional gondola, for example as represented by gondola 71, is preferably joined into the circuit using a half wavelength section 80 of (coaxial) 50 Ω transmission line. Preferably, the last gondola will be left open circuited at the last secondary controller (i.e., no gondola will be connected after the last secondary controller). This results in an effective open circuited stub length that is always a multiple of a half wavelength that appears invisible to the system at the design frequency when the secondary controllers 30 are placed in close proximity within each gondola.

[0031] In accordance with another exemplary embodiment, a matching circuit may be formed from a common coaxial cable (45, 46) as shown in FIG. 5. In this configuration, a 50 Ω terminator 42 (whose impedance is equal to the characteristic impedance of the system) is placed on the output of the last gondola, that is, after the last secondary controller 30 in the gondola 70. If this were not the last gondola, a half wavelength section of cable 80 would be used instead of the terminator 42. Using Ohm's law, the combined effect of a 50 Ω antenna loop 10 in parallel with the 50 Ω terminator 42 would be a 25 Ω impedance at point "c". A series quarter wave section of 50 Ω coaxial cable 45 transforms the 25 Ω to 100 Ω at point "d". Then a series quarter wave section of 75 Ω coaxial cable 46 transforms the impedance to a value approximately 50 Ω at point "e".

[0032] In accordance with an embodiment of the invention, a plurality of antennae 10 having associated tuning circuits 20, secondary controllers 30, and associated wiring, may all be contained in or on a physical structure, as shown, for example, in FIG. 6 as gondola 70 and gondola 71. A "gondola" may comprise, for example, one or more fixtures capable of supporting, for example, antennae, items, or other objects. The term "gondola" is used herein to refer to a fixture capable of supporting antennae, items, or objects and may comprise single or multiple shelves. The terms "shelf" or "gondola," however, are not meant to be limiting as to the physical attributes of any structure that may be used to implement embodiments of the invention, but used merely for convenience in explaining the embodiment. Any known structure for storing housing or otherwise supporting an object may be used in implementing the various embodiments of the invention. As shown in FIG. 6, gondolas 70 and 71 are each provided with multiple antennae 10 that are each connected to a reader 50 by one or more transmission cables including cable 60. The cable 60 interconnects between the tuning circuits 20 and the secondary controller 30. Cables 80a and 80b may be used to interconnect the different gondolas (70, 71), and cable 110 is routed back through an impedance matching circuit 40 to reader 50.

[0033] The example in FIG. 6 illustrates the reader 50 being controlled by a primary controller or controller 100 that sends commands or control signals along control cable 105 to select which antenna is active at any time. Between gondolas (70, 71), the commands or control signals may be carried on control cable 81a and 81b. Within a gondola the commands or control signals may be carried by cables 35. The primary controller 100 may be a processing device (e.g., microprocessor, discrete logic circuit, application specific integrated circuit (ASIC), programmable logic circuit, digital signal processor (DSP), etc.). Furthermore, the shelves may also be configured with secondary controllers 30 that co-operate with the primary controller 100 to select antennae. The secondary controllers 30 may also be a processing device with sufficient outputs to control all the antennae within an associated gondola or shelf.

[0034] The controller 100 may selectively operate any or all the switches by sending commands through a digital data communication cable 105 by sending a unique address associated with each tuning circuit 20. The addresses could be transmitted through the use of addressable switches such as, for example, ones identical or functional equivalent to a Dallas Semiconductor DS2405 "1-Wire®" addressable switch. Each such addressable switch provides a single output that may be used for switching a single antenna. Preferably, the controller 100 may selectively operate any or all the switches by utilizing one or more secondary controllers 30. For example, the secondary controller 30 may be a processing device which can provide multiple outputs for switching more than one antenna, such as all the antennas in proximity to the secondary controller 30. The controller 100 may also be any processing device. Communications between the controller 100 and the secondary controller 30 can be implemented by using communication signals in accordance with well known communication protocols (e.g., RS-232, RS-485 serial protocols, Ethernet protocols, Token Ring networking protocols, etc.).

