RF transponder

• US 6,693,599 B1
• Filed: 02/13/2002
• Issued: 02/17/2004
• Est. Priority Date: 04/16/1999
• Status: Expired due to Fees

• Current Assignee: National University of Singapore
• Original Assignee: National University of Singapore
• Inventors: Cher, Daryl Lee Song, Ng, We Peng Jason, Ang, Chip Hong, Chia, Michael Yan Wah
• Primary Examiner(s): PHAN, THO GIA
• Application Number:
  US09/936,125
• Time in Patent Office: 734 Days
• Field of Search: H01/Q 1.112, 343/700.MS, 343/741, 343/742, 343/743, 343/744, 343/797, 343/866, 343/867, 343/868, 340/505, 340/572.5, 363/21.14, 363/60, 363/61
• US Class Current: 343/741
• CPC Class Codes: G06K 19/0701 at least one of the integrated circuit chips comprising an arrangement for power management
• 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: H01Q 1/2225 used in active tags, i.e. provided with its own power source or in passive tags, i.e. deriving power from RF signal
• CPC Class Codes: H01Q 1/241 used in mobile communications, e.g. GSM H01Q1/247, H01Q1/248 take precedence
• CPC Class Codes: H01Q 1/248 provided with an AC/DC converting device, e.g. rectennas
• CPC Class Codes: H01Q 1/38 formed by a conductive layer on an insulating support patch antennas H01Q9/0407; microstrip dipole antennas H01Q9/065; microstrip slot antennas H01Q13/106; transmission line microstrip antennas H01Q13/206; manufacturing reflecting surfaces using insulating material for supporting the reflecting surface H01Q15/142
• CPC Class Codes: H01Q 21/06 Arrays of individually energised antenna units similarly polarised and spaced apart
• CPC Class Codes: H01Q 21/29 Combinations of different interacting antenna units for giving a desired directional characteristic H01Q25/00 takes precedence
• CPC Class Codes: H01Q 7/00 Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
• CPC Class Codes: H01Q 9/0435 using two feed points
• CPC Class Codes: H02M 1/009 having two or more independently controlled outputs for DC-DC converter with intermediate AC H02M3/33561
• CPC Class Codes: H02M 7/06 using discharge tubes without control electrode or semiconductor devices without control electrode

Abstract

An RF transponder having an antenna comprising at least two ports operable to receive signals such that, in use, the signals in combination establish at least two current nulls on the antenna, each of the ports being located substantially at a current null.

Claims

1. An RF transponder having an antenna, the antenna comprising at least two ports operable to receive signals such that, in use, the signals in combination establish at least two current nulls on the antenna, each of the ports being located substantially at a current null.

2. An RF transponder according to claim 1, wherein the antenna is a loop antenna.

3. An RF transponder according to claim 2, wherein the loop antenna is formed as a coplanar structure.

4. An RF transponder according to claim 2, wherein the loop antenna is a rectangular loop.

5. An RF transponder according to claim 1, wherein the number of current nulls is two.

6. An RF transponder according to claim 1 wherein the length of the perimeter of the antenna is substantially equal at least two half wavelengths of at least one of the signals.

7. An RF transponder according to claim 1 wherein, the signals are 90°

out of phase with each other.

8. An RF transponder according to claim 1 wherein a coplanar stripline is provided for feeding the signals to the antenna.

9. An RF transponder according to claim 1, wherein the number of ports is two.

10. A rectifying circuit containing two ports, each port being operable to have an oscillating voltage applied thereacross by a signal, a first rectifier being connected to the first port and being constructed such that, in operation, the output of the first rectifier is substantially constant, and a second rectifier being connected to the second port and being constructed such that, in operation, the output of the second rectifier fluctuates in phase with the applied oscillating voltage.

11. A circuit according to claim 10, wherein the rectifier has an output comprising the outputs of the first and second rectifier combined with one another.

12. A circuit according to claim 11, wherein the combined output of the first and second rectifier is of sufficient magnitude to be read directly by conventional digital circuits without being amplified.

13. A circuit according to claim 11, wherein the outputs of the first and second rectifier arc combined by summation.

14. A circuit according to claim 11, wherein the combined output is bridged by a DC storage capacitor to provide a DC power source.

15. A circuit according to claim 10, wherein the first rectifier performs a voltage multiplication effect.

16. A circuit according to claim 10, wherein the second rectifier performs a voltage multiplication effect.

17. A circuit according to claim 10, wherein the first rectifier comprises first and second diodes and first and second capacitors, the capacitance of the second capacitor being sufficiently large to provide a smoothing effect that, in operation, renders the output of the first rectifier approximately constant.

18. A circuit according to claim 10, wherein the second rectifier comprises third and fourth diodes and third and fourth capacitors, the capacitance of the fourth capacitor being sufficiently small that, in operation, the output of the second rectifier fluctuates in phase with the applied oscillating voltage.

19. An RF transponder including a rectifying circuit according to claim 10, wherein the combined output of the first and second rectifiers comprises a demodulated signal for the transponder and the output is Anther bridged by a DC storage capacitor to provide a DC power source for the transponder.

20. An RF transponder having an antenna, the antenna comprising at least two ports operable to receive signals such that, in use, the signals in combination establish at least two current nulls on the antenna, each of the ports being located substantially at current null, the transponder further comprising a rectifying circuit containing two ports, each port being operable to have an oscillating voltage applied there across by a signal, the first rectifier being connected to the first port and being constructed such that, in operation, the output of the first rectifier is substantially constant, and the second rectifier being connected to the second port and being constructed such that, in operation, the output of the second rectifier fluctuates in phase with the applied oscillating voltage.

21. An RF transponder according to claim 20, in combination with two dipole antennae.