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Intelligent station using multiple rf antennae and inventory control system and method incorporating sameIntelligent station using multiple rf antennae and inventory control system and method incorporating same description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060238307, Intelligent station using multiple rf antennae and inventory control system and method incorporating same. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims the benefit of priority under 35 U.S.C. .sctn. 119(e) of provisional application Ser. Nos. 60/346,388, filed Jan. 9, 2002, and 60/350,023, filed on Jan. 23, 2002, the disclosures which are incorporated herein in their entireties. FIELD OF THE INVENTION [0002] The present invention relates generally to the field of using multiple RF (radio frequency) antennae in an intelligent station to track items tagged with RFID (radio frequency identification) tags. More generally, the present invention is directed to an inventory control method and system that uses the intelligent station to track and inventory items that are tagged with RFID tags. BACKGROUND OF THE INVENTION [0003] 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. One example of such a RFID system including details of suitable RF antennae is described in U.S. Pat. No. 6,094,173, the contents of which are incorporated herein in their entirety. In order to improve the detection range and expand "coverage" it is known to use coplanar antennae that are out of phase. One example of such an antenna is provided in U.S. Pat. No. 6,166,706. [0004] 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 are moved past a group of tagged items in order to detect all the tagged items since the tagged items are typically 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 were 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 this configuration may be awkward to set up keeping in mind that space is often at a premium. [0005] However, 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. [0006] By way of background, FIG. 1 is a block diagram that illustrates the basics of a prior art RFID system. A reader unit 100 may typically be connected through RS-232 or similar digital communication to a terminal 102 such as a computer terminal. The reader unit 100 is connected by a cable 203 to a reader antenna 200. The reader antenna 200 typically consists of at least a loop 201 and a tuning circuit 202. Although the tuning circuit 202 is shown as a localized part in FIG. 1, one skilled in the art would recognize that it might be distributed around the loop 201. The reader antenna 200 in turn communicates by low power radio waves 105 with one or more RFID tags 106 that are typically associated with items, objects (animate or inanimate) or persons that are to be tracked by the RFID system. [0007] The transmission cable 203 is typically characterized by its impedance, which in a simplified form, is approximately the square root of inductance L divided by capacitance C of the transmission cable. For coaxial cables, the impedance is commonly 50 or 75 ohms. [0008] Generally, the transmission cable 203, antenna loop 201, and tuning circuit 202 are connected together in a manner that most efficiently utilizes the RF power at a desired frequency, which for a given RFID system using a loop antenna, such as antenna 200, is typically a "high" frequency such as 13.56 MHz. Another common "low" frequency that is often used for RFID systems is 125 kHz. "Ultrahigh" (UHF) frequencies such as 900 MHz or 2.45 GHz within the RF range are also used with different antenna designs. [0009] A system using multiple antennae powered by a single reader unit and using a multiplexer switch to alternate between the antennae has also been known. Such a system is conceptually represented in FIG. 2 where two separate antennae 200a and 200b are connected to a reader and multiplexer unit 101 through respective transmission cables 203a and 203b. The use of multiple antennae typically improves the spatial coverage when reading tags, without requiring more than one reader unit. The main disadvantage of the arrangement disclosed in FIG. 2 is the need for a separate transmission cable to each of the antennae. Since space is often at a premium, the use of these separate cables is a disadvantage because additional space is needed to install or position each of these separate cables. This disadvantage is accentuated when more than two antennae are used with one reader unit since all of these multiple antennae require separate transmission cables. SUMMARY OF THE INVENTION [0010] In one aspect, the present invention provides an intelligent station that tracks RFID tags, the intelligent station including: a reader unit that transmits and receives RF signals; a first RF antenna connected to the reader unit by a first transmission cable through a first switch; and one or more additional RF antennae connected to the reader unit by the same first transmission cable through one or more additional switches. The term "intelligent," as used herein, means that the system can, through transmission of radio frequency signals, capture, store, and lookup data, and monitor unique identifiers associated with trackable items. [0011] In a further aspect, each of the first and one or more additional RF antennae includes a loop and a tuning circuit. [0012] In another aspect of the present invention, the reader unit includes a tuning circuit for the first and one or more additional RF antennae, with the tuning circuit connected to the first and one or more additional RF antennae through the first transmission cable. [0013] In another aspect, the present invention includes: a reader unit that generates and receives RF signals; and a control unit that is operatively connected to the reader unit and to first and one or more additional switches, wherein the control unit is configured to selectively operate the first and one or more additional switches to connect the reader to the first and one or more additional RF antennae, respectively. The reader unit and the control unit may be separate devices or combined in a single unit. [0014] In yet another aspect of the present invention, the intelligent station further includes a second transmission cable that connects the reader unit to auxiliary RF antenna loops, each of the auxiliary RF antenna loops arranged proximate to a corresponding one of the first and one or more additional RF antennae. The auxiliary antennae receive an unmodulated RF signal that powers up the tags, which are normally not powered in the absence of an RF signal. As used herein, "unmodulated RF signal" is an RF signal without superimposed data. A "modulated RF signal" is an RF signal carrying superimposed data. [0015] In a further aspect, the reader unit includes a second tuning circuit, proximate to the reader unit, that is connected to the auxiliary RF antenna loops through the second transmission cable. The second tuning circuit is configured to tune the auxiliary RF antenna loops. [0016] In yet another aspect, the present invention provides a second transmission cable that connects the reader unit to the first and one or more additional RF antennae through the first and one or more additional switches, respectively. The reader unit transmits an unmodulated RF signal to the first and one or more additional RF antennae through the second transmission cable, and transmits a modulated RF signal to the first and one or more additional antennae through the first transmission cable. [0017] In a further aspect of the present invention, the first switch is configured to operate in only three states: a first state such that the first switch only transmits the modulated RF signal to the first RF antenna; a second state such that the first switch only transmits the unmodulated RF signal to the first RF antenna; and a third state such that both the modulated RF signal and the unmodulated RF signal bypass the first RF antenna. The second switch includes a multi-pole switch configured to operate in only three states: a first state such that the second switch only transmits the modulated RF signal to the associated second RF antenna; a second state such that the second switch only transmits the unmodulated RF signal to the second associated RF antenna; and a third state such that both the modulated RF signal and the unmodulated RF signal bypass the associated second RF antenna. Each of the switches can be controlled independently of each other, thus, for example, the first and second switches may be set to transmit modulated and unmodulated signals, respectively, at the same time. In addition, a two-pole switch may be used which is configured to operate in one of two states (one state being to pass modulated RF signals to the associated antenna, and the other state being to pass no signals to the associated antenna). [0018] In a further aspect, the present invention provides: additional RF antennae connected to the reader unit through the same first transmission cable; and additional switches arranged between the first transmission cable and the additional RF antennae, respectively. [0019] In one aspect, an RF transmission cable has a single branch serving all antennae, that is antennae are connected to a reader unit through a RF transmission cable in a series arrangement. [0020] In another aspect, an RF transmission cable has two or more branches, each serving one or more antennae, That is, antennae are connected to the reader unit through the RF transmission cable in a parallel-series arrangement, with each branch on the RF transmission cable selectable by use of a switch. Continue reading about Intelligent station using multiple rf antennae and inventory control system and method incorporating same... 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