Multi-band RFID encoder
View Patent ↗In one embodiment, a multi-band near-field antenna for an RFID encoder includes a substrate; an internal coil antenna defined within the substrate; an annular ground plane defined on a first surface of the substrate; a second ground plane defined on an opposing second surface of the substrate, wherein the annular ground plane and the second ground plane form a Faraday cage for the internal coil antenna; and a second antenna disposed on the opposing second surface within the annulus defined by the annular ground plane.
1. A multi-band near-field RFID encoder, comprising:
a substrate;
an internal coil antenna defined within the substrate;
an annular ground plane defined on a first surface of the substrate;
a second ground plane defined on an opposing second surface of the substrate, wherein the annular ground plane and the second ground plane form a Faraday cage for the internal coil antenna; and
a second antenna disposed on the opposing second surface within the annulus defined by the annular ground plane.
2. The multi-band near-field RFID encoder of claim 1 , further comprising:
a coaxial feed coupled to the internal coil antenna and the second antenna.
3. The multi-band near-field RFID encoder of claim 2 , wherein the annular ground plane and the second ground plane couple to a ground within the coaxial feed.
4. The multi-band near-field RFID encoder of claim 1 , wherein the second antenna includes: a first plurality of serially-connected stripline conductors on the second surface of the substrate, the serially-connected stripline conductors in the first plurality being arranged within a first area of the second surface, and
a second plurality of serially-connected stripline conductors on the second surface of the substrate, the serially-connected stripline conductors in the second plurality being arranged within a second area of the second surface, the encoder being configured to drive the first plurality of serially-connected stripline conductors with an RF signal and to drive the second plurality of serially-connected stripline conductors with a phase-shifted version of the RF signal.
5. The multi-band near-field RFID encoder of claim 4 , wherein each of the stripline conductors in the first and second plurality is arranged in parallel with the remaining stripline conductors.
6. The multi-band near-field RFID encoder of claim 4 , wherein the first and second plurality of stripline conductors are each arranged in a fractal pattern.
7. The multi-band near-field RFID encoder of claim 1 , further comprising:
a stripline feed on the second surface for receiving the RF signal;
a first connector stripline connecting the stripline feed to the first plurality of stripline conductors so that the first plurality of stripline conductors is driven with the RF signal; and
a second connector stripline connecting the stripline feed to the second plurality of stripline conductors, wherein the second connector stripline has a different length than the first connector stripline so that the second plurality of stripline conductors is driven with the phase-shifted version of the RF signal.
8. The multi-band near-field RFID encoder of claim 4 , further comprising a variable phase shifter for providing the phase-shifted version of the RF signal.
9. The capacitive encoder of claim 4 , wherein a spacing between each of the stripline conductors in the first plurality is at least as large as a thickness of the substrate, and wherein a spacing between each of the stripline conductors in the second plurality is at least as large as the thickness of the substrate.
10. The capacitive encoder of claim 4 , wherein a characteristic impedance for the stripline conductors in the first and second plurality is at least 50 Ω.
11. A system comprising:
a bar code printer;
a capacitive near-field RFID encoder integrated with the bar code printer, wherein the capacitive RFID encoder includes:
a substrate having a first ground plane on a first surface;
a plurality of capacitive elements on an opposing second surface of the substrate, each capacitive element including a plurality of serially-connected stripline conductors, the RFID encoder being configured to drive a first selected one of the capacitive elements with an RF signal and to drive a second selected one of the capacitive elements with a phase-shifted version of the RF signal; and
an annular ground plane on the opposing second surface, the annular ground plane surrounding the capacitive elements.
12. The system of claim 11 , wherein the annular ground plane is symmetrically arranged with regard to plurality of capacitive elements.
13. The system of claim 11 , wherein the annular ground plane is substantially rectangular, and wherein one side of the annular ground plane has a first width and the remaining sides of the annular ground plane have a second width.
14. The system of claim 11 , further comprising:
a coil antenna defined within the substrate, wherein the annular ground plane and the first ground plane form a Faraday shield for the coil antenna.