A radio frequency mixer circuit comprises a first terminal, a local oscillator terminal and a second terminal, a wave propagation medium having a first and second end, a circulator coupling together the first terminal, the first end of the wave propagation medium and the second terminal, a switching means operable according to a signal coupled to the LO terminal, the switching means being coupled to the second end of the wave propagation medium for causing a reflection with unchanged voltage wave polarity when the switching means is in an open state, or a reflection with inverted voltage wave polarity when the switching means is in a closed state, at the second end of the wave propagation medium when a wave is travelling therein.