[0035] In the previously mentioned patent applications, the term "intelligent station" is used as a general term to describe equipment, such as a gondola, which may include a secondary controller, switches and/or tuning circuitry, and/or antennae. More than one intelligent station may be connected together and connected to or incorporated with an RFID reader. A primary controller can be used to run the RFID reader and the intelligent stations. The primary controller itself may be controlled by application software residing on a computer. The term "intelligent station" can refer to an "intelligent gondola" or an "intelligent shelf."

[0036] In a preferred embodiment, the intelligent shelf system is controlled through an electronic network 120, as shown in FIG. 6. A controlling system that controls the intelligent shelf system will send command data to the primary controller 100 via Ethernet, RS-232 or other signaling protocol. These commands include but are not limited to instructions for operating the RFID reader unit 50 and antenna switches associated with tuning circuit 20. The controller 100 is programmed to interpret the commands that are transmitted through the unit. If a command is intended for the reader unit 50, the controller 100 passes that command to the reader unit 50. Other commands could be used for selecting antennae 10, and these commands will be processed if necessary by controller 100 to determine what data should be passed through digital data communication cable 105 to the secondary controllers 30. [0037] Likewise, the secondary controllers 30 can pass data back to the primary controller 100, as can the reader unit 50. The controller 100 then relays result data back to the controlling system through the electronic network 120. The inventory control processing unit 130, shown in FIG. 6, is one example of such a controlling system. As discussed further herein with respect to the intelligent shelf system, the electronic network and controlling system are used interchangeably to depict that the intelligent shelf system may be controlled by the controlling system connected to the intelligent shelf system through an electronic network 120.

[0038] Controller 100 of FIG. 6 typically decides whether a command from the electronic network 120 should be sent to reader 50, or should be sent through the digital communication cable 105. Also, controller 100 must relay data it receives from the digital communication cable 105, and from reader unit 50, back to the electronic network 120. Under one configuration, the electronic network would issue a command to read a single antenna. The controller 100 would then (a) set the proper switch for that antenna, (b) activate the reader, (c) receive data back from the reader, (d) deactivate the reader, and (e) send the data back to the electronic network 120. Further details of the processing of command signals from a host by the controller can be found in US provisional patent application 60/346,388 (filed January 9, 2002), which has been incorporated by reference in its entirety herein.

[0039] An additional advantage of placing the controller 100 between the electronic network 120 and the reader units as shown in FIG. 6 is that different types of readers 50 can be used as needed. The commands from the electronic network to the controller may be transmitted using generic control data (not reader-specific), thus allowing for expanded uses by various types of readers.

For example, the electronic network can send to the controller a "read antennas" command. The controller in turn can then translate this command into the appropriate command syntax required by each reader unit. Likewise, the controller can also receive the response syntax from the reader unit (which may differ based on the type of the reader unit), and parse it into a generic response back to the electronic network. The command and response syntax may differ for each type of reader unit 50, but the controller 100 makes this transparent to the electronic network.

[0040] Continuing with FIG. 6, the block diagram further shows digital communication cable 105 connecting primary controller 100 to the secondary controllers 30, and RF transmission cable 110 connects the reader 50 to the antennae 10. The primary controller 100 or secondary controller 30 may operate a tee switch 32 that selects which of the gondolas (for example 70, or 71) will be selected. The tee switch 32 may be separate from or part of a gondola as would be recognized by one skilled in the art. In FIG. 6, the tee switch 32 is used with a "parallel-series" RF connection arrangement. That is, controller 100 and reader 50 operate the shelves in series, with the RF and digital communication lines branched off (i.e., connected with a multi-drop or "tee" arrangement with each of the branches arranged in parallel) to antennae within shelves that are arranged in series, or in series-parallel. This configuration allows the RF signal to be switched by the tee switch 32 into a gondola, or to bypass the gondola altogether. The tee or multi-drop configuration shown in FIG. 6 may be used to reduce the number of switching elements through which the RF transmission cable passes.

