Spatially selective UHF near field microstrip coupler device and RFID systems using device
View Patent ↗A system having a UHF RFID transceiver is adapted to communicate exclusively with a single electro-magnetically coupled transponder located in a predetermined confined transponder operating region. The system includes a near field coupling device comprising a plurality of lines connected in parallel with an unmatched load. The near field coupling device may be formed, for example on a printed circuit board with a plurality of electrically interconnected traces and a ground plane. The system establishes, at predetermined transceiver power levels, a mutual electro-magnetic coupling which is selective exclusively for a single transponder located in a defined transponder operating region. Also included are methods for selective communication with the transponder in an apparatus such as a printer-encoder.
1. A near field coupling device, comprising:
a plurality of lines electrically interconnected in parallel to form a one half wavelength transmission line or multiple thereof;
a ground plane spaced away from the plurality of lines; and
a terminating resistor coupled to the plurality of lines, the terminating resistor selected not to match a characteristic impedance of the plurality of lines such that the near coupling device operates as a one-half wavelength unmatched transmission line.
2. The near field coupling device of claim 1 , wherein the plurality of lines are formed as at least a first trace on a printed circuit board and the ground plane is formed as a second trace on a printed circuit board.
3. The near field coupling device of claim 1 , wherein at least one of the plurality of lines has a zig-zag characteristic.
4. The near field coupling device of claim 1 , wherein the plurality of lines are spatially aligned coplanar and parallel to each other.
5. The near field coupling device of claim 1 , wherein the length, width and interspacing of the plurality of lines is selected for a desired bandwidth.
6. The coupler of claim 1 wherein the characteristic impedance of the plurality of lines is lower than the terminating resistor.
7. A near field coupler for communication with a transponder located in a transponder operating region, comprising:
a plurality of lines coupled to a terminating resistor selected not to match a characteristic impedance of the plurality of lines such that the near coupling device operates as a one-half wavelength unmatched transmission line or multiple thereof; the near field coupler receiving an RF communication signal and configured to produce an array of spaced near field concentrations responsive to the RF communication signal, the spacing of said near field concentrations along a predetermined direction being significantly less than a smallest dimension of said transponder in said predetermined direction such that said transponder overlaps and is excited by a plurality of said field components when located in said transponder operating region.
8. The coupler of claim 7 wherein said near field concentrations are formed by said lines configured in an array with a spaced parallel geometry.
9. The coupler of claim 8 wherein said lines comprise leaky edges formed in a microstrip coupler.
10. The coupler of claim 8 wherein said lines have a zig-zag configuration.
11. The coupler of claim 8 wherein said lines are formed as a trace on a printed circuit board having a separate ground plane.
12. The coupler of claim 7 wherein the characteristic impedance of the plurality of lines is lower than the terminating resistor.