Patent ID: 7439828

Claim:
A tunable multi-stage semi-coaxial cavity band pass filter, in which adjacent stages are electromagnetically coupled, comprising: an outer conductor having inside a plurality of separate cavities separated by partitions; a rod-shaped inner conductor fixed on a bottom surface of each cavity, but not fixed on a top surface which faces the bottom surface of each cavity; a frequency-adjusting screw made from a conductor and screwed through the top surface which faces the bottom surface of each cavity, or through a lateral surface of each cavity; an input/output connector attached to the outer conductor; and a coupling slit provided in each partition provided between the adjacent cavities, in each cavity, a dielectric bar extending from said top surface for being electromagnetically coupled with said inner conductor, said dielectric bar being held by a holder, which is movably inserted through the outer conductor, and into said cavity, and a plurality of the holders have respective projecting portions which project out of the outer conductor, and the plurality of projecting portions are coupled by a movable coupling member disposed outside said outer conductor and located laterally offset from the inner conductors, wherein a movement of said coupling member causes the respective dielectric bars of said plurality of holders to move simultaneously in a defined plane that is perpendicular to said top surface for varying said electromagnetic coupling between the dielectric bars and the inner conductors.