Load isolated article surveillance system and antenna assembly

Claim 2

An interrogation antenna assembly for use in an electronic theft detection system, said assembly comprising a transmitter loop antenna (84) lying in a flat plane, a capacitor (94) connected to said transmitter loop antenna (84) to form a resonant circuit therewith, a flat panel (56) of electrically conductive material extending parallel to and aligned with said loop antenna (84) and positioned close enough to said antenna (84) to produce inductive loading thereof and thereby minimize the loading effects of other electrically conductive objects positioned in the vicinity of said antenna (84), said panel (56) being spaced far enough from said antenna (84) to permit interrogation fields generated by said antenna (84) to extend therefrom in a direction away from said panel.

Claim 3

An antenna assembly according to claim 1, wherein said flat panel (56) extends over a greater area than the area covered by said transmitter loop antenna (84).

Claim 4

An antenna assembly according to claim 1 or 2, wherein said flat panel and said transmitter loop antenna (84) are mounted in a common framework assembly (34).

Claim 5

An antenna assembly according to claim 3, wherein said capacitor (94) is mounted in said framework assembly (34).

Claim 6

An antenna assembly according to claim 3 or 4, wherein said framework assembly (34) includes a foam plastic material (FIG. 7) between said panel and said transmitter loop antenna (84).

Claim 7

An antenna assembly according to anyone of claims 3 to 5, wherein said framework assembly (34) includes at least one mounting tube (62) extending vertically between said panel (56) and said transmitter loop antenna (84).

Claim 8

An antenna assembly according to anyone of claims 3 to 6, wherein said antenna assembly (34) includes a mounting base (100) configured as a boot (104) to accommodate insertion of said framework assembly (34).

Claim 9

An antenna assembly according to anyone of claims 3 to 7, wherein said antenna assembly (34) includes at least one receiver coil (88a, 88b).

Claim 10

A theft protected store checkout apparatus comprising in combination, a plurality of store checkout stations (14, 16) spaced apart from each other and forming therebetween parallel passageways (22) to accommodate store customers and shopping carts (18), a plurality of theft detection systems for de­tecting the presence in respective passageways of targets (32) mounted on articles of merchandise (10) and having special electromagnetic response characteristics, each theft detection system including an interrogation antenna assembly positioned alongside each passageway, each said antenna assembly comprising a transmitter loop antenna (84) lying in a flat vertical plane, a capacitor (94) connected to the transmitter loop antenna to form a resonant circuit therewith and a flat panel (56) of an electrically conductive material extending parallel to and aligned with said loop antenna and spaced from said antenna (84) at a distance sufficient to produce induction loading thereof and thereby to minimize the loading effects of other electrically conductive objects positioned in the vicinity of said antenna (84), said panel (56) being spaced far enough from said antenna to permit interrogation fields generated by said antenna to extend a substantial distance into its respective passageway (22), said panel (56) being located farther from said passageway than said antenna (84).

Claim 11

A theft protected store checkout apparatus comprising in combination, a plurality of store checkout stations (14, 16) spaced apart from each other and forming therebetween parallel passageways (22) to accommodate store customers and shopping carts (18), a plurality of theft detection systems for de­tecting the presence in respective passageways of targets (32) mounted on articles of merchandise (10) and having special electromagnetic response characteristics, each theft detection system including an interrogation antenna assembly positioned alongside each passageway, each said antenna assembly comprising a transmitter loop antenna (84) lying in a flat vertical plane, a capacitor (94) connected to the transmitter loop antenna to form a resonant circuit therewith and a flat panel (56) of an electrically conductive material extending parallel to and aligned with said loop antenna and spaced from said antenna (84) at a distance sufficient to produce induction loading thereof and thereby to minimize the loading effects of other electrically conductive objects positioned in the vicinity of said antenna (84), said panel (56) being spaced far enough from said antenna to permit interrogation fields generated by said antenna to extend a substantial distance into its respective passageway (22), said panel (56) being located farther from said passageway than said antenna (84).

Claim 12

A store checkout apparatus according to claim 9, wherein said panel (56) is positioned adjacent a checkout station (14, 16).

Claim 13

A store checkout apparatus according to claim 9 or 10, wherein two checkout stations (14, 16) are arranged to form therebetween two adjacent parallel passageways (22).

Claim 14

A store checkout apparatus according to claim 11, wherein an interrogation antenna assembly (84) is arranged along each passageway (22).

Claim 15

A store checkout apparatus according to claim 12, wherein the electrically conductive panel (56) of each interrogation antenna assembly (84) is positioned adjacent an associated checkout station (14, 16).

Claim 16

A store checkout apparatus according to anyone of claims 11 to 13, wherein the interrogation antenna assemblies for each of two adjacent passageways (22) are arranged along a common line between the passageways but at different locations along the passageways (Fig. 4).

Claim 17

An electronic article surveillance system for detecting the unauthorized movement of protected articles, said system comprising a transmitter antenna assembly (84) including a transmitter loop antenna (84) lying in a flat plane, a capacitor (94) connected to said transmitter loop antenna (84) to form a resonant circuit therewith, a flat panel (56) of electrically conductive material ex­tending parallel to and aligned with said transmitter antenna (84), a receiver loop antenna (88) arranged parallel to and aligned with said transmitter antenna (84) and located on the same side of said transmitter antenna (84) and located on the same side of said panel (56) as said transmitter an­tenna (84), a signal generator (120, 122, 124, 126) arranged to drive said transmitter antenna assembly (84) at its resonant fre­quency, a receiver (130, 132, 134, 136) connected to said receiver loop antenna (88) to process electrical signals generated by said receiver loop antenna (88) and to detect those signals which result from the presence of a detectable target (32) in the vicinity of said antennas (84, 88), said receiver (130, 132, 134, 136) including gates (132) synchronized with said signal generator to permit detection only of signals which occur at predetermined phase relationships relative to the phase of the signal generator (120, 122, 124, 126).

Claim 18

An electronic article surveillance system for detecting the unauthorized movement of protected articles, said system comprising a transmitter antenna assembly (84) including a transmitter loop antenna (84) lying in a flat plane, a capacitor (94) connected to said transmitter loop antenna (84) to form a resonant circuit therewith, a flat panel (56) of electrically conductive material ex­tending parallel to and aligned with said transmitter antenna (84), a receiver loop antenna (88) arranged parallel to and aligned with said transmitter antenna (84) and located on the same side of said transmitter antenna (84) and located on the same side of said panel (56) as said transmitter an­tenna (84), a signal generator (120, 122, 124, 126) arranged to drive said transmitter antenna assembly (84) at its resonant fre­quency, a receiver (130, 132, 134, 136) connected to said receiver loop antenna (88) to process electrical signals generated by said receiver loop antenna (88) and to detect those signals which result from the presence of a detectable target (32) in the vicinity of said antennas (84, 88), said receiver (130, 132, 134, 136) including gates (132) synchronized with said signal generator to permit detection only of signals which occur at predetermined phase relationships relative to the phase of the signal generator (120, 122, 124, 126).

Claim 19

A surveillance system according to claim 15, wherein said gate (132) is synchronized with said signal generator (120, 122, 124, 126) such that it does not pass signals during intervals of the driving of the transmitter antenna assembly (84) which correspond to the occurrence of received distur­bances caused by the presence of targets (32) on the opposite side of said panel (56) from said transmitter loop antenna (84).