Security Tag System with Improved Range Consistency

摘要

A radio transmitter used to transmit an activation signal for radio tags held by individuals or the like provides multi-dimensional polarization to an activation signal so as to allow more consistent range detection of an individual with a tag having a single axis of sensitivity. Circular or spherical polarization can be obtained using the system which may include an antenna design permitting decoupling of antennas necessary for the polarization, a quadrature locking system simplifying proper phase control of the necessary signals and a system for tuning the same.

主权项

1. A control unit for a wirelessly activated security tag comprising:
a first and second antenna having mutually perpendicular first and second transmission axes respectively; a first radiofrequency amplifier communicating with the first antenna to provide a first activation signal at a first center frequency; a second radiofrequency amplifier communicating with the second antenna to provide a second activation signal at the first center frequency and having a 90 degrees phase shift with respect to the first activation signal; and a radiofrequency receiver for receiving an identification signal from a security tag activated by one of the first and second activation signals to provide an output control signal.