Asymmetrical antennas for use in electronic security systems
First Claim
1. For use in an electronic security system having a transmitter for providing in a surveillnance zone an electromagnetic field of a frequency which is repetitively swept over a predetermined frequency range, a resonant tag of resonant frequency within the swept range and a receiver for detecting the presence of the resonant tag in the surveillance zone and to provide an alarm indication thereof, an antenna system comprising:
- a transmitting antenna adapted for coupling to said transmitter and having at least one loop lying in a plane;
a receiving antenna adapted for coupling to said receiver and having at least two twisted loops lying in a common plane, each loop being twisted 180° and
in phase opposition with each adjacent loop;
said antennas having a different number of loops and a mutual magnetic coupling therebetween and said receiving antenna having an effective total loop area of one phase equal to the effective total loop area of opposite phase;
said transmitting antenna and said receiving antenna being disposed in spaced substantially parallel relationship on respective opposite sides of a passage through which said tag must pass for detection.
3 Assignments
0 Petitions
Accused Products
Abstract
An antenna system for use in an electronic security system and having a transmitting antenna with at least one loop lying in a plane, and a receiving antenna having at least two twisted loops lying in a common plane with each loop being twisted 180° and in phase opposition with each adjacent loop. The transmitting and receiving antennas are disposed in spaced substantially parallel relationship across an aisle or passage through which a resonant tag circuit must pass for detection.
165 Citations
7 Claims
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1. For use in an electronic security system having a transmitter for providing in a surveillnance zone an electromagnetic field of a frequency which is repetitively swept over a predetermined frequency range, a resonant tag of resonant frequency within the swept range and a receiver for detecting the presence of the resonant tag in the surveillance zone and to provide an alarm indication thereof, an antenna system comprising:
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a transmitting antenna adapted for coupling to said transmitter and having at least one loop lying in a plane; a receiving antenna adapted for coupling to said receiver and having at least two twisted loops lying in a common plane, each loop being twisted 180° and
in phase opposition with each adjacent loop;said antennas having a different number of loops and a mutual magnetic coupling therebetween and said receiving antenna having an effective total loop area of one phase equal to the effective total loop area of opposite phase; said transmitting antenna and said receiving antenna being disposed in spaced substantially parallel relationship on respective opposite sides of a passage through which said tag must pass for detection. - View Dependent Claims (2, 3, 4, 5)
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6. For use in an electronic security system having a transmitter for providing in a surveillance zone an electomagnetic field of a frequency which is repetitively swept over a predetermined frequency range, a resonant tag of resonant frequency within the swept range and a receiver for detecting the presence of the resonant tag in the surveillance zone and to provide an alarm indication thereof, an antenna system comprising;
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a transmitting antenna adapted for coupling to said transmitter and having two twisted loops lying in a common plane, each loop being in phase opposition with each adjacent loop; a receiving antenna adapted for coupling to said receiver and having three twisted loops lying in a common plane each loop being in phase opposition with each adjacent loop; each antenna having an effective total loop area of one phase equal to the effective total loop area of opposite phase.
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7. An antenna system for use in an electronic security system for detection of unauthorized removal of items containing a resonant tag circuit, said antenna system comprising:
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a transmitting antenna coupled to the security system transmitter and a receiving antenna coupled to the security system receiver, said antennas being disposed in spaced parallel relationship and between which said items must pass for detection; the transmitting antenna having two coplanar loops lying successively along an antenna axis, each loop being twisted 180°
with respect to the adjacent loop to be in phase opposition;the receiving antenna having three coplanar loops lying successively along an antenna axis, each loop being twisted 180°
with respect to each adjacent loop to be in phase opposition;
the center loop being of one phase and the outer loops each being of opposite phase to that of the center loop;each antenna having an effective total loop area of one phase equal to the effective total loop area of opposite phase.
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Specification