| 摘要 |
PCT No. PCT/JP97/00861 Sec. 371 Date Sep. 22, 1998 Sec. 102(e) Date Sep. 22, 1998 PCT Filed Mar. 28, 1997 PCT Pub. No. WO98/42041 PCT Pub. Date Sep. 24, 1998Described herein is a variable directional antenna apparatus wherein an electrical length of a parasitic antenna of a paired two-element Yagi antenna is varied to change antenna directivity. A radio device (12) outputs a received signal corresponding to the intensity of an electric field received by a first antenna. A control circuit (15) outputs a control signal to a variable impedance circuit (14) according to the result of detection of the received signal so as to change the impedance of the variable impedance circuit (14) according to the control signal. Thus, an electrical length of a second antenna (13) placed in parallel away from the first antenna (10) is changed to thereby activate the second antenna as a director or reflector, whereby antenna directivity is varied.
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