Abstract: 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).

Abstract: A radio frequency filter has a band-pass type frequency response which is controllable in a manner such that the frequency response may be moved between the transmission frequency (TX') and reception frequency (RX') of associated radio equipment. Thus the radio frequency filter may be used both as a transmission filter and as receiving filter, provided that the transmission and reception take place at different times. The radio frequency filter includes a change-over switch, which connects the radio frequency filter to a transmitter when the pass band of the radio frequency filter is in the transmission frequency, and which connects to the receiver when the pass band of the radio frequency filter is in the reception frequency.