[0041] In FIG. 6, a portion of the control cable 81a that extends beyond gondola 70, and a portion of the RF cable 80a extends beyond gondola 70, are shown outside of the gondola. However, as would be recognized by those skilled in the art, these extended portions of the cables may also be contained within the gondola. Additional extended control cable portions 81b and additional extended RF cable portions 80b may be used to connect to more shelves or groups of shelves. Likewise, additional gondolas (not shown) may be added to groups of gondolas, for example to gondolas 70 or 71 as would be apparent to those skilled in the art.

[0042] The item information data collected by the reader units 50 from each of the intelligent gondolas 70, 71, etc. is transmitted to an inventory control processing unit 130. The inventory control processing unit 130 is typically configured to receive item information from the intelligent gondolas 70, 71 etc. The inventory control processing unit 130 is typically connected to the intelligent shelves over an electronic network 120 and is also associated with an appropriate data store 140 that stores inventory related data including reference tables and also program code and configuration information relevant to inventory control or warehousing. The inventory control processing unit 130 is also programmed and configured to perform inventory control functions that are well known to those skilled in the art. For example, some of the functions performed by an inventory control (or warehousing) unit include: storing and tracking quantities of inventoried items on hand, daily movements or sales of various items, tracking positions or locations of various items, etc.

[0043] In operation, the inventory control system would determine item information from the intelligent gondolas (70, 71, etc.) that are connected to the inventory control processing unit 130 through an electronic network 120. In one embodiment, the various intelligent gondolas 70, 71, etc. would be under the control of inventory control processing unit 130 that would determine when the reader units 50 under control of controller 100 would poll the antennae 10 to determine item information of items to be inventoried. In an alternate embodiment, the controller(s) 100 may be programmed to periodically poll the connected multiple antennae for item information and then transmit the determined item information to the inventory control processing unit using a reverse "push" model of data transmission. In a further embodiment, the polling and data transmission of item information by the controller 100 may be event driven, for example, triggered by a periodic replenishment of inventoried items on the intelligent shelves. In each case, the controller 100 would selectively energize the multiple antennae connected to reader 50 to determine item information from the RFID tags associated with the items to be inventoried.

[0044] Once the item information is received from the reader units 50 of the intelligent gondolas 70, 71 etc., the inventory control processing unit 130 processes the received item information using, for example, programmed logic, code, and data at the inventory control processing unit 130 and at the associated data store 140. The processed item information is then typically stored at the data store 140 for future use in the inventory control system and method of the invention.

[0045] The following examples are intended to further illustrate exemplary implementations of embodiments of the invention.

EXAMPLES

[0046] An exemplary application of Antenna 200 of FIG. 1 is for use in RFID or any other RF (or non-RF) applications. In an exemplary implementation, antenna 200 has a planar "figure-eight" geometry. Sample dimensions of antenna 200 include: the antenna width 190 of approximately 12.425", the height 191 of approximately 7.5", and the width of the trace 192 of approximately 0.25" uniformly throughout the antenna structure.

[0047] FIG. 7 illustrates in greater detail an exemplary tee switch 32 on a gondola 70 in accordance with an exemplary embodiment. The tee switch 32 is shown in FIG. 7 as being within secondary controller 30, but it should be understood that the tee switch 32 may also be incorporated outside as well. The tee switch 32 has a PIN (P-type, I-type, N-type) diode 31, which acts as a switch in the exemplary embodiment. A secondary controller 30 associated with gondola 70 may activate PIN diode 31 to allow the RF signal from RF cable 110 into gondola 70, where it may be routed through switches 20 to antennae 10. The RF energy also may continue along RF cable 80a to optional additional tee switches, and finally to a terminator (not shown) if the impedance matching circuit 40 does not contain a terminator.

