| 摘要 |
An antenna element (1) has a linear antenna rod (1b) of predetermined length and a top load (1a) at the end of the rod (1b). The antenna element (1) takes a first position in which the rod is extended out of a housing (8), and a second position in which the rod is retracted within the housing. There are provided two feed terminals (5, 6) along the rod (1b). The first feed terminal (5) is essentially matching the impedance of a node point in a current distribution in the resonant antenna element, and feeds the antenna element at the end of the rod in the first position. The second feed terminal (5) is matching the impedance of an anti-node point in a current distribution in the resonant antenna element, and feeds the antenna element at approximate center of the rod in the second position. A first feed terminal (5) might contact the rod in a second position, but it does not feed the same because of mismatching. Thus, the antenna system is always fed with matched condition whether it is extended or retracted, through the automatic switching of feed terminals.
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