Rotating field antenna with a magnetically coupled quadrature loop
First Claim
1. A multiple loop antenna comprising:
- (a) a loop having a figure eight shape, the loop having an upper loop and a lower loop connected in parallel with each other, the loop including a crossover region between the bottom of the upper loop and the top of the lower loop;
(b) a drive element for driving the figure eight loop; and
(c) a center loop overlapping only a portion of the crossover region and a portion of the figure eight loop, wherein the center loop has no direct or physical electrical connection to the figure eight loop or to the drive element, and wherein magnetic induction produces a 90 degree phase difference between the phase of the figure eight loop and the phase of the center loop, the antenna thereby producing a rotating composite field when driven by the drive element.
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Accused Products
Abstract
A rotating field antenna is provided which includes a figure eight shape loop, a center loop magnetically coupled to the figure eight shape loop, and a drive element for driving the figure eight loop. The figure eight shape loop has an upper loop, a lower loop and a crossover region therebetween. The center loop overlaps at least a portion of the crossover region and at least a portion of one or both of the upper and lower loops. The center loop has no direct or physical electrical connection to the offset figure eight shape loop. Magnetic induction produces a 90-degree phase difference between the phase of the figure eight loop and the phase of the center loop. The antenna thereby produces a rotating composite field when driven by the drive element. The figure eight loop and the center loop are coplanar. The drive element may be an amplified voltage source which has a fundamental frequency of about 13.56 MHz, thereby providing a multiple loop antenna which is useful for electronic article surveillance systems that use RFID tags which resonate at 13.56 MHz.
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Citations
13 Claims
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1. A multiple loop antenna comprising:
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(a) a loop having a figure eight shape, the loop having an upper loop and a lower loop connected in parallel with each other, the loop including a crossover region between the bottom of the upper loop and the top of the lower loop; (b) a drive element for driving the figure eight loop; and (c) a center loop overlapping only a portion of the crossover region and a portion of the figure eight loop, wherein the center loop has no direct or physical electrical connection to the figure eight loop or to the drive element, and wherein magnetic induction produces a 90 degree phase difference between the phase of the figure eight loop and the phase of the center loop, the antenna thereby producing a rotating composite field when driven by the drive element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A rotating field antenna comprising:
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(a) a figure-8 shape loop, the figure-8 shape loop being an offset figure-8 shape loop having an upper loop, a lower loop and a crossover region therebetween; (b) a single drive element for driving the figure-8 loop; and (c) a center loop magnetically coupled to the figure-8 shape loop whereby the center loop overlaps only a portion of the crossover region and a portion of one or both of the upper and lower loops, and the center loop has no direct or physical electrical connection to the offset figure eight shape loop. - View Dependent Claims (13)
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Specification