Broad bandwidth, high impedance transponder for electronic identification system

• US 20020014993A1
• Filed: 06/18/2001
• Published: 02/07/2002
• Est. Priority Date: 06/19/2000
• Status: Active Grant

• Current Assignee: ZIH Corp. (Zebra Technologies Corporation)
• Original Assignee: Andries Petrus Cronje Fourie, Christopher Gordon Gervase Turner, David Edwin Proctor
• Inventors: Fourie, Andries Petrus Cronje, Proctor, David Edwin, Turner, Christopher Gordon Gervase
• Granted Patent: US 6,891,466 B2
• Time in Patent Office: Days
• US Class Current: 343/700MS
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 19/07749 the record carrier being capable of non-contact communication, e.g. constructional details of the antenna of a non-contact smart card
• CPC Class Codes: H01Q 1/24 with receiving set
• CPC Class Codes: H01Q 5/371 Branching current paths
• CPC Class Codes: H01Q 9/0407 Substantially flat resonant element parallel to ground plane, e.g. patch antenna dipole H01Q9/285; monopole H01Q9/40
• CPC Class Codes: H01Q 9/0421 with a shorting wall or a shorting pin at one end of the element H01Q9/0414 takes precedence

Abstract

A transponder 14.1 for an electronic radio frequency identification system comprises an antenna 18 having an antenna impedance at a feedpoint thereof. The transponder further comprises an electronic circuit 19 having an input connected to the antenna. The antenna impedance having impedance characteristics for developing first and second voltage maxima (36, 38) across the input at first and second frequencies (f_L and f_H) respectively, thereby to provide a continuous operative frequency band for the transponder including the first and second frequencies.

Claims

1. A transponder for an electronic radio frequency identification system comprising:

an antenna having an antenna impedance at a feedpoint thereof;

an electronic circuit having an input impedance at an input thereof, the input being connected to the feedpoint; and

the antenna impedance having impedance characteristics for developing first and second voltage maxima across the input at first and second frequencies respectively, thereby to provide a continuous operative frequency band for the transponder including the first and second frequencies.

2. A transponder as claimed in claim 1 wherein the input impedance comprises a real component and a capacitive reactive component.

3. A transponder as claimed in claim 2 wherein an inductive element is connected between the antenna and the circuit in parallel with the input impedance and which is operative to resonate with the capacitive component of the input impedance.

4. A transponder as claimed in claim 2 wherein the real component of the input impedance is at least 400 ohms.

5. A transponder as claimed in claim 1 wherein the first frequency is between 850 MHz and 900 MHz and the second frequency is between 900 MHz and 1 GHz.

6. A transponder as claimed in claim 1 wherein the antenna comprises one of a combination of a patch antenna and a transmission line both connected to the feedpoint, a combination of a shorted ring patch antenna and a transmission line both connected to the feedpoint, and a combination of a loop and an appendage to the loop.

7. A transponder as claimed in claim 1 wherein the first and second frequencies are associated with first and second dimensions of the antenna and wherein the first and second frequencies are selectable by selection of the first and second dimensions.

11. An electronic radio frequency identification system comprising a reader and at least one transponder as claimed in claim 1.

8. An antenna for a transponder of an electronic identification system, the antenna having an antenna impedance at a feedpoint thereof, the antenna impedance having impedance characteristics for developing first and second voltage maxima at first and second frequencies respectively across an input impedance of the transponder.

9. An antenna as claimed in claim 8 comprising one of a combination of a patch antenna and a transmission line both connected to the feedpoint, a combination of a shorted ring patch antenna and a transmission line both connected to the feedpoint, and a combination of a loop and an appendage to the loop.

10. An antenna as claimed in claim 9 wherein the antenna comprises a combination of a first loop and an appendage to the first loop and wherein the appendage comprises a second loop linked to the first loop.