| 摘要 |
In an electronic article surveillance system, quadrature transmitting and receiving antennas are used to improve field distribution. A transmitting antenna arrangement includes first and second adjacent co-planar antenna loops and excitation circuitry 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, respective signals received from two adjacent co-planar antenna loops are respectively phase-shifted by +45 DEG and -45 DEG , and the resulting phase-shifted signals are summed. A far-field cancelling transmitting antenna arrangement includes four loops 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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