Tunable filter

The invention relates to a tunable filter, which is characterized in that each cavity of the filter is internally provided with a resonant column to form a structure close to a coaxial resonant cavity, the side wall of the quasi-coaxial structure is provided with at least two gaps which surround the resonant column and are arranged in the axial direction, a dielectric sheet extends into the resonant cavity through the gaps to realize the adjustment of the passband frequency range of the tunable filter. The tunable filter is suitable for the lower frequency band of microwave point-to-point communication, and the volume of the filter can be reduced through the loading of the resonant columns and the quasi-coaxial cavity loading technology. The band cross coupling is realized by a double-layer dielectric sheet structure which is matched with the cavity arrangement. In the whole tuning range of the tunable filter, the distance between a transmission zero point realized by cross coupling and a passband can be basi