Electrical surveillance apparatus with moveable antenna elements

[8. Apparatus according to claim 7, characterized in that said radiator comprises a first dipole microwave antenna for radiating said microwave carrier signal, and said receptor comprises a second dipole microwave antenna disposed orthogonally to said first dipole antenna for receiving from any said marker said microwave carrier signal

• with said electrostatic field signal modulated thereon.] 9. Apparatus for detecting the presence within a surveillance zone of a body of high permeability material wherein a transmitter is coupled to a first coil element for establishing in said zone an AC magnetic field, and a receiver is coupled to a second coil element for detecting a predetermined disturbance to said field caused by the presence of said body within said field, characterized in that said coil elements are mounted respectively on opposite sides of said zone, each element for rotation about a vertical axis, said elements being constructed and arranged to confine to a region straddled by said axes substantially all of said field that is effective
• for detecting said body. 10. Apparatus according to claim 9, characterized in that said elements are constrained to assume a standby orientation extending across the space between said axes transverse to the path of any body traversing said surveillance zone and are constructed and arranged to move from said standby orientation upon passage of said body whenever said
• body traverses said zone. 11. Apparatus according to claim 10, characterized in that said coil elements are of generally planar pancake construction and disposed within a respective panel structure, said structures being mounted on said axes as swinging gates, and said standby orientation is such that said structures extend toward each other in a
• common vertical plane. 12. Apparatus according to claim 11, characterized in that said first coil element is configured as a loop with all of its turns encircling a center point in the same direction and with mirror symmetry about both a vertical and a horizontal axis passing through said point, and said second coil element is configured as a vertically oriented figure eight with the upper and lower halves of the eight electrically balanced with respect to undisturbed magnetic field signals received
• directly from said first coil element. 13. Apparatus according to claim 12, characterized in that said coil elements have substantially equal external dimensions and said panel structurs are substantially identical
• in external size and configuration. 14. Apparatus according to claim 11, characterized in that said first and second coil elements are constructed and arranged to minimize the generation, in any electrically conductive material disposed adjacent the boundary of said region, of a third
• harmonic signal detectable by said receiver. 15. Apparatus according to claim 11, characterized in that said first and second coil elements are constructed and arranged to minimize reception by said receiver of any
• line frequency signals generated in proximity to said region. 16. Apparatus for detecting, within a surveillance zone confined to a pathway along which a pedestrian is constrained to travel when proceeding between two areas within a building, the presence of an electrical energy responsive marker wherein a transmitter is coupled to an electrical energy field radiator for establishing throughout said zone an AC energy field, and a receiver is coupled to an electrical energy field receptor for detecting a predetermined alteration of said AC energy field caused by the presence of said marker within said AC energy field, characterized in that at least one gate-like structure is mounted on one side of said pathway for rotation to and fro about a vertical axis, said structure being rotatable about said axis between positions respectively barring and permitting passage of said pedestrian along said pathway, and at least one of said radiator and receptor is disposed in said structure, at least one of said radiator and receptor being movable relative to the other thereof, substantially all of said structure extending horizontally to one side of said vertical axis, said structure being constrained to
• assume a standby orientation extending across said pathway. 17. Apparatus for detecting, within a surveillance zone region of an aisle traversed by shopping carts, the presence of an electrical energy responsive marker wherein a transmitter is coupled to an electrical energy field radiator for establishing throughout said zone an AC energy field, and a receiver is coupled to an electrical energy field receptor for detecting a predetermined alteration of said AC energy field caused by the presence of said marker within said AC energy field, characterized in that at least one of said radiator and receptor is disposed in a gate-like structure that is rotatably mounted relative to said aisle for movement between two positions, one of which is transverse to said aisle for barring passage of said cart along said aisle while the other of which is arranged to permit passage of said cart, and said radiator and receptor establish an effective surveillance zone for detecting all said markers that are carried along said aisle past said gate-like structure by a person propelling said cart, at least one of said radiator and receptor being movable relative to the other thereof, said structure being constrained to assume a standby orientation extending across said aisle. 18. Apparatus according to claim 17, characterized in that said radiator and receptor are in the form of generally planar pancake coil elements disposed within respective gate-like structures mounted on respective vertical axes as swinging gates constrained to assume said one position as a standby orientation with said structures extending toward each other in a common vertical plane, said coil elements being constructed and arranged to minimize the generation in the electrically conductive material of an adjacent checkout counter of a third harmonic signal detectable by said receiver, and to minimize reception by said receiver of any line frequency components emanating from any cash register
• at said counter. 19. Apparatus for detecting, within a surveillance zone region of an aisle traversed by shopping carts, the presence of an electrical energy responsive marker wherein a transmitter is coupled to an electrical energy field radiator for establishing throughout said zone an AC energy field, and a receiver is coupled to an electrical energy field receptor for detecting a predetermined alteration of said AC energy field caused by the presence of said marker within said AC energy field, characterized in that at least one of said radiator and receptor is disposed within a gate-like structure mounted for rotation about an axis positioned relative to said aisle for establishing said zone within said aisle and movable between a first position transverse to said aisle for engagement by a shopping cart traversing said aisle and a second position substantially parallel to said aisle for permitting passage of said cart thereby, at least one of said radiator and receptor being movable relative to the other thereof, said structure being constrained to assume
• a standby orientation across said aisle. 20. Apparatus for detecting the presence within a surveillance zone of an electrical energy responsive marker wherein a transmitter is coupled to an electrical energy field radiator for establishing throughout said zone an AC energy field receptor for detecting a predetermined alteration of said AC energy field caused by the presence of said marker within said AC energy field, characterized in that at least one of said radiator and receptor is mounted for rotation about an axis through an arc no greater than 180.degree., and positioned relative to said zone, for confining to a region substantially entirely on one side of a given plane containing said axis, as it is rotated about said axis, that field which is effective to detect said marker, at least one of said radiator and receptor being movable relative to the other thereof in a gate-like structure that is mounted for such rotation, said structure being constrained to assume a standby orientation at about a mid-position in said arc of rotation.