Abstract: A tuneable resonator filter consisting of cavity resonators. In the partition wall separating the successive resonators on the transmission path of a resonator filter there is a coupling opening (CPO) with a typically constant width. The coupling strength between the resonators is adjusted by a tuning element which is supported to the partition wall on the opposite sides of the coupling opening so that it can be moved. The tuning element is conductive and grounded so that the impedance between its ends and the partition wall is low. For moving the tuning element, it is linked by a dielectric rod to an electrically controllable actuator being located on the filter lid. By means of the tuning mechanism the bandwidth of a filter can be set automatically.