| 摘要 |
The input side and the output side of a first bandpass filter circuit BPF1a are magnetically coupled to each other in a jump-coupling manner by the first mutual inductance (L31a, L41a) for connection between an input port IN and the input side of the first bandpass filter circuit BPF1a and connection between an output port OUT and the output side of the bandpass filter circuit BPF1a. The input side and the output side of a second bandpass filter circuit BPF2a whose center frequency is higher than that of the first bandpass filter circuit BPF1a are magnetically coupled to each other in a jump-coupling manner by the second mutual inductance (L32a, L42a) for connection between the input side of the first bandpass filter circuit BPF1a and the input side of the second bandpass filter circuit BPF2a and connection between the output side of the first bandpass filter circuit BPF1a and the output side of the second bandpass filter circuit BPF2a. This multiband filter circuit is capable of improving the degree of steepness by generating a number of transmission zeros in the vicinity of a plurality of passbands with a simple construction.
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