[0048] FIG. 8 shows an exemplary circuit diagram in accordance with an embodiment of the invention for an RF switch that may be used, for example, within the tuning board 20, discussed earlier herein with respect to various embodiments of the invention. FIG. 8 is not intended to limit the invention since those skilled in the art would recognize various modifications, variations, and alternatives thereof. As shown in FIG. 8, the RF switch utilizes a PIN diode 21 which acts in a similar way to a regular PN diode except that it is able to block an RF signal when the switch contact is open. When the switch contact is closed, the PIN diode 21 becomes forward biased and conducts the RF signal. The control signal used to select the antenna may also be superimposed (not shown) on the RF signal that is used to read the RFID tags. Such a control signal could be separated from the RF signal by a band pass filter and then go on to an addressable switch, which selectively activates the RF switch utilizing a PIN diode. In FIG. 8, the control signal is provided on separate wiring instead of using the RF signal cable. While superimposing the control signal on the RF signal cable may require fewer conductors and/or connectors between antennae or between intelligent stations, it requires additional electronic components to separate the signals at each antenna. Thus it may be more efficient to have separate wiring for the control signal.

[0049] FIG. 9 shows another exemplary circuit diagram in accordance with an embodiment of the invention for a circuit that may be incorporated within tuning board 20, where a PIN diode 22 is used to tune the antenna loop 10. Here the loop is in tune when PIN diode 22 is energized. Therefore, the PIN diode 22 is not required to remain on while the loop is not being read, thus resulting in potential power savings and reduced heat generation.

[0050] It should be understood that, whether or not add-on or peripheral devices are used, other kinds of electrical power (e.g., direct current (DC)) may be used by the stations in addition to (or substitution for) RF power. For example, direct current (DC) may be used by the secondary controller 30, as well as by the tuning boards 20. One or more dedicated wires may provide such electrical power, or it may be incorporated into the digital communication highway or with an RF cable. An RF cable may be configured using two conductors (e.g., coaxial cable), wherein both the center conductor and the sheath conductor are utilized in the system. While the RF cable carries an RF signal, a DC voltage may be superimposed on the RF signal, in the same RF cable, to provide DC power to intelligent stations. Voltage regulators may subsequently be used to control or decrease excessive voltages to within usable limits.

[0051] FIG. 10 shows an exemplary antenna housing 250 in accordance with an embodiment of the invention. The assembly includes one or more planar antenna boards 200. Each planar antenna board 200 may further include a conductor loop 201, shown in the figure-eight shape discussed previously in connection with FIG. 1. Conductor loop 201 may be formed, for example, as an etched copper conductor path on a substrate, or any other suitable materials. The planar antenna board 200 has a pair of connection points 202 for attachment of antenna lead wires 203. The planar antenna board 200 may also have holes 204 for attachment to supports.

[0052] Planar antenna boards 200 are attached to a support plate 210, which has holes 211, through which antenna lead wires 203 may pass. Support plate 210 also has support posts 212 on which the planar antenna boards 200 may attach. The support plate 210 is preferably made of metal, and the support posts 212 further provide a standoff distance to hold the planar antenna boards 200 a set distance away from the metal support plate 210. The support plate 210 may also have flanges 213 at the sides or ends. Attachment holes 214 may be provided for attaching a cover 220, provided with matching holes 221. Cover 220 is a non-metal material such as plastic, and is transparent to RF.

[0053] FIG. 11 shows the back side of a backplane 300 from a support fixture (or "gondola") such as a display unit used to hold optical disk media. During use, backplane 300 is preferably in a vertical position, but may be used in other positions, such as a face-up position. The face-down position is illustrated in FIG. 11. Shelves (not shown in FIG. 11) and the antenna housings 220 would be attached to the front of the backplane. Backplane 300 in this instance includes integral mounting hooks 301 for mounting onto a support frame (not shown). Also shown are backplane slots 302 through which shelves (not shown) may be attached from the opposite (front) side of backplane 300. Backplane 300 may further include flanges such as 303 and ribs such as 304 for mechanical stiffness.

