Loop antenna and electronic equipment including loop antenna

• US 20070158438A1
• Filed: 03/08/2006
• Published: 07/12/2007
• Est. Priority Date: 12/15/2005
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Nikawa, Susumu, Ogino, Manabu, Fukuda, Toshinari
• Granted Patent: US 7,458,518 B2
• Time in Patent Office: Days
• US Class Current: 235/492
• 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 1/2225 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 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

Abstract

The present invention is intended to improve the receiving performance of a loop antenna to be connected to an IC chip that is incorporated in an IC card or a portable cellular phone. A loop antenna that is connected to an IC chip which has a CPU and a memory mounted thereon and which is incorporated in a casing, and that transmits or receives predetermined electromagnetic waves to or from a reader writer includes a main loop antenna and at least one sub-loop antenna disposed away from the main loop antenna. The sub-loop antenna is connected to the IC chip in parallel with or in series with the main loop antenna. A transmission/reception frequency at which the sub-loop antenna transmits or receives electromagnetic waves may be different from the one at which the main loop antenna transmits or receives electromagnetic waves.

Claims

1. A loop antenna that is connected to an IC chip which has a CPU and a memory mounted thereon and which is incorporated in a casing, and that transmits or receives predetermined electromagnetic waves to or from a reader writer, comprising:

a main loop antenna; and

at least one sub-loop antenna disposed away from the main loop antenna.

2. The loop antenna according to claim 1, wherein the sub-loop antenna and the main loop antenna are connected in parallel with each other to the IC chip.

3. The loop antenna according to claim 1, wherein the sub-loop antenna and the main loop antenna are connected in series with each other to the IC chip.

4. The loop antenna according to claim 1, wherein a transmission/reception frequency at which the sub-loop antenna transmits or receives electromagnetic waves is different from a transmission/reception frequency at which the main loop antenna transmits or receives electromagnetic waves.

5. The loop antenna according to claim 1, wherein a transmission/reception frequency at which the sub-loop antenna transmits or receives electromagnetic waves is identical to a transmission/reception frequency at which the main loop antenna transmits or receives electromagnetic waves.

6. The loop antenna according to claim 4, wherein:

the number of sub-loop antennas is two;

the transmission/reception frequency of one sub-loop antenna is set to a frequency higher by a predetermined frequency than a transmission/reception frequency at which the reader writer transmits or receives electromagnetic waves; and

the transmission/reception frequency of the other sub-loop antenna is set to a frequency lower by a predetermined frequency than the transmission/reception frequency of the reader writer.

7. The loop antenna according to claim 1, wherein the loop antenna includes a resonant circuit realized by connecting a capacitor in parallel with part of the loop antenna.

8. The loop antenna according to claim 1, wherein the loop antenna is incorporated in an IC card.

9. The loop antenna according to claim 1, wherein the loop antenna is incorporated in a casing of electronic equipment.

10. The loop antenna according to claim 9, wherein the electronic equipment is a portable cellular phone.

11. The loop antenna according to claim 10, wherein the main loop antenna is disposed around a rechargeable cell included in the portable cellular phone, and the sub-loop antenna is located adjacent to the rechargeable cell within the casing so that it will not be superposed on the main loop antenna.

12. The loop antenna according to claim 2, wherein a transmission/reception frequency at which the sub-loop antenna transmits or receives electromagnetic waves is different from a transmission/reception frequency at which the main loop antenna transmits or receives electromagnetic waves.

13. The loop antenna according to claim 2, wherein a transmission/reception frequency at which the sub-loop antenna transmits or receives electromagnetic waves is identical to a transmission/reception frequency at which the main loop antenna transmits or receives electromagnetic waves.

14. The loop antenna according to claim 3, wherein a transmission/reception frequency at which the sub-loop antenna transmits or receives electromagnetic waves is different from a transmission/reception frequency at which the main loop antenna transmits or receives electromagnetic waves.

15. The loop antenna according to claim 3, wherein a transmission/reception frequency at which the sub-loop antenna transmits or receives electromagnetic waves is identical to a transmission/reception frequency at which the main loop antenna transmits or receives electromagnetic waves.

16. The loop antenna according to claim 6, wherein the loop antenna includes a resonant circuit realized by connecting a capacitor in parallel with part of the loop antenna.

17. The loop antenna according to claim 16, wherein the loop antenna is incorporated in a casing of electronic equipment.

18. The loop antenna according to claim 17, wherein the electronic equipment is a portable cellular phone.

19. The loop antenna according to claim 18, wherein the main loop antenna is disposed around a rechargeable cell included in the portable cellular phone, and the sub-loop antenna is located adjacent to the rechargeable cell within the casing so that it will not be superposed on the main loop antenna.

20. Electronic equipment having a built-in antenna, wherein the antenna includes:

a main loop antenna; and

at least one sub-loop antenna disposed away from the main loop antenna.