Antenna structure for an electronic article surveillance system

• US 5,103,235 A
• Filed: 12/30/1988
• Issued: 04/07/1992
• Est. Priority Date: 12/30/1988
• Status: Expired due to Fees

• Current Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Original Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Inventors: Clemens, Thomas G.
• Primary Examiner(s): Wimer, Michael C.
• Assistant Examiner(s): Brown, Peter Toby
• Application Number:
  US07/292,361
• Time in Patent Office: 1,194 Days
• Field of Search: 343/742, 343/744, 343/841, 343/842, 343/853, 343/867, 343/741, 340/572
• US Class Current: 343/742
• CPC Class Codes: H01Q 7/04 Screened antennas H01Q7/02, H01Q7/06 take precedence

Abstract

The transmitting and/or receiving antenna of an electronic article surveillance system utilizes a paired-lead loop configuration. One lead forms the active loop.

The other lead forms a passive loop, which parallels and is mutually coupled to the active loop, but not conductively connected to it. This other lead is resistively loaded.

The passive loop of the receiving antenna can also be used to conduct signals between the receiver circuitry and the alarm reporting devices associated with the receiver.

Claims

1. An antenna formed of paired leads in the form of a twin-axial cable and including a first lead for connection to an active load, and a second lead extending along said first lead, for connection to a passive load, said second lead being mutually coupled with but not conductively connected to said first lead, wherein said active load is a receiver, said receiver forms part of an electronic article surveillance system, and said electronic article surveillance system includes means for reporting alarms, said means being electrically connected to said receiver by said second lead.

2. The antenna of claim 1 wherein said passive load is resistive.

3. The antenna of claim 2 wherein said passive load modifies the overall response of said antenna.

4. The antenna of claim 3 wherein said antenna exhibits a relatively constant amplitude response and relatively linear phase response over a predetermined frequency range.

5. The antenna of claim 4 wherein said predetermined frequency range corresponds to a range of resonant frequencies of the resonant circuits associated with tags of said electronic article surveillance system.

6. The antenna of claim 1 wherein said electronic article surveillance system further comprises a transmitter.

7. The antenna of claim 1 wherein said antenna is configured as a far-field cancelling loop antenna structure.

8. The antenna of claim 1 wherein the paired leads of said twin-axial cable are twisted about each other.

9. The antenna of claim 1 wherein said paired leads are substantially uniformly spaced from one another along their length.

10. The antenna of claim 1 wherein said antenna exhibits a relatively constant amplitude response and relatively linear phase response over a predetermined frequency range which corresponds to a range of resonant frequencies for resonant circuits associated with tags of said electronic article surveillance system.

11. An electronic article surveillance system for interacting with tag means including a resonant circuit, comprising:

a transmitter for generating a signal having a frequency at the resonant frequency of said resonant circuit;

a first antenna connected to said transmitter for producing a field exposed to said tag means;

a second antenna for receiving signals generated by said tag means responsive to said field; and

a receiver connected to said second antenna for detecting the signals generated by said tag means;

wherein at least said first antenna or said second antenna is formed of paired leads in the form of a twin-axial cable including a first lead for connection to an active load, and a second lead for connection to a passive load and mutually coupled with, but not conductively connected to said first lead.

12. The system of claim 11 wherein said active load is said transmitter, and said passive load modifies the characteristic response of said first antenna to said transmitter without resistively loading said transmitter.

13. The system of claim 11 wherein said active load is said receiver, and said passive load modifies the characteristic response of said receiver to said second antenna without resistively loading said receiver.

14. The system of claim 13 wherein said electronic article surveillance system includes means for reporting alarms, electrically connected to said receiver by the second lead of said second antenna.

15. The system of claim 11 wherein the paired leads of said twin-axial cable are twisted about each other.

16. The system of claim 11 wherein both said first antenna and said second antenna are formed of a twin-axial cable including a first lead for connection to an active load, and a second lead for connection to a passive load and mutually coupled with, but not conductively connected to said first lead.

17. The system of claim 11 wherein said first antenna and said second antenna are configured as far-field cancelling loop antennas.