Patent ID: 7573356

Claim:
A tunable filter, comprising: an input/output line formed on a dielectric substrate; at least two coupling sections inserted in series in the input/output line at a distance from each other in the longitudinal direction of the input/output line, each of the coupling sections including a gap dividing the input/output line in a width direction thereof, and one or more coupling electrodes arranged in the gap in the longitudinal direction of the input/output line; a resonator connected to the input/output line between every adjacent two of said coupling sections and configured to vary a resonance frequency thereof; switch means for performing at least one of selective grounding of the coupling electrodes of the coupling sections and selective short-circuiting among the coupling electrodes or between the coupling electrodes and the input/output line to vary a frequency bandwidth of each coupling section; and resonance frequency varying means for varying the resonance frequency of the resonator in association with the switch means.