A sub-harmonic mixer comprising first and second input ports, and an output port, and arranged to output products of signals applied at the input ports. The sub-harmonic mixer comprises a first stage a second stage arranged in series with each other, with the input ports of the sub-harmonic mixer being input ports of the first stage, and the output port of the sub-harmonic mixer being an output port of the second stage. An output port of the first stage is connected to an input port of the second stage. The first stage is arranged to generate a fundamental product and a first third order intermodulation distortion product in-phase with each other. The second stage is arranged to generate a second third order intermodulation distortion product in anti-phase to the fundamental product generated by the second stage.