| 摘要 |
<p>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° 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° and -45°, 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°, 90°, 180° and 270° respectively. All four loops may be co-planar, with any bucking vertical segments being horizontally displaced from each other. Alternatively, the 0° and 180° loops may also be arranged in a common plane that is close to and parallel with another plane in which the 90° and 270° loops are arranged.</p> |