[0054] Tuning board mounting plate 320 and secondary controller mounting plate 327 are attached to backplane 300, for holding tuning boards 20 and secondary controller boards 30, respectively. Under the exemplary embodiment, secondary controller mounting plate 327 is placed with three secondary controllers 30 attached in the center of the backplane 300 as shown in FIG. 11. A tuning board mounting plate 320 is also placed on each side of backplane 300, where each tuning board mounting plate 320 has four tuning boards 20 attached. A single secondary controller 30 may control all eight tuning boards 20 on the backplane 300. The other two secondary controllers 30 shown on the backplane may each be used to control an additional eight tuning boards 20 on two other backplanes (shown in reduced scale as backplanes 305 and 306, with some features omitted for clarity). These latter two backplanes each have two tuning board mounting plates 320, but are each shown without a secondary controller mounting plate 327, since the secondary controllers 30 to control backplanes 305 and 306 may be located on backplane 300.

[0055] Continuing with FIG. 11, wiring is run through the backplane slots 302 from the antennae within the antenna housing 220, through point 322. Holes 321 may be provided at convenient points in the tuning board mounting plate to allow antenna wiring to pass through. This wiring may be connected to the tuning boards 20 on terminal posts 325, or through other connector means. The RF signal may be connected to the tuning boards 20 using solder pads 326, or other connector means. The tuning boards 20 are preferably connected to respective connections on the appropriate secondary controller 30, such as solder pad 328. The secondary controller 30 may be connected to an RF cable such as cables 110 or 80 (not shown in FIG. 11), using connectors such as coaxial connector 329.

[0056] Slots 323 are also provided in the tuning board mounting plate, or in the secondary controller mounting plate. The slots 323 provide room for allowing protrusions, coming from shelves, to pass through. When the backplanes are installed in a face-forward configuration, the protrusions would come through the front of the backplane 300, through the backplane slots 302, to support the shelves. Standoff supports 324 may be provided on the support plates 320 or 325 in order to raise the tuning boards 20 or secondary controllers 30 to give clearance from the protrusions and to prevent shorting of circuitry to the backplane.

[0057] A cover (not shown) may also be added to protect and conceal the circuitry on the back of backplane 300. RF and control wiring may enter and leave the circuitry through connectors (not shown) that may be mounted in connector plates 310. Connectors for control wiring are not shown in FIG. 11, but numerous connector styles may be used as are known to one skilled in the art.

[0058] FIG. 12 shows a front view of a display fixture, incorporating three backplanes 300, 305, and 306, with attached shelves 307. Also shown are the antenna housings 220 that are in the approximately vertical plane at the back of each shelf 307. This display fixture is useful for monitoring inventory of RFID tagged items such as optical disk media 308 shown upon shelf 307. The optical disk media 308 have an attached RFID tag 309 that is detected by the RFID system.

[0059] FIG. 13 shows an example of wiring between circuitry components on a backplane 300. The backplane holds secondary controllers 30a, 30b, and 30c in the center, and tuning boards 20 on the sides. RF cable 390a enters the backplane through connector plate 310. This RF cable is attached in turn to the secondary controllers 30 for example through coaxial connectors 329. The RF cable continues out through connector plate 310 and on to additional gondolas as cable 390b.

[0060] Control signals from controller 100 enter via cable 392a through connector plate 310, and are attached in turn to the secondary controllers 30. The control signals continue out through connector plate 310 and on to additional gondolas as cable 392b.

[0061] Secondary controller 30a may route RF from a solder pad connector such as 328 through cable 390d for example to a lower level backplane, and may route antenna switching signals to the same backplane through cable 392d. Secondary controller 30b may route RF through cable 390c for example to an upper level backplane, and may route antenna switching signals to the same backplane through cable 392c. Secondary controller 30b may route RF through cable 391 to antenna tuning boards 20 on its own backplane 300, for example using solder pads 326, and may route antenna switching signals to the same antenna tuning boards through additional wiring (not shown).

