Pulsed magnetic eas system incorporating single antenna with independent

Abstract

A single antenna transmits and receives signals. The single antenna has first and second antenna loops substantially lying in a common plane and partially overlapping. First and second transceiver circuits are coupled to the first and second antenna loops respectively, for respectively generating in a first mode of operation first and second pulsed magnetic fields together defining an interrogation zone for a marker generating a characteristic response to the magnetic fields in the interrogation zone, and for receiving signals from the interrogation zone in a second mode of operation. The first and second transceiver circuits alternately generate the first and second magnetic fields substantially in phase with one another and substantially out of phase with one another. The partially overlapping antenna loops prevent detuning of the transceivers otherwise resulting from the phase alternating. Each of the first and second transceiver circuits has a phase controllable transmitter section and a phase controllable receiver section. A controller independently phase controls the transmitter and receiver sections. Each receiver section is coupled across the tuned circuit of its respective transceiver circuit.