Abstract: An electronic theft detection system has a transmitting antenna and a receiving antenna located on the floor and overhead of a passageway being monitored. The antennas have conductors extending along and crossways of the passageway in staggered arrangement to provide system sensitivity for different paths of egress and different planes of orientation of resonant circuits to be detected. The transmitting antenna consists of a plurality of overlapping loops connected in phase, whereas the receiving antenna consists of a plurality of overlapping loops connected with alternating phase to provide cancellation of extraneous electrical disturbances.

Abstract: An electronic theft detection system includes antenna clusters connected to electromagnetic wave transmitter and receiver means. Each antenna cluster comprises a group of spaced apart parallel loops connected in phase opposition or bucking relationship. Electromagnetic waves emitted from the transmitting cluster are detectable close by, i.e., at distances substantially less than one wavelength, but not at far distances due to cancellation effects; and, conversely, electromagnetic waves incident upon the receiving antenna cluster are sensed by it only if they originate from sources close to the cluster, i.e., substantially less than one wavelength.

Abstract: An electromagnetic interrogation field in a theft detection system is made effectively more uniform by energizing different antenna windings lying in different planes at the same frequency but at different phases so that the resulting field pattern rotates in the vicinity of the antenna windings.