| 摘要 |
PROBLEM TO BE SOLVED: To quickly realize the directivity to a desired direction with a simple constitution by connecting plural antennas, which are a specific length distant from one another, with the same phase or opposite phases to select the directivity. SOLUTION: First to third antennas 21 to 23 are connected to a radio part 11 through an antenna selection circuit 13, and two antennas selected from three antennas 21 to 23 and connected to the radio part 11 in common. That is, two antennas selected by the antenna selection circuit 13 are connected to the radio part 11 and function as a transmission antenna and a reception antenna. The length between antennas 21 and 22, that between antennas 22 and 23, and that between antennas 21 and 23 are set to aboutλ/2 whereλis the length of one wave or a transmission/reception signal. In this constitution, the directivity is selected by combination of two antennas to be used and the connection state (in-phase or anti-phase connection) of these two antennas.
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