A phase detector for indicating the magnitude of a phase difference between two electrical signals applied to it, is provided with means for introducing a deliberate phase shift into one of the signals so that the measured phase difference never closely approaches 0° or a multiple of 360°. The detector is capable of providing a smooth output signal over a very wide range of phase difference which can exceed many multiples of 360°. Furthermore, the phase comparator is never required to perform measurements in those regions of least accuracy close to zero phase difference.