Transmit and receive antenna having angled crossover elements

• US 5,373,301 A
• Filed: 01/04/1993
• Issued: 12/13/1994
• Est. Priority Date: 01/04/1993
• Status: Expired due to Term

• Current Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Original Assignee: CHECKPOINT SYSTEMS, INC. (CCL Industries Incorporated)
• Inventors: Lizzi, Philip J., Bowers, John H.
• Primary Examiner(s): Hajec, Donald
• Assistant Examiner(s): LE, HOANGANH T
• Application Number:
  US08/000,321
• Time in Patent Office: 708 Days
• Field of Search: 343/742, 343/866, 343/867, 343/741, 343/842, 343/743, 343/744, 343/870, 340/572
• US Class Current: 343/742
• CPC Class Codes: H01Q 1/2216 used in interrogator/reader equipment
• CPC Class Codes: H01Q 11/12 Resonant antennas
• CPC Class Codes: H01Q 7/04 Screened antennas H01Q7/02, H01Q7/06 take precedence

Abstract

An antenna for simultaneously transmitting and receiving electromagnetic energy is disclosed. The antenna includes first and second transmit elements and a transmitter for supplying a first current to the first transmit element and a second current to the second transmit element such that the first and second transmit elements radiate electromagnetic fields. Preferably, the supplied first and second currents are substantially equal. The antenna also includes a sensor for sensing differences between currents flowing through the first and second transmit elements. The differences are caused by an electromagnetic field external to the antenna such that the antenna effectively receives the external electromagnetic field by sensing the current differences.

Claims

1. An antenna for simultaneously transmitting and receiving electromagnetic energy, comprising:

first and second transmit elements;

means for supplying a first current to the first transmit element and a second current to the second transmit element such that the first and second transmit elements radiate electromagnetic fields, wherein the supplied first and second currents are substantially equal; and

means for sensing differences between currents flowing through the first and second transmit elements, wherein the differences are caused by an electromagnetic field external to the antenna such that the antenna effectively receives the external electromagnetic field by sensing the current differences.

2. The antenna of claim 1, wherein the first and second transmit elements each comprises an antenna loop having an axis, a first section having first and second ends, and a second section extending between the first and second ends of the first section at a predetermined angle relative to the axis, the first and second transmit elements being generally parallel to each other and spaced slightly apart along the respective second sections, the predetermined angle of the first transmit element and the predetermined angle of the second transmit element being substantially equal to a value other than 90°

such that an angled null zone is achieved.

3. The antenna of claim 2, wherein the first section comprises first and second sides each generally parallel to the axis, and a third side generally perpendicular to and extending between the first and second sides.

4. The antenna of claim 1, wherein the first and second transmit elements each comprises an antenna loop having an axis, first and second sides each generally parallel to the axis, a third side generally perpendicular to and extending between the first and second sides, and a fourth side extending between the first and second sides at a predetermined angle relative to the axis, the first and second transmit elements being generally parallel to each other and spaced slightly apart along the respective fourth sides, the predetermined angle of the first transmit element and the predetermined angle of the second transmit element being substantially equal to a value other than 90°

such that an angled null zone is achieved.

5. The antenna of claim 1, wherein the first transmit element comprises an antenna loop.

6. The antenna of claim 1, wherein the first and second transmit elements comprise first and second antenna loops, respectively.

7. The antenna of claim 6, wherein the first and second antenna loops comprise a single conductive wire.

8. The antenna of claim 1, wherein the first transmit element is substantially equal in area to the second transmit element, and wherein the means for supplying the first and second currents comprises means for supplying the first current in a first angular direction to the first transmit element and for supplying the second current in a second angular direction opposite the first angular direction to the second transmit element, such that far field cancellation of electromagnetic fields generated by the antenna is substantially achieved.

9. The antenna of claim 1, wherein the sensing means comprises a transformer having a primary winding, the transformer being connected to the first and second transmit elements such that current in the first transmit element flows through the transformer primary winding in a first direction and current in the second transmit element flows through the transformer primary winding in a second direction opposite the first direction, such that electromagnetic flux generated by the transformer is zero when the currents flowing through the first and second transmit elements are equal and not zero when the currents flowing through the first and second transmit elements are not equal.

10. An antenna for simultaneously transmitting and receiving electromagnetic energy, comprising:

a primary antenna;

a non-radiating load circuit having an impedance substantially equal to an impedance of the primary antenna;

means for supplying a first current to the primary antenna such that the primary antenna radiates electromagnetic fields;

means for supplying a second current to the non-radiating load circuit wherein the supplied second current is substantially equal to the first current supplied to the primary antenna; and

means for sensing differences between currents flowing through the primary antenna and the non-radiating load circuit, wherein the differences are caused by an electromagnetic field external to the antenna such that the antenna effectively receives the external electromagnetic field by sensing the current differences.