[0062] Depending on the number of display fixtures, the RF connections between fixtures may be made with a variety of connection paths. FIG. 14 shows a block diagram representing an exemplary implementation of the RF connection paths shown in FIG. 5, for example, connecting a group of three fixtures. RFID reader 50 is connected to a quarter-wavelength section 46 of 75 ohm coaxial cable, which is in turn connected to a feed (e.g., quarter-wavelength section 45 of 50 ohm coaxial cable) leading to a node (e.g., point "c") A 50 ohm resistor 42 is connected to a node (e.g., point "c") A first fixture 401 is also connected to a node (e.g., point "c") The 1/4 or 1/2 wavelength section lengths of feed (e.g., coaxial cable) as described herein refer to the total length of a section, for example, between node or connection point "c" and a secondary controller, or between two secondary controllers. Since part or parts of this length may be inside a fixture, the length outside a fixture may be less than the total length of the section. [0063] A second fixture 402 is connected to first fixture 401, using a feed (e.g., half -wavelength section 405 of 50 ohm coaxial cable). A third fixture 403 is connected to second fixture 402, using a feed (e.g., half-wavelength section 405 of 50 ohm coaxial cable). FIG. 14 thus represents in block diagram form an exemplary implementation of the circuitry of FIG. 5, except that the 50 ohm resistor 42 is shown outside of a fixture (but may also be used instead within the fixture). As in FIG. 3A, the RF connection is carried through each fixture 401-403, with connections within the fixture for switching, tuning, etc. As will be apparent to those of ordinary skill, more or fewer than three fixtures may be used with this exemplary architecture.

[0064] FIG. 15 shows in block diagram form another exemplary implementation of the RF connection path for a group of seven display fixtures. RFID reader 50 is connected as described previously, with a connection to first fixture 411 at a node (e.g., point "c") Additional fixtures are connected as follows: from first fixture 411, through a feed (e.g., half-wavelength section 405 of 50 ohm coaxial cable), to second fixture 412, then through another coaxial cable 405 to a third fixture 413, then through another feed (e.g., coaxial cable 405) to a fourth fixture 414. Also from first fixture 411, through a feed (e.g., half- wavelength section 405 of 50 ohm coaxial cable), to fifth fixture 415, then through another feed (e.g., coaxial cable 405 to a sixth fixture 416), then through another feed (e.g., coaxial cable 405 to a seventh fixture 417). As will be apparent to those of ordinary skill, more or fewer than seven fixtures may be used with this exemplary architecture.

[0065] FIG. 16 shows in block diagram another exemplary implementation of the RF connection path for a single display fixture 420. RFID reader 50 is connected to a feed (e.g., quarter-wavelength section 46 of 75 ohm coaxial cable), which is in turn connected to a feed (e.g., quarter-wavelength section 45 of 50 ohm coaxial cable) leading to a node (e.g., point "c") A 50 ohm resistor 42 is connected to point "c." Fixture 420 is also connected to a node (e.g., point "c")

[0066] FIG. 17 shows in block diagram another exemplary implementation of the RF connection path for a single display fixture 430, which in this case has a fixture extension 431 for example having one or more additional shelves. RFID reader 50 is connected as described previously to a node (e.g., point "c") Fixture 430 is also connected to a node (e.g., point "c") From fixture 430, a feed (e.g., half-wavelength section 405 of 50 ohm coaxial cable) leads to fixture extension 431. In the foregoing figures, the conductor for the RF signal is shown as a single line, representing, for example, a feed such as a coaxial cable. It will be understood to those skilled in the art that a coaxial cable includes a grounding or return conductor (not shown).

[0067] While preferred embodiments of the invention have been described and illustrated, it should be apparent that many modifications to the embodiments and implementations of the invention can be made without departing from the spirit or scope of the invention. For example, the "figure eighf'-geometry of antenna 200 may be in a single or multiple planes, and may be made of multiple loops (in one or more planes) sharing the same feed point 202. The antenna structures 10 described in connections with the embodiments depicted in FIGS. 4 through 7 may take the form of a "figure eight" geometry or any other known antenna form. Although embodiments have been described in connection with the use of a shelf structure, it should be readily apparent any structure that may be used in selling, marketing, promoting, displaying, presenting, providing, retaining, securing, storing, or otherwise supporting an item or product may be used in implementing embodiments of the invention. [0068] Although specific circuitry, components, or modules (e.g., tuning circuit 20, tee switch 32, impedance matching circuit 40, RF switch, etc.) may be disclosed herein in connection with exemplary embodiments of the invention, it should be readily apparent that any other structural or functionally equivalent circuit(s), component(s) or module(s) may be utilized in implementing the various embodiments of the invention.

