A resonator for a channel filter is provided. The resonator includes a cavity; a sidewall which at least partially surrounds and forms the cavity, wherein at least one lateral opening is provided in the sidewall; a first adjusting unit with an adjusting element. A first recess is provided at the adjusting element. The adjusting unit is arranged such that the adjusting element adjoins the lateral opening. The adjusting element is movable relative to the lateral opening such that a resonator frequency of the resonator can be adjusted depending on a position of the adjusting element with reference to the lateral opening.