A radio-frequency filter for a radio apparatus operating on two frequency bands is based on impedance step resonators, wherein two interconnected resonator sections (L2, L1) having different impedances are dimensioned such that the resonator's fundamental resonating frequency (f0) is on the lower operating frequency band and a certain harmonic resonating frequency (fs1) is on the higher operating frequency band. The filter may have separate ports (port 2, port 3) for the signals of the different frequency bands and they can be isolated from each other using additional filtering (LC1, LC2).