[0069] The modules described herein, particularly those illustrated or inherent in, or apparent from the instant disclosure, as physically separated components, may be omitted, combined or further separated into a variety of different components, sharing different resources as required for the particular implementation of the embodiments disclosed (or apparent from the teachings herein). The modules described herein, may where appropriate (e.g., reader 50, primary controller 100, inventory control processing unit 130, data store 140, etc.) be one or more hardware, software, or hybrid components residing in (or distributed among) one or more local and/or remote computer or other processing systems. Although such modules may be shown or described herein as physically separated components (e.g., data store 140, inventory processing unit 130, controller 100, reader 50, secondary controller 30, etc.), it should be readily apparent that the modules may be omitted, combined or further separated into a variety of different components, sharing different resources (including processing units, memory, clock devices, software routines, etc.) as required for the particular implementation of the embodiments disclosed (or apparent from the teachings herein). Indeed, even a single general purpose computer (or other processor-controlled device), whether connected directly to antennas 10, tuning circuits 20, gondolas 70, 71, or connected through a network 120, executing a program stored on an article of manufacture (e.g., recording medium such as a CD-ROM, DVD-ROM, memory cartridge, etc.) to produce the functionality referred to herein may be utilized to implement the illustrated embodiments.

[0070] One skilled in the art would recognize that inventory control processing unit 130 could be implemented on a general purpose computer system connected to an electronic network 120, such as a computer network. The computer network can also be a public network, such as the Internet or Metropolitan Area Network (MAN), or other private network, such as a corporate Local Area Network (LAN) or Wide Area Network (WAN), Bluetooth, or even a virtual private network. A computer system includes a central processing unit (CPU) connected to a system memory. The system memory typically contains an operating system, a BIOS driver, and application programs. In addition, the computer system contains input devices such as a mouse and a keyboard, and output devices such as a printer and a display monitor. The processing devices described herein may be any device used to process information (e.g., microprocessor, discrete logic circuit, application specific integrated circuit (ASIC), programmable logic circuit, digital signal processor (DSP), Microchip Technology Inc. PICmicro® Microcontroller, Intel Microprocessor, etc.).

[0071] The computer system generally includes a communications interface, such as an Ethernet card, to communicate to the electronic network 120. Other computer systems may also be connected to the electronic network 120. One skilled in the art would recognize that the above system describes the typical components of a computer system connected to an electronic network. It should be appreciated that many other similar configurations are within the abilities of one skilled in the art and all of these configurations could be used with the methods and systems of the invention. Furthermore, it should be recognized that the computer and network systems (as well as any of their components) as disclosed herein can be programmed and configured as an inventory control processing unit to perform inventory control related functions that are well known to those skilled in the art.

[0072] In addition, one skilled in the art would recognize that the "computer" implemented invention described herein may include components that are not computers per se but also include devices such as Internet appliances and Programmable Logic Controllers (PLCs) that may be used to provide one or more of the functionalities discussed herein. Furthermore, while "electronic" networks are generically used to refer to the communications network connecting the processing sites of the invention, one skilled in the art would recognize that such networks could be implemented using optical or other equivalent technologies. Likewise, it is also to be understood that the invention utilizes known security measures for transmission of electronic data across networks. Therefore, encryption, authentication, verification, and other security measures for transmission of electronic data across both public and private networks are provided, where necessary, using techniques that are well known to those skilled in the art.

[0073] It is to be understood therefore that the invention is not limited to the particular embodiments disclosed (or apparent from the disclosure) herein, but only limited by the claims appended hereto.

Claims

CLAIMSWhat is claimed as new and desired to be protected by Letters Patent of the United States is:

1. An antenna structure comprising width and length portions that together form adjacent loops separated and defined on one side by two center feed contacts, wherein said center feed contacts together form a feed point.

