ASYMMETRIC RFID TAG ANTENNA
First Claim
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1. A radio frequency identification (RFID) antenna for use with radio waves of a nominal wavelength, the RFID antenna comprising:
- a first antenna arm comprising a variable dimension capacitive load having a first tunable RFID antenna dimension and a second tunable RFID antenna dimension, wherein the second tunable RFID antenna dimension corresponds to a RFID antenna width;
a second antenna arm comprising a folded conductor and an inductive matching stub;
wherein the folded conductor forms a closed loop with the capacitive load of the first antenna arm;
wherein a position of the inductive matching stub corresponds to a third tunable RFID antenna dimension;
wherein the third tunable RFID antenna dimension is selected to cause resonance with a selected capacitance corresponding to a capacitance of RFID tag circuitry to be used with the RFID antenna; and
wherein the first and second antenna arms are arranged to provide a greatest RFID antenna dimension of less than one quarter of the nominal wavelength of the radio waves to be used.
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Abstract
The invention provides an asymmetric UHF RFID tag antenna that variously comprises a capacitive load, a folded loop conductor and an inductive matching element, which provides a differential input for RFID tag circuitry. The design provides a small form factor while maintaining a high gain and impedance tuning properties. Various refinements and associated devices and systems using the design are provided and disclosed according to a host of optional embodiments.
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Citations
28 Claims
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1. A radio frequency identification (RFID) antenna for use with radio waves of a nominal wavelength, the RFID antenna comprising:
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a first antenna arm comprising a variable dimension capacitive load having a first tunable RFID antenna dimension and a second tunable RFID antenna dimension, wherein the second tunable RFID antenna dimension corresponds to a RFID antenna width; a second antenna arm comprising a folded conductor and an inductive matching stub; wherein the folded conductor forms a closed loop with the capacitive load of the first antenna arm; wherein a position of the inductive matching stub corresponds to a third tunable RFID antenna dimension; wherein the third tunable RFID antenna dimension is selected to cause resonance with a selected capacitance corresponding to a capacitance of RFID tag circuitry to be used with the RFID antenna; and wherein the first and second antenna arms are arranged to provide a greatest RFID antenna dimension of less than one quarter of the nominal wavelength of the radio waves to be used. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A radio frequency identification (RFID) tag system comprising:
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a RFID antenna; RFID tag circuitry, wherein the RFID tag circuitry is at least operable to receive signals from the RFID antenna; wherein the RFID antenna further comprises; a first antenna element comprising a capacitive load with first and second antenna dimensions, wherein the second antenna dimension corresponds to RFID antenna width; a second antenna element comprising a folded conductor and an inductive matching element, wherein the folded conductor forms a closed loop with the capacitive load; wherein a location of the inductive matching element relative to the first and second antenna elements corresponds to a third antenna dimension; wherein the third antenna dimension is adjustable to resonate with a capacitance of the RFID tag circuitry; wherein the RFID antenna is substantially impedance matched to the RFID tag circuitry by, at least, adjusting one or more of the first, second, and third antenna dimensions. - View Dependent Claims (11, 12, 13, 14)
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15. A method of manufacturing a radio frequency identification (RFID) antenna on a nonconductive substrate defined by an X-Y plane, the method comprising:
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determining a RFID tag circuitry capacitance, impedance, and nominal operating wavelength; selecting a capacitive load to be formed on the substrate having X-Y plane dimensions corresponding to first and second RFID antenna dimensions and that is selected to resonate with the determined RFID tag circuitry capacitance; selecting an inductive matching stub location on the substrate, wherein the inductive matching stub location in the X-Y plane corresponds to a third RFID antenna dimension; selecting a conductor length to be formed on the substrate adjacent to the inductive matching stub; adjusting, at least, one or more of the first, second, and third RFID antenna dimensions to substantially match the RFID antenna impedance with the RFID tag circuitry impedance; and forming on the substrate the conductor length, the inductive matching stub, and the capacitive load such that a closed loop is formed thereby, wherein the longest RFID antenna dimension is less than one quarter wavelength of the RFID tag circuitry operating wavelength. - View Dependent Claims (16, 17, 18, 19, 20)
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21. An asymmetric radio frequency identification (RFID) tag antenna comprising:
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a polygon-shaped capacitive load; a folded arm that forms a closed loop with the polygon-shaped load, the folded arm having an inductive matching stub that is used to resonate with a capacitance of a chip tag, the loop having a length; and a location for receiving the chip tag. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28)
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Specification