Communications: radio wave antennas – Antennas – High frequency type loops
Patent
1995-06-07
1997-02-11
Le, Hoanganh T.
Communications: radio wave antennas
Antennas
High frequency type loops
343867, 340572, H01Q 1112
Patent
active
056025564
ABSTRACT:
A transmit and receive loop antenna includes a first loop element coupled to an electrical circuit element for generating near fields and far fields and a shunt loop element surrounding the first loop element such that voltages are induced in the shunt loop element by the fields generated by the first loop element. The shunt loop element is constructed from a continuous loop of conductor to maximize current from the voltages induced in the shunt loop element. The current in the shunt loop element generates fields which largely cancel the fields generated by the first loop element in the far field. Thus, the first loop element and the shunt loop element establish a surveillance zone in an area proximate the loop elements. A second loop element, such as a figure-8 loop element may be placed proximate the first loop element and the shunt loop element for receiving electromagnetic energy radiated by a tag circuit which enters the surveillance zone. The tag circuit inside the surveillance zone may be powered by the emitted electromagnetic field of the first loop element and the shunt loop element.
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Check Point Systems, Inc.
Le Hoanganh T.
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