2. The antenna structure as recited in claim 1, wherein the antenna structure has a figure-eight geometry.

3. The antenna structure as recited in claim 1, wherein the antenna structure is planar.

4. A method of displaying products having associated therewith RFID tags, the method comprising the steps of:

providing at least one RFID reader antenna on a product support structure; and

placing at least one product on the product support structure such that an RFID tag associated with the at least one product is substantially parallel to a portion of the RFID antenna.

5. The method of claim 4, wherein said step of providing at least one RFID antenna comprises providing a single, planar antenna structure having width and length portions that form adjacent loops separated by two center feed portions.

6. The method of claim 5, wherein said step of placing at least one product comprises the step of positioning the at least one product such that its associated RFID tag is substantially parallel to the length portion of the single, planar antenna and is in a plane perpendicular to the plane of the single, planar antenna.

7. The method of claim 5, wherein said step of placing at least one product comprises the step of positioning the at least one product at an acute angle relative to the single, planar antenna.

8. The method of claim 4, wherein the product support structure comprises a horizontal shelf, for supporting a bottom portion of the at least one product, co-joined with a vertical backplane, for supporting a back portion of the at least one product, and wherein said step of providing at least one RFID reader antenna comprises incorporating a plurality of RFID reader antennas on the backplane.

9. The method of claim 8, wherein:

said step of providing at least one RFID reader antenna comprises incorporating a plurality of antennas having a figure-eight geometry; and

said step of placing at least one product on the product support structure comprises positioning the at least one product such that an RFID tag associated with the at least one product is substantially parallel to all of the portions of the RFID antenna.

10. A feed system for an RFID reader antenna system comprising:

a plurality of resonant loop antennas; at least one antenna switching board, said at least one antenna switching board being coupled to the plurality of loop antennas;

at least one secondary switching board said at least one secondary switching board being coupled to the plurality of loop antennas; and

an RFID reader, said reader providing a feed to said antenna and secondary switching boards; and

an impedance match circuit, coupled to said RFID reader, wherein the impedance match circuit further includes a shunt device, said shunt device and impedance matching circuit operating to provide a resistively matched feed from the RFID reader with overcurrent protection.

11. An RFID enabled system comprising:

an RFID reader; and

a plurality of reader antennae, coupled to said RFID reader through a single RF cable, wherein each reader antenna has a respective switch to trigger the reader antenna; and

a controller, coupled to each switch, said controller sending control signals to each switch to select one or more reader antennae in a sequence for reading RFID tags attached to items.

12. The RFID enabled system of claim 11, wherein the reader antenna is coupled to said RFID reader in series.

13. The RFID enabled system of claim 11, wherein the reader antenna is coupled to said RFID reader in a series-parallel arrangement.

14. The RFID enabled system of claim 11, wherein the reader antenna is coupled to said RFID reader in a series-branched arrangement.

15. The RFID enabled system of claim 11, further comprising an impedance matching circuit, coupled in series between said RFID reader and said controller.

16. The RFID enabled system of claim 15, wherein said impedance matching circuit is made up of a length of coaxial cable.

17. The RFID enabled system of claim 11, wherein said controller comprises a primary controller and a secondary controller.

18. The RFID enabled system of claim 17, further comprising an inventory control processing unit coupled to said primary controller.

19. The RFID enabled system of claim 18, wherein said inventory control processing unit is coupled to said primary controller through an electronic network.

20. The RFID enabled system of claim 11, wherein said plurality of reader antennae are coupled to said controller through a first connection, the system further comprising:

a second plurality of reader antennae; and

a second controller, coupled to said second plurality of reader antennae through a second connection; wherein the first and second connections are approximately the same length.

21. An RFID enabled system comprising:

an RFID reader connected through a feed to a node;

a resistor connected to a node; and

a plurality of fixtures connected through a feed to the node, each fixture comprising a plurality of reader antennae, coupled to said RFID reader through a single RF cable, wherein each reader antenna has a respective switch to trigger the reader antenna.