摘要 |
In an electronic article surveillance system (24), quadrature transmitting and receiving antennas are used to improve field distribution. A transmitting antenna arrangement includes first and second adjacent co-planar antenna loops (42, 44) and excitation circuitry (46) for generating respective alternating currents in the first and second loops such that the respective alternating currents are 90 DEG out of phase. In a receiving arrangement (300), respective signals received from two adjacent co-planar antenna loops (302, 304) are respectively phase-shifted by +45 DEG and -45 DEG , and the resulting phase-shifted signals are summed. A far-field canceling transmitting antenna arrangement includes four loops (66', 78, 68, 70) operated at phases of 0 DEG , 90 DEG , 180 DEG and 270 DEG respectively. All four loops may be co-planar, with any bucking vertical segments being horizontally displaced from each other. Alternatively, the 0 DEG and 180 DEG loops may also be arranged in a common plane that is close to and parallel with another plane in which the 90 DEG and 270 DEG loops are arranged.
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