The present invention relates to a mixer for signals at different frequencies comprising a network of diodes formed by a pair of diodes mounted in an anti-parallel manner, the first linking point of the diodes being connected to the ground, the second linking point being connected to the ports of transmission/reception signal paths and to the port of a local oscillator path at different frequencies. An impedance matching network for dual-mode use is connected in series in the diode network between the first linking point connected to the ground and the anode of one of the diodes of the diode network. A filtering network is connected between the second linking point and each of the ports of the transmission/reception paths and of the local oscillator path.