| 摘要 |
A low pass filter (LPF) can realizes a sophisticated transmission filter usable in a dual-band application. The transmission filter features a compact size, a low cost, a lower insertion loss, and an excellent harmonics-suppression characteristic. In the LPF, a high pass filter (HPF) section working in a high frequency band or a band pass filter (BPF) section, is coupled with a first LPF section in parallel between an input terminal and an output terminal. The HPF section or the BPF section includes a switch circuit formed of one diode that switches the pass band thereof to a rejection band. In one case, a signal passing through the HPF section or the BPF section is input to the input terminal. In the other case, a signal passing thorough the first LPF is input to the input terminal. When a signal supposed to pass through the first LPF section is input to the input terminal, the switch circuit is activated to change the HPF or the BPF section to the rejection band for blocking a second harmonics component from passing through the HPF or the BPF section.
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