| 摘要 |
PROBLEM TO BE SOLVED: To provide an antenna in which grounding is surely performed in the manner of high frequency and antenna characteristics are stabilized. SOLUTION: A central conductor 22 at one end of a coaxial cable 20 for power feeding is connected to a base end (a) of an antenna element 18, a wound part 30 is formed by winding one part of the coaxial cable 20, and an inductance component is provided at an external conductor 24 at that part. Capacitance 32 is interposed between both the ends of the external conductor 24 at the wound part 30, a trap circuit is formed from the inductance component and the capacitance 32 parallelly connected to this component, its trap frequency is set to the frequency of the transmission/reception signal of the antenna element 18, and the current of the transmission/reception signal to flow on the outer wall side of the external conductor 24 of the coaxial cable 20 is blocked. Besides, an electric length L of the coaxial cable 20 from the base end (a) of the antenna element 18 to the trap circuit is set to the odd-number multiple of 1/4 wavelength of the frequency of transmission/reception signal and a ground impedance at the base end (a) is reduced.
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