A unidirectional sampling mixer utilizes a stepped phase modulation to shift the frequency of an input signal. An RF input signal is supplied to an RF input switch from an RF input port. An ordered set of phase shift values to be applied to the RF input signal and a set of times each element of which correspond to a time at which a phase shift value is be applied to the RF signal are determined. For each phase shift value within the ordered set of phase shift values, a controller controls the RF input switch to select an input of a phase shifting device and controls an RF output switch to select an output of the phasing shifting device. The input of the phase shifting device and the output of the phase shifting device are selected to apply the phase shift value at its corresponding time to the RF input signal. A frequency shifted signal is supplied to an RF output port from an output of the RF output switch. This Abstract is not to be considered limiting, since other embodiments may deviate from the features described in this Abstract.