| 摘要 |
A bandpass filter includes a combline bandpass filter including tapped-line input and output terminals, at least three resonators, and a loading capacitor for each resonator. The bandpass filter further includes a plurality of loading inductors, each loading inductor being connected between one of the resonators and its respective loading capacitor; and a direct coupling capacitor connected between any two of the at least three resonators that are separated by at least one other resonator. By adding a direct coupling capacitor to a combline bandpass filter, an additional lower-passband side attenuation pole is created. The attenuation and rolloff characteristics of the lower-passband side can be controlled by altering the value of the direct coupling capacitance. By adding loading inductors to a combline bandpass filter, an upper-passband side attenuation pole is created. The attenuation and rolloff characteristics of the upper-passband side can be controlled by altering the value of the loading inductors.
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