A dual mode radio apparatus has an integrated filtering part (51) which includes an antenna port (51a) for connection to an antenna (21), at least one port (51b, 51c, 51d) for connection to each of the system-specific radio-frequency parts (54, 55) of the dual mode radio apparatus and filtering means for directing the propagation of signals between ports on the basis of the signal frequency. The integrated filtering part replaces earlier separate filters and their impedance matching circuits as well as some of the required radio-frequency switches.
A filter (1) for filtering certain frequencies of an electric signal. The filter (1) comprises components (HX1-HX4) for forming the frequency response of the filter, and components (A,C) for accomplishing coupling and impedance matching. The filter is provided with a directional coupler (10) composed of two transmission lines (A,B), one of them being a coupling line (A) or an impedance matching line.