| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the need for a low pass filter for cutting off disturbing wave and to attain miniaturization by connecting a feeder earth conductor to ground at a position apart from a connecting point by n/4 (n is an odd number) of a transmission reception signal wavelength. SOLUTION: For example, an external conductor connects to ground by an earth 16 at a position apart from a feeding point 14 of a semi-rigid cable 9 by 1/4λ(λis a wavelength) with respect to a fundamental wave frequency f0 . Thus, the impedance of the outer conductor of the able 9 at the feeding point 14 is seen open at the frequency f0 and the fundamental wave passes thorough the outer conductor. The distance between the feeding point 14 and the earth 16 is equal toλat the 2nd harmonic 2f0 and the travelling wave is short-circuited at the feeding point 14, then the 2nd harmonic wave does not pass through. This is similar in the case that the distance between the feeder 14 and the earth 16 is nλ/4. Since the 2nd harmonic wave effecting most the circuit is eliminated by the cable 9 in this way, it is not required to provided a 2nd harmonic wave eliminating low pass filter to a branching filter 5 and then the circuit